宜巴高速公路巴东组软岩碎屑土夹层的非饱和特性研究

发布时间：2018-06-06 08:38

本文选题：巴东组软岩 + 路堑边坡　；参考：《中国地质大学》2014年博士论文

【摘要】：巴东组红层在我国鄂西、湘西北、川东和黔北分布很广,其中三叠系中统巴东组紫红色软岩在巴东县辖区内分布广泛,该软岩属于人们俗称的“巴二”地层,是典型的“易滑地层”。巴东组软岩含有一定量的伊利石和蒙脱石或伊利石与蒙脱石互层结构,导致其易发生水-岩相互作用,使其具有一定的膨胀和崩解特性,加速其物理化学风化进程。巴东组软岩中软弱夹层十分发育,而控制岩体变形破坏特性的往往是这些软弱夹层,许多岩体变形失稳都是沿软弱夹层面产生。随着西部大开发战略的推进,公路、铁路建设事业蓬勃发展,而高速铁路、公路在上述地区的修建不可避免的会穿越上述地层,软弱夹层对边坡工程产生的病害不断发生。特别是对于修建于巴东组软岩地区内的高速公路,开挖形成的路堑边坡失稳事故时有发生。宜昌-巴东高速公路有30公里穿越“巴东组”地层,开挖形成的部分路堑边坡发育碎屑土夹层,一定条件下边坡有沿碎屑土夹层产生失稳破坏的风险。研究区部分路堑边坡发育碎屑土夹层,降雨之后,此类边坡的稳定性会随碎屑土夹层含水状态的增大而变差,有失稳破坏的风险。目前针对研究区此类边坡的病害,可借鉴的成熟理论和经验并不丰富。为此,本文结合宜巴高速路某典型含碎屑土夹层的巴东组软岩路堑边坡,以碎屑土夹层作为研究对象,从非饱和土角度研究其工程特性,以全面了解水对该类软弱夹层工程特性的影响,进而分析其对软岩路堑边坡稳定性的影响。研究成果对指导当地工程实践活动,具有重要的工程意义。本文在收集研究区巴东组软岩及碎屑土夹层的地层沉积资料、路堑边坡病害特征等工作基础上,通过X射线衍射矿物鉴定试验、化学成分分析试验、基本物理力学性质试验、土水特性试验、非饱和土强度试验、非饱和土蠕变试验、数值模拟试验等手段,详细研究了碎屑土夹层的矿物组成、化学成分、物性指标、土水特性、非饱和强度特性、非饱和蠕变特性、不同含水状态对路堑边坡稳定性影响,定性分析了巴东组软岩碎屑土夹层的工程特性,定量研究了基质吸力对碎屑土夹层强度与变形特性的影响,并总结其不同基质吸力状态对软岩路堑边坡稳定性的影响。取得的研究成果如下： (1)巴东组软岩碎屑土夹层的工程地质性质与物理力学性质研究。通过对宜昌-巴东高速公路软岩路堑边坡发育的软弱夹层的工程地质性质研究,并结合现场地质调查,初步掌握了研究区软弱夹层的赋存环境,掌握了其成因及形成过程,并对其进行了分类。针对研究区路堑边坡的主要工程问题,重点调查了巴东组软岩碎屑土夹层的分布特征,介绍了其对路堑边坡存在的潜在危害,工程中应对此类软岩路堑边坡加以重视。利用X-矿物衍射试验、化学全分析试验,并结合碎屑土夹层的基本物理力学性质试验,得到了碎屑土夹层的矿物及化学成分、基本物性指标,初步掌握了水对其强度特性的影响,进而为后期定量开展水对其强度与变形性质影响提供参考依据。研究表明巴东组软岩碎屑土夹层的粘土矿物含量较高,水敏感性强,水对其工程特性影响较大,碎屑土夹层的粘聚力、内摩擦角随含水率的增大而减小,强度性质变差。密实状态对碎屑土夹层的强度也具有一定的影响,夹层土越密实,其粘聚力越大,整体强度也越大。 (2)巴东组软岩碎屑土夹层的土水特性。利用压力板仪测试了不同干密度、不同初始含水率、不同颗粒级配碎屑土夹层的土水特征曲线,采用VG模型对土水曲线进行拟合,求取各拟合参数,绘制延伸的土水特曲线。研究表明碎屑土夹层的基质吸力随含水率的增大而减小。干密度相同,大初始含水率土样的土-水特征曲线落在小初始含水率土样的曲线上方,初始含水率越高,基质吸力随含水率变化越敏感。随着初始含水率的增大,土样的进气值、残余含水率都随之增大。进气值随着初始含水率增大而增大的幅度,又随着土样干密度的增大而降低；对于初始含水率相同的土样,干密度越大,土样的进气值也越大,这种变化的增幅又随土样初始含水率的增大而降低。