Abstract
In modeling geodynamic risk, the issues of developing special models of risk on the territories of distribution of loess and loess-like subsident soils under technogenic impact are of great relevance. Developing such models is a multi-stage process, which requires developing a model of the geological structure of a studied massif and setting predicted values of the properties of loess soils for preliminary quantitative evaluation of possible deformations in the natural conditions and in the zone of impact of constructions. Standard quantitative evaluation concerning the subsidence is carried out using results of testing the sample in limit states. Prognosis of the degradation of subsidence properties as a result of the break-up of the microaggregates in the zone of aeration is possible in conditions of impact of changes in the microaggregate compound on the subsidence. Using the method of defining the granulometric composition of the soil allows one to determine the area of soil condition in relation to dispersity. The method of GMDH allows one to develop a mathematical model of degradation of subsidence properties and calculate the predicted values of deformation in the zone of insufficient water content. The degradation of the subsidence properties of subaerial horizons is manifested most significantly at mild (30% of possible) increments of moisture and pressure of 0.1 mPa. In the area of additional pressure, predicted values of deformation insignificantly increase under moisture due to degradation, with increased moisture the break-up of the aggregates of sand fraction is followed by increase in the number of aggregates of smaller size (large-grained pulverescent ΔА3). The content of free thin fine-grained sandy (ΔM2), and clayey particles (ΔМ5, ΔМ6) increases, connected with aggregates of thin fine-sandy and large-grained clayey. The share of aggregates of large-grained pulverescent fraction also increases; the content of particles of this fraction assembled in the aggregates decreases. The dependency of deformation intensity in conditions of degradation of paleosol is of another character: the intensity of degradation increases as the pressure rises. The analysis of predicted values of aggregate content, free and assembled particles when there is change in moisture conditions showed that the process of the break-up of thin fine-sandy aggregates and increase in the share of large-grained clayey aggregates (composed of thin fine-sandy particles) is followed by occurrence of free particles of thin fine-sandy and thin clayey fractions.
Highlights
The notion geodynamic “risk” is related to the calculation of possibility of damage, vulnerability (Osipov et al, 2017)
The issues of developing special models of risk on the territories of distribution of loess and loess-like subsubsident soils under technogenic impact are of great relevance
The algorithm of developing models of risk conditioned by the degradation can be described with the following sequence of the stages: experimental defining of the area of changes in the microaggregate and granulometric composition, indicators of subsidence of soils; developing a mathematical model of connection between dynamics of microaggregate composition and values of relative subsidence; prognosis of degradation of subsidence properties in set conditions; developing a special model of subsidence degradation
Summary
On some aspects of modeling geodynamic risk in the territory of distribution of subsident soils. Received 30 September 2017 Received in revised form 21 October 2017 Accepted 13 November 2017
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