Shoring, Underpinning & Excavation Support for Los Angeles Residential Construction

Shoring is the system of temporary or permanent structural support that keeps the earth from moving when you excavate next to something that needs to stay in place. That something might be a neighboring house, a public street, a hillside slope, a utility corridor, or the owner's own existing structure. On any project where excavation extends below the foundation of an adjacent building, below the lateral support plane of a public right-of-way, or into a slope that would otherwise be unsupported, some form of excavation support system is required to maintain stability during construction and, in many cases, permanently.

This guide covers soldier pile and lagging, soil nail walls, secant piles, tiebacks, underpinning, slot cutting, waterproofing, and what owners and architects need to understand about temporary and permanent excavation support on complex residential sites.

Last updated: March 2026

WHY SHORING MATTERS ON LA RESIDENTIAL PROJECTS

Los Angeles residential construction encounters shoring requirements more frequently and at greater complexity than most markets in the country. Several characteristics of the LA built environment drive this. The hillside topography across the Santa Monica Mountains, the Hollywood Hills, Pacific Palisades, Bel Air, and the canyons of Malibu means that building pads are regularly cut into slopes, creating excavation faces that range from 10 feet to 40 feet or more on the uphill side of the site. The prevalence of subterranean construction in high-end residential - basement living spaces, wine cellars, home theaters, multi-level underground garages - means that even flat-lot projects on the greater Westside and in Beverly Hills frequently involve excavations of 15 to 30 feet below grade. The tight lot conditions on the Westside, where properties are close together and building envelopes push toward property lines, mean that excavation regularly occurs immediately adjacent to neighboring structures. And the variable soil conditions across the basin - everything from competent sandstone and decomposed granite in the hills to loose alluvial fill and expansive clay in the flatlands - add a layer of geotechnical complexity to every shoring design.

Seismic requirements compound all of these conditions. Every shoring system in Los Angeles must account for earthquake loading, which increases the lateral pressures the system must resist and adds engineering requirements that do not exist in non-seismic regions. The combination of steep topography, deep excavation, tight lot lines, variable soils, and seismic demand makes shoring one of the most technically complex and expensive elements on many LA residential projects.

The scope of this page focuses on the excavation support systems themselves: how they work, when each type is appropriate, how they are designed and permitted, what they cost, and how they integrate with the overall construction sequence. Related topics including retaining walls as permanent structures, foundation systems and geotechnical engineering, hillside construction challenges, and grading regulations are covered on their respective pages and cross-linked throughout.

SHORING ENGINEERS AND THE DESIGN-BUILD SHORING MODEL

Shoring is typically not designed by the project's structural engineer of record. It is designed by a specialty shoring engineer, a licensed civil or structural engineer who works for or is retained by the shoring subcontractor. This is an important distinction that owners and architects sometimes do not fully appreciate at the outset of a project: the structural engineer who designs the house, the foundation, and the permanent retaining walls is usually not the same person who designs the temporary shoring system that makes it possible to build those elements. The shoring engineer is a specialist whose practice focuses on excavation support, earth retention, and the interaction between temporary support systems and the surrounding soil, rock, and adjacent structures.

This design-build model exists for practical reasons. Shoring is means-and-methods work. The contractor who will install the system is best positioned to design it because they know their equipment capabilities, their crew's experience with specific installation techniques, the sequencing that works in LA soils, and the practical constraints of getting drill rigs and concrete trucks to residential sites with limited access. The project's structural engineer designs the permanent structure. The shoring engineer designs the temporary support that allows the permanent structure to be built. The two disciplines interface at the point where the temporary system transfers loads to or is replaced by the permanent structure, and this interface is where coordination between the two engineers is critical.

Once the shoring subcontractor produces their design, the review process involves multiple parties. The geotechnical engineer reviews the shoring design to confirm that the soil parameters and design assumptions are consistent with the geotechnical report. The structural engineer of record reviews the interface between the shoring system and the permanent structure, confirming that the shoring loads, deflection limits, and construction sequence are compatible with the permanent design. LADBS reviews and permits the shoring as part of the overall building permit or, in some cases, as a separate shoring permit. When the excavation is adjacent to a public right-of-way, the Bureau of Engineering also reviews the shoring design and issues a separate Excavation E-Permit for lateral support. On complex sites with deep excavation, sensitive adjacent structures, or unusual soil conditions, this review process can be iterative, with comments from the geotechnical engineer or the plan check engineer requiring revisions to the shoring design before approval.

A complete shoring submittal package typically includes a plan view showing pile or nail locations and spacing, cross-sections showing excavation depths, pile embedment, tieback or nail geometry, and the relationship to adjacent structures, structural calculations supporting the design, a detailed installation sequence (particularly important for slot cutting and phased excavation work), monitoring requirements specifying the type, location, and frequency of survey readings, and notes addressing adjacent structure protection, maximum allowable wall deflection, and concrete cure times between construction phases. The level of detail in these submittals reflects the complexity and liability exposure of shoring work - this is not a scope where abbreviated plans or generalized details are acceptable.

SOLDIER PILE AND LAGGING

Soldier pile and lagging is the most common shoring system on residential projects in Los Angeles. It is versatile, well understood by shoring subcontractors in the region, and effective across a wide range of soil conditions and excavation depths. The system works by installing vertical steel beams (soldier piles) at regular intervals along the excavation perimeter and then placing horizontal lagging boards between the piles as excavation proceeds downward, creating a wall that retains the soil behind it.

The Piles

The soldier piles are typically wide-flange steel I-beams (W-shapes). Common sizes range from W12 to W24 depending on the loads, excavation depth, and surcharge conditions, but the shoring engineer sizes the beams based on the specific site conditions. Installation begins before excavation: a drill rig bores a hole at each pile location, typically 24 to 30 inches in diameter, the steel beam is set into the hole, and the hole is backfilled with concrete - either a lean mix (low-strength concrete used when the pile is temporary) or structural-strength concrete when the pile will carry permanent loads or will be incorporated into the finished structure.

The critical design dimension for each pile is the embedment depth below the bottom of excavation. This embedded portion is what provides the passive soil resistance that keeps the pile from kicking out at the base. Embedment depth depends on soil conditions, excavation depth, surcharge loads from adjacent structures or slopes above the wall, and seismic requirements. On a typical 12- to 15-foot excavation in competent native soil, embedment depths of 8 to 12 feet below subgrade are common. On deeper excavations or in weaker soils, embedment can be substantially more, and the pile may also require tiebacks or other supplemental support rather than relying on embedment alone to resist the lateral loads.

Pile spacing is typically 6 to 8 feet on center, though the shoring engineer adjusts this based on the lateral earth pressure, the lagging span capacity, and any point loads from adjacent structures. Closer spacing increases the cost (more piles, more drilling) but reduces the span that the lagging must bridge and reduces deflection. On walls adjacent to sensitive structures where deflection must be tightly controlled, pile spacing may be reduced to 4 to 6 feet.

Lagging

As the excavator removes soil between the piles, working from the top down in controlled lifts, horizontal lagging boards are placed between the pile flanges to retain the exposed soil face. Standard lagging is rough-sawn Douglas fir or similar structural lumber, typically 3x12 or 4x12 members. The lagging boards slide behind the flanges of the I-beams, bearing on the inner face of each flange, and span horizontally between piles.

Lagging is installed progressively as excavation proceeds. The soil face between the bottom of the last installed lagging and the current excavation level is temporarily unsupported during this process, which is why the lift height is limited. In competent soils that can stand unsupported for a short period, lifts of 4 to 5 feet are typical. In weaker or less cohesive soils, lifts may be reduced to 2 to 3 feet, and the time the soil face is exposed must be minimized.

