At the SOCOTEC geotechnical laboratory, we can determine the thermal conductivity of specific soil layers for you.
This test is important when, for example, an underground construction is being built that emits heat or has a temperature different from its surroundings. Think, for example, of high-voltage lines and pipelines. We can also determine the thermal conductivity, or the coefficient of thermal conductivity, of bentonite and other finishing materials used in the underground.
To measure thermal conductivity, a thermal needle, equipped with a heat source and a temperature sensor, is inserted into an (undisturbed) sample. Based on the measurement of a heat impulse, the thermal conductivity can be calculated. We use the Hukseflux system at the SOCOTEC geotechnical lab. Thermal conductivity is expressed in W/(mK) and is usually performed as two or three replicate measurements.
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To determine soil compaction, at SOCOTEC we can offer you a Proctor test and the minimum-maximum test; both performed in accordance with RAW 2020. Determining compaction is crucial in construction work. For example, certain compaction requirements often apply to the construction of flood defences or embankments, but also to the construction of roads and motorways.
In the Proctor test, a curve is plotted by determining the compaction with (at least 5) different water contents. The maximum Proctor density is reached at maximum compaction, which is therefore also characterised by an associated optimum water content. To check whether the required density has been achieved during the construction work, our Monitoring Department can install a soil sample ring on site. This determines the wet and dry volumetric weight and water content at the site, whereby the results can be directly tested against the results of the Proctor test.
At the SOCOTEC geotechnical lab we can determine the permeability of soil samples for you using the Falling Head and the Constant Head methods.
With the Falling Head method, a cohesive sample is built into a compression set-up to which a burette with water is connected. Initially, the ground stress is applied to the sample until it is consolidated. After this we allow a certain volume of water to flow through the sample, with the volume decay being measured over time. This data allows the permeability coefficient to be calculated.
The other option is to measure the coefficient of permeability (k-value) using a Constant Head test. Here an often-non-cohesive sample is built into a (triaxial) cell where water can flow through the sample at a constant water pressure. The volume and pressure of the water flow and the time it takes to do so are measured during the test to determine the k-value of the soil.
Determining the botanical composition of organic soil
When constructing and testing flood defences, the botanical composition of peat is a criterion that can be determined. At the SOCOTEC geotechnical lab, we can determine the botanical composition of organic soils in accordance with Technical Report 16: “Geotechnical Characteristics of Peat”. Characteristics such as strength and compressibility are used along with a number of tests including those for water content and fibre content. An indication is also often given of the kind of fibres it contains, which also accurately determines the type of peat.
Pocket Penetrometer test
To determine the indicative compressive strength of an undisturbed cohesive sample, we can use a pocket penetrometer in the laboratory. This test can be carried out where necessary on very high consistency soils. As with the Torvane test, the correct attachment must be chosen for the pocket penetrometer, depending on the hardness of the soil. After this, the penetrometer is pressed into the sample until the mark on the pocket penetrometer is level with the surface of the sample. The indicative compressive strength can then be read out directly or an associated multiplication factor must be used, depending on the attachment.
With the Torvane test we can quickly and easily determine the indicative shear strength of the soil for you in our geotechnical laboratory. The indicative undrained shear strength should be determined with a Torvane (hand-held vane) using a cohesive undisturbed sample. For the implementation, a suitable vane must be selected; the consistency of the soil determines the type of vane. The vane is then pressed into an undisturbed sample so that the vanes fully pierce the sample. The device is slowly rotated clockwise, with the sample providing resistance. When there is no more resistance, the maximum resistance can be read. Using a multiplication factor, the value can be converted to the indicative shear strength. Again, a parameter that can be important for characterising soil layers.
Photos of undisturbed samples
To conclude a (large-scale) soil survey project, we always advise SOCOTEC to request photos of the undisturbed samples. All undisturbed samples are digitally recorded per drilling. The described drill logs with the complementary photographed samples from a bore are a valuable addition to projects and can serve as a very detailed and important reference material.
When taking the photos, the samples are cut lengthwise. This is of course only possible once all the tests have been carried out and approved. Subsequently, the samples are photographed per a maximum of 10 (contiguous) samples. The soil structure, internal layers, layer transitions and inhomogeneities are clearly visible in these photos. In addition, the locations can be indicated where each test was carried out. In short, photos of the samples help visualise the underground and are important to schematically represent the structure of this subsurface in more detail.