Stress-strain state of a borehole determined analytically using drilling-out as a technology of reducing differential settlement

Abstract

The existing approaches for reducing the differential settlements of buildings and structures have their own advantages and disadvantages. Lowering of a building or part of it is one of the promising methods to reduce the differential settlements of shallow foundations resting upon weak silt-loam soils. The effect is achieved by drilling-out vertical boreholes in the immediate vicinity of the foundation from the minimal settlements. Method: Russian and foreign scientists have been involved in the development of calculation procedures for horizontal and inclined drilling-out of boreholes. It has been important to determine drilling parameters when using this technology and how soil characteristics and stress state of soils around the borehole influence the reduction of differential settlements. The paper discusses the influence of the strength characteristics of soils on the stress state of the soil massif around the borehole, as well as the influence of the borehole radius on the formed areas of limit state. The analytical solution is based on the well-known ratio used to determine the stress state around the borehole during pressure tests. Tangential and radial stresses are determined from this ratio; next, they are checked according to the condition of the strength law, and thus, the stress state around the borehole becomes evident. Result: The stress state of the soil around the boreholes has been calculated by the given method; it has made it possible to calculate the areas of soil destruction and determine the parameters of boreholes and their geometry depending on the purposes when regulating the settlements of slab foundations. It has been established that drilling behind the foundation contour in relation to drilling in the foundation contour makes it possible to increase the radius of the plastic deformation zone up to two times under the same soil conditions and well geometry.