Lab Testing

In House Lab Testing

We have the capacity to carry out lab testing in house. This is of benefit as it can accelerate job reporting time and save customers money. Our lab supports both the Geotechnical and Stru ctur al sides of the business. An overview of our Lab testing services are outlined below:

Determination of particle size distribution by the wet sieving method

This test involves the wet sieving of silt and clay particles, followed by dry sieving of the remaining coarser fractions. It is used to inform engineers of the mechanical properties of samples including their permeability and suitability as fill material, while providing a straightforward breakdown of particle size disparities.
The method requires the oven drying of the sample overnight at 105°C-110°C before being passed through test sieves ranging from 50mm to 0.063mm. The retained particulate from each sieve aperture is then dried overnight and weighed the following day, with the coarse fraction subsequently dry sieved.

Sedimentation sample in measuring cylinder

Sedimentation by the hydrometer method

This involves the quantitative determination of particle size distribution in soils ranging from coarse sand to clay. Combining wet sieving with a sedimentation test enables a classification and depiction of a continuous particle size distribution curve from coarse to clay sized particles.

A representative amount is taken from the sample, varying on the predominant particle size present, and dispersant solution added to disaggregate the sample. Following several hours the sample is wet sieved through a 2mm, 0.6mm, 0.212mm and 0.063mm sieve with a collecting pan on the bottom of the stack. The contents of the pan are then transferred to a measuring cylinder. The measuring cylinder is then shaken thoroughly to agitate the sample, and a hydrometer is immersed in the suspension, with readings taken after periods of 1 min, 2 min, 3 min, 4 min, 8 min, 30 min, 120 min, 480 min and 1440 min. The results of sedimentation analysis are then plotted on a semi-logarithmic graph displaying a continuous curve.

Moisture Content testing

The moisture content of soil, taken to designate a proportion by mass of the dry solid particles, significantly affects soil behaviour, and provides a useful means of classifying different soil types. This test is carried out by extracting a representative amount of the sample and placing it in a drying oven overnight at 105°C-110°C. As such, a samples moisture content can be expressed as such:

Moisture content (w%)= (mass of moisture/mass of dry soil)

Saturation Moisture content lab testing

Saturation moisture content of intact chalk lumps can be used to quantify and classify chalk in relation to its behaviour as a freshly placed fill material. This method involves covering the chalk in wax and immersing it in water and relaying information to engineers regarding the extent to which the pores fill with water.

Plasticity Index testing

Plastic limit testing involves working out the empirically established moisture content at which a soil becomes too dry to be classified as plastic. This test type, used together with the liquid limit test, a method of ascertaining the moisture content at which a soil passes from a liquid to a plastic state, determines the plasticity index of soil, providing a form of cohesive soil classification.

This test involves drying the sample overnight before passing it through a 425µ test sieve into a collecting pan. The retained particulate is weighed while the fine fraction is dried overnight. Once the sample has reached the right consistency for testing it is moulded between the fingers and rolled into threads using enough pressure to lower the diameter of the soil. Some heavier clay samples require more movement when close to the plastic limit due to them hardening at this stage. Maintaining a uniform rolling pressure is paramount. This process should be repeated until the thread shears in both longitudinal and transverse directions. The first crumble of the soil is its plastic limit. The crumbling soil is gathered and weighed, before being dried overnight.

This test is done to assess the shrinkage limit (wS) of clays, the moisture content below which a clay stops shrinking. It is useful in quantifying the level of shrinkage likely in clays, specifically the shrinkage ratio, volumetric shrinkage and linear shrinkage. Engineers then use this information to assess whether construction conditions are suitable for a client’s needs.

Soil samples rolled to determine plasticity

Triaxial compression shear strength test

Determination of the undrained shear strength via Triaxial compression

This test involves the specimen being wrapped in an impervious membrane with end caps in a Triaxial cell pressurised by water. The axial load is then increased by applying a constant rate of strain until the specimen fails. This test informs of the stiffness and shear strength of soil, influencing geotechnical design and construction decisions.

Compressive strength testing of cubes, bricks & cores

This method of lab testing involves the soaking and subsequent compression of concrete cubes, cores and bricks. This yields information regarding the materials compressive strength, angle and type of compression, the presence of reinforcement and comparative received and tested densities. Both concrete and bricks have wide ranging structural uses including columns, beams, foundations and floors. As such assessing the loads at which these materials can withstand is of paramount importance to engineers.