Determination of proper position of grouting during lifting the existing subway

Because of the construction disturbance,the existing subway would be influenced when a new subway was built near it.When the influence reached a certain degree,the operating security of the existing subway would be threatened.For increasing the project security or decreasing the construction difficulty,lifting the existing subway by grouting was used in general to recover its elevation and to decrease differential settlement during or after the construction.The model of lifting the existing subway by grouting was created and the concept of grouting in the weak position was put forward.It was indicated that grouting in the week position would decrease the settlement and induce little stress concentration.The practical grouting program of the existing Beijing subway line 5 in the Chongwenmen station was analyzed.It was indicated that the settlement was decreased by grouting,but the degree of the stress concentration was some how large.Therefore,the lifting effect was significant and the safety of the existing subway in operation was increased.