Development of infrastructure located in cryolithozone requires the use of modern geotechnical technologies for frozen soil investigation. Accurate soil temperature measurement is the necessary condition for engineering-geocryological survey and geotechnical monitoring. In the article a new method is considered on how to measure soil temperature by cone penetration testing (CPT). The cone temperature stabilization is described in detail, including the existing criteria of thermal stabilization of a cone. The results of temperature measurements are presented for both frozen and non-frozen soils and obtained by CPT (cone with a temperature sensor) and using borehole thermometry (thermistor string), which measured in both holes drilled by a rig and left after the cone penetration testing completion. Detailed analysis of accuracy of soil temperature measurement is also provided. The comparison of the obtained results is performed and the discrepancy of the measured soil temperature in absolute values is estimated. As a result of the analysis, it was shown that all the soil temperature values measured by different methods are sufficiently close to each other and the true value of the natural soil temperature are all located in the zone of intersection of the confidence intervals of each temperature measurement, performed at corresponding depths by different methods. All obtained temperature values do not cross the accuracy limits of temperature sensors, used both in cone penetration testing and borehole thermometry. High accuracy of temperature measurement by CPT is proved and feasibility of CPT application for soil temperature measurement is justified as an express-monitoring method.
The article provides the analysis of the results of the permafrost soils field and laboratory tests. The undisturbed permafrost samples were collected using cone penetration testing (CPT) equipment and MOSTAP sampler. The sampling technology using CPT equipment was applied on permafrost soils for the first time. The full scope of tests for physical properties were carried out on the collected samples. Based on the test results, several engineering-geological elements (EGE) were identified and confirmed, one of which is composed of frozen silty clay. The results of statistical data processing were compared. The data on the coefficient of variation of the values of the ultimate long-term resistivity of soils against cone penetration (characteristic of long-term strength) for the frozen EGE are presented.
The climatic conditions in Moscow limit to a certain extent the utilization of renewable energy sources for heat supply. Long heating period, relatively low average daily sunshine hours during heating period, and low outside temperatures act as barriers to realising the full potential of renewable energy sources. The paper presents an evaluation of feasibility and effectiveness of using various renewable energy sources in the heat supply system of Block 23 of the National research university «MPEI». The system arrangement for heat supply of the building with renewable energy sources is described. Experimental data have been obtained on the basis of this system. The calculated time dependences of building heat consumption and heat pump system (HPS) outputs are given. In addition, for the air-source heat pump system, the dependence on the outdoor temperature is given. Values of HPS efficiency indices are also presented. A comparative analysis of the efficiency of air-source HPS and liquid-to-liquid HPS with a geothermal circuit in winter conditions is carried out.
Geothermal energy is a renewable energy resource. Nowadays it can be considered as a promising alternative to various fossil fuels. Ground source heat pumps are efficient installations enabling the intensive use of underground energy for heating and cooling of modern residential and commercial buildings. However, climatic conditions often limit the use of this type of installation to a certain extent. This paper presents a description of an existing system comprising a liquid-toliquid heat pump and a geothermal field consisting of 4 boreholes. The system is used to investigate the intensity of ground temperature potential decrease in winter and its recovery in summer in the Moscow city environment with a detailed study of the properties of individual soil layers, as well as to study the mutual influence of boreholes on each other, represented by the conditional radius of thermal influence of individual boreholes. Graphs of soil temperature changes at different depths are presented.
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