INFLUENCE OF EXCAVATION TO THE TEMPERATURE CONDITION OF PERMAFROST

Transcription

1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 10, Issue 01, January 2019, pp , Article ID: IJMET_10_01_201 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed INFLUENCE OF EXCAVATION TO THE TEMPERATURE CONDITION OF PERMAFROST E. V. Markov, S. A. Pulnikov, Yu. S. Sysoev, N.V.Kazakova Transportation institute, Tyumen industrial university, Tyumen , Tyumen Oblast, Russia ABSTRACT Permafrost is a very complex ground for foundation. Predicting the stability and reliability of constructions in a rapidly changing climate is impossible without predicting the temperature condition of permafrost soil. Stabilization of permafrost soils on local object is provided with a considerable margin, due to the use of ventilated cellar, thermopiles and monitoring systems. On linear objects such as pipelines, laying above the ground or the use of thermopiles is a very expensive engineering protection method. Therefore, the pipeline is laid underground with the use of ring insulation. Thawing of permafrost soils leads to significant uneven vertical deformations of the pipeline. Therefore, the accuracy of predicting the temperature of the permafrost is a priority problem. Underground pipeline laying is accompanied by excavation and backfilling of the soil. In this case, the structure of the soil is destroyed, the density is decreased and the water content is increased due to mixing with snow and penetrating of precipitation. The article presents the results of a numerical experiment of influence of excavation to the temperature condition of soil. Soil loosening and filling the empty pore by water significantly increases the average soil temperature of plastic frozen soil (the soil with annual average temperature in the interval of the most intense phase transformations). Thus, the stability of constructions is determined not only by their impact on the permafrost, but also by changing the structure of the soil during excavation. Key words: excavation of permafrost, temperature of permafrost. Cite this Article: E. V. Markov, S. A. Pulnikov, Yu. S. Sysoev, N.V. Kazakova, Influence of Excavation to the Temperature Condition of Permafrost, International Journal of Mechanical Engineering and Technology 10(1), 2019, pp editor@iaeme.com

2 E. V. Markov, S. A. Pulnikov, Yu. S. Sysoev, N.V. Kazakova 1. INTRODUCTION Permafrost soils cover about 65% of the territories of the Russian Federation. Volume of construction on permafrost soil increases every year. These are mainly oil and gas fields in the north of Western and Central Siberia. Usually local objects are built using cellar and have a high safety margin and special systems for monitoring the temperature condition of the permafrost. Linear objects, such as pipelines, are laid underground in many cases. An overground laying or thermopiles is a very expensive technical solution, so thermal insulation of the surface of the pipeline is used to protect permafrost from the thermal influence of the pipeline. Despite the calculations performed at the design stage, it is not always possible to ensure the normative level of reliability of pipeline systems. This is obviously related to some unaccounted factors in predicting the temperature of the permafrost. One of these factors is the destruction of the soil [1-3]. The excavation of soil in the trench destroys the bonds between the frozen soil particles. The soil is removed from the trench in a temporary dump using an excavator. After the pipeline is lowered into the trench, the soil from the temporary dump is moved back to the trench using a bulldozer. At the same time the mixing of soil and snow is happed. As the result, the soil in the backfilling is no longer identical to the one that was investigated at the geotechnical survey stage: the density and content of water differ. Therefore, any calculations of the temperature condition of the permafrost are not quite correct, if they do not take into account the destruction of the soil. In this article, the authors solved the problem of estimating of changes in the temperature condition of permafrost due to changes in the soil structure in the pipeline trench: an increase in the content of water and decrease of density of dry soil. 2. MATERIAL AND METHODS To calculate the temperature condition of the permafrost, the authors used a mathematical model, which is described in earlier articles [4-6]. Authors used the classical non-stationary heat equation [7-12]: ( ) ( ), (1) where isobaric heat capacity of soil, J/(kg K); soil density, kg/m 3 ; latent heat capacity of water, J/kg; content of liquid phase of water, kg/m 3 ; thermal conductivity of soil, W/(m K). The approximation of isobaric heat capacity, content of liquid phase of water and thermal conductivity is done with the using of transition function: ( ) ( ), (2) ( ) ( ), (3) ( ) ( ), (4) where, isobaric heat capacity of frozen and thawed soil, J/(kg K);, thermal conductivity of thawed and frozen soil, W/(m K); the temperature of the beginning of freezing, ºC; total water content of thawed soil, kg/m 3 ; content of nonfreezing water in soil, kg/m 3 ; temperature interval of freezing, ºC; Transition function between temperature of the beginning of freezing and temperature of the end of freezing calculated as follows: editor@iaeme.com

