生产建设项目工程堆积体边坡土壤侵蚀过程

发布时间：2018-04-25 02:24

本文选题：侵蚀过程 + 土石比　；参考：《西南大学》2015年硕士论文

【摘要】：随着生产建设项目数量不断增加和类型多样化,各种工程建设活动在施工过程中形成了大量的工程堆积体,使原地貌单元不断被塑造成特殊的人为地貌单元。工程堆积体作为一种物质组成极不均匀、离散程度很大的土石混合物,其结构松散、内摩擦角和粘聚力小、植物根系与有机质缺乏,是人为水土流失的主要地貌单元。在降雨或暴雨条件下,其强烈的水土流失破坏了土地资源和生态平衡。由于工程堆积体发生来源和土石含量不同,不同工程堆积体在地表径流冲刷作用下的土壤侵蚀特征差异性较大。本文以重庆市生产建设中广泛存在的紫色土堆积体和黄壤堆积体为研究对象,通过野外调查及土工试验方法,分析了其来源特征及物理性质变化特征；采用野外实地放水冲刷法及水力学、泥沙运动力学等理论,深入研究了不同土石比工程堆积体边坡坡面径流侵蚀过程中水动力学参数变化特征、坡面入渗、产流、产沙过程及细沟发育过程,建立了边坡坡面水沙关系方程及侵蚀临界条件；通过研究不同土石比工程堆积体物理性质、水动力学参数、径流泥沙及细沟发育特征,深入分析工程堆积体边坡坡面土壤侵蚀过程,并进一步探讨其边坡失稳机制,可为生产建设项目水土流失量预测和水土保持措施布置提供基本参数和技术依据。主要结论如下：(1)不同土石比工程堆积体边坡物理性质特性差异明显。土质(≤10mm)含量较高时,土体容重、非毛管孔隙均较小,而毛管孔隙较大,有利于边坡植物恢复,但其丰富土质或细颗粒是径流侵蚀的泥沙来源；而石质(10mm)较高时则相反,其水土流失发生的可能性较小。紫色土和黄壤堆积体土质含量均表现为土质偏土质土石混合质,其中紫色土依次为86.47%,79.19%和57.16%,黄壤依次为76.88%和60.69%,而石质含量则相反,除土质紫色土外,其它堆积体颗粒分布均匀且级配良好；紫色土堆积体十体容重以土质(1.317g/cm3)最小,土石混合质最大(1.562g/cm3),而黄壤堆积体为偏土质大于土石混合质；两种堆积体体边坡冲刷前的初始含水率均表现为土质偏土质土石混合质,土质含量多的堆积体较含量少的侵蚀危险性越高。工程建设形成的各种扰动地貌单元降低了项目区水源涵养功能,其中3a,2a和1a弃渣堆积体土壤有效库容比原地貌中最小的坡耕地依次减少了12.3%,16.8%,22.7%。(2)不同土石比工程堆积体边坡坡面径流侵蚀过程中水动力学参数变化明显。在边坡坡面侵蚀过程中水流流态以紊流和缓流为主,且各水动力学参数均呈不同程度波动式变化,其中流速v随冲刷时间呈“强-弱”波动、阻力系数f呈“弱-强”波动、剪切力τ呈“弱-强-弱”波动、功率P呈“强-弱”波动；紫色土和黄壤堆积体v均随放水流量增加呈幂函数增加,其幂指数最大和最小值分别为0.526,0.179；同一放水流量下土质或偏土质堆积的v均为最大,含石量越小时坡度及坡长对v影响较小。在一定条件下/随土石比的减小而增大,即土质偏土质土石混合质。τ受土石比和地形条件(坡度或坡长)影响很大,其随放水流量增加而增大且黄壤堆积体增加速率较紫色土快,其中紫色土堆积体在24.571～83.743 Pa之间,而黄壤为22.000～57.154 Pa。P也随放水流量增加而增大,两种堆积体P均表现为土质或偏土质大于土石混合质。(3)不同土石比工程堆积体边坡径流泥沙特征差异明显。入渗过程存在迅速降低(前3min)、缓慢降低(3-20min)和趋于稳定(20min后)三个阶段；紫色土和黄壤堆积体边坡在冲刷过程中的平均入渗率均表现为土质或偏土质大于土石混合质。产流过程则呈先增加后趋于稳定变化且存在不同程度突变或波动现象,产流率突变主要发生在产流后的9 min内；细沟侵蚀是影响产流量的重要因素；土石比对产流率有重要影响且随放水流量增加而增强,流量从5增加到25 L/min土质堆积体平均产流率增加量最大(19.337 L/min),而土石混合质最小。产沙过程呈连续性的多峰多谷特点且波动程度随放水流量增加而增强,细沟沟壁土体在重力作用下的崩塌脱落是造成产沙过程波动的重要原因。各水动力学参数对边坡坡面产沙量影响程度依次为γ Qγhγbγ,fγvγpγτ,其关联度在0.5183～0.9284之间,其中放水流量对产沙量影响最大；产沙量与放水流量可用M=0.0072Q 3.0287进行回归拟合,小流量下(5L/min)两种堆积体边坡平均产沙率均以土石混合质最大,而在大流量下则表现为土质偏土质土石混合质。(4)工程堆积体边坡坡面细沟侵蚀主要发生在产流3min后,可分为细沟发展阶段(3～45min)和稳定阶段(45min后),其径流含沙量呈波动减小的变化,而坡面细沟形态与产沙量密切相关。在径流冲刷后黄壤堆积体一般形成单一主沟,而紫色土堆积体则形成较多细沟；土石混合质紫色土堆积体边坡细沟条数、平均沟宽、平均沟深总体上随放水流量增加而增大,而细沟宽深比则相反,坡度增大会加剧沟底下切；当放水流量在10～30 L/min范围时其平均沟深在1.58～7.67 cm之间变化,而细沟平均密度在1.0～2.27m/m2。工程堆积体边坡坡面产沙量与平均沟深呈极显著正相关,其可用M=0.2187h2.9508进行回归拟合,而与侵蚀沟条数、平均沟宽、细沟密度以及细沟宽深比相关性不明显。(5)工程堆积体边坡细沟发育过程中的重力侵蚀发生在细沟两侧及沟头,是影响坡面产沙重要因素,也是导致坡面含沙量波动变化重要原因。边坡细沟发育过程中的重力侵蚀产沙贡献最大为96.6%,最小为10.9%,相同条件下重力侵蚀产沙贡献随边坡坡度增加而增大。不同土石比边坡坡面的侵蚀临界条件不同,偏土质紫色土堆积体边坡坡面发生侵蚀的临界水流功率较小(6.699N/(m·s)),而其土石混合质较大(7.265N/(m·s))；土石比相同时,黄壤堆积体临界水流功率小于紫色土堆积体,黄壤堆积体较紫色土堆积体易侵蚀；工程堆积体边坡侵蚀临界坡度随放水流量增加而减小,放水流量由10增加到30 L/min时土石混合质紫色土堆积体侵蚀临界坡度依次为35。,35。,30。,32.5。和30。。(6)工程堆积体边坡的入渗产流过程对边坡稳定性影响很大,其径流冲刷过程会直接造成坡面粗糙化、石砾化,而水分入渗过程则会增大土体含水率和土体容重,降低土体抗剪强度,造成边坡失稳。在非降雨条件和中雨(历时18h且雨量为23.3mm)条件下,基于SLOPE/W模型的紫色土堆积体边坡安全系数分别为2.863和1.600,非降雨条件下堆积体边坡滑动面发生在母岩表面与底层土壤之间,而中雨条件下则发生在堆积体底部与表层土壤之间,表层土壤在水分的作用下容易发育成软弱面或滑带土。工程堆积体边坡稳定性受多因素的复合作用,主要包括边坡土体工程特性、边坡形态和地质地貌等内部因素和降雨、边坡植被、外力作用、风化作用以及人类活动等外部因素。
