Pile Top Research Articles

An Experimental Study of Horizontal Bearing Capacity of Vertical Steel Floral Tube Micropiles with Double Grouting

This paper examines the performance of a novel technology, vertical steel floral tube micropiles with double grouting. It is the combination of micropile technology and double grouting technology. A large-scale model tank was applied to impart horizontal bearing capacity, and the slope soil pressure and flexural performance of the micropile were investigated under four experimental conditions. The peak grouting pressure during the double grouting process was defined as the fracturing pressure of the double grouting, and it was positively correlated to the interval time between first grouting and secondary grouting. Compared with traditional grouting, double grouting increased the horizontal bearing capacity of the single micropile with the vertical steel floral tube by 24.42%. The horizontal bearing capacity was also 20.25% higher for the structure with three micropiles, compared with a 3-fold value of horizontal sliding resistance. In the test, the maximum bending moment acting on the pile above the sliding surface was located 2.0–2.5 m away from the pile top, and the largest negative bending moment acting on the pile below the slip surface was located 4.0 m away from the pile top. The ultimate bending moment of the single pile increased by 12.8 kN·m with double grouting, and the bending resistance increased by 96.2%. The experimental results showed that the double grouting technology significantly improved the horizontal bearing capacity of the micropile with the steel floral tube, and the soil reinforcement performance between piles was more pronounced. Also, the shear capacity and the flexural capacity were significantly improved compared with the original technology.

Study on longitudinal vibration of a pile with variable sectional acoustic impedance by integral transformation

A study on longitudinal vibration of a pile with variable sectional acoustic impedance subjected to arbitrary form of external excitation is conducted. The analytical solution of transfer function is primarily solved by Laplace transform, and then its corresponding impulse response function is solved by residue method of inverse Laplace transformation. With impulse response function, the analytical solution of response at pile top can be obtained by convolution calculation, which overcomes the limit of previous analytical solutions subjected to prescribed time-harmonic load. The accuracy of presented solution is verified by compared with existing solutions subjected to semi-sine excitation and low-strain test of model piles. To take advantage of presented solution, this paper also proposes a case study of imposed excitation considering superimposed high-frequency interference component, and some conclusions derived from this case can provide practical guidance for engineering implementation.

Displacement and Stress Characteristics of Tunnel Foundation in Collapsible Loess Ground Reinforced by Jet Grouting Columns

Collapsible loess tunnel foundation reinforcement is a new challenge in the construction process of tunnel engineering. According to the field displacement and stress monitoring of the Fujiayao loess tunnel, this paper investigates the reinforcing effect of a high-pressure jet grouting pile on a collapsible loess tunnel foundation in the deep large-span tunnel. The field monitoring method was employed to address the performance of tunnel foundation settlement, additional stress, earth pressure, rock pressure, etc. The results indicate that the stress on the pile tops and the earth pressure between piles increase gradually over time in two stages: stress increases rapidly in the first 45 days and, after this period, stress tends to gradually stabilize. Further, stress increases uniformly with the distance from the centerline of the tunnel, and the rock pressure of the tunnel sidewalls tends to be stable within two months of being constructed. Additional stress on the tunnel foundation increases linearly with time, and it is uniformly distributed in the vertical and horizontal directions of the tunnel section. Settlement of the tunnel foundation also gradually increases with time, and it tends to be stable at 50 days from the time of construction. Additionally, the settlements of different monitoring points are similar at the same depth. The research results will further improve the theoretical knowledge of tunnel bottom reinforcement in the loess tunnel, which not only can effectively guide the design and construction of the loess tunnel and reduce disease treatment cost but also can provide the necessary basic research data and scientific theoretical basis for revision of the corresponding specifications of highway tunnels and railway tunnels.

