Development of mathematically motivated hybrid soft computing models for improved predictions of ultimate bearing capacity of shallow foundations

Ultimate bearing capacity(UBC)is a key subject in geotechnical/foundation engineering as it determines the limit of loads imposed on the foundation.The most reliable means of determining UBC is through experiment,but it is costly and time-consuming which has led to the development of various models based on the simplified assumptions.The outcomes of the models are usually validated with the experimental results,but a large gap usually exists between them.Therefore,a model that can give a close prediction of the experimental results is imperative.This study proposes a grasshopper optimization algorithm(GOA)and salp swarm algorithm(SSA)to optimize artificial neural networks(ANNs)using the existing UBC experimental database.The performances of the proposed models are evaluated using various statistical indices.The obtained results are compared with the existing models.The proposed models outperformed the existing models.The proposed hybrid GOA-ANN and SSA-ANN models are then transformed into mathematical forms that can be incorporated into geotechnical/foundation engineering design codes for accurate UBC measurements.

New design equations for estimation of ultimate bearing capacity of shallow foundations resting on rock masses

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.

Study of the Bearing Capacity at the Variable Cross-Section of A Riser- Surface Casing Composite Pile

Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development.The offshore oil well structure includes a riser and a surface casing.The riser,surface casing and oil well cement can be considered special variable cross-section piles.Replacing or partially replacing the steel pipe pile foundation with a variable cross-section pile to provide the required bearing capacity for an offshore oil platform can reduce the cost of foundation construction and improve the economic efficiency of production.In this paper,the finite element analysis method is used to investigate the variable cross-section bearing mode of composite piles composed of a riser and a surface casing in saturated clay under a vertical load.The calculation formula of the bearing capacity at the variable section is derived based on the theory of spherical cavity expansion,the influencing factors of the bearing capacity coefficient N_(c) are revealed,and the calculation method of N_(c) is proposed.By comparing the calculation results with the results of the centrifuge test,the accuracy and applicability of the calculation method are verified.The results show that the riser composite pile has a rigid core in the soil under the variable cross-section,which increases the bearing capacity at the variable cross-section.

Influence of the Spudcan Angle on the Ultimate Bearing Capacity of Jack-up Platform

Jack-up platforms of the Ocean engineering structures always withstand the vertical gravity loads which are applied to the seabed by spudcan, so it is important to determine the bearing capacity and the penetration depth of the spudcan for its geometry. In fact, it is up to the deformation law and the failure modes of soil surrounding the spudcan which can calculate the ultimate bearing capacity of the spudcan foundation on the soil seabed. By using the finite element analysis software Abaqus, the deformation law of soil around the spudcan is analyzed in detail, and the failure modes of soil surrounding the spudcan foundation are achieved. At the same time, based on the limit equilibrium theory, by use of static permissible slip-line field, the ultimate bearing capacity of the spudcan foundation is analyzed and the lower limit solution is derived theoretically, and the effect of the spudcan angle on the ultimate bearing capacity is investigated. The numerical results are compared with those obtained by the theoretical formulas deduced in this paper. On the basis of the lower limit solutions in this paper, the effect of the spudcan angle on the ultimate bearing capacity is revealed, and a practical bearing capacity formula is given to take the effect of the spudcan angle into consideration.

Analysis of the Ultimate Bearing Capacity of Oil Field Drilling Masts

In order to improve the safety of drilling operations, this paper presents a new method for forecasting the ultimate bearing capacity of oil field drilling masts. The method is based on a double nonlinear finite element theory and applies a referential stress method for measuring defects and defacements. The lab mast model was analyzed using the proposed method. The relative error, which was less than 5.0% between the forecast results and the destructive experiment values,verified the correctness of this method. It also forecasts the ultimate bearing capacity for a local drilling mast.

Construction of improved rigid blocks failure mechanism for ultimate bearing capacity calculation based on slip-line field theory

Based on the slip-line field theory, a two-dimensional slip failure mechanism with mesh-like rigid block system was constructed to analyze the ultimate bearing capacity problems of rough foundation within the framework of the upper bound limit analysis theorem. In the velocity discontinuities in transition area, the velocity changes in radial and tangent directions are allowed. The objective functions of the stability problems of geotechnical structures are obtained by equating the work rate of external force to internal dissipation along the velocity discontinuities, and then the objective functions are transformed as an upper-bound mathematic optimization model. The upper bound solutions for the objective functions are obtained by use of the nonlinear sequential quadratic programming and interior point method. From the numerical results and comparative analysis, it can be seen that the method presented in this work gives better calculation results than existing upper bound methods and can be used to establish the more accurate plastic collapse load for the ultimate bearing capacity of rough foundation.

