Working Method And Experimental Study Of The Permafrost Slope Supported By The New Frame Ventilation Anchor Rod

Human engineering activities and the global temperature increase year by year have intensified the thermal thawing and slumping trend of frozen soil slopes,making frozen soil slope projects facing serious threats of frost heave and thawing settlement.However,the L-shaped retaining walls and traditional supporting structures such as frame prestressed anchors cannot change the temperature-sensitive characteristics of frozen soil.Based on the design concept of "active cooling and protection of frozen soil",a new type of frame ventilation anchor was developed,which can not only lower the temperature and raise the freeze-thaw interface,but also maintain the stability of the slope.The thermal and mechanical problems of the interaction with the slope are studied by a combination of theory,numerical simulation and model test.The design index of the new frame ventilation anchor is given.The specific content is as follows:(1)Considering the nature of permafrost thermal thawing and slumping,based on natural ventilation mechanism,gravel thermal diodes and thermal shielding effects,a new frame ventilation anchor that integrates ventilation,cooling,anchorage,and expansion and shock absorption is proposed.(2)The thermal and mechanical mechanism of the new frame ventilation anchor is theoretically analyzed.The relationship between air intrusion and temperature difference and gravel laying radius under the effect of natural convection is deduced;the formula for calculating the cooling capacity of the new type of anchor into the slope is given,and the freezing and thawing interface of the slope under the action of the new type of bolt is calculated.A simplified calculation model for the cooperative work of the new frame ventilation anchor and the soil in the freezing and thawing process is established,and the internal force calculation formula of the new anchor rod under the freezing and thawing action is given.The analysis of the calculation example shows that the new frame ventilation anchor can not only lift the freeze-thaw interface,but also has a good ventilation and cooling effect.Additionally,it also can anchor the frame and reduce the frost heave force of the frame.(3)To verify the rationality of the proposed simplified calculation model,and further understand the thermal and mechanical properties of the new frame ventilation anchor supporting permafrost slopes.Based on the similarity theory,a new frame ventilation with a similarity ratio of 1:10 was designed and carried out.model test of anchor support for permafrost slopes.The distribution law of temperature and moisture at different positions of the slope during the freezing and thawing process was compared and analyzed,and the internal force of the new frame ventilation anchor rod during the freezing and thawing process was studied.The test results show that in a freeze-thaw cycle,the change of soil temperature and moisture in the slope has a hysteresis effect compared with the change of air temperature.The new type of ventilation anchor rod has a significant cooling effect on the surrounding soil,and the supporting effect is obvious.(4)To more intuitively understand the mechanism of the slope supported by the new frame ventilation anchors,the coupled control equations of frost heave,thawing settlement and consolidation of the slopes supported by the new frame ventilation bolts were established,and the control equations were discretized by the Galerkin method.The finite element format is derived,and the multi-field coupling analysis software is compiled.Comparing the calculated results of the software with the measured values of the model test verifies the reliability of the programmed program.Numerical calculation results show that the soil temperature around the new anchor presents a wave-shaped distribution in the ventilation section of the anchor rod.With the increase of freezing and thawing times,the low-temperature area around the anchor rod expands,and the internal temperature distribution of the slope becomes more stable.The internal force of the structure during the freezing period is greater than the melting period,which is consistent with the test results.