Uplift Behavior of Belled Short Piles in Weathered Sandstone

Field pull out test results of 500 kV double-circuit line of Luping-Fule are presented in this paper to investigate the uplift bearing behavior of rock-socketed belled short piles. A calculation model of rock-socketed belled short pile has been proposed. During the initial stage of loading test, uplift load is shared by even section and bell of the pile, and the bell continues to bear uplift load after the lateral resistance of even section pile reaches the limit. A different performance has been found on the case of long belled pile. At the ultimate state, the uplift resistance provided by bell accounts for about 54.9% and 34.7% of the total uplift capacity for the 6.0 m long and 7.0 m long piles, respectively. Increasing pile length has been found to noticeably increase the ultimate uplift bearing capacity, while it has less effect on the displacement of pile top. The uplift capacity of even section pile is associated with the shear strength of rock mass around the pile, and the test results demonstrate that the ultimate resistance can be equal to the shear strength. The calculation method proposed in this paper is proven to be able to accurately predict the ultimate uplift bearing capacity of the rock-socketed belled short piles.

Performance of Cement–Soil Pile Composite Foundation with Lateral Constraint

A lateral constraint can effectively reduce the foundation settlement and reduce the stress of a pile shaft in a foundation treatment. Based on the characteristics of railway engineering and soft soil engineering, this paper studied the influence that lateral constraint exerted on the stress and settlement of cement–soil pile composite foundation by using indoor large-scale model testing. A comparative analysis of the stress and settlement of cement–soil pile and soil following load change is performed, and the mechanism of lateral constraint is discussed. The results show that the settlement of the pile top with lateral constraint is 8–30% lower and that of the soil around the pile is 7–9% lower when comparing the settlement values of the composite foundation with and without lateral constraint in the cement–soil pile composite foundation. The stress value of the pile top in the composite foundation with the lateral constraint is 18–32% lower than that without any lateral constraint. The stress of the cement–soil pile shaft first increases and then decreases with the depth, and the maximum stress appears at 0.15–0.35 times the pile length from the top. The position of the maximum axial force of the pile without a lateral constraint is lower than that with a lateral constraint, and the maximum stress value of the pile is 112–153% of the stress value of the pile top. Therefore, setting the lateral constraint can effectively stop the lateral deformations of soft soil, reducing the settlement of the composite foundation and pile shaft stress.

Thermo-mechanical behaviour of floating energy pile groups in sand

This paper presents the experimental results of small-scale model tests of an instrumented floating energy pile group in which the piles were embedded in dry medium-dense sand and subjected to the seasonal temperature pattern of the city of Nanjing in China. The study also included a model test to assess the effect of including nonthermal piles on the thermo-mechanical behaviour of the floating energy pile group. For comparison, a model test of a single floating energy pile embedded in the same soil and subjected to a similar temperature pattern was also conducted. The results show that the thermo-mechanical behaviour of an energy pile group is different from that of a single energy pile in terms of the thermally induced change in axial pile stress and the displacement of the pile top and tip. This difference in behaviour could be explained by the higher lateral confining pressure expected on a single pile than on a pile in a group due to pile interaction effects, which could lead to different end restraint boundary conditions. We conclude that the thermo-mechanical behaviour of an energy pile is controlled mainly by the end restraint boundary conditions.

Performance of a foundation pit supported by bored piles and steel struts: A case study

Retaining structures with bored piles and temporary inclined steel struts are suitable for the reinforcement of underground projects located in urban areas of high-density development as they are convenient for use in earth excavations and their use leads to considerable savings in time and cost. However, few data are available on foundation pits supported by bored piles and inclined steel struts. This paper presents a case study to investigate the behavior of a large-scale foundation pit supported by bored piles and inclined steel struts, in which the movement of the foundation pit and the displacement of the retaining structure are reported. The measured results along the length of the foundation pit were found to be smaller than those along the width (with a difference of approximately 13.5–30.0%), including the vertical and lateral displacement of the foundation pit, as well as the lateral displacement of the bored piles. The lateral displacement at the top of the bored piles, δh, was 0.2–0.5% of the excavation depth, He. The lateral displacement of the bored piles decreased with the decreasing distance from the corner (with a difference of approximately 50%), which demonstrated the corner effect on the movement of the bored piles. Based on the measured results of this field case, it was found that the maximum settlement and the lateral displacement were located at the cross section through the center of the west side of the foundation pit. In order to predict the distribution of settlement at the surface and the basal heave at this section, plane-strain finite element analyses were conducted to estimate the location where the maximum settlement occurred at the surface of the foundation pit. The difference between the numerical results and the measurements was found to be in the range of 2.6–33.0%, which validates the numerical model with some reasonable accuracy. The numerical results show that the maximum surface settlement occurred at a distance of 0.6 He away from the top of the foundation, whereas the settlement at the bottom of the foundation was almost uniform at the final construction stage (e.g., 25 mm).

