基于辅助气压模式的破碎软岩地层盾构下穿砖混房屋施工安全技术研究

Research on Construction Safety Techniques for Shield Under⁃passing Brick⁃concrete House in Fracture Zones and Soft Rock Based on Air Pressure⁃assisted Tunnelling

为解决基于辅助气压模式土压平衡盾构在裂隙发育的破碎软岩地层中始发下穿结构老旧浅基础砖混房屋的施工难题,以广州地铁某区间为例,首先从周边环境及地质情况分析本次施工重难点。然后分别从施工前准备、过程控制、工后保护3个角度开展了关键施工技术研究。最后从工程效益、经济效益、社会效益开展综合评估。研究结论表明:辅助气压工法允许地层存在一定程度的发育裂隙,但需利用其他辅助措施以满足土仓保压要求,同时需结合地层保压性,积极调整土仓渣土高度;在盾构始发阶段,需通过勤调泡沫空气流量或螺旋机转速,有效减小仓内瞬间压力波动;渣土经改良至一定流塑态后,以闸门开度与螺旋机转速为双控指标,并利用辅助气压工法可保证掘进速度。在软岩地层中掘进时,适当提高刀盘转速并降低贯入度,可减小盾构下穿诱发的建筑物沉降。

To solve the construction problem that the earth pressure balance(EPB)shield based on the auxiliary air pressure mode starts to underpass through the old brick⁃concrete building with shallow foundation in the fractured soft rock stratum,a section of Guangzhou Metro is taken as a case.Firstly,the key and difficult points of this construction were analyzed in accordance with the surrounding environment and geological conditions.Then,the key construction technology was studied from three aspects,namely,pre⁃construction preparation,process control and post⁃construction protection.Finally,a comprehensive evaluation of the construction technology was carried out from the perspectives of engineering,economic and social benefits.The results show that the auxiliary air pressure method allows the formation to have a certain degree of development cracks,but other auxiliary measures need to be applied to meet the pressure requirements of the soil bin.Meanwhile,it is necessary to actively adjust the height of the soil bin residue in combination with the pressure retention of the formation.In the shield launching stage,it is necessary to adjust the foam air flow rate or the screw machine speed frequently to effectively reduce the instantaneous pressure fluctuation in the soil bin.After the muck is improved to a certain flow plastic state,the gate opening and the screw machine speed are taken as the double control indices,and the auxiliary air pressure method can be used to ensure the tunneling speed.When tunneling in soft rock strata,properly increasing the cutterhead speed and reducing the penetration can reduce the settlement of buildings induced by shield tunneling.