Vertical Bearing Capacity Research Articles

Vertical bearing capacity of HSCM pile groups in marine soft clay

Vertical bearing capacity of HSCM pile groups in marine soft clay

Influence of the Internal Friction Resistance on the Vertical Compressive Bearing Capacity of Large-Diameter Steel Pipe Piles

Current calculation methods for the vertical bearing capacity of steel pipe piles are predominantly designed for smaller diameters and do not account for the soil inside the pile. This necessitates an evaluation of their applicability to piles with diameters exceeding 2.0 m. This study aims to refine the existing formula for calculating vertical bearing capacity, as outlined in the Port Engineering Foundation Code of China, by investigating the vertical bearing capacity of large-diameter steel pipe piles through numerical simulations. By analyzing the relationship between the internal friction resistance of the soil core within the pipe and the bearing capacity for diameters ranging from 2 m to 10 m, this paper proposes a revised formula specifically tailored for steel pipe piles with diameters greater than 2 m, incorporating the effect of the soil core. The validity of the proposed formula is then confirmed through comparison with field data from four large-diameter steel pipe piles. The results demonstrate that the modified method proposed in this study performs better than the original formula when compared with the measured data.

Analysis of the Vertical Dynamic Response of SDCM Piles in Coastal Areas

The stiffened deep cement mixing (SDCM) pile, as a new type of rigid–flexible composite pile, significantly enhances the vertical bearing capacity of traditional precast piles, thus holding broad application prospects in the substructure construction of nearshore bridges and marine energy structures. This paper investigates the vertical dynamic response of SDCM piles through theoretical derivation and parameter analysis. Firstly, based on elastic dynamics theory and the three-phase porous media model, vertical vibration control equations for both SDCM piles and fractional-order viscoelastic unsaturated soils are established. Secondly, theoretical derivations yield exact analytical solutions for the surrounding dynamic impedance, top dynamic stiffness, and dynamic damping of the SDCM pile. Finally, through numerical examples and parameter studies, the impact mechanisms of physical parameters in the SDCM pile–unsaturated soil dynamic coupling system on the top dynamic stiffness and dynamic damping of the SDCM pile are analyzed. The research results presented in this paper indicate that reducing the radius of the rigid core pile while increasing the thickness of the exterior pile has a positive effect on enhancing its vibration resistance. Additionally, increasing the length of SDCM piles contributes to improved vibration performance. However, an increase in the elastic modulus of the cement–soil exterior pile is detrimental to the vibration resistance of the rigid composite pile. On the other hand, an increase in the elastic modulus of the concrete core pile only enhances its ability to resist vibration under low-frequency load excitation. Furthermore, enlarging the soil saturation, decreasing the intrinsic permeability, and enlarging the soil relaxation shear modulus have a significant positive impact on improving the vibration resistance of SDCM piles. In contrast, changes in porosity have a negligible effect on the ability to resist vertical vibrations of SDCM piles.

Experimental study on seismically isolated systems using a novel roller-type bearing with energy dissipation capacity

The roller-type isolation bearing is highly effective in limiting the transmission of lateral seismic forces to the superstructure. This paper introduces a novel roller-type bearing with energy dissipation capacity (RB-EDC), which includes flat bearing seats, rollers, limit plates with energy dissipation capability, and limit rings. The RB-EDC is characterized by its excellent energy dissipation capacity, simple manufacturing process, low cost, vertical tensile bearing capacity and stable performance in extremely cold regions due to its specific configuration and materials. The design procedure for the RB-EDC is detailed herein. Subsequently, pseudo-dynamic comparison tests were conducted on both a seismic isolation system specimen and a RC column specimen under frequent and rare earthquake conditions to validate the damping performance of the RB-EDC. The seismic isolation system consists of the RB-EDC and an RC column identical to the RC column specimen. The results indicate that, compared to the RC column specimen, the column in the seismic isolation system specimen significantly reduces crack distribution ranges, rebar strain, concrete strain, and displacement at the column top under seismic actions. The RB-EDC exhibits significant energy dissipation capacity even during frequent earthquakes, demonstrating effective damping performance. However, the residual displacement of the RB-EDC increases with seismic intensity, which may impact the damping performance of the bearing in future potential earthquakes, indicating the need for further redesign to incorporate self-centering capacity.

