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Mohamed A. Shahin 《Geomechanics and Geoengineering》2015,10(2):109-125
In this paper, the feasibility of using evolutionary computing for solving some complex problems in geotechnical engineering is investigated. The paper presents a relatively new technique, i.e. evolutionary polynomial regression (EPR), for modelling three practical applications in geotechnical engineering including the settlement of shallow foundations on cohesionless soils, pullout capacity of small ground anchors and ultimate bearing capacity of pile foundations. The prediction results from the proposed EPR models are compared with those obtained from artificial neural network (ANN) models previously developed by the author, as well as some of the most commonly available methods. The results indicate that the proposed EPR models agree well with (or better than) the ANN models and significantly outperform the other existing methods. The advantage of EPR technique over ANNs is that EPR generates transparent and well-structured models in the form of simple and easy-to-use hand calculation formulae that can be readily used by practising engineers. 相似文献
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《地学前缘(英文版)》2016,7(1)
Rock masses are commonly used as the underlying layer of important structures such as bridges, dams and transportation constructions. The success of a foundation design for such structures mainly depends on the accuracy of estimating the bearing capacity of rock beneath them. Several traditional numerical approaches are proposed for the estimation of the bearing capacity of foundations resting on rock masses to avoid performing elaborate and expensive experimental studies. Despite this fact, there still exists a serious need to develop more robust predictive models. This paper proposes new nonlinear prediction models for the ultimate bearing capacity of shallow foundations resting on non-fractured rock masses using a novel evolutionary computational approach, called linear genetic programming. A comprehensive set of rock socket, centrifuge rock socket, plate load and large-scaled footing load test results is used to develop the models. In order to verify the validity of the models, the sensitivity analysis is conducted and discussed. The results indicate that the proposed models accurately characterize the bearing capacity of shallow foundations. The correlation coefficients between the experimental and predicted bearing capacity values are equal to 0.95 and 0.96 for the best LGP models. Moreover, the derived models reach a notably better prediction performance than the traditional equations. 相似文献
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Analysis based on Discrete Element Method (DEM) is presented for estimating bearing capacity of foundations. Soil mass in the present model is treated as comprising of blocks which are connected by elasto-plastic Winkler-springs. By considering the conditions of compatibility, the boundary stresses on the failure surface and the ultimate bearing capacity of shallow foundations can be obtained. The computed boundary stresses from the present method satisfy equilibrium conditions and do not exceed the material strength. Formulation of the method is presented. Examples are shown to demonstrate the applicability of the method to the analysis of bearing capacity of shallow foundations. Effects of stiffness of Winkler-springs and mesh pattern on the computed results are investigated. The present method is shown to be a useful tool for analyzing bearing capacity of foundations with unusual geometry and loading conditions. 相似文献
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随着对地基承载力理论研究的深入及大量工程实践的开展,暴露出弹性理论的诸多缺陷。基于弹-塑性理论,对以前学者的地基分类进行改进,推导出地基的临塑承载力、弹-塑性承载力以及极限承载力的公式,并且为了更好地进行地基土处于非线性变形阶段弹-塑性承载力的计算,提出了弹-塑性承载力利用率的概念;针对以前学者提出的危险度的概念,由于其不能在工程实际工程中很好地推广应用的缺点,给出了具有工程意义的弹-塑性承载力安全度Kep这一参数。结合工程实际说明只要Kep满足要求,地基土可用到非线性变形阶段,由此理论设计地基基础,造价将大大降低。 相似文献
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A modified bearing capacity equation is proposed for skirted strip foundations on dense sand. A series of tests on foundation
models were carried out to study the factors that affect the bearing capacity of foundations with skirts. Several factors
including foundation base friction, skirt depth, skirt side roughness, skirt stiffness and soil compressibility were studied
and incorporated in the equation. The results obtained from the proposed equation were compared with the results obtained
from Terzaghi, Meyerhof, Hansen and Vesic bearing capacity equations for foundations without skirt. Comparison shows that
the use of structural skirts can improve the bearing capacity by a factor of 1.5 to 3.9 depending on the geometrical and structural
properties of the skirts and foundation, soil characteristics and interface conditions of the soil-skirt-foundation system.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Semih S. Tezcan Ali Keceli Zuhal Ozdemir 《Geotechnical and Geological Engineering》2006,24(1):203-218
Firstly, the historical background is presented for the determination of ultimate bearing capacity of shallow foundations.
The principles of plastic equilibrium used in the classical formulation of the ultimate bearing capacity are reviewed, followed
by a discussion about the sources of approximations inherent in the classical theory. Secondly, based on a variety of case
histories of site investigations, including extensive bore hole data, laboratory testing and geophysical prospecting, an empirical
formulation is proposed for the determination of allowable bearing capacity of shallow foundations. The proposed expression
corroborates consistently with the results of the classical theory and is proven to be reliable and safe, also from the view
point of maximum allowable settlements. It consists of only two soil parameters, namely, the in-situ measured shear wave velocity, and the unit weight. The unit weight may be also determined with sufficient accuracy, by means
of another empirical expression, using the P-wave velocity. It is indicated that once the shear and P-wave velocities are
measured in-situ by an appropriate geophysical survey, the allowable bearing capacity is determined reliably through a single step operation.
