土工织物散体桩桩体大三轴试验研究
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摘要
对密实状态的土工织物散体桩桩体进行大三轴试验,研究其在不同围压和不同聚丙烯土工编织布筋材强度下的应力–应变特性,并据此提出桩体强度及模量理论计算公式。研究结果表明:土工织物散体桩桩体在三轴压缩下呈剪胀破坏,其剪切带上主要是筋材的横向筋丝产生断裂,且桩体剪切角与碎石的莫尔–库仑理论破裂角比较接近;在加载初期,土工织物散体桩应力–应变曲线下凹,而后近似线性增长至峰值应力,随后应力随应变减小并趋于稳定,表现为应变软化特性;同一筋材强度、不同围压的土工织物散体桩桩体强度所对应的轴向应变值比较接近;土工织物散体桩桩体的似黏聚力随筋材强度呈较好的线性增长关系,其较碎石的似黏聚力大很多,而筋材对桩体碎石的内摩擦角影响不大;建立了土工织物散体桩桩体强度及模量的理论计算公式,并采用试验值对理论公式进行修正,经修正后的结果与试验值吻合很好。
Large triaxial compression tests are performed on geosynthetic-encased granular columns(GEGC) with gravels in dense state. The stress-strain characteristics of GEGC with different strengths of polypropylene woven geotextiles and different confining pressures are investigated. The theoretical formulas to compute the strength and modulus of GEGC are then proposed. The results show that the GEGC exhibits dilative shear failure under triaxial compression, and mainly the horizontal textile slices at the shear band break. The shear angle is close to the rupture angle of the Mohr-Coulomb strength theory. The stress-strain curve of GEGC at the preliminary loading stage is concave down, then its stress approximately increases linearly up to a peak stress, and subsequently decreases to a stable value, showing strain softening characteristics. The axial strains corresponding to the strengths of GEGC with the same reinforcement strength under different confining pressures are even close. The quasi-cohesion of the GEGC has a good linear relationship with the strength of reinforcements, and it is much larger than that of the gravels, but the strength of reinforcements has little effect on the internal friction angle of the gravels of GEGC. Theoretical formulas are established to compute the strength and modulus of the GEGC. The formulas are verified through the test data, and the correction factors for the formulas are obtained. The results of the modified formulas agree well with the test ones.
Large triaxial compression tests are performed on geosynthetic-encased granular columns(GEGC) with gravels in dense state. The stress-strain characteristics of GEGC with different strengths of polypropylene woven geotextiles and different confining pressures are investigated. The theoretical formulas to compute the strength and modulus of GEGC are then proposed. The results show that the GEGC exhibits dilative shear failure under triaxial compression, and mainly the horizontal textile slices at the shear band break. The shear angle is close to the rupture angle of the Mohr-Coulomb strength theory. The stress-strain curve of GEGC at the preliminary loading stage is concave down, then its stress approximately increases linearly up to a peak stress, and subsequently decreases to a stable value, showing strain softening characteristics. The axial strains corresponding to the strengths of GEGC with the same reinforcement strength under different confining pressures are even close. The quasi-cohesion of the GEGC has a good linear relationship with the strength of reinforcements, and it is much larger than that of the gravels, but the strength of reinforcements has little effect on the internal friction angle of the gravels of GEGC. Theoretical formulas are established to compute the strength and modulus of the GEGC. The formulas are verified through the test data, and the correction factors for the formulas are obtained. The results of the modified formulas agree well with the test ones.
引文
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[2]陈建峰,王波,魏静,等.加筋碎石桩复合地基路堤模型试验研究[J].中国公路学报,2015,28(9):1–8.(CHEN Jian-feng,WANG Bo,WEI Jing,et al.Model tests of embankments on soft foundation reinforced with geosynthetic-encased stone columns[J].China Journal of Highway and Transport,2015,28(9):1–8.(in Chinese))
[3]RAJAGOPAL K,KRISHNASWAMY N R,LATHA G M.Behaviour of sand confined with single and multiple geocells[J].Geotextiles and Geomembranes,1999,17(3):171–184.
[4]WU C S,HONG Y S.Laboratory tests on geosyntheticencapsulated sand columns[J].Geotextiles and Geomembranes,2009,27(2):107–120.
[5]MIRANDA M,COSTA A D.Laboratory analysis of encased stone columns[J].Geotextiles and Geomembranes,2016,44:269–277.
[6]JTG E40—2007公路土工试验规程[S].2007.(JTG E40—2007 Test methods of soils for highway engineering[S].2007.(in Chinese))
[7]JGJ 79—2012建筑地基处理技术规范[S].2013.(JGJ 79—2012 Technical code for ground treatment of buildings[S].2013.(in Chinese))
[8]甘霖,袁光国.大型高压三轴试验测试及粗粒土的强度特性[J].大坝观测与土工测试,1997,21(3):9–12.(GAN Lin,YUAN Guang-guo.Large high pressure triaxial test and strength properties of coarse-grained soil[J].Dam Observation and Geotechnical Tests,1997,21(3):9–12.(in Chinese))
[9]阮龙飞,王永庆.中远船务启东海工基地坞口围堰工程的设计与施工[J].水利水电科技进展,2009,29(6):90–94.(RUAN Long-fei,WANG Yong-qing.Design and construction of dock-gate cofferdam of cosco Qidong marine base[J].Advances in Science and Technology of Water Resources,2009,29(6):90–94.(in Chinese))
[10]李传旦.加筋系袋式软体排在界牌水道整治工程中的应用[J].水运工程,1995(11):32–35.(LI Chuan-dan.Application of mattress with reiforced strip and tied sand bag in Jiepai waterway regulation works[J].Port&Waterway Engineering,1995(11):32–35.(in Chinese))
[11]杨艳燕,黄婧.应用不同缝纫方法的土工织物接缝强度比较研究[J].科技创业月刊,2007,20(6):176–177.(YANG Yan-qing,HUANG Jing.Comparison of the strength applied different seaming methods in geotextile[J].Pioneering with Science&Technology Monthly,2007,20(6):176–177.(in Chinese))
[12]陆士强.土工合成材料应用原理[M].北京:水利水电出版社,1994:1–21.(LU Shi-qiang.Application principles of geosynthetic materials[M].Beijing:China Water Power Press,1994:1–21.(in Chinese))
[13]秦尚林,陈善雄,韩卓,等.巨粒土大型三轴试验研究[J].岩土力学,2010,31(增刊2):189–193.(QIN Shang-lin,CHEN Shan-xiong,HAN Zhuo,et al.Large-scale triaxial test study of behavior of over coarse-grained soils[J].Rock and Soil Mechanics,2010,31(S2):189–193.(in Chinese))