3 Influence of Excavation to the Temperature Condition of Permafrost ( ) ( ( ) ) ( ( ) ) (5) If the soil temperature is greater than the beginning of freezing, then the transition function is 1. If the soil temperature is lower than the end of freezing, then the transition function is 0. The author explored two main types of soil: sand and clay. The soil temperature at a depth of 20 m was chosen as С and С. The calculation scheme is shown in Figure 1. On the left for the trench in sand, on the right for the trench in clay. a) b) z Inward heat flux z Inward heat flux Sand 2 or Sand m Sand m 45 y Clay loam 2 or Clay loam m m 0.5 m 8.0 m Clay loam 1 y 12.0 m 12.0 m Sand 1 Clay loam 1 Figure 1 Calculation schemes for numerical investigation Six calculations were performed, each of which consisted of two stages. At first, the mathematical model was adapted to the temperature at a depth of 20 m below the surface of the ground. To adapt the models the coefficient of snow cover thickness reduction was used [13-15]. Then, at stage 2, the soil in the trench was replaced with a less dense one. The duration of the calculation at stage 2 was 30 years. Table 1 shows a list of numerical studies, including the number of the design scheme, number of soil at a depth of 8 m, soil in a trench and temperature at the depth of 20 m. Table 2 shows the thermal properties of soils, table 3 shows the physical properties of soils. The thermal properties of soils were calculated in accordance with the methodology given in the state regulatory documentation [16]. Sand 1 corresponds to sand 2 taking into account the decrease in the density of the soil skeleton as a result of excavation. Sand 3 can be obtained from sand 2 if you fill all the empty pores with water. Similarly for clay loams 1, 2, editor@iaeme.com

4 E. V. Markov, S. A. Pulnikov, Yu. S. Sysoev, N.V. Kazakova Table 1 Parameters of numerical studies Calculation scheme Soil Soil in trench 1 a Sand 1 Sand 2 2 a Sand 1 Sand 3 3 b Clay loam 1 Clay loam 2 4 b Clay loam 1 Clay loam 3 5 b Clay loam 1 Clay loam 2 6 b Clay loam 1 Clay loam 3 Temperature, С Table 2 The thermal characteristics of the soils Soil Name (J/(kg K)) (W/(m K)) ( C) (kg/m 3 ) 1 Sand ,57 1,86-0,1 0,8 2 Sand ,42 1,65-0,1 0,8 3 Sand ,57 1,82-0,1 0,8 4 Clay loam ,51 2,93-0,2 0,2 5 Clay loam ,15 2,5-0,2 0,2 6 Clay loam ,5 2,92-0,2 0,2 Table 3 The physical characteristics of the soils Soil Name (kg/m 3 ) (kg/m 3 ) (kg/m 3 ) (kg/m 3 ) (kg/m 3 ) 1 Sand Sand Sand Clay loam Clay loam Clay loam It the tables 2 and 3 was used the next conventions: skeleton, J/(kg K); density of dry soil, kg/m 3. isobaric heat capacity of soil 3. RESULT AND DISSCUSION The results of calculations No. 1, 2, 5, 6 show insignificant fluctuations in the temperature of the soil, approximately 0.03 ºC. This indicates that the excavation of a trench with a change in density and water content does not significantly influence to the temperature of the permafrost if average annual temperature below the temperature of the end of freezing. The result of calculation No. 3 also shows an insignificant change in temperature, which means that loosening without changing the water content does not influence to the temperature conditions of the permafrost editor@iaeme.com

5 Influence of Excavation to the Temperature Condition of Permafrost The result of calculation No. 4 shows an increase in the temperature of the soil by 0.1 C (Figure 2, 3). The isotherm of C under the section with trenches goes deeper by 2.5 m than on the section with soil of natural structure. Such an increase in temperature significantly changes the strength properties of the soil and can be a significant danger, because soil is in a plastic-frozen state. The risks of the development of thermokarst and uncontrolled subsidence of the soil are increasing, which represents a danger to the any construction T, C Year Figure 2 Dependence of the soil temperature at point z=-3 m, y=0 m Figure 3 The distribution of the temperature in the soil at 30 year. Thus, for any construction changing of water content in permafrost after excavation presents a significant danger if average annual temperature in the interval of the most intense phase transformations of water (plastic frozen soil) 4. CONCLUSIONS Numerical studies of the temperature condition of permafrost under trenches with loosened soil showed a slight temperature change in the case when the average annual temperature of the permafrost is lower the interval of intense phase transformations of water. In addition, the temperature condition is slightly affected only by loosening the soil without changing the content of water y, m T, C editor@iaeme.com

