添加砾石对崩岗岩土无侧限抗压强度的影响

Effects of gravel addition on unconfined compressive strength of Benggang soil

崩岗是中国南方红壤地区常见的一种土壤侵蚀类型,该研究对砾石含量、形状和直径三因素进行正交设计,分析不同组合的砾石对崩岗岩土无侧限抗压强度的影响。结果表明,崩岗4层土体的无侧限抗压强度均值由大到小依次为淋溶层A、黏化层Bt、淀积层B、母质层C,效果较好的处理分别为:淋溶层A,质量分数15%,直径2~4 mm,圆砾;黏化层Bt,质量分数15%,直径5~7 mm,圆砾;淀积层B,质量分数15%,直径5~7 mm,圆砾;母质层C,质量分数15%,直径5~7mm,圆砾。4层土体的轴向应力随轴向应变均呈急剧上升、急剧下降、减速衰减和衰减稳定4个阶段,但砾石复合土高于未加砾石土。4层土体在较好处理下的无侧限抗压强度分别比未加砾石土提高59.56%、71.70%、49.51%和83.64%,且二者呈线性递增函数关系(R2=0.99)。添加砾石的土柱在受压时破坏程度较小,其中淋溶层A和母质层C主要集中为下部破碎,黏化层Bt和淀积层B主要为土柱一侧破碎。该研究可为崩岗侵蚀预防和分层治理提供理论依据。

Benggang,a typical geo-hazard,is widely distributed in the granite area of southern China.It is characterized by strong sudden onset and rapid development,and is usually accompanied by a large amount of soil and water loss,which poses a serious threat to the ecological environment.Previous studies have focused on Benggang soil erosion process and the influencing factors,sediment yield characteristics and hydrodynamics mechanism.However,there is still limited study on mechanical strength effect of gravel addition on Benggang soil and its engineering application.This study explored the effects of gravel addition on unconfined compressive strength of Benggang soil.Different combinations of gravel content(5%,10%,and 15%),diameter(2-4,5-7,and 8-10 mm),and shape(round and angular gravels)were considered.In addition,soil without gravel addition was considered as control.In June 2018,the Benggang soil was sampled.Eluvial layer A,argic layer Bt,deposition layer B,and parent layer C were distributed along the soil profile.The physic-chemical properties of these soil samples were measured.The unconfined compressive strength values of different combinations of soils were also determined.The results showed that the eluvial layer A had relatively uniform particle size,good structure,and fine texture.However,the contents of particle sizes differed greatly in the other three layers,with weak adhesive,poor texture,and loose particles.The average value of unconfined compressive strength of different combinations was the highest in the eluvial layer A,followed by argic layer Bt,deposition layer B and parent layer C.The unconfined compressive strengths of four soil layers were higher in combinations of 15%gravel content,diameter of 2-4 and 5-7 mm,and round shape.The gravel additions increased soil compressive strength by elevating the friction,cohesion and occlusion area of soil particles.The axial stress of all combinations showed the same variation tendency with the increase of axial strain,with four stages of rapid increase,sharp decrease,slow decrease and stable decrease.The axial stress of soil with gravel addition was higher than that of soil without gravel,especially in the eluvial layer A and argic layer Bt.Compared with soil without gravel addition,the unconfined compressive strength of soil with gravel addition increased by 59.56%(eluvial layer A),71.70%(argic layer Bt),49.51%(deposition layer B),and 83.64%(parent material layer C),respectively.A positive linear function could describe the relationship between the compressive strength of soil with and without gravels in the four soil layers.Thus,the addition of gravel enhanced the mechanical strength of Benggang soil obviously.The broken degree of soil without gravel was more severe than that of soil with gravel.Overall,the addition of gravel improved soil compressive strength,while the compressive mechanism in different soil layers was quite different.The difference was affected by the friction and concavity of particle shape,and the physic-chemical properties for different soil layers.The results above laid basis for the prevention and control of Benggang erosion,and proposed engineering practice instructions for the treatment of different soil layers.