Vertical Ultimate Bearing Capacity Research Articles

ULTIMATE VERTICAL BEARING CAPACITY OF CLAYEY SQUEEZE BREAKDOWN USING RIGID-PLASTIC FINITE ELEMENT METHOD

The relations of ultimate bearing capacity for foundations are specified in the guideline published by the Architectural Institute of Japan for design of building foundations. The rigid-plastic finite element method developed by Tamura and Ohtsuka has been employed to estimate the ultimate bearing capacity of footings. The characteristic of this method is that, in contrast to deformation analysis, it applies limited soil constants; only the strength parameters, such as cohesion and friction angle, are used since the method deals with the limit state directly by disregarding the deformation of the building and ground. In this study, a series of rigid plastic finite element analyses were performed to compare the ultimate bearing capacities of spread foundation for clayey squeeze breakdown obtained by simulations and the formulae of the Architectural Institute of Japan. The change in the failure mode of the ground was discussed considering the geometrical ratio between the width of the footing and the surface clay layer. In addition, inclined load was considered for clayey squeeze breakdown. The applicability of rigid plastic FEM to the assessment of ultimate vertical bearing capacity of clayey squeeze breakdown was demonstrated.

A Numerical Study and Simulation of Vertical Bearing Performance of Step-Tapered Pile Under Vertical and Horizontal Loads

In the present work, a numerical simulation of vertical bearing performance of step-tapered pile was carried out. The effects of pile geometry and the soil profile on the vertical bearing capacity of the step-tapered pile under vertical and horizontal loads were studied. Numerical results indicate that increasing diameter (D) of the enlarged upper part of step-tapered pile can increase its vertical ultimate bearing capacity when the other geometric parameters remain unchanged. When the distance (L) between the upper enlarged surface and the top of step-tapered pile is within a threshold value, the increase in the distance (L) can improve the vertical ultimate bearing capacity of the pile. Also, increasing the length (H) of the enlarged upper part of step-tapered pile can significantly bring up the vertical ultimate bearing capacity of the pile. Strengthening the soil around the step-tapered pile and at the pile tip can increase the ultimate bearing capacity of the pile. The distribution of axial force changes abruptly at the lower end of the enlarged part of the step-tapered pile in saturated clay, silty clay and sandy soil, and the axis force at the lower end of the enlarged part is greatly attenuated.

The ultimate bearing capacity of shallow strip footings using slip-line method

Based on the limit equilibrium theory, an accurate approach is proposed to solve the ultimate bearing capacity of shallow strip footings under general conditions. The foundation soil is considered to be an ideal elastic-plastic material, which obeys the Mohr-Coulomb yield criterion, and is assumed to be an ideal continuous medium which is isotropic, homogeneous and incompressible or non-expansive. Through analyzing the relative motion and interaction between the footing and soil, the problem of the ultimate bearing capacity of shallow strip footings is divided into two categories. A minimum model with the total vertical ultimate bearing capacity as its objective function is established to solve the ultimate bearing capacity using the slip-line method with no need to make any assumptions on the plastic zone and non-plastic wedge in advance. A convenient and practical simplified method is also proposed for practical engineering purposes. Furthermore, the first category of the problem in the case of the same uniform surcharges on both sides of footings is the focus of the study: the applicable conditions of Terzaghi’s ultimate bearing capacity equation as well as the theoretical exact solutions to its three bearing capacity factors are derived, and a new bearing capacity equation is put forward as a replacement for Terzaghi’s equation. The geometric and mechanical similarity principle is proposed by a dimensionless analysis. The results show that for perfectly smooth footings, the total vertical ultimate bearing capacity obtained by the present method is in good agreement with those by existing methods, whereas the existing methods underestimate the ultimate bearing capacity in the case of perfectly rough footings. The classic Prandtl mechanism is not the plastic failure mechanism of the ultimate bearing capacity problem of perfectly smooth footings on weightless soil.

