Pile Method Research Articles

Analytical model of skin friction for bored pile socketed into weak rocks in ice-rich permafrost regions

Bored piles constructed in permafrost regions often need to be socketed into weak and weathered rock strata, such as marl stratum. When these strata are ice-rich, the meltwater caused by construction will form an ice film at the pile-rock interface during refreezing, leading to a reduction in pile bearing capacity. By analyzing the shear mechanism of pile-rock interface with ice film, an interface shear model was proposed in this paper. Based on this model, the load transfer analytical method of rock-socketed bored piles was improved. Finally, the effects of pile-rock interface roughness, ice filling degree, and residual friction angle on skin friction were analyzed. The results show that the shear stress-displacement curve of the ice-containing interface unit exhibits two peaks and can be divided into four stages: ice film shear stage, ice film extrusion stage, concrete-rock relative sliding stage, and interface residual sliding stage. Increasing either the dilation angle or half-wavelength can improve the interface's shear resistance when only one variable is altered. Furthermore, the peak shear strength of the interface decreases as the filling degree increases. The interface residual shear stress is positively correlated with both the residual friction angle of weak rock (ϕu−r) and ice (ϕi−r), and increasing the proportion of ice in the residual sliding surface will lead to the reduction of residual shear stress.

Study on the Mechanical Characteristics and Ground Surface Settlement Influence of the Rise–Span Ratio of the Pile–Beam–Arch Method

The pile–beam–arch method (PBA) method is increasingly being used in the construction of metro stations with complex traffic conditions. The rise–span ratio of the arch not only affects the height of the station, but also affects the rationality of the design of subway stations and the safety of construction. The mechanical response of steel pipe piles with different rise–span ratios and the effect of controlled surface settlement have been investigated in the interactions involved in pile–soil system. In this paper, the finite element model of each rise–span ratio was established, and the rationality of the model was demonstrated by comparing the numerical simulation calculation with the field surface settlement monitoring data. The mechanical characteristics and influence analysis of the surface deformation during the excavation of the cave pile method were investigated. The results show that the maximum axial force of the central pile first decreases and then increases with the increase in the rise–span ratio. The maximum bending moment of the arch decreases as the rise–span ratio increases, and the maximum axial force of the arch is negatively correlated with the rise–span ratio. The maximum axial force of the central pile is located at the bottom plate. Due to the symmetry of the structure, the bending moment of the centre pile is small, but the maximum bending moment of the whole station is located at the side wall of the bottom plate. As the rise–span ratio increases, the surface settlement first decreases and then increases. The construction of the pilot tunnel and the upper arch is the most important factor leading to the surface settlement, so it is necessary to strengthen the soil layer.

Research on the Bearing Capacity and Sustainable Construction of a Vacuum Drainage Pipe Pile

The vacuum drainage pipe (VDP) pile is a new type of pipe pile on which the current research is mainly focused on laboratory tests. There is little research on bearing characteristics and carbon emissions in practical engineering. To further explore the bearing capacity and sustainable construction of vacuum drainage pipe piles, static load tests were conducted to investigate the single-pile bearing capacity of ordinary pipe piles and vacuum drainage pipe piles, as well as soil settlement monitoring around the piles. Then, the Q-S curves of the two piles, the pile-side friction resistance under different pile top loads, and the development law of pile end resistance were compared and analyzed. Finally, based on the guidelines of the IPCC, the energy-saving and emission-reduction effects of VDP piles in practical engineering were estimated. The results indicate that, after vacuum consolidation, the VDP pile basically eliminates the phenomenon of soil compaction and does not cause excessive relative displacement of the pile and soil. VDP piles have increased lateral friction resistance, and compared to traditional piles, their ultimate bearing capacity is increased by 17.6%. Compared with traditional methods, the VDP pile method can reduce carbon emissions by 31.4%. This study provides guidance for the production and design of future VDP piles and demonstrates the potential of VDP piles for energy conservation and emission reduction in comparison to traditional methods.

Resilience-oriented planning method of local emergency power supply considering V2B

Private electric vehicles (EVs) have great potential to conduct emergency power supply, considering the rapid development of EVs and vehicle-to-building (V2B) technologies. To enhance the resilience of the building power supply, charging piles can be upgraded to support bi-directional power supply, thus enabling EVs to help restore the buildings affected by disasters. A planning method for the charging piles’ upgrade is proposed. First, a scenario set is generated to consider the influence of uncertainties during the planning period. The uncertainties of disasters, EVs, and building load are included. Then, a two-stage stochastic programming model is established to decide the upgrade plan. Pre-disaster decisions are made in the first stage and the building is restored in the second stage. The method is applied to two different types of buildings and the test results verify the effectiveness of the proposed method.

