| The geological conditions of Three Gorges Reservoir area are very complex,where distribute numerous Reservoir Slope,and landslide disaster prevention of Reservoir Slope is very important.During the normal operation of Three Gorges project,how to avoid and reduce the landslide hazard of the major reservoir bank scientifically is an urgent problem for researchers.Researchers have disputes on the understanding of scope of Huangtupo landslide,boundary condition,factor,long-term stability.In view of this,in 2009,China University of Geosciences(Wuhan)started the construction of Badong field large-scale comprehensive testing ground in Huangtupo landslide,and established a platform integrating landslide hazard teaching,scientific research and production.Its excavation was the most sufficient disclosure of the landslide body,sliding zone and landslide bed of Huangtupo riverside slumping mass I#ever since investigating in Huangtupo landslide.It has provided favorable conditions for deeply research into the landslide.Main research contents and methods in this article are as below:(1)Geological model of Huangtupo riverside slumping mass I#.Based on different viewpoints on the boundary and deep sliding zone of Huangtupo landslide,field investigation,tunnel chamber exploration and comparison on different exploration units’ data was carried out.Through comprehensive analysis of them,the spatial form of Riverside slumping mass I#was corrected,and the geological model of Huangtupo riverside slumping mass I#was rebuilt.(2)Mechanics test and creep model of sliding zone soil with natural grain size composition.Through large-scale creep tests,the author analyzed the creep deformation of zone soil with natural grain size composition,and proposed a creep model applicable for different confining pressure conditions,and discussed its long-term strength.(3)Deformation and stability analysis on Riverside slumping mass I#under the condition of reservoir water fluctuation.Based on corrected geological model and mechanics tests results of zone soil with natural grain size composition,the author verified the deformation parameters,strength parameters,permeability coeff-icients combining with field tests and monitoring data.Then the stability of Riverside slumping mass I#under the actual working conditions during two hydrological years was analyzed,and finally unfavorable operating conditions was discovered.(4)Stability numerical simulation of Riverside slumping mass I#under change decreasing conditions of reservoir water.To improve the stability of Riverside slumping mass I#during the declining process of reservoir water,the author proposed and designed decreasing series conditions of reservoir water,and then worked out the slope stability in different conditions by using a numerical simulation method,and finally researched the laws of stability of Riverside slumping mass I#under the reservoir water decreasing series conditions.To sum up,through interior theories and exterior practice,model’s property-determination and condition quantification,test and numerical simulation combined comprehensive research method,this article obtained following conclusions:(1)Newly recognized geological model of Huangtupo riverside slumping mass I#based on landslide spatial form.Boundary of hydrological team is the sub-landslide of the boundary of Yangtze River Committee.To confirm the boundary of Huangtupo riverside slumping mass I#,we combined with U series dating method to test Badong field large-scale comprehensive testing ground and revealed the age of sliding zone,the article found that:①5#sub-tunnel sliding zone is located in about 30m downside of original sliding zone,but drill hole HZK9 did not reach the sliding zone.It is estimated that there is a deep layer sliding zone in the middle-rear part of Riverside slumping mass I#;②K5+21.4m sliding zone in 5#sub-tunnel is connected with KO+670m sliding zone in main tunnel;③Dating results of K3+138m sliding zone in 3#sub-tunnel(about 40 thousand years ago)is greatly different with the dating results of deep layer sliding zone(about 100 thousand years ago),thus K3+138m sliding zone in 3#sub-tunnel reveal the sliding zone of the sub-sliding zone of Riverside slumping mass I#.Therefore,the author speculated that there is a deep layer sliding zone in the middle-rear part of Riverside slumping mass I#and the boundary of Yangtze River committee would be more reasonable.(2)Physical properties,constitutive model and long-term strength of sliding zone soil with natural grain size composition.