CBR In situ

This test covers the determination of the California Bearing Ratio (CBR) of a soil tested in-situ, with a selected overburden pressure, by causing a cylindrical plunger to penetrate the soil at a given rate and comparing the relationship between force and penetration into the soil to that for a standard material.

CBR Laboratory, Soaked Single Point

The California Bearing Ratio test, commonly abbreviated to CBR, is normally used an empirical measure of road sub-grade strength. This strength value is then often used as either a guide to the design of road layer thicknesses, or to assess compliance of sub-grade against minimum specification values. The test therefore is of use to both contractors and to specifying authorities.

The single point laboratory method is used when the CBR characteristics of the soil are required to be known for a given density and moisture content of the soil, which may differ from conditions in-situ. This is then useful for determining whether a material may meet specification CBR parameters before its actual use on-site.

CBR Laboratory, Soaked Single Point

This test covers the determination of the California Bearing Ratio (CBR) of a soil tested in the laboratory, with a selected overburden pressure, by causing a cylindrical plunger to penetrate the soil at a given rate and comparing the relationship between force and penetration into the soil to that for a standard material. The material is first prepared in moulds to three known densities and moisture contents, to assess the materials CBR performance at varying levels of compaction and moisture.

Chloride Content

Concrete in contact with soil bearing high levels of chloride could suffer from early ingress of this chloride, leading to corrosion of any embedded reinforcement. Measures of chloride levels in soils are often taken to check whether the soil will be suitable to be used adjacent to concrete.

Methods of measurement are most often made by traditional wet chemistry methods.

Electrical Resistivity

Measurement of soil electrical resistivity is often used in assessing the soils' potential for initiating or accelerating the corrosion of metal structures in contact with it. It is, therefore, a useful tool for contractors in assessing the suitability of new sources of backfill, where it may be used to bury metal structures. In addition, the test is also useful to specifies, when appropriate limits of resistivity are devised, to ensure any soil used will be inert.

Resistivity can also be used to study lateral changes and vertical cross-sections of the natural hydro-geologic setting. In addition, it can also be used to study contamination of soil and groundwater.

Linear Shrinkage

This test covers the determination of the linear shrinkage characteristics of a soil with particles greater than 425um removed. The soil is mixed with water to a moisture content equal approximately to the soil's liquid limit value. The soil is then used to fill a mould of known dimensions which is dried over a period of time. When the soil is completely dry the change in length due to shrinkage is measured.

Modified Procter Compaction Test

This test method covers laboratory compaction procedures used to determine the relationship between moisture content and dry density of soils. The test involves applying a standard compactive effort to five separate samples of increasing moisture content, and measuring the resulting dry density of each sample.

The test result when then yield a value of maximum dry density for a given moisture content, which can then be used to establish a target density for on-site compaction of earthworks.

Organic Matter Content

When soil is used as a construction material for back-fill, it is important that any material contained in it which is readily compressible, such as organic matter, is kept to a minimum. A test for organic matter content can be used to measure such levels and check whether the soil meets current specifications for maximum organic matter content.

Particle Size Distribution by Hygrometer

This test method covers the determination of percentile quantity of particles smaller than can be sieved, typically 63µm diameter, normally silt and clay sized particles. The specimen first has larger particles removed by sieving. The material passing the sieve is made up into a suspension with water. The suspension’s reducing density is measured over time, as the particles settle. Using Stokes Law, the diameter of the specimens can then be calculated, based on the speed at which they settle, measured indirectly by the fall in density of the suspension.

The analysis of particle size of this type is useful in aiding classification of the soil, and hence its performance as a fill material.

Particle Size Distribution by Sieve Analysis

This test method covers the determination of percentile quantity of particles of soil within a sample. The specimen can be either passed through a set of standard sieves in its natural state, or if a significant amount of binding material is present, such as clay, then the sample can first be washed over a small aperture sieve to remove the binding material.

The analysis of particle size is useful in predicting the physical performance characteristics of a soil when used as fill for roads and structures.

Plasticity Index

This test method covers the determination of liquid limit, plastic limit and then plasticity index by calculation. For liquid limit, the soil's resistance to penetration by a standard cone is measured at varying moisture contents. The moisture content at which the soil permits a cone penetration of 20mm is then taken as the value of liquid limit. For plastic limit, a soil sample is slowly dried, using the heat of the hands until it can no longer be rolled into a three millimeter thread without cracking and shearing. At this point the moisture content is measured.

The analysis of plasticity index is useful in aiding classification of the soil, and hence its performance as a fill material, with particular regard to swelling and shrinking. Plate Bearing

The Plate Bearing (or Loading) Test, is normally used to measure the short term settlement of road sub-grade or building footings under their proposed design load. The value of settlement against load is then used to check that the soil meets design load settlement criteria. The test therefore is of use to both contractors and to specifying authorities.

In addition to values of settlement, other soil parameters can be measured, or calculated from the plate-bearing test. These include Modulus of Sub-Grade Reaction, permanent deformation characteristics of the soil and in some instances shear strength of the soil.

Sulphate Content

Concrete in contact with soil bearing high levels of sulphate can suffer attack. Measures of sulphate levels in soils are often taken to check whether special cements need to be incorporated into a concrete mix to prevent such attack.

Methods of measurement are most often made by traditional wet chemistry methods.