深厚淤泥地层超静水压力条件下超深灌注桩施工孔壁稳定性研究

Study on the Stability of the Hole Wall of Ultra-deep Piles Under Excess Water Pressure in Deep Silty Formation

依托某地铁车辆段管桩施工后超静水压力条件下的钻孔灌注桩工程,研究了超静水压力条件下钻孔孔壁的稳定条件。推导出了孔壁坍塌的临界水力坡度公式和保证孔壁稳定性的临界固结度公式,并分析了土体固结对孔壁稳定的影响;探讨了新奥法原理在淤泥质软土超静孔隙水压力下灌注桩成孔中的应用。研究结果表明:饱和淤泥质地层中管桩施工后超静孔隙水产生的渗透力是造成灌注桩钻孔过程中孔壁变形失稳的主要因素;土体的黏聚力是影响钻孔缩颈和塌孔的关键参数;超静水压力下软土中钻孔孔壁的稳定条件主要是圆拱支撑力和渗透力;钻孔期间孔壁土体的蠕变大、渗透路径短和土体能在较短时间内发生较大的固结可使孔壁达到稳定的平衡状态;超静孔隙水压力条件下的软土可以借鉴新奥法原理进行钻孔灌注桩成孔。

Based on the bored pile project under excess water pressure conditions after the construction in a subway depot,the stability conditions of the borehole wall were studied.The critical hydraulic slope formula for hole wall collapse and the critical consolidation formula to ensure the stability of the hole wall were derived.The influence of soil consolidation on the stability of the hole wall was analyzed;Under excess pore water pressure,the application of New Austrian Tunneling Method(NATM)in the process of piles formation in silty soft soil is discussed.The results show that the seepage force generated by excess pore water in saturated silty strata after the construction of the pipe pile is the main factor of the deformation and instability of the hole walls during the drilling of the pile;The soil cohesion is the key parameter affecting the necking and collapse of the borehole;The stability conditions of borehole walls are mainly the supporting force and the penetration force of the round arch;During the drilling,the large creep of hole wall,short penetrating path and the soil consolidation in short time make the hole wall in stable state;New Austrian principle can be applied in bored pile for the soft soil under excess pore water pressure.