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旁压试验在软岩地区单桩承载力估算中的应用

Implementation of Pressuremeter Test for the Calculation of Pile Vertical Bearing Capacity in Soft Rock Area

  • 摘要: 目前软岩地区桩基承载力估算多数依赖于勘察单位的工程经验,存在较大不确定性。限于国产旁压设备试验压力较低,现行《地基旁压试验技术标准》(JGJT 69-2019)未给出基于旁压试验成果估算岩石地区桩基承载力的经验公式。本文依托某工程实例,采用适用于软岩的进口旁压试验设备,并结合国内外研究成果,总结提出通过Menard旁压试验成果估算软岩地区的后注浆灌注桩桩基竖向抗压承载力的计算方法,对比分析了基于勘察报告参数及后注浆增强系数修正的国内规范法、欧洲规范Eurocode 7公式法、Baguelin-彭柏兴修正公式法计算结果,并与静载荷试验双曲线法极限承载力预测结果进行对比验证,结果表明:(1)进口TEXAM型预钻式旁压试验仪,其最大试验压力可达8.0 MPa,用于软岩地区桩基承载力评价具有良好的适用性;(2)基于旁压试验成果,采用Baguelin-彭柏兴修正公式计算的单桩承载力极限值与实测曲线的预测极限值相比误差在5%以内;采用欧洲规范公式计算会高估单桩承载力约8%~15%;(3)采用基于勘察报告经验参数的国内规范方法计算结果较为保守,约有24%~32%的安全富余度。相比于基于勘察报告经验参数的国内规范方法,采用Menard旁压试验原位测试方法并结合Baguelin-彭柏兴修正公式,可充分挖掘软岩地区单桩竖向抗压承载力。

     

    Abstract: The bearing capacity of pile in the soft rock area so far is estimated based on the engineering experience of the survey company, which has great uncertainty. Limited to the ultimate pressure of domestic pressuremeter test equipment, Technical Standard for Foundation Pressuremeter Test (JGJT 69-2019) doesn't provide the experience formula for the calculation of vertical bearing capacity based on pressuremeter test for pile embedded on rock ground. Based on a certain engineering project and combined with the existing domestic and foreign research results, this article tries to summarize and propose how to estimate vertical bearing capacity of the post-grout pile at pile toe in the soft rock area through the pressuremeter test results obtained from imported pressuremeter test equipment suitable for soft rocks. The results of different methods for the determination of vertical bearing capacity are compared, including the Chinese national standard specification method based on the survey report parameters and the post-grouting enhancement coefficient correction, the European specification EUROCODE 7 formula method, the Baguelin-Peng correction formula, and the ultimate bearing capacity obtained from the static load test using bilateral trend prediction method. The results show that: (1)TEXAM pre-boring pressuremeter, whose maximum test pressure can reach more than 8.0 MPa, has a good applicability for the pile bearing capacity assessment in the soft rock area with high critical pressure or extreme pressure; (2) the distinction between ultimate vertical bearing capacity calculated using Baguelin-Peng amended formula and the predicted ultimate value of the real test pile curve is less than 5%, and the ultimate vertical bearing capacity of the single pile may be overestimated for about 8% to 15% by implementing European Code 7 formula; (3) the calculation method of using Chinese national standard specification considering empirical parameters offered by geotechnical report is relatively conservative, with about 24% to 32% of the safety richness, compared with which, the method of using the Menard pressuremeter test and combined with Baguelin-Peng amended formula, which can fully tap the vertical bearing capacity of pile embedded in soft rock.

     

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