The lagging does not need to be structurally heavy because it benefits from soil arching. The soil behind the wall naturally arches between the piles, transferring most of the lateral earth pressure to the piles rather than to the lagging. The lagging retains the soil that would otherwise ravel or slough between the piles, but it does not carry the full theoretical earth pressure across its span. This arching effect is why relatively light wood members can retain soil at significant depths, and it is one of the reasons soldier pile and lagging is economical compared to systems that require a continuous structural wall.

Concrete Piles with Bolted Angle for Lagging

An alternative to steel I-beams is cast-in-place concrete piles (drilled shafts) with steel angles bolted to the exposed face to create a ledge for the lagging boards. This approach is sometimes used when the permanent structure will incorporate the piles - for example, when the pile becomes part of the basement wall - or when site conditions favor concrete piles over steel beams. The bolted angle provides the equivalent of the I-beam flange that the lagging sits behind. A concrete pile can also receive waterproofing membrane and the permanent wall finish directly, eliminating the need to construct a separate foundation wall outboard of the shoring line. This dual-purpose approach can be cost-effective on projects where the shoring alignment coincides exactly with the permanent basement wall location.

Shotcrete Facing in Lieu of Lagging

Instead of wood lagging between piles, some designs call for shotcrete (pneumatically applied concrete) sprayed directly onto the soil face between and over the piles. This creates a continuous reinforced concrete facing rather than a series of individual lagging boards. The construction sequence for shotcrete facing is: excavate a lift, install reinforcing steel (welded wire fabric or a rebar mat) against the soil face, apply shotcrete to the specified thickness (typically 4 to 8 inches), allow the shotcrete to gain strength, then excavate the next lift.

Shotcrete facing is more expensive per square foot than wood lagging but provides several advantages in specific conditions. It creates a rigid, continuous retention surface with no gaps between boards (which matters when the soil is granular and prone to raveling through lagging gaps). It can serve as the permanent wall surface with appropriate waterproofing and finish treatment, eliminating the cost of building a separate wall behind the shoring. And it integrates structurally with the soldier piles to create a composite wall system with greater stiffness than piles with timber lagging.

When Each Approach Is Appropriate

The choice between wood lagging and shotcrete facing is a design decision driven by several factors: whether the shoring is temporary or permanent, the soil conditions (granular soils that ravel through gaps in wood lagging may require shotcrete), water conditions (shotcrete provides a more continuous barrier against seepage), whether the shoring piles will be incorporated into the permanent structure, the required wall stiffness and deflection limits, and cost. On most temporary shoring applications where the shoring will be abandoned behind a new permanent foundation wall, wood lagging is the standard and most economical choice. When the shoring system will serve as the permanent wall, or when soil or water conditions make wood lagging impractical, shotcrete facing becomes the better approach despite the higher unit cost.

SOIL NAIL WALLS

Soil nail walls are another common excavation support system in Los Angeles, particularly on hillside sites where existing slopes need to be retained during or after construction. The system works by reinforcing the in-place soil with steel bars (nails) drilled and grouted into the face of the cut, then applying a shotcrete facing over the nail heads to create a continuous structural surface. The result is a reinforced soil mass that functions as a gravity retaining structure, with the nails tying the facing to stable ground behind the potential failure plane.

How Soil Nailing Works

Steel bars, typically #8 to #10 rebar or threaded bar, are drilled into the existing soil or rock face at a regular grid pattern, commonly 4 to 6 feet on center in both directions, angled slightly downward at 10 to 15 degrees from horizontal. After each nail is placed, the drill hole is filled with cement grout, which bonds the nail to the surrounding soil along its full length. A reinforced shotcrete facing is then applied over the nail heads to create a continuous structural wall. Bearing plates and hex nuts at each nail head transfer the nail forces into the facing, and the facing distributes those forces between nails and provides the weathering surface.

Top-Down Construction Sequence

Soil nail walls are built from the top down as excavation proceeds, following a sequence that is conceptually similar to soldier pile and lagging but differs in the construction method. The crew excavates a lift of 4 to 5 feet, drills and grouts the row of nails for that lift, installs drainage provisions (typically a geocomposite drain board placed against the soil face before the shotcrete), places reinforcing steel (welded wire fabric or rebar mat), and applies shotcrete to the specified thickness. After the shotcrete has cured sufficiently, the next lift is excavated and the process repeats. This means the wall is constructed in the same sequence as the excavation - the retention system is being built as the excavator works downward, one lift at a time.

The lift height is limited by the ability of the native soil to stand unsupported for the time required to drill the nails, place the reinforcing, and shoot the shotcrete. In most of the native hillside soils found across the Los Angeles basin - decomposed granite, sandstone, siltstone, and shale - a 4- to 5-foot lift height is typical. In weaker soils or soils with less cohesion, the lift height may need to be reduced, and the time the face is exposed must be minimized to prevent raveling or sloughing.

Where Soil Nails Work and Where They Do Not

Soil nailing works well in soils that have enough cohesion to stand unsupported for the height of one lift while the nails and shotcrete are installed. This includes most of LA's native hillside materials. It does not work well in loose granular soils that cave immediately upon exposure, in high water table conditions where the grout cannot set properly in saturated soil without special measures, or in very soft clays with low shear strength. When any of these conditions are present, the shoring design typically shifts to a pre-installed system like soldier pile and lagging or, in extreme water table cases, to secant piles.

Nail Design Parameters

The shoring engineer designs the nail length, diameter, spacing, and inclination based on the soil conditions, wall height, surcharge loads (from structures, slopes, or roadways above the wall), and seismic requirements. Nail lengths typically range from 60 to 100 percent of the wall height - a 20-foot-high soil nail wall might have nails 12 to 20 feet long - though this varies significantly with soil conditions and the required factor of safety. The shotcrete facing is typically 4 to 8 inches thick for temporary walls and 6 to 12 inches for permanent walls, with welded wire fabric or rebar reinforcement.

Temporary Versus Permanent Soil Nail Walls

The distinction between temporary and permanent soil nail walls affects materials, corrosion protection, facing thickness, and drainage provisions. Temporary walls (shoring that will be buried behind a separate permanent structure) may use unprotected steel nails, thinner shotcrete facing, and minimal architectural treatment. Permanent soil nail walls (the finished retaining structure that will be exposed for the life of the building) require corrosion protection on the nails - typically epoxy coating or encapsulation in a corrugated sheathing - thicker facing, proper engineered drainage behind the wall, and typically an architectural finish surface such as form liner texture, concrete stain, or stone veneer applied over the shotcrete.

Nail Encroachment Beyond Property Lines

Some neighbors are willing to grant nail easements, particularly when the nails are temporary and will be effectively abandoned (left in place but no longer serving a structural function) after the permanent structure is built. Other neighbors refuse, either on principle or because they have future development plans of their own and do not want subsurface encumbrances on their property. When a neighbor refuses to grant an easement, the shoring design must be revised to a system that does not encroach beyond the property line - typically a cantilevered soldier pile system, a braced or raker-supported system, or a system using tiebacks only within the owner's own property. This constraint can significantly increase shoring cost and complexity, and it is one of the reasons that a property line survey and early conversations about adjacent property conditions should happen during pre-construction rather than after shoring design is underway.

TIEBACKS, RAKERS, AND INTERNAL BRACING

When a soldier pile and lagging wall or other shoring system is too tall or too heavily loaded to function as a cantilever (relying only on the pile embedment below the excavation to resist the lateral earth pressure), additional lateral support is required. The three primary methods of providing that support are tiebacks, rakers, and internal bracing (struts). Each approach has distinct advantages and constraints, and the choice between them often determines the cost, schedule, and constructability of the shoring scope.

