Study Of Multi-tube Frozen Wall Model Test And Artificial Frozen Soil Frost Heaving Law

Currently, the new built mine represented by Huainan and Huaibei region through the thickness of the surface soil is increasing, In order to ensure the smooth progress of the wellbore dig puzzle, the mine built mostly used three or even four cycles freezing pipes to increase the frozen wall’s thickness to resistant the huge pressure. But at present, the soil’s basic frost heave characteristics of the deep stratum and the internal characteristic parameters variation of the frozen wall in the multi-circle pipes freezing process are still not fully grasped at home and abroad, therefore the further expansion of the relevant basic research is required.In view of the lack of multifunctional and boundary variable frost heaving test apparatus at domestic present, developed a perfect functional freezing and thawing compression test system which integrate temperature, moisture and pressure control into one of the computer-controlled in the premise of national and industry standards. It can make the conditions of test outer boundary consistent with the freezing method sinking scene boundary by setting the relative outer boundary conditions. Based on the experiment apparatus, we test the frost heaving force(rate) of soil under different big loading, then come to the conclusion that the most sensitive range which the load influences the frost heave force(rate). And there is a good logarithmic function relationship between the freezing front migration level h and the freezing timet. Through frost heaving force tests in single and two-way freezing modes, it concluded that frost heaving force changing with the temperature of cold source can all be described by the index function. And two-way freeze model has a better quadratic function relationship between the frost heaving force and cold junction temperature than in single freeze model, the rate of freeze front migration in two-way freezing mode is almost as two times as in unidirectional freezing. At the same time, by measuring the frost heaving force under the condition of reserving different frost heave space, we indirectly win the relationship of the quadratic parabola function decline tendency between the frost heaving force of soil and the frost heaving rate through the test instrument displacement closed loop control system. When the frost heave space of soil is greater than the largest frost heave rate of42%, the reduced rate of the frost heaving force was accelerated. Through the experiments, we grasp the soil frost heave basic characteristics of the deep overburden stratum.Because the grasp of frozen wall internal temperature field, stress field and moisture field is not comprehensive in the multi-circle pipes freezing process, a twice, total of six regional multi-circle pipes of frozen wall model tests are carried out by adjusting the circle diameter of the inside, the middle and the outer freezing circles and the space of the freezing holes, which gets much data of the frozen wall’s internal temperature field, moisture field and stress field. Combining with the finite element software ADINA simulation and comparative analysis of the freezing temperature field about different schemes, it describes the frozen wall thickness and the average temperature and other parameters’variation characteristics in the multi-circle pipes freezing process. It comes to many conclusions under the condition of frozen pipe without deviation. If the circumferential gap of freezing hole increases (decreases)0.1m, the time of delivered circles will increases (decreases)4days accordingly. If the distance of two circle hole increases (decreases)1m, the time of delivered circles will increase (decrease)8～10days accordingly. If the (circle) diameter of The outer ring hole increases1m, the effective thickness of the frozen wall will increase0.3～0.4m. If the (circle) diameter of the inner ring increases1m, the temperature of the sidewall will increase1.3～1.7℃. The results of the stress field analysis show that the distribution of frost heaving force along the radial direction is nonuniform. It accumulates mainly near the frozen pipes inside the outer ring holes. The effect of freezing hole circle diameter on the circumferential frost heaving force is less than the effect on the radial frost heaving force, however, the effect of freezing holes’ space on the circumferential frost heaving force is greater than the effect on the radial frost heaving force. If the freezing holes’ space increases (decreases)0.1m, the frost heaving force will decrease (increase) about10%. In the process of the frozen wall forming, the moisture migrates intensely, which mainly occurs in the measuring point temperature5℃to the freezing temperature stage. Difference of the soil moisture content in different locations can reached11.25%. Considering the effect of the deflection of the freezing pipes on the frozen wall characteristic parameters into the finite element software, it is concluded that the deflection of the freezing pipes will have a small effect on the effective thickness of the frozen wall, but it will have a greater effect on the average temperature of the frozen wall and the temperature of the sidewall, and particularly easy to form a closed un-frozen water warehouse between the outer and inner ring holes.Under the background of Huainan mine ventilation shaft freezing engineering, using the frozen wall temperature field analysis and information visualization software, this paper analysis the temperature field development properties of the frozen wall in different times of the freezing process, as well as the key strata’s stress field and moisture field. By comparing the field test results, the numerical calculation results and the model test results, obtain that three different analysis ways of the frozen wall internal characteristic parameters’ changing rules are consistent.Based on the results of the indoor basic test, the model test, the numerical simulation and the field test, concluded that temperature, the moisture content and the stress of the frozen wall are changing along with the radial direction in the process of freezing, which causes different intensity of the frozen wall along the radial direction. So we should notice that the frozen wall belongs to the heterogeneous material in the design of the frozen wall. The paper also proposed some recommendations to multi-tube freezing hole layout scheme, and notice that the design should combine the frozen wall thickness, the average temperature and the sidewall temperature and give full play to these three joint action.The paper mastered the variation of artificial multi-tube frozen wall internal characteristic parameters, which can provide the reference for the frozen wall’s design in the deep mine.