Triaxial test ;

The triaxial test is one of the most versatile and widely performed tests in the geotechnical laboratory. It allows shear strength and stiffness of soil and rock to be determined for use in geotechnical design.

– Procedure of triaxial test :-

The triaxial test typically involves subjecting a cylindrical specimen of soil, whose diameter ranges from 38mm to 100mm, into a cell that can be pressurized. Most of the specimens have an approximate 2:1 height to dia ratio and are sealed with a rubber membrane. The specimen preparation generally depends upon the type of soil. Cohesive soil samples are prepared directly from saturated compacted samples, either undisturbed or remolded. The specimen for cohesion-less soil is prepared with the help of the mold that maintains the required shape of the specimen.

And then the specimen is vertically covered with a thin rubber membrane and placed between two rigid ends inside a pressure chamber. The upper plate can move vertically and apply vertical stresses to the specimen. The axial stress/strain of the sample is controlled by the movement of this vertical axis. The water pressure surrounding the sample in the pressure chamber controls the confining pressure. Also, the volume change of the sample is controlled by measuring the exact volume of moving water.

There are three primary triaxial test carried out in a laboratory, depending upon the combination of loading and drainage condition ;

• Consolidated – Drained (CD)
• Consolidated – Undrained (CU)
• Unconsolidated – Undrained (UU)

Triaxial test is significant to know soil property because it determines the ability of soil to resist shear stress and strain. Different combination of confining and axial stresses can be applied. Drained and undrained test can be carried out. The types of properties of soil which can be known by triaxial test are followed ;

1. Shear strength and stiffness of soil
2. Stress/Strain behavior
3. Pore water pressure of soil

Rock outcrops are defined as visible exposures of bedrock or other geologic formations at the surface of the Earth. Rock outcrops take many different forms within the Park, ranging from the massive granite boulders of Old Rag Mountain, to the sheer cliffs of Little Stony Man, and the jumbled boulder fields of Blackrock.

Most civil engineering projects involve some excavation of soils and rocks, or involve loading the Earth by building on it. In some cases, the excavated rocks may be used as constructional material, and in others, rocks may form a major part of the finished product, such as a motorway cutting or the site f or a reservoir. The feasibility, the planning and design, the construction and costing, and the safety of a project may depend critically on the geological conditions where the construction will take place. This is especially the case in extended ‘greenfield’ sites, where the area affected by the project stretches for kilometres, across comparatively undeveloped ground. Examples include the Channel Tunnel project and the construction of motorways. In a section of the M9 motorway linking Edinburgh and Stirling that crosses abandoned oil-shale workings, realignment of the road, on the advice of government geologists, led to a substantial saving. In modest projects, or in those involving the redevelopment of a limited site, the demands on the geological knowledge of the engineer or the need for geological advice will be less, but are never negligible. Site investigation by boring and by testing samples may be an adequate preliminary to construction in such cases.