Flat Dilatometer Test (DMT) in Edinburgh

Edinburgh's geology is a mosaic of glacial tills, raised marine deposits, and river terrace gravels from the Water of Leith. This variability means that a single borehole can miss critical changes in soil stiffness and horizontal stress. The Flat Dilatometer Test (DMT) is designed precisely for these conditions. It measures the lateral stress history and modulus of deformation in situ, giving us reliable data for foundation design on sites like the Meadows or Leith Docks. We typically complement DMT readings with an ensayo SPT to cross-check penetration resistance and a presurometro when we need a direct measure of modulus for deep excavations. The combination is powerful for Edinburgh's complex ground.

The DMT reveals the hidden stress history of glacial soils, giving engineers the confidence to design shallow foundations where others default to piles.

Scope of work in Edinburgh

A common mistake contractors make in Edinburgh is assuming that the dense till beneath the city centre behaves uniformly. The DMT exposes the real variation. We run the test following BS EN ISO 22476-11, pushing the stainless steel blade into the ground at a controlled rate. The equipment records two pressures: the lift-off pressure (p0) and the pressure to expand the membrane 1.1 mm (p1). From these, we calculate the material index (ID), horizontal stress index (KD), and dilatometer modulus (ED). Each parameter tells a different story about the soil. For example, a low KD in the soft clays of the Forth estuary can indicate underconsolidation, while high ED values in the till confirm good bearing capacity. When we find loose granular deposits, we often recommend a placa de carga to validate the modulus under working loads. The DMT gives us the profile; the plate test confirms the settlement prediction.

Flat Dilatometer Test (DMT) in Edinburgh

Parameter	Typical value
Material Index (ID)	0.1 (clay) to 10 (sand) — indicates soil type
Horizontal Stress Index (KD)	1.5 to 8 — reflects overconsolidation ratio
Dilatometer Modulus (ED)	0.5 to 50 MPa — stiffness parameter for settlement analysis
Lateral Stress Ratio (K0)	Derived from KD — critical for retaining wall design
Undrained Shear Strength (Su)	Calculated for clays using ID and KD correlations
Constraint Modulus (M)	Used in settlement calculations under Eurocode 7

Working video

Typical technical challenges in Edinburgh

We worked on a site near Bruntsfield Links where the contractor assumed stiff till from 3 m depth. The DMT profile showed a 2 m thick layer of soft clayey silt at 4.5 m with a KD of 1.8, indicating near-normally consolidated conditions. That layer would have caused differential settlement of over 40 mm under a six-storey building. The design was changed to a raft foundation with Improvement. Skipping the DMT would have meant accepting a structural risk that could take years to appear. In Edinburgh's variable glacial terrain, the DMT is not an extra cost, it is an insurance policy against hidden soft layers.

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Applicable standards: BS EN ISO 22476-11 — Standard Test Method for Performing the Flat Plate Dilatometer, Eurocode 7 (EN 1997-1:2004) — Geotechnical design using DMT-derived parameters, BS 5930:2015 — Code of practice for ground investigations, including In-Situ

Our services

Our DMT service in Edinburgh covers the full workflow, from field testing to interpreted reports ready for structural engineers.

DMT Profile Testing

Continuous or discrete readings at 0.2 m intervals from ground surface to depths of 40 m. Suitable for all soil types encountered in Edinburgh, from soft estuarine clays to dense glacial till.

Seismic DMT (SDMT)

Combines the standard DMT blade with a seismic module to measure shear wave velocity (Vs). Provides small-strain stiffness (G0) for dynamic analyses and soil classification per NEHRP.

Consolidation & Settlement Parameters

Derivation of constrained modulus (M), coefficient of consolidation (ch), and preconsolidation pressure from DMT data. Critical for designing foundations on Edinburgh's compressible deposits.

Interpreted Geotechnical Report

A full report with profile plots, parameter tables, and design recommendations compliant with Eurocode 7. Includes comparisons with SPT and laboratory data for cross-validation.

FAQ

How does the DMT differ from the SPT in Edinburgh soils?

The SPT measures resistance to hammer blows, giving a crude strength index. The DMT measures actual lateral stress and stiffness at rest. In Edinburgh's glacial tills, the DMT provides a continuous profile of modulus and stress history, while the SPT gives a point measurement that can miss thin soft layers. We use both together: SPT for borehole correlation and DMT for detailed stiffness profiling.

Can the DMT be performed in Edinburgh's dense glacial till?

Yes, but it requires a powerful CPT rig or a dedicated push unit. The DMT blade needs a steady penetration rate of 20 mm/s, which is achievable in most tills around the city. In extremely dense or gravelly zones, pre-drilling may be needed. We assess the soil profile from trial pits or boreholes first to confirm feasibility.

What is the typical cost range for a DMT investigation in Edinburgh?

For a standard project with 5 to 10 test points to 20 m depth, the cost typically falls between £710 and £780. This includes mobilisation, field testing, data processing, and a full interpreted report. Larger volumes or deeper profiles reduce the per-metre rate.

How does the DMT data feed into foundation design under Eurocode 7?

The DMT provides direct inputs for settlement calculations (constraint modulus M), bearing capacity (undrained shear strength Su in clays, friction angle in sands), and lateral earth pressures (K0). These parameters are used in Design Approaches 1 and 2 of Eurocode 7. The report includes partial factors and characteristic values ready for the structural engineer.