相同初始含水率、不同干密度土样的土水特征曲线的位置和形状各不相同,在低基质吸力范围内,小干密度土样的土水特征曲线落在大干密度土样的曲线上方,这主要是因为小干密度土样的饱和含水率更高。在高基质吸力范围内,小干密度土样的土水特征曲线落在大干密度土样的曲线下方,表明小干密度土样的基质吸力随含水率变化更敏感。干密度变大,土样的基质吸力随含水率变化的敏感性降低,残余含水率确有所增高,持水能力增强。对比不同颗粒级配土样的土水特征曲线,可见粗粒含量高土样的土水特征曲线在下方。相同含水率下,粗粒含量少的土样的基质吸力值更大,饱和含水率更低。粗颗粒含量高的土样的进气值更低,持水能力更强,残余含水量也低。总之巴东组软岩碎屑土夹层的土-水特性明显,孔隙结构(干密度、初始含水率)、粒径对碎屑土夹层的土-水特性影响很大,研究成果对从非饱和土力学角度分析不同物理状态对碎屑土夹层的工程性质及边坡稳定性的影响具有重要的参考意义。 (3)巴东组软岩碎屑土夹层的非饱和强度与变形特性。利用GDS非饱和三轴仪开展了碎屑土夹层的饱和、非饱和三轴压缩试验,结果表明基质吸力对巴东组软岩碎屑土夹层的强度与变形特性影响显著。饱和三轴试验表明碎屑土夹层土样在不同围压下的应力-应变都呈现应变硬化特性,偏应力都随着应变的增加而增大,最终达到峰值强度。相同应变下,土样的偏应力随围压的增大而增大,峰值强度随围压的增大而明显增大。由应变-体变曲线可见,土样体积在剪切过程中均发生剪缩,随着剪切的进行体变量最终趋于稳定。土样剪切产生的体变也随着围压的增大而增大,剪缩效应也越明显,说明围压对碎屑土夹层的变形性质影响显著。根据试验求取了巴东组软岩碎屑土夹层的饱和强度指标,粘聚力c为2.25kPa,有效内摩擦角φ'为31。。碎屑土夹层的非饱和强度试验表明其应力-应变曲线都呈现应变硬化特性,偏应力随应变增加而快速增大,最终趋于稳定值,达到峰值强度。对比不同基质吸力下土样的应力-应变曲线,可见相同应变下土样的偏应力随基质吸力的增加而增加,破坏时的峰值强度也随着增大,说明土体的抗剪强度随基质吸力的增大而明显增大。对比土样的应变-体变曲线,可见土样体积在剪切的过程中均发生剪缩,最终趋于稳定,基质吸力越大,土样剪切产生的体变量也越大,说明基质吸力对碎屑土夹层的变形性质影响显著。根据试验结果,求取了非饱和碎屑土夹层的强度指标,c'为2.25kPa,φ'为31°，φb,矿在基质吸力100kPa、200kPa、300kPa、400kPa下分别为30°、24°、23°、23°,可见φb不是常数,随基质吸力的增大而不断减小,最终趋于定值。在工程实践中,应根据巴东组软岩碎屑土夹层的实际含水状态,选择相应的φb角进行强度计算。不同基质吸力下碎屑土夹层的总粘聚力均大于饱和土的粘聚力,且基质吸力越大,总粘聚力越大,即碎屑土夹层的非饱和抗剪强度远远大于饱和抗剪强度,基质吸力对巴东组软岩碎屑土夹层的强度与变形性质影响显著,其抗剪强度随着基质吸力的增加而增大。 (4)巴东组软岩碎屑土夹层的非饱和蠕变特性。利用GDS非饱和三轴仪对碎屑土夹层开展了非饱和蠕变试验研究,分析了其蠕变特性,建立了非饱和蠕变模型,并对模型进行了验证。同时求取了碎屑土夹层的长期强度,为后期路堑边坡稳定性分析提供参考依据。研究结果表明巴东组软岩碎屑土夹层的非饱和蠕变特性显著,基质吸力对其蠕行为影响明显,碎屑土夹层蠕变后的长期强度明显降低,对于含巴东组软岩碎屑土夹层的路堑边坡而言,这些特性对其稳定性不利,应加以重视。巴东组软岩碎屑土夹层土样的非饱和蠕变曲线呈现一定的非线性,应力水平越高,变形随时间增长越明显。对于不同基质吸下土样的蠕变曲线,当偏应力大小相同时,基质吸力越小,土样产生的应变越大,即同一应力水平下含水量高的土样产生的变形更大,这种趋势在高应力水平时更明显。当土样的基质吸力大小相同时,偏应力越大,土样产生的轴向应变越大。根据蠕变曲线,将碎屑土夹层的非饱和土蠕变过程分为蠕变开始、衰减蠕变、等速蠕变三个阶段。根据蠕变试验数据,建立了3种预测巴东组软岩碎屑土夹层蠕变特性的非饱和经验蠕变模型,其中2种模型是基于Singh-Mitchell蠕变模型、Mesri蠕变模型,对其进行改进而得到的,使其模型中包含了基质吸力变量。