Bearing Capacity Theory Research Articles

Softening-based interface model and nonlinear load-settlement response analysis of piles in saturated and unsaturated multi-layered soils

This work presents a simplified method for the nonlinear analysis of the load–displacement response of piles in multi-layered soils. As a starting step, a new interface model based on the disturbed state concept (DSC) is put forth to simulate the interface shear stress-displacement relationship by considering the nonlinear hardening–softening behaviour. In the new model, input parameters can be conveniently calibrated using conventional interface shear tests or on-site tests. The good agreement between predictions and experimental data from interface direct shear tests validated the performance of the proposed DSC model. The DSC model performed better in terms of predictions when compared to the hyperbolic one. Next, the soil-structure interface model and bearing capacity theory are coupled to provide a theoretical framework for the analysis of pile load-transfer in saturated and unsaturated multi-layered soils, where the DSC model is employed to represent base resistance as well as skin friction. This work also discusses the profile of steady-state in-situ matric suction, soil–water characteristic curve, and pore-water pressure of unsaturated soils. The proposed method has the advantage of being used in practice as it is simple to obtain input parameters from laboratory tests, as well as Standard Penetration or Cone Penetration Tests. The proposed framework is finally applied to the analysis of five well-documentedcase studies. The proposed approach and the static load test results from the field measurements are found to be in satisfactory agreement, indicating that the proposed method performs well. The proposed method is suggested to be utilised for preliminary analysis, planning a suitable programme of loading tests, as well as optimizing the pile design by back analysis ofthe load test results.

Soil suction effects on CPT data interpretation

The Cone Penetration Test (CPT) is one of the most widely used in situ test for site characterization and estimation of geotechnical parameters estimative. Its benefits include speed, reliability, repeatability, and the ability to provide continuous data. Although the interpretation is well-established for saturated and dry soils, it remains limited for unsaturated soils. This paper presents and discusses the influence of the unsaturated condition in CPTs performed on tropical soil site. Four CPT campaigns and gravimetric water content profiles have been determined in different periods over two years. Soil-water retention curves (SWRC) were used to estimate in situ soil suction. It was observed that the CPT data were influenced by soil suction up to 6.0 m depth. Two semi-empirical approaches based on bearing capacity theory and effective stress principle were used for data interpretation. These approaches allowed to assess the soil suction influence on CPT and to define the typical test profile with no suction effects. The importance of considering soil suction in the CPT interpretation on unsaturated soils is highlighted, and the effective stress approach is suggested as a starting point.

Response of shallow foundations in tire derived aggregate

This study investigates the quasi-static bearing stress-settlement response of shallow foundations in monolithic tire derived aggregate (TDA) layers having a total thickness of 3 m using a large-scale container and loading system. Tests were performed on footings having a range of widths, embedment depths, shapes, and loading inclinations. In tests where tilting was restricted, a clear bearing capacity was not observed for settlements up to 1.2B, where B is the footing width, but in tests where tilting was permitted bearing capacity was observed between settlements of 0.2B to 0.7B. Surface settlements indicate a dragdown response of the TDA adjacent to the footing extending out to more than 3B from the footing center, while settlement plates beneath the footing indicate a zone of influence of induced settlements of 14% at a depth of 4B. While bearing capacity theories for frictional geomaterials provided a reasonable prediction of the bearing capacity of footings in TDA for most tests, the corresponding settlements may be excessive for engineering applications. Accordingly, a correlation was developed between the theoretical bearing capacity and bearing stress at a settlement of 0.1B. A test with sustained loading indicates slight creep settlements with some stress dependency with magnitudes consistent with past studies.

Investigating the influence of root layer quantity on the pullout bearing characteristics of root piles in coral sand foundations

Root piles with good load-bearing characteristics can be used as foundations for offshore wind power facilities. By conducting model tests on root piles with varying numbers of root layers in coral sand foundations and studying the theoretical pullout ultimate bearing capacity, the influence of the number of root layers on the pullout bearing characteristics of root piles is analyzed. Subsequently, a formula for calculating the pullout ultimate bearing capacity of root piles is derived, drawing on the Vesic foundation bearing capacity theory and the Rankine soil pressure theory. The results indicate that increasing the number of root layers enhances the ultimate bearing capacity of root piles, enabling them to better withstand pullout forces and control displacement. The axial force curve of the roots exhibits a step-like pattern. Additionally, the maximum lateral mechanical resistance of the root piles in 3 and 5 layers gradually shifts downwards with increased loading. While the total bearing capacity of the root section increases, the rate of increase diminishes over time. Model test data validates the proposed theoretical formula for calculating bearing capacity, affirming its reliability. These research findings furnish a theoretical groundwork for the practical application of root piles in engineering.

