共查询到20条相似文献，搜索用时 46 毫秒
1.
Presented and discussed in this paper is an exact analytical solution of the nonhomogeneous partial differential equation governing the conventional one‐dimensional consolidation under haversine repeated loading. The derived analytical solution to the 1D consolidation equation is compared with the numerical solution of the same consolidation problem via FEM. The series solution takes into account the frequency of repeated loading through a dimensionless time factor T0. The paper reveals that an increase in the frequency of imposed repeated haversine loading (a decrease in period of repeated loading) causes an increase in the number of cycles required to achieve the steady state, whereas the effect of frequency on the maximum excess pore water pressure at the bottom of a clay layer with permeable top and impermeable bottom for the range of frequencies studied is generally insignificant. The effective stress at the bottom of the clay deposit with permeable top and impermeable bottom increases with time but with some fluctuations without changing the sign. These fluctuations become more pronounced for increasing values of T0. An increase in T0 also causes an increase in maximum effective stress. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
2.
This note presents an analytical solution to one-dimensional consolidation in unsaturated soils with a finite thickness under confinement in the lateral direction and vertical loading varying exponentially with time. The boundary conditions are that the top surface is permeable to water and air and the bottom is impermeable to water and air. The transfer relationship between the state vectors at the top surface and any depth is gained by applying the Laplace transform and Cayley-Hamilton mathematical methods to the governing equations of water and air, Darcy’s law and Fick’s law. The excess pore-air and pore-water pressures and settlement in the Laplace-transformed domain are obtained by using the Laplace transform with the initial and boundary conditions. By performing the inverse Laplace transforms, the analytical solutions of the excess pore-air and pore-water pressures at any depth and settlement are obtained in the time domain. 相似文献
3.
This paper presents a semi-analytical solution to one-dimensional consolidation of viscoelastic unsaturated soils with a finite thickness under oedometric conditions and subjected to a sudden loading. The solution is obtained by using Lee’s correspondence principle based on the semi-analytical solution to one-dimensional consolidation of elastic unsaturated soils. The boundary contains the top surface permeable to water and air and the bottom impermeable to water and air. A typical example is given to show the evolution of excess pore-air and pore-water pressures as well as the total degree of consolidation of the soil layer with time for different ratios of air–water permeability coefficient, elastic modulus and viscoelastic coefficient. The one-dimensional consolidation behavior of viscoelastic unsaturated soil is discussed according to the semi-analytical solution. These results contribute to a better understanding of the consolidation behavior of viscoelastic unsaturated soils. 相似文献
4.
Based on Fredlund’s one-dimensional consolidation equation for unsaturated soil, Darcy’s law and Fick’s law, a semi-analytical solution was presented to the free drainage well with a finite thickness under application of uniform vertical loading and the boundary of the top and bottom surfaces impermeable to water and air. According to the polar governing equations of water and air phases and the boundary and initial conditions, the excess pore-air and pore-water pressures and the soil layer settlement in the Laplace transformed domain are obtained by performing the Laplace transform and utilizing the Bessel functions. Crump’s method is used to perform the inversion of Laplace transform in order to obtain numerical solutions in the real time domain. Finally, a typical example is given to illustrate the changes in the excess pore-air and pore-water pressures and soil layer settlement with time factor at different ratios of air–water permeability coefficient and/or different distances from the well. 相似文献
5.
Previous analytic solutions to the problem of the consolidation of a deep clay stratum subjected to a surface loading, have been obtained for the assumed condition of a completely permeable upper surface. This may not be so in many applications, where the foundation causing the loading may be impermeable, and therefore only that part of the clay surface outside the loading is free to drain.In this paper a method is presented which may be used to obtain the time-settlement behaviour of a circular loading applied over an impermeable region of the surface of the clay. The solution technique involves representing the continuous values of fluid flow along the surface boundary as uniform blocks of flow. The solution is found in Laplace transform space and a numerical inversion technique is then used to obtain the time dependent solution.Two types of surface loading are examined; a completely uniform loading and a loading distribution which is approximately that of a rigid footing. For the uniform loading case, comparisons are made with previous solutions (permeable surface) and it is shown that the assumption of an impermeable loaded region leads to significant changes in the time-settlement behaviour of the loading. 相似文献
6.
