Field pilot tests on combined method of vacuum preloading and pneumatic fracturing for soft ground improvement

To overcome the shortcomings of the traditional vacuum preloading method, a new technique is proposed to combine the vacuum preloading with the pneumatic fracturing. This study presents the concept, mechanism, construction procedures and field validation of this new combined method. Field pilot tests were conducted to compare the performances of the proposed new method and the traditional vacuum preloading method in a construction section of Jiangdu-Haian highway. The vacuum degrees, pore water pressures, surface settlements, deep horizontal displacements and groundwater levels were monitored during the field tests. The effectiveness of soft ground improvement is demonstrated by the comparison of CPTU tests and soil property tests before and after ground treatment. The test results show the improvement effects of the proposed method are better than those of the traditional vacuum preloading method by enhancing the vacuum transfer efficiency into the deep soil layers. The proposed method raises the effective treatment depth of the vacuum preloading method and reduces the preloading time of the vacuum loading. The combined method of vacuum preloading and pneumatic fracturing can be widely used in the improvement practice of soft ground.