Calculation method for the ultimate bearing capacity of pressure-cast-in-situ pile with spray-expanded frustum

In this paper, the new type of Pressure-cast-in-situ pile with spray-expanded frustum (PPSF) developed by the authors is composed of pile body, ribbed plate, and expanded body with double frustum. The PPSF has the advantages of high bearing capacity, small settlement, high construction speed, and significant economic and environmental benefits. To evaluate the ultimate bearing capacity of PPSF, a calculation method is proposed considering the special shape of PPSF. The ultimate bearing capacity of PPSF is considered as the sum of three parts, e.g., the ultimate bearing capacity of expanded body with double frustum, the ultimate skin friction of pile body, and the ultimate end resistance of pile base. The failure mode of the soil around the expanded body with double frustum is described based on the Meyerhof’s bearing capacity theory. The calculation formula for the ultimate bearing capacity of the expanded body with double frustum is established using the sliding block balance method. The rationality of the calculation method is verified by three cases.

Deterministic and probabilistic analysis of the response of shallow footings on unsaturated soils due to rainfall

Due to rainfall, footings are usually subjected to effects of water table fluctuations which results in the variation of ultimate bearing capacity in unsaturated soils. However, the conventional bearing capacity theories don’t account for the variation of suction as the water table position changes. In this paper, an equation based on Terzaghi theory is proposed to evaluate the variation of bearing capacity due to suction variations due to rainfall. The proposed equation results in higher bearing capacity values compared to the conventional Terzaghi equation. Further, a comparison of the bearing capacity obtained using the proposed equation is made with those obtained from Barcelona Basic model (BBM), Mohr-Coulomb model and Terzaghi equation. It is observed that BBM results in lower values of bearing capacity compared to Mohr-Coulomb model as the former considers the loss of suction upon infiltration. Soil properties like porosity, permeability and soil water characteristic (SWCC) influence the bearing capacity in unsaturated soils. Thus, probabilistic analysis is carried out by using an efficient kriging surrogate model in order to analyze the impact of variation of the associated parameters on the bearing capacity. The surrogate model can predict the surface displacements of footing upon infiltration with enhanced accuracy and computational efficiency. Considering the uncertainty associated with rainfall loads, it is observed that as the return period of rainfall increases, failure probability increases.

Experimental and Analytical Investigation of the Bearing Capacity of Bulbs for Squeezed Branch Piles

Reasonable estimation of the bearing capacity of bulbs is essential for the design of squeezed branch pile (SBP) foundations, and existing analytical methods cannot be applied to SBPs. This study investigated the bearing capacity of bulbs by model tests, field tests, and theoretical and numerical analysis. From the laboratory model loading test and transparent soil model test assisted by particle image velocimetry technology, the bearing features of SBPs and the displacement field around a bulb under failure state were investigated, respectively. It was found from the tests that the bulb’s bearing ratio is up to approximately 50% out of the total applied load to the pile at failure. Furthermore, by referring to Meyerhof’s theory of bearing capacity for deep foundations, an analytical method was proposed to calculate the bearing capacity of a bulb for an SBP considering its unique geometry. Finally, field tests with a real-size SBP and numerical study were conducted to verify the proposed method. The ultimate bearing capacity (UBC) of the bulb estimated by the proposed method has an acceptable difference of 4.21% from the model test and 17.6% from the numerical field cases. The proposed solution can be used as an effective explicit solution to evaluate the UBC of the single bulb of SBPs considering the pile’s dimensions and soil parameters.

Failure envelope considering the ultimate tensile capacity of suction caissons in sand

Little analytical work has been done to elucidate the ultimate capacity of suction caissons under vertical tensile (V), lateral (H), and moment (M) loads in soils. In this paper, in order to reveal the effect of vertical tensile, lateral, and moment loads on the ultimate capacity of suction caissons in sand, an analytical investigation was made using a traditional bearing capacity theory. Taking account of the vertical equilibrium of an annular element of a skirt, through the vertical tractions inside and outside the skirt of a suction caisson when a vertical tensile load is applied, the vertical displacement of the soils adjacent to the skirt of the suction caisson was presented. The most appropriate bearing capacity equation for predicting the experimental results was shown for suction caissons having an embedment larger than a diameter in sand. For the deformation-load responses of suction caissons with various embedment ratios in sand, subjected to inclined tensile loads, there was a good agreement between the results obtained from laboratory tests and those predicted by the present method. The failure surfaces, considering the ultimate tensile capacity in the H-M, H-V, and M−V planes, and in the H-M−V space, for suction caissons in sand, were presented.

