Study On The Influence Of Precast Joints On The Mechanical Properties Of Loess

The joint surface of loess is the dominant surface of soil strength degradation,soil erosion and cave formation in loess area,and it is also the bad control surface of geological disasters.Therefore,the research on the influence of joint on the mechanical strength of loess has certain research significance to reveal the sliding promoting effect of joint interface in loess landslides.Taking a loess excavation slope in Fuxian County of Shaanxi Province as the research site,the slope loess is selected as the test material to carry out the strength test of the loess sample with prefabricated joints.The influence of joint size and distribution direction on the strength and deformation characteristics of the loess sample is revealed.The research results are as follows:(1)The results show that the mechanical strength of the loess sample is significantly affected by the prefabricated joints.Compared with the intact sample,the uniaxial compressive strength of the sample with prefabricated joints is reduced by 7.5%-43.5%,and the triaxial compressive strength is reduced by 16.7%-66.7%.(2)The shear failure modes of jointed loess samples can be divided into three types: through joint plane,through joint plane and shear soil failure.According to this,the joint distribution angle can be divided into three types: gentle angle,transition angle and steep angle.When the prefabricated joint fracture is gentle,the angle of specimen shear fracture surface increases with the increase of prefabricated joint angle;when the prefabricated joint distribution angle is at the transition angle,the specimen shear fracture surface is distributed along the direction of prefabricated joint surface;when the prefabricated joint distribution angle is steep,the angle of specimen shear fracture surface decreases with the increase of prefabricated joint angle.(3)The distribution angle of the prefabricated joint has a significant impact on the strength and deformation properties of the loess sample.With the increase of the angle of the prefabricated joint,the uniaxial compressive strength of the sample decreases first and then increases.The curve of the relationship between the two changes in the shape of "V".When the angle of the prefabricated joint is close to the optimal shear angle of the loess sample 45 ° + φ /2,the shear strength of the loess sample reaches the minimum.(4)With the increase of fracture length,the crack initiation time and crack propagation time of joint fracture specimen will be earlier,and the plasticity and brittleness of specimen will decrease gradually.When the angle of joint fracture deviates from the optimal shear angle by 45 ° + φ / 2,the size effect of joint fracture is weaker.That is to say,when the joint fracture changes from 0 ° to 90 °,the size effect of joint fracture first increases and then weakens.(5)The results of triaxial compression test show that the angle of the prefabricated joint has a bad effect on the shear strength index.When the angle of the prefabricated joint is steeper than that of the gentle angle,it has little effect on the cohesion.When the angle of the joint is in the range of the transition angle,its effect on the cohesion decreases obviously.