| Based on the project "Study on the Engineering Geological Characteristics of Soft Rock and Soil and Its Im Pact on the project in Central Yunnan Water Diversion project(Wanjia-Xinzhuang)",this paper studies the engineering geological characteristics of Neogene Lufengpithecus lufengensis(N2S)soft rock in Central Yunnan Water Diversion project,and analyzes the stability of Neogene soft rock under creep and fluid-solid coupling respectively through numerical simulation software modeling.The Wanjia-Xinzhuang section of the water diversion project in central Yunnan has a total length of 141.91 Km and 9 tunnels,with a cumulative length of 129.68 Km,accounting for 90.74% of the total length of the line.Neogene soft rocks are widely distributed.The Neogene strata along the line are all from Lufengpithecus lufengensis,pliocene Series,with new age,low diagenetic degree and weak cliff,which are soft rocks or extremely soft rocks.They are mainly distributed in Cenozoic basins.The sedimentary environment is arid to semi-arid fluvial and lacustrine deposits,and the lithology is mainly claystone,siltstone,carbonaceous mudstone and conglomerate.In this paper,direct shear test,portable shear test,triaxial test,shear creep test,swelling test and disintegration resistance test after swelling are used as research methods to study the engineering geological characteristics of Neogene pliocene Series Lufengpithecus lufengensis(N2S)soft rock in the water diversion project in central Yunnan,such as Physical mechanics,water-rock interaction and deformation.The conclusions are as follows:(1)Neogene soft rocks tested include sandy clayey rock and argillaceous siltstone,which have low cohesion and weak mechanical Pro Perties.In engineering application,the internal friction angle and cohesion should be taken in the range of 27 ~ 55 and 0.26MPa~0.48 MPa,and the weathering status,fracture development and saturated state of rock mass should be correspondingly reduced.(2)The mechanical properties of Neogene sandy clay rock are extremely poor in the saturated-dehydrated cycle state.In this state,the pore water and minerals in the rock mass undergo Physical and chemical reactions,which greatly weaken the shear strength and mechanical properties of Neogene clay rock.The shear stress Tau in this state is 24% and 55% lower than that in the natural state of red bed mudstone in central Yunnan.The cohesion C is reduced by 16% and 94% res Pectively compared with the natural state and long-term saturated state of red bed mudstone in central Yunnan.(3)The softening coefficient of Neogene soft rock ranges from 0.35 to 0.42,with obvious softening effect in the Presence of water;the average swelling force can reach 980 KPa,showing strong swelling;the collapse resistance coefficient after expansion is less than 0.7,showing moderate and strong disintegration.Through comparative analysis,the expansibility analysis standard of Neogene soft rock in central Yunnan is obtained,which Provides a theoretical basis for the development of the project.(4)The softening coefficiency of Neogene argillaceous siltstone ranges from 0.35 to 0.42,with obvious softening effect when meeting water.The average expansion force can reach 980 KPa,showing strong expansion.After expansion,the disintegration resistance coefficient is less than 0.7,showing medium-strong slaking characteristic.(5)In order to understand the influence of time on Neogene soft rock surrounding rock after tunnel excavation,this paper establishes a creep model of Liujiacun tunnel excavation of Yunnan diversion project.It is concluded that one month after tunnel excavation,the top of the tunnel moves downward within 1.5 times the tunnel diameter,and the maximum displacement is 60 mm,which is about twice as much as the Pure excavation of the tunnel;and the bottom of the tunnel moves u Pward within 3 times the tunnel diameter.The maximum displacement is 68 mm,which increases about 1.42 times com Pared with the pure excavation of the tunnel.The displacement range of the left and right wall of the tunnel is within 3 times the diameter of the tunnel,and the displacement nephograms on both sides are symmetrical,the maximum displacement is 45 mm,which increases about 0.67 times compared with the pure excavation.(6)Through Flac 3D simulation,the initial creep of surrounding rock at the top and bottom of the tunnel is 40 mm,and the initial creep of surrounding rock at the left and right tunnel walls is 20mm;Within one month after excavation,the constant velocity creep of the roof,left and right cave walls and cave bottom can reach 20 mm,with an average creep speed of 0.67 mm/d.(7)Through Flac 3D tunnel excavation simulation,when the tunnel is excavated,pore water flows into the tunnel from the week of the tunnel,and the minimum pore water pressure value appears at the periphery of the tunnel,and increases continuously from the tunnel wall along the radius direction of the tunnel into the cliff.Negative pore water pressure appears in the wee K of Neogene soft rock surrounding cave,which is harmful.After tunnel excavation,pore water should be treated and supported in time. |
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