Tiebacks

A tieback is a tensioned anchor drilled at a downward angle through the shoring wall into the soil or rock behind it. The distal end of the anchor is grouted into a stable zone (the bond length) located beyond the potential failure plane. The proximal end passes through the shoring wall and is secured to a bearing plate on the wall face. After the grout has cured and the anchor is bonded into the soil, the tieback is stressed with a hydraulic jack to a specified design load and locked off. The tension in the tieback provides horizontal resistance against the shoring wall, preventing it from deflecting inward under the lateral earth pressure.

Tiebacks are common on deep soldier pile walls where the excavation depth exceeds what a cantilevered pile can handle - generally above about 12 to 15 feet in typical LA soils, though this threshold varies with soil conditions and surcharge. On deep walls (20, 30, 40 feet), multiple rows of tiebacks at different elevations are installed as excavation proceeds past each row's elevation. The tieback loads increase with depth because the lateral earth pressure increases with depth, meaning longer anchors and higher-capacity hardware for the lower rows.

Every tieback must be load-tested before it is accepted. Performance tests, which load the anchor to 133 to 150 percent of the design load, verify that the anchor can carry the required load without excessive creep or displacement. Proof tests, which load to 120 to 133 percent of design, are conducted on the remaining production anchors. If a tieback fails testing, it is supplemented with an additional anchor or replaced. This testing is a critical quality assurance step that adds time and cost but provides documented verification that every anchor in the system is performing as designed.

Property Line Complications with Tiebacks

Tiebacks share the same encroachment issue as soil nails - they extend into the ground behind the wall, which may be under a neighboring property or a public right-of-way. On private property, a temporary construction easement from the neighbor is required. The tiebacks are typically de-stressed and abandoned after the permanent structure is built (they are temporary elements), but the easement must be in place before installation begins. When the excavation is adjacent to a public street, the Bureau of Engineering reviews the tieback installation as part of the E-Permit process for lateral support, and specific requirements apply under Special Order No. 003-0201 for deep excavation and tieback installation on sites adjacent to public ways.

In jurisdictions and situations where tiebacks cannot extend beyond the property line - because the neighbor refuses an easement, because the adjacent ground contains utilities that cannot be penetrated, or because the City restricts subsurface encroachment - the shoring design must use an alternative lateral support method that stays within the excavation footprint.

Rakers

Rakers are diagonal steel braces that extend from a connection point on the face of the shoring wall down to a concrete deadman, footing pad, or reaction block on the excavation floor. The raker transfers the lateral load from the wall face down to the base of the excavation, where the reaction block bears against the subgrade. Rakers are used when tiebacks are not feasible due to property line constraints, adjacent underground obstructions, or soil conditions that will not hold grouted anchors.

The principal disadvantage of rakers is that they occupy interior space within the excavation. A raker extending at a typical 45-degree angle from a wall 20 feet tall reaches 20 feet into the excavation before it meets the floor. On a narrow excavation, rakers from opposite walls can nearly meet in the middle, leaving very little room for construction equipment and activity. Rakers must also be removed in a specific sequence as the permanent structure is built to take over the lateral support - the structural engineer of record must confirm that the permanent floor slabs, foundation walls, and framing are capable of carrying the lateral loads before each raker is cut. This sequencing adds complexity and schedule time to the structural construction phase.

Internal Bracing and Struts

Horizontal steel members spanning across the excavation from one shoring wall to the opposite wall provide mutual lateral support. Internal struts are only feasible on relatively narrow excavations where the span between opposing walls is manageable - they become impractical on wide excavations where the unsupported span of the strut would require an extremely heavy section. Struts are less common on residential projects than on commercial or infrastructure work, but they are occasionally used on tight basement excavations where the plan dimensions allow cross-bracing and where tiebacks are not an option.

Like rakers, struts obstruct the interior of the excavation and must be phased out as the permanent structure replaces them. The construction sequence for strut removal is coordinated with the structural engineer of record to ensure that each strut is not removed until the permanent structure at that level can carry the lateral load.

UNDERPINNING: PROTECTING ADJACENT STRUCTURES

When excavation is adjacent to and below the foundation of a neighboring structure - or the owner's own existing structure being partially retained - the adjacent foundation must be underpinned to prevent settlement or failure. Underpinning extends an existing foundation deeper, to below the new excavation level, so that the supported structure continues to bear on competent soil even though the ground beside and below its original footing has been removed. This is one of the highest-liability scopes on any residential construction project, and the regulatory framework in Los Angeles reflects that.

The Legal and Regulatory Framework

California Civil Code Section 832 establishes the fundamental rights and obligations of adjacent property owners when excavation occurs. Each property owner is entitled to the lateral and subjacent support that their land receives from adjoining land. An owner intending to excavate must provide reasonable notice to adjacent owners stating the intended excavation depth and start date. When excavation will be deeper than nine feet below curb level (defined as the "standard depth of foundations") and the neighboring structure's foundation extends to that depth or deeper, the excavating owner must protect the adjacent property and its structures at no cost to the neighbor, and is liable for any damage resulting from the excavation, with the limited exception of minor settlement cracks.

When the geotechnical engineer determines that the proposed building or shoring system can adequately support the adjacent structure without traditional underpinning, the code allows an alternative path: the owner records a sworn affidavit with the Office of the County Recorder, acknowledging that the lateral support of a portion of the adjacent building's footings is provided by the subterranean walls of the new building. This recorded affidavit runs with the land and informs future owners of the property that the neighbor's foundation support is dependent on the continued existence and structural integrity of the subterranean walls. This is a significant long-term obligation that persists beyond construction completion.

Pre-Construction Condition Survey

The survey includes photographs, video, and measurements. It is typically performed by a firm specializing in pre-construction documentation, not by the general contractor or the shoring subcontractor, to maintain independence and credibility.

Underpinning Methods

Several methods are used to underpin adjacent foundations on residential projects, and the selection depends on the depth of underpinning required, the soil conditions, the structural loads, access constraints, and cost.

Pit underpinning (mass pour) is the traditional method and remains the most common approach on LA residential projects. Pits are excavated in alternating slots beneath the existing foundation, extending down to below the new excavation level. Each pit is filled with concrete to create a new footing section that extends the foundation deeper. The work proceeds in a strict slot-cutting sequence (discussed in the next section) to ensure that the existing foundation is never unsupported across too wide a span. The sequence is conservative by design - each slot must be completed and the concrete must reach a specified minimum strength before the adjacent slot can be excavated. This makes pit underpinning one of the most time-consuming operations in the shoring sequence, but the methodology is well established and reliable.

Micropiles (mini-piles) are small-diameter drilled and grouted piles, typically 6 to 12 inches in diameter, installed adjacent to or through the existing foundation. A steel bracket or cap beam transfers the foundation load from the existing footing to the micropiles, which extend down to competent bearing below the new excavation level. Micropiles are less invasive than pit underpinning and can be installed with smaller equipment that fits in the tight spaces typical of residential lot lines. They are particularly useful where access beneath the existing foundation is limited or where the structural loads are relatively concentrated.

Push piers and helical piers are steel elements driven or screwed to bearing depth beneath the existing foundation. Push piers use the weight of the existing structure as a reaction force to hydraulically drive steel pipe segments to competent soil. Helical piers are screwed into the ground using a hydraulic torque motor. Both methods are more commonly encountered in structural remediation of existing foundations than in new construction shoring, but they are occasionally used for underpinning in conditions where conventional pit underpinning or micropiles are not practical.

Monitoring During and After Excavation

Underpinning and adjacent excavation require a monitoring program that tracks ground and structure movement throughout the construction period. Survey monitoring points are installed on the adjacent structure and on the shoring wall, and readings are taken at specified intervals - typically weekly during active excavation, potentially more frequently during critical operations, and bi-weekly or monthly during the less active phases that follow. Crack monitors may be installed across existing cracks documented in the pre-construction survey to detect any changes in width.

