No abstract

The highly versatile engineering method of layer-by-layer summation for settlement calculation, which also defines the so-called linearly deformable model of the soil bed, is established for geologicengineering surveys, and design and installation of structures. The method of layer-by-layer summation, which differs appreciably from the method presented in Construction Rules and Regulations II-15-74 and 2.02.01-83, is described in [1].Practice indicates that actual settlements are considerably lower than those calculated by the method of layer-by-layer summation when the compression moduli E of the soils obtained from compression tests are used [2]. For settlement calculation of Class-I and -II buildings, Building Codes [1] recommend that E be determined from in-situ tests using plates with an area of from 2,500 to 5,000 cm 2 , and for Class-III structures, the value of E be multiplied by a factor ranging from 2 to 6 from Agishev's table. Why is this so, however; there is no analysis, the reasons for this recommendation are not investigated, and there is no validation of the other components of layer-by-layer summation, which lead to noncorrespondence between computed and actual settlements.To ascertain the reasons, we conducted a series of experiments in the tray of an MF-1 testing device (designed by Yu. N. Murzenko) ( Fig. 1) with circular plates of different diameter. D-2 tensometric deformometers were used to measure normal stresses (Fig. 2). The relationship between E and the diameter of the plate was revealed. Consequently, the recommendations cited in [1] for determination of E from in-situ tests contain contradictions even for a uniform bed. Determination of E on the basis of in-situ plate tests raises even more questions in the case of nonuniform beds. It follows, therefore, that as compared with compression tests, determination of E from plate tests not only offers advantages, but also disadvantages.The plate tests were conducted on a bed formed dense sand of medium fineness in the air-dry state.The average load dependence of the depth of the compressible stratum was obtained as result of experiments with a circular plate having a diameter D = 28 cm. On comparing this dependence with the A modernized method of layer-by-layer summation for settlement calculation, which takes into account the structural strength of the soils, and approximates the computed to the observed settlement, is discussed.