崩岗岩土体无侧限抗压强度及室内改良技术研究

发布时间：2018-06-16 18:15

本文选题：崩岗 + 无侧限抗压强度　；参考：《华中农业大学》2017年硕士论文

【摘要】：崩岗是中国南方热带、亚热带花岗岩低山丘陵地区水土流失的一种特殊类型。崩岗侵蚀的发生发展与其岩土体力学性质有着密切的联系,由于花岗岩风化壳土体疏松深厚,且内部存在软弱结构面,并伴随有大量的原生节理和构造裂隙,导致崩岗岩土特性差异明显,因此,崩岗不同层次岩土体力学性质不稳定。崩岗崩壁岩土体在无侧向约束的条件下,抵抗轴向压力发生剪切破坏的极限强度称为无侧限抗压强度,是反映土体力稳性的一项重要指标。因此,有必要对崩岗岩土体无侧限抗压强度进行系统性研究,这对于丰富和完善崩岗岩土体力学性质具有重要的指导意义。目前,崩岗侵蚀的治理中多采用工程措施和生物措施相结合的方法,但关于新工艺和新技术却应用不足,同时由于崩岗岩土体粘结性差,且在现实中存在剧烈的干湿变化,极易导致崩岗崩壁失稳坍塌。因此,有必要对崩岗岩土体进行适当改良,以提高崩岗土体强度和稳定性。本文以湖北省咸宁市通城县典型崩岗作为研究对象,通过野外调查与室内试验相结合的方法,分别开展典型崩岗不同层次岩土体基本特性研究,揭示崩岗侵蚀成因的物质基础;制备重塑土试样研究崩岗不同层次岩土体无侧限抗压强度,探讨干密度和含水率以及干湿循环效应对无侧限抗压强度的影响;利用黄麻纤维和石灰对崩岗不同层次岩土体进行改良研究,探讨改良崩岗岩土体无侧限抗压强度的变化规律。得到相关研究结果如下:(1)崩岗土体容重的变化规律为碎屑层斑纹层红土层表土层;总孔隙度的变化规律为碎屑层表土层红土层斑纹层;土壤机械组成变化规律为从红土层开始随着采样深度的增加,砂粒含量不断增加,而黏粒含量则不断减少;红土层液塑限含水量均为最大,而碎屑层液塑限含水量均为最小;土壤有机质含量随着土层深度的增加而显著减少,其中碎屑层有机质含量极少;崩岗土体的pH值均较低,呈酸性;碎屑层阳离子交换量最小;而游离氧化铁含量则存在明显差异。(2)崩岗土体无侧限抗压强度随着含水率的增加呈先增加后减小的趋势,且出现最大值时的含水率都在15%或20%左右;随着干密度的增加,无侧限抗压强度先缓慢增加后呈近似线性减小,且减幅较大,出现最高值时的干密度均为1.30 g/cm3左右;干密度和含水率对崩岗岩土体无侧限抗压强度产生了明显的交互效应,在等值线图中可分为三个区域:干密度主效应区、含水率主效应区、干密度和含水率交互效应区,在三维曲面图存在“山谷”、“山峰”、“山脊”等曲线形态。(3)崩岗土体的无侧限抗压强度均随着干湿循环次数的增加而逐渐衰减,直至最后趋于稳定,其变化规律大致分为3个阶段:急速衰减、减速衰减、衰减稳定,其中在第1次干湿循环后衰减幅度最大,分别为26%、15%、40%和49%,在第2~4次干湿循环后衰减幅度逐渐减小,在第5次干湿循环后基本保持不变;随着干湿循环次数的增加,崩岗土体无侧限抗压强度总体表现为表土层红土层斑纹层碎屑层。崩岗土体无侧限抗压强度与干湿循环次数之间呈现较好的指数函数关系,且在通过考虑崩岗不同层次土体深度比和干湿循环次数的共同影响下,建立无侧限抗压强度的预估模型。(4)通过对崩岗土体的正交试验设计,初选出黄麻纤维的最优加筋条件,其中表土层:加筋长度15 mm、加筋率0.35%、整体加筋;红土层:加筋长度15 mm、加筋率0.25%、上部加筋;砂土层:加筋长度15 mm、加筋率0.35%、整体加筋;碎屑层:加筋长度15 mm、加筋率0.30%、下部加筋;黄麻纤维加筋土的应力-应变曲线变化规律可分为3个阶段:急速衰减阶段、减速衰减阶段、衰减稳定阶段。在最优加筋条件下崩岗土体的无侧限抗压强度分别提高了27.81%、29.73%、23.26%、39.58%。(5)采用响应面设计优化得出掺灰率、龄期、含水率三者最佳配比组合。表土层:掺灰率8.99%、龄期28 d、含水率25%;红土层:掺灰率8.98%、龄期28 d、含水率25%;斑纹层:掺灰率5.84%、龄期18 d、含水率20%;碎屑层:掺灰率6.58%、龄期28 d、含水率23%。(6)在今后的崩岗治理工作中,应考虑改良材料的组合使用以提高崩岗岩土体的力学性能,黄麻纤维是一种成本低且绿色环保的改良材料,可在崩岗表土层和红土层治理工作中加以利用,以提高土体强度;而石灰是一种效果明显且施工方便的改良材料,可在崩岗斑纹层和碎屑层治理工作中加以利用。
[Abstract]:Avalanche is a special type of soil erosion in the low mountain and hilly region of tropical granite in southern China. The occurrence and development of the landslide erosion is closely related to the mechanical properties of rock and soil, because the soil of the granite weathering crust is loose and deep, and there is a weak structural surface in the interior, and there are a large number of primary joints and structural fractures. Therefore, the mechanical properties of rock and soil in different layers are not stable. Under the condition of no lateral constraint, the ultimate strength of the rock and soil body of the collapse and avalanche is called the unconfined compressive strength, which is an important index to reflect the stability of the earth's physical strength. Therefore, it is necessary to take the landslides. The systematic study of unconfined compressive strength of soil is of great guiding significance for enriching and perfecting the mechanical properties of the rock mass. At present, many methods are used to combine the engineering measures and biological measures in the treatment of the landslide erosion, but the new technology and new technology are not applied, at the same time, the cohesiveness of the landslides is poor. There is a severe dry and wet change in reality, which is very easy to cause the collapse of the collapse and collapse of the wall. Therefore, it is necessary to improve the soil strength and stability of the landslide soil. This paper takes the typical landslides in Tongcheng County of Xianning City, Hubei as the research object, through the method of combining field investigation and indoor test, respectively. The basic characteristics of rock and soil soil at different levels of the typical landslides were carried out to reveal the material foundation of the causes of the erosion, and the remolded soil samples were prepared to study the unconfined compressive strength of rock and soil soil at different levels of the landslides, and to explore the effect of dry density, moisture content and dry and wet cycle on the unconfined compressive strength. The same layer of rock and soil soil is improved to study the change law of the unconfined compressive strength of the soil of the improved rock mass. The results are as follows: (1) the change law of the bulk density of the landslides is the clastic layer red soil layer soil layer; the variation law of the total porosity is the red soil layer of the clastic layer soil layer, and the change of soil mechanical composition With