①Application of sand hole in large-size sliding soil mechanics tests.Summarize the achievements in early-stage mechanics tests of sliding soil,we explore the sample-preparation methods for large-size sliding soil mechanics tests.Due to poor water permeability of sliding soil,to guarantee the moisture content in different part of specimen can reach test requirement,punch sand holes was made along the test-piece lengthwise direction(Diameter 1cm,sand hole interval 7.5 cm).Distribution of moisture content in different parts inside test-piece with sand holes and without sand holes showed that,test-piece without sand holes have lower moisture content(saturability),which could not meet the experimental requirements.After punching sand holes,interior moisture content of test-piece can basically satisfy test requirement.②Improvement of Singh-Mitchell creep model of zone soil with natural grain size composition.Analysis on data of creep test of zone soil with natural grain size composition showed that,ln(ε/t)has strict linear relation with In t.Creep model ε=ec1ec2Drtc3 was obtained by polynomial fitting,which belong to Singh-Mitchell model.However,different confining pressure corresponding to different creep model parameters has limited the application of creep model.To solve the problem,variable σ3 was added,we obtain a composite function(?),which is applicable for different confining pressure.Improved creep model is more feasible.③Long-term strength of zone soil with natural grain size composition.Draw stress-strain isochronal curves based on creep test data,we could obtain the long-term strength indexes of sliding zone soil with natural grain size composition as below:long-term strength index of sliding zone soil in 3#adit are Cs=14kPa,φs = 13°,long-term strength index of sliding zone soil in TP4 are,＝46kPa,φs = 14°。long-term strength index of sliding zone soil in 5#adit are Cs=8kPa,φs=15°.(3)Analysis on the deformation and stability of Riverside slumping mass I#under the reservoir water change condition.①Sliding plane 1 is located in the front edge of slope,its stability coeff-icient is 1.08-1.32,and it is positive correlated with reservoir water level.Sliding plane 2 is the potential trajectory of Riverside slumping mass I#whole slip,its stability coefficient 1.13-1.23,and it is positive correlated with reservoir water level.②Shallow slope stability of the front edge is greatly influenced by reservoir water level change.When the water level in Yangtze River increases to high level,slope stability of the front edge is larger than slope overall stability.When water level in Yangtze River declines,slope stability of the front edge is gradually smaller than slope overall stability.So the slope in front edge is easy to lose stability.③Water level decline in Yangtze River will have adverse influence on the stability of Riverside slumping mass I#.(4)The influencing laws of water level declining mode in Yangtze River on the stability of Riverside slumping mass I#under change decreasing conditions of reservoir water.In the process of reservoir water decline,reservoir water’s daily decrease,“abrupt and slow sequence",sawtooth shape,and the number of sawtooth control the stability of Riverside slumping mass I#.Daily decrease of reservoir water influences the slope stability most,“abrupt and slow sequence" secondly,sawtooth shape,and the number of sawtooth have little influence on the slope stability.①The influence of reservoir water daily decrease on landslide overall stability is larger than front-edge shallow slope.When the water level in Yangtze River is 175m,the stability coeff-icient in shallow slope is 1.260,overall stability coeff-icient is 1.183.As the reservoir water decreasing speed increases from 0.2m/d to 2.0m/d,and when reservoir water level declines to 145m,the stability coefficient of shallow slope declines by 2.6%,from 1.072 to 1.044;the stability coefficient of deep layer slope declines by 4.0%from 1.159 to 1.113.As Yangtze River water level decreasing speed increases,pore water pressure increases,seepage force outboard of directional slope increases,slope stability decreases.② "Abrupt and slow sequence" of reservoir water has certain degree influence on slope stability.Reservoir water decreases by "abruptly first and slowly then"is helpful for the stability of Riverside slumping mass I#.Take condition 1 and 2 as examples,comparing with“abrupt and slow" reservoir water,reservoir water decreases by "abruptly first and slowly then" makes the stability coefficient of potential shallow slope increase by 0.8%and the stability coeff-icient of deep layer slope increase by 0.4%.③Reducing the height of sawtooth and increasing the amount of sawtooth can improve the stability of landslide within 0.1%,which can be ignored for now. |
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