考虑颗粒级配影响的高聚物改良钙质砂抗剪强度特性试验研究

基于南海某岛礁典型回填工程面临的钙质砂问题,提出采用环保固化剂高聚物对钙质砂地基进行加固。制作不同级配、不同高聚物含量的固化钙质砂试样,开展一系列直剪试验和SEM微观结构试验,研究高聚物固化钙质砂的抗剪强度、粘聚力、内摩擦角等参数随着高聚物掺量和颗粒级配变化的演变规律,以及高聚物改良钙质砂力学性能的微观机理。试验结果表明,随着高聚物掺量的增加,高聚物改良钙质砂的抗剪强度明显增大,试样的剪应力-位移曲线由硬化特征逐渐呈现为软化特征；高聚物主要通过影响钙质砂的粘聚力来改变其抗剪强度,对内摩擦角的影响十分有限；钙质砂中粗颗粒含量越多,其孔隙越大,高聚物改良钙质砂的反应越明显,对其强度的提升作用也越明显; 高聚物主要包裹在钙质砂颗粒表面或填充于颗粒之间,从而改变钙质砂材料原本的力学性质,使得土体的抗剪强度明显增长。

Shear Behavior of Calcareous Sands Improved by Polyurethane Foam Adhesive Considering Effects of Particle Size Distribution

To address problem of calcareous sand encountered at the backfill project at the island reef in the South China Sea, in this work, an eco-friendly agent, i.e., polyurethane foam adhesive (PFA), was proposed to improve the ground associated with calcareous sand. Evolution of shear strength, cohesion and internal friction of PFA-improved calcareous sand with various particle size distribution and PFA content, as well as the stabilization mechanism were investigated by performing a series of direct shear tests and microstructural analysis using scanning electron microscope (SEM). The test results show that, as the PFA content increases, the shear strength of calcareous sand significantly increases and the shear stress-displacement curve gradually transits from hardening to softening behavior, where the shear stress increases to a peak value following by a subsequent reduction with the increase of shear displacement. The increase of PFA content would result in a significant increase in the cohesion of improved calcareous sand, in contrast, it has limited influence on the change of internal friction angle of the specimen. The higher content of coarse calcareous sand particles in the specimens, the higher effectiveness of using PFA in improving the shear strength of calcareous sands due to its larger inter-granular pore space where the PFA could be readily filled in with active chemical reaction. The SEM results also reveal that the polyurethane foam adhesive could be effectively coated on the surface of the calcareous sand particles and filled among its void space, thereby significantly improving the shear strength of the calcareous sands.