Electrical Resistivity Survey & VES Testing in Shreveport

Shreveport’s subsurface isn’t what you’d expect from the surface—we’ve seen clean-looking lots underlain by 40 feet of fat clay sitting on the Wilcox Group, and that contrast wreaks havoc on foundation design if you don’t map it early. Rather than punching borings every 50 feet, the crew runs vertical electrical sounding to stitch together a continuous resistivity profile across the site. You end up with a clear picture of where the low-resistivity clay pockets sit, how deep the water table actually is at 32.5°N, and whether the sand lenses are thick enough to carry footing loads. Because the Red River alluvium shifts so much across Caddo Parish, combining VES lines with a few targeted test pits or an SPT drilling program gives us ground truth to calibrate the geophysics and keep the client’s earthwork quantities tight.

Resistivity lines across a Shreveport site often reveal buried Red River channels that standard boring grids miss.

Process and scope

In Broadmoor you’re typically dealing with stiff to hard clays that read 8–15 ohm-m, while out toward Cross Lake the sandy silts jump to 40–80 ohm-m—same city, completely different electrical signature. The Schlumberger array we run here expands electrode spacing from 1.5 meters out to 200 meters, so you capture both the near-surface fill and the deep Eocene bedrock contact in one VES sounding. Data are inverted with least-squares smooth models, and we flag any RMS error above 5% for a rerun before leaving the site. When the profile suggests a paleochannel crossing the building pad, we usually recommend following up with a CPT test to confirm tip resistance and pore pressure right where the resistivity drops. The electrical method picks up the boundaries; the CPT pins down the engineering parameters. This two-step approach prevents over-excavation in the sandy zones and catches soft spots that a grid of borings might miss entirely.

Electrical Resistivity Survey & VES Testing in Shreveport

Site-specific factors

A developer we worked with off Youree Drive had a 14-story mixed-use tower where the preliminary borings showed competent clay to 60 feet, but the electrical lines picked up a 20-foot-wide low-resistivity trough crossing the northwest corner—turned out to be an abandoned channel filled with organic silt that the borings missed by 30 feet. We flagged it before the auger-cast pile layout was finalized. In Shreveport, missing a buried paleochannel or a perched water pocket can mean differential settlement of an inch or more across the mat, and once the superstructure is up, remediation costs dwarf the survey fee. The resistivity survey, run at the right electrode spacing and tied to a couple of verification borings, catches those hidden features while the site is still a dirt lot. We always insist on at least one calibration CPT test where the resistivity contrast is sharpest, because the CPT’s sleeve friction and pore-pressure data tell you whether the anomaly is an engineering problem or just a mineralogical curiosity.

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Standards used

ASTM D6431-18, IBC 2021 (geophysical investigation chapter), ASCE 7-22 (seismic site class inputs)

Complementary services

1D Vertical Electrical Sounding (VES)

Schlumberger array with AB/2 to 200 m. Delivers resistivity-depth curves, water-table depth estimate, and clay/sand interface picks for foundation design.

2D Electrical Resistivity Tomography

Multi-electrode Wenner-Schlumberger line with 5 m spacing. Used for pipeline corridors, levee assessments along the Red River, and detecting lateral pinch-outs that VES alone might miss.

Correlation Drilling & CPT

One or two verification borings or CPT soundings placed on resistivity anomalies to calibrate the geophysical model and deliver direct engineering parameters for the geotechnical report.

Typical parameters

Parameter	Typical value
Array configuration	Schlumberger (standard), Wenner on request
Max electrode spread	AB/2 up to 200 m; typical depth penetration ~40–50 m
Measurement range	0.1 ohm-m to 500,000 ohm-m
Output	1D resistivity-depth curves, 2D pseudosections
Data inversion	Least-squares smooth model; RMS error ≤5%
Standard followed	ASTM D6431-18
Coordinate control	Sub-meter GNSS on each sounding point

FAQ

What does an electrical resistivity survey in Shreveport typically cost?

For a standard package with four to six VES soundings and a basic 2D line, budget between US$720 and US$1,120. The final figure moves with site acreage, electrode spread length, and whether we need to clear heavy brush or work around existing structures.

How deep can VES see in the soils around Shreveport?

With a maximum AB/2 of 200 meters, we typically reach 40 to 50 meters depth in the clay-sand sequences common across Caddo Parish. Actual penetration depends on the resistivity contrast—thick saturated clay attenuates the signal faster than dry sand, so we adjust the spread after the first sounding if we’re not hitting the Wilcox Group contact clearly.

Can you run resistivity lines inside an existing building or under pavement?

VES and 2D lines need direct electrode-ground contact, so we cannot operate through concrete slabs or asphalt without coring. For interior or paved sites we switch to alternative geophysical methods or rely on targeted borings and CPT soundings to get the subsurface data.

How long does a VES survey take on a typical Shreveport lot?

Four to six soundings on a half-acre lot usually take a single field day. We process the data overnight, invert the curves, and deliver a draft resistivity profile the following morning. Larger lots or multi-line 2D grids can run two to three days depending on access and weather.