Rock Landslide Groundwater Dynamic Evolution Rule And Its Influence On The Stability Of The Landslide

After the continuous heavy rain, the rise of ground water level causes theincreasing of hydrostatic pressure within the potential sliding surface and trailing edgecracks, and the view of rock landslide is triggered by hydraulic power has been widelyaccepted, but the dynamic evolution of the groundwater is not yet fully understood.Therefore, it is necessary to discuss the rock landslide groundwater dynamic evolutionlaw, and its changing on influence to the landslide stability. Through the preliminarydiscussion on the dissertation, it has some theoretical and practical meaning on boththe understanding and application of the hypothesis of the rock landslide groundwaterand the optimizing of the analysis and calculation of rock landslide stability.In this dissertation, taking two kinds of rock landslides, plane failure and wedgefailure, as study objects, selecting Kualiangzi landslide, Chengkou landslide as thetypical examples, through the model test, field monitoring and hydrological test etc.,the groundwater dynamic evolution rule and its influence on the stability were studied,and the main conclusions and understanding as follows:1. Through rock landslide slip surface pressure distribution model test, thecharacteristics of the hydraulic pressure initial formation process and distributionpatterns along the slip line direction about the plane failure and wedge failurelandslide were summarized:(1) The characteristics of the hydraulic pressure initial formation process in thesliding surface about the plane failure landslide: triangular distribution graduallyextended and developed to forward edge, and when the water reached and penetratedat the slope toe, hereby hydraulic pressure was developing in the model of neartriangular distribution until it was being in stable state after reaching the peak value.(2) The characteristics of the hydraulic pressure initial formation process in the sliding surface about the wedge failure landslide: the distribution model of hydraulicpressure from triangular�'Ⅰtrapezium type�'Ⅱtrapezium type�'Ⅲ trapezium type.And the position of the hydraulic pressure peak gradually moved to backwards. Underthe condition of good seepage in the front of the slope and big water-flooding in theback of the slope, finally the hydraulic pressure distribution would turn to triangularmodel from near trapezium type.(3) The test results, to some extent, gave the proof to the triangular distributionhypothesis proposed by E.Hoek, and its value under some particular conditions wasthe biggest one.2. Through groundwater field monitoring and tracer test on the Kualiangzilandslide, landslide groundwater dynamic evolution rule was preliminary summarizedand analyzed under the process of rainfall:(1) Through the groundwater field monitoring results, the response process inflood season and the attenuation process in non-flood season of the groundwaterunder different aquifer systems (porous aquifer system&fractured aquifer system)showed significant differences, the main detailed information:①compared to theloose pore water, the bedrock fissure water monitoring values were relatively small,and some monitoring points results showed little changing “un-normal” phenomena,no recognizable groundwater table.②during the flood season groundwatermonitoring process, the monitoring data fluctuated, but the whole tendency wasdefinite in the bedrock fissure water. During the rainfall process, little increasingwater level, long time response, and plunge phenomena features were found inbedrock fissure water.③After the flood season, the bedrock fissure water attenuatedrapidly, attenuation process showed non obvious tendency, and some local districtattenuated to the negative pore pressure state.(2) Through the groundwater tracer test results, landslide groundwater velocityand flow direction had the obvious advantage movement characteristics, the maindetailed information:①in the plane direction, the groundwater flowed along thecrack network formed by two sets preferred plane in the slope, and the direction of theplanes intersecting line was in accord with the groundwater flow.②in the verticaldirection, groundwater flow controlled by topography moved from high position tolow position.For Kualiangzi landslide groundwater flow, was controlled by crack structuralplane in plane direction, and controlled by topography in vertical direction, therefore,jointly formed three-dimensional moving features. 3. Using rigid limit equilibrium method, taking the Kualiangzi and Chengkoulandslide as examples, the dynamic changing features of the slope stability coefficientchanging with water pressure (including hydrostatic pressure in the trailing edge pullcrack and uplift pressure in the bottom sliding surface) were analyzed.(1) The stability calculation results of the Kualiangzi landslide showed:①being the flood season, the landslide stability obviously declined with the four rainfall.②surface displacement speed increased rapidly during7/22-7/27, so did thegroundwater level in tension trough during7/18-7/24. In7/23, monitoring borepressure declined rapidly from the deep bedrock osmometer monitoring results, and itwas highly consistent with the calculation result that the landslide was in unstablestate, which also proved the hypothesis of the suddenly decline was right.③thetension trough water level HWand the landslide stability coefficient Fs was significantnegative correlation relationship, through the analysis of curve regression obtained thefitted equation:FS1.1710.012HWDuring the duration rainfall action, the landslide displacement failure, occurringin the middle or later stage of the flood season, lagged behind the rainfall process, thecharacteristics was very similar to the two dramatically sliding in the landslide slidinghistory.(2) The stability calculation results of the Chengkou landslide showed:①thelandslide stability coefficient gradually dropped with the groundwater graduallygathering in the back extension cracks. And with the increasing of the groundwaterlevel, the attenuation speed of the landslide stability coefficient was quickening.②through the hypothesis of the inflection point position I and the height of water headHXin near trapezium type hydraulic pressure distribution, the landslide stability wassimply quantification compared in different hydraulic pressure distribution model.The results showed, under the same water level in back tension trough, and using thedifferent hydraulic pressure distribution hypothesis, the relationship of the landslidestability coefficient was: triangular＞Ⅰtrapezium type＞Ⅱtrapezium type＞Ⅲtrapezium type.③quantification compared results were consistent with therecognition, meaning that under the same water level in back tension cracks in slope,and the inflection point in trapezium model distribution made the two sides hydraulicpressure dramatically increasing, leading to disadvantage to the landslide stability.