为了能更好的预测碎屑土夹层的蠕变行为,分别对应变-时间曲线、应力-应变曲线进行非线性拟合,组合函数建立了本文提出的包含基质吸力-应力-应变-时间的非饱和蠕变模型。结果表明改进的Mesri模型及本文建立的蠕变模型基本能够实现预测蠕变曲线的开始阶段、衰减蠕变阶段、等速蠕变阶段,虽然当偏应力水平较高时,在等速蠕变阶段,预测曲线都高于试验点,模型预测存在偏差,但对于工程实践来说,尤其是巴东组软岩碎屑土夹层,误差在可接受的范围内。综合对比3种非饱和蠕变模型的预测精度,可见改进的Mesri模型预测碎屑土夹层的蠕变行为的精度较好,本文建立的非饱和蠕变模型效果一般,改进的Singh-Mitchel模型预测效果较差,传统的Mesri模型、Singh-Mitchel模型预测效果最差。根据蠕变试验数据,利用等时曲线法确定了碎屑土夹层土的长期强度值。可见不同基质吸力下土样的长期强度较瞬时强度都有大幅降低,强度产生折损,损失率在34%-62%之间,说明巴东组软岩碎屑土夹层在荷载的长期作用下强度值会越来越低。随着基质吸力的增大,碎屑土夹层的长期强度也呈线性增大的趋势,即碎屑土夹层的含水率越低,其在荷载长期作用下的强度越高。碎屑土夹层的基质吸力越小,强度损失率越大,即对于巴东组软岩碎屑土夹层而言,含水率越高,其在荷载长期作用下的强度越小,强度损失越大,并且随着含水率的不断增大,强度损失率增加的幅度也不断增大。 (5)利用数值模拟技术分析了是否含碎屑土夹层、碎屑土夹层的不同基质吸力状态对巴东组软岩路堑边坡稳定性的影响。结果表明碎屑土夹层对巴东组软岩路堑边坡的稳定性影响很大,不含碎屑土夹层的软岩路堑边坡在天然工况下是很稳定的,安全系数很高。当巴东组软岩路堑边坡发育碎屑土夹层时,天然工况下也是稳定的,但碎屑土夹层出现了塑性屈服带,边坡前缘产生了剪切应变及位移增量,在外力(地震)及降雨条件下,碎屑土夹层可能成为路堑边坡失稳破坏的滑动面。对于含碎屑土夹层的巴东组软岩路堑边坡而言,碎屑土夹层的不同基质吸力状态对边坡稳定性影响也很大。当碎屑土夹层的基质吸力不断减小时,碎屑土夹层会产生塑性屈服直至贯通,边坡后缘由于张拉应力而产生的塑性区也不断增大,主要集中在碎屑土夹层前缘的剪应变增量范围也明显增大,最终贯通整个碎屑土夹层,夹层及坡体后缘的剪应力增量最大,夹层上部坡体各部位的位移量也不断增大,最后直至整个边坡产生滑动破坏,碎屑土夹层成为滑动面。通过计算分析巴东组软岩路堑边坡的稳定性系数,表明天然工况下,含碎屑土夹层路堑边坡的稳定性远远低于不含碎屑土夹层的路堑边坡。对于发育顺层碎屑土夹层的巴东组软岩边坡而言,碎屑土夹层的基质吸力对边坡的稳定性影响很大,碎屑土夹层的基质吸力越小,边坡的稳定性越差。巴东组软岩碎屑土夹层存在一个界限基质吸力状态,当碎屑土夹层的基质吸力等于该值时,边坡处于极限平衡状态。当碎屑土夹层的基质吸力高于该值时,边坡稳定。当碎屑土夹层的基质吸力低于该值时,碎屑土夹层在坡体应力作用下更容易产生塑性屈服,甚至剪切破坏,边坡可能沿碎屑土夹层产生滑动破坏。对于实际工程,可以根据当地气候条件及碎屑土夹层发育分布情况,在开挖过程中综合预判此类边坡的稳定性及碎屑土夹层能够引起其失稳破坏的含水率范围。研究成果为含碎屑土夹层的巴东组软岩路堑边坡稳定性分析及防护治理提供了参考依据。 (6)高速公路建设过程中不可避免的开挖形成路堑边坡,对于研究区的巴东组软岩路堑边坡而言,如果边坡发育顺层碎屑土夹层,则对边坡稳定性十分不利。在综合分析碎屑土夹层的工程特性、非饱和特性及对路堑边坡稳定性影响的基础上,为预防此类路堑边坡病害的产生,从公路勘察、施工以及后期运营三个方面提出了一些预防措施与建议。
[Abstract]:The red beds of Badong Formation are widely distributed in eastern Hubei , northwest of Hunan , eastern Sichuan and northern Guizhou .