INTERPRETATION OF PILE INTEGRITY TEST RESULTS OBTAINED FROM MODEL CONCRETE PILES HAVING TWO DEFECT LOCATIONS

The most common query for piles is that whether their integrity is acceptable. Another problem that has been rarely questioned is that whether a minor defect under a major defect is properly detected. This study constructed model concrete piles having the dimensions of 0.15 by 0.15 by 5.00 m with two defects intentionally created at 2.50 and 3.50 m from the pile top. The first defect was created to have a constant β value of 40%; while the second defect was varied such that the β values were from 95, 90, 85, 80, 65, 50, 35, and 20%. A pile integrity testing equipment was used to detect those defects; and the results were compared to the actual ones created. Testing was conducted on the piles being in the air and under the ground in order to observe whether skin friction would affect the signals. For the first defect, it was found that the average measured β values for both defects are about 76% and 89% higher than those of the actual ones. This is an important factor that engineers should bear in mind when interpreting the signals from a report. For instance, a defect reported is probably less than what has happened to the pile. In the case of the second defect, the results revealed that if a β value is 89% and higher, the pile should be acceptable. However, if it is lower than 89%, other types of pile integrity testing should be carried out to clarify the result.

Strength Properties of Coated Paper with Cuminum cyminum L. and Prunus mahaleb L.

Coating of the paper surface against to microorganism to making it suitable for food packaging is crucial in terms of improving antimicrobial properties. Cuminum cyminum L. known as cumin and Prunus mahaleb L. have the abundant chemical compound. Cumin has antiviral activity that making it proper for coating due to its various components. Mahaleb as well has rich fragrance make it eligible for sugary snacks and chocolate package. After coating with such biomaterials, thanks to varied fatty acids impart protective feature from oxidation to paper surface. It was observed that the odor of substances was trapped from paper samples. Wrapping paper selected as a base paper in this study. Cationic starch used for emulsifying the coating chemical. Cumin and mahaleb added the starch emulsion and coating suspension applied on the top pile of the paper with # 0 drawdown bar. Coating application reduced the paper's tear index results but increase tensile and burst index results in both cases. Mahaleb gives better Cobb60 value and bursting and tensile index and comparing to Cumin. However, cumin coated papers tensile index results in machine direction was better than mahaleb. Both natural substances are suitable material as an additive to the coating.

Horizontal Bearing Test and Optimization of m Value for Precast Piles in Alluvium Stratum of the Yellow River

For a pile foundation design, the value of proportional coefficient m to define the soil horizontal resist force is a significant parameter. However, different geological conditions and experimental environment have led to different m values. In this paper, an in situ test is firstly carried out on the horizontal bearing capacity of large-size precast square-piles. The piles deformation is then derived by using the optimization method from the measured data. Secondly a back analysis model is established to calculate the m value by using the simplex method, which reveals the evolution rule of the value of proportional coefficient m. Results show that the horizontal bearing characteristics of precast piles depend on the interaction force of piles and soils. The action mechanism of the soils around the piles is gradually developed with the increase in the concrete content. The horizontal critical load and the Eigenvalue of horizontal bearing capacity increased by 16.7% and 20%, respectively. It is also seen that the higher the content of the cement-soil around the piles and the longer the pile length, the bigger the m value obtained. The variation of the proportional coefficient m with the horizontal displacement of pile top is defined by three stages: rapid decaying stage, slow decaying stage, and balanced stage, respectively. The inverse analysis method on the proposed m value can accurately reflect the actual working state of piles and soils. In the depth of 3~18m in the west of Ji'nan, the range of m value is recommended as 4~6.58 MN·m-4. When Δ takes 12mm, the values of m are consistent with the result from the back analysis. In summary, the obtained m value can be effectively used to guide the design of enclosure structure in the super deep foundation pit in the Yellow River alluvial stratum.