Study Method of Pile near Cohesionless Slope under Reversed Lateral Load Considering Sand Strength State and Lateral Deflection of Pile

A p-y curve method of pile near cohesionless soil slope under reversed lateral load is proposed. This method takes into account the failure mode of soil around the pile under reversed lateral load and the interaction mode between pile and soil, and derives the ultimate soil resistance of the pile. Considering the change of the original stress state of soil due to the lateral deflection of the pile foundation, the influence of the relative density, the initial mean effective stress and the lateral deflection of pile foundation on the internal friction angle of the sand is evaluated to further accurately calculate the soil resistance value at each depth. The prediction results of this method are well verified by comparing with the FE results and centrifuge test results. Finally, the influence of the process of lateral deflection of pile on the strength state of soil around the pile and the bearing capacity of pile is studied.

Buckling failure mechanism and critical buckling load prediction method of super-long piles in soft-clay ground in deep water

Buckling may be a possible failure mode of super-long piles in soft-clay ground in deep water as concerned by several researchers. Although there are many studies on the failure mode of super-long piles in sands or silts deposits, few studies have been carried out thoroughly on mechanical mechanism of buckling instability in soft-clay ground in deep water and the corresponding calculation method. In this paper, first, the Riks Arc-Length method in ABAQUS was evaluated and verified using the FEM simulation and the analytical results from Bhattacharya. It is observed that buckling failure is indeed one of failure modes of super-long piles in soft-clay ground. And then, the buckling capacities of super-long piles were assessed due to various influential parameters. The results show that the critical buckling load of super-long piles increases with the increase of elastic modulus and embedding rates of piles, and the increase of elastic modulus and cohesion of soil, while decreases with the increase of slenderness ratios of piles and horizontal loads. Finally, a prediction method of the critical buckling load for super-long piles was presented based on the above sensitivity analysis for influential parameters and the Euler buckling formula, and the criterion for buckling instability for super-long piles was proposed as well.

Rapid Three-Dimensional Reconstruction of Underwater Defective Pile Based on Two-Dimensional Images Obtained Using Mechanically Scanned Imaging Sonar

Three-dimensional (3-D) reconstruction based on sonar imaging is an intuitive and comprehensible form for describing an underwater defective pile. Most existing 3-D reconstruction methods are inefficient as they require the extraction of numerous feature points from many sonar images. A rapid 3-D reconstruction method for underwater defective piles based on two-dimensional (2-D) images obtained using mechanically scanned imaging sonar (MSIS) is proposed herein. First, the correspondences between the geometric features of MSIS images and actual defects are established based on the mapping relationship between actual object and MSIS image. Subsequently, no more than three feature points are extracted from 2-D MSIS images to recognize the contour segments. The contour segments are assembled into the entire cross section and then into the entire defective pile. The applicability of the proposed method is verified via a 3-D reconstruction for a scaled-down pile with multiple defect distributions.

Observation of soil-structure interaction in double sheet pile method using X-ray CT

A new earth retaining method, head-fixed double sheet pile method, is being developed to rationalize open-cut construction. To clarify the behavior of the soil between two sheet piles (‘inner soil’), which is important for studying the reinforcement effect of this method, model experiments were conducted with an X-ray CT system to study the interaction between the sheet pile and the inner soil. In one case, a model sheet pile fabricated using polycarbonate without sand attachment was used, while two cases with increased friction between the sheet pile and the inner soil were compared. Low frictions led to shear failure at the boundary between the sheet pile and the inner soil. In contrast, high surface friction between the sheet pile and the inner soil led to shear failure in the inner soil. This indicates that the reinforcement mechanism of this structure changes with the conditions of soil-structure interaction between the sheet pile and the inner soil. Thus, it is important to provide sufficient friction between the sheet pile and the inner soil to improve the effective reinforcement of the inner soil. This study indicates that soil-structure interaction is an important parameter for establishing a rational design for this method.

