Hydraulic Heave Equations
Hydraulic heave refers to the potential for soil to heave due to water seepage forces. As excavations get deeper, hydraulic heave can get more important, especially when more permeable layers are encountered under clays.Various building codes specify how hydraulic heave should be calculated, in general an approach according to a service analysis is to formulate hydraulic heave as:
FS Hydraulic heave = (total vertical stress - uTop)/ (water pressure - uTop)
where the total vertical stress and water pressure at are a point of interest, and Utop is the water pressure at the ground surface when the ground is submerged.
Figure 1: Basic formulation of hyrdaulic heave
Hydraulic heave according to Eurocode 7 has to be calculated according to the following:
FS Hydraulic heave = LF stabilizing (total vertical stress - uTop)/ [LF destabilizing (water pressure - uTop)]
Where LF stabilizing = Stabilizing load factor, and LF destabilizing is the destabilizing load factor according to the examine design scenario.
In general, the hydraulic heave safety factor should be greater than 1.5. For example, most Eurocode 7 national annexes define 1.35 on LF destabilizing, and 0.9 of LF stabilizing.
Figure 2: Groundwater flownet analysis with our DeepEX software program.
Figure 3: Groundwater flownet analysis with our DeepEX software program showing ground water head contours.
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