基于Fredlund非饱和土一维固结理论,研究了有限厚度的表面透水透气、底面不透水不透气的线弹性和黏弹性非饱和土地基在加荷随时间指数性变化时的一维固结特性。分别得到了两类地基在固结过程中同时考虑液相、气相渗透系数非线性变化和仅考虑液相渗透系数变化两种情况下的半解析解答。利用典型算例进行计算,分析了不同情况下两类地基中超孔隙水、气压力消散以及地基固结度随时间的变化规律,并与不考虑渗透系数变化时的半解析解计算结果进行了对比。结果发现：固结过程中渗透系数呈非线性变化;只考虑液相渗透系数变化时,超孔隙气压力的消散变化不大,超孔隙水压力的消散加快;气相渗透系数变化对超孔隙气的消散产生明显影响,对超孔隙水压力消散影响不大。同时考虑液相和气相渗透系数变化时,土体中超孔隙水、气压力的消散均有明显变化,土体固结速度也相应加快;分析结果对非饱和土固结的进一步研究具有重要意义。 相似文献
7.
8.
近年来,在浙江省北部钱塘江河口湾地区发现并开发了大量的晚第四纪浅层生物气藏。末次盛冰期,全球海平面的下降使河流梯度增加,下切作用增强,导致钱塘江下切河谷的形成。下切河谷内的沉积序列从下到上可划分为4种沉积相类型,分别为河床相、河漫滩-河口湾相、河口湾-浅海相和河口湾砂坝相。 所有的商业浅气田和气藏都分布于太湖下切河谷和钱塘江下切河谷及其支谷的河漫滩-河口湾相砂体中。钱塘江下切河谷的河漫滩-河口湾砂体埋深30～80 m,厚3～7 m,被非渗透的黏土包围,可能代表了下切河谷内分布的潮流沙脊。快速堆积的河口湾-浅海相沉积物为生物气藏的形成提供了充足的源岩和良好的保存条件。 河漫滩-河口湾相的黏土层为研究区浅层生物气藏的直接盖层,主要分布在下切河谷内,其埋深、残留地层厚度和孔隙度范围分别为30～80 m、10～30 m和42.2％～62.6％。河口湾-浅海相的淤泥层为间接盖层,覆盖了整个下切河谷,其埋深、残留地层厚度和孔隙度范围分别为5～35 m、10～20 m和50.6％ ～53.9％。黏土层和淤泥层的孔隙水压力远大于下伏砂体的孔隙水压力,其差值可达0.48 MPa。在储集层和盖层分界面即浅气藏的顶部,孔隙水压力值达到最大。黏土层和淤泥层的孔隙水压力可以超过砂质储集层中气体压力和孔隙水压力之和。黏土和淤泥盖层的高孔隙水压力可能是浅层生物气被完全封闭住的最重要因素。直接盖层的封闭能力比间接盖层要好。黏土层和淤泥层的孔隙水压力消散时间很长,有时候很难达到稳定状态,这表明黏土层和淤泥层的渗透性差、封闭性好。随着埋深的增加,其压实程度和封闭性能增加。与黏土层和淤泥层相比,砂层的孔隙水压力消散较快,很容易达到稳定状态,而且消散时间与埋深无关,表明砂层渗透性好、封闭性差。气体一旦进入砂层,孔隙水就不能有效释放,导致砂层的孔隙水压力消散时间比黏土层和淤泥层的要长,这可能与生物气在孔隙水压力释放后的快速补充有关。 相似文献
9.
10.
非饱和土层一维固结特性分析 总被引：1，自引：0，他引：1
在Fredlund非饱和土的一维固结理论的基础上进行假设,由得出的液相及气相的控制方程、Darcy定律及Fick定律,采用Laplace 变换、逆变换等数学方法得到了大面积均布瞬时加载下表面为透水透气面、底面为不透水和不透气面的非饱和土层一维固结时间域内的超孔隙水压力、超孔隙气压力及土层沉降的解析解;应用典型算例,分析了不同气、水渗透系数比情况下土体超孔隙水压力、超孔隙气压力消散及土层沉降随时间的变化规律以及不同时间超孔隙水压力、超孔隙气压力消散随深度的变化规律。将得出的结果退化成相应的饱和土的解与太沙基饱和土固结理论结果比较,验证了其正确性。 相似文献
11.
