Our field crew arrives on site with a backhoe mounted with a 24-inch bucket, ready to dig test pits up to 15 feet deep across the Lehigh Valley. In Allentown, where the underlying geology shifts from weathered shale to glacial till within a single block, we rely on these direct excavations to inspect soil stratification and groundwater seepage before any retaining wall design begins. The equipment’s hydraulic hammer helps break through cemented layers common near the Little Lehigh Creek, and we log each stratum using ASTM D2488 while collecting bulk samples for laboratory classification. This on-the-ground reconnaissance gives us the confidence to recommend the right wall type, whether it is a cantilevered reinforced concrete wall or a mechanically stabilized earth system, tailored to the specific soil conditions found at each property in Allentown.
We model active and passive earth pressures using the Rankine method, factoring in surcharge loads from adjacent parking lots or foundations, all while complying with IBC 2018 and ASCE 7-16.
Method and coverage
Allentown’s post-industrial redevelopment has pushed construction onto former rail yards and brownfield sites along the Jordan Creek corridor, where fill soils up to 12 feet deep sit atop natural alluvium. These heterogeneous deposits, often containing brick fragments and slag, require careful characterization to avoid differential settlement behind a wall. We integrate the results of our test pits with laboratory tests such as limites-atterberg to determine plasticity and shrinkage potential, and we run ensayo-proctor compaction curves to verify the backfill’s achievable density. For walls exceeding four feet in height, we model the active and passive earth pressures using the Rankine method, factoring in surcharge loads from adjacent parking lots or foundations, all while complying with IBC 2018 and ASCE 7-16 load combinations. Our laboratory follows ISO 17025 procedures, ensuring that every Atterberg limit and compaction value is traceable and defensible.
Technical reference image — Allentown
Regional considerations
In the West End of Allentown, where homes sit on well-drained glacial outwash, retaining walls typically experience limited hydrostatic pressure. But across town in the South Side flats, near the confluence of Jordan Creek and the Lehigh River, high groundwater tables and silty clay soils create a different scenario. A wall built without a proper drainage blanket and filter fabric can fail within two rainy seasons due to pore pressure buildup behind the stem. We address this by specifying a 12-inch gravel drain with a perforated pipe at the base, connected to a positive outfall, and we model the seepage using a flow net analysis. Our team has seen walls in the South Side rotate more than four inches when drainage was omitted, so we always insist on a comprehensive subsurface investigation before finalizing the retaining wall design.
2,000 psf to 6,000 psf (depending on glacial till vs. fill)
Drainage design storm
10-year, 24-hour event with weep holes at 4 ft o.c.
Complementary services
01
Subsurface Exploration with Test Pits
We excavate test pits up to 15 ft deep using a track-mounted backhoe, logging soil types and groundwater levels in real time. This method is ideal for shallow walls where continuous sampling is needed across the wall alignment.
02
Backfill Compaction Testing
After wall construction, we perform field density tests using a nuclear gauge or sand cone to verify that the backfill meets the specified 95% standard Proctor compaction, preventing long-term settlement behind the wall.
Standards that apply
ASCE 7-16 (Minimum Design Loads and Associated Criteria), IBC 2018 (International Building Code, Chapter 18), ASTM D2488 (Description and Identification of Soils), AASHTO LRFD Bridge Design Specifications (Section 11 — Abutments and Retaining Walls)
Quick answers
What soil conditions in Allentown most affect retaining wall design?
The most challenging conditions are the soft alluvial clays and silts found along the Lehigh River floodplain, which have low shear strength and high compressibility. In these areas, walls often require deeper embedment and a wider base to resist sliding and overturning. We also encounter weathered shale on the hillsides, which can be stable but erodes quickly if exposed.
How much does a geotechnical investigation for a retaining wall cost in Allentown?
For a typical residential wall up to 8 ft high, the investigation including two test pits and laboratory tests ranges between US$910 and US$2,400. Larger commercial walls requiring four or more test pits and advanced triaxial testing can cost between US$3,200 and US$4,800. These figures exclude design fees but cover all field work and lab analysis.
Do I need a permit for a retaining wall in Allentown, and what geotechnical data is required?
Yes, the City of Allentown requires a building permit for any wall exceeding 4 ft in height. The permit application typically demands a soils report that includes a boring log, soil classification, groundwater depth, and a recommendation for the wall’s bearing capacity and lateral resistance. Our reports fulfill these requirements under IBC 2018.
Location and service area
We serve projects across Allentown and its metropolitan area.
