Study On Deformation And Instability Mechanism Of Shatter Mountains Landslide Induced By Rainfall

In this paper, Dashuwan shattered landslide as a starting point, based on thestudy of the structural characteristics of the shattered mountain and fracturecharacteristics of the earthquake, analysis the basic characteristics of landslide,including feature of boundary, material composition, characteristics ofaccumulation. Then analysis the damage characteristics of Dashuwan shatteredmountains, including the damaged characteristics of rock’s structures and theattenuation characteristics of rock’s strength. Simultaneously，analysis the action ofshattered rock under rainfall, including the physical effect of softening andmechanical action of the water. On this basis, analysis the cracks of shattered rockunder rainfall, including extended type of rock deformation, expansion criterion, andfracture toughness of shattered rock and solving of homogeneity. Therefore,calculate the critical head of fracture initiation by fracture mechanics. At the sametime, use RFPA analysis software based on damage mechanics to simulate andverify its truth.Based on the earthquake cracks boundary effects and the aboveanalysis, landslide formation mechanism analysis, to get the critical head height ofslope instability, then use RFPA software simulation and verification landslidedeformation instability process, thereby clear explicitly instability mechanism of thislandslide.Finally analysis the chain effect characteristics of landslide-debris flowdisaster. Now this paper, the main results achieved as follows:(1) Dashuwan landslide is a rock landslide of sliding along the rocky strata. Themain sliding direction is109°approximately. Siding source in plane is like a shapeof "chair-like".And average degree of slippery slope source area is about36°.Landslide’s lengthwise is450m. The average lateral width is150m. The left slidingbody thickness is20~80m. The right sliding body thickness is10~20m. The averagethickness is30m. The total volume is about202.5×104m3. This landslide caused10deaths and damaged eight houses, clogged rivers, caused huge economic losses.(2) The accumulation area of Landslide is divided into six parts. Landslide is divided into the slip source region, scraping region, collision region, circulationscraping region, high shed region, disaster region. Disaster region is the dominatedaccumulation region of accumulation. The maximum accumulation thickness isabout50m, the average thickness is about32m. Through statistical analysis ofparticle size, indicate that the sliding body collide constantly to disintegration inmotion. The degree of debris material is increased. The body gradually disintegratedinto small chunks body. The main diameter of the block is0.1~0.2m in disasterregion.(3) According to the survey shows, cracks of generate soil and rock shock arecracks macroscopic characteristics of the shattered mountain. The top of slopedeveloped13large cracks in the soil body. They develope along the ridge. Andcracks closed the ridge is larger, which have a higher distribution to landslideboundary. It shows that, cracks play an important role in control the formation andscale of shatter boundaries. It shows the boundary effects of cracks. There are twocategories in shattered rock cracks. Under the force of the earthquake, one is that theoriginal rock structure’s surface move, open and so on. The wall generally have ruststained wall or membrane attached to the mud. The other is propagation,connectivity in crack and generate gets new structure’s surface. This wall is morefresh, no rust stained, jagged fracture. It shows tensile mechanical properties.(4) Based on the effect of strongly shattered areas and weakly shattered areas,to compare regional rock structure. The author selected the rock of rear wall andslide to do measuring in fine-side network. Obviously, compared with stronglyshattered areas and weakly shattered areas, each opening of the rock structuralsurface, connectivity rate, fissures degree are increased in strongly shattered areas.Steeply dipped structural surface has significantly increases, which gets a greaterdegree of damage. Simultaneously, based on rebound test in the field, the rockstrength are the same in strongly shattered areas and weakly shattered areas. It tellsus that effect of earthquake on rock is mainly the damage rock’s structures. Androck’s strength intensity decay is not obvious.(5) Using the dimensionless fracture length α is equivalent to the averageconnectivity rate of the steeply dipped structural surface. Taking α=0.35specimenrepresents the lower portion of the rear wall in weakly shattered areas. Takingα=0.54specimen represents the upper portion of the rear wall in strongly shatteredareas, which the fracture toughness of shattered rock is the smallest(0.6487Mpa*m1/2). This will be used as the Identified fracture toughness in the expansion of rock calculation. The greater the degree of shattered rock, the fracture toughness issmaller. And the m of value corresponding homogeneous degree is smaller. m=2.5conform to the structure of the upper steep shattered rock at the rear wall ofDashuwan landslide.(6) The effect of earthquake and rainfall after earthquake is the main reason forinducing the Dashuwan landslide. Earthquake is the basis and rainfall is thepredisposing factor. Meanwhile, the internal causes of the ramp is also a necessarycondition for the formation of the landslide. Landslide formation process is asfollows. Due to the impact of the earthquake, rock structure is damaged. Cracks inthe trailing edge generate tension. A lot of rain into the slope along the crack. Thecrack get a certain height of the water column. When the column height is greaterthan13.5m, the water column would have split the rock, leading the deformationand expansion of shatter rock. Cracks expand along the crack tip, until the potentialweak slipped zone. Water bodies with rock slide along with a downward flow.Then the downward extension of cracks is stopped. So, slipped zone weakened againafter rainwater infiltration besides earthquake damage. As the rain continuedinfiltration, stabilizing force continue to decrease. The slope sliding force continuesto increase. Eventually, when the trailing edge of the crack head height gets52.0m~65.5m, under pressure the trailing edge of the water column and uplift forcesof thrust dual water at the bottom, the bottom surface was cutted. So the slipperyrock band was cut to form a landslide.(7) Since the earthquake occurred, the area forms a complete post-earthquakechain of disaster, which is "Shattered mountainâ†'Dashuwan landslideâ†'Debrisflowâ†'Clogging lake ". Shattered mountain is the source of the disaster’s chain.Dashuwan landslide induced by rainfall is the key link in the chain of disaster.Debris flow is the evolution of the disaster’s chain. Clogging lake is embodied in theform of disaster’s chain. This series links are interlocking, mutually reinforcing.