An Introduction To Geotechnical Testing Methods

Geotechnical testing methods is used to obtain important information about the physical properties of substrate, rock and soil around a potential construction site. This produce is underpinned by three core methods. These tests are conducted by geotechnical engineers and drilling contractors with the required specialist knowledge and equipment. The information gained through geotechnical testing is crucial to understanding whether a site is suitable for any proposed earthworks or structures.

Soil Sampling and Soil Boring

Soil sampling and boring can be a simple part of geotechnical testing or highly complicated, depending on the landscape and the materials used. The most basic tool for soil sampling is the shovel, which is used to gather a sample of the surface soil that is then analysed to understand the properties of the site. However, this form of soil sampling is categorized as “disturbed” due to the fact that the tests for the structural properties of the sample will be viable but not accurately portray the soil, as it would be found in-situ. These “disturbed” sampling methods are still useful for accurately measuring various properties of the soil such as the distribution of grain sizes and water content.

Soil boring is a form of soil sampling that, in comparison to more commonplace methods, is highly specialized and technical. Thus it requires the expertise of a drilling contractor to conduct the geotechnical drilling. Borings are principally split in to two main categories known as large-diameter and small-diameter. The expense and acknowledged safety concerns of large-diameter boring make it a rarely used form of soil sampling. Small-diameter borings are instead frequently used to extract rock cuttings or soil samples and often at a considerable depth. Soil boring as a geotechnical test is classified as “undisturbed” and thus allows engineers to have a reliable understanding of on-site soil conditions.

Laboratory Testing

An incredibly large array of laboratory tests can be performed on a sample to understand the soil properties.  “Disturbed” samples can be tested for soil properties that are inherently part of the soil matrix and thus not affected when a sample is significantly altered from its on-site conditions. Laboratory tests such as particle-size analysis, hydraulic conductivity tests and soil classification are used on “disturbed” samples. Whereas, the Atterberg limits test, California bearing ratio and soil compaction tests all require “undisturbed” samples gained from soil boring.

In-situ Testing

A standard penetration test (SPT) is a dynamic penetration in-situ test that collects a disturbed sample that can be used for the simple laboratory tests of soil classification and grain-size analysis. A more complicated cone penetration test (CPT) uses a conical drill tip that is hydraulically punched into soil at a regular and controlled rate. By collecting data on tip resistance and then correlating it to lab data, a number of soil properties can be determined.

These are the three main geotechnical testing methods, however as boring technology advances and laboratory testing improves there will be more an increased demand for specialized drilling contractors to engage in geotechnical drilling for modern construction projects.