Laboratory tests

Accredited laboratory testing of soils and rocks

It is precisely this breadth of scope that separates a reliable geotechnical project from a risky one: accurate input data can only be obtained through methodically performed laboratory analyses. That is why we cover the full range of materials and projects — from the foundations of single-family houses to demanding geological investigations for high-rise buildings, tunnels and industrial complexes. Below we present, grouped by category, the tests we perform and the data they provide.

Physical properties of materials – from moisture content to loss on ignition

Determining physical properties is the starting point of every geotechnical analysis. Our laboratory routinely measures moisture content, particle density and bulk density, performs grain-size sieving with washing and hydrometer analysis, and pays particular attention to loss on ignition as a key indicator of the organic matter content in soil — a figure that directly affects the assessment of ground suitability for foundations and the design of embankments. For clayey soils we also determine water adsorption according to Neff (Enslin apparatus) and the content of active clays using the methylene blue test (MB test).

Atterberg consistency limits – the basis for classifying clays

Determining the Atterberg consistency limits is one of the most frequently requested tests in the characterisation of cohesive soils. In accordance with SIST EN ISO 17892-12:2018, we determine the liquid limit, the plastic limit and the plasticity index — indispensable parameters for assessing the behaviour of clays as moisture content changes. These data are especially important for preventing landslides and for assessing the long-term stability of slopes on clayey or mixed terrain.

Shear strength of semi-rocks and rocks

A specialised field that calls for experience and dedicated equipment is determining the shear strength of semi-rocks — materials whose strength lies between soft rocks and firm soils. This transitional category frequently occurs in the Slovenian geological setting (flysch layers, weathered rocks, conglomerate) and requires a tailored testing approach. We perform the direct shear test (3 points) according to SIST EN ISO 17892-10:2019, the rotational shear test (3 points), the undrained shear test using the Vane and Fall-cone methods, and the uniaxial compressive strength of rocks and semi-rocks according to SIST EN 1926:2007. The results serve as input parameters for stability analyses and the design of retaining structures.

Brazilian test – tensile strength of rocks

The Brazilian test (indirect tensile strength) is a standardised method for determining the tensile strength of rocks according to SIST EN 13286-42:2004. We carry it out on drilled cores or cut rock pieces, which are loaded with a diametral force until failure. The method is particularly suitable for rocks that are strong in compression but fail predominantly in tension — which applies to most sedimentary and metamorphic rocks. Together with the uniaxial compressive strength and the point load strength index (ASTM D5731), it provides a complete picture of a rock’s mechanical properties.

Laboratory testing for mineral raw material deposits

When the task is to evaluate geological materials with economic potential, somewhat different analyses are required than in conventional geotechnical design. Laboratory testing for mineral raw material deposits includes determining the grain-size composition, the mineral and chemical properties of samples, the organic matter content (loss on ignition), the physical parameters of aggregates and water absorption. On the basis of our laboratory reports, investors obtain reliable data for assessing extraction prospects and preparing technical studies.

Geological investigations for landslide prevention and the analysis of unstable ground

Landslides and ground settlement are often the result of insufficient knowledge of the geomechanical properties of the subsoil. In the laboratory, geological investigations for landslide prevention cover the determination of compressibility and consolidation parameters using an oedometer (according to SIST EN ISO 17892-5:2017), the swelling potential of clays, water permeability, and the Atterberg plasticity limits. On the basis of these data it is possible to predict settlement, assess the risk of landslides and plan appropriate measures for ground reinforcement or drainage. Particularly when building on soft clayey or organic ground, early laboratory characterisation of the material is crucial for preventing costly remediation in later construction phases.

Quality, standardisation and traceability of results

All tests in our laboratory are carried out in accordance with applicable international standards (the SIST EN ISO 17892 series, SIST EN 1926, ASTM and others) and are supported by internal quality control. Our quality management system is certified to the ISO 9001 standard, which ensures the traceability of procedures, the calibration of measuring equipment and the reliability of results. Reports are prepared in a form suitable for direct use in project documentation — with descriptions of methods, tables of results, charts and geotechnical interpretations.