Study On Mechanical Properties And Damage Model Of X-shaped Jointed Rock Mass Under The Coupling Action Of Freeze-thaw Cycles And Loads

As a large number of key projects represented by the Sichuan-Tibet Railway continue to advance to cold regions,engineering rock masses are often in the environment of large temperature differences in cold regions,and often have long-term freeze-thaw weathering with the outside world,resulting in deterioration of rock mechanical properties.At the same time,due to the influence of tectonic stress,in addition to the parallel joint rock mass,there are also a large number of X-shaped joint rock mass in the engineering rock mass in the self-cold area,and the geometric characteristics of the joint space have an important impact on the mechanical properties of the rock mass.At present,under the influence of mutual interference between intersecting joints and the coupling of freeze-thaw cycles,the failure mechanism of X-joint rock mass is still unclear,which limits the scientific evaluation of related rock mass engineering.This paper takes the typical X-jointed rock mass as the research object,and takes the engineering environment of the rock mass under the coupled action of freeze-thaw cycle and load as the background.The rock mesoscopic pores are abstracted into numerous circular holes and rocks surrounding the holes.Based on the theory of circular hole expansion and volumetric frost heaving,considering the mesoscopic evolution of rock’s mode I fracture toughness,a model of mode I fracture toughness degradation with weakened effective tensile area is established by using the rock mass unit characterization method.Considering the interference effect between two intersecting joints,according to the geometric characteristics of the joints,the stress distribution of the joint structure surface,the frost heave force between the structure surfaces and other parameters,the stress intensity factor of the tip of the X-type primary and secondary joints is obtained,and the freeze-thaw cycle is applied to Combining the I-type fracture toughness degradation model with the I-type stress intensity factor at the tip of the joint,the macro-structural surface expansion model of the rock mass is established,and the X-type joint rock mass is used for loading tests of similar materials,and high-speed cameras and other refined measurement methods are used to verify Structural surface extension model for interference effects between intersecting joints.Comprehensive use of fracture mechanics,damage mechanics and other theories to deeply study the interference between intersecting joints and the deterioration of fracture toughness to build an X-shaped jointed rock mass damage model.Using this model to reveal the mutual interference mechanism between intersecting joints and the mechanism of freeze-thaw cycles on the mechanical properties of X-joint rock mass deterioration can provide a theoretical basis for the scientific evaluation of related rock mass engineering in cold regions.