土工织物散体桩桩体单轴压缩试验

土工织物散体桩是一种新型的复合地基桩基，为了研究其在轴向荷载下的强度和变形特性，并探讨桩体强度和模量的确定方法，选用了3种相对密度（D_r=0.42，0.62，0.78）的碎石和4种筋材强度（T=33，43，52，65 kN·m^-1）的无接缝聚丙烯土工编织布套筒，制备成12组直径为300 mm，高度为600 mm的大尺寸土工织物散体桩桩体试样，对试样进行单轴压缩试验至破坏。研究结果表明：单轴压缩下土工织物散体桩桩体应力-应变曲线在加载初期因碎石受到初始压密而上凹，而后近似线性增长至桩体强度，随后应力随应变减小呈现应变软化特性；当加载接近至桩体强度时，编织布套筒中间部位明显鼓胀，该处横向筋丝逐根断裂直至桩体失效，故横向筋丝的强度对桩体的强度起控制作用，在实际应用中可加强横向筋丝的强度以进一步提高桩体的竖向承载力；土工织物散体桩桩体强度与碎石相对密度无相关关系，而与筋材强度呈较好的线性统计关系，可以通过筋材强度确定土工织物散体桩的桩体强度；土工织物散体桩桩体模量随筋材强度或碎石密实度的增大而明显增大，在同一碎石密实度下，桩体模量随筋材强度呈线性增长关系；建立了土工织物散体桩桩体模量理论计算公式，并采用试验值对理论公式进行修正，修正系数κ=2.4，修正后的结果与试验值吻合很好。

Uniaxial Compression Test of Geosynthetic-encased Stone Columns

Geosynthetic-encased stone columns (GESCs) are a new type of column bodies for a composite foundation. In this work,12 large-scale samples of GESCs with 300 mm diameter and 600 mm height were made using gravels of three different relative densities (D_r=0.42,0.62,0.78), and seamless sleeves of four different strengths (T=33, 43, 52, 65 kN·m^-1) were also made using polypropylene woven geotextiles. These samples were used for studying the strength and deformation characteristics of GESCs subjected to a uniaxial loading, and subsequently to establish a method to determine their strength and modulus. Uniaxial compression tests were performed on the samples until failure. The results show upward concave stress-strain curve of GESCs at the preliminary loading stage presumably due to the initial densification of gravels under the uniaxial compression. After the initial nonlinear stage, stress increases approximately linearly up to the strength of GESCs, and subsequently decreases, indicating strain-softening characteristics. Once the loading approaches the strength of GESCs, the GESC bodies apparently bulge in the middle, where the horizontal slices of the geotextiles break sequentially until failure of the GESCs. Therefore, the strength of the horizontal slices ultimately controls the strength of GESCs. The bearing capacity of GESCs can thus be enhanced in practice by strengthening the horizontal slices. The strength of the GESCs is independent of the relative density of gravels but varies somewhat linearly with the geotextile strength. The strength of the GESCs can, therefore, be determined from that of the geotextile. The modulus of the GESCs apparently increases with an increase of either the geotextile strength or the gravel density, however, for a fixed gravel density the modulus increases linearly with the geotextile strength. A theoretical formula was established to compute the modulus of the GESCs. The formula was verified with the test data, and a correction factor of κ=2.4 was obtained to arrive at a better agreement with the test results.