Study on bearing characteristics of single pile in heterogeneous layered foundation

Based on a project in Lanzhou City, Gansu Province, China, the bearing and internal force characteristics of 2 piles of different lengths under vertical load were tested and analyzed by using BOFDA technology and anchor pile method static load test. The results show that long pile has higher vertical bearing capacity and greater elastic working range, but the axial force of long pile and short pile has the same trend. The lateral friction resistance of the soil layer around the pile plays a role earlier than the pile tip resistance, and the lateral friction resistance of the upper soil layer plays a role earlier than the lower soil layer. The increasing amplitude of lateral friction resistance in different soil layers is also different. The settlement of short pile top is mostly caused by the displacement of pile bottom, and the pile tip resistance is more affected by the pile tip sediments. The relationship between pile end resistance and displacement under the influence of sediments can be analyzed by three-fold line model.

Research on the mechanism of impact of vibrational loads on the bearing capacity of drilling surface conductor

The surface conductor is the first structural pipe in the development of deep-water oil and gas resources, bearing the top load and suspending various casing layers. Vibrational loads can cause soil structural damage and increase pore pressure, reducing the bearing capacity of the surface conductor and threatening the safety and stability of the subsea wellhead. Based on the vertical force analysis of the surface conductor and considering the impact of vibrational loads on soil strength, a model for the vertical bearing capacity of the surface conductor was established. Utilizing the dynamic Winkler model for pile foundation horizontal dynamic response, the surface conductor was simplified as a bending beam subjected to harmonic vibration, and a control equation for lateral deformation of the surface conductor was established. The effects of vibration load amplitude and frequency on the vertical bearing capacity of surface conductors were analyzed through simulation experiments, resulting in an equivalent bearing capacity coefficient for surface conductors ranging from 0.88 to 0.97. Combining the engineering data from a deep-water block in the South China Sea, the reliability of the theoretical calculation model was validated. The analysis indicates that the maximum bending moment of the surface conductor is approximately 6m below the mudline; low-frequency(0.05Hz–0.2Hz) vibrational loads can reduce the ultimate bearing capacity of the surface conductor by 3%–11%, with the effect gradually diminishing over time. This research provides a theoretical basis for the design of surface conductor in deep-water oil and gas wells.

A frictional arch model for pile-cap-beam-supported embankment

The pile-cap-beam-supported (PCBS) system can strength the soil arching effect of embankment, increase the lateral stiffness, bending resistance and vertical bearing capacity of the rigid pile, however there is no frictional soil arch model of PCBS embankment. In this paper, first a frictional arch model for PCBS embankment modified from Russell’s frictional arching model was proposed. The proposed model in this paper considers the algorithm of lateral pressure coefficient k and a changing critical height of soil arch. In this new method, the influence of pile spacing, filling properties, height and pile spacing on critical height soil arch was comprehensively considered. Second, a series of numerical cases were performed to verify the effectiveness of the proposed model and study the arching effect of PCBS embankment. By comparing the vertical stress and settlement between the theoretical and simulation results, the rationality of the proposed method to estimate the stress and critical height of arch was validated. The effectiveness of the proposed method was further validated by comparing loading efficacy to a reported case. Last, the stress and deformation of PCBS and pile-cap-supported (PCS) embankment were analyzed and the superiority of PCBS system in improving the performance of embankment was observed finally.

Performance Analysis of Pile Group Installation in Saturated Clay

In offshore pile engineering, the installation of jacked piles generates compaction effects within soil, thus further affecting previously installed adjacent piles. This study proposes a three-dimensional numerical model for pile group installation, soil consolidation, and loading analysis. Subsequently, the effect of pile spacing and pile length-to-diameter ratio on the deformation, internal forces, and vertical bearing capacity of adjacent piles are investigated. The results indicate that with an increase in pile center distance, the peak lateral displacement of the adjacent piles decreases, whereas the peak vertical displacement increases. As the pile length-to-diameter ratio increases, the peak vertical and lateral displacements of the adjacent piles are enhanced. In addition, the peak axial force of the adjacent piles initially decreases and then increases with the penetration depth of the subsequent pile, whereas the peak bending moment initially increases and then decreases. The vertical bearing capacity of the subsequent pile is significantly superior to that of the adjacent piles. Therefore, the effects of pile installation on adjacent piles should be included in pile engineering. The impact of the subsequent pile installation on the bearing capacity of adjacent piles can be significantly reduced by increasing the pile center distance and pile length-to-diameter ratio. The findings provide useful guidance for pile group engineering.