Load bearing capacity of finite half space agricultural homogeneous soil

A comprehensive plate-sinkage equation is necessary for the description of the load bearing capacity of soils. In the last century, several improvements to the existing equations were attempted but with limited success. The main aim of this paper is to verify, evaluate and develop a load bearing capacity theory of finite half space soil. Agricultural soils may be regarded as a finite half space in which the tilled soil layer is comparable to the loading diameter. Harder soil is found below the tilled soil layer and this hard soil can be considered as a rigid layer. A new consideration is the compacted cone-shaped zone developing under a loading device and its possible interaction with the rigid bottom surface. Theoretical and experimental investigations reported in this paper have shown that these approaches have facilitated deriving new relationships valid for finite half space. These include two independent variables and developing a dimensionless load bearing number. This paper introduces a new dimensionless plate-sinkage equation describing soil deformation in a general form.

Experimental Study on Materials and Mechanical Properties of Steel Tube-Confined Coral Concrete Reinforcement Mechanism

Filling steel tubes with coral concrete to form concrete filled steel tube composite structures for compression members can compensate for its low aggregate strength. In order to demonstrate the reinforcement mechanism of coral concrete hoop under steel tube restraint and to propose the strength theory under the hoop effect, it is necessary to obtain the theoretical analysis based on the theory of triaxial compressive bearing theory of normal concrete. Therefore, starting from the failure mechanism of coral concrete under triaxial compression, the hoop reinforcement mechanism of coral concrete under different lateral pressure conditions is studied analytically. By the axial compression bearing capacity comparative test between normal concrete and coral concrete under steel tube restraint, comparative relationship between lateral pressure and circumferential strain is calculated and the conditions for taking values are acquired, which lays the foundation for the calculation theory of the compressive bearing capacity of it.

Bearing capacity and deformation behavior of rigid strip footings on coral sand slopes

Porous coral sands formed by the remains of marine organisms are important foundation-filling materials for artificial island construction and other marine geotechnical projects. A typical situation is that the significantly reduced bearing capacity of a rigid footing adjacent to coral sand slopes threatens the safety and stability of the upper structures. In this study, a series of model-scale tests were conducted to investigate the bearing capacity and deformation behavior of a rigid strip footing resting on the top of coral sand slopes with consideration of the effects of edge distance, slope height, slope angle, number of geogrid layers, burial depth and spacing of the geogrid layer. The measured deformation field based on particle image velocimetry (PIV) technology indicates that the unreinforced coral sand slope is dominated by unilateral sliding patterns, and its bearing area is significantly smaller than that of the geogrid reinforced coral sand slope (GRCSS). The bearing capacity in unreinforced coral sand slopes increases with the increasing edge distance, and the decreasing slope height and angle. Although the geogrid reinforcement significantly improves the bearing capacity, it is also affected by the number of layers, burial depth and spacing between reinforcement layers. Besides, the reduction coefficient of bearing capacity (RCBC), the bearing capacity factor (Nγq) and the normalized bearing capacity (Nγq/NγqR) were further calculated and discussed based on the test results and classical bearing capacity theory.

Research review on steel–concrete composite joint of railway hybrid girder cable-stayed bridges

PurposeThis study aims to research the development trend, research status, research results and existing problems of the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge.Design/methodology/approachBased on the investigation and analysis of the development history, structure form, structural parameters, stress characteristics, shear connector stress state, force transmission mechanism, and fatigue performance, aiming at the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge, the development trend, research status, research results and existing problems are expounded.FindingsThe shear-compression composite joint has become the main form in practice, featuring shortened length and simplified structure. The length of composite joints between 1.5 and 3.0 m has no significant effect on the stress and force transmission laws of the main girder. The reasonable thickness of the bearing plate is 40–70 mm. The calculation theory and simplified calculation formula of the overall bearing capacity, the nonuniformity and distribution laws of the shear connector, the force transferring ratio of steel and concrete components, the fatigue failure mechanism and structural parameters effects are the focus of the research study.Originality/valueThis study puts forward some suggestions and prospects for the structural design and theoretical research of the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge.

