基于大型叠环剪切试验的松散土石体强度及变形特性试验研究

Experimental study on the stress-strain and strength characteristics of loose rock-soil aggregates based on large-size stacked ring shear test

松散土石体广泛存在于自然界及实际工程中。以强风化板岩松散碎石料为研究对象,在对松散土石体制样方法成功尝试后,采用大型叠环式剪切试验机对不同相对密度(D_r)及不同干湿状态的松散土石体开展系统力学试验,得到以下主要结论:松散土石体颗粒组构间约束效应及机械咬合弱,其应力–应变曲线无显著峰值,大变形过程主要呈现为颗粒间的滑动摩擦与翻转;对于试验中所选取的3种D_r(0.30,0.35和0.40),干燥状态下松散土石体内摩擦角由D_r=0.30时的13.18°小幅升至D_r=0.40时的13.97°,黏聚力则由6.95 kPa略降至4.90 kPa,湿润和浸水状态下亦呈现此规律,表明相同干湿状态时该松散度区间内土石体强度基本保持稳定;干燥状态松散土石体剪应力峰值显著高于湿润及浸水状态,表现出显著的水敏感性;以D_r=0.40为例,经与常规三轴试验成果对比,凸显了采用叠环式剪切试验研究松散土石体工程特性的优势与适用性。研究初步揭示了松散状态土石体强度及变形特性,其显著的水敏感性可定量解释松散堆积体、松散滑坡等受水的影响而发生大变形或失稳的机制。

Loose rock-soil aggregates（LRA） is widespread in nature environment and practical engineering. A kind of LRA that composed by strong weathered slate is selected as the research object. Firstly, the sample preparation method for LRA is achieved successfully, then based on large-size stacked ring shear apparatus, a series mechanical tests for LRA under different relative density（Dr） and different dry and wet state is conducted, the research shows that, because the restraint effect and mechanical bite among LRA is weak, the peak value in stress-strain curve is not significant, the big deformation mainly composed by interparticle friction and rolling; for the three Dr（0.30, 0.35 and 0.40 respectively） conditions in experiment, when LRA keep dry state, the friction angle slightly increased from 13.18° （Dr = 0.30） to 13.97° （Dr = 0.40）, and cohesion slightly decreased from 6.95 kPa （Dr=0.30） to 4.90 kPa （Dr = 0.40）, it means the strength of LRA nearly keeps stable in this loose range, and when the sample is wet or submerged in water also meet to this law; the peak shear stress of dry LRA is much higher than that in wet and submerged in water, the water sensitivity characteristic is obvious; Dr = 0.40 is selected as a case study, based on a comparative test, it＇s clear that in researching engineering properties of LRA, stacked ring shear test is more advantages and applicability than conventional triaxial test. This research preliminarily reveals the strength and deformation characteristics of LRA, obvious water sensitivity of LRA are very useful in quantitatively explain the mechanism for large deformation and failure of loose deposit and landslide.