Study On The Fracture Failure Mechanics Of Slope Soil In The Rain

As a global geological disaster, the slope failure brings a huge damage to theproperty and life of mankind. This paper focuses on the fracture mechanics of slope soil,especial in the rain condition, employing the mean of experiment、methods of limitequilibrium、 failure mechanism and creep deformation for the destruction to draw thefollowing innovative conclusion.(1) Based on the principle of three point bending test, this paper attempts to revisesthe testing method slightly. It rotates the sample900along the bottom edge. By usingthis horizontal loading method, the deadweight of sample and loading direction isperpendicular, avoiding the gravity effect on the test results. This paper also obtains thesoil fracture toughness KΙCwith a self-devised soil fracture testing assembly.(2)Discussing on the formation mechanism of circular sliding surface and tensioncrack in uniform soil slope, constructing a cracking model of soil slope in thehydrostatic pressure, seepage force, runoff erosion and gravity, and establishing acalculation method of the internal tensile stress with a rainfall effect, this paper obtainsthe relationship between the soil slope saturation area and tensile stress, deducescracking criterion of the potential fracture surface, and determines the location of thecrack. This paper also divides the saturated depth of slope according to the creep stages:decelerating creep saturation depth, creep saturation depth and accelerating creepsaturation depth.(3) This paper analogies the slope of the crack seam to macroscopic crack,establishing a crack propagation computation method with the effects of gravity, waterpressure, the crack scouring force and seepage force. It also decomposes the tensilefracture model into2parts: uniform tensile stress and crack water pressure, whichestablishing the calculation formula of fracture intensity factor of crack seam tippropagation with the application of fracture mechanics. Putting forward a concept ofcalculation of crack depth by stress intensity factors and the saturated region, this paperdivides the expansion of crack with rainfall effect into three stages: no expansion stage,expansion stage controlled by the saturated zone, expansion stage of instability.(4)Slope internal tensile stress in the same saturation depth is increased with theincrease of slope length; while in the same saturation depth, internal tensile stress isincreased with the increase of slope length. From this, it is clear that the tensile stress of the slope alone the trailing edge is the largest, most likely to crack in the case of rainfall.When the slope forms vertical fractures, with the absence of rainwater infiltration, theincreasing of the stability safety factor of the slop in the rain infiltration alone with thecrack extending is not obvious. Conversely, the stability safety factor of the slop in therain filtration alone with the crack extending is decreasing significantly, the criticalcrack depth value of the fracture slope is less obvious, even critical crack depth arecompletely disappeared.