含粗颗粒花岗岩残积土大型直剪试验研究

Large direct shear test study on coarse-grained granite residual soil

花岗岩由于风化不完全,所以其砾石颗粒含量一般较高,颗粒直径从几厘米到数米不等,直径较大的颗粒通常演化成风动石、石碑等自然景观。粗颗粒含量对土体的强度变形特性以及颗粒破碎有一定的影响。本文利用大型直剪仪,对福州地区花岗岩残积土进行不同粗颗粒含量下的大型直剪试验,并且对每次试验前后进行颗分试验,以研究剪切过程颗粒破碎的影响。试验结果表明:混合土体在不同的竖向压力下,均表现出应变硬化特征;当粗颗粒含量较大(P 5≥30%)、竖向压力较高(σ=300 kPa、400 kPa)时,应力应变曲线没有出现峰值;随着粗颗粒含量的增加,花岗岩残积土的粘聚力c呈现先减小后增加的趋势,转折点在P 5=30%,而内摩擦角φ则一直呈现上升的趋势;粗粒土颗粒破碎率与粗颗粒含量和竖向压力皆呈正相关关系,但是竖向压力和粗颗粒含量较低时,粗颗粒之间互相接触的作用力没有达到粗颗粒承载极限值,颗粒破碎现象不明显。

Due to the incomplete weathering of granite,the content of gravel particles is generally high.Particle diameters range from a few centimeters to several meters,and larger diameter particles usually evolve into natural landscapes such as wind moving stones and stone monuments.The coarse particle content has a certain influence on the strength and deformation characteristics of the soil and the particle breakage.In this study,a large direct shear test was carried out on the granite residual soil in Fuzhou area under different coarse particle contents,and the particle test was carried out before and after each test to study the effect of particle breakage during the shear process.The test results show that the mixed soil exhibits strain hardening characteristics under different vertical pressures.When the coarse particle content is large(P 5≥30%)and the vertical pressure is high(σ=300kPa,400kPa),there is no peak in the stress-strain curve.With the increase of coarse particle content,the cohesive force c of granite residual soil first decreases and then increases.The turning point is P 5=30%,while the internal friction angleφalways shows an upward trend.The particle breakage rate of coarse-grained soil is positively correlated with the coarse particle content and vertical pressure,but when the vertical pressure and coarse particle content are low,the force of contact between the coarse particles does not reach the coarse particle bearing limit value,and the particle breakage phenomenon is not obvious.