A theoretical study is made of the consolidation of a composite foundation reinforced by columns. A more reasonable initial condition for the consolidation of a composite foundation is derived from the equilibrium equation and the equal strain assumption. Then, the general analytical solutions for excess pore water pressures in the column and in the surrounding soil are obtained using this new initial condition under the influence of several important factors. These factors include: the gradual variation of horizontal permeability in the disturbed soil, the change in the total average stress in a composite foundation with depth, and the effect of time-dependent external loads. The general expressions for the overall average degree of consolidation of a composite foundation, both in terms of stress and in terms of deformation, are then derived. On the basis of the above theory, the explicit solutions for a particular case, which considers ramp loading and a linear change of total stress with depth, are given in detailed forms. Finally, a parametric study and a comparison of some available solutions are made. The results show that the average degree of consolidation obtained in terms of stress and in terms of deformation is the same; the increase in construction time, the disturbance intensity during column construction and the size of the disturbed zone reduce the consolidation rate of a composite foundation. For the case of PTIB (pervious top surface and impervious bottom surface), the increase in the ratio of top total stress to bottom total stress in the composite foundation accelerates consolidation. 相似文献
12.
根据某一大型油罐软基加固处理工程方案设计和优选需要,按照离心模型相似律,开展了三组模型试验,分别模拟了天然地基、土工合成材料袋装碎石垫层和既在填土层中设置袋装碎石垫层又在淤泥质粘土层设置土工合成材料排水板三种情况,以研究这一加固布置形式对减小高压缩性软土层地基上油罐罐底的差异沉降效果反应。模型油罐地基采用原型土重塑制备,现场土工合成材料袋装碎石采用柔性机织玻璃纤维细管塞装粗砂条模拟,并在不停机运转条件下模拟了多次充放水预压加载。试验结果表明,油罐软弱地基经土工合成材料袋装碎石加固后,罐底总沉降值和差异沉降值均明显小于天然地基情形下对应的沉降值,罐底畸变得到显著减小,就本文所述的土质条件、土层厚度和预压荷载强度,地基经加固处理后,油罐罐底畸变减小了近50 %。最后就土工合成材料在加固油罐地基布置形式的合理性进行了初步探讨。 相似文献
13.
Yi--> Tian Wenbing Wu Guosheng Jiang M. Hesham El Naggar Guoxiong Mei Meijuan Xu Rongzhu Liang 《国际地质力学数值与分析法杂志》2020,44(8):1170-1183
In engineering practice, a rapid loading rate can result in ground failure when the strength of soft soils is relatively low, and a multistage loading scheme is always utilized to deal with this situation. Firstly, under a multistage load and the continuous drainage boundary, an analytical solution of excess pore-water pressure and consolidation degree is obtained by virtue of the superposition formula of excess pore-water pressure, and a more general continuous drainage boundary under arbitrary time-dependent load is developed. Then, a comparison with existing analytical solutions is conducted to verify the present solution. A preliminary attempt on applying the continuous drainage boundary into the finite element model is made, and the feasibility of the numerical model for the one-dimensional consolidation under the continuous drainage boundary is verified by comparing the results calculated by FEM with that from present analytical solution. Finally, the consolidation behavior of soil is investigated in detail for different int erface parameters or loading scheme. The results show that, in land reclamation projects, a horizontal drain should be placed close to the boundary with a smaller interface parameter to improve the consolidation efficiency. The degree of consolidation is also related to the applied time-dependent load and interface parameters. 相似文献
14.
General approximate analytical solutions are developed for one-dimensional consolidation with consideration of the threshold gradient under a time-dependent loading. A comparison is made between the present solution and some available numerical solutions for a particular case, and the results show that the approach employed in this article is reasonable. The influence of the threshold gradient and the loading period on consolidation behaviour is investigated, and the results show that the moving boundary of seepage moves downward gradually. The greater the threshold gradient is, the slower the boundary moves. The excess pore pressure will not be completely dissipated at the end of consolidation, and the larger the threshold gradient is, the greater the residual excess pore pressure is. The average degree of consolidation considering the threshold gradient defined by settlement is different from that defined by pore pressure. Moreover, the greater the threshold gradient is, the larger the average degree of consolidation in terms of strain, whereas the smaller the average degree of consolidation in terms of stress. It is also shown that the longer the loading period is, the longer the time moving boundary takes to reach the bottom of the layer, and the greater the average degree of consolidation is. 相似文献
15.
