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Construction Services: Trench and Test Pit Sampling

29 May 2020

Excavating and digging certain parts of a land area are typically done to effectively establish the structural foundation of a specific property. Alternatively, excavation works can also be done to remove layers of topsoil, rocks, sand, and other unwanted materials, bury service lines, pipelines, and sewer systems, construct basement, and many more.

But before all these excavation works are initiated and conducted, contractors and engineers would typically conduct trench and test pit sampling first. Excavating trench and test pits enable professionals to closely assess, gather, and classify the features and properties of soil and rock sample materials. These excavation works are typically done with an excavator, backhoe, trenching machines, draglines, clamshells, bulldozers, and other power excavating equipment.

Conducting Trench and Test Pit Sampling

With the help of the previously mentioned excavating equipment, trench sampling is done through excavating a rectangular or cross-section trench that has a minimum bottom width of around 0.6 m. The length of this specific excavation can be extended whenever necessary. As the trench area deepens, its sides must be sloped, step cut, or shored to prevent the sudden displacement of soil or rock materials that can subsequently destabilise the site.

What is great about trench sampling is that it can readily provide a continuous two-dimensional profile of the subsurface material along a certain line or section. This method of sampling can be beneficial for works that involve shallow explorations of foundation, borrow, or aggregate materials. 

Test pit sampling, on the other hand, is intended to expose foundation and construction materials and gather them for further studies. Through hand or power equipment, a contractor can excavate a rectangle or square pit with a dimension of 0.9 by 1.5 m as the minimum. Same with trench sampling excavations, the test pit must be supported with structures to avoid caving or sudden displacement or materials. Sloping the walls can also be done to stabilise the excavated area.

For test pit sampling, getting materials by hand would be the best way to obtain the most illustrative samples of a specific soil layer, formation, or structure. 

Benefits of Trench and Test Pit Sampling

All materials that will be picked and gathered on trenches and test pits are brought as samples for laboratory testing. The tests are done to clearly identify and examine the relationships between the sample rock materials and the soil layer. Once the properties are identified, engineers and other involved professionals can now determine if some possible hazards or risks are present in working with the whole or certain parts of the land area.

Aside from identifying hazards and risks, the samples from the trench and test pit can also tell the structure and stability of the ground layers along a specific horizontal or vertical line on the site. Groundwater conditions, fault evaluation studies, abnormalities evaluation, and other elements and variables are also established and verified through trench and test pit sampling. Conducting trench and test pit sampling may be expensive in some cases and situations, but the information they provide can certainly help construction companies in performing subsequent excavation and construction works safely and securely.

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