Shear band propagation and mechanical behaviours of landslides under top loading

The configuration of slip surface is conventionally regarded as a key characteristic to distinguish slope failure modes that are embedded in the limited equilibrium method and the bearing capacity theories. However, few studies indicated that a different way of propagating a slip surface with the same configuration might affect the mechanical behaviour and failure mode of the slope. In this paper, the mechanical behaviour is studied in two slopes that have a similar configuration of slip surface with different processes of shear band evolution. Advances in transparent soil technology allow the non-intrusive observation of shear band development in the laboratory slope models. This paper presents shear band development inside slopes using the transparent soil technique and then analyse the mechanical behaviour via the discrete element method (DEM). In order to reproduce the laboratory results, the real shape of transparent soil particles is used in the DEM model, and the microscopic parameters are calibrated by response surface methodology (RSM). The mechanical parameters such as movement, stress, void ratio and energy dissipation are measured in different stages of shear band evolution and are measured in four regions: the weak plane, the shear band, the slope mass above the slip surface, and the slope mass below the slip surface. This paper presents the role of shear band propagation in the mechanical behaviour of slope and discusses the possibility of monitoring the mechanical behaviour of slope to predict the coalescence of slip surface.

Model Test and Numerical Simulation of Water Conservancy Foundation Bearing Capacity.

In order to further improve the construction quality of water conservancy projects under different soil conditions and ensure the safety, stability, and durability of water conservancy project foundation construction under special circumstances, this study takes the bearing capacity of water conservancy land foundation as the research direction, takes frozen soil foundation and bag gravel pier composite foundation as examples, and further optimizes the parameters of foundation bearing capacity by using the theory of foundation ultimate bearing capacity and related algorithms. The P-S curve of bearing capacity shows that when the foundation is frozen to −15°C and the foundation sum is about 190 kN, the P-S curve trend at this time changes significantly, which is not different from the indoor simulation result of 170 kN. The final numerical analysis of foundation bearing capacity is relatively reliable, which can provide a powerful reference for the calculation of foundation bearing capacity of hydraulic engineering.

Failure surface considering the ultimate tensile and compressive capacities of suction caissons in clay

One of the important issues for suction caissons is to demonstrate the effect of the contact between the base and the soil on the ultimate capacities of vertical (V), lateral (H), and moment (M) loads. It has not yet been analytically revealed how the ultimate capacities of suction caissons are dependent on the contact conditions of tension and no-tension interfaces under combined loads including vertical compressive and tensile loads. In this article, an analytical investigation into the effect of interfaces on the ultimate vertical, lateral, and moment capacities of suction caissons in nonhomogeneous clay is made using a traditional bearing capacity theory with tension and no-tension interfaces. For failure envelopes of suction caissons in clay subjected to lateral and moment loads under vertical compressive and tensile loads, the results predicted by the present method are compared with those obtained from the finite element analysis. In order to compare failure envelopes obtained from a tension interface and those obtained from a no-tension interface under general loading, failure envelopes in the H-V, M-V, and H-M planes and in H-M-V space for suction caissons in clay are investigated.

Design method of fire-resistance capacity of reinforced-concrete-filled steel tube column under axial compression

Concrete-filled steel tube (CFST) columns are widely used in high-rise and superhigh-rise buildings because of their good mechanical properties, and the fire protection design of building structures must be considered. Under the same conditions, reinforced-concrete-filled steel tube (RCFST) columns show better fire-resistance performance than CFST columns. The theoretical calculation formula of its axial compressive fire-resistance capacity was derived in this study. The current structural design method adopted in China is a partial factor method based on reliability, in which the partial factors at room temperature are generally used for structural design at high temperatures. The strength of materials has greater dispersion at high temperatures, and it is necessary to develop reliability design methods for CFST columns at such temperatures. To consider this change fully, reliability theory was used to obtain the material partial factor at high temperatures. Then, based on the calculation theory of the axial bearing capacity of the RCFST column at high temperatures, a fire-resistant design method for the RCFST column was developed.