[Abstract]:With the increasing number and variety of the production and construction projects, a large number of Engineering accumulation bodies have been formed during the construction process, and the original geomorphic units have been moulded into special man-made geomorphic units. Loose, internal friction angle and cohesive force and lack of plant root and organic matter are the main geomorphic units of artificial soil erosion. Under the conditions of rainfall or rainstorm, the strong soil erosion has destroyed the balance of land resources and ecological balance. The characteristics of soil erosion are different. In this paper, purple soil heap and yellow soil accumulation in Chongqing production and construction are studied. Through field investigation and geotextile test, the characteristics of the source and physical properties of the soil are analyzed. The characteristics of the variation of hydrodynamic parameters, the infiltration, runoff production, sediment production and rill development of the slope surface runoff erosion process of different soil and rock slope surface runoff are studied, and the relationship equation of water and sediment and the critical condition of the slope are established, and the physical properties of the different soil and stone than the engineering accumulation body are studied. Dynamic parameters, runoff and sediment and rill development characteristics, in-depth analysis of soil erosion process in the slope of Engineering accumulation slope, and further discuss the mechanism of slope instability, which can provide basic parameters and technical basis for the prediction of soil erosion and soil and water conservation measures in production and construction projects. The main conclusions are as follows: (1) different soil and rock ratio Engineering The physical properties of the pile slope are very different. When the content of soil (less than 10mm) is high, the bulk density of soil and the non capillary pores are small, but the pores of the capillary are large, which are beneficial to the restoration of the slope plants. But the rich soil or fine particles are the sediment sources of runoff erosion; while the high 10mm is the opposite, and the possibility of soil erosion is more likely. The soil content of purple soil and yellow soil accumulation body is all soil mass soil and stone mixture, purple soil is 86.47%, 79.19% and 57.16%, yellow soil is 76.88% and 60.69% in turn, and the content of stone is the opposite. Besides the purple soil, the other accumulation body particles are evenly distributed and the gradation is good, and the ten body bulk density of purple soil heap body is soil. The mass (1.317g/cm3) is the smallest, the soil and rock mixture is the largest (1.562g/cm3), but the yellow soil accumulation body is larger than the soil and rock mass, and the initial water cut before the two kinds of pile body slope scour is all soil mass soil and rock mixture, the less accumulation of soil content is more dangerous. The dynamic geomorphic unit reduced the water conservation function of the project area, in which the soil effective storage capacity of 3a, 2a and 1A residue deposits decreased by 12.3%, 16.8%, 22.7%. (2), and the variation of hydrodynamic parameters in the erosion process of slope surface runoff in the slope surface of the slope. The flow state is mainly turbulence and slow flow, and the hydrodynamic parameters are fluctuating in varying degrees. The flow velocity V fluctuates with the "strong weak" fluctuation with the scouring time, the resistance coefficient f is "weak strong" fluctuation, the shear force is "weak strong weak" fluctuation, the power P is "strong weak" wave, and