Fire after earthquake assessment of 3D reinforced concrete structures

Despite that, an earthquake's occurrence can lead to dramatic effects with significant damage in urban areas, including human and material losses. Fire after an earthquake amplifies the overall impact and becomes a catastrophic event. Most constructions in Algeria are made of reinforced concrete, and current regulations overlook fires after earthquakes. Structural designs are inadequate to handle such events. This study aims to investigate the behaviour of 3D reinforced concrete frames, as part of a residential building, designed according to internal codes, CBA93 and RPA99 v2003. This 3D RC structure is exposed to several load levels of its vertical load bearing capacity. The structural system is assumed to undergo seismic scenarios characterised by various levels of story drift and damage level types. The structure is then exposed to the standard fire ISO834 model. Numerical investigations are carried out for thermo-mechanical analysis using the finite element software ANSYS, taking into account geometric and material non-linearities. Results highlight the significant impact of vertical loads, story drifts, fire scenarios, and structural damage on a building's response to fire following an earthquake. These factors collectively influence the collapse probabilities, underlining the importance of holistic risk assessment in structural design.

Assessing the effects of horizontal loads on the ultimate vertical bearing capacity of energy piles: A comparative numerical and analytical study

Previous studies have not extensively explored the collective impact of lateral, axial, and thermal loading on the ultimate vertical bearing capacity of energy piles, qu. This study investigates qu values for energy piles in dry sandy and clayey soils under varying lateral loads and temperature conditions using numerical and analytical solutions, considering temperature-dependent variables. The numerical results were validated against experimental data. The analytical solution aligns well with numerical analyses, though it yields slightly higher qu values in sandy soil. Both numerical and analytical solutions show that cooling and heating can respectively increase and decrease qu under corresponding conditions. Numerical simulations indicate that in clay, lateral load enhances qu, with increases ranging from 8 % to 20 % across different thermomechanical conditions. In sand, the effect of lateral load depends on thermal conditions, increasing by 2 %–5 % during cooling and decreasing by 3 %–5 % during heating. The analytical solution showed that increasing lateral load would increase qu in sand by 0.5 %–2 % and in clay by 1 %–5 %, with a more significant increase in clay. Analytical and numerical parametric studies also revealed the higher influence of soil cohesion and pile diameter on qu values under different thermomechanical conditions.

Research on the vertical compressive bearing characteristics of offshore wind power steel pipe piles

In the absence of a comparison of static load test results for large-diameter steel pipe piles at home and abroad, optimize the design parameters based on the test pile results to guide later construction. This paper is based on the pile foundation design calculation method of API specification, as well as the relationship between the t-z, Q-z, p-y curve modes suggested by this specification, vertical ultimate bearing capacity, and stratum parameters. The conclusions and results obtained are limited to pile foundation calculations using API specifications. Analyze and back-analyze the results of static load tests on large-diameter steel pipe piles, and verify the pile foundation parameters. Combined with the data obtained from the test pile tests, analyze the stratum parameters to guide the optimization design of pile foundations in the construction drawing design stage of the offshore wind farm expansion project.

Study on the structure parameters and design method optimization of blade-type screw steel pipe pile

The rationality of structure parameters of the blade-type screw steel pipe pile is the major factor in determining the safety, applicability, and economy of a pile foundation, but the existing design methods have not defined the specific approaches to calculating structure parameters of blades and steel pipes. To address this issue, an analysis of the strength theory was performed on spatial helical blades, revealing the ratio of blade width to steel pipe radius as the core index to do the structure parameters design of blade-type screw steel pipe pile and established a mathematical calculation model between the vertical bearing capacity of single pile and a. The rational value of a is 2.0–3.0 using numerical calculation. The correlation between blade thickness and wall thickness of steel pipes was determined using the force analysis based on the synergy between blades and steel pipes. Then the structure parameters design method of blade-type screw steel pipe pile with coordinated parameters was proposed. The rationality and superiority of this design method were verified by comparing the existing test data and the finite element simulative analysis. Based on this design method and the current specifications, such as the Technical Code for Building Pile Foundations, a safe, applicable, and economical optimization design method and flow of blade-type screw steel pipe piles were further proposed for engineering design reference.

Critical behavior of thick rubber bearings under compression and shear

Thick rubber bearings (TRBs) are used for seismic isolation as well as for subway-induced vertical vibration mitigation. Under earthquake ground shaking, TRBs typically undergo large horizontal displacements that lead to a reduction of their vertical bearing capacity, which should be carefully evaluated during design. This study investigates the performance of TRBs under compression and compression-shear loading. Eight full-scale TRB specimens were designed and tested. The test results show that increasing the axial load increases the compressive stiffness of TRBs. During compression-shear loading, TRBs under design level axial loads failed due to rubber rupture at shear strain γ > 350 %, while under higher axial loads, they failed because of instability at γ ＜ 300 %. In addition, in cyclic shear deformation under axial loads larger than twice the design level axial load, the TRBs exhibited negative stiffness at the unloading branch of the F-u loop. The effective damping ratio significantly increased with increased axial load. Then, the test data were used to validate existing mechanical models for the prediction of the compression-shear behavior of elastomeric bearings. Existing analytical models were modified by accounting for the compressive stiffness change due to increased axial loads, leading to more accurate prediction. Finally, models for the critical load of TRBs under zero and lateral displacement were examined and improved.

