土工格栅-碎石界面力学特性拉拔试验研究

Pull-out test study on mechanical characteristics of geogrid-aggregate interface

土工格栅常用于复合地基的碎石垫层,可有效限制其侧向位移并减小差异沉降,这有赖于土工格栅与碎石颗粒间的相互作用。采用3种不同的级配碎石和双向、三向两种土工格栅进行了一系列大尺寸拉拔试验。试验结果表明,更高的法向应力、更好的颗粒级配和更合理的碎石颗粒尺寸可以使拉拔阻力明显增加。冲剪破坏模型可以很好地解释双向格栅横肋在拉拔过程中与碎石层的剪切作用,该模型也适用于三向格栅的斜肋,只需合理计算斜肋的有效剪切长度。此外,还提出了一种考虑网孔和碎石颗粒尺寸与颗粒嵌固作用的土工格栅峰值拉拔阻力的计算方法,并给出了关键颗粒的概念用来评价格栅与碎石颗粒尺寸的匹配程度,可以帮助设计者合理选择材料,提高加固效果。

Geogrids are often used in the aggregate cushion of the composite foundation to limit the lateral displacement and reduce the differential deformation.It depends on the interaction between geogrids and aggregate particles.In this study,a series of large-size pull-out tests was performed on bi-axial and tri-axial geogrids embedded in aggregates with three particle-size gradations.The test results showed that higher normal stress,better gradation and more suitable aggregate particle sizes yielded the increase of the pull-out resistance.The classic punching-shear failure model was proven to be valid for explaining the shear effect between transverse ribs of bi-axial geogrids and the aggregate layer during the pull-out process.The bearing resistance of oblique ribs of tri-axial geogrids can also be calculated based on this theory,as long as the effective length of the oblique rib is calculated in a reasonable manner.Furthermore,an empirical method was proposed to calculate the peak pull-out resistance of the extruded geogrid embedded in the aggregate considering the sizes of apertures and aggregates,and interlock effect.The concept of key particles was proposed in this paper to measure how well the apertures of geogrids match the size of the particles.This may help designers choose the type of geogrids and improve the reinforcement effect.