隧道开挖致使土层缺失对桩基稳定性影响研究

Study on the Influence of Soil Loss Caused by Tunnel Excavation on the Stability of Pile Foundation

隧道开挖致使地层缺失对邻近桩基的影响问题不容忽视。通过考虑隧道开挖下土层缺失的自由场位移,根据地基反力系数法及桩侧水平向荷载传递机理,建立了桩基受力变形简化计算模型,并通过有限差分法和增量法对桩身内力和位移进行求解,对比分析发现理论值与现场实测数据较为吻合,验证了理论计算模型的合理性;进而对桩径、桩-隧相对距离等参数进行影响因素分析。研究表明,桩身弯矩随桩径增大而增加,而桩身水平位移呈非线性减小,桩径由1.2 m增大至2.0 m,桩身最大水平位移减幅为21.3%;增大桩径可一定程度提高桩身水平承载能力,减小桩身水平位移。随桩-隧相对距离增加桩身水平位移和弯矩均减小,桩-隧相对距离由4 m增大至12 m时,桩身最大水平位移减幅为54.3%,桩身最大弯矩减幅为96.0%;桩身水平位移和弯矩均在隧道中轴线附近达到峰值;相较于桩径,桩-隧相对距离变化对桩基的稳定性影响更大。

The influence of stratum loss caused by tunnel excavation on adjacent pile foundation should not be ignored.In this paper,by considering the tunnel excavation under the free field displacement of the soil loss according to the modulus of subgrade reaction method to the load transfer mechanism of pile side and pile stress deformation of the simplified calculation model is established,and through the finite difference method and incremental method to solving of pile body internal force and displacement,contrast analysis found that the theoretical value tallies with the actual measured data,The rationality of theoretical calculation model is verified.Then,the influence factors of pile diameter and relative distance between pile and tunnel are analyzed.The results show that the bending moment of pile increases with the increase of pile diameter,while the horizontal displacement of pile decreases nonlinearly.The maximum horizontal displacement of pile decreases by 21.3% with the increase of pile diameter from 1.2 m to 2.0 m.Increasing pile diameter can improve the horizontal bearing capacity of pile to a certain extent and reduce the horizontal displacement of pile.The horizontal displacement and bending moment of pile decrease with the increase of pile-tunnel relative distance.When the pile-tunnel relative distance increases from 4 m to 12 m,the maximum horizontal displacement and bending moment of pile decrease by 54.3% and 96.0% respectively.The horizontal displacement and bending moment of pile reach the peak near the central axis of tunnel.Compared with pile diameter,pile-tunnel relative distance has a greater influence on the stability of pile.