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STRUCTURAL STRENGTH AND ITS INFLUENCE ON GROUND DEFORMATION PROCESSES

Journal: Academic Journal "Industrial Machine Building, Civil Engineering" (Vol.3, No. 45)

Publication Date:

Authors : ;

Page : 152-160

Keywords : structural strength; permanent deformation; cyclically-increasing load; bathymetric magnetic mark; the relative deformation.;

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Abstract

Two types of deformations, elastic and permanent ones, develop from the external load in the subsoil. The boundary separating them is the structural strength of the ground. Its value is the parameter defining the zone border of the permanent deformations, which is situated at a depth where the sum of the stress from the additional load and the weight of the soil is balanced by the structural strength. The extreme pressure when the increase of the permanent deformations begins was named by different researchers in different ways: «initial pressure», «structural strength», «safety margin». The structural strength of the ground is determined either in laboratory or in field conditions. In the field conditions it is determined by the movement of the bathymetric magnetic marks, which are put in the foundation soil under experienced foundations and foundation beds. They measure the soil settlement and layer-by-layer soil movement. The research technology depends on the size of the foundations. For the small-sized foundation with the area of 0,03 ... 0,1 m2 the tests are carried out by the method of cyclically-increasing load. According to the results of measurements the graphs of settlement relationships and its residual component are made, as well as the depth of the zone of complete and permanent deformations all along the pressure. The intersections of permanent deformations with the axis of the pressure determine the value of the structural strength. For the foundations of various sizes the structural strength is determined in the process of increasing load. According to the value of the final foundation settlement and the movement of the ground marks the depth of the zone of the permanent deformations is determined. At the lower boundary of the permanent deformations the structural strength is equal of the sum of the tensions from the additional load and the weight of the soil. The results of observations of foundation settlement of 16-storey residential building with the area of foundation base 645 m2 are shown in this research article. Based on the result of observations over the soil marks put at different depths beneath their foundation beds the deformation diagrams are made. According to the deformation diagrams the values of the relative deformations were determined for all reference layers located between the adjacent soil marks with several pressure values on the foundation bed. The graphs of the deformation relation are made. The intersection of the graphs with the stress axis defines the value of the structural strength of this horizon. The values of the structural strength within the loessial soil beneath the initial position of the foundation bed were determined in this research. Besides testing the foundations of shallow laying the structural strength can be determined by the testing results of soils by the pile using the cyclically-increasing load method in conjunction with the stress relaxation one bringing it to the critical load – «failure». The structural strength of the natural soil under the pile toe is determined by the ultimate load value. Based on the research carried out at other sites, the graph of structural strength values for the loessial soils of Odessa region was made.

Last modified: 2016-07-25 20:23:49