Field Load Testing Study of Vertical Bearing Behavior of a Large Diameter Belled Cast-in-Place Pile

To investigate the vertical bearing behavior of manually excavated large diameter belled concrete piles (LDBCPs), field loading tests were performed on a total of 16 LDBCPs, ranging from 0.8 to 3.5 m in base diameter from 6.1 to 18.0 m in embedment length. The end bearing stratum is sand and gravel. The influence of pile dimensions (i.e., size of enlarged base D, embedment length L, and length-to-diameter ratio L/D) on the vertical bearing behavior of a belled pile is presented and discussed. Comparison is also made of the vertical bearing behavior of a belled pile and of a conventional straight pile under otherwise similar conditions. The results indicate that: 1) The vertical bearing capacity of a belled pile is significantly greater than that of a conventional straight pile provided the debris at the bottom of a belled pile is properly removed; 2) over 65% of the vertical bearing capacity for a belled pile is attributed to the tip resistance (Qe); 3) compared to the contribution of pile length L, increasing enlarged base D is a more effective way to increase the vertical ultimate bearing capacity of a belled pile (Qu); 4) the optimum length-to-enlarged base ratio (L/D) for belled piles to achieve maximum vertical bearing capacity is around 3.2.

Field test on Ultimate bearing capacity of Composite Pile made up of Jet-mixing Cement and PHC Pile with Core Concrete

Composite pile made up of jet-mixing cement and PHC pile with core concrete (CPCP) is a new kind of pile. It is formed by inserting PHC core promptly into the cement soil mixing pile. According to the single pile static load test and PHC pile cement soil bond strength test, differences between CPCP and pipe pile in bearing capacity and coordination deformation mechanism are studied. The results show that presence of peripheral cement soil has greatly improved the bearing capacity of CPCP. Three different loading modes have no obvious effect on CPCP bearing capacity, but the more significant effects on settlement. When the cement soil and soil interface destroyed, pile and cement soil interface friction resistance is much smaller than the bond strength, indicating that the bond strength can ensure coordination between the pile and cement soil. On this basis, the design formula for calculating the bearing capacity of CPCP pile is proposed. Comparing calculated values with field measured values, it has been found that the results are less error and the formula has a certain reliability in the calculation of vertical ultimate bearing capacity of CPCP pile, providing a certain reference for the design and calculation of this type of piles.

Failure Envelopes of Wide-Shallow Composite Bucket Foundation for Offshore Wind Turbines in Silty Sand

The wide-shallow composite bucket foundation (WSCBF) is a new type of offshore wind power foundation that can be built on land and rapidly installed offshore, thereby effectively reducing the construction time and costs of offshore wind power foundation. In this study, the horizontal bearing capacity is calculated by finite element simulation and compared with test results to verify the validity of results. In this process, the vertical load and bending load are respectively calculated by the finite element simulation. Under the vertical load effect, the bucket foundation and the soil inside are regarded as a whole, and the corresponding buckling failure mode is obtained. The ultimate vertical bearing capacity is calculated using empirical and theoretical formulas; the theoretical formula is also revised by finite element results. Under bending load, the rotational center of the composite bucket foundation (in a region close to the bucket bottom) gradually moves from the left of the central axis (reverse to loading direction) to the nearby compartment boards along the loading direction. The H–M envelope line shows a linear relationship, and it is determined that the vertical and bending ultimate bearing capacities can be improved by an appropriate vertical load.

A Study of PHC Pipe Pile Vertical Ultimate Bearing Capacity Calcula-tion Method and its Numerical Simulation Analysis

According to the PHC pipe pile design of Xinwan Plaza, Huaiyuan, Anhui and pile test results of static sounding method and experience method using the ultimate bearing capacity of single pile are calculated, considering the effect of soil plug the influence of vertical ultimate bearing capacity of single pile, and the formula for calculating the lateral resistance and end resistance, static sounding method and the correction formula to calculate the bearing capacity calculated results was coincident with the results of test pile. Combining with the project of Xinwan Plaza, Huaiyuan, Anhui, through the static load test, a study of the load transfer mechanism of PHC pipe pile, analyzes the vertical load, the change rule of the settlement of pile body and pile and the use of finite difference software FLAC3D simulation of the PHC pipe pile static load test, the simulation results agreed with the measured load-settlement curve.