6 E. V. Markov, S. A. Pulnikov, Yu. S. Sysoev, N.V. Kazakova The loosening of permafrost and filling the empty pores by water (during precipitation) and at the same time at the average annual permafrost temperature inside the interval of intense phase transformations (plastic frozen soil), a significant increase in the average soil temperature is observed. In the case considered in the article, the increase was +0.1 ºC. For plastic-frozen soils, such an increase in temperature is a significant factor that accelerates the degradation of permafrost and thermal erosion. Thus, the stability of structures on permafrost is determined not only by the thermal effect by constructions, but also by the change in the soil structure during excavation. REFERENCES [1] Gorkovenko, A. I. The bases of theory for calculating the spatial position of an underground pipeline under the influence seasonal processes, 1st Edition. Tyumen: Tyumen oil and gas university, 2006, pp.305. [2] Mikhaylov, P.Yu. Dynamics of heat and mass transfer processes and the heat and force interaction of freezing soils with underground pipeline, 1st Edition. Tyumen: University of Tyumen, [3] Kutateladze, S. S. Osnovy teorii massoobmena "Basis of the theory of mass exchange", 1st Edition. Moscow : Atomizdat, 1979, pp [4] Markov, E. V., Pulnikov, S. A., Sysoev, Yu. S. Comparison of calculating methods of the heat transmission parameters for underground pipeline in a wide range of product temperature, International Journal of Civil Engineering and Technology, 9(7), 2018, pp [5] Markov, E. V., Pulnikov, S. A., Sysoev, Yu. S. Methodology for calculating the safe stop time of underground pipeline with high pour point oil, International Journal of Civil Engineering and Technology, 9(8), 2018, pp [6] Markov, E. V., Pulnikov, S. A., Sysoev, Yu. S. Study of frost mound temperature condition, International Journal of Civil Engineering and Technology, 9(9), 2018, pp [7] Madhu, B., Venkatesh, G., Reddy, K.J., Gurudatthreya, G.S., A study on phase change material based thermal energy storage system, International Journal of Mechanical Engineering and Technology, 8(12), 2017, pp [8] Prasad, A.R., Vasudevan, N., Krishnaraj, S., Suresh, S.M., Balaji, S. Design and development of phase change material oriented cold storage flask, International Journal of Mechanical Engineering and Technology, 9(8), 2018, pp [9] Ali, K.K., and Hassan, Hatem A., A Numerical - Experimental Study of Turbulent Heat Transfer Flow a Cross Square Cylinder In A Channel, International Journal of Mechanical Engineering and Technology, 9(8), 2018, pp [10] Pathak, K.K., Giri, A., Lingfa, P., Evaluation of heat transfer coefficient of a shrouded vertical array of heat sinks (fins): A computational approach, International Journal of Mechanical Engineering and Technology, 8(4), 2017, pp [11] Bhaskar, B.S., Choudhary, S.K., Experimental investigation of heat transfer through porous material heat exchanger, International Journal of Engineering Research and Technology, 10(1), 2017, pp editor@iaeme.com

7 Influence of Excavation to the Temperature Condition of Permafrost [12] Sidibé, M., Soro, D., Fassinou, W.F., Touré, S. Reconstitution of solar radiation on a site of the littoral in Cȏte D'ivoire, International Journal of Engineering Research and Technology, 10(1), 2017, pp [13] Markov, E. V., Pulnikov, S. A., Sysoev, Yu. S. Methodology for calibration of soil heat transfer model in accordance with results of measurements, International Journal of Civil Engineering and Technology, 9(9), 2018, pp [14] Markov, E. V., Pulnikov, S. A., Sysoev, Yu. S., Evaluation of the effectiveness of ring thermal insulation for protecting a pipeline from the heaving soil, Journal of Engineering Science and Technology, 13(10), 2018, pp [15] Kalyuzhnyy, I.L., Lavrov, S.A.. Hydrophysical processes in the catch basin: Experimental studies and modeling, 1st Edition. St. Peterburg: Nestor-Istoriya, 2012, pp [16] SP Soil bases and foundations on permafrost soils. The Research Center of Construction, 2012, pp editor@iaeme.com