Mechanism and Application Study on Pipe Shed Supported in Advance for Mined Tunnel in Sand and Gravel Stratum
Research purposes:Because of the high compressive strengthen and disordered particle distribution in sand and gravel stratum,great disturbance of surrounding soil is induced,the support effect of long pipe shed can not be ensured,and it has become one of the bottlenecks that restrict the application of mined tunnel.In this paper,based on the practical project of one subway station which was constructed with guided tunnel through underground excavation,the combination of site test and numerical was adopted.In order to reveal the best support parameters of long pipe shed adopted in mined tunnel in sand and gravel stratum,the mechanism and support effects of different pipe diameters and different circumferential spacing were deeply studied.Research conclusions:(1)In sand and gravel stratum,the reduction rate of formation settlement transferring from deep ground to the surface is about 0.91 mm/m along the height direction.(2)The decisive role of the support effective of long pipe shed on tunnel safety is made clear,and all kinds of possible measures should be adopted to minimize the stratum settlement caused by pipe construction.(3)According to the results of single factor sensitivity analysis,the ground settlement increases with the increase of the support length and the circumferential spacing distance of pipe sheds,and it is positively correlated.(4)In order to control the ground settlement and improve economic benefit,it is suggested that the circumferential spacing distance should be 35 cm as for 127 mm diameter pipe shed,and the corresponding supporting length should be 40 m.It is recommended that the circumferential spacing distance should be 40 cm as for 159 mm diameter pipe shed,and the corresponding supporting length should be 40 m.And the circumferential spacing distance should be 45 cm as for 209 mm diameter pipe shed,and the corresponding supporting length should be 50 m.The positive relationship between diameter and optimal length of pipe shed is made clear.(5)The research result can lead a reference for the large range adopt of large diameter shield in urban railway.
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