Research On Seepage Field Evolution Law Of Fully Weathered Granite Slope In Longling District Under Rainfall Infiltration

With the advent of the rain-off period,the transient saturated zone gradually migrates and dissipates from the slope to the lower soil,while the transient saturated zone at the bottom of the model gradually dissipates from the inward seepage port;the saturated-unsaturated boundary is distributed with the transient saturated zone The law is the same,as the rainfall continues to move to the deep part of the slope,the greater the slope,the faster the migration rate of the saturated-unsaturated boundary becomes as the rainfall duration increases.With the rapid development of oil and gas pipeline construction,the impact of geological disasters caused by extreme rainfall weather on pipeline sections is increasing.The effect of rain is undoubtedly the cause of these disasters.Rainwater infiltration often changes the internal seepage field parameters of the slope.Therefore,it is necessary to fully discuss and study the evolution law of the seepage field inside the slope under rainfall conditions before further research on the stability of the slope under rainfall conditions.This article takes the fully weathered granite on both sides of the Longling section of the China-Myanmar oil and gas pipeline as the experimental research object,and uses theoretical analysis,indoor physical model tests and numerical simulation simulation methods to carry out the research work.Three sets of slope model tests are built indoors.Observe the erosion and damage phenomenon of the slope and the changes of related physical quantities such as the water content of the slope and the suction of the matrix.At the same time,based on the indoor experimental model test,a two-dimensional finite element seepage model was established to simulate the evolution of the seepage field of the slope under intermittent rainfall conditions with different slopes.The specific research results are as follows:(1)Using tensiometer method and filter paper method to measure the water-soil characteristic curve of fully weathered granite under two dry density conditions and VG model fitting analysis,the results show that the saturated water content decreases with the increase of dry density.The residual moisture content increases accordingly,and the soil intake suction value becomes larger,and the water holding capacity increases;the two methods have the same parameter change form under different dry densities,and there are local differences.The tensiometer characteristic curve intake value,curve The slope and residual moisture content are both larger than the value of the filter paper method,but the saturated moisture content value obtained by the filter paper method characteristic curve is greater than that of the tensiometer method.The two measurement methods are not much different in the low suction section.(2)Based on laboratory tests,the erosion and destruction effects of fully weathered granite slopes mainly go through raindrop splash erosion stage-runoff erosion stagecollapse failure stage.The steeper the slope of the slope model,the more serious the damage of the slope surface,and the more comprehensive the experience of erosion and damage stage.Severity of soil erosion: 40°>20°>10°;the order of slope damage location: foot,middle,top.(3)The change law of rainfall infiltration rate is obtained based on laboratory experiments: the rainfall infiltration rate gradually decreases with the increase of the number of rainfall fields,and the rainfall infiltration rate of 40° slope decreases the fastest.(4)The volumetric water content changes with intermittent rainfall in a wave shape,and has a certain hysteresis to the stop-descent moment.The shorter the lag time close to the slope infiltration interface,the faster the water content change rate,and vice versa,the response lag time of the deep part to stop rainfall.Longer,the rate of change of water content is relatively slow.The 40° slope is the most severely damaged.Combined with the evolution of the slope damage,it is concluded that there are two failure modes of the measuring point sensor.One is that when the slope is partially damaged by flowing soil,the water content of this location suddenly increases to a critical value and then rapidly decreases.The critical value of the failure process ranges from 38.2% to40.2%.In the other,the water content curve at the measuring point destroyed by runoff erosion increases slowly and then decreases rapidly,with the maximum value ranging from 35% to 40%.(5)The suction of the matrix exhibits a stage of stable value-decrease-restabilization with the rainfall duration,and the decrease rate of the suction value at the deepest measuring point at the foot of the slope is less than that of the upper soil.The matrix suction time-varying curve and the volumetric water content time-varying curve have a high degree of similarity.The suction response time of the measuring point is more consistent with the volumetric water content response time.The slope of the suction decrease is greater than the slope of the increase of the water content,but the decrease and increase of the two are positive.Correlation.(6)From the simulation calculation results,it can be seen that the simulation results show that the time-varying curves of negative pore water pressure and volumetric water content are consistent with the time-varying curves of matrix suction and water content measured by the physical rainfall model,but due to the influence of the intermittent stop period and hysteresis of rainfall,The measuring point growth rate and response time are different;the change rule of the transient saturation zone: 20° and40° slopes mainly extend from the toe of the slope to the top of the slope and the deep part of the slope.The slope of the 10° slope is relatively slow and transient.The saturation zone appears parallel to the slope and gradually extends into the slope.With the advent of the rain stop period,the transient saturated zone gradually migrates and dissipates from the slope to the lower soil,while the transient saturated zone at the bottom of the model gradually dissipates from the inward seepage port;the saturatedunsaturated boundary is distributed with the transient saturated zone The rules are the same,with the rain continuously moving to the deep part of the slope,the rainfall rate of the 10° model is controlled at 10cm/field;the first two rains of the 20° model are at10cm/field,and the last field is 30cm/field;the 40° model The moving rates are respectively 10cm/field and 40cm/field;as the slope increases,the toe of the slope is more likely to have a saturated zone,and more attention should be paid to the drainage of the toe.