新型吊脚墙支护二元基坑变形特征与地层适应性研究

Research on Deformation Characteristics and Stratum Adaptability of New Type End⁃suspended Wall Supported Soil⁃rock Mixed Stratum Foundation Excavation

在上土下岩的二元基坑支护中,吊脚墙底需留有岩肩作为吊脚墙底部的嵌固支点,并需要采取预应力锚索锁脚措施。提出无岩肩无预应力锚索锁脚的新型吊脚墙支护体系,并在广州某地铁车站基坑中实施。通过对比有无岩肩与预应力锚索锁脚和不同地层下基坑变形特征,探讨该新型吊脚墙支护体系的地层适应性。研究表明:采用无岩肩新型吊脚墙支护体系和传统预留岩肩吊脚墙支护体系,在不同地层条件下变形特征与支护效果差异很小,取消岩肩与预应力锁脚锚索合理可行。当下卧岩层质量较好时,随土岩交界面深度增大,土层段变形增大,岩壁段保持稳定。随下卧岩层质量弱化,基坑变形先增大后影响不大,吊脚墙变形逐渐增大,岩壁段变形增大,有向外滑移趋势。无岩肩新型吊脚墙支护体系和传统预留岩肩吊脚墙支护体系均具有较好的地层适应性,在下卧岩层质量偏差时,需对岩壁段进行喷锚支护,或考虑采用传统嵌岩围护结构。

In the foundation excavation support of soil-rock mixed stratum,the rock shoulder should be left at the bottom of the end-suspender wall as the embedded fulcrum,and the prestressed anchor cable should be adopted to lock the feet.It is the first time that a new type of end-suspender wall support system with no rock shoulder and no prestressed anchor cable locking feet has been proposed,and it has been implemented in the foundation excavation of a subway station in Guangzhou.As a part of the theoretical research,this paper discussed the formation adaptability of the new type of end-suspension wall support system by comparing the deformation characteristics of foundation excavation under different strata with or without rock shoulder and prestressed anchor cable locking foot.The research shows that there is little difference in deformation characteristics and support effect between the new rock-shoulder and the traditional reserved rock-shoulder supporting system under different stratum conditions,and it is reasonable and feasible to cancel the rock-shoulder and prestressed locking anchor cable.When the quality of the lying strata is good,the deformation of the soil layer section increases with the depth of the soil-rock interface,and the rock wall section remains stable.With the weakening of the quality of the underlying rock,the deformation of the foundation excavation increases first and then has little influence,the deformation of the hanging wall gradually increases,the deformation of the rock wall section increases,and there is a tendency of outward sliding.Both the new bolt-foot wall support system without rock shoulder and the traditional reserved bolt-foot wall support system have good formation adaptability.When the quality of the underlying rock strata is deviated,the rock wall section should be supported by shotcrete anchor,or the traditional rock-socking enclosure structure should be considered.