Experimental investigations on ultimate bearing capacity of peat stabilized by a group of soil–cement column: a comparative study

The aim of this paper was to determine the ultimate vertical bearing capacity of rectangular rigid footings resting on homogeneous peat stabilized by a group of cement deep mixing (CDM) columns. For this purpose, a series of physical modeling tests involving end-bearing and floating CDM columns were performed. Three length/depth ratios of 0.25, 0.5, and 0.75 and three area improvement ratios of 13.1, 19.6, and 26.2 % were considered. Bearing capacity of the footings was studied using different analytical procedures. The results indicated that compared to unimproved peat, the average ultimate bearing capacity (UBC) improvement of floating and end-bearing CDM columns were 60 and 223 %, respectively. The current study found that simple Brom’s method predicted the UBC of the peat stabilized with floating CDM columns with reasonable accuracy, but underestimated the UBC by up to 25 % in the case of end-bearing CDM columns. Published laboratory experiences of stabilizing soft soils using soil–cement columns were also collated in this paper.

Bearing behavior of wide-shallow bucket foundation for offshore wind turbines in drained silty sand

The failure mode of the wide-shallow bucket foundation is different from that of the traditional suction caisson and the narrow-deep bucket foundation. Results from elasto-plastic analyses of 3D finite element models are presented, aimed at defining the shape of the yield envelope in the V–H, V–M, H–M and V–H–M spaces and the failure mode of the bucket foundation. The compressive bearing capacity of the wide-shallow bucket foundation was determined by the displacement. The corresponding load under a vertical displacement of 0.06D was the vertical ultimate bearing capacity. The vertical loading had an amplification effect on the horizontal load-bearing and moment capacity, and the horizontal loading which was in the opposite direction to the moment increased the moment capacity by 20–40%. New simplified calculation methods were proposed for the vertical load-bearing capacity and the overturning stability. In the proposed method, the vertical capacity consisted of a top plate resistance of the bucket and a side frictional resistance. The overturning stability was determined by the safety factor method, and depended on the location of the rotation point. A comparison between results from the finite element analysis and the simplified calculation methods showed that the proposed equations properly predicted the capacities of the wide-shallow bucket foundations.

The Experiment on how the Ratio of Diameter to Height D/H Influences the Bearing Capacity of Bucket Foundation

Through eight groups of room model experiments based on bucket foundation, P-S curve can be plotted for each group according to the experiments results and be able to get the ultimate strength and ultimate displacement for them. Therefore how the ratio of the ultimate vertical bearing capacity and the ultimate displacement changes with the ratio of diameter to height can be analyzed. When the ratio of diameter to height is less than 1.2, the ratio of the ultimate vertical bearing capacity and the ultimate displacement changes significantly; and when the ratio of diameter to height is greater than 1.2, the ratio of ultimate vertical bearing capacity and ultimate displacement is not affected obviously. When the ratio of diameter to height is 1.2, it reaches the maximum utilization of the materials, and the cost of the project can be effectively reduced. So the paper considers that the ratio of diameter to height = 1.2 can be used as the optimum point of the ratio of diameter to height of the bucket foundation.

Geometry Optimization and Engineering Applications of Transmission Tower Foundation in the Slope

Combining with practical engineering, geometry optimization and engineering applications of transmission tower foundation in the slope is researched by using the finite-difference software FLAC3D. The variation of the pullout, vertical and horizontal ultimate bearing capacity with the diameter and length of the pile is analyzed. And optimization program of actual project is given. Research shows that when the pile length is constant, the variation of the pullout and vertical ultimate bearing capacity is increasing with the diameter increasing significantly and the horizontal ultimate bearing capacity is not significant. When the diameter is constant, the pullout, vertical and horizontal ultimate bearing capacity is increasing with the length increasing significantly. By analyzing nonlinear regression analysis of calculation data, the formula of the ultimate bearing capacity is carried out, which can consider the different pile diameters and lengths. When the gradient and distance of slopes is constant, the pullout, vertical and horizontal ultimate bearing capacity can be carried out with the formula, which can provide a reference to specification revision and engineering.