the increase of the depth of the red soil, the content of sand increases with the increase of the sampling depth, while the content of clay particles is decreasing, and the water content of the clay layer is the largest, while the plastic limit water content of the clastic layer is the smallest, and the soil organic matter content decreases with the increase of the depth of the soil layer, and the content of the organic matter in the clastic layer is very small; The pH value of the soil soil is low and acidity, and the amount of free iron oxide in the clastic layer is the smallest, while the content of free iron oxide is obviously different. (2) the unconfined compressive strength of the sentry soil increases first and then decreases with the increase of water content, and the water content of the maximum value is about 15% or 20%. With the increase of dry density, the unconfined limit is unconfined. The compressive strength increases slowly first and decreases approximately linearly, and the decrease is larger. The dry density of the highest value is about 1.30 g/cm3, and the dry density and water content have obvious interaction effect on the unconfined compressive strength of the rock mass, and can be divided into three regions in the contour map: the main effect area of dry density, the main effect area of water cut, dry There are "valleys", "mountain peaks", "ridge" and other curvilinear forms in the three-dimensional surface maps. (3) the unconfined compressive strength of the landslides gradually attenuates with the increase of the number of dry and wet cycles, until finally tends to stability, and its variation rules are roughly divided into 3 stages: rapid attenuation, deceleration attenuation and attenuation. After first dry and wet cycles, the attenuation amplitude is the largest, which is 26%, 15%, 40% and 49% respectively. After the 2~4 dry wet cycle, the attenuation amplitude decreases gradually. After the fifth dry and wet cycles, the attenuation range is basically kept unchanged. With the increase of the dry and wet cycle times, the unconfined resistance to pressure of the landslide soil body is generally expressed as the red soil layer clastic layer of the soil layer. There is a good exponential function relationship between the unconfined compressive strength of the landslide soil and the number of dry and wet cycles, and the prediction model of unconfined compression strength is established under the influence of the depth ratio of soil mass and the number of dry and wet cycles in different levels of the landslide. (4) through the orthogonal design of the landslide soil, the jute fiber was first selected. Optimum reinforcement conditions, in which the topsoil layer: reinforcement length 15 mm, reinforcement ratio 0.35%, overall reinforcement; laterite: reinforcement length 15 mm, reinforcement ratio 0.25%, upper reinforcement; sand layer: reinforcement length 15 mm, reinforcement ratio 0.35%, integral reinforcement; detrital layer: reinforcement length 15 mm, reinforcement ratio 0.30%, lower reinforcement; jute fiber reinforced soil stress strain curve change The law can be divided into 3 stages: rapid attenuation stage, deceleration and attenuation stage, and attenuation stability stage. Under the optimal reinforcement conditions, the unconfined compressive strength of the landslide soil soil is increased by 27.81%, 29.73%, 23.26%, 39.58%. (5), using the response surface design optimization to get the best mixture ratio, age and water content three. Topsoil layer: ash blending ratio 8.99%, Age 28 d, water content 25%, red soil layer: lime content 8.98%, age 28 d, water content 25%, striped layer: ash mixing rate 5.84%, age 18 D, water content 20%; detrital layer: ash mixing rate 6.58%, age 28 d, water content 23%. (6) in the future of the collapse of the work, should consider the combination of improved materials to improve the mechanical properties of the rock mass, jute fiber is A modified material with low cost and green environment can be used in the treatment of the soil layer and the red soil layer to improve the soil strength, and the lime is a kind of improved material with obvious effect and convenient construction, which can be used in the treatment of the landslides and debris layer and debris layer.
【学位授予单位】：华中农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S157.1

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