Study On Slope Stability Of High Earth-rock Cofferdam On Deep Overburden Foundation

Cofferdam is a temporary water-retaining structure to enclose foundationditch during diversion project and ensure hydraulic structure to beconstructed on dry ground,the layout and constructure procedure playsdecisive action to project’s construction pattern and has important effectto engineering’s total progress and quality.The safety of cofferdam isfatal,it affects the safety and the schedule of the entire construction,alsothe safety of the downstream. In recent years, with the core of hydropowerengineering construction further transfer to southwest region. Problems ofdeep and thick overburden is more and more prominent, cofferdam’sconstruction operation management become more difficult. This thesis takesa deep and thick overburden rockfill cofferdam as the object to study, andcarries out the research on stability of cofferdam slope on the basis ofseepage analysis. The prime task are as follows:(1)The basic principles and methods of seepage analysis and slopestability analysis are introduced, based on nonlinear coarse soil shearstrength theory and a new kind of dam slope’s most dangerous sliding arcsearch method, a set of dam slope’s stability analysis program thatconsidering nonlinear shear strength be compiled.(2)The cofferdam’s construction and operation phrase are simulated: dikeclosuring, foundation pit pumping, foundation pit excavation, upstream flowrecession and so on,during every phase, cofferdam seepage field changes andanalysis of stability against sliding about cofferdam slope be carried out.(3)The effect to cofferdam seepage of the velocity of pumping water ofthe foundation ditch, the velocity of excavation of the foundation ditch, thevelocity of recession of the upstream flow, the permeability characteristicof overburden and the different form and different level local damage of cutoffwall and so on are calculated and analyzed, and some conclusions are proposedfrom seepage line overflow export ratio-grade, unit width flux and the biggestratio-grade of cutoff wall.(4)On the basis of seepage analysis, using the nonlinear shear strengthdam slope stability analysis program, the stability of cofferdam slope under different operating modes are computed. It is concluded that the mostdangerous sliding surface and the minimum safety factor. Considering severalfactors affecting the seepage, analyzing the stability of cofferdam slope,the conclusion are proposed through the minimum safety factor of stabilityagainst sliding.