GEOLOGICAL SURVEY
OF NAMIBIA

Earth Sciences for Namibia's sustainable development

Soil and Rock Mechanics Laboratories

This laboratory facility is equipped with equipment for testing of soil properties for their subsequent use in civil engineering projects and other related engineering areas. All the tests described below are conducted in accordance with appropriate British Standards Method of Test for Soils for Civil Engineering Purposes. The types of tests that can be conducted in this laboratory facility include the following;

Moisture content of the soil is the percentage of water present by mass of a given soil sample. Moisture content is one of the parameters used in classifying a given soil type for use in any engineering project.

The soil index properties are used extensively by engineers to discriminate between the different types of soils within  broad categories. For instance, clay soil will exhibit a wide range of engineering properties that will depend on its mineralogical composition. The index property tests that can be conducted in the soil mechanics laboratory include the following;

• Determination of particle size distribution using Sedimentation by Hydrometer method.

• Computerised instrumentation in the Industrial Mineral laboratory can be used to determine fine particle size distribution.

• Determination of plastic limit, shrinkage characteristics, density and particle density (specific gravity).
• Liquid limit test depending on the soil type (e.g. Clays); this test can be conducted by using either Casagrande method or cone penetration method.

Permeability Characteristics

The soil mechanics laboratory also has equipment for testing soil permeability characteristics. The Constant Head Apparatus is used specifically for soils with high permeability such as Sands and Gravel. The permeability characteristics of soils is required in many construction projects where drainage is an important feature. These projects include, landfill site design, earth dam and sheet-pile wall design, contaminated land investigations,  and groundwater lowering feasibility studies.

Direct Shear Test

Direct shear test for cohesionless and cohesive soils can conducted using a motorised and manual mode shearbox equipment.  Soil shear strength parameters  are important for stability as every physical structure will impose some load on the soil that supports the foundations. The stress set-up in the soil may cause soil  deformation. This failure mechanism is known as shear failure and occurs when shear stresses set up in the soil mass exceeds the maximum shear resistance that the soil or rock can offer.

This test was developed in California, USA, for estimating the bearing value of highway subbase and subgrades, hence its name. The test provides data with respect to the performance of soil for subsequent use in the civil engineering projects such as road construction.

Using Consolidation Apparatus (Oedometer), evaluation of Consolidation Characteristics of soils of low permeability can be conducted. The data from this test together with classification data and the knowledge of the soils loading history enable estimates to be made of the behaviour of the foundation under load.

Soil Compaction Test

Most civil engineering projects require the use of soil as filling material. It is necessary for the soil to be compacted to a dense state so that satisfactory engineering properties can be acquired. The soil mechanics laboratory has equipment for conducting this test.

The compaction tests will shed light on the following mechanical properties of a soil:

• Relationship between dry density and moisture content for a given degree of compactive effort achievable.
• Moisture content at which maximum dry density is achievable.
• Value of the maximum dry density achievable.

Efforts are currently underway for setting-up facilities for conducting rock tests such as triaxial, uniaxial, permeability, durability and other related rock strength tests. These tests are important in projects undertaken in most parts of Namibia where rocks outcrop. The rock mechanics laboratory will be useful in projects such as in the promotion of dimension stone (quality assurance), mining industry, construction industry, foundation engineering and environmental protection.