Research On Mechanical Properties Of Clay Interlayer Lenticle And Its Influence On The Stability Of Tailings Dam

There are more than12,000tailings pond in China,above85%are constructed byupstream method.Tailings pond is important danger sources of no-coal mine. Tailingsdam is the main structure of the tailings pond,tailings dam accidentare always caused byinstability of slope. Therefore, Chinahas increased investment in technology oftailingsfield, in order to improve safety management of tailings pond.During tailings dam areconstructed by upstream method, the clay interlayer lenticle are caused by the method willnot only affect seepage field, but also affect the stability of the tailings dam.This paperis based on soil mechanics, fluid mechanics, geotechnical engineeringand multi-disciplinary, applying theoretical analysis,laboratory test, numericalsimulation and combining projectstostudy mechanical properties of clay interlayerlenticle and its influence on the stability and the seepage field of tailings dam.The mainwork and the researchresult completedas follows:(1) Through laboratory experiments to test the physical and mechanical propertiesof the clay interlayer lenticle, the results are:①Consolidation: at100kPa~200kPa pressure, increasing the thickness of theinterlayer, compression coefficientof the specimen is improving, the compressionmodulus is getting small;at initial stage, void ratio is decreasing, e-p curve is gettingsteep, and gradually approaching the clay interlayer (tail silt) e-p curve. If the interlayerhas the same thickness, the compression coefficientrank are: medium sand <fine sand <silt, then it is opposite of compression modulus.②Permeability: compression coefficient could be reduced twoorders of magnitudeby clay interlayer. at the same interlayer thickness, permeability rank: silt<fine sand<medium sand.③Shear strength: at the same interlayer thickness, variation of particle size fromcoarse to fine,the change of cohesion and friction angle are not obvious.But thickness isincreasing, the cohesion is improved, the friction angle is decreased.(2) The effects of clay interlayer lenticleon seepage field:①The affected area: Lenticles are located near the phreatic line will have animpact on the burialdepth and shape.The distribution is above or away from the phreaticline, will not affect the phreatic line. but it will change seepage field of surroundinglocal area of lenticles. ②Location: along the phreatic line from dam crest to initial dam, the scropeinfluence of lenticel is getting lager, the phreatic line above the lenticle is graduallyuplifted.③Dimension: The dimension of lenticles increases along the horizontal direction,it not only uplift the phreatic line above the lenticle, and the phreatic line below thelenticle will also be uplifted,it has a great influence on the stability of the dam.Increasing the dimension of the lenticle in the vertical direction, phreatic line above thelenticle will be uplifted, and phreatic line below the lenticle will be reduced, the shapeof phreatic line gradually become an "S".④Influenceof multiple lenticles: Lenticles are uniformly distributed along thephreatic line, the shape of phreatic line change into ladder-type, and the phreatic lineabove the lenticle is uplifted, it will affect the stability of tailing dam; when lenticles aredistributed randomly,only they are located near the phreatic line will have an impact onthe burialdepth and shape.The distribution is above or away from the phreatic line, willnot affect the phreatic line.(3) The effects of clay interlayer lenticle on the stability of tailings dam:①The deformation of tailings dam including lenticles is obvious,when strengthreduction factor is1.4,displacement mutation of sampling point of dry benchisoccurred,local failure is occurred too. when strength reduction factor is1.6,some yieldarea began to appear at the lowest of tailings dam, and then, expand rapidly until casethe instability of the tailings dam.②Without lenticles, as friction and cohesion of tailings are reduced, the safetyfactor of Tailings dam is gradually decreasing. The safety factor of the part of initialdam decrease obviously.③Including lenticles,when strength reduction factor is1.2, the maximum slidingresistance is decreased by500kPa, This value is25times greater than without lenticles.④Including lenticles, as strength reduction factor is getting larger, safety factor isgetting smaller,Falling gradient is bigger than does not contain the lenticles.