Analytic solutions to the problem of the time-settlement behaviour of raft foundations have been limited in the past to flexible or rigid loadings, and have treated the foundation as being completely permeable. In this paper, solutions are presented for smooth circular rafts of any flexibility causing consolidation of a deep homogeneous clay layer, where the raft may be considered permeable or impermeable. Results for the time-dependent behaviour of contact stresses, pore pressures, raft displacements and moment in the raft are presented. 相似文献
16.
天津滨海吹填场区典型的“上软下硬”的双层软黏土地基具有复杂的物理性质和工程特性,其在不同荷载作用模式下的变形特性有所不同,在工程实践中往往会产生较大的工后沉降和不均匀沉降,从而导致修建于其上的建筑物出现诸多工程问题。现阶段对于不同荷载作用下吹填场区形成的“上软下硬”双层软黏土地基的变形特性及机理研究甚少,导致理论研究远远落后于工程实践,制约了吹填场区经济建设的快速发展,因此对此类地基的变形特性展开研究显得尤为重要。基于此,本文针对吹填场区“上软下硬”的双层软黏土地基,开展了反复荷载和恒定荷载作用下的一维固结试验和扫描电镜试验(SEM),得到了不同荷载模式作用下的压缩特性及其微观机理,为吹填场区双层软黏土地基变形模型建立及长期工后沉降预测提供理论依据。研究表明:双层软黏土地基的压缩系数和固结系数在反复荷载作用初期明显减小,而后缓慢减小直至趋于稳定; 与反复荷载相比,恒定荷载作用下试样的压缩系数初期值增加,固结系数初期值减小,其变化量均在40% ~50%的范围内; 当荷载等级一定时,反复荷载作用引起双层软黏土地基产生的沉降量相比于恒定荷载作用多30% ~45%; 随着荷载等级的增加,土样内部大孔隙受到挤压而减少,孔隙的圆度和定向性加强,土体结构更密实,均一化程度提高; 相比于恒定荷载模式,反复荷载作用下土样内部孔隙形状更接近于圆形,孔隙定向性更好,土体内部结构强化程度大,但有序性相对较差。 相似文献
17.
Soft clay exhibits creep behavior, but simple methods of surcharge preload assessment generally do not take into account creep during primary consolidation. Because Yin–Graham’s model can predict both primary and secondary settlement, it is employed in this paper to obtain the formulae for critical settlement at the unloading time during surcharge preload and for final settlement at the end of the service life. Because “aged” soft natural clay exhibits obvious apparent preconsolidation pressure during a long-term sedimentary history as a result of creep effects and because the field permeability coefficient is considerably larger than the laboratory permeability coefficient, most field measurements indicate that the theoretical excess pore pressure based on Terzaghi’s theory is greater than the measured excess pore pressure even in soft natural clay with obvious viscous behavior. Because of the widespread application of the degree of consolidation in terms of effective stress based on Terzaghi’s theory in real preload projects, the analytical solution for the surcharge preload period subject to creep is derived through the combination of Yin–Graham’s model and Terzaghi’s theory for consolidation. Compared with the existing solution considering secondary settlement, the formula for the preload period presented in this paper is easily applied to assess the preload period using a chart. The case study described indicates that when the consolidation parameters of Terzaghi’s theory are calculated from field-measured excess pore pressure in preload tests, the surcharge preload period determined as described in this paper is suitable for preload design and performance. 相似文献
18.
