EXPERIMENTAL FIELD investigations OF DEFORMABILITY of claystones and sandstones

Subject: the “load”-“deformation” dependence and phases of the stress-strain state of claystones and sandstones. Research objectives: perform stamp and pressuremeter tests, analyze results of field tests and create recommendations for the design and calculation of foundations on claystones and sandstones. Materials and methods: in this article the field methods of testing of claystones and sandstones are considered. Stamp and pressuremeter tests were performed, the “load - settlement” dependence was obtained and phases of the stress-state for claystone and sandstone were identified. The design strength of the soil for the drill pile buried in claystones and sandstones by more than 0.5 m was determined. Results of field tests are processed by mathematical statistics methods in accordance with GOST 20522-2012. The obtained results are analyzed and compared with the previous results of tests on foundations. Results: the scientific novelty of this work consists in revealing the regularities in the formation of the stress-strain state in claystones and sandstones under the action of the load in various directions. The deformation mode and development of phases of the stress-strain state in claystones and sandstones differ significantly from modern clays and sands. In 58 % of the stamp tests, the loss of the bearing capacity of the base, composed of claystones and sandstones, was observed only after reaching the load of 3.0 MPa. In 19 % of the stamp tests, the deformations sharply increased already at the load level of 0.6…2.2 MPa, which is characteristic of less stable varieties of claystones and sandstones. In 23 % of the experiments, the vertical deformations of sandstones and claystones had a linear character for the entire “load”-“settlement” graph and the phase of soil bearing capacity loss was not achieved. A similar picture was observed when performing pressuremeter tests: the phase of bearing capacity loss was not achieved for claystones at a maximum horizontal pressure of 0.85 MPa and for sandstones - at a maximum horizontal pressure of 1.0 MPa, and the deformations of the soil were predominantly linear, which is typical for compaction phase and phase of local shears. Conclusions: claystones and sandstones have high values of design strength and can be a reliable low-compressible base for buildings and constructions with loads from 0.2 to 0.3 MPa. Calculations can be made using the theory of a linearly deformed soil when designing the foundations of buildings and constructions on claystones and sandstones. However, it should be taken into account that this observation is valid for one-time loading, since claystones and sandstones have residual deformations associated with the destruction of cementation bonds between soil particles. It is rational to use in calculations of foundations on claystones and sandstones the values of the strength parameters of the soil obtained in laboratory or field tests with soaking, taking into account the possible deterioration of the properties of these soils.