Critical Skirt Spacing for Shallow Foundations under General Loading

Finite-element limit analysis is used to identify the critical internal skirt spacing for the undrained failure of shallow skirted foundations under conditions of plane strain based on the criterion that the confined soil plug should ideally displace as a rigid block, such that optimal bearing capacity is realized. General loading (vertical, horizontal, and moment) is considered for foundations with skirt embedments ranging from 5 to 50% of the foundation breadth in soil having either uniform strength or strength proportional to depth. The results explicitly identify the number of internal skirts required to ensure soil plug rigidity under arbitrary combinations of horizontal and moment loading expressed as a function of the normalized skirt embedment and the maximum expected level of vertical loading as a fraction of the ultimate vertical bearing capacity. It is shown that fewer internal skirts are required with increasing normalized foundation embedment, but more internal skirts are required with increasing soil strength heterogeneity. The results also indicate the potential for a significant reduction in capacity if insufficient skirts are provided, such that plastic deformation is permitted to occur within the soil plug.

Analysis of Principal Component - Application of SVM Model in Prediction of Ultimate Bearing Capacity of Static Pressure Pipe Pile

Vertical ultimate bearing capacity of static pressure pipe pile is influenced by comprehensive factors, such as pile body, soil around pile and construction conditions., and the relationship between the impact factors and ultimate bearing capacity of a single pile is highly complexity and non-linear. This paper is based on collecting the data from static load tests in typical geological conditions of Liao-shen area, construction records, and test pile sites. And then combine analysis of principal component with SVM to analysis the prediction of the single pile’s vertical ultimate bearing capacity. This model can reduce the number of SVM input variable dimension to improve speed of training support vector effectively. At the same time it can eliminate the influence factors of multiple correlation. The results show that the proposed principal component analysis SVM model has good predictive accuracy and generalization ability, and opens up new avenue of research for analysis of static pressure pipe pile vertical bearing properties.

Study on Vertical Bearing Capacity and Time Effect of the Jacked-in PHC Pipe Pile in the Cohesive Soil Area

The static load test of 34 jacked-in PHC pipe piles of medium length are performed in the cohesive soil area, the relationship between the vertical ultimate bearing capacity and the final pressure, and the time effect of vertical bearing capacity of the jacked-in PHC pipe pile are studied. The data of static load test is analyzed statistically with software SPSS, the regional empirical coefficient about the vertical ultimate bearing capacity and final pressure, and the time effect formula about vertical bearing capacity of the jacked-in PHC pipe pile in the cohesive area are obtained. According to the regional empirical coefficient, the pile pressing machine and counterweight can be chosen reasonably and the vertical ultimate bearing capacity of single pile can also be estimated rapidly, then we can instruct the design and construction of the jacked-in PHC pipe pile. According to the time effect formula, the vertical bearing capacity at different periods of the jacked-in PHC pipe pile can be obtained, the cost of the foundation engineering can be reduced by considering the time effect influence to the vertical bearing capacity of the jacked-in PHC pipe pile.

Research on the Relationship between SPT and the Ultimate Vertical Bearing Capacity of Jacked Pile in Shenyang District

Though the wide applications of jacked pile in engineering in Shenyang district, the problem is also exist in engineering for the capacity of the jacked pile is hard to account. The relationship between the standard penetration test and the ultimate vertical bearing capacity of jacked pile is established in this paper; also an empirical formula is put forward for calculating the ultimate vertical bearing capacity of the jacked pile in this district with blow count of standard penetration test (SPT). The engineering examples indicated that the empirical formula is feasible because the calculating bearing capacity of the silent pipe pile is coincided with the static load tests. The calculated results satisfy the engineering requirement andt can be concluded that the method is also convenient to choose the diameter and length of the pile during the initial stage of design.