Provenance of iron,bauxite and clay deposits of the Carboniferous Benxi Formation in southern margin of North China Craton: An example from Da'an bauxite and clay deposit of Sanmenxia area,Henan Province 
下载免费PDF全文
下载免费PDF全文 Liu Xue-Fei Wang Qing-Fei Ma Yao Li Zhong-Ming Zhao Li-Hua Zhou Zhi-Hui Liu Bai-Shun Ma Xin-Li 《古地理学报》1999,22(5):965-976
During the Middle Ordovician to Late Carboniferous period,the North China Craton(NCC)was exposed and experienced prolonged weathering that resulted in the formation of large-scale iron,clay and bauxite deposits. The source of ore-forming material has always been a research focus,in particular,whether the sources of the iron ore and the Fe-bearing clay at the bottom of Benxi Formation are the same as the upper bauxite and clay deposit is still unclear. In this study,the Da'an bauxite and clay deposit at the southern margin of the NCC was chosen to carry out a detailed analysis of the micro-region mineral composition and elemental geochemical characteristics for further exploring the sources of iron,bauxite and clay deposits. The composition of the ore-bearing rocks in the Da'an bauxite deposit from the bottom to top includes Fe-bearing clay(locally iron ore),bauxite,and bauxitic clay;locally,in karstic uplift,bauxitic clay layer is directly overlying on the Fe-bearing clay. The Fe-bearing clay is dominated by siderite,pyrite,and illite in the karstic depression,and hematite,illite,and kaolinite in the uplift. Bauxite is mainly composed of diaspore,illite,and anatase,while bauxitic clay is mainly composed of illite. Mineral microanalysis revealed the development of large amounts of moissanite and small amounts of natural silica,silicalite,and chromite at the bottom of bauxitic clay layer. Regional comparison and correlation reveal that the ophiolite in the Shangdan suture zone and Erlangping Group in the North Qinling orogenic belt(NQOB)likely provides source materials for bauxite and clay deposits. The obvious differences in immobile element ratios (e.g., Zr/TiO2,Hf/TiO2,Nb/TiO2,Ta/TiO2)between the bottom Fe-bearing clay layer and the upper bauxite and clay layer in Da'an deposit,revealing that they are from different sources. The bottom Fe-bearing clay and iron ore layers are the products of in-situ weathering of underlying carbonates,while the top bauxite and clay are allochthonous. The regional uplift of the NQOB during the Late Carboniferous period provided important ore-forming materials for the formation of the NCC bauxite and clay deposits. 相似文献
19.
循环荷载作用下单桩动力模型试验与桩−土界面特性研究 总被引：1，自引：0，他引：1
通过开展红黏土中单桩轴向循环振动模型试验,研究不同循环荷载比和加载频率对桩长期动力特性的影响,从桩侧土剪切刚度和侧阻退化两方面出发,对循环荷载作用下桩顶累积沉降机制进行分析。在FLAC3D中,实现能够反映剪切刚度疲劳退化的修正Hardin-Drnevich（H-D）模型,并对常法向刚度（CNS）循环剪切下侧阻退化进行数值模拟。试验发现,循环荷载幅值是桩顶累积沉降变化的重要影响因素;桩顶动刚度在加载初期要先经历一个迅速降低的短暂过渡阶段,之后则不随振次的增加而改变;桩身振动在桩周土中引起的超孔压较小,有效应力的降低不足于使侧阻力发生较大程度的退化;随着加载速度的增大,桩顶动刚度和加速度均随之增大。采用修正H-D模型得到的理论滞回曲线与数值结果基本吻合,验证了程序编制的正确性。 相似文献
20.
华北克拉通在中奥陶世至晚石炭世期间一直出露地表,经历了长期的风化作用,形成大规模的铁-铝黏土矿,其成矿物源一直是研究的热点,尤其是本溪组底部铁矿和铁质黏土矿与上部铝黏土矿是否为同一来源尚未查清。本研究选取克拉通南缘大安铝黏土矿床作为研究对象,展开微区矿物及元素地球化学组成分析,进一步探讨铁-铝黏土矿物质来源。大安矿床内含矿岩系自下而上包括铁质黏土岩、铝土矿、铝质黏土矿;局部喀斯特高地缺失铝土矿,铝质黏土矿直接覆盖于铁质黏土岩之上。铁质黏土岩在洼地以菱铁矿、黄铁矿和伊利石为主,在隆起区以赤铁矿、伊利石和高岭石为主。铝土矿以硬水铝石、伊利石和锐钛矿为主;铝质黏土矿主要矿物为伊利石。矿物微区分析在黏土矿底部发现大量的碳化硅和少量自然硅、硅铁矿、铬铁矿;区域对比揭示北秦岭造山带内商丹缝合带和二郎坪群中的蛇绿岩为铝黏土矿形成提供了成矿物质。本溪组底部铁质黏土与上部铝黏土矿稳定元素比率(例如Zr/TiO2、Hf/TiO2、Nb/TiO2、Ta/TiO2)存在明显差异,揭示二者为不同来源: 底部铁质黏土岩和铁矿层为底板碳酸盐岩原地风化的产物;而上部铝黏土矿是异地搬运物,北秦岭造山带在晚石炭世的整体抬升为华北铝黏土矿形成提供了重要的成矿物质。 相似文献