Landfill Geotechnics in Arlington

The subsurface conditions beneath Arlington vary dramatically between the floodplains of the Trinity River and the upland terraces near the Parks Mall. Landfill geotechnics in Arlington must account for the high-plasticity clays (CH) that dominate the eastern half of the city, while the western sectors overlie the Woodbine Formation with interbedded sandstones. A proper geotechnical investigation for a landfill in Arlington requires understanding both the low-permeability clay liners that can be sourced locally and the need for infiltration testing to verify the natural barrier performance. The contrast between these two geologic settings directly influences liner design, leachate management, and long-term settlement predictions.

Illustrative image of Rellenos sanitarios in Arlington

High-plasticity clays in East Arlington provide natural low-permeability barriers, but only if the desiccation cracking is controlled during dry-season construction.

Methodology and scope

A recent cell expansion project near the Arlington Landfill off Bowman Springs Road required a 15-meter-thick waste lift over alluvial clays. The design team deployed a double composite liner system with a geosynthetic clay liner (GCL) over compacted clay. For this type of facility, landfill geotechnics in Arlington relies on the CBR test for access roads to ensure heavy truck traffic does not rut the cover system. The testing program included:

Triaxial permeability tests on remolded clay samples (ASTM D5084) targeting k ≤ 1×10⁻⁷ cm/sec
Consolidation tests to estimate primary and secondary compression of the waste column
Direct shear tests on the GCL-clay interface to check sliding stability on the 3:1 side slopes

Each parameter feeds directly into the stability models that satisfy the Texas Commission on Environmental Quality (TCEQ) rules for municipal solid waste landfills.

Local considerations

Arlington sits within the Eastern Cross Timbers region, where average annual rainfall reaches 940 mm, concentrated in spring thunderstorms. This climate creates a recurring risk for leachate mounding within the waste mass if the drainage layer clogs. Landfill geotechnics in Arlington must also address the potential for differential settlement at the interface between old unlined cells and new lined expansions. Without careful characterization of the existing waste using a georadar survey, operators risk tearing the geomembrane when the foundation shifts. The 2021 IBC seismic provisions apply to Arlington, requiring pseudo-static slope stability checks for peak ground accelerations of 0.15 g.

Technical parameters

Parameter	Typical value
Saturated hydraulic conductivity (clay liner)	≤ 1×10⁻⁷ cm/sec per TCEQ
Waste unit weight (typical)	10–14 kN/m³
Primary settlement ratio (Cα′/Cε)	0.03–0.08 for MSW
Interface friction angle (GCL–clay)	18°–24° direct shear
Factor of safety for side slopes	≥ 1.5 static, ≥ 1.1 seismic (IBC 2021)

Associated technical services

Liner System Design Verification

We evaluate the in-situ clay barrier and design the compacted clay liner thickness (typically 60–90 cm) to meet the TCEQ permeability target. Testing includes Atterberg limits, Proctor compaction, and flexible-wall permeability on undisturbed samples.

Waste Settlement and Stability Analysis

Using the Sowers method and rheological models, we predict long-term settlement of the waste column. Slope stability analysis with Slide or FLAC evaluates the factor of safety for both static and seismic loading scenarios.

Frequently asked questions

What is the typical cost range for a landfill geotechnics study in Arlington?

The range for a complete investigation including drilling, lab testing, and stability analysis is US$2,070 to US$7,260, depending on the number of borings and the complexity of the liner system.

Which ASTM standards apply to clay liner permeability testing?

ASTM D5084 is the primary standard for saturated hydraulic conductivity of compacted clay liners. For field verification, we also follow ASTM D6391 for constant-head borehole tests and ASTM D5092 for monitoring well installation.

How does the Trinity River floodplain affect landfill foundation design?

The floodplain deposits consist of soft alluvial clays with low shear strength (typically 20–40 kPa undrained). Deep soil mixing or stone columns may be required to control differential settlement under the waste load. Our studies include consolidation testing to quantify the magnitude and rate of primary consolidation.