A Simplified Deformation Estimation Method for Anchor Piles of Sheet Pile Quay Walls under Kinematic Forces during Earthquakes

In the seismic design of quay walls, it is necessary to evaluate the deformation of the walls during earthquakes as well as the safety of structural members. However, conventional seismic design methods for sheet pile quay walls cannot accurately determine the degree of deformation. One reason for this is that conventional methods do not consider kinematic forces acting on an anchor pile due to the deformation of the ground. This study proposes a simplified estimation method for anchor pile deformation under the influence of kinematic forces. The results of two-dimensional finite element analysis reveal that anchor pile deformation involves rotational and translational components caused by the kinematic forces, which the conventional methods do not consider. The deformation of the anchor pile caused by kinematic forces was 30%–40% of the total deformation at the pile head. It was clarified that unlike horizontally stratified ground, shear stress is generated in the ground before an earthquake resulting in the kinematic force acting on the anchor pile during the earthquake. Furthermore, a simplified method for estimating the deformation of the anchor pile under kinematic forces that uses one-dimensional seismic response analysis considering the predicted shear stress based on a theoretical equation is proposed. It was demonstrated that the proposed method accurately reproduces the anchor pile deformation.

Load random access method of intelligent charging pile based on distributed energy

Load random access method of intelligent charging pile based on distributed energy

EVALUATION OF PILE TENSION LOADS USING PULL-OUT AND PUSH-OUT METHODS

Strain gauge instrumented static tension load testing in bored piles can give the designers a variety of useful information based on the geotechnical conditions. Traditional tension or uplift tests are performed using the pull-out method, which is sometimes inappropriate economically and technically. For the past few decades, Bidirectional Static Load Testing method (BDSLT, commonly known as the O-cell method) has been proven advantageous over the conventional pile load testing method for compression piles. However, the application of BDSLT in tension load tests (push-out), an alternative to the traditional method (pull-out), is seeking wide acceptance in the construction industry. This push-out method provides the facility to install sacrificial jacks within the toe level of the pile and extend an additional reaction pile below the design toe level. In this article, a comparison of the upward behavior of the shaft using instrumented pull-out and push-out methods is studied. The piles of 900mm diameter, 6.0m length were instrumented with 4 levels of vibrating wire strain gauges and tested up to 5000kN for a high-rise building project in Qatar. The maximum settlement observed was 4.60 mm for the pull-out test and 4.20 mm for the push-out test, respectively. The unit shaft friction shows a maximum of 312 kPa for the pull-out test and 395 kPa for the push-out test, indicating that the outcomes are fairly similar. The results of this study suggest that push-out tests can be used as an innovative alternative to conventional technique to bring economic and project executional benefits.

Load random access method of intelligent charging pile based on distributed energy

Load random access method of intelligent charging pile based on distributed energy

Study on Local Scour Protection Countermeasures of Bridge Pier

The scouring effect is a crucial factor affecting the stability of the bridge foundation. Many engineering methods have been developed to reduce the impact of local scour on bridge structures. Among the commonly used protection methods, each method has its limitations and advantages. In this paper, passive method, active method and combination method are used to describe the effects of riprap, collars, slot, sacrificial pile, and vanes methods on the erosion protection effect. The overall judgment of each method is made through the analysis of the factors that may affect the efficiency of protection and the possible shortcomings in the use of protection methods. Then, the inference of device size is derived by combining the various scenarios of the method, so as to help the protection efficiency of the protection method reach the optimal state. Finally, the future development trend and application prospect of the protection method were prospected.

A case study on the bearing characteristics of a bottom uplift pile in a layered foundation

The bottom uplift pile, which has been applied in practical projects, has the following advantages: the pile body is not easy to crack, good bearing characteristics, and small displacement of the pile top. Based on the bearing capacity test of foundation piles in the third stage expansion project of Lanzhou Zhongchuan International Airport, the upper part pile of the self-balancing test method was used to simulate the bottom uplift pile, and the anchor piles in the anchor pile method were regarded as normal uplift piles. The bearing characteristics of the bottom uplift pile in a layered foundation were studied by comparing these two kinds of piles. The results show that under the same displacement of the pile top, the ultimate uplift bearing capacity of the bottom uplift pile can be more than twice that of the normal uplift pile because of the fully exerted frictional resistance of the soil at the bottom of the pile, the Poisson effect of the pile body and the avoidance of the influence of pile body deformation on the pile top displacement. The maximum axial force of the bottom uplift pile appears at the bottom of the pile and gradually decreases from the bottom to the top, which is opposite to that of the normal uplift pile. The properties and thickness of the soil layers around the pile have a great influence on the distribution curves of the frictional resistance along the pile length of the two kinds of uplift piles. With changing soil layer conditions, the distribution curve may be a "parabola", a "straight line" or a "double line". The soil property plays a decisive role in the frictional resistance, which may cause softening. The influence of the pile diameter on the ultimate uplift bearing capacity is greater than that of the pile length, while the elastic modulus of the pile has little influence.

