不同性状碎石土地基系数m值取值模型试验研究

发布时间：2018-06-15 18:18

本文选题：表观m值 + 本底m值　；参考：《成都理工大学》2017年硕士论文

【摘要】：长期遭受水平作用力的桩基础,其水平载荷能力是直接影响桩基安全稳定的关键性因素。水平受荷桩的承载能力主要受桩身性质与地基土体性质控制,其中地基土的水平抗力系数的比例系数m值是关系到桩-土相互作用的地基土的物理参数,是衡量地基土体水平抗力大小的物理量,也是计算桩基水平承载力的参数值。地基土体性质是影响m值的主要因素,不同土性、不同设计要求m值取值不尽相同;对于甲级设计要求建筑桩基需要通过现场单桩水平静载试验获取m值,而大部分一般建筑桩基则通过规范经验取值与工程类比综合确定,因此m值的取值是否合理直接关系到水平受荷桩的承载力设计是否恰当。本文基于西南山区输电线塔基出现最多的碎石土地基开展m值取值研究;而碎石土分类广,性质差异性大,规范取值范围大,综合选取随意性大;经文献查阅后发现密实度与含石量是影响碎石土性质的主要两个因素,其不同性状碎石土地基桩-土相互作用下表观m值取值差异大,不同性状碎石土地基能够发挥的极限水平抗力大小也欠缺研究。因此本文采用室内物理模拟试验方法,针对不同性状碎石土地基进行表观m值与本底m值取值探讨,设计并开展了改变碎石土地基密实度、含石量及桩宽的单桩水平静载荷模型试验与水平压缩试验,主要得到以下结论与认识:(1)单桩水平静载荷试验得到的表观m值是由地基土体性质控制的地基系数。密实度的变化对m值的影响最显著,其次是含石量,而桩宽的变化几乎对表观m值几乎不影响。碎石土密实度Dr每增加20% ,表观m值提高1.83倍,在Dr=60.0%的碎石土地基表观m值为175.61MN/m~4。含石量P5每增加10% ,表观m值提高1.24倍。(2)桩基在水平力作用下的临界荷载Hcr与极限荷载Hu随密实度Dr、含石量P5及桩宽的增加而增大。最松散的土体性质最差,桩顶容许位移最小。密实度及含石量较高的土体在高水平荷载作用下土体的变形主要由粗颗粒之间的错动产生。含石量高的碎石土偏于硬化,可以有效提高土体水平承载能力。(3)m值是由地基土体性质直接影响的土体本底物理量参数,反应地基土体水平抗力与水平应变的关系规律,密实度对碎石土本底m值的影响最为显著,随密实度的增大m值会明显增大。工程结构的作用使得土体不能完全发挥其水平抗力性能,从而使得出m值偏小,在无桩身作用下进行水平压缩可以获得最大的本底m值。比较两种试验获得的m值,水平压缩载荷试验获取的本底m值比表观m值要大,更能反应碎石土的水平抗力性能;一般本底m值比表观m值大1.37倍,相比相同桩宽、相同密实度碎石土地基,不同加载方式得到的m值也有较大差别,桩身挤压土体量越多m值越大。(4)碎石土地基水平受荷单桩泥面位移x与表观m值呈现为非线性的幂指数关系,关系式为m=b_m(x/B×10~3)~(-1.038),bm取值参考表5-5 ,碎石土地基幂指数平均k值为-1.038。(5)利用综合刚度原理提出的双参数法分析各密实度单桩静载模型试验数据进行计算分析,土抗力系数K随深度非线性变化,K=mz0.7。对于碎石土地基在1/n=0.7时计算得到的各内力最贴切实测数据桩土综合刚度比桩身刚度要小,在碎石土地基中桩土之间是负附着形式作用,桩的一部分是作为土体。
[Abstract]:The horizontal load capacity is the key factor affecting the safety and stability of pile foundation for a long time. The bearing capacity of the pile is mainly controlled by the character of the pile body and the soil properties of the foundation, and the ratio coefficient m of the horizontal resistance coefficient of the foundation soil is the physics of the foundation soil which is related to the pile soil interaction. Parameter is the physical quantity to measure the horizontal resistance of foundation soil, and it is also the parameter value of calculating the horizontal bearing capacity of the pile foundation. The soil property of the foundation is the main factor affecting the m value. The different soil properties and the different design requirements of the m value are not the same; for the first grade design, the building pile foundation needs to obtain the m value through the static load test of the single pile. Most general building piles are determined by the standard experience value and engineering analogy, so whether the value of m value is reasonable directly relates to the proper design of the bearing capacity of the horizontal bearing pile. This paper is based on the study of the value of the m value based on the most lithotripsy ground base of the transmission line tower base in the southwest mountain area; and the classification of the gravel soil is wide and the nature is poor. It is large in heterosexual, large range of standard values and comprehensive selection of randomness. After consulting the literature, it is found that density and stone content are the two main factors affecting the properties of gravel soil. The apparent m values of different properties of gravel soil under the interaction of soil foundation pile soil interaction are very different. Therefore, in this paper, the indoor physical simulation test method is used to study the apparent m values and the values of the base m values for different properties of the gravel soil foundation. A