A recent commercial project on a 3-acre site near the Trinity River floodplain in Arlington revealed a common challenge: variable alluvial soils with low blow counts in the upper 15 feet. The geotechnical team needed to determine the allowable bearing capacity for a mat foundation supporting a 4-story structure. Standard SPT borings per ASTM D1586 showed N-values ranging from 4 to 12 in the clayey sands, indicating that a conventional spread footing would require significant over-excavation. That is when a detailed bearing capacity analysis became the hinge point of the foundation design. Combining Terzaghi's bearing capacity equation with local site-specific factors allowed the team to recommend a net allowable bearing pressure of 3,500 psf at 4 feet depth. Before that final recommendation, the analysis was cross-checked with a study of expansive soils to rule out shrink-swell issues affecting the bearing stratum.
In Arlington's high-plasticity clays, bearing capacity can drop 40 percent from dry to saturated conditions; seasonal analysis is non-negotiable.
Methodology and scope
Arlington sits in the Blackland Prairie ecoregion, where the dominant soils are high-plasticity clays (CH) and clayey sands (SC) derived from Cretaceous marl and chalk. These soils undergo significant volume changes with moisture variation, which directly affects bearing capacity under sustained structural loads. Dry summers cause desiccation cracks, while spring rains saturate the clay, reducing shear strength by up to 40 percent. The bearing capacity analysis in Arlington must therefore account for the wettest seasonal condition. The team uses direct shear tests (ASTM D3080) and consolidated-undrained triaxial tests (ASTM D4767) on undisturbed samples to capture the effective stress parameters c' and φ'. An analysis of slope stability is often run in parallel when the building pad is near a drainage swale, because lateral movement can reduce the vertical bearing capacity. The combination of these methods gives a realistic safe bearing value for each specific parcel.
Technical reference image — Arlington
Local considerations
The primary risk in Arlington is underestimating the influence of perched water tables and seasonal moisture on bearing capacity. IBC 2018 Section 1805.2 requires that bearing pressures be based on the weakest anticipated condition. A dry-season boring alone can overestimate capacity by a factor of two. The team follows NCEER guidelines for correcting SPT N-values for overburden and rod energy, then applies the Terzaghi-Meyerhof bearing capacity equations with local calibration. In Arlington, the combination of high-plasticity clays and shallow groundwater (5 to 12 feet below grade) makes the drained analysis the governing case. The bearing capacity analysis must explicitly state the groundwater assumption used; otherwise, differential settlement risk remains hidden.
Terzaghi and Meyerhof methods applied to spread footings, continuous footings, and mat foundations. Includes settlement analysis (elastic and consolidation) and groundwater corrections.
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Deep Foundation Bearing Capacity
End-bearing and skin friction calculations for drilled shafts and driven piles using α- and β-methods. Correlated with SPT N-values and CPT cone resistance when available.
Applicable standards
IBC 2018 Section 1805 — Bearing Capacity of Soils, ASCE 7-16 Chapter 12 — Geotechnical Basis of Design, ASTM D1586-18 — Standard Test Method for SPT
Frequently asked questions
What is the typical bearing capacity of soils in Arlington?
In Arlington, allowable bearing capacity for shallow foundations on clay typically ranges from 2,000 to 4,000 psf. Sandy zones with N-values above 20 can reach 6,000 psf. The exact value depends on the soil type, moisture condition, and footing depth.
How does the presence of expansive clay affect bearing capacity analysis?
Expansive clays in Arlington undergo volume changes that reduce shear strength when wet. The analysis must use the weakest seasonal condition, typically the saturated state after prolonged rainfall. Laboratory swell tests and Atterberg limits help quantify the risk.
What is the difference between net and gross allowable bearing capacity?
Net allowable bearing capacity is the additional stress the soil can carry beyond the existing overburden pressure. Gross allowable includes the weight of the footing itself. In Arlington, net capacity is the value used for foundation design, with the overburden subtracted from the total resistance.
How much does a bearing capacity analysis cost in Arlington?
The cost for a bearing capacity analysis in the Arlington area typically ranges between US$710 and US$1,920, depending on the number of borings, laboratory tests, and the complexity of the site. A standard residential study with two SPT borings falls at the lower end; a commercial project with triaxial testing sits at the higher end.
Location and service area
We serve projects across Arlington and its metropolitan area.