The geotechnical engineer or a specialty monitoring firm provides regular reports comparing measured movement to the allowable thresholds specified in the shoring design. These thresholds are typically expressed in fractions of an inch - maximum allowable lateral deflection of the shoring wall, maximum allowable settlement or tilt of the adjacent structure. If monitoring readings approach or exceed these thresholds, work pauses until the geotechnical engineer evaluates the data and determines whether it is safe to proceed, whether additional shoring measures are needed, or whether the situation requires further investigation. The monitoring program typically continues through the completion of the permanent structure, not just through the shoring and excavation phase.

Liability

Insurance coverage for both the owner and the general contractor needs to specifically address adjacent property damage as part of the project's insurance program.

SLOT CUTTING: SEQUENCING EXCAVATION FOR SAFETY

Slot cutting is the method of excavating and constructing shoring or underpinning in alternating sections rather than all at once. It is fundamental to how shoring works, and it is one of the most commonly misunderstood aspects of excavation support - particularly by owners who wonder why the shoring phase takes as long as it does. The answer, in most cases, is the slot-cutting sequence and the concrete cure time between phases.

Why Slot Cutting Exists

You cannot excavate the full face of a shoring wall or underpin an entire foundation simultaneously. If you removed all lateral support at once, the retained soil (or the supported foundation) would fail before the new support system could be installed. Slot cutting sequences the work so that at any point during construction, only a limited width of the face is unsupported, with completed and cured sections on either side providing passive support for the adjacent ground.

A/B Slot Cuts (Two-Phase Sequencing)

The most common approach divides the wall into alternating "A" slots and "B" slots. All A slots are excavated and constructed first, with the B sections left intact between them. The intact B sections provide passive support to the ground while the A sections are being built. After all A sections are complete and the concrete has reached the specified minimum compressive strength, the B slots are excavated and constructed. At the point when a B slot is being excavated, it has a completed and cured A section on each side, so the maximum unsupported width at any point in the sequence is one slot width.

Multi-Phase Sequencing

On walls with more demanding conditions - poor soil, heavy surcharge from adjacent structures or slopes, or very sensitive adjacent buildings - the sequence may be divided into three or more phases (A/B/C or even A/B/C/D) with narrower slot widths and more conservative sequencing. Each additional phase adds time to the shoring operation because each phase must complete and cure before the next begins, but it reduces the unsupported width at any given time and minimizes ground movement.

Slot Widths

Typical slot widths range from 4 to 8 feet, depending on soil conditions, surcharge loads, and the engineer's assessment of the soil's ability to arch between completed sections. In good soil with no sensitive adjacent structures, wider slots are feasible and reduce the number of construction phases required. Adjacent to an existing foundation, in weak soil, or under heavy surcharge, slots may be narrowed to 3 to 4 feet, with correspondingly more phases and longer overall duration. The shoring plans specify the exact slot widths and the required sequence.

Cure Time Between Phases

High-early-strength concrete mixes can reduce the waiting period, but the shoring engineer specifies the minimum strength and the minimum wait time, and these requirements are not discretionary.

Slot Cutting for Underpinning

DEEP SHORING SYSTEMS

When excavation depths exceed what standard cantilevered or single-tieback systems can handle - roughly beyond 20 to 25 feet in typical conditions - the shoring systems become substantially more complex and expensive. The lateral earth pressure against a retaining or shoring wall increases with depth, and the structural demands increase roughly with the square of the wall height. A wall twice as deep does not cost twice as much; it costs significantly more because the piles must be larger, the embedment deeper, and the lateral support (tiebacks, rakers, or bracing) must resist much greater loads. Deep excavation on LA residential projects is driven by multi-level subterranean garages, basement living spaces, and hillside sites where the building pad is cut deep into the slope.

Multi-Level Tieback Systems

Deep walls often have two, three, or more rows of tiebacks at different elevations to control wall deflection and manage the increasing earth pressure at each depth. Each row is installed and stressed as excavation proceeds past that level. The tieback loads increase with depth, requiring longer anchors with greater bond length and higher-capacity hardware for the lower rows. The installation sequence is coordinated with the excavation sequence: excavate to the first tieback elevation, install and stress the first row, excavate to the second tieback elevation, install and stress the second row, and so on. Each row of tiebacks locks in the wall position at that elevation before the additional earth pressure from deeper excavation is imposed on the system.

Secant Pile Walls

For deep excavations with a high water table, very soft soils, or running sand conditions where open-face systems like soldier pile and lagging will not work, secant pile walls provide a continuous structural barrier that is both structurally capable and water-resistant. A secant pile wall is constructed by drilling overlapping concrete piles in a specific sequence: unreinforced or lightly reinforced "soft" piles are drilled first at regular spacing, then reinforced "hard" piles are drilled between them, with each hard pile cutting into the soft piles on each side. The result is an interlocking wall of overlapping concrete cylinders that forms a continuous, relatively water-tight barrier.

Secant pile walls are relatively uncommon on residential projects in most of Los Angeles, where native soils are typically competent and the water table is deep. They become relevant on coastal properties in Malibu and the Palisades beachfront where the water table is shallow, or on sites with running sand or other problematic soil conditions that rule out systems with gaps or joints through which water and soil can migrate. Secant walls are significantly more expensive than soldier pile and lagging - often two to three times the cost per square foot of wall face - but they solve problems that other systems cannot address.

Tangent Pile Walls

Similar in concept to secant piles but without the overlap: tangent piles are drilled touching (tangent to) each other, forming a nearly continuous wall. Because the piles do not interlock, tangent pile walls are less water-tight than secant walls but are simpler to construct and somewhat less expensive. They are used where a continuous wall is needed for structural reasons but where groundwater cutoff is not the primary design requirement.

Diaphragm Walls (Slurry Walls)

On the extreme end of deep excavation support, diaphragm walls are continuous reinforced concrete walls constructed in slurry-filled trenches before excavation begins. A narrow trench is excavated under bentonite slurry (which prevents the trench walls from caving), a reinforcement cage is lowered into the slurry-filled trench, and concrete is placed by tremie pipe from the bottom up, displacing the slurry. The result is a structural concrete wall in place before any soil is removed from the excavation interior. Diaphragm walls are extremely rare on residential projects due to cost, equipment requirements, and the scale of operation, but they are occasionally encountered on large-scale mixed-use developments in Los Angeles that include residential components with very deep subterranean levels.

WATERPROOFING SHORING WALLS

When the shoring wall becomes the permanent below-grade wall or is directly adjacent to it, waterproofing is a critical consideration that must be addressed in the shoring design phase, not after the fact. The relationship between the shoring system and the building's waterproofing strategy depends on whether the shoring is temporary or permanent and on how the permanent below-grade wall is constructed relative to the shoring.

Temporary Shoring with a Separate Permanent Wall

On many residential projects, the soldier pile and lagging wall or soil nail wall is left in place, and a new concrete foundation wall is poured inside of it with a gap between the two. In this configuration, the permanent wall is waterproofed independently using standard below-grade waterproofing applied to the exterior face of the new wall before the gap is backfilled. The shoring serves only a temporary function and does not need to be water-tight itself, though any water migrating through the shoring during construction must be managed to keep the work area dry enough for foundation construction.

The space between the shoring and the permanent wall - typically 12 to 24 inches, though it varies with the design - becomes a construction issue in itself. It must be accessible enough to install waterproofing membrane, drainage board, and drain pipe on the exterior face of the new wall before backfilling. On tight sites where the shoring is at or very near the property line, this gap may be the only available space for the waterproofing system, and the construction sequence must allow for membrane installation before the gap is closed.