Dynamic characteristics of a large‐diameter pile in saturated soil and its application

SummaryThis study theoretically investigates the dynamic response of an end‐bearing pile embedded in saturated soil considering the transverse inertial effect of the pile. The saturated soil surrounding the pile is described by Biot poroelastic theory, and the pile is represented by a Rayleigh‐Love rod because both the vertical and radial displacements at the soil‐pile interface are considered. The potential function decomposition method and variable separation method are introduced to solve the governing equations of the soil, in which the vertical and radial displacement components are coupled. The governing equation of the pile is solved using the continuity conditions at the pile‐soil interface. Next, the velocity admittance in the frequency domain and the velocity response in the time domain at the pile top are presented based on the Laplace transform and inverse Fourier transform, respectively. Subsequently, the reduced solution is compared with a 1‐dimensional model solution to verify the validity, and the influences of the slenderness ratio of the pile on the transverse inertial effect of the pile are analyzed. Moreover, Poisson ratio, the slenderness ratio of the pile, and the pile‐soil modulus ratio are studied. Finally, the theoretical and measured curves in the engineering project are compared, and the results demonstrate the good application prospects of the solution presented in this article.

Probabilistic structural assessment of conical grouted joint using numerical modelling

Conical grouted joints have been proposed as a solution for the relative settlement observed between the sleeve and the pile on monopiles for wind turbines. In this paper, the influence of the design parameters such as steel wall thicknesses and conical angle on the failure modes associated to continual loadings are assessed based on finite element analysis. It is found that both the sleeve's and pile's wall thicknesses have a significant impact on the grouted joint health. Namely, the larger are the wall thicknesses, the more vulnerable the grout is with respect to fatigue and material degradation but the more limited the progressive settlement is, and inversely. This implies that the appropriate wall thicknesses should be chosen by designers having in mind that neither extreme is conservative. Based on statistical modeling, the grout length is found to be the most influential parameter of the settlement caused by extreme loadings: longer grout significantly contributes to the reduction of extreme settlement. To ensure that the inevitable settlement does not jeopardize the joint's structural integrity, a probability-based method has been developed to estimate the minimal gap between the pile top and the brackets required to achieve a targeted annual reliability index (of 3.3).

Bearing Capacity Evaluation and Reinforcement Analysis of Bridge Piles under Strong Earthquake Conditions

This paper investigates the Minjiang River Bridge No. 3 in Dujiangyan based on actual bridge tests and theoretical methods of analysis; here, we analyze the bearing capacity and the strengthening of the bridge. The detailed reinforcement measures for the bridge pile included the following actions: taking pile-patching measures on both sides of the severely scoured pile, adding bearing platforms, and adopting concrete-filled steel tube on the part of the pile leakage that lies above the current scour line. The bearing capacity evaluation of the bridge was performed before the reinforcement under strong earthquake and current scour conditions. After reinforcement, a bearing capacity evaluation for the bridge was performed under strong earthquake and current scour conditions using the load test for bridge piles. The analysis indicates that under current scour conditions, the maximum bending moments at the tops of piles 15-1, 15-3 and 16-3 are -4,824.5 kN.m, 5,206.9 kN.m, and 5,229.9 kN.m, respectively. These values are greater than the yield bending moment 4,787.7 kN.m obtained by the M-ϕ curve. Thus, the pile foundation will incur bending failure. The bearing capacity of the bridge after reinforcement can meet the design requirements and tends to be stable under the action of a strong earthquake. Through static load tests using vehicles, the maximum strain effect coefficient was 0.62, which meets the specific requirements for calibration coefficients (i.e., ξ ≤ 1.0). The maximum pier settlement was 0.01 mm, and the settlement tended to stabilize during the loading process. After unloading, the settlement nearly completely recovered, and the bridge foundation was stable; thus, the strengthening scheme is feasible. These results provide an important reference for bridge reinforcement in earthquake-prone areas and river erosion areas.

