EVALUATION OF DISTURBED PARAMETERS OF THE NATURAL STRUCTURE OF THE LABORATORY SAMPLES OF CLAY DEPOSITS DURING ENGINEERING AND GEOLOGICAL SURVEYS IN SAINT-PETERSBURG TERRITORY AND NEAREST AREAS

Abstract

In Russian technical standards there are no criteria for the natural structure disturbance degree of laboratory samples of coherent dispersed soils. At the same time, such soils are widely represented in various regions of the country, in particular, in St. Petersburg. The paper discusses various criteria for estimating the degree of natural structure disturbance of laboratory samples, and also considers various methods for restoring the strength of samples. The main attention is paid to the evaluation of the degree of violation of the natural structure of laboratory samples when performing odometric tests. The statistical results of such an assessment are given for more than 3,000 oedometer tests of quaternary soils of different genesis based on deformation criteria. The quality assessment of laboratory samples was evaluated at 130 sites performing engineering and geological surveys (by various organizations) in St. Petersburg from 2003 and 2018. According to the results of statistical analysis, it was shown that the quality of samples by the criterion of the relative change in the porosity coefficient at the effective household stress corresponds to "poor" or "very poor" (according to the scale proposed by Т. Lunne and others). The main causes of the violation of the natural structure of the samples (sampling without primers, violation of sampling and storage rules, as well as transportation of samples) are described. Based on the results of a statistical analysis of the deformation parameters of laboratory soil samples during the implementation of complex geological survey in St. Petersburg, it was concluded that it is impossible to use the test results of these samples for performing geotechnical calculations using modern models of soil mechanics without special correction procedures.