Such an approach, is considerably cost and time-saving, in practice. 相似文献
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海洋浅基础设计所遇地层条件通常由于基础大尺寸的特点而涉及多土层剖面,其中“硬-软-硬”三层黏土是最常见的地层条件之一。现行海洋浅基础设计常用的API和ISO规范尚无针对“硬-软-硬”黏土竖向承载力的计算方法。本文基于自升式平台基础设计规范推荐的“bottom-up”预测模型,假定“硬-软-硬”黏土上基础的承载力为“硬-软”黏土冲剪破坏产生的侧向摩阻力与“软-硬”黏土挤压破坏提供的承载力之和。通过有限元模拟分析,验证了“bottom-up”方法所假定破坏模型的合理性,但由于规范推荐的相关公式忽略了上覆土层对挤压破坏模式的影响,使其严重低估了“软-硬”黏土挤压破坏产生的承载力。基于变参数有限元分析结果,本文对挤压破坏承载力公式进行了修正,提出了“硬-软-硬”三层黏土上圆形基础竖向承载力的预测方法。 相似文献
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轴向荷载对斜桩水平承载特性影响试验及理论研究 总被引：1，自引：0，他引：1
斜群桩受水平荷载作用时,群桩中的基桩受到径向荷载、轴向荷载和弯矩的共同作用。为研究轴向荷载对斜桩水平承载特性的影响,完成了3根单桩以及1组1×2斜桩的大尺寸模型试验。试验结果表明：轴向拉力作用会降低斜桩的水平刚度和极限承载力;而轴向压力作用则会使其水平刚度和极限承载力提高。基于桩侧浅层土体楔形破坏假定,推导了考虑轴向荷载影响的斜桩水平极限土抗力计算公式,提出了桩侧土抗力的p-y曲线方法,并通过模型试验及现场试验验证其合理性。 相似文献
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作为新型的深水海洋基础型式,吸力式沉箱基础被广泛地用于系泊深水海洋设施中,从而承受巨大的倾斜上拔荷载。在上拔荷载水平分量与竖向分量的共同作用下,吸力式沉箱的承载特性及其工作性能评价是海洋工程设计与建设中的关键技术问题之一。然而现有的理论分析与试验研究并不能满足工程实践的需要,因此,对吸力式沉箱基础的极限承载力分析建立了有限元数值计算方法。当沉箱基础在快速拔出过程中,正常固结黏土处于完全不排水状态,沉箱基础发生整体破坏时表现出反向地基承载力失稳模式,此时沉箱基础所发挥的极限承载能力往往最大。为此,在数值计算中直接假定沉箱基础及其周围土体处于完全不排水状态,针对不同的沉箱长径比,分别确定了在竖向上拔荷载和水平拉拔的单独作用下沉箱基础极限承载力。对比发现：竖向上拔极限承载力有限元解能够较好地与理论计算结果相符合,而水平极限承载力解与理论计算结果存在一定的差异。 相似文献
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Onshore and offshore oil spills contaminate soil. In addition to environmental concerns for ground water pollution and other possible effects, the geotechnical properties of the contaminated soil such as the shear strength and the hydraulic conductivity are also altered. This note is a report of research in progress to evaluate the variation of the shear strength of a sand contaminated by a crude oil and thus the ultimate bearing capacity of shallow foundations. The limited results of the tests reported here relate to only one type of sand and one crude oil. The oil content was varied from zero to 4.2%. Results of direct shear tests for determining the soil friction angle are given. Along with these, laboratory model test results for the ultimate bearing capacity of a surface strip foundation supported by crude oil-contaminated sand are also presented. Based on these test results, the effect of oil contamination in drastically reducing the bearing capacity is discussed. 相似文献
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The bearing capacity of shallow foundations in a non-homogeneous soil profile has been a challenging task in geotechnical
engineering. In this paper, a limit equilibrium method is used for calculating bearing capacity factors of shallow foundations
constructed on a two-layered granular soil profile. The main objective has been to determine the ultimate bearing capacity
computed from equivalent bearing capacity factors Nq and Nγ and comparing that with numerical analysis using finite element methods. It will be shown that the data obtained form the
developed method are well comparable with those obtained from FE approach, specially when the difference between shear strength
parameters of layers is low which is a practical case for sedimentary soil profiles and also for artificially compacted soils.
