Vertical Bearing Research Articles

Development and field test of Red mud-Fly Ash Geopolymer pile (RFP)

Red mud is an industrial solid waste obtained from the extraction of alumina from bauxite. In order to study the resource utilization of red mud and improve its comprehensive utilization rate, based on the principle of geological polymers, red mud based geological polymers are prepared using raw materials such as red mud, fly ash, blast furnace slag powder, sand, stone, and alkaline solution as pile materials. Through lab experiments, the ratio of red mud and fly ash geopolymer mixtures that can be used for underwater injection and pumping has been obtained; Through on-site experiments, the complete construction process and the bearing characteristics of red mud-fly ash geopolymer piles (RFP) was studied. Environmental impact assessments were conducted by monitoring the changes in water quality around the RFP. The research results laid the foundation for the engineering application of RFP piles. It was found that: (1) At a liquid-solid ratio of 0.55, the geopolymer mixture of red mud: fly ash: sand: crushed stone: GGBS=(1:2:2:4.94:0.1) has good workability. The geopolymer with this mix ratio can meet the performance requirements of pumping and underwater perfusion, the slump can be controlled between 220-225mm, and the strength after 28 days of room temperature curing is 13.9MPa. (2) Developed a complete set of construction techniques for RFP, including drying, grinding and sieving of red mud, preparation of alkaline activator solution, sequence of material mixing, and related processes for pile drilling, placement of conduits, and conduit method grouting. (3) The load test results show that in a silty clay foundation, the ultimate vertical compressive bearing capacity of a single RFP with a pile length of 10.0 meters and a pile diameter of 520mm is 753kN. When the pile spacing is 1.5m, the bearing capacity of single-pile composite foundation is 240kPa. The Q-S curve and the stress distribution curve of the pile indicate that its load transfer characteristics are consistent with those of ordinary concrete piles. The results of the core sampling test on the pile body show that the core sample taken from the 10m pile is relatively complete, the rate of core recovery reaches over 99%,it shows that the pile body is intact. The compressive strength experiment shows that the strength of core samples at different depths is above 10MPa,and up to 19.5MPa. (4) The continuous water quality monitoring results for 5 months indicate that the implementation of RFP has not cause significant adverse effects on the quality of surrounding water bodies.

Bearing behaviors of rock-socketed piles in layered dynamically compacted soil-rock mixtures: A case study

After layered dynamic compaction (DC) treatment in a mountainous area with deep backfill in Chongqing, China, a series of pile tests and analyses were conducted to evaluate the vertical bearing capacity of rock-socketed piles and to investigate their mechanical characteristic and load-bearing behavior. Static pile load tests (SPLT) were carried out on three types of rock-socketed piles with different diameters (800 mm, 1000 mm, and 1200 mm). Based on the test data of pile reinforcement stress, the pile axial force, frictional resistance, and load-sharing ratio were calculated and analyzed. The results indicate that load-settlement curves of static load tests for all piles change progressively, and the S-lgt curves are relatively straight lines without obvious downward bending. The pile axial force exhibits the characteristics of “large at the top and small at the bottom”, resulting in stress concentration at the pile top, especially prominent in longer piles (lengths of 33.2–37.1 m). Additionally, the overall frictional resistance increases with the increase of pile top load. In shorter piles (lengths of 16.5–22.6 m), the frictional resistance presents a C-type curve with depth, while in longer piles, it presents an S-type curve distribution. Comparatively, the test pile bears the upper load mainly by the side friction resistance, which is more prominent in the longer pile. With the increase of pile top load, the load-sharing ratio of side friction decreases and the load-sharing ratio of pile tip resistance increases.

Upper bound solution of the vertical bearing capacity of the pile-bucket composite foundation of offshore wind turbines

Pile-bucket composite foundations are regarded as a promising solution for offshore wind power infrastructure. However, accurately assessing their vertical ultimate bearing capacity remains a technical challenge. Therefore, establishing an upper bound solution of the ultimate bearing capacity of the composite foundations is of significant importance for their promotion and application. This study begins with small-scale model tests, using Abaqus for modeling based on the relevant test conditions. Next, following model validation, the vertical bearing capacity of the composite foundations under different H/D ratios and the corresponding soil failure modes are investigated. According to the upper limit method and the ultimate equilibrium theory, the kinematic velocity field is subsequently constructed to derive the upper bound solution of the vertical bearing capacity. Finally, the effectiveness and accuracy of the proposed theoretical upper bound solution are verified against the results of model tests, and this study hopes to provide a reference for the future design of vertical bearing capacity of pile-bucket composite foundations.

Experimental investigation on bearing capacity of rock-socketed bored piles in silty clay stratum in beach areas

In this study, six rock-socketed bored piles were tested in the field to investigate the bearing characteristics of rock-socketed bored piles in silty clay formations in coastal areas, and the model piles were simulated and optimized using the finite element (FE) method. The results showed that the lateral resistance of the piles in the clay layer is less than 50 kPa, and the lateral resistance of the rock-embedded portion is within 136.2−166.4 kPa. Compared with increasing the rock-embedded depth, increasing the diameter of the test piles can improve their vertical bearing capacity more effectively. The average horizontal critical load (Hcr) increased by 84.54 %, and the average horizontal ultimate load (Hu) increased by 50.3 % for the 800 mm diameter piles compared to the 600 mm diameter piles. Also, at the end of the test, the 600 mm diameter test piles showed severe damage at 6−9.5 D below the mud surface and were more susceptible to instability damage than the 800 mm diameter test piles. In soft clay strata, the 'm' values converged rapidly with increasing horizontal displacement and stabilized when the displacement exceeded 10 mm. The FE simulations confirmed that the horizontal displacement of the pile mainly occurs at 4 m depth below the mud surface, and the displacement of the test pile can be effectively reduced by reinforcing the soil around the pile. The silt at the bottom of the pile is one of the critical factors causing the uneven settlement of the test pile, severely affecting the vertical bearing capacity of the pile foundation.

