Temporary Shoring & Underpinning Guide for Contractors | Projul

If you have been in the trades long enough, you have probably driven past a job site where a neighboring building started cracking because somebody dug too deep, too fast, without proper support. That scenario is every contractor’s nightmare, and it is completely avoidable when you understand shoring and underpinning.

This guide walks through the practical side of temporary shoring and underpinning, covering when you need it, which systems work for different situations, what the engineering looks like, and how to keep everyone safe on site. Whether you are digging a new basement next to an occupied building or adding a story below grade on a commercial project, this is the information your crew needs before breaking ground.

When Shoring and Underpinning Are Needed

Not every excavation requires shoring, and not every foundation needs underpinning. But when the conditions call for it, skipping these steps is not an option.

Shoring is typically required when:

• You are excavating deeper than five feet in unstable soil (OSHA’s baseline threshold for protective systems)
• The excavation is adjacent to an existing structure, road, or utility corridor
• Soil conditions include loose sand, fill material, high water tables, or expansive clay
• Trenches cannot be sloped or benched due to site constraints
• Vibration from equipment or traffic could destabilize the cut

Underpinning comes into play when:

• A new excavation will go deeper than the bottom of an adjacent building’s foundation
• An existing foundation sits on soil that cannot carry the loads from a planned addition or renovation
• Settlement has already occurred and the foundation needs to reach a more competent bearing layer
• You are converting a crawl space to a full basement, which means deepening the existing footings

The key takeaway is that both shoring and underpinning are responses to specific site conditions, not things you decide on a whim. A thorough excavation plan starts with understanding the soil, the adjacent structures, and the loads involved. Get a geotechnical report early. It will tell you what you are dealing with below grade and inform every decision that follows.

Many contractors overlook shoring requirements on what seem like simple residential projects. But a 10-foot dig for a new basement wall that sits three feet from the property line can absolutely undermine the neighbor’s foundation if you do not plan for lateral soil support. The lawsuits from that scenario will cost you far more than the shoring ever would.

Types of Temporary Shoring Systems

There are three main categories of shoring systems you will encounter in the field: hydraulic, timber, and pneumatic. Each has its place depending on soil conditions, excavation depth, site access, and budget.

Hydraulic Shoring

Hydraulic shoring uses aluminum or steel rails with hydraulic cylinders that apply pressure against the trench walls. This is the most common system for utility trenches and moderate-depth excavations.

Advantages:

• Quick to install and remove (a two-person crew can set a section in minutes)
• Adjustable to varying trench widths
• Lightweight components are easy to transport
• No cutting or fitting required on site

Best for: Utility trenches, sewer line installations, and excavations up to about 20 feet deep where soil conditions are relatively predictable.

Limitations: Not ideal for very wide excavations or situations where you need to support heavy surcharge loads from adjacent buildings.

Timber Shoring

Timber shoring uses wooden planks (lagging) held in place by vertical soldier piles (typically steel H-beams) and horizontal walers. This is one of the oldest shoring methods and still gets plenty of use, especially on residential projects and sites with limited access for heavy equipment.

Advantages:

• Materials are readily available at any lumber yard
• Can be custom-cut to fit irregular excavation shapes
• Lower material cost compared to steel sheet piling
• Works well for shallow to moderate depths

Best for: Residential basement excavations, small commercial projects, and sites where the shoring needs to fit around existing utilities or odd geometries.

Limitations: Labor-intensive to install. Timber members can degrade if exposed to water for extended periods. Load capacity is lower than steel systems, so your engineer will specify larger members as depth increases.

Pneumatic Shoring

Pneumatic shoring works similarly to hydraulic shoring but uses air pressure instead of hydraulic fluid to brace the trench walls. These systems are lighter and often faster to deploy than hydraulic alternatives.

Advantages:

• Very lightweight, making them easier to handle in tight spaces
• No risk of hydraulic fluid leaks contaminating the excavation
• Fast setup and breakdown

Best for: Environmental remediation sites where hydraulic fluid is a concern, shallow utility trenches, and quick-turnaround jobs.

Limitations: Generally limited to shallower depths and lighter loads compared to hydraulic systems. Air compressor must remain on site and operational.

Other Systems Worth Knowing

Beyond the big three, you should also be familiar with:

• Steel sheet piling: Interlocking steel sheets driven into the ground to create a continuous wall. Common on waterfront projects, deep excavations, and sites with high water tables. Requires pile-driving equipment.
• Soldier pile and lagging: Steel H-piles driven at regular intervals with timber or concrete lagging placed between them as excavation proceeds. Very common for deep urban excavations.
• Soil nailing: Steel bars (nails) drilled and grouted into the excavation face, then covered with shotcrete. Creates a reinforced soil mass that acts as a gravity retaining structure.

Your project scheduling should account for shoring installation and removal as distinct activities, because they will affect your critical path.