the V of purple soil and yellow soil accumulation body increases with the discharge flow rate. The maximum power exponent and the minimum value of the power exponent are 0.526,0.179, and the V of the soil and the partial soil under the same discharge flow is the largest, the hourly slope and the length of the rock are less affected by the v. In certain conditions / with the decrease of the soil and rock ratio, the soil and rock mass mixture. Tau is subjected to the soil rock ratio and the topographic strip. The slope or slope length has great influence, which increases with the increase of discharge flow and the increase rate of the yellow soil accumulation body is faster than the purple soil, and the purple soil heap is between 24.571 and 83.743 Pa, and the yellow soil is 22 ~ 57.154 Pa.P with the increase of the discharge flow, and the two kinds of accumulation body P are all soil or more than the soil and rock mass. 3) the difference of runoff and sediment characteristics of different soil and rock slope is obvious. Infiltration process has a rapid decrease (former 3min), slow decrease (3-20min) and stabilization (after 20min), and the average infiltration rate of purple soil and yellow soil accumulation slope in the process of erosion is both soil and soil mass greater than soil and rock mixture. The process is increased first and then tends to be stable and varied, and there are different degrees of mutation or fluctuation. The mutation of the rate of production mainly occurs in the 9 min after the flow. The rill erosion is an important factor affecting the flow rate; the soil and stone has an important influence on the rate of production and increases with the increase of the discharge flow, and the flow rate increases from 5 to 25 L/min soil accumulation. The increase of average yield is the largest (19.337 L/min), but the soil and rock mixture is the smallest. The process of sediment yield is a continuous multi peak and multi Valley characteristic and the fluctuation degree increases with the increase of discharge flow. The collapse and fall off of the soil under the action of gravity is the main reason for the fluctuation of the sand production process. The degree of influence in turn is gamma Q gamma h gamma B gamma and f gamma V gamma P gamma ray. The correlation degree is between 0.5183 and 0.9284. The discharge flow rate has the greatest impact on the sediment yield, and the sediment yield and discharge flow can be fitted with M=0.0072Q 3.0287, and the average sediment yield of the two accumulation slopes under small flow (5L/min) is the largest in the soil and rock mass, and under the large flow rate. (4) the rill erosion of the slope surface of the slope of the engineering accumulation mainly occurs after the flow of 3min, which can be divided into the development stage of the rill (3 ~ 45min) and the stable stage (after 45min), and the sediment concentration in the runoff is fluctuating and decreasing, and the form of the rill in the slope is closely related to the sediment yield. In general, the body forms a single main trench, while the purple soil heap forms more rill; the number of slill strip in the slope of the soil and rock mixed purple soil heap is wide. The average furrow depth increases with the increase of the discharge