single pile horizontal static load model test and horizontal compression test are designed and carried out to change the soil base density, stone content and pile width. The main conclusions are as follows: (1) single The apparent m value obtained by the static load test of the pile is the foundation coefficient controlled by the soil properties of the foundation. The change of the density has the most significant influence on the m value, followed by the stone content, and the change of the pile width almost has no effect on the apparent m value. The gravel soil density Dr increases 20%, the apparent m value increases 1.83 times, and the apparent m in the gravel soil base of Dr=60.0% is m. The value of the 175.61MN/m~4. stone content P5 increases 10% and the apparent m value increases 1.24 times. (2) the critical load of the pile foundation under horizontal force and the limit load Hu increases with the density Dr, the rock content P5 and the pile width. The most loose soil property is the worst, the allowable displacement of the pile top is minimum. The soil with high density and high stone content is in the high horizontal load. The deformation of the soil is mainly caused by the dislocation between the coarse particles. The gravel soil with high stone content is partial to hardening and can effectively improve the horizontal bearing capacity of the soil. (3) the m value is the physical parameter of the soil base, which is directly affected by the soil properties of the foundation, and the relationship between the horizontal and horizontal strain of the soil soil, and the compactness to the gravel. The effect of the m value on the soil base is the most significant, with the increase of the compactness, the m value will increase obviously. The effect of the engineering structure makes the soil not fully play its horizontal resistance performance, so that the m value is smaller and the maximum bottom m value can be obtained under the horizontal compression without the pile body. Compared with the m value obtained from the two tests, the horizontal compression load test is compared. The base m value obtained is larger than the apparent m value, and it can reflect the horizontal resistance performance of the gravel soil more than the apparent m value. The general background m value is 1.37 times larger than the apparent m value. Compared with the same pile width, the same compactness gravel land base, the m value of the different loading ways also has greater difference, the greater the m value of the pile body extrusion soil. (4) the gravel soil base level is loaded single pile. The surface displacement X and the apparent m value are nonlinear power exponent relation, the relation is m=b_m (x/B x 10~3) ~ (-1.038), BM value reference table 5-5, the average K value of the lithotripsy soil foundation power exponent is -1.038. (5) using the double parameter method proposed by the comprehensive stiffness principle to analyze the static load model test data of each compactness single pile, and the soil resistance coefficient K. With the nonlinear variation of depth, the most accurate measured data of the internal forces obtained by K=mz0.7. for the gravel soil base at 1/n=0.7 are smaller than the pile stiffness. The pile and soil are negative in the gravel soil foundation, and a part of the pile is used as the soil.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.1

【参考文献】