Underpinning Methods Explained

Underpinning is a different animal from shoring. Where shoring is temporary, underpinning makes permanent changes to an existing foundation. There are three primary methods you will see specified on plans.

Mass Concrete Underpinning (Pit Method)

This is the traditional method and still the most common for residential and light commercial work. You excavate in short sections (called pins or pits) beneath the existing footing, then fill each section with concrete before moving to the next one.

How it works:

1. The engineer divides the foundation into numbered sections, typically three to five feet wide
2. You excavate one section at a time to the new bearing depth
3. Place reinforcing steel as specified
4. Pour concrete and let it cure to the required strength
5. Move to the next section (never work adjacent sections simultaneously)

Best for: Residential foundation deepening, adding basements to existing homes, and situations where the new bearing depth is within about six feet of the existing footing.

Watch out for: The sequential nature of this work makes it slow. You cannot rush the curing between pours. Budget realistic timeframes when you are putting together estimates for underpinning projects.

Mini-Pile Underpinning

When the competent bearing layer is too deep for mass concrete underpinning, mini-piles (also called micropiles) are the go-to solution. These are small-diameter drilled piles, typically 6 to 12 inches, that transfer the building load down to bedrock or a strong soil layer.

How it works:

1. Drill through or adjacent to the existing footing
2. Install steel casing or reinforcing bar
3. Grout the pile from the bottom up
4. Connect the pile to the existing footing with a pile cap or bracket

Best for: Commercial buildings with heavy loads, sites where the bearing layer is 20 feet or more below the existing foundation, restricted-access locations where larger piling rigs cannot fit, and projects near sensitive structures where vibration must be minimized.

Cost consideration: Mini-piles are significantly more expensive per unit than mass concrete underpinning, but they are often the only viable option when depth or access constraints rule out traditional methods.

Jet Grouting

Jet grouting creates columns of soil-cement mixture by injecting high-pressure grout into the ground. The grout stream erodes and mixes with the native soil, creating a hardened column that can support foundation loads or act as a groundwater cutoff.

How it works:

1. Drill to the target depth
2. Withdraw the drill string while injecting grout at extremely high pressure (5,000+ psi)
3. The grout jet erodes the surrounding soil and mixes with it
4. The resulting soil-cement column hardens over several days

Best for: Sites with very poor soil conditions, high groundwater, or where you need both structural support and water control. Common on large commercial and infrastructure projects.

Limitations: Expensive, requires specialized equipment and experienced operators, and generates significant spoil material (waste grout and soil) that must be managed. Not typically used on residential projects unless conditions are extreme.

Engineering Requirements and Documentation

Here is the part that separates professional contractors from the ones who end up in court: documentation. Every shoring and underpinning project needs proper engineering, and every step needs to be recorded.

What Your Engineer Will Provide

A licensed professional engineer (PE) should produce:

• Shoring design drawings showing member sizes, spacing, bracing details, and connection hardware
• Underpinning sequence plans specifying the order of excavation, maximum open section lengths, concrete strength requirements, and curing times
• Load calculations documenting the surcharge loads from adjacent structures, equipment, and soil
• Monitoring plans detailing what instruments to install, where to place them, and what readings trigger action
• Contingency procedures describing what to do if movement exceeds allowable limits

Permits and Inspections

Most jurisdictions require:

• A building permit specifically for shoring and/or underpinning work
• Sealed engineering drawings submitted with the permit application
• Inspections at key stages (before backfill, after each underpinning pour, before shoring removal)
• Notice to adjacent property owners (required in many cities, and a good practice everywhere)

Make sure your project management workflow includes tracking permit submittals, inspection scheduling, and engineer site visits. Missing an inspection can mean ripping out completed work.

Insurance Considerations

Shoring and underpinning work carries significant liability. Before you bid these projects, verify that your general liability and professional liability policies cover this type of work. Many standard policies exclude foundation work or have sub-limits that may not be adequate. Your construction insurance setup should specifically address excavation support and underpinning operations.

Thousands of contractors have made the switch. See what they have to say.

Also confirm that your subcontractors carry appropriate coverage if they are performing any of this work. Get certificates of insurance before they set foot on site.

Safety Protocols for Shoring and Underpinning

There is no part of construction where safety matters more than when you are working in and around deep excavations next to existing structures. The consequences of a shoring failure are catastrophic and immediate.