Stability Analysis of Space Compcoite Structore and Its Ultimate Bearing Capacity

In this paper, using incremental equilibrium equation, the authors have studiedthe effeet of ultimate bearing capacity of every component on structuralstability, and discussed the stability analysis method for space compositestructures. With the help of the test results for the concrete filled ateel tubeskeleton of the long-spen RC arch bridse, it is proved that the proposed methodis accurate and reliable.

Evaluation of ultimate bearing capacity of Y-shaped vibro-pile

Based on Mindlin stress solution, a numerical computational method was proposed to calculate the stresses in the ground induced by side friction and the resistance of Y-shaped vibro-pile. The improved Terzaghi's and ЪерезанцевВГ's methods for ultimate bearing capacity evaluation were proposed by considering the stress strength induced by friction resistance at pile head level of Y-pile. A new method to calculate the ultimate bearing capacity of Y-pile was also proposed based on the assumptions of soil failure mode at the tip of Y-pile and the use of Mohr-Coulomb soil yield criterion and Vesic compressive correction coefficient with the induced stresses in the ground. Based on the comparisons with the field static load test results, it is found that the improved Terzaghi's method gives higher ultimate capacity, while the other two methods shows good agreement with the field results.

Ultimate Bearing Capacity of Subsoils to Marine Pipelines

Based on the theory of limit analysis, the Finite Difference Method (FDM) is established for evaluating the ultimate bearing capacity of subsoils to bear the unburied pipelines. The analytical results of bearing capacity of the ideal clay is given. The approach to bearing capacity evaluation of cohesionless subsoils without surcharge is suggested. The results from this method are consistent with those obtained from model tests.

Methods for Estimating the Ultimate Bearing Capacity of Layered Foundations

The Meyerhof and Hanna′s(M-H) method to estimate the ultimate bearing capacity of layered foundations was improved. The experimental results of the load tests in Tianjin New Harbor were compared with predictions with the method recommended by the code for the foundations of harbor engineering, i.e. Hansen′s method and the improved M-H method. The results of the comparisons implied that the code and the improved M-H method could give a better prediction.

Theoretical Analysis of Bearing Capacity of Shallowly Embeded Rectangular Footing of Marine Structures

In this paper, the finite element analysis software ABAQUS is used to analyze the ultimate bearing capacity of three-dimensional rectangular footing of marine structures. The deformation law and the failure mode of homogeneous seabed soil beneath the rectangular footing are analyzed in detail. According to the equivalent plastic strain of soil under rectangular footing, an allowable velocity field of homogeneous seabed soil is reasonably constructed. Based on the plastic limit analysis theory of soil mass and by using the Mohr-Coulomb yield criterion, an upper bound solution of the ultimate bearing capacity of three-dimensional rectangular footing on general homogeneous seabed soil is derived, and a correction factor of ultimate bearing capacity of three-dimensional rectangular footing is given. To verify the rationality and applicability of this theoretical solution, some numerical solutions are achieved using the general-purpose FEM analysis package ABAQUS, and comparisons are made among the derived upper bound solution, the solution of Vesic, and the solution of Salgado et al. The results indicate that the upper bound solution of the three-dimensional shallowly embedded rectangular footing proposed in this paper is accurate in calculating the bearing capacity of homogeneous seabed soil. For undrained saturated clay foundation and sandy foundation with smaller internal friction angle, this upper bound solution can evaluate the ultimate bearing capacity of rectangular footing; with the gradual increase of the internal friction angle of the soil, the ultimate bearing capacity of the proposed upper bound solution is slightly higher than that of the rectangular footing.