Shoring as the Permanent Wall

When the shoring system is designed to serve as the permanent below-grade wall - soldier piles with permanent shotcrete facing, permanent soil nail walls, or secant pile walls that form the building envelope - the waterproofing approach changes fundamentally. Because the exterior face of the wall is already against the soil and is inaccessible after construction, waterproofing must be applied to the interior face of the wall, between the shoring and the occupied space. This is a different detail than conventional below-grade waterproofing and requires coordination between the shoring engineer, the waterproofing consultant, and the architect.

Interior-side waterproofing on shoring walls typically involves a drainage layer (dimple board or drainage mat) applied to the interior face of the shoring, a waterproofing membrane over or behind the drainage layer, and then the interior finish wall. Any water that penetrates through the shoring is captured by the drainage layer, directed down to a perforated drain pipe at the base of the wall, and collected in a sump for removal. This system acknowledges that a shoring wall - particularly one built by shotcreting against irregular soil - may not be perfectly water-tight, and it provides a redundant drainage path to manage any infiltration.

Groundwater and Shoring

On sites with a shallow water table, groundwater management becomes a major component of the shoring design and construction. Dewatering - actively pumping to lower the water table within the excavation during construction - may be required to maintain a dry excavation and to allow foundation construction to proceed. Dewatering has its own engineering requirements, permitting implications (a discharge permit from the Los Angeles Regional Water Quality Control Board is required for dewatering discharge), and cost. Sustained dewatering over the duration of construction can affect neighboring wells, contribute to subsidence in adjacent properties, and require environmental monitoring.

SHOTCRETE IN SHORING APPLICATIONS

Shotcrete (pneumatically applied concrete) is used extensively in shoring construction - for soil nail wall facings, as a replacement for timber lagging on soldier pile walls, for permanent wall facing, and for slope stabilization. Because shotcrete appears in nearly every shoring system discussed in this guide, it is worth understanding the material and application method in its own right.

Wet-Mix Versus Dry-Mix

There are two methods of shotcrete application. In wet-mix shotcrete, the concrete is pre-batched and mixed at the plant or on site, pumped through a hose as a wet material, and compressed air is added at the nozzle to propel it onto the target surface. Wet-mix is the more common method on larger shoring applications because it provides consistent material quality and higher production rates. In dry-mix shotcrete, the dry cement and aggregate are conveyed through the hose by compressed air, and water is added at the nozzle by the operator. Dry-mix allows finer control of the water-cement ratio and is sometimes preferred for small areas, thin applications, and repair work. In both methods, the skill of the nozzleman is the most critical variable in the quality of the finished product. Proper application angle (perpendicular to the surface), distance (typically 3 to 6 feet from the nozzle to the target), and technique (steady, systematic passes) determine whether the shotcrete achieves full compaction and bond to the substrate or contains voids, laminations, and poor encapsulation of the reinforcement.

Reinforcement

Welded wire fabric (WWF) or rebar mats are installed against the soil face or over the existing shoring piles before shotcrete is applied. The reinforcement is tied to the soldier piles, soil nail heads, or temporary anchors and held at the correct cover distance from the soil face using chairs or ties. The shotcrete must fully encapsulate the reinforcement without voids behind the bars. Poor encapsulation - caused by shadowing behind the bars, insufficient nozzle angle, or too-rapid buildup - is the most common quality defect in shotcrete shoring and is why special inspection by a qualified inspector is required for structural shotcrete applications.

Thickness and Strength

Shoring shotcrete facing thickness ranges from 4 inches for temporary soil nail wall facings to 8 to 12 inches for permanent structural walls carrying significant lateral loads. The thickness is specified by the shoring engineer and verified during construction using depth gauges embedded in the face at regular intervals. Shotcrete for shoring is typically specified at 3,000 to 4,000 psi compressive strength at 28 days, with higher strengths (4,500 to 6,000 psi) occasionally specified for permanent structural applications. Strength is verified by test panels shot alongside the wall, from which cores are extracted and tested at 7 and 28 days to confirm the material meets specification.

Rebound

When shotcrete is sprayed, a percentage of the material bounces off the target surface rather than adhering. This rebound can range from 10 to 25 percent of the sprayed volume depending on the application angle, surface conditions, aggregate size, and application technique. Rebound material that accumulates at the base of the wall must be removed before subsequent lifts are shot - it cannot be incorporated into the wall because the rebounded material has lost much of its cement content during the impact and is essentially loose aggregate without structural capacity. On large shoring shotcrete operations, managing rebound removal is a significant logistical consideration.

SLOPE STABILITY AND TEMPORARY CUT STABILITY

Slope stability is related to but distinct from structural shoring. When a hillside is cut for construction, the exposed slope must remain stable during the construction period (and permanently, if the cut is permanent). Not every exposed cut requires a structural shoring wall - some cuts can be made at a stable angle and left as open slopes, at least temporarily - but the determination of whether a slope is stable and what support it needs is an engineering decision based on the specific soil and rock conditions at the site.

Temporary Cut Slopes

When a hillside is excavated and a temporary slope is left exposed during construction before the permanent retaining structure is built, the slope must be cut to an angle that will remain stable for the duration of exposure. The geotechnical engineer specifies the temporary cut slope ratio - the ratio of horizontal distance to vertical height - based on the soil type, moisture conditions, surcharge loads, and the expected duration of exposure. Common temporary cut slopes in LA hillside soils range from 1:1 (45 degrees) to 1.5:1 (approximately 34 degrees), though competent rock may be cut steeper and weak or saturated soils require shallower angles.

The tradeoff between slope angle and shoring is space. A shallower cut requires more horizontal distance, which means more of the site is consumed by the slope rather than being available for construction. On tight hillside lots where the building footprint extends close to the property lines, there may not be enough room for a sloped cut at a stable angle, and a structural shoring wall becomes necessary to hold the cut at a steeper (or vertical) angle. The geotechnical engineer's recommendation on temporary cut stability often determines whether a project needs full structural shoring or whether a sloped cut with erosion protection is sufficient.

Rock Faces

Some hillside sites in Los Angeles cut into competent bedrock - sandstone, siltstone, or harder formations. Rock cuts can stand at steeper angles than soil cuts, sometimes near-vertical, because the intact rock has significant compressive and tensile strength. However, rock is rarely uniformly competent across the full height and width of a cut. Bedding planes, fractures, joints, weathered zones, and clay seams within the rock create potential failure surfaces that can release blocks or wedges of rock from the cut face. The geotechnical engineer evaluates the rock structure - bedding orientation, joint spacing and persistence, weathering grade - to determine safe cut angles and whether rock stabilization measures are needed.

Rock stabilization on residential hillside sites typically involves rock bolts (steel bars drilled and grouted into the rock face to pin potential failure blocks in place), wire mesh draped over the rock face to catch small loose fragments (particularly important where the cut face is above occupied areas or access paths), and shotcrete applied to the rock face to prevent weathering and spalling of the exposed surface. These measures are distinct from full structural shoring - they are stabilizing an inherently competent rock mass against localized failure rather than retaining soil that has no ability to stand on its own.

Slope Stabilization with Shotcrete and Soil Nails

Temporary or permanent slopes that the geotechnical engineer determines cannot maintain stability at the required cut angle can be stabilized with a soil nail and shotcrete system applied to the cut face. This effectively converts an open slope into a structural wall, with the soil nails tying the facing to stable ground behind the potential failure surface. This approach is common on hillside residential projects where the geotechnical report indicates that the native soil cannot maintain a stable slope at the angle needed to accommodate the building design.

Slope Drainage

Water is the primary driver of slope instability. Surface water must be diverted away from cut slopes with berms, swales, and V-ditches at the top of the cut. Subsurface water may require horizontal drains (perforated pipes drilled horizontally into the slope face to relieve pore water pressure) or subdrains behind soil nail walls. During LA's rainy season, November through March, water infiltration behind cut slopes or shoring walls can dramatically change the stability conditions compared to the dry months when the cut was originally made. The shoring and slope stabilization design must account for wet-season conditions, and the construction team should be monitoring for signs of distress - increased seepage, surface cracking above the cut, muddy discharge at weep holes - during and after rain events.

