A commercial development on Chandler Boulevard required a 9-meter tall retaining wall to split two grade levels for a parking structure. The native soils here consist of silty sands and clayey gravels from the Santa Cruz River terrace deposits, which can shift under load if not properly confined. Mechanically stabilized earth walls offered the best solution for this site because the reinforcement layers distribute lateral stress evenly through the backfill mass. Before specifying the geogrid spacing and facing panels, we ran a resistivity survey to map the soil stratigraphy across the entire slope face. That data helped confirm the zone of competent bearing material behind the wall alignment. For the foundation prism itself, we used a plate load test to verify the subgrade reaction modulus at 2-meter intervals. The final design incorporated a drainage blanket and filter fabric behind the wall face, following standard practice for arid environments where flash floods can saturate the backfill quickly.
For walls over 6 meters in Chandler, reinforcement length must extend 0.7 times the wall height to resist the seismic lateral pressures calculated per ASCE 7-16.
Methodology and scope
- Internal stability: geogrid tensile capacity and pullout resistance in silty sand (SM) and poorly graded sand (SP) layers
- External stability: sliding, overturning, and bearing capacity against the foundation soil
- Seismic loading: peak ground acceleration of 0.24g per ASCE 7-16 for Maricopa County, requiring reinforcement lengths of 0.7H to 1.0H
- Corrosion potential: pH and resistivity of the backfill material to avoid long-term degradation of the galvanized steel strips
Local considerations
Chandler grew rapidly from agricultural fields to suburban subdivisions in the 1990s and 2000s, and many older retaining walls were built without proper drainage or reinforcement. The geotechnical risk in older MSE walls comes from two sources: first, the backfill often contained on-site silty clay with low permeability, which traps water behind the panels. Second, the reinforcement strips from early designs were galvanized steel with insufficient corrosion protection for the local sulfate-rich groundwater. We have inspected walls in the Ocotillo area where the facing panels bulged 30 cm outward because the drainage aggregate was clogged with fines. A proper design now requires a geotextile separator between the drainage layer and the retained soil, plus a corrosion study using resistivity testing of the backfill material before specifying steel reinforcement.
Applicable standards
AASHTO LRFD Bridge Design Specifications (9th Edition, Section 11), IBC 2021 Chapter 18 (Seismic earth pressures), ASCE 7-16 (Seismic loading), FHWA-NHI-10-024 (Design and construction of MSE walls)
Associated technical services
Geotechnical investigation for wall alignment
Boreholes and test pits along the proposed wall footprint to determine soil stratigraphy, strength parameters, and groundwater conditions.
Reinforcement selection and pullout analysis
Evaluation of geogrid or steel strip capacity, including pullout resistance calculations based on direct shear tests on the backfill material.
Seismic design and deformation analysis
Pseudo-static stability checks using Mononobe-Okabe method, plus deformation estimates for the design earthquake event.
Construction quality assurance
Field verification of backfill compaction, reinforcement placement, and panel alignment during construction per approved shop drawings.
Typical parameters
Frequently asked questions
What is the minimum reinforcement length for an MSE wall in Chandler?
For standard walls on competent ground, the reinforcement length must be at least 0.6 times the wall height. For seismic conditions in Chandler (0.24g PGA), we recommend 0.7H to 0.8H to accommodate the lateral accelerations and avoid pullout failure.
How much does MSE wall design cost in Chandler?
The design cost for a typical MSE wall in Chandler ranges from US$1,190 to US$5,130, depending on wall height, number of reinforcement layers, and whether seismic analysis is required. This includes the geotechnical investigation and the structural calculations.
What soil types are best for MSE wall backfill in Chandler?
Granular soils with less than 15 percent fines are ideal. Silty sands (SM) and poorly graded sands (SP) are common in Chandler and work well, provided they are compacted to 95 percent of modified Proctor density. Clayey soils (CL) require stabilization or replacement.
Do MSE walls in Chandler need a drainage system?
Yes, absolutely. Even in an arid climate, the monsoon season can produce intense rainfall that saturates the backfill. A drainage blanket with a perforated pipe at the base and a geotextile separator is required to prevent hydrostatic pressure buildup behind the panels.
What facing options are available for MSE walls in Chandler?
Common options include segmental precast concrete panels, modular block units, and wrapped-face geogrid with welded wire mesh. The choice depends on the project aesthetics and budget. Precast panels offer the most durable finish for commercial projects in Chandler.