Soils laboratory is one of the main Central Testing Laboratories Sections in MTRD. The laboratory test disturbed soil samples for pavement construction. Our clients include Road Contractors, Resident Engineers for various Road Projects,   Consultant Engineer in different Projects, Road Authorities (KeNHA, KURA, KeRRA) and a variety of other Individuals in the Road Sector in general.

Test carried out in the laboratory are physical tests and can be broadly grouped into three categories:

1. Soils Classification Tests. These include:

• Particle size analysis (or grading test, Wet and Dry). This helps to classify the soils as either Corse grained, Medium grained or Fine grained).
• Atterberg limits (Liquid Limit LL, Plastic Limit PL, Plastic Index PI, and Linear Shrinkage LS). This helps in determining the bonding properties of the soil fines in the presence of water. The soils can then be classified as either cohesive or non-cohesive.

1. Soil Compaction Tests. There are three types of compaction tests carried out in the laboratory specific to different types of materials. These include:

• Standard Compaction (AASHTO T99) on fine soils i.e. for alignment soils, subgrades, improved subgrades and fill layers.
• Heavy Compaction also called “Modified AASHTO” (AASHTO T180) on gravels, material sites and pavement materials i.e. gravel base and subbase material.
• Vibrating Hammer method (BS 1377 test 14) on crushed rock material ie Graded Crushed Stone (GCS).

These compaction tests help in determining the density/ moisture relationship of the soil material and provide key parameters of the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) critical in the construction quality control.

1. Soil Strength Tests: These include:

• California Bearing Ratio (CBR)
• Unconfined Compressive Strength (UCS).

These two test give an indication of the strength of the soil. CBR test is carried on soils sampled compacted at a specified compaction e.g. 100% OMC and 95% MDD AASHTO T180 or 100% OMC and 100%MDD AAAHTO T99 after 4 days soak or 7 days cure and 7 days soak for those treated with stabilizers. Samples that can be extruded especially those treated with cement may also be cured and tested for UCS.

Samples are penetrated or crushed to give the CBR Strength value or the UCS strength

All the above test are therefore important in the selection of suitable soil materials for use in pavement construction and for pavement construction quality control. The laboratory is also capable of carrying out a variety of field test e.g. Field Compaction tests (Sand replacement Method) and Dynamic Cone Penetration, DCP.