| In the southwest mountainous area,the construction and operation of high-speed railway and the safety of people's lives and property are seriously threatened by rock fall on high and steep slope.The calculation method for unstable rock is relatively backward in the current geological disaster prevention and control survey specification,which is difficult to meet the current survey and design requirements.In this paper,the determination method of fracture water pressure is studied through experiments,and the modified calculation formula of dangerous rock stability is put forward.The results of rainfall infiltration test show that the water filling heights of 0.5cm and1 cm fractures increase linearly with the increase of rainfall intensity,and the water filling heights of 0.1cm and 0.2cm fractures decrease gradually with the increase of rainfall intensity.The water filling heights are basically linear with the rainfall duration.In the same width of the cracks,the greater the rainfall intensity,the faster the water filling speed.Under the same rainfall intensity,the smaller the fracture width,the shorter the time required for the crack to fill with water.In unclosed crack: the smaller the fracture width,the higher the water filling height.The curve of the water-filled height is basically arc-shaped,and the water head decreases slowly at a distance closer to the closed end,and closer to the open end,the water head drops faster,and finally stay at a certain height.Stable water head surfaces are formed in these fractures in a short period of time(9s?30s)under different rainfall intensities.On the whole,in the same conditions,the smaller the fracture width,the higher the water-filled height and the longer the time required for the water-filled height to stabilize.The simulation test of the failure mechanism of jointed rock mass under rainfall conditions shows that under a certain rainfall intensity,if the two sides or bottom of the fractured rock mass has strong permeability,the rising height of the fractured water level is limited,and the fractured water pressure is not enough to promote the rock slip;When the permeability on both sides and bottom of the rock mass is poor,the water level of the crack rises,when the slip conditions are met,the rock block can be pushed to slip.When the rock block slips,the crack becomes loose,and the permeability of both sides and bottom surface increases and the width of the crack increases due to slipping,the water level of the crack drops,the water pressure decreases,then the rock mass stops slipping;the rock mass after loosening the slipping,the crack opens further,and under the effects of later weathering and erosion,both sides and bottom of the rock gradually either muddy or filling and sealing,resulting in reduced permeability,which provides conditions for the rise of the fracture water level during the next rainfall.The next rainfall or more intense rainfall conditions may cause the rock mass to slip further or tipping.The above process can be completed in one rainfall,or it can be completed after multiple slips under multiple rainfall conditions.The calculation method of fracture water pressure is obtained through experimental research and theoretical derivation.The correction calculation methods for the stability of three types' rock falls are derived respectively.The calculation results of the stability of the rock fall at a certain construction site of the Chongqing-Qianjiang high-speed railway shows that the main failure mode of the rock fall at this site is slipping.In this area,for fractured rock masses with a fracture width greater than 1 cm and strong permeability,it is not necessary to consider the effect of water pressure in the stability calculation. |
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