We recently worked on a mixed-use development off Battlefield Boulevard where the geotechnical profile shifted from stiff sand to soft clay within 15 feet. That kind of variability is routine in Chesapeake — the city sits on the Atlantic Coastal Plain, with Pleistocene terraces and deep marine deposits. The Flat Dilatometer Test (DMT) was the right tool there. It gave us continuous readings of horizontal stress index and material index every 0.2 meters, without needing a borehole. For that project, we paired the DMT with a CPT to cross-check cone resistance and pore pressure response, which helped the structural team settle on a shallow foundation system instead of piles. The DMT doesn't replace boring, but in Chesapeake it often reduces the number of boreholes needed when you're covering a large site.
In Chesapeake's coastal plain soils, the DMT delivers the lateral stress history and stiffness profile that SPT alone cannot provide.
Approach and scope
Site-specific factors
The DMT blade is a 95 mm wide steel blade with a 60-degree tip, pushed by a hydraulic rig mounted on a truck or tracked carrier. In Chesapeake, the biggest risk is hitting a buried utility or a shallow obstruction like riprap or old fill. We review utility maps and perform a geophysical scan with a GPR before each sounding. Another risk is membrane rupture if the blade encounters gravel or shell fragments — common in the Pleistocene terrace deposits. We carry spare membranes and calibrate the blade before each shift. The crew tracks the expansion pressure in real time and stops if the reading jumps abruptly. This keeps the data clean and avoids false readings that could mislead the interpretation of OCR or K0 in sensitive Atlantic Coastal Plain soils.
Relevant standards
ASTM D6635-01 — Standard Test Method for Performing the Flat Plate Dilatometer, ASTM D2487 — Standard Practice for Classification of Soils for Engineering Purposes, ASCE 7-22 — Minimum Design Loads and Associated Criteria for Buildings, IBC 2021 — International Building Code, Chapter 18 (Soils and Foundations)
Related technical services
Standard DMT Sounding
Continuous readings at 0.2 m intervals using a 20-ton push rig. Output includes ID, KD, ED, constrained modulus M, OCR, and K0. Suitable for deep foundation design and settlement analysis in the clay layers underlying Chesapeake.
DMT with Dissipation Testing
Adds pore pressure dissipation readings at select depths. Ideal for estimating the coefficient of consolidation (ch) in the soft estuarine deposits near the Intracoastal Waterway. We run 3 to 5 dissipation stages per sounding.
DMT Seismic Module (SDMT)
Incorporates a seismic receiver to measure shear-wave velocity (VS) at 1 m intervals. Combined with DMT parameters, this gives you small-strain stiffness (G0) for dynamic analysis and site classification per ASCE 7. Recommended for schools and hospitals in Chesapeake.
Typical parameters
FAQ
What is the Flat Dilatometer Test and how does it work in Chesapeake soils?
The DMT is an in-situ test where a steel blade with a flexible membrane is pushed into the ground at 2 cm/s. At each 0.2 m stop, we expand the membrane and record A and B pressures. In Chesapeake, this test works well in both the stiff sands of the Surry Scarp and the soft clays of the Dismal Swamp deposits. The output includes the material index, horizontal stress index, and dilatometer modulus, which we use to derive OCR and K0.
What is the typical cost range for a DMT sounding in Chesapeake?
For a standard DMT sounding with continuous readings to 20 m depth, the cost ranges between US$800 and US$920 per sounding. This includes mobilization within Chesapeake, calibration, field testing, and a report with interpreted parameters. Volume discounts apply for five or more soundings on the same site.
How does the DMT compare to the Standard Penetration Test (SPT) for Chesapeake projects?
The SPT gives you blow counts and disturbed samples, which are useful for classifying soil and estimating relative density. The DMT provides continuous profiles of stiffness, lateral stress, and OCR — parameters that SPT cannot measure directly. For settlement calculations in Chesapeake's soft clays, the DMT's constrained modulus is more reliable than correlations from N-values. We often run both tests on the same site.
At what depths and soil types is the DMT most effective in Chesapeake?
The DMT is most effective from 1 m to about 30 m depth in Chesapeake. It performs well in clays, silts, sands, and mixed soils. It struggles in gravelly layers or soils with cobbles, which can rupture the membrane. In the soft organic clays near the Elizabeth River, the DMT gives excellent dissipation data and OCR values. We recommend combining it with a CPT for a complete stratigraphic picture.