| With the expansion of cold engineering construction scale and global climate warming,the scale and frequency of thaw slumping of permafrost slope increases gradually,which brings more and more threat to human life and normal operation of engineering in cold regions,so it is imperative to prevent and control thermal thawing instability of slope.Aimed at freeze-thaw landslide,the investigation of field disaster of permafrost slope and engineering technology of permafrost are studied in this paper.Based on the deep understanding of the characteristics of permafrost slope,the new technology for the cure of slope freeze-thaw disaster is explored and developed,and a new type of supporting structure which has an active cooling effect on permafrost slope is proposed.Using a combination of the theoretical,numerical and experimental methods,the working mechanism and characteristics of the new structure for permafrost slope are studied systematically.It is expected that a scientific basis can be provided for the solution of the key technical problems in permafrost slope disaster cure,such as provided a reasonable protective structures.The main conclusions are as follows:(1)The damage causes,disaster-causing mechanism of permafrost slope engineering and the problems existing in the disaster cure for permafrost slope are found out.Basing on the concept of “active cooling protect permafrost”,combined with the advantages of hot rod and frame anchor technology,a new type of frame heat anchor pipe supporting structure for permafrost slope is proposed and its technical principle is expounded.Which can not only anchor and support,but also has an active cooling effect and reduce frost heave damage through its own deformation.In order to eliminate the degradation of the upper limit of frozen soil of slope and prevent the thaw slumping,taking account the ultimate bearing capacity and the heat balance as the control index,a design idea and the corresponding design and calculation steps was presented,which provides a new technology and idea for the thaw slumping disaster government of permafrost slope.(2)Based on the theory of equivalent thermal resistance,the calculation model of heat transfer for heat anchor pipe is established and the heat transfer radius is solved.According to the proposed design idea,two practical calculation methods for the thermo-mechanical co-controlling are given: a)Load structure design method;b)Calculation method considering the cooperative work of frame-heat anchor pipe-soil.Via example shows that the new frame heat anchor pipe can resist the degeneration of the upper limit of permafrost slope and its supporting effect is remarkable;Under the action of frost heave,the internal force distribution of the structure is uniform and the deformation is synchronized,which can not cause stress concentration resulting in structural damage.The calculation method has a clear physical concept,has a better describe for the working mechanism and is a fast and practical design method,which can provide theoretical basis for its design.(3)Based on the heat-exchange mechanism of heat anchor pipe and multi field coupling theory,the coupling analysis model of moisture,heat and stress fields of atmosphere-frame heat anchor pipe-slope system is established,the coupling equation was solved by using finite element method,and the finite element program which can reflect the coupling mechanism of frame heat anchor pipe soil is developed on the MATLAB platform.The program is used to analyze the classical freezing test,and the reliability of the program for the coupling of moisture,heat and stress fields is verified.The pure soil slope and the permafrost slope with frame heat anchor pipe under the conditions of excavation disturbance and climate warming are calculated by using the program,the results show that: a)The upper limit of newly excavated slope degrades obviously under the action of freezing-thawing and climate warming,and the freezing-thawing instability damage is easily induced;The upper limit of frozen soil slope is uplifted under the action of heat anchor pipe.At the same time,there is a perennial low temperature freezing zone under the seasonal activity layer,and the moisture migration rate increases on the slope;b)The stress state of the slope dynamically changes with seasonal freezing-thawing,and the stress on the slope is redistributed under the action of frame heat anchor pipe.In a freeze-thaw cycle,the tensile strength of the heat anchor pipe increases firstly and then decreases,the initial state can not be restored.c)When freezing,the horizontal displacement of the frame heat anchor pipe slope is much larger than that of thawing,and it is much smaller than that permafrost slope,which further explains that the new frame heat anchor pipe structure has a significant cooling effect and supporting capacity.(4)In order to give a practical analysis method for the stability of the frame heat anchor pipe supporting slope,a simplified stability analysis model is established by using the oblique slice method according to the thaw slumping failure mode of permafrost slope.In order to consider the effect of temperature and moisture on slope stability,the stability analysis model of coupling of moisture,heat and stress fields finite element limit equilibrium method was established,the most dangerous slip surface and the minimum safety factor are obtained based on the coupling theory proposed in section 3,the calculation shows that: The safety factor of slope under the action of the frame heat anchor pipe is obviously improved;The oblique slice model can reflect the variation of the force between strips caused by the redistribution of slope internal force and its influence on the stability under the new structure;The analysis model of coupling of moisture,heat and stress fields finite element limit equilibrium makes up for the deficiency of oblique method,and it reasonably takes the impact that the temperature,moisture,soil strength and deformation has on the stability of the frame heat anchor pipe supporting slope into account,which is a rigorous analysis method.(5)In order to verify the effectiveness of the structure and the rationality of the calculation method proposed in this paper,a model test for the new frame heat anchor pipe supporting frozen soil slope and permafrost slope is designed based on the similarity theory.The changed laws of temperature,moisture,displacement of the slope and structure internal force under freezing and thawing,different initial moisture content and load are analyzed.The results show that: a)Under the action of frame heat anchor pipe,the slope temperature reduces faster,the slope is frozen longer and the temperature is lower in thawing period;b)In a freeze-thaw cycle,the content of unfrozen moisture of slope first decreases and then increases with time,but can not restore to the initial value;c)The temperature gradually decreases with time,the tension of the heat anchor pipe constantly increases.When the temperature becomes warmer,the frost heave force decreases,the tension of the heat anchor pipe suddenly decreases,the tension during thawing period is almost the same,and the tension during freezing period is greater than that during thawing period.d)During the initial freezing,the slope has a cold shrink phenomenon.The moisture has a frost heave with the continuous freezing,the slope produces a forward horizontal displacement and continuously increases.In thawing period,the horizontal displacement of permafrost slope continuously increases,while the horizontal displacement of the frame heat anchor pipe slope decreases firstly in the early thawing period,and finally keep basically the same.e)Comparing the test with the theoretical calculation,the results show that the laws of temperature,moisture,internal force and deformation are consistent.And the reasonable of the theoretical calculation method in this paper is verified.Through the experimental and theoretical analysis,it is shown that the cooling effect of the new frame heat anchor pipe structure is remarkable,and the supporting performance is superior,which is a feasible and effective support structure for permafrost slope. |
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