Time-dependent probabilistic capacity degradation assessment of prestressed concrete piles in marine environment

As coastal infrastructure systems are continuously exposed to deterioration, it is increasingly crucial to analyse their current and future serviceability performance. This paper investigates effects of chloride corrosion on the lateral force capacity and ductility of a wharf-supporting prestressed concrete marine pile and provides new insights into the state of marine structures. A probabilistically generated finite element modelling approach is developed for piles, which includes discrete concrete pile cross-sectional models connected to steel tendon non-linear elements via a series of non-linear springs that simulate bonding behaviour. Moreover, a prestressed material model is established that incorporates alternate failure modes including stress corrosion cracking and brittle failure to capture chloride-induced pitting corrosion in piles. It is shown that various failure modes cause an overall decrease in the maximum force capacity as piles age. Specifically, the alternate failure modes result in 31 and 56% reductions in the maximum capacity of the pile and associated top pile displacement, respectively, as the age of the pile increases from 25 years to 75 years. The presented methodology and results can greatly assist in decision-making for repair or replacement of wharves and aid in the design of new wharves considering their future performance.

Dynamic response of a large-diameter pile with variable section in layered saturated soil considering construction disturbance effect

ABSTRACTAn analytical solution is developed in this paper to investigate the vertical time-harmonic response of a large-diameter variable-section pile, and it considers the radial inhomogeneity of the surrounding soil caused by construction disturbance. First, the saturated soil surrounding the pile is described by Biot’s poroelastic theory and a series of infinitesimally thin independent layers along the shaft of the pile, and the pile is represented by a variable-section Rayleigh–Love rod. Then, the dynamic equilibrium equations of the soil and pile are solved to obtain an analytical solution for the impedance function at the pile top using the complex stiffness transfer method and impedance function transfer method. Finally, the proposed solution is compared with previous solutions to verify its reliability, and a parameter study is conducted to provide insights into the sensitivity of the vertical dynamic impedance of the pile and velocity response in low-strain integrity testing on defective piles.

Numerical Simulation Study on Lateral Displacement of Pile Foundation and Construction Process under Stacking Loads

Lateral displacement of pile foundation is crucial to the safety of an overall structure. In this study, a numerical simulation on the lateral displacement of pile foundation under stacking loads was conducted to determine its relation with different influencing factors. Simulation results demonstrated that stacking loads at the pile side mostly influence the lateral displacement of pile foundation. The lateral displacement of pile foundation increases by one order of magnitude when the stacking loads increase from 100 kPa to 300 kPa. Other influencing factors are less important than stacking loads. Lateral displacements of the pile body and at the pile top can be reduced effectively by increasing the deformation modulus of surface soil mass, reducing the thickness of soft soil, and expanding pile diameter. Our analysis indicates that a nonlinear relationship exists between the lateral displacement at the pile top and the pile diameter. The lateral resistance of the pile body can be enhanced by coupling the stacking load along piles and the axial force at the pile top. An actual large-scale engineering project was chosen to simulate the effects of postconstructed embankment on lateral displacement and axial force of bridge pile foundation under different construction conditions and to obtain the lateral displacement of the pile body and the negative frictional resistance caused by soft soil compression under stacking loads. On the basis of the calculated results, engineering safety and stability were evaluated, and a guide for the design and construction was proposed.

Subway‐Induced Vibration Measurement and Evaluation of the Structure on a Construction Site at Curved Section of Metro Line

Metro property buildings developed rapidly in metropolitan cities over last several years in China. The subway‐induced vibration, which may influence the serviceability of the buildings and the comfortability of their occupants over or near the metro lines, has been paid more and more attention by professional and academic experts. Based on the vibration measurement data of a construction site over Shenzhen Metro line No. 1, this paper utilizes the reasonable and completed data processing method to handle and analyse the measured data. Through the analysis of the data, the subway‐induced vibration propagation trend of free field along the perpendicular direction to metro line was investigated. It is demonstrated that the subway‐induced vibration propagation along the perpendicular direction to metro line was damped out on free field as a whole. But there may exist “rebound phenomenon” at local zones. The responses on pile top and soil adjacent to pile in the vertical shaft along three directions were investigated, and their characteristics in time and frequency domains are compared. Comparison indicates that the subway‐induced vibration on pile top is stronger than soil site near the pile. The measurement results on free field reveal that the most obvious feature of this metro line with curved section is that the vibration along the perpendicular direction is stronger than the other directions. But the measurement results in the vertical shaft show that the vertical vibration mainly transferring through the pile and pile’s vibration in the vertical direction is dominant. Finally, the dynamic time‐history analysis of the building model under the measured acceleration was conducted. The analytical results show that the vibration response of two evaluation indicators increases with the decrease of damping ratio along all three directions. The vertical vibration is more dominant than other two directions at each floor of building. The vibration levels decrease with the increase of story number along vertical direction and firstly decrease and then increase with the increase of story number increasing along two lateral directions.

