Influence of ground water

By default the program performs the stability analysis of a rock wedge without considering ground water. If interested on the influence of ground water on a rock wedge it is necessary to introduce the height of GWT from the line of intersection of slip surfaces and rock face (the GWT takes an arbitrary position over the entire height of a rock wedge). The program assumes that water can flow freely discontinuities located below the GWT (no restrictions, e.g. due to ice blocks, are considered).

The water pressure acts in the direction normal to the slip surfaces against normal components of the passive forces. If the height y_w above the point of maximal pressure P_max is equal or larger than Z/2 and it is fully contained by the rock wedge, then its value is assumed to be equal to Z/2 (case A). If the height y_w above the point of maximal pressure P_max is less than Z/2 (case B), then its value reduced as: 

where:	L*	-	length of the line of intersection of slip surfaces A1, A2
	α1	-	gradient of rock face
	δ	-	gradient of the of line of intersection of slip surfaces

The resulting water pressure on slip surfaces 1 and 2 is given by:

where:	Z	-	height of GWT above the line of intersection of slip surfaces and rock face
	Pmax	-	maximal water pressure on the line of intersection of slip surfaces
	γw	-	bulk weight of water
	A1w	-	are of the wetted part of the slip surface 1
	A2w	-	area of the wetted part of the slip surface 2

A)                                                                                B)

Distribution of water pressure on the line of intersection of slip surfaces

If a tension crack is found either entirely or partially below the GWT, then the influence of water pressure is reflected both on slip surfaces 1 and 2 through forces P₁ and P₂ acting on intersection of these surfaces and on tension crack through force P₃ acting in the direction normal to the tension crack.

Distribution of water pressure when considering GWT in tension crack