A computer program has been developed to investigate the influence of various parameters on bearing capacity factors. 相似文献
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Ashis Kumar Bera Ambarish Ghosh Amalendu Ghosh 《Geotechnical and Geological Engineering》2007,25(3):315-325
This paper focuses on the effective utilization of pond ash, as foundation medium. A series of laboratory model tests have
been carried out using square, rectangular and strip footings on pond ash. The effects of dry density, degree of saturation
of pond ash, size and shape of footing on ultimate bearing capacity of shallow foundations are presented in this paper. Local
shear failure of a square footing on pond ash at 37% moisture content (optimum moisture content) is observed up to the values
of dry density 11.20 kN/m3 and general shear failure takes place at the values of dry density 11.48 kN/m3 and 11.70 kN/m3. Effects of degree of saturation on ultimate bearing capacity were studied. Experimental results show that degree of saturation
significantly affects the ultimate bearing capacity of strip footing. The effect of footing length to width ratio (L/B), on increase in ultimate bearing capacity of pond ash, is insignificant for L/B ≥ 10 in case of rectangular footings. The effects of size of footing on ultimate bearing capacity for all shapes of footings
viz., square, rectangular and strip footings are highlighted. 相似文献
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分析了确定复合地基承载力的现况。根据收集到的复合地基承载力检测资料,用双曲线模型、指数模型、灰色模型对复合地基极限承载力进行了预测,并对模型的预测效果进行了分析对比,提出了适合天津市区复合地基的极限承载力预测模型。对预测值进行了修正。根据预测值建立了极限承载力和承载力特征值的关系。 相似文献
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海平面上升导致的地下水入侵沿海地区的建筑地基造成显著风险。提出了一个考虑地下水侵入导致土壤强度退化的沿海建筑地基韧性模型。该模型由地基的性能函数在服役期内的积分得到。考虑条形基础的韧性,其极限承载力由Terzaghi公式描述。韧性模型考虑气候变化背景下地下水位的上升对土壤强度的影响。通过一个算例,展示了所提出的韧性模型的适用性。结果表明,如果不考虑气候变化影响下地下水位的上升,则会得到不保守的结构韧性评估结果。结构全寿命周期内的韧性也取决于所采用的维护措施（即,修复受损的结构性能）。未来的研究中,还应考虑其他因素（如锈蚀）对沿海建筑地基性能退化的联合影响。 相似文献
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Maher Omar Khaled Hamad Mey Al Suwaidi Abdallah Shanableh 《Arabian Journal of Geosciences》2018,11(16):464
This research proposes the use of artificial neural network to predict the allowable bearing capacity and elastic settlement of shallow foundation on granular soils in Sharjah, United Arab Emirates. Data obtained from existing soil reports of 600 boreholes were used to train and validate the model. Three parameters (footing width, effective unit weight, and SPT blow count) are considered to have the most significant impact on the magnitude of allowable bearing capacity and elastic settlement of shallow foundations, and thus were used as the model inputs. Throughout the study, depth of footing was limited to 1.5 m below existing ground level and water table depth taken at the level of the footing. Performance comparison of the developed models (in terms of coefficient of determination, root mean square error, and mean absolute error) revealed that the developed artificial neural network models could be effectively used for predicting the allowable bearing capacity and elastic settlement. As such, the developed models can be used at the preliminary stage of estimating the allowable bearing capacity and settlements of shallow foundations on granular soils, instead of the conventional methods. 相似文献
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针对中风化砂岩地质条件,开展了单锚基础和承台式群锚基础的现场足尺试验研究,得到了荷载-位移曲线,分析了基础的破坏模式和承载性能。通过锚筋应变测试,研究了锚杆基础的内力分布规律和有效锚固深度。研究结果表明,岩石锚杆基础应用于中风化砂岩地基分布地区,满足输电线路上部结构对基础承载力的要求,具有良好的经济和社会效益;当锚杆锚固深度小于有效锚固深度时,增加锚固深度和承台嵌岩深度能够有效地提高基础的抗拔承载性能;水平荷载不是基础发生破坏的控制因素,但水平荷载对群锚基础上拔稳定存在不利影响。 相似文献
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新型螺旋成孔根植注浆竹节管桩是一种新的组合桩型,具有承载力高、技术含量高和安全性能好等特点。为了更好地了解新型组合桩的抗压承载机制,应用ABAQUS软件进行抗压数值模拟。通过将模拟结果与现场试验结果对比,验证了数值模型的可靠性。分析模拟结果,发现桩身竹节处存在2～3倍桩径的应力影响范围,并且存在1.6～1.8倍桩径的空壳区,竹节极限承载力从上到下排列线性增长（除第1节和最后一节）。结果还表明,竹节间距、水泥土厚度、桩侧土弹性模量以及桩端土弹性模量都对组合桩极限承载力有影响,而水泥土弹性模量的影响则可忽略。以往相似工法的极限承载力公式都不能很好地诠释本桩型的受力特性,因此,结合理论分析与抗压受力机制,提出考虑侧阻竹节影响系数的单桩极限承载力公式,与现场试验结果对比,较为接近。 相似文献