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

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.