flow, while the width depth ratio of the rill is the opposite, and the increase of the slope will aggravate the bottom cutting. When the discharge flow is in the range of 10~30 L/min, The average furrow depth varies between 1.58 and 7.67 cm, while the average density of the rill average density is very significant positive correlation with the average furrow depth in the slope surface of the engineering accumulation body from 1 to 2.27m/m2.. It can be regressed with M=0.2187h2.9508, but the correlation with the number of gully, the average groove width, the rill density and the width depth ratio of the rill are not obvious. (5) the construction of the project is not obvious. Gravity erosion occurred on both sides of the rill and the head of trench during the development of the rill of the slope. It is an important factor affecting the sediment yield in the slope. It is also an important cause of the fluctuation of the sediment content in the slope. The maximum contribution of gravity erosion to sediment yield is 96.6% and the minimum is 10.9%. The contribution of gravity erosion to sand production under the same condition is with the slope slope. The critical flow power of different soil and rock is different than that of slope slope, and the critical flow power of the slope surface erosion of the purple soil heap slope is smaller (6.699N/ (M. S)), and the soil and rock mixture is larger (7.265N/ (M. S)), and the critical flow power of the yellow soil accumulation body is less than the purple soil heap, Huang Rangdui. The critical slope of the slope erosion of the engineering accumulating body decreases with the increase of the discharge flow, and the critical slope of the soil and rock mixed purple soil heap erosion is 35., 35., 30., 32.5. and 30.. (6) Engineering heap slope influence on the slope stability in order to reduce the critical slope of the slope erosion of the slope of the engineering accumulation body. The critical slope of the slope erosion of the slope of the engineering accumulation body decreases with the increase of the discharge flow. The process of runoff scouring will directly cause slope roughness and gravel, and water infiltration will increase soil moisture content and soil bulk density, reduce soil shear strength and cause slope instability. Under the condition of non rainfall and rain (18h and rainfall of 23.3mm), the slope safety system based on SLOPE/W model is based on the model of purple soil. The numbers are 2.863 and 1.600 respectively. The sliding surface of the pile slope under non rainfall conditions occurs between the surface of the parent rock and the bottom soil, while the medium rain occurs between the bottom of the pile and the surface soil. The surface soil is easily developed into soft surface or slide soil under the action of water. The stability of the slope of the engineering accumulation body is complex by multiple factors. The effects mainly include the engineering characteristics of slope soil, the internal factors of slope shape, geological and geomorphology and other internal factors, such as rainfall, slope vegetation, external force, weathering and human activities.

【学位授予单位】：西南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：S157

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