HOW LONG DOES SHORING STAY IN PLACE?

This is a practical question that owners and architects often do not consider early enough in the design process, and the answer affects the shoring design, the materials, the cost, and the construction sequence.

Temporary Shoring Lifespan

Temporary shoring is designed for the construction period - typically 12 to 24 months on a residential project, though complex projects can extend beyond that. The shoring engineer specifies a design service life for the temporary system, and the materials and corrosion protection (or lack thereof) are selected accordingly. Steel soldier piles left in the ground during a 12-month construction period do not need the same corrosion protection as piles intended to remain in service for 50 years. If the construction schedule extends significantly beyond the original design service life - due to project delays, design changes, financing issues, or any of the other factors that can stretch a residential construction timeline - the shoring may need to be re-evaluated by the shoring engineer to confirm that it remains adequate for continued service.

When Shoring Comes Out

On a typical basement or subterranean construction project, the construction sequence after shoring installation follows a general pattern. The permanent foundation walls and floor slab are constructed inside the shoring envelope. Waterproofing is applied to the exterior face of the permanent walls (in the gap between the permanent wall and the shoring) or to the interior face of the shoring (if the shoring is the permanent wall). Backfill is placed between the permanent wall and the shoring if there is a gap. Then the above-grade structure is built, providing the permanent lateral bracing that replaces the temporary shoring.

When Shoring Becomes Permanent

On some projects, the shoring system is designed from the outset to serve as the permanent retaining structure. Soil nail walls with architectural shotcrete facing, soldier pile walls with permanent shotcrete or concrete facing, and secant pile walls can all function as the permanent below-grade wall. In these cases, the wall is designed to permanent structure standards: the steel elements receive corrosion protection (epoxy coating, galvanizing, or encapsulation), the facing is designed for a 50- to 75-year service life, waterproofing and drainage are integrated into the wall system, and the wall receives an architectural finish appropriate to its visibility and function.

Transition from Temporary Shoring to Permanent Structure

This transition is a critical construction sequence that requires coordination between the shoring engineer, the structural engineer of record, and the general contractor. The permanent structure must be designed and built to take over the lateral loads from the temporary shoring before the shoring is de-stressed or removed. On a basement project, this typically means the floor slab (which acts as a horizontal brace at the bottom of the wall) and the first-floor framing (which braces at the top) must both be in place and have reached adequate strength before tiebacks can be de-stressed or rakers can be removed. The structural engineer of record specifies the sequence of shoring removal in coordination with the permanent structure completion milestones, and this sequence is documented on the structural plans.

DRAINAGE AND WATER MANAGEMENT IN SHORING SYSTEMS

Water behind a shoring wall is a problem that affects both the structural performance of the wall and the long-term habitability of the below-grade spaces it protects. This topic was introduced in the waterproofing section but warrants its own treatment because drainage is an engineered system with specific components, design requirements, and failure modes that differ from the waterproofing membrane itself.

Why Drainage Is Critical Behind Shoring

Beyond the structural concern, water seeping through gaps in lagging boards or through cracks and joints in shotcrete facing carries soil fines with it. This process, called piping, erodes the soil behind the wall, creating voids that can propagate to the surface and cause settlement or collapse of the ground above. Proper drainage prevents both the structural overload from hydrostatic pressure and the erosion and void formation from piping.

Drainage System Components

A complete drainage system behind a shoring or below-grade wall typically includes several components working together. A geocomposite drain board (dimple board) is placed against the soil face or against the back of the shoring facing to create a drainage channel between the soil and the wall. A filter fabric on the soil side of the drain board prevents soil fines from migrating into and clogging the drainage channels. A perforated drain pipe at the base of the wall collects water from the drain board and routes it to a sump or gravity outlet. Weep holes through the wall face at regular intervals allow water to pass through the wall rather than building pressure behind it. On permanent walls, the drain pipe connects to the building's subdrain system, which in turn connects to a sump pump or to the storm drain system per the site's drainage plan.

Construction-Period Water Management

During construction, water reaching the base of a shoring wall must be managed to maintain a workable excavation. Temporary sump pits and pumps are used to collect and remove water from the excavation. The discharge of this water is regulated - pumping sediment-laden groundwater directly into the street gutter or storm drain without treatment is a violation of stormwater regulations. The discharge must either go to the sanitary sewer (with an appropriate permit from the Bureau of Sanitation) or be treated on site to meet discharge standards before entering the storm drain system. On projects with significant groundwater, the dewatering operation can be a substantial ongoing cost throughout the excavation and substructure construction phases.

Seasonal Considerations

CHOOSING THE RIGHT SYSTEM: A DECISION FRAMEWORK

The preceding sections describe the individual shoring systems available. This section explains how the site conditions and project requirements on a specific project determine which system is appropriate. Shoring system selection is not a matter of preference or habit - it is an engineering decision driven by real constraints. Understanding these constraints helps owners and architects evaluate the shoring engineer's recommendation and understand why the recommendation may differ from what was used on a different project, even one that appeared similar.

Excavation Depth

Shallow cuts (under 10 to 12 feet) may not require structural shoring at all if the geotechnical engineer confirms that a sloped cut at a stable angle is feasible and there is enough site area to accommodate the slope. Medium-depth excavations (12 to 25 feet) are the range where most residential shoring systems operate - soldier pile and lagging, soil nail walls, and cantilevered or single-tieback pile systems are all effective in this range. Deep excavations (25 to 40 feet or more) typically require multi-level tieback or raker-supported pile walls, secant pile systems in wet conditions, or other specialized deep shoring approaches. The cost curve steepens significantly as depth increases because the structural demands scale non-linearly with wall height.

Soil and Rock Conditions

The soil and rock conditions identified in the geotechnical report are the primary input to system selection. Competent soils that can stand unsupported for one lift (4 to 5 feet) while nails and shotcrete are installed favor soil nail walls, which are typically less expensive than pre-installed pile systems and do not require heavy drill rigs for pile installation. Loose or caving soils that collapse immediately upon exposure require pre-installed systems - soldier piles are drilled and set before any excavation begins, so the retention system is already in place when the soil is removed. Competent rock may need only bolting and mesh rather than a full structural wall. And highly variable conditions - common in LA where a site may have competent sandstone in one area and loose fill in another - may require different shoring approaches on different portions of the same excavation.

Water Table

Dry conditions leave all shoring options available. A shallow water table narrows the options significantly. Open-face systems (soldier pile and lagging with timber lagging) allow water to flow through the gaps between boards, which is unacceptable when the water carries soil fines and creates piping. Soil nailing is difficult in saturated conditions because the grout does not cure properly without special measures. Shallow groundwater pushes the design toward water-tight systems - secant piles, sheet piles, or continuous concrete walls - combined with dewatering. The cost and complexity increase substantially when groundwater control becomes part of the shoring scope.

Adjacent Structures

When the excavation is adjacent to and below the foundation of a neighboring structure, the shoring system must limit deflection to fractions of an inch to protect the adjacent building. This requirement rules out some of the lower-cost, more flexible systems and favors stiffer configurations: soldier piles with tiebacks, closely spaced piles with shotcrete facing, or secant piles. The underpinning, pre-construction survey, monitoring program, and affidavit requirements described earlier in this guide all apply in addition to the shoring wall itself. The combination of structural shoring, underpinning, and monitoring is one of the most expensive and time-consuming configurations in residential construction.