Probabilistic assessment of bearing capacity of skirted foundation under combined loadings with a rigid base

Skirted foundations are critical components in offshore applications where combined loads are common in deep‐water environments. Their ultimate capacity under VH (vertical‐horizontal) combined loading is traditionally determined using VH failure envelopes, which are primarily constructed using numerical methods. These methodologies, however, frequently ignore the spatial variability inherent in seabed soils due to geological formations. This paper investigates the effect of spatial variability of undrained shear strength and embedment ratio impact on the capacity of skirted foundations subjected to VH combined loading. For this, OptumG2 software is used to perform Monte Carlo simulation combined with random finite element limit analysis. This paper investigates the stochastic analysis of bearing capacity and failure envelopes, with a particular emphasis on understanding the effect of spatial correlation on undrained shear strength. The study focuses on the horizontal scale of fluctuation and the soil strength heterogeneity index, shedding insight on previously undiscovered areas. Novel findings highlight how a rigid base affects VH failure envelopes and offer insights into evaluating the vertical bearing capacity of skirted foundations. [Correction added on 8 July 2024, after first online publication: The above statement has been updated in this version.]

The pull-out capacity of torpedo anchor in clay considering the full opening cavity

Torpedo anchors are increasingly being considered for mooring floating facilities in deep waters owing to their efficient and economical installation. The anchor was released from a specified height above the seabed to allow it to gain velocity as it fell freely into the water before penetrating the seabed. A cavity was formed above the anchor shaft after the anchor installation. The formation of this post-installation cavity is largely dependent on the soil strength conditions and affects the anchor capacity after installation. However, there is a lack of understanding regarding the formation mechanisms of the cavity and its effect on the bearing capacity of a torpedo anchor. Thus, this study focuses on the effects of the post-installation cavity on the bearing capacity of the torpedo anchor. The impact of a fully open post-penetration cavity on both the vertical and inclined bearing capacity of a torpedo anchor without fins was investigated using the Coupled Eulerian–Lagrangian (CEL) method in ABAQUS with three-dimensional large deformation finite element (LDFE) analysis. A method for evaluating the vertical bearing capacity of a torpedo anchor, considering the effect of a post-installation cavity, was proposed. This study provides insight into the installation effect on the bearing capacity of torpedo anchors.

Numerical analysis on the behavior of suction anchor under partial drained conditions

The vertical bearing capacity of the suction anchors is closely related to the loading rate. The loading rate is a critical parameter. In this study, ABAQUS was used to perform a numerical analysis of the behavior of suction anchors under partially drained conditions, considering the passive suction generated by the soil, which is the main feature during the uplift process of suction anchors. The results indicated that the suction anchor gradually moved from the drained condition to the undrained condition with an increase in the normalized rate V. When 0.1<V<47, it is partially drained, and the uplift force and negative pressure inside the anchor are more sensitive to the loading rate at this stage.

Static and dynamic characteristics of large-span six-slider closed hydrostatic guideway considering pitch moment and yaw moment

Purpose The purpose of this study is to design a closed hydrostatic guideway has the ability to resist large-side load, pitch moments and yaw moments, has good stiffness and damping characteristics, and provides certain beneficial guidance for the design of large-span closed hydrostatic guideway on the basis of providing a large vertical load bearing capacity. Design/methodology/approach The Reynolds’ equation and flow continuity equation are solved simultaneously by the finite difference method, and the perturbation method and the finite disturbance method is used for calculating the dynamic characteristics. The static and dynamic characteristics, including recess pressure, flow of lubricating oil, carrying capacity, pitch moment, yaw moment, dynamic stiffness and damping, are comprehensively analyzed. Findings The designed closed hydrostatic guideway has the ability to resist large lateral load, pitch moment and yaw moment and has good stiffness and damping characteristics, on the basis of being able to provide large vertical carrying capacity, which can meet the application requirements of heavy two-plate injection molding machine (TPIMM). Originality/value This paper researches static and dynamic characteristics of a large-span six-slider closed hydrostatic guideway used in heavy TPIMM, emphatically considering pitch moment and yaw moment. Some useful guidance is given for the design of large-span closed hydrostatic guideway.

