Supported by Marches Small Equipment Grant & European Regional Investment Fund

In-situ Strength Testing

• Plate Load Testing

• CBR (California Bearing Ratio)Testing by Plate Load Method

• Rapid in-situ CBR values by MEXE Cone Soil Assessment Cone Penetrometer (SACP)

• approximate CBR Profiles by TRL (Formerly Transport Research Laboratory), Dynamic Cone Penetration (DCP) tests

Such tests are typically used to determine the physical properties of formations or subgrades, placed capping layers and sub-base.

What is Plate Load Testing?

Plate Load Testing is a form of field test that records the force, deformation and time taken for a plate to penetrate the ground.

How does a Plate Load Test work?

A counterweight or kentledge often in the form of a mechanical excavator is used to apply an increasing load upon a specified diameter circular plate to induce settlement. The vertical deformation is recorded by settlement gauges. Ultimate bearing strength of the soil may be determined from plate load test data. It is also possible to calculate an equivalent CBR value by using the modulus of sub grade reaction.

When do you need a Plate Load Test?

Plate load testing is a method typically used to test the strength of various layers including formation or subgrade, placed capping layers and sub-base. This test method is widely used when establishing the strength of crane bases, piling pads or crane outriggers, as well as foundations for building slabs or commercial building stanchion bases, to ensure the required loading can be achieved

Plate Load Tests may be used when a CBR value is required but the maximum particle size of soil exceeds 20mm. Plate load test by CBR method may also be more suitable when a deeper loading profile is appropriate.

What is CBR Testing?

CBR Testing (California Bearing Ratio) is primarily undertaken to provide data for road pavement design. It was first developed by the California State Highway Department.

It is a penetration test which is used to evaluate the subgrade strength primarily of roads, pavements and foundations.

The CBR test often forms part of the overall site investigation and is useful for determining the thickness of materials needed for the proposed construction.

How does a CBR Test work?

A CBR Test works by testing the pressure required to penetrate a soil sample with a plunger of the standard area and measuring this.

This measurement is divided by the pressure needed to achieve an equal penetration on a standard, high quality crushed rock material. The harder the surface, the higher the CBR value.

The CBR test can be carried out on soils with a maximum particle size of 20mm. Tests are most usually undertaken at surface level or at depths of between 500-1000m, most commonly in 20-30mm intervals along the proposed construction centreline.

On a typical site with prepared surfaces, multiple CBR tests are usually undertaken in a day by a single operator. Provisional results are often available on site.

How does a CBR Test work?

A CBR Test works by testing the pressure required to penetrate a soil sample with a plunger of the standard area and measuring this.

This measurement is divided by the pressure needed to achieve an equal penetration on a standard, high quality crushed rock material. The harder the surface, the higher the CBR value.

On a typical site with prepared surfaces, multiple CBR tests are usually undertaken in a day by a single operator. Provisional results are often available on site.

When do you need a CBR test?

Pavement Design

A Flood Risk Assessment is compiled using third party data sources. These can include data from the Environment Agency modelling, or independent data collected by the consultant or EMS Geotech. An analysis of the data sets will be undertaken to get a full overview of the site and any associated flood related risks identified.

Foundation Design

The purpose of foundations is to transfer loads from a structure to competent soil/rock. They come in the form of traditional shallow spread foundations (strips, pads and rafts) or deep foundations (piles and ground improvement). The main factors influencing foundation design is the stability of the underlying ground and settlement.

Foundation depths will be influenced by the strength of the ground, seasonal moisture variations, the effects of tree roots, frost action, river erosion, groundwater elevation and buried structures / ground disturbance.

How Can EMS Geotech Help?

EMS Geotech can provide a quick indicative assessment of subgrade CBR using a TRL Dynamic Cone Penetration (DCP) or MEXE Cone (SACP) apparatus.

The TRL DCP is generally suitable for granular mixed soils and the SACP is suitable for fine grained soils.

For more accurate measurements for in-situ CBRs, EMS are able to provide (via a specialist testing laboratory) vehicle mounted plate load testing.

EMS Geotech can provide preliminary recommendations regarding the type and depth of foundation, bearing capacity of underlying soils and settlements to aid with design.