Failure surface for shallow foundations in sand using a classical bearing capacity

Much effort has been made to elucidate the ultimate capacity of shallow foundations under the general cases of vertical (V), lateral (H), and moment (M) loads in soils. The nature of the dependency of the ultimate capacity of shallow foundations on the combination of V, H, and M loads, the ratio of embedment to diameter, and soil properties has has not yet been analytically revealed. In this paper, an analytical investigation into failure effect of V, H, and M loads applied to shallow foundations in nonhomogeneous sand is made using a classical bearing capacity theory. Of the bearing capacity equations proposed thus far, the most appropriate bearing capacity equation which can predict experimental results of shallow foundations in sand is presented. A no-tension interface between a foundation base and a soil and an effective diameter of the foundation are used to analyze the base failure produced by the vertical stress of the soil below the foundation base when vertical and moment loads are applied. For shallow foundations with various embedment ratios in sand under the two different loading ways, the displacement-load curves and failure envelopes in the H-M, H-V, and M−V planes and in the H-M−V space are presented. For failure envelopes in the H-M plane under a constant vertical load for shallow foundations in sand, the results obtained from experiments are well predicted by the present method.

Design and analysis of geosynthetic-reinforced and floating column-supported embankments

ABSTRACT Geosynthetic-reinforced column-supported system is an economic and effective solution to support embankments constructed on soft soils. In this solution, both end-bearing and floating columns are commonly used in practice. For deep soil foundation depths, floating columns are more economical than end-bearing piles. The design of a floating column foundation involves complex soil–structure interactions and there are still no clear uniform guidelines available for the design of embankments supported by floating columns. The main focus of this paper is to present a design method for the geosynthetic-reinforced floating column-supported (GRFCs) embankments. The main features of the proposed method are combining the bearing capacity theory for the floating columns, the arching theory for fill soils, the tensioned membrane theory for the geosynthetic, and considering interaction models between geosynthetic, soil, and piles. Using the proposed method, the influences of the pile geometry, soft clay, geosynthetic, and embankment fills properties were investigated. It was observed that the geosynthetic membrane inclusion enhances the load transfer mechanism and reduces significantly the differential settlements of floating pile-supported embankments. The floating columns with a higher ultimate bearing capacity cause more soil arching. In general, the soil shear strength properties and column geometry (length, diameter, column spacing) have a strong influence on the GRFCs embankment behaviour. Finally, the proposed method is compared with the BS 8006–1 and EBGEO design standards considering several experimental and numerical models to investigate its validity. The results showed that the proposed method is able of very good prediction performance and allows conducting the design optimization of GRFCs embankment.

Upper-bound limit load of rigid pavements resting on reinforced soil embankments – Kinematic approach

This study evaluates the influence of inclined ground on the ultimate load-carrying capacity of rigid concrete pavements laying on unreinforced and reinforced soil embankments. The solution procedure is developed based on the kinematic approach of the limit analysis. The carrying capacity is sequentially obtained by satisfying the energy principle of the upper-bound theorem alongside the associated flow rule. A multi-block collapse mechanism is assumed for the intended purpose, which is later optimized to obtain the proper upper-bound limit solution. The ultimate carrying capacity of the pavement is seen to be improved further by reinforcing the embankment and modifying the soil properties. The effect of individual parameters influencing the results is discussed in detail. The available bearing capacity theories developed for rigid foundations are invoked for validation and comparison to bolster the legitimacy of the present solution.

Bearing Capacity Factor of Circular Footings on Two-layered Clay Soils

Geotechnical engineers often deal with layered foundation soils. In this case, the soil bearing capacity assessment using the conventional bearing capacity theory based on the upper layer properties introduces significant inaccuracies if the top layer thickness is comparable to the rigid footing width placed on the soil surface. Under undrained conditions the cohesion increases almost linearly with depth. A few theoretical studies have been proposed in the literature in order to incorporate the cohesion variation with depth in the computation of the ultimate bearing capacity of the strip and circular footings. Rigorous solutions to the problem of circular footings resting on layered clays with linear increase of cohesion do not appear to exist. In this paper, numerical computations using FLAC code are carried out to assess the vertical bearing capacity beneath rough rigid circular footing resting on two-layered clays of both homogeneous and linearly increasing shear strength profiles. The bearing capacity calculation results which depend on the top layer thickness, the two-layered clays strength ratio and the cohesion increase rates with depth are presented in both tables and graphs, and compared with previously published results available in the literature. The critical depth for circular footing is found significantly less than for strip footing. Doi: 10.28991/cej-2021-03091689 Full Text: PDF