In this paper , the influence of water on the slope stability of soft rock graben is analyzed from the viewpoint of unsaturated soil . The research results are of great significance to guide local engineering practice activities .

In this paper , the influence of matrix suction on the stability of soft rock slope is studied by means of X - ray diffraction mineral identification test , chemical composition analysis , basic physical mechanical property test , soil water characteristic test , unsaturated soil strength test , unsaturated soil creep test and numerical simulation test .

( 1 ) The engineering geological property and the physical and mechanical properties of soft rock debris soil interlayer in Badong Formation are studied . Based on the study of the engineering geological properties of the soft interlayer in Yichang - Badong expressway , the authors have studied the distribution characteristics of the soft interlayer in the study area .

( 2 ) The soil water characteristics of soft rock debris soil interlayer in Badong Formation . The soil water characteristic curves of different dry density , different initial water content and different particle size distribution clastic soil layers are tested by using a pressure plate instrument . The soil water curve is fitted by VG model . The soil - water characteristic curve of the soil sample with the same dry density decreases with the increase of water content . The higher the initial moisture content , the soil - water characteristic curve of the soil sample increases . As the initial water content increases , the water content of the soil sample increases . The air inlet value decreases with the increase of the initial water content and decreases with the increase of the dry density of the soil sample .
The soil water characteristic curve of small dry density soil sample falls below the curve of dry density soil sample . The soil water characteristic curve of small dry density soil sample falls below the curve of soil sample with high dry density .

( 3 ) The unsaturated strength and deformation characteristics of soft rock debris soil interlayer in Badong Formation . The saturated and unsaturated triaxial compression tests of debris soil interlayer were carried out by using a non - saturated triaxial apparatus . The results show that the matrix suction has a significant influence on the strength and deformation characteristics of the soft rock debris soil interlayer in the Badong Formation .

The saturated triaxial test shows that the stress - strain of the debris soil sample under different confining pressures exhibits strain hardening characteristics , and the partial stress increases with the increase of confining pressure , and the peak strength increases with the increase of confining pressure . The stress - strain curves of soil samples under different matrix suction are compared with the increase of matrix suction . The results show that the shear strength of soil samples increases with the increase of matrix suction .

( 4 ) The non - saturated creep property of soft rock debris soil interlayer in Badong Formation is studied . The creep property is analyzed , the unsaturated creep model is established , and the model is verified .

Based on the creep test data , the creep behavior of soil samples with high water content is more obvious . The results show that the improved Mesri model and the creep model can be used to predict the creep behavior of debris soil interlayer . The higher the water content , the smaller the strength under the long - term load of the load , the greater the strength loss , and the increase of the strength loss rate as the water content increases .

( 5 ) The influence of different matrix suction states of debris soil interlayer on the stability of soft rock graben slope in Badong Formation is analyzed by using numerical simulation technique .

Based on the analysis of the stability coefficient of the soft rock slope in the Badong Formation , it is shown that the stability of the debris - soil interlayer slope is far lower than that of the cutting slope with no debris - soil interlayer under the natural working condition . The slope stability is more easily caused by the matrix suction of the debris - soil interlayer . When the matrix suction of the debris - soil interlayer is higher than the value , the slope is stable . When the matrix suction of the debris - soil interlayer is equal to the value , the slope stability is more easily generated . When the matrix suction of the debris - soil interlayer is equal to the value , the stability of the slope and the soil interlayer of the debris soil can be comprehensively pre - determined during the excavation process .

( 6 ) During the construction of the expressway , the unavoidable excavation forms the cutting slope . For the soft rock slope of the Badong Formation in the study area , the stability of the slope is very unfavorable . Based on the comprehensive analysis of the engineering characteristics , unsaturated characteristics and the influence of the stability of the cutting slope , some preventive measures and suggestions are put forward from three aspects of highway survey , construction and later operation .
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：U416.1

【参考文献】