Study on Construction Process for Small Clear Distance Overlapping Shield Tunnel
Taking the construction of the section between Huanchengnan Road Station to Kunming Railway Station on Kunming Metro Line 2 as an example,the numerical calculation method is used to study the difference between the construction sequence of 'first down and then up'and'first up and then down'on the control of surface settlement.The results show that during the'first down and then up'construction,the surface settlement caused by the construction of the lower tunnel accounts for 82.6%of the total settlement,while the additional settlement caused by the construction of the upper tunnel accounts for about 17.3%of the total settlement;during the'first up and then down'construction,the surface settlement caused by the construction of the upper tunnel accounts for 18.8%of the total settlement,while the additional settlement caused by the construction of the lower tunnel accounts for approximately 81.1%of the total settlement.During the 'first down and then up' construction,the construction of the upper tunnel has an impact on the construction of the lower tunnel,as the settlement trough curve is flattened and elongated;during the 'first up and then down' construction,after the construction of the lower tunnel,the maximum surface settlement rapidly increases,and the settlement trough forms a deep"V"shape.The excavation face support pressure ratio mainly affects the final settlement value,while the shield tail grouting pressure affects the shape of the settlement curve and the final settlement value.From the calculation results,it can be seen that the sensitivity of excavation support pressure to settlement control is higher.According to relevant regulatory control requirements,the recommended range for excavation face support pressure ratio and grouting pressure ratio during construction in this project is 0.8～1.2.
万方数据
维普
