| Rainfall is one of the most important external factors inducing landslides.Rainwater infiltration under rain increases the weight of the landslide and reduces the shear strength of the soil layer,resulting in landslides.Many landslides are characterized by “heavy rain,small slip,no rain and no slip”,Studying the mechanism of rainfall-induced landslides is an important research topic in this field,and the physical model test of artificial rainfall landslide is one of the important research methods.We can get the weather days,daily rainfall,and accumulated rainfall in the landslide area from the meteorological department,but the daily rainfall data accurate to the hour is rarely noticed.This also led to the current use of artificial rainfall landslide physical model test simulation of rainfall process is often simulated using a 24-hour continuous rainfall process,whether this continuous rainfall process is the most dangerous rainfall process has not been documented.In this paper,theoretical analysis,numerical simulation and model test comparison methods are used to study the influence of rainfall on slope stability,taking the Hualien landslide as the research object,the finite element software Geo-Studio was used to study the continuous rainfall,the interval-based rainfall process in hours,and the most dangerous rainfall process in the interval-based rainfall process,the main research contents and achievements of the different rainfall courses on the leading edge,trailing edge and overall stability of the landslide are systematically studied as follows:1)The system summarizes and analyzes the historical rainfall situation and the limit rainfall process in the Three Gorges reservoir area,it is known that the average annual heavy rain days in the reservoir area is 8.5 days,the maximum daily rainfall is 121.4?306.9mm,the maximum rainfall in the reservoir area is 142 mm in one hour,and the maximum continuous rainfall is 600 mm.The main evaluation indicators for determining the dangerous rainfall process in this paper are rainfall intensity,rainfall duration,single-day rainfall intensity,and accumulated rainfall in the previous period,at the same time,it is considered that the occurrence of landslides in the Three Gorges reservoir area is mostly caused by the coupling of rainfall and reservoir water level fluctuations.The cumulative rainfall studied in this paper needs to be greater than the continuous limit rainfall in the region,which is determined to be 10 days of rainfall and 900 mm of accumulated rainfall.2)Taking Hualien landslide as an example,five kinds of accumulated rainfalls of 100 mm,300mm,500 mm,700mm and 900 mm are used.The rainfall process is continuous rain for 10 days,and the rainfall is 24 hours per day.Under this continuous rainfall condition,when the accumulated rainfall reaches 700 mm,the safety factor of the trailing edge of the landslide first drops significantly,at this time,the rainfall intensity is closest to the soil permeability coefficient,and the slope is in a critical stable state;when the rainfall is more than 700 mm,the runoff phenomenon begins to appear on the surface of the slope.When the rainfall reaches 900 mm,the trailing edge of the slope begins to destabilize,and the initial rainfall intensity increases,the safety factor decreases,and the minimum safety factor is 0.9622.3)In the process of non-continuous rainfall in units of time interval,four cumulative rainfalls of 300 mm,500mm,700 mm and 900 mm are used.The rainfall interval of each accumulated rainfall is divided into 1 day,2 days and 3 days,the rain time is 10 days.When the rainfall intensity is less than the permeability coefficient,there is no significant change in the safety factor of each part of the slope;when the rainfall intensity is close to the permeability coefficient,the trailing edge safety factor begins to decrease significantly,and the sensitivity of each part to rainfall intensity is consistent with continuous rainfall conditions.When the accumulated rainfall reaches 900 mm,the slope is not unstable,which indicates that the water consumption caused by the rain during the rain has a certain impact on the slope stability,the shorter the rain stop time,the smaller the minimum safety factor,the smallest.The safety factor is 1.036 and the corresponding rainfall intensity is 90mm/d.The most dangerous rainfall process under such rainfall conditions is two days per rain and one day of rain.4)In the rainfall process with hourly interval units,the cumulative rainfall is 900 mm,the rainfall interval is 2,4,8,12,16,20 hours,and the working conditions are increased by 3,3.2 hours,the rainfall time is 10 days and the rainfall intensity is 90mm/d.The greater the initial rainfall intensity,the more unfavorable the stability of the slope,the trailing edge is unstable during the 3.2 hours,4 hours and 8 hours of daily rainfall,indicating that the short-time heavy rainfall process has a great impact on the slope stability;When the cumulative rainfall of long-term rainfall is 700 mm,the safety factor of the trailing edge will also drop significantly.The most dangerous rainfall process under such rainfall conditions is: the dangerous rainfall process at the trailing edge is 900 mm total rainfall,cumulative rainfall is 10 days,rainfall intensity is 11.25mm/h,rain 8 hours per day,stop rainfall for 16 hours.The most dangerous rainfall process on the leading edge and the whole is 3.2 hours of rain per day,stop rainfall for 20.8 hours,and a rainfall intensity of 28 mm/h.5)Through comparative analysis of the three-dimensional physical model test of Hualien landslide,in the state of reservoir water level of 175 m,by continuous rain reduction 8mm / d(rainfall 18.67mm)and 10 mm / d(rainfall 10mm),the rainstorm after the day is stopped 60 mm / d(rainfall 23mm),resulting in the final overall of the landslide Instability and destruction,the actual rainfall converted to the actual prototype is 702.7mm.In the numerical calculation of this paper,the same 700 mm rainfall under continuous uniform rainfall conditions,the slope is not unstable,compared with the numerical calculation results of this paper,we can see that: rainfall duration,rainfall intensity at each time,whether the rainfall process is continuous,etc.The stability is closely related.According to the research in this paper,for the example of the Hualien landslide we selected,the most dangerous rainfall process with trailing edge instability is cumulative rainfall of 900 mm,rainfall intensity of 11.25 mm/h,rain 8 hours per day for 10 days,stop for 16 hours;the leading edge and overall dangerous rainfall process is 10 days of rainfall,rainfall intensity of 28mm/h,and rain 3.2 hours per day for 10 days,stop for 20.8 hours.This conclusion is of great significance for us to carry out the physical model test of artificial rainfall landslide. |
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