粉细砂地层双线盾构施工实测地表沉降规律分析与预测OA北大核心CSTPCD

Field tests were carried out to observe surface settlement induced by twin shield construction in silty fine sand stratum,based on the project of Nantong Metro line 2.The applicability of the twin peck formula for silty fine sand stratum is examined through measured data.The ground loss rate,the width of the preceding tunnel and the rear tunnel were analyzed.The results show that in silty fine sand soil,the secondary perturbation effect of tunnel construction on the rear tunnel induces a significant increase in surface settlement above the axis of the preceding tunnel.The secondary perturbation effect in silty fine sand stratum is more obvious than that in other soft soil layers,but less than that for sand layer.Compared with silty soil layer,the impact of shield stoppage on ground settlement is more significant in silty fine sand stratum.The ratio of ground loss rate η1/η2 caused by the twin shield construction ranges from 1 to 5 with a mean value of 2.3,and the ratio of the surface settlement trough width parameter K1/K2 between the leading tunnel and the trailing tunnel ranges from 1 to 2 with a mean value of 1.4;The ratios of ground loss rate η1/η2 in sand,silty fine sand,and silt soil stratums all exceed 1.Furthermore,none obvious relationship can be found between ratios of ground loss rate η1/η2,width parameter K1/K2 and the ratio of cover depth to diameter(H/D).