| The study based on the Hefei Metro Line 2 that from Qingyang Road Station to Xiyuan Road station area passing through Changjiang West Road,a three-dimensional numerical model was established using Midas GTS NX software to analyze the earth pressure in soil warehouse and Two-lane tunnel interaction caused the law of surface deformation during the construction of the double shield tunnel.Conclusions were as follows:(1)No matter of the earth pressure in soil warehouse was too large or too small,it will produced an adverse effect on the surface uplift.When the earth pressure in soil warehouse was too large,it will caused soil uplift of 2D in front of the excavation surface(D is the tunnel diameter);In contrast,if the earth pressure in soil warehouse was too small,the amount of ground settlement will be too larger.Both of these conditions will caused certain adverse effects on the building structure.So during the shield construction process,only when the soil cover depth was 2.5D and the suggested ratio coef0 k value between 0.5 to 1.1(this was the relationship coefficient between the assumed soil pressure and the soil's own weight stress),the soil pressure and the soil water pressure in front of the cutterhead can basically reach equilibrium and the shield construction had less impact on the surface uplift,which can effectively ensure the stability of the soil in front of the cutterhead.(2)In the condition that other factors were unchanged in double-line parallel shield tunnel,the distance between the centerline of the two tunnels had a potential influence on ground surface settlement.When the tunnel centerline spacing was less than 2.5D,interfere and superimpose with each other of two tunneal which will cause the cross-section ground surface settlement appears as a groove type(single peak);When the tunnel centerline spacing was 3D,the groove type was also appeared,but the settlement curve was more gentle,similar to the shape of a "pan";When the tunnel centerline distance was greater than 4D,the two tunnels had less influence on each other and the surface settlement curve presented two settler troughs(double peaks).During the construction of shield tunnels,with the increase of tunnel spacing,the surface settlement decreased gradually and the settlement curve gradually changed from a steep single peak to a gradual “pan” shape.When the distance exceeded 4D,the settlement curve will change form a single peak to a bimodal shape.(3)When lag distance existed and the tunnel space between double-line paralleltunnel was a centian value,construction of any tunnel will have an impact on the other tunnel was mainly concerned with surface settlement.In regard to cross-section direction,the ground surface settlement curve caused by the first excavation tunnel construction presenting as a groove type,and the maximum settlement generally occured above the tunnel centerline;After the completion of the tunnel construction,the double-line surface settlement curve also appeared as a groove.However,the maximum settlement occurred above the middle position of the double-line cross-section and the settlement was greater.This was due to the disturbance of the soil around the excavation tunnel caused by the construction of the excavation tunnel.With regard to vertical tunnels,when constructing a double-line parallel tunnel,any tunnel construction will cause the surface of the other tunnel to slightly bulge and then settled.The final surface settlement caused by tunneling after tunneling was generally larger than that of tunnel excavation,this was due to the disturbance of the soil above the back tunneling area during the construction of the excavation tunnel,which results in early release of soil stress and final settlement increased.When the double-line parallel tunnel construction had a certain lag distance and the tunnel spacing was constant,attention should be paid to the mutual influence of tunnel construction and reduced the potential construction risk. |
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