Prediction of Ground Settlements Associated with Shield Tunnelling

Abstract

There is much uncertainty to estimate the ground settlement associated with shield tunnelling due to the complicatedly interacted conditions between tunnelling methods and soil characteristics. Accordingly, if the shape of the ground settlement could be quantitatively predicted, it would be very effective for the assessment of its influence on the existing structures. It is presented that the shape of the ground settlement trough can be expressed as the product of the normal distribution function and the error function by introducing the mathematical model. The field observations were also carried out at the four sites of the shield tunnel construction in the Metropolitan areas. Besides, the model test was done, in which the settlements of sand layers were measured by the X-ray techniques. The following conclusions are obtained. The lateral and longitudinal profiles of the ground settlement trough are well fitted with the normal distribution curve and the error function curve, respectively. The parameter which represents the width of settlement is roughly proportional to depth of tunnel and its proportional constant depends upon soil characteristics. In clay the ratio of lost ground is positively correlated with OFS (Simple Overload Factor) defined by construction conditions and soil characteristics. Consequently the maximum settlement can be calculated by using these relationships.