The design circuit of definition of pressure of a soil on a protecting construction and its displacement is developed during an extraction of foundation pit. In an initial position a protecting construction (sheet pile screen, sturry wall, row of piles ) is enclosed by a soil from both sides. Then we begin digging a soil from the left side of a protecting construction. During account is analyzed a modification of pressure of a soil from both sides of a protection. The critical cut depth of foundation pit is defined, at which there is a fall of a wall. The protecting construction is simulated in the design circuit elastic beam (plate). The soil is described by nonlinear model, in which the modulus of rigidity decreases in process of an approximation of the intense condition of a soil to limiting. The mathematical procedure is reduced to iterations of sequential separate accounts on a method of Gauss.