Property Line Constraints

Soil nails and tiebacks extend beyond the wall face into the ground behind it. If that ground is a neighbor's property, an easement is required, and if the neighbor will not grant one, the design must change to a system that stays within the owner's property. Cantilevered pile systems (relying only on pile embedment, with no tiebacks or nails extending beyond the wall), and raker-braced systems (with the rakers inside the excavation footprint) are the alternatives when subsurface encroachment is not permitted. On tight lots in Bel Air, Beverly Hills, Brentwood, and the greater Westside where homes are close together, this property line constraint is often the single factor that determines the shoring system selection, overriding what would otherwise be the most economical engineering choice.

Temporary Versus Permanent

If the shoring will be abandoned behind a separate permanent wall, lighter and less expensive temporary systems are appropriate. If the shoring is the permanent wall - the finished below-grade surface of the building - it must be designed for permanent loads, a 50- to 75-year service life, corrosion protection, waterproofing integration, and architectural finish. The permanent path costs more up front but can save money overall by eliminating the need to build a separate foundation wall behind the shoring.

Access and Equipment Constraints

Hillside lots with narrow streets, tight driveways, and limited staging area may restrict the size of drill rigs and cranes that can reach the site. This access constraint can push the design toward smaller-equipment systems - micropiles, hand-excavated underpinning, smaller drill rigs for shorter soldier piles - even when a larger, more efficient system would be the better engineering choice on an unrestricted site. Access is a practical reality on many hillside construction projects, and it directly affects both the shoring system selection and the installation cost.

Cost Hierarchy

In general, from least to most expensive per square foot of wall face: a temporary sloped cut (if space allows) is the least costly because it involves no structural system at all, only excavation and erosion protection. Soil nail walls in suitable soil conditions are typically the next most economical. Soldier pile and lagging follows. Soldier pile with tiebacks costs more than cantilevered pile and lagging due to the anchor installation. Secant pile walls are at the upper end of the cost range. But site conditions routinely invert this general hierarchy - a soil nail wall in ideal conditions can cost less than a soldier pile and lagging wall that looks simpler on paper but requires dewatering, neighbor easements, or complex phasing. The shoring engineer's recommendation is driven by the site-specific engineering and construction reality, not by a generic cost ranking.

PERMITTING SHORING IN LOS ANGELES

Shoring in the City of Los Angeles involves a regulatory framework that spans two city departments and several permit types, depending on the scope and location of the excavation. Understanding this framework is important for project scheduling because the permitting process directly affects when shoring work can begin, and delays in shoring permit approval can cascade through the entire construction timeline.

LADBS Building Permit and Shoring Plan Check

Shoring plans are typically submitted to LADBS as part of the overall building permit package or, in some cases, as a separate submittal within the same permit application. Because shoring is usually a design-build scope, the shoring plans may not be available at the time the initial building permit application is submitted - the shoring subcontractor develops the design after the project team is assembled and the geotechnical report is complete. This creates a sequencing consideration: the building permit may be in plan check review while the shoring design is still being developed, or the shoring plans may need to be submitted as a supplemental package after the main building permit is already under review.

LADBS plan check for shoring includes review of the shoring engineer's structural calculations, the pile or nail layout and sections, the construction sequence (including slot-cut widths and phasing), the relationship between the shoring and adjacent structures, and consistency with the geotechnical report recommendations. The shoring engineer's calculations must demonstrate that the system meets the lateral earth pressure, surcharge, and seismic loading requirements of the Los Angeles Building Code (LAMC Section 91.3307 and related sections). Plan check corrections are common and may require revisions to the shoring design, recalculation of specific elements, or additional documentation of adjacent structure protection measures.

Bureau of Engineering E-Permit for Lateral Support

When the excavation is adjacent to a public right-of-way and the shoring or excavation will remove or affect the lateral support of the public street, a separate Excavation E-Permit is required from the Bureau of Engineering (BOE). This is a distinct permit from the LADBS building permit and is processed through a separate department with its own review procedures, fees, and insurance requirements. The E-Permit process requires submission of the shoring plans, the geotechnical report, the LADBS grading department approval letter, and proof of general liability insurance naming the City as additional insured. If dewatering is anticipated, additional documentation including a dewatering plan and settlement monitoring program must be submitted.

The BOE review focuses on the protection of the public right-of-way - ensuring that the excavation and shoring will not cause settlement of the sidewalk, street, or underground utilities, and that tiebacks or other elements extending under the public way meet the City's requirements. Special Order No. 003-0201 specifically addresses requirements for deep excavation and tieback installation on sites adjacent to public ways. The BOE E-Permit must be issued before shoring work affecting lateral support of the public way can begin, and the permit carries a cash bond or surety bond requirement per LAMC Section 62.02.

Adjacent Property Notification

LAMC Section 91.3307 requires that before a permit can be issued for excavation that will be deeper than the foundation of an adjoining structure and closer to the property line than the depth of excavation, the property owner must provide LADBS with evidence that the adjacent property owner has received 30-day advance written notice by certified mail, return receipt requested, stating the intended excavation depth and start date. This notification is a permit prerequisite - the excavation portion of the permit cannot be issued without proof that the notice was sent. Additionally, California Civil Code Section 832 requires reasonable notice to adjacent owners for any excavation, independent of the LADBS requirement.

The Underpinning Affidavit

When the geotechnical engineer determines that the proposed building's subterranean walls (rather than traditional underpinning) will provide the lateral support for an adjacent building's foundation, the property owner must record a sworn affidavit with the Los Angeles County Recorder's Office. This affidavit informs future owners that the structural integrity of the subterranean walls is necessary to maintain the lateral support of the adjacent property's foundation. Recording the affidavit is a condition of permit issuance and creates a permanent obligation that runs with the land.

Inspections

LADBS inspects shoring installations at key construction milestones: soldier pile installation (verifying pile size, spacing, and embedment), tieback installation and testing, shotcrete placement, and waterproofing installation. In addition to LADBS inspections, the shoring engineer and/or the geotechnical engineer provide special inspection (observation and testing by the engineer of record or their designated representative) at these same milestones. Special inspection for shoring is a code requirement, not an optional service - it is the mechanism by which the engineer of record confirms that the work in the field matches the approved plans and that the materials and installation meet the specification.

Shoring Removal and Decommissioning

When temporary shoring is decommissioned - tiebacks de-stressed, rakers removed, temporary lagging abandoned - the structural engineer of record must confirm that the permanent structure is capable of carrying the lateral loads that were previously carried by the shoring. This confirmation may be documented as a letter to the building department, a field inspection report, or a sign-off on the structural plans. LADBS may require this documentation before issuing certain progress inspections or the certificate of occupancy for the permanent structure.

COSTS

Shoring costs on LA residential projects are highly site-specific, and the same 20-foot-deep excavation can cost dramatically different amounts depending on soil conditions, adjacent structure loads, water table depth, access constraints, property line encroachment issues, and whether the shoring is temporary or permanent. The ranges below reflect current pricing in the Los Angeles residential market as of early 2026 and are intended to provide order-of-magnitude guidance for budgeting and cost planning purposes, not as substitutes for a project-specific estimate from a shoring subcontractor.

Shoring Engineering and Design

On design-build shoring projects, the engineering cost is typically embedded in the shoring subcontractor's lump sum price rather than appearing as a separate line item. When the shoring engineering is procured separately - because the project team wants an independent design, or because the project is being bid competitively to multiple shoring subcontractors using a common design - shoring engineering fees for a residential project typically range from $15,000 to $50,000 or more, depending on the complexity of the site and the number of review iterations required. This fee covers the shoring plan development, structural calculations, coordination with the geotechnical engineer and the structural engineer of record, and response to plan check comments.

