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Project GuideResidential/Commercial

Building a Retaining Wall?

When do you need a geotechnical report for a retaining wall? Here's the answer, plus what's involved.

Not Every Wall Needs a Geotech — But Most Do

The question we hear most: "Do I need a soils report for my retaining wall?" The answer depends on the wall height, the slope it's retaining, and your jurisdiction's requirements. Generally, if the wall is over 3-4 feet tall, or if it's retaining sloping ground, you need geotechnical engineering.

A retaining wall geotechnical report provides the design parameters your structural engineer needs: lateral earth pressure, bearing capacity, drainage recommendations, and seismic design criteria. Without these parameters, your structural engineer can't design the wall, and the building department won't approve it.

We work on retaining walls across Southern California — from simple garden walls to complex tiered systems on hillside lots. We know when a wall needs a full investigation and when a simplified approach is acceptable.

What You'll Need

Engineering deliverables for retaining wall projects:

Usually Required

🔩

Geotechnical Investigation

Borings or test pits adjacent to the proposed wall location. We evaluate soil type, strength, groundwater, and any conditions that affect lateral pressure or wall stability.

Required

⚖️

Lateral Earth Pressure Parameters

The geotechnical report specifies active and passive earth pressure coefficients, surcharge loads, and whether the wall needs to resist additional loads from slopes or structures above.

Required

🏗

Bearing Capacity & Settlement

Foundation design parameters for the wall footing — allowable bearing pressure, footing depth, and estimated settlement. Critical for preventing wall tilting or failure.

Required

💧

Drainage Recommendations

Retaining walls must have drainage to prevent hydrostatic pressure buildup. The geotech report specifies subdrain requirements — typically gravel backfill and perforated pipe behind the wall.

Required

🌊

Seismic Design Parameters

California walls must resist seismic loading. The report provides site-specific seismic coefficients your structural engineer uses to design for earthquake forces.

Often Required

✅

Construction Observation

For walls over a certain height (varies by jurisdiction), we observe backfill placement and compaction to verify it matches the design assumptions.

Why Retaining Wall Failures Are Expensive

Retaining walls fail when the lateral earth pressure exceeds what the wall was designed for. This happens when the geotech parameters were wrong, when drainage wasn't installed properly, or when the wall wasn't built per the approved plans. The result: walls that tilt, crack, or collapse entirely.

We've seen garden walls designed without geotechnical input that failed within a year. We've seen hillside walls that didn't account for slope surcharge loads and had to be torn out and rebuilt. The cost of proper geotechnical engineering upfront is a fraction of the cost of rebuilding a failed wall.

3-4 ft

Typical height where jurisdictions require geotechnical engineering for retaining walls

35-65 pcf

Typical range for residential retaining wall equivalent fluid pressure, depending on soil type, drainage, and slope of backfill

100%

Of retaining wall failures we've investigated had inadequate drainage or missing subdrains

What to Expect

Wall Review & Proposal

We review your plans (or site photos if plans aren't ready yet) and determine what level of investigation is needed. Proposal includes field work, lab testing, and report.

Field Investigation

We drill borings or excavate test pits near the wall location. Soil samples are collected for laboratory testing to determine strength and expansion potential.

Geotechnical Report

We provide lateral earth pressure parameters, bearing capacity, drainage recommendations, and seismic design criteria. Your structural engineer uses this to design the wall.

Construction Observation (If Required)

For taller walls, we observe backfill placement and compaction to verify the drainage system is installed correctly and backfill meets design assumptions.

Building Something Else?

ADU Engineering Guide

Engineering deliverables for ADU construction in California.

Read Guide →

Hillside Development Guide

Slope stability, specialized foundations, and hillside engineering requirements.

Read Guide →

Pool Engineering Guide

Pool soils reports and foundation engineering.

Read Guide →

Common Questions

It depends on the jurisdiction and whether the wall is retaining sloping ground. Some cities require geotechnical engineering for all walls over 3 feet. Others set the threshold at 4 feet. And if the wall is on a slope or supporting a surcharge load, even shorter walls may require engineering.

No. Retaining wall reports require specific parameters — lateral earth pressure, passive resistance, drainage design — that aren't included in a standard foundation investigation. The geotech needs to know you're building a wall.

Active pressure is the lateral load the soil exerts on the back of the wall (what the wall must resist). Passive pressure is the resistance provided by soil in front of the wall. Your structural engineer uses both to design the wall.

Without drainage, water accumulates behind the wall and creates hydrostatic pressure — which can double or triple the lateral load on the wall. Subdrains (perforated pipe in gravel backfill) prevent water buildup.

From field work to report delivery, typically 1-2 weeks. Simple walls with shallow test pits can be faster; complex hillside walls with deep borings take longer.

Ready to Get Your Retaining Wall Started?

Tell us about your retaining wall project and we'll send a proposal with every deliverable you need — scope, fee, and timeline.

Request a Proposal Talk to an Engineer