Bearing Capacity Analysis of Shallow Foundations Supported on an Artificial Fill(Substation at Kashari,Tirana)

The paper presents conclusions related to the design of shallow foundations,at the site where the Substation at Kashari,in Tirana is foreseen to be constructed.The project includes buildings with small to medium structures with 1-3 stories.The geological survey works include 6 boreholes of a depth 20.0 m,90 SPT(Standard Penetration Tests)tests,and laboratory works include 13 direct shear tests,27 unconfined and compressive strength tests,7 CU(consolidated undrained)tests and 9 UU(unconsolidated undrained)tests,etc.The foundation design must fulfill both,bearing and settlement criteria,but in this case the settlements of foundations are not possible to be calculated,since the laboratory works do not include any consolidation test.So,the local bearing capacity is expected to control the design in terms of bearing capacity and settlements.The local bearing capacity of shallow square foundations is evaluated by using Terzaghi’s formula,based on reduced shear strength parameters of soils below the bottom of foundations.The results are compared with the bearing capacity values calculated by using Burland and Burbdige(1984)method,based on the data of SPT tests.This method is used for checking the settlement(serviceability)criterion in the foundation design,when the direct settlement calculation is missing.The paper presents some conclusions related to local bearing capacity foundation-based design.

Bearing capacity of concrete filled bidirectional FRP tube subjected to axial compression

External confinement by fiber reinforced polymer (FRP) is an efficient technique to increase the bearing capacity and ductility of concrete. To better study the mechanical behavior of bidirectional FRP confined concrete, the yield criterion of bidirectional FRP is presented based on the static equilibrium condition in this paper, and a model for calculating the bearing capacity of bidirectional FRP confined concrete is established. The model can capture the character of bidirectional FRP confined concrete. Effects of the confinement effect coefficient, the unconfined concrete strength and the material properties of FRP on bearing capacity are analyzed. Results show that each parameter has different effects on the bearing capacity of bidirectional FRP confined concrete.

Ultimate bearing capacity of concrete dam involved in geometric and material nonlinearity

To get the actual ultimate bearing capacity of concrete dam, the effect of geometric nonlinearity and strain softening on it, which appears in the failure process of concrete dam, is studied. Overload method is adopted to obtain the bearing capacity of a concrete dam by taking into consideration strain softening in the material constitutive law, geometric nonlinearity in geometric equation and equilibrium differential equation. Arc-length method is used to find the extreme point and descending branch of the load-displacement curve of the dam. The results present that the effect cannot be ignored. And geometric nonlinearity of structure and strain softening of materials should be considered for numerical analysis of ultimate bearing capacity of a concrete dam.

Slope stability of increasing height and expanding capacity of south dumping site of Hesgoula coal mine:a case study

This paper is devoted to improve the containment capacity of the Hesgoula south dumping site.The general geology of the dumping site was obtained through geological surveys.Physico-mechanical properties of silty clay and bedrock layers that have a large impact on the stability of the dump were measured by direct shear tests and triaxial tests in laboratory.Then ultimate bearing capacity of the substrate were analyzed and calculated.This paper proposed three capacity expansion and increase plans and used GeoStudio software for comparison.Through computation of the stability of the dump site slope after capacity expansion and increase for each plan,the capacity expansion plan was determined.The capacity expansion and increase plan will solve the problem of the current insufficient containment capacity of the Hesgoula south dumping site,which is of great significance for saving mine transportation costs,improving work efficiency,and reducing grassland occupation.

考虑不同破坏形式下隧道锚承载力及破坏阶段研究

现有研究多以锚岩接触面出现塑性区域或应力峰值点转移作为达到极限状态的判别标准,但不同工程地质情况会导致隧道锚(TTA)破裂面线形存在较大差异,很难准确推导出隧道锚的极限承载力.为了进一步探求隧道锚在拉拔荷载下的工作过程,得到更加明确的隧道锚极限承载力的表达形式,采用幂指数函数形式表征倒锥形破坏破裂面的线形,基于Mindlin应力解与峰值剪应力控制理论得到界面破坏应力分布形式,推导了界面破坏与倒锥台破坏形式下的承载能力公式;采用国内5座悬索桥隧道锚承载力进行算例验证,同时分析研究了不同参数对隧道锚极限承载力的影响.研究表明:两种破坏形式下,承载力的主要来源为破裂面的黏结力,占总承载力的50%以上,承载力均随着长度与内聚力的增加而线性增加;承载力随着倾斜角的增加而增加,但增长速度减慢,界面破坏形式下出现先增加后减小的现象.对比以往试验以及数值模拟结果,与该文推导结果基本一致,分析公式计算结果和位移增长曲线,发现隧道锚工作过程明显呈现3个阶段,最终破坏形式为界面破坏和倒锥形破坏两种破坏模式的结合.

