Study On The Deformation Mechanism Of The Xie Tan Wastewater Treatment Plant Unstable Slope During The Initial Rise And Fall Of Reservoir Water Level

When the initial impoundment of the Three Gorges Reservoir area reached172.79m,the Xietan Sewage Treatment Plant slope in Zigui County appeared large deformation and local damage,which resulted in the abandonment of the newly built Xietan Sewage Treatment Plant due to the cracking of foundation and structure in different degrees.This paper takes the accumulation body of Xietan Sewage Treatment Plant slope affected by the rise and fall of reservoir water as the research object,and simulates the infiltration process of gravel soil in the process by using the self-developed infiltration device.The permeability test and triaxial compression test on the influence of reservoir water immersion on hydraulic parameters and strength parameters of gravel soil were carried out.Based on saturated-unsaturated seepage theory and fluid-solid coupling theory,the seepage field of groundwater and displacement field of the slope were calculated by ABAQUS software under the condition of dynamic changes of hydraulic parameters and strength parameters of accumulation body during the initial rise and fall of reservoir water level.Based on the above research results,the intrinsic mechanism of deformation and failure of the slope during the initial rise and fall of reservoir water level is discussed.?1?During the initial rise of reservoir water level,gravel soil of accumulation body is significantly affected by reservoir water.The fine particles?particle size0.005mm<d<2mm?are migrated and lost in this process,its mass percentage decreased from 27.65%to 22.95%.The saturated permeability coefficient of gravel soil increased from 5×10^-5cm/s to 1×10^-3cm/s,and in the soil-water characteristic curve,the volumetric water content corresponding to the high matrix suction section?10¹0⁴kPa?decreased gradually,the unsaturated permeability coefficient of soil samples increased gradually.During the process of reservoir water level slowly decreasd,the loss of fine particles in gravel soil were gradually decreased,and its saturated permeability coefficient,soil-water characteristic curve and permeability coefficient function were gradually stabilized.?2?During the initial rise and fall of reservoir water level,the compressive strength,shear strength and elastic modulus of gravel soil deteriorate obviously.The peak compressive strength?100kPa,200kPa,400kPa?decreased by 52%,51%and 48%,the cohesion and internal friction angle decreased by 49%and 21%,and elastic modulus?100kPa,200kPa,400kPa?decreased by 53.4%,45.7%and 37.3%,respectively,compared with the natural samples.?3?During the initial rise and fall of reservoir water level,on the one hand,the seepage field is greatly affected by reservoir water,and the rapid infiltration of reservoir water into the slope to recharge groundwater makes the groundwater level change synchronously with reservoir water level.On the other hand,when reservoir water level rised to 172.79m,the horizontal displacement of the deposit immersed in reservoir water increases sharply and plastic zone is formed in the elevation range of160m to 172.79m.The horizontal displacement of the middle-upper part of the slope?172.79m²20m elevation?also increased rapidly,at this time,the horizontal displacement of the monitoring point XTW5'was 4 mm,and the monitoring point XTW2'^XTW4'were 2.55 mm,1.18 mm and 1.69mm,respectively,the monitoring point XTW0'and XTW1'were 3.56 mm and 0.7 mm.It can be seen that the displacements at XTW2'and XTW0'were obviously larger than those at XTW1',XTW3'and XTW4'.In addition,slip deformation and plastic zone appeared in the upper part of the slope,and displacement demarcation line appeared at the location of the sewage treatment plant and the highway platform at rear edge of the slope.?4?When the reservoir is impounded to 172.79m,the effective stress,compressive strength,shear strength and other strength parameters of the front deposit submerged by reservoir water decreased greatly due to the effect of the reservoir water.And at this time,the anti-sliding force of the deposit immersed in reservoir water also decreased greatly.This results in a sharp increase in horizontal deformation of the deposit and plastic failure occurred in local areas,which leaded to a rapid increase in horizontal deformation of the deposit above 172.79m elevation,slip deformation of accumulations above 210m elevation and the plastic failure occured at the highway platform,which leads to deformation and failure signs such as tension cracks in the upper-middle part of the slope.In the process of slope deformation and failure,the main cause of deformation is the deterioration of strength parameters of accumulation body,and the decrease of effective stress of slope caused by the rise of reservoir water level plays a certain role in promoting deformation.