Bearing Characteristics of Screw-Groove Piles: Model Test and Numerical Analysis

Screw-groove piles, a new type of precast pile, are economically and environmentally friendly and improve the load-bearing performance of piles through a unique screw-groove structure. To reveal the load-transfer characteristics and bearing mechanism of the screw-groove pile, the axial force, load–settlement curve, skin friction, bearing capacity, and response characteristics of the foundation for piles under vertical loading were analyzed. Furthermore, a parameter analysis of the ultimate bearing capacity and material utilization of screw-groove piles was performed using the finite element method. The results demonstrate that the screw-groove pile had an ultimate bearing capacity 1.85 times higher than that of the circular pile, and its material utilization rate was 2.85 times higher. The screw-groove surface end resistance and pile-tip resistance formed a multipoint vertical bearing mode. It efficiently utilized the soil’s shear strength and mobilized a larger volume of surrounding soil to share the load. The screw-groove structure increased the pile–soil interaction surface, thereby increasing the skin friction resistance of the pile. Additionally, increasing the inner radius of the screw groove boosts the pile’s bearing capacity but may reduce material utilization. An optimal screw-groove spacing balances both factors, while excessive groove thickness lowers material use. The pile shows high sensitivity to soil parameters.

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.

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.

Experimental Investigation of the Axial Load Capacity of Bilateral Helix-Stiffened Cement Mixing Piles in Soft Marine Soil

Bilateral helix-stiffened cement mixing piles (BHCMPs) are a new type of robust composite pile. In this paper, the influence of design parameters, such as the diameter of inner helix plates and the number and size of outer mixing helix plates, on the vertical bearing performance of the pile foundation and the behavior of the pile diameter are investigated through laboratory model tests. The results indicate that incorporating a reverse-mixing process in the pile formation of helix-stiffened cement mixing piles can enhance the overall ultimate bearing capacity and strengthen the soil-cement of the piles. In the case of the same double-blade inner drill pipe, for every 22 mm increase in the blades, its ultimate compressive load-bearing capacity was increased by 10% to 25%, and its pullout load-bearing capacity was increased by 15% to 45%. With further increases in the blades, the percentage increase in the compressive and pullout load-bearing capacity was reduced. With an increase in the number of external mixing blades, its compressive load capacity increased in the range of 5% to 20%, and the elevation load capacity increased in the range of 10% to 25%. Increasing the number of reverse-mixing helix plates on the outer casing enhances the soil-cement strength of the pile body by approximately 15–20% for each additional plate. The average strength of the pile-body soil-cement for each additional plate is estimated to be 1 to 1.4 times that of the previous set, indicating that increased mixing iterations can enhance the perimeter soil-cement strength of the pile. The average bond diameter of soil-cement piles with double-blade internal drilling rods could be seen from the diameter of the piles formed, which was 1.02 to 1.21 times the diameter of the blades.

Vertical bearing capacity of HSCM pile groups in marine soft clay

Helix Stiffened Cement Mixing (HSCM) piles were a new type of composite pile developed in recent years, synchronized with grouting during the installation of helical piles to form a composite pile comprising cement soil. In this study, HSCM piles were installed in groups. This study evaluated the compressive bearing capacity of HSCM pile groups with varying numbers of piles (2, 3, and 4) and different cap configurations (high cap and low cap) in clay soil using laboratory model tests. The load-displacement curves, group pile effect, and load sharing by the cap were analyzed, and finite element models were created for further analysis. Increasing pile spacing enhances the influence of pile number on the ultimate bearing capacity of HSCM pile groups. At higher pile spacings, the group pile effect became minimal or negligible. Furthermore, for low cap HSCM pile groups, the cap distributes the load more effectively, thereby increasing the ultimate compressive capacity.

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.

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.

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.

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.

Investigation and numerical simulation study on the vertical bearing mechanism of large-diameter overlength piles in water-enriched soft soil areas

Abstract With the development of urbanization, there is an increasing demand for higher land utilization rates, leading to the emergence of high-rise residential and commercial complexes. Additionally, in coastal areas, the presence of soft soil and low bearing capacity of the foundation necessitate higher foundation bearing capacity. Large-diameter, super-long piles have been widely employed in engineering projects to address these challenges effectively. This study analyzes their vertical bearing characteristics through field load tests and determines vertical load distribution and transfer mechanisms by using Brillouin Optical Time Domain Reflectometry. A numerical computation and analysis method based on PLAXIS 3D was established, examining the effects of parameters such as pile diameter, length, and soil modulus on the vertical bearing characteristics. Results indicate that large-diameter, super-long piles mainly bear loads through side friction, with the tip bearing less load. As load levels increase, axial force increases linearly above 40 m depth and becomes nonlinear below. Frictional resistance is significant below 40 m at 3,700 kN load. Parameter analysis shows that increasing pile length and diameter enhances bearing capacity, suggesting this method to improve pile foundation capacity in engineering.

Experimental Investigation of Vertical and Lateral Bearing Behaviors of Single Piles

Experimental Investigation of Vertical and Lateral Bearing Behaviors of Single Piles