约束注浆挤扩钻孔灌注桩是一种结合等向高压注浆和约束挤扩的新型桩,具有抗压承载力高、成桩质量好的优点.由于挤扩体的存在,使得对桩-土共同作用的竖向承载力与破坏机理尚缺乏清晰的认识.因此,基于室内可视化半模型桩试验,结合有限元分析法,研究约束注浆挤扩钻孔灌注桩的承载机理.根据相似原理开展缩尺可视化静荷载半模型桩试验,分析基桩的承载特性;利用数字图像相关(digital image correlation,DIC)技术,得到桩周土体的位移规律,分析基桩的承载力组成和失效破坏机理,并提出挤扩端阻修正系数.借助ABAQUS数值计算软件,选用修正Cam-Clay (modified Cam-Clay,MCC)模型,构建不同尺寸参数的约束注浆挤扩钻孔灌注桩模型,开展抗压静载试验的数值模拟,讨论挤扩体尺寸参数对极限承载力和桩端承载力的影响,进一步研究挤扩端阻修正系数的取值.最终,建立承载力计算公式,并与现场静载试验结果进行对比,结果表明约束注浆挤扩钻孔灌注桩属于端承摩擦桩,桩端土体的剪切破坏会导致基桩失效.结合工程实际尺寸参数,得到挤扩端阻修正系数取值范围为1.92~2.30.根据基桩尺寸参数,选取挤扩端阻修正系数,将桩端阻力修正为桩端联合承载力,极限承载力较为接近实测值,误差为9.3%.所得研究结果可为约束注浆挤扩钻孔灌注桩的设计和推广提供理论与实践参考.

Bored piles with constrained grouting expansion (BPCGE) are an innovative approach for piling that integrates isotropic high-pressure grouting with constrained expansion techniques. This method is recognized for its robust compressive load-bearing capabilities and superior pile quality. However, the presence of an expansion body complicates the understanding of vertical compressive pile-soil interactions, particularly those associated with the load-bearing capacity and failure mechanisms. Hence, a visual semi-model pile testing schema is developed in this study. Experimental and finite-element analyses are conducted to investigate the bearing capacity and failure mechanisms of BPCGE. Initially, a visual static load test is conducted on a semi-modeled pile based on the principle of similarity to discern the load-bearing characteristics of the pile. Digital image correlation is used to measure the displacement and deformation patterns of soil around the pile. An expansion correction coefficient for the bottom resistance is introduced following the analysis. Subsequently, numerical simulations are performed using the ABAQUS software, where the modified Cam-Clay model is utilized to simulate the compressive static-load test of BPCGE under various size parameters. The effects of these parameters on the ultimate bearing capacity and the pile’s end-bearing capacity are investigated, which are then considered to further refine the expansion correction coefficient for the bottom resistance. Finally, a formula for calculating the bearing is established, and the calculated values are compared with data from field static-load tests. The findings indicate that BPCGE can be classified as end-bearing friction piles, with the shear failure of the pile tip soil being the primary cause of failure. Meanwhile, the expansion correction coefficient for the bottom resistance should be set from 1.92 to 2.30, based on practical project considerations. By selecting an appropriate coefficient based on the size parameters of BPCGE, the pile end resistance can be adjusted to account for combined end resistance. The ultimate bearing capacity calculated using the proposed formula is consistent with actual measurements, with an error margin of 9.3%, as compared with the field test results. This study provides theoretical insights and practical guidelines for the design and implementation of BPCGE.