Study On The Pullout Bearing Characteristics Of Anchors In Uniform And Permafrost Ground With Ice

In recent years,with the rapid development of infrastructure construction in cold areas of China,a large number of anchoring projects have appeared in cold areas.Perennial permafrost is widely distributed in alpine regions,and the quality of permafrost anchorage works depends on the interaction between anchors and permafrost.Permafrost is an ice-bearing soil below 0℃,and its nature is highly sensitive to temperature,resulting in extremely complex anchor bearing characteristics in permafrost.In this paper,the bearing characteristics of anchors in uniform permafrost and ice-bearing permafrost are studied according to the connection between anchors and permafrost in perennial permafrost strata,which can provide reference for the design of permafrost anchorage engineering.(1)The stratum of multi-year permafrost area is divided into uniform permafrost and ice-bearing permafrost,and when anchors pass through the two types of permafrost,the free section of anchors is located in the seasonal freeze-thaw layer,and the anchorage section is located in uniform permafrost or ice-bearing permafrost.In order to study the bearing characteristics of anchors in permafrost strata,firstly,the basic physical properties of the test soil were determined,including the particle gradation curve,the limiting moisture content and the optimum moisture content;secondly,the standard strength of cement mortar with early strength agent was tested under negative temperature maintenance conditions.(2)In order to investigate the bearing characteristics of anchors in uniform permafrost strata,six anchors pullout tests with soil temperatures of 0,-1,-2,-3,-4 and-5℃ were carried out to analyze the damage forms,pullout load-displacement characteristics,axial force and shear stress variation law at the anchor-soil interface.The pull-out load-displacement relationship equation of anchors in permafrost strata was given by fitting the test values.Based on the load transfer and Kelvin displacement solution method,the axial force and shear stress distribution functions of the anchor in permafrost under the pullout load are derived,and the axial force and shear stress distribution functions are also modified by combining the test results.The study shows that the pullout force increases and then decreases to a constant value during the pullout process of anchors with different soil temperatures,and the axial force decreases nonlinearly along the anchorage depth,and the shear stress increases and then decreases along the depth.Under the same load,the lower the soil temperature,the faster the decay rate of the anchor shaft force along the depth,and the smaller the peak shear stress;the corrected theoretical calculation value is in good agreement with the test results of each working condition.(3)In order to investigate the load-bearing characteristics of ice and ice-bearing permafrost anchors,unit anchor solid-ice,ice and ice-bearing permafrost anchor pullout tests were carried out.The damage forms,pullout load-displacement characteristics,axial force and shear stress variation law of anchor-soil interface were analyzed The pullout load-displacement curves of anchors with uniform and ice-bearing permafrost were compared.The results show that the anchor-solid-ice pullout damage interface of the prefabricated unit is the anchor-ice interface,and the anchor-solid-ice pullout damage interface of the grouted unit is the reinforcement-anchor solid interface,where the anchor-ice interface damage is brittle damage and the reinforcement-anchor solid interface damage is plastic damage,and the ontological relationship between the unit anchor-solid-ice interface and the unit anchor-solid-permafrost interface fitted by the fractional model is in good agreement;in the ice anchor In the pull-out test,the anchor solid diameter was larger than the design diameter by more than 10 mm.the anchor solid-soil interface was damaged at-1℃ in ice-containing frozen soil,and the reinforcement-anchor solid interface was damaged at-3℃ in ice-containing frozen soil,and the anchor solid was dislodged.The local protrusion of the anchor at the ice layer will enhance the anchor’s occlusion with the ground;the anchor pullout force increases first and then decreases during the anchor pullout test in ice-bearing permafrost and finally tends to a constant value,the anchor axial force decreases nonlinearly along the anchorage depth as a whole,and the shear stress is distributed in a multi-peak curve along the anchorage depth direction.By comparing the load-displacement curves of anchor pullout in uniform and ice-bearing permafrost,the load carrying capacity of anchor in ice-bearing permafrost is greater than that of anchor in uniform permafrost.