Analysis Of The Ground Settlement Caused By The Construction Of The Portal Of The Shield Starting Shaft In The East Huai'an Station

Shield construction is widely used in subway construction in China.Shield construction is not affected by weather and season,and the construction speed is fast.Due to the complexity of the underground situation,in the shield construction,it is generally necessary to reinforce the soil mass of the tunnel portal.In order to carry out the project more safely and effectively,it is necessary to study the reinforcement technology and construction scheme of shield tunnel portal.In this paper,taking the shield starting shaft of Huai'an east station as an example,the surface displacement caused by the construction of double track tunnel of Huai'an east station is studied by using peck formula,numerical simulation and other methods.Using peck formula to calculate the shield tunnel portal without reinforcement will lead to 18.92 mm ground settlement;using Midas finite element software to simulate shield tunnel excavation,16.9mm settlement results are obtained.Whether it is the result of theoretical calculation or numerical simulation,the settlement of shield tunnel is large.In order to consider the construction safety,it is necessary to reinforce the shield tunnel portal.This paper proposes the scheme and construction process of the shield tunnel portal reinforcement.The three-axis mixing pile and MJS construction method are used to reinforce the shield starting station of Huai'an east station.The numerical simulation calculation is carried out for the excavation of the reinforced double line tunnel.After the tunnel portal reinforcement construction,the shield tunneling will lead to the surface settlement of 3.76 mm and the uplift of 2.57 mm.The actual monitoring surface displacement shows that the maximum ground settlement is 4.76 mm and the maximum uplift is 3.74 mm.Both groups of data show the good effect of shield tunnel portal reinforcement construction,which greatly reduces the displacement of tunnel portal and makes shield construction safer.By comparing the settlement curves of numerical simulation and actual monitoring,it is known that after the portal reinforcement construction,the settlement groove curve will become irregular.No matter the actual monitoring data or numerical simulation data,the settlement groove does not show the "W" or "V" type summarized by the previous laws.It shows that although the reinforcement construction of tunnel portal greatly reduces the ground displacement,it also makes the change of ground displacement over the tunnel portal more unpredictable in a certain range.Figure [29] table [9] reference [75]...