Comparison of Induced Deflection and Forces in Piles Adjacent to Tunnelling and Deep Excavation in 2D and 3D Problems

There is a trend in Malaysia and Singapore, engineers tend to model the effect of TBM tunneling or deep excavation to the adjacent piles in 2D model. In the 2D model, the pile is modelled using embedded row pile element which is a 1-D element. The user is allowed to input the pile spacing in out-of-plane direction. This gives an impression to engineers the embedded pile row element is able to model the pile which virtually is a 3D problem. It is reported by Sluis (2014) that the application of embedded pile row element is limited to 8D of pile length. It is also reported that the 2D model overestimates the axial load in pile and the shear force and bending moment at pile top and it is not realistic in comparison to 3D model. In this paper, the centrifuge results of single pile and 6-pile group - tunneling problem carried out in NUS (National University of Singapore) are back-analysed with Midas GTS 3D and a 2D program. In a separate case study, pile groups adjacent to a deep excavation is modelled by 3D and 2D program. This paper compares the deflection and forces in piles in 2D and 3D models.

Numerical modeling of parallel seismic method for detecting existing piles in layered soil

For piles connected to superstructures, whose pile tops are inaccessible, a lateral horizontal impact on the side of the piles through the generation of a flexural wave of the pile shaft is a more feasible approach. This paper presents a parallel seismic (PS) method based on the flexural wave of the pile shaft that combines down-hole tests for the length and an integrity evaluation of existing piles in layered soil. It is suggested that two PS tests be conducted by horizontal striking on the side surface of the pile along and perpendicular to the pile-to-borehole direction, respectively. The first arrivals of the transmitted P-wave and S-wave at the pile-soil interface obtained in these two PS tests and the results of down-hole tests are combined to analyze the pile length and to distinguish the embedded defects for the pile integrity evaluation. A simplified theoretical model for PS tests in layered soil is established, and a correction formula is proposed to correct the initial estimated pile length accordingly. A three-dimensional finite element model is then established to verify the effectiveness and reliability of the proposed PS method in layered soil and the correction formula.

Study on Bearing Capacity of Prestressed Pipe Pile Foundation Under Horizontal Load

Background and Objective:Prestressed high strength concrete pipe pile (PHC) shows brittle fracture when subjected to more than its own bearing capacity. Therefore, the non-prestressed steel bar is added to the PHC pipe pile, that is, the mixed reinforced pipe pile (PRC). The mechanical behavior of PRC group piles and PHC group piles under horizontal force is studied, and the bending moment diagram and displacement diagram of the pile body are compared so as to find the weak parts.Material and Method:In this paper, Φ600 pipe piles are chosen, and the PRC pipe piles are made of non prestressed steel bars of the same number as the prestressing steel bars, and the two steel bars are spaced apart. Referring to a specific project of Binhai New Area, the geological parameters are used, and the force analysis of group piles under horizontal force is carried out by using the ANSYS software.Results:ANSYS simulation results show that, under the horizontal loading, when the number of piles in group piles is different, the locations of maximum bending moments are different. Increasing the number of the PRC pipe pile with non prestressed reinforcement can effectively reduce the maximum bending moment of the pile body.Conclusion:Under horizontal load, with the increase of pile number and the pile cap aggrandizement, the position of maximum moment of pile body is shifted from 5-8 times diameter of pile to the top of pile. When the pile number reaches a certain amount, the maximum bending moment will appear at the joint between the pile cap and the pile body. At the same time, increasing the non prestressed steel bar does not influence the bending moment, and the reinforcement of the pile cap and the pile top should be strengthened.