How to Perform Dewatering in PLAXIS Featured

The problem of changing water conditions is omnipresent in geotechnical engineering. Groundwater is systematically found beneath the Earth's surface in soil pore spaces and rock formation fractures. The flow of groundwater is a fundamental aspect that controls the strength and compressibility of soil, impacting soil's ability to sustain structural loads. The study of groundwater is essential for geotechnical engineers who construct building foundations, tunnels, water conveyance channels, dams, mines, and other structures.

In this context, PLAXIS 2D and PLAXIS 3D are fully equipped with a complete set of tools to model changes of pore water pressure and, more specifically, dewatering, along with its influence on soil mechanical behavior.

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Terzaghi principle of effective stress

Total stress σ = Effective stress σ’+ Pore water pressure u

Figure 1: Terzaghi effective stress principle

Lowering the groundwater will reduce the pore water pressure u and hence will cause an increase and redistribution of soil effective stresses, which will then lead to the settlement and evolution of active and passive pressure in surrounding buried structures.

Water levels and hydrostatic pore pressure distribution

Figure 2: Steady-state pore pressure definition on a 3D model

The definition of water levels in PLAXIS can be performed during soil stratigraphy definition when defining boreholes or within Flow mode. The Flow mode enables the definition of additional water levels different than the initial one. Additional water levels might then be referenced (globally, or locally in some limited numbers of soil clusters in the model) to simulate the process of dewatering.

(b) Considered pore water pressure distribution in PLAXIS Output Figure 3: Dewatering by means of the phreatic method

Groundwater flow analysis

Such groundwater analyses require the definition of additional parameters for the constitutive materials, such as:

Porosity
Unsaturated zone behavior eventually

Closed flow
Seepage flow boundary
Drains
Wells (both infiltration and extraction)
Precipitations

(b) Vector plot of groundwater flow Figure 4: Dewatering by means of the groundwater flow calculation method

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Sources: How to Perform Dewatering in PLAXIS, PLAXIS Productivity Strategies Blog

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