Nonlinear Analysis of Bearing Characteristics of Stiffened Deep Cement Mixing Piles under Vertical Loading

Stiffened deep cement mixing (SDCM) piles are composite piles that combine the advantages of single large-diameter deep cement mixing (DCM) and precast concrete piles. They comprise precast concrete piles as the core and cast-in-place DCM piles as the outer layer. This study evaluates the bearing characteristics of SDCM piles under vertical loading. The composite modulus of elasticity of SDCM piles is first introduced and determined using the area-weighted average method. Then, the reliability of the proposed method is described by comparing the calculated results with the findings of the existing literature. Furthermore, a nonlinear simplified analysis method based on the load transfer method is proposed for vertical bearing characteristics of equal- and short-core SDCM piles under vertical loading. This method is developed by the finite difference method. The accuracy of the simplified method is validated by comparing its results with those from existing tests, theoretical analysis, and finite element simulations. The results of their study indicated that the area-weighted average method calculates the composite modulus of elasticity of the composite pile section of the SDCM piles with an error below 0.5% compared to the analytical method. This finding represents sufficient accuracy. The simplified calculation method established in this study is computationally stable. When the iteration factor is set to 10−6, as the number of discrete nodes n on the pile increases, the calculation results are stable with a good convergence when n &gt; 30. The vertical bearing capacity and pile top stiffness of SDCM piles increased with the length of the core piles. There was a reasonable core-to-length ratio for SDCM piles in specific scenarios. An excessively long DCM pile section made its lower part force-free for a given length of core piles. The appropriate length of core piles should be determined in actual projects to avoid unnecessary material waste. An optimum ratio of core piles for SDCM piles was determined. Beyond this optimal value, an increase in the ratio of core piles controlled the pile settlement in a limited manner.

Analysis of influencing factors of penetration mechanism and vertical bearing characteristics of monopile in calcareous sand: Laboratory model testing and in-situ testing

The construction of islands and reef engineering structures in marine environments has been a hot topic in recent years, and calcareous sand, which possesses unique physical properties, is widely distributed on islands and reefs. Due to the properties of calcareous sand, engineering problems such as pile slipping while driving and a low bearing capacity during service can occur. To address the key problem of pile‒soil interactions in calcareous sand foundations, laboratory model and in situ tests were conducted, accounting for factors such as impact energy, relative density, pile-forming method, and pile aspect ratio. First, the penetration mechanism of hammered piles in calcareous sand was studied. Then, the differences in vertical bearing characteristics between hammered and pre-embedded piles under different conditions were explored. The pile driving test results showed that a higher impact energy and lower relative density are more conducive to pile sinking. Moreover, as the number of hammer drops and dynamic penetration resistance increase with increasing burial depth, the pile tip resistance is the main factor limiting pile penetration in calcareous sand. The vertical static loading test revealed that particle breakage accelerates soil redistribution around the pile and that compaction enhances the bearing capacity of the pile. The pile aspect ratio, relative density and pile-forming method also play major roles in the vertical bearing capacity of piles in calcareous sand. In addition, the skin friction of a pile rapidly increases to the ultimate value along a multisegment trend of polyline functions. Similarly, the pile tip resistance rapidly increases at the initial loading stage, exhibiting the behavior of an end-bearing pile. The in situ test results indicated that the pile penetration depth in coral calcareous sand is an important factor affecting the bearing capacity.

Vertical bearing capacity of spun precast concrete pile in liquefiable soil: a case study

Spun precast prestressed concrete (SPC) pile has been used in many parts of the world as a viable foundation alternative. This study assesses the load-carrying capacity of SPC piles passing through a deep soft subsoil layer and resting on a dense sand layer. The vertical bearing capacity of the SPC pile has been estimated using various analytical methods and static pile load tests for the Jolshiri area of Dhaka. The liquefaction potential of the site has been assessed using local seismic site conditions, field and laboratory test data. The liquefaction analysis suggests that the topsoil layer is liquefiable to a depth of 4.5 m. The capacity obtained from the load test is compared with those obtained from the different methods, ultimate push-in load, and local design guidelines. Finite Element Analysis (FEA) was performed considering the hardening soil (HS) model using PLAXIS 3D to simulate field conditions. The load settlement response obtained from FEA shows a good agreement with the test results. The capacity examinations primarily suggest that the SPC pile can be a viable foundation solution for the subsoil conditions of Jolshiri Abasion area of Dhaka.