Prediction of Vertical Ultimate Bearing Capacity in Piles Based on the Improved Hyperbolic Model

Vertical static load test is widely used in the determination of pile bearing capacity, the mathematical model used to fit test pile data in determining the bearing capacity is essential. From the perspective of analytic geometry, the paper analyzes the traditional method of hyperbola, of which the asymptotic line of equilateral hyperbola was used to determine the ultimate bearing capacity. By extending the equal-axed conditions, a more general form of hyperbolic equation is derived and feasibility of such method is also analyzed, which indicates that the maximum point of curvature in such hyperbolic curve can determine the ultimate bearing capacity and such method is proved to be reasonable in practical projects.

SVM Model Based on the Influencing Factors Evaluation and Prediction of Ultimate Bearing Capacity of Statically-Pressured Pipe Pile

The prediction accuracy of vertical ultimate bearing capacity of statically-pressured pipe pile is difficult to ensure with traditional methods, because it is influenced by comprehensive factors, such as pile body, soil around pile and construction conditions. In this paper, a support vector machine (SVM) model based on the influencing factors importance evaluation was established to predict the vertical ultimate bearing capacity of single pile. This method would consider grey relational analysis and variable projection importance analysis as the attribute preprocessor facilities, which could determine the vertical bearing character in typical geological conditions through the analysis results of these two methods. Then, the SVM model was established with the main factors influencing ultimate bearing capacity as input to predict ultimate bearing capacity of single pile. The results showed that this method would have better precision of prediction, and the established model would have better generalization ability, which would open up a new way for the theoretical analysis of bearing characters of statically-pressured pipe pile and provide references for future relevant research.

Prediction Method of Vertical Ultimate Bearing Capacity of Single Pile Based on Support Vector Machine

By comprehensively analyzing the main factors affecting vertical ultimate bearing capacity of single pile, a prediction model of Support Vector Machine (SVM), which discusses the nonlinear relationship between vertical ultimate bearing capacity of single pile and influencing factors and analyzes the parameters on the performance of the model through sample knowledge learning, is established in this paper. The research results indicate that, SVM model, which is compared with BP neural networks model, possesses simple structure, flexible adaptability, high precision and powerful generalization ability, and can accurately reflect the actual mechanical characteristics of pile, therefore, SVM is an effective method for predicting vertical ultimate bearing capacity of single pile.

Artificial Neural Network Model for Time-Dependent Vertical Bearing Capacity of Preformed Concrete Pile

Mechanism of time effect on vertical ultimate bearing capacity (VUBC) of preformed concrete pile is analyzed. The effect strongly depends on seven parameters of pile engineering. Pile length, area of pile section, soil friction angle, soil consolidation coefficient, soil elastic module and time after pile installation and pile type are them. Considering time effect and soil consolidation, artificial neural network model to predict this time-dependent VUBC is established. Input layer includes seven parameters discussed above. Conjugate gradient method is adopted to train the net. Based on calculation of practical piles, results of the model are found to be in good agreement with field tests, and the efficiency of the present model is signalized.

Ultimate Bearing Capacity Analysis of a Super-Long Rock-Socketed Filling Pile Based on Catastrophe Theory

Based on the catastrophe theory of nonlinear science, a cusp catastrophe model of a super-long pile under axially load is established, and the vertical ultimate bearing capacity expression of super-long pile is derived. By fitting pile load-settlement field test data, the coefficients of a hypothetical super-long pile load-deformation curve and the value of ultimate bearing capacity are obtained. The results show that: the cusp catastrophe model is applicable to the determination of ultimate bearing capacity, and can be used to predict the buckling failure of a super-long pile. In addition, a fold catastrophe model is established to investigate the effects of plastic softening on the ultimate bearing capacity. The derived ultimate bearing capacity expression implies that the radius of the elastic and the plastic softening zones are relevant to the ultimate bearing capacity.