Soil Matrix

Published: August 23, 2021 | Last updated: July 5, 2023

What Does Soil Matrix Mean?

A soil matrix is a mass of soil consisting of solid particles and voids filled with water and air. Trenchless construction techniques such as horizontal directional drilling (HDD) and microtunneling excavate below the earth’s surface through the soil matrix. As excavation proceeds, the soil matrix is disturbed and becomes unsupported. This can lead to settlement or soil subsidence, i.e., the downward movement of soil caused by change in the natural stress state of the soil matrix.

Trenchlesspedia Explains Soil Matrix

To prevent problems such as subsidence or heaving during a trenchless construction project, it is important to understand the physical properties, chemical composition and bearing capacity of the soil through which the bore will pass. For this purpose, soil investigation is carried out in-situ and in a lab to ascertain the properties of the soil matrix.

The topography of an area may look straightforward, but below the surface, the soil conditions may be drastically different. Since tunneling sometimes involves passing through vast swaths of land, the soil conditions may vary a number of times. Carrying out a comprehensive geological survey by professional surveyors helps the project designer to consider all kinds of ground conditions to arrive at a sustainable design for the tunnel.

Mixed-face soil, where two or more different kinds of soil are present in the path of the machine, can also be encountered during a tunneling operation. Mixed-face soil can present a wide range of geology types, including boulders, cobbles, hard clay, glacial till, soft clay and dry alluvium. All these soil conditions require different kinds of cutting tools. If these soil conditions are not known prior to commencement of the project, it can lead to the collapse of the borehole, damage to the drill head or cutting head, and ultimately failure of the project.

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