Soldier Pile and Lagging

The cost of soldier pile and lagging is driven primarily by excavation depth, pile size and spacing, and whether the system is temporary or permanent. For temporary cantilevered walls up to about 15 feet deep, installed costs (including piles, drilling, lagging, and excavation coordination) typically fall in the range of $35 to $75 per square foot of wall face. For deeper walls requiring tiebacks (15 to 25 feet), the range increases to $60 to $120 per square foot. For deep walls with multiple tieback rows (25 to 40 feet), costs can reach $100 to $175 per square foot or more. These ranges reflect LA market conditions, which carry a premium over many other regions due to labor costs, equipment mobilization on residential sites with limited access, and the seismic design requirements that apply to every system.

Soil Nail Walls

Soil nail walls in suitable soil conditions are typically less expensive than soldier pile and lagging for equivalent wall heights, primarily because they do not require the pre-drilling and installation of large steel piles. Costs for temporary soil nail walls with shotcrete facing typically range from $30 to $70 per square foot of wall face for walls up to about 20 feet. Permanent soil nail walls with corrosion-protected nails, thicker facing, and architectural finish range from $60 to $130 per square foot. The cost range is wide because nail length, spacing, shotcrete thickness, and the difficulty of the installation (access constraints, cure time requirements, multiple phases) all affect the installed price.

Shotcrete Facing

Shotcrete facing as a component of a shoring system (applied over soldier piles, soil nails, or directly on the soil face) typically costs $15 to $40 per square foot for temporary applications (4 to 6 inch thickness) and $25 to $60 per square foot for permanent structural applications (6 to 12 inches) including reinforcement, nozzle application, and finishing. These numbers overlap with the all-in system costs noted above because shotcrete is a component of those systems, not an add-on.

Tiebacks

Individual tiebacks are priced per anchor, with the cost driven by the anchor length, the load capacity, and the difficulty of installation. Grouted tieback anchors in typical LA soil conditions range from $3,000 to $8,000 per tieback installed and tested, with the lower end representing shorter anchors at moderate loads and the upper end representing deep anchors with high design loads and extended bond lengths. Helical tiebacks, which can be installed and tested more quickly (no grout cure time), may offer cost savings in specific conditions but are not universally applicable. On a deep wall with multiple tieback rows, the anchor cost alone can represent a significant portion of the total shoring budget.

Raker Bracing

Rakers are highly variable in cost depending on the wall height, the load, and the configuration of the reaction block at the base. Individual rakers on a residential project typically cost $5,000 to $15,000 each, including the steel brace, the concrete reaction block, the connection hardware, and installation. The cost of rakers must also account for the schedule impact of working around them during the substructure construction phase and the cost of sequenced removal as the permanent structure takes over.

Underpinning

Pit underpinning (mass pour) costs depend on the depth of underpinning required, the slot-cut width and number of phases, the length of foundation being underpinned, and the cure time between phases. Typical ranges are $400 to $1,200 per lineal foot of underpinned foundation, with the width of the range reflecting the variability in depth (underpinning 4 feet below an existing footing is very different from underpinning 15 feet below it). Micropile underpinning is typically more expensive per lineal foot of supported foundation ($600 to $2,000 or more) but may be faster and less disruptive where access is limited.

Secant Pile Walls

Secant pile walls are among the most expensive shoring systems used on residential projects. Costs typically range from $80 to $200 per square foot of wall face, reflecting the precision drilling required for overlapping piles, the reinforcement in the "hard" piles, and the equipment and expertise involved. On coastal sites where secant walls are required for groundwater control, the shoring cost can be a defining element of the overall construction budget.

Dewatering

Dewatering costs include mobilization and installation of wells or wellpoints ($10,000 to $40,000 depending on the system and depth), ongoing pumping and monitoring costs ($2,000 to $8,000 per month during active dewatering), discharge permitting (LARWQCB permit fees and compliance monitoring), and potential settlement monitoring of adjacent properties if the dewatering drawdown extends beyond the site. On projects where dewatering runs for 6 to 12 months, the cumulative cost can be significant.

Supporting Costs

Several additional cost items are associated with shoring scope but are sometimes overlooked in early-stage budgeting. A pre-construction condition survey of adjacent properties typically costs $3,000 to $8,000 per property surveyed, depending on the size of the structure and the level of documentation required. Survey monitoring during construction (reading monitoring points on the shoring wall and adjacent structures at regular intervals) runs $1,500 to $4,000 per month depending on the number of points and frequency of readings. The underpinning affidavit filing and certified mail notification to adjacent owners are relatively minor administrative costs (a few hundred dollars) but must be completed before permits can be issued. Performance and payment bonds, if required by the shoring contract, add 1 to 3 percent of the shoring contract value.

WORKING WITH YOUR PROJECT TEAM ON SHORING

Shoring involves more parties and more coordination interfaces than most other construction scopes on a residential project. Each team member has a specific role, and the interfaces between those roles are where coordination problems are most likely to occur. Understanding who does what - and who is responsible for what - helps owners and architects engage effectively in the process.

The owner bears ultimate legal liability for adjacent property protection under California Civil Code Section 832. The owner is the party who files the underpinning affidavit, sends the 30-day notification to adjacent property owners, provides the insurance and bonds required by the city, and is liable for damage to neighboring properties resulting from the excavation. The owner does not design or install the shoring, but the legal and financial exposure rests with the owner regardless of which professionals are retained to execute the work.

The structural engineer of record designs the permanent structure that will eventually replace or supplement the temporary shoring. The structural engineer reviews the shoring engineer's design for compatibility with the permanent structure, specifies the sequence in which temporary shoring elements can be removed as the permanent structure takes over, and confirms that the permanent structure can carry the lateral loads at each stage of shoring decommissioning.

The geotechnical engineer provides the soil and groundwater parameters that the shoring system is designed on. The geotech reviews the shoring design for consistency with the geotechnical report, may specify monitoring requirements and movement thresholds, and evaluates monitoring data during construction. On complex sites, the geotechnical engineer's involvement is continuous from the initial site investigation through the completion of below-grade construction.

The shoring engineer designs the shoring system, typically working for the shoring subcontractor in a design-build arrangement. The shoring engineer produces the plans and calculations, responds to plan check comments, specifies the construction sequence and monitoring program, and may provide field observation during critical installation operations.

The shoring subcontractor installs the shoring system per the shoring engineer's design. The shoring sub carries their own general liability insurance and typically carries specific coverage for adjacent property damage. On design-build shoring, the subcontractor is responsible for both the design adequacy and the installation quality of the system.

The construction manager or general contractor coordinates the shoring work with the overall construction sequence, manages the interfaces between the shoring subcontractor and other trades (excavation, foundation, waterproofing, drainage), oversees the monitoring program, and ensures that the slot-cut sequence, cure times, and installation procedures specified on the shoring plans are followed in the field. The CM/GC is the party responsible for making sure the shoring plan is actually executed as designed - that the right piles are in the right locations at the right depth, that the slot-cut sequence is followed without shortcuts, that tiebacks are tested and documented, and that monitoring readings are taken and reviewed on schedule. This coordination role is one of the reasons that shoring-intensive projects benefit from having a construction manager engaged during pre-construction rather than after the shoring design is complete.

The surveyor or monitoring firm reads the survey monitoring points and provides regular reports documenting wall movement, adjacent structure movement, and any changes relative to the established thresholds. These reports go to the geotechnical engineer for evaluation and to the CM/GC for construction management purposes.

FREQUENTLY ASKED QUESTIONS

The information provided on this page is for general educational purposes and reflects current construction practices and regulatory requirements in the Los Angeles area as of the date of publication. Building codes, permit procedures, and regulatory requirements are subject to change. Cost ranges are approximate and reflect current market conditions in the Los Angeles residential market; actual project costs depend on site-specific conditions, project scope, and market timing. This content does not constitute engineering advice. All shoring, underpinning, and excavation support systems require project-specific design by licensed engineers based on site-specific geotechnical investigation. Consult with qualified professionals for guidance specific to your project.