间断焊接包管加固圆钢管构件轴压极限承载力研究

为研究间断焊接包管加固杆件的轴心受压性能,设计了13组试件进行单调加载静力试验。对试件极限承载力、破坏模式、荷载-位移曲线和截面应变发展规律进行分析,对比了负载加固与非负载加固对试件极限承载力的影响。结果表明:包管构件的破坏模式可分为整体失稳破坏和内管外伸段强度破坏;包管构件内外管协同工作、共同受力,内管和外管都在屈服后发生整体失稳破坏;负载加固与非负载加固试件的极限承载力基本一致,相差2.2%,非负载加固试件与未加固试件相比,极限承载力最大提高了479.9%。根据试验结果对包管构件的ABAQUS有限元模型进行修正,并用该模型分析了各主要影响因素对包管构件极限承载力的影响规律。提出了包管构件极限承载力经验计算公式,且公式计算结果与试验结果吻合较好。

静压桩残余应力对极限承载力影响

为研究静压桩回弹特性,明确静压桩残余应力性状,使静压桩承载力能够得到有效发挥,通过静压桩沉桩及静载荷试验,结合有限元模拟方法,对不同沉桩速率和卸荷速率作用下静压桩的回弹特性进行分析,总结桩端残余应力对静压桩极限承载力的影响规律。结果表明:卸荷过程中桩体回弹量占桩体总沉降量的80%,卸荷完成桩体回弹位移逐渐稳定;沉桩结束后,桩周土体应力最大达到被动土压力的4.5倍,卸荷后浅部土体桩周侧压应力消散程度大于深部土体;桩端土体应力消耗越多,桩端残余应力越小,卸荷后桩端土体回弹量越多;沉桩速率和卸荷速率增加都会导致桩端残余应力减小,从而桩端土体能够提供的承载力降低,致使桩体承载力降低。研究认为静压桩残余应力是影响承载力的主要因素,卸荷速率对静压桩残余应力的影响最为明显。

砂土中冲刷条件下三筒基础水平承载特性研究

通过开展小比尺三筒基础承载力模型试验,研究冲刷条件下三筒基础水平承载特性,建立数值模型对模型试验结果进行验证与扩展,分析水平和弯矩荷载下,冲刷率e和相对筒间距S/D对极限承载力的影响,提出三筒基础极限承载力的冲刷修正系数dhe、dme的计算方法;采用固定荷载比方法,通过数值模型计算M-H加载条件下三筒基础的破坏包络线,分析冲刷率e和相对筒间距S/D对复合加载特性的影响,提出冲刷条件下三筒基础M-H破坏包络线公式。研究结果表明:冲刷条件下的三筒基础受水平和弯矩作用直至破坏的过程,经历弹性变形—塑性变形—失稳破坏3个阶段;三筒基础的水平极限承载力随冲刷率e的增大而下降,且下降速率逐渐增大,相同长径比的三筒基础的水平极限承载力随相对筒间距的减小而降低;随着冲刷率e的提高,三筒基础的M-H破坏包络线向内移动,随着相对筒间距S/D增大,归一化破坏包络线呈上凸的趋势。

锚杆钢-木组合托盘极限承载力学性能研究

为降低动压冲击对支护系统的破坏,适应大变形巷道的需要;基于球壳结构理论构建锚杆拱形钢托盘承载力学模型,给出钢托盘最大承载力计算式,分析钢托盘各参数尺寸对其承载力的影响关系,研究木托盘压缩实验特征;通过Abaqus软件对钢托盘与组合托盘开展有限元静态力学强度实验,对比分析钢托盘与组合托盘受压状态下的不同特征,分析让压距离对组合托盘承载性能的影响规律。结果表明:对钢托盘承载力的影响顺序为拱高>拱底圆半径>孔口半径,拱高与承载力服从对数增加关系,拱底圆半径、孔口半径与托盘承载力基本成线性增加关系;钢-木组合托盘中木托盘先受力,并经历了压密阶段、弹性变形阶段和塑性变形阶段,木托盘被压缩可降低钢托盘30.03%的承载受力,组合托盘的应力-位移曲线右移,组合托盘的极限承载力增加;钢托盘受压破坏从孔口处开始,基本成圆形向四周扩展,托盘底部四边中间区域与四角区域形成的高应力差是导致托盘四角破坏的主要原因。