A Method for Evaluating Subgrade Bearing Capacity of Deep Rock Mass Using Load-Transfer Piles

Based on the Guangdong Shiziyang Bridge project， the reasonable bearing capacity of the foundation bearing layer was determined for the anchorage foundation of the super long-span suspension bridge. The double-walled bored cast-in-place pile technology was adopted to construct the load-transfer piles for the deep loading plate test. The inner steel cage was wrapped in a 0.8 m diameter steel casing that served as the inner wall， thereby minimizing the pile side friction and ensuring the full transfer of the applied load to the pile tip. For the outer layer， a 1.2 m steel casing was used for borehole wall protection， with gravel filled between the inner and outer walls to ensure the stability of both the load-transfer pile and the borehole wall. In addition， the sediment removal process at the pile tip was optimized by tightening the control standards for slurry density and ensuring a seamless transition between the commencement of the initial concreting and the completion of the second-stage hole cleaning. The test Q-s curve was obtained through methods employing pre-embedded rebar gauges on the pile body to monitor tip stress and pre-installed settlement monitoring rebars to measure tip settlement. The bearing capacity characteristic values of the bearing layer were then determined through analysis. The test results demonstrated that the characteristic value of the bearing capacity for the moderately weathered bearing layer was recommended to be 2461 kPa， and confirmed the effectiveness and feasibility of the deep loading plate test method using the double-walled bored pile technology.