OSHA Requirements

OSHA’s excavation standard (29 CFR 1926 Subpart P) sets the baseline:

• Excavations over 5 feet deep require a protective system (sloping, benching, shoring, or shielding) unless the excavation is in stable rock
• A competent person must inspect excavations daily and after every rain event, freeze-thaw cycle, or vibration event
• The competent person has authority to shut down work immediately if conditions change
• Means of egress (ladders, ramps, or stairways) must be within 25 feet of every worker in the excavation
• Spoil piles must be set back at least two feet from the edge of the excavation

Site-Specific Safety Plans

Beyond OSHA minimums, every shoring and underpinning project should have a site-specific safety plan that addresses:

• Emergency response procedures including rescue plans for trench collapse scenarios
• Exclusion zones around the excavation perimeter where equipment and material storage are prohibited
• Vibration monitoring protocols if pile driving, heavy equipment operation, or blasting occurs nearby
• Dewatering procedures including pump locations, discharge points, and monitoring of adjacent structures for settlement caused by groundwater drawdown
• Communication protocols so every person on site knows who the competent person is and how to report concerns

Daily Checklists

Your competent person should complete a documented inspection every morning before anyone enters the excavation and again after any condition change. The checklist should cover:

• Condition of shoring members (any bowing, cracking, displacement, or corrosion)
• Water accumulation in the excavation
• Condition of the excavation walls (sloughing, cracking, bulging)
• Position of surcharge loads (equipment, materials, soil piles) relative to the excavation edge
• Status of monitoring instruments (survey points, tilt meters, crack gauges)
• Condition of access and egress routes

Keep these checklists on file. They are your first line of defense if something goes wrong and investigators start asking questions. Good crew scheduling practices should make sure your designated competent person is always on site when excavation work is happening.

Monitoring During Excavation Near Existing Structures

When you are digging next to an occupied building, a retaining wall, or any other existing structure, monitoring is not optional. It is how you catch problems before they become disasters.

What to Monitor

• Vertical settlement of adjacent structures using survey points (typically brass pins epoxied to the building at regular intervals)
• Lateral movement of the excavation support system using inclinometers installed in the shoring or adjacent soil
• Tilt of adjacent structures using tiltmeters mounted on the building face
• Crack propagation using crack monitors (simple devices that show whether existing cracks are widening)
• Groundwater levels using piezometers, especially if dewatering is part of the excavation plan
• Vibration levels using seismographs if pile driving, heavy compaction, or demolition is occurring nearby

Monitoring Frequency

Your engineer will specify monitoring frequency, but a typical schedule looks like:

• Before excavation begins: Establish baseline readings for all instruments. Document existing conditions on adjacent structures with photographs and written descriptions. This pre-construction survey is critical for resolving disputes later.
• During active excavation: Daily readings on settlement points and inclinometers. Continuous vibration monitoring if applicable.
• After excavation reaches final depth: Continue daily readings until the permanent structure is in place and backfilled.
• During shoring removal: Increased monitoring frequency, because removing bracing can cause movement.

Trigger Levels and Response Plans

Your monitoring plan should define three levels of response:

1. Green (normal): Readings within expected ranges. Continue work as planned.
2. Yellow (alert): Readings approaching allowable limits. Notify the engineer, increase monitoring frequency, and review whether construction methods need to change.
3. Red (action): Readings exceeding allowable limits. Stop work immediately, evacuate the excavation, notify the engineer, and do not resume until the engineer authorizes it in writing.

The specific trigger values depend on the project. For a typical urban excavation next to a masonry building, the engineer might set yellow at 1/4 inch of settlement and red at 1/2 inch. For a modern steel-frame building with deep foundations, the tolerances might be more generous.

Documentation Is Everything

Keep a complete record of every monitoring reading, every inspection, and every communication with the engineer. If a neighboring property owner claims your excavation damaged their building, your monitoring data is the evidence that either confirms or refutes the claim. Without it, you are at the mercy of expert witnesses arguing about what probably happened.

Photograph adjacent structures thoroughly before you start digging. Get inside the buildings if possible and document pre-existing cracks, floor levelness, and door/window operation. Use a good project management system to store all monitoring data, photos, and engineering correspondence in one place where your whole team can access it.

Bringing It All Together

Shoring and underpinning are not glamorous work. Nobody drives by a job site and admires the hydraulic shores in the trench. But getting this work right is what separates contractors who build lasting businesses from those who end up dealing with collapsed excavations, damaged neighbors, lawsuits, and OSHA citations.

The process is straightforward even if the execution takes skill:

1. Start with good geotechnical data so you know what the soil is doing
2. Get a qualified engineer to design the shoring and underpinning systems
3. Pull the right permits and schedule the required inspections
4. Install monitoring before you start digging
5. Follow the engineered plans exactly, with daily documented inspections
6. Remove shoring only when the engineer says it is safe to do so

If you are bidding shoring and underpinning work for the first time, partner with a specialty subcontractor who has done it before. Watch, learn, and build your own capabilities over time. These are high-stakes operations, and experience matters.

For managing the complexity of these projects, from tracking the engineering submittals to scheduling inspections to storing monitoring data, having the right construction management software in place makes a real difference. When every document, photo, and communication lives in one system that your office and field teams can both access, nothing falls through the cracks.

Book a quick demo to see how Projul handles this for real contractors.

Stay safe out there.