Assessment of ultimate bearing capacity of the pile for jacking & rotary piling method

Techniques of pile installation such as jacking, dropping weight, vibration, and explosion were applied but these methods were discovered to have weaknesses, such as high friction resistance and high settlements. To overcome these problems, this study introduces new method of pile installation which is Jacking and Rotary method (J&R). The objective of this study is to determine pile behaviour for static load test using common method namely jacking (J), and a new method, J&R through the ultimate pile capacity achieved by both methods. A stainless steel 25 mm circular pile, a 50 mm circular pile and a screw pile were used as test piles for this investigation. To achieve the objectives, this study employed graphical methods such as Brinch Hansen 80% and Tangent method to determine the ultimate pile capacity for both piling installation methods. Results revealed that for jacking method, the highest ultimate pile capacity value for the 50 mm circular pile was 1.186 kN, whereas the 25 mm circular pile had the lowest pile capacity reading of 0.539 kN. Screw pile shows the reading of 1.068 kN for its pile capacity. While for J&R, the highest average for both graphical methods are screw pile with 0.683 kN, while the 50 mm circular pile produced the lowest pile capacity which was 0.491 kN. For 25 mm, pile capacity using J&R is 0.543 kN. Result shows the acceptable for J&R methods to be introduced with further investigation such as the response of pile under axial loading and others.

Evolution of tunnel uplift induced by adjacent long and collinear excavation and an effective protective measure

Tunnel uplift control is an important issue for excavation construction near an existing tunnel, especially for long and collinear excavations. In this study, an effective anti-floating measure combining shaft excavation with the frictional pile slab (FPS) was proposed based on a long and collinear foundation pit above existing metro tunnels. The convergence of the shield segments was carefully measured using automatic total stations over 800 days. Numerical simulation was applied to analyze the effect of the width of the shaft excavation and geometric dimension of the frictional pile on the tunnel uplift. Furthermore, a multiobjective optimization procedure was proposed to optimize anti-floating design considering both safety and economy. A comparison between the FPS method and the high-pressure jet-grouting pile (HJP) method shows that the FPS method is a more effective way to control the heave of the underlying tunnel induced by long and colinear excavation due to its small-scale graded unloading and integral portal anti-floating structure. Combining the FPS method with sectional excavation, all the heaves of the underlying tunnel can be controlled to be less than 9 mm. For granite residual strata, the width of shaft excavation is advised to be lower than 8 m, and the length of the frictional pile is suggested to be longer than the distance between the pit bottom and tunnel invert. The heave of the tunnel crown is suggested as the key index to evaluate the excavation-induced disturbance on the underlying tunnel. The unloading ratio and construction time are the key factors that influence the magnitude of tunnel heave. Compared with the actual design, an optimal design with a lower cost and better anti-floating effect is obtained with the proposed multiobjective optimization procedure. The presented tunnel deformation data, advised anti-floating method and construction sequence can provide useful guidance for similar scenarios.

Efficiency investigation of mitigation effect of isolation piles on tunneling-induced ground settlements

In order to study the control efficiency of isolation pile on the settlement of the surface and deep soil, we analyze the implementation method of simulated isolation pile in Plaxis^2d, and establish the finite element model of the tunnel and isolation pile interaction to study the effects of the pile length, pile diameter, buried depth of pile top, pile horizontal position and tunnel buried depth on the control effectiveness. The results show that the control effectiveness of the isolation pile on the ground surface and deep soil strata subsidence is different. Under the uniform radial contraction mode of the tunnel, the pile length has the most obvious impact on the ground surface. In practical projects, it should be at least one radiu at the bottom of the deep tunnel to ensure the control effect on surface subsidence. The closer the isolation pile is set to the tunnel, the better the control efficiency is, especially to the settlement of deep soil. Within 0.6 ~ 1.4 m pile diameter changes on the isolation is of little influence on the pile settlement control effectiveness. The control efficiency of buried isolation pile on ground settlement is not much different from that of non-buried one, but the control efficiency of deep soil settlement in the ground is obviously better than that of the non-buried isolation pile. For the same isolation pile, the deeper the tunnel is buried, the lower the control efficiency of the isolation pile on surface settlement. In this study, the control efficiency of isolation piles on the settlement of deep soil mass is basically negative, indicating that the placement of isolation piles increases the original settlement of deep soil mass, instead, resulting in negative effects. The research can provide a reference for the design and construction of isolation pile.

A Novel Method for Testing the Effect of Base Post-Grouting of Super-Long Piles

The base post-grouting technology is widely used in pile foundation engineering to improve its behavior. For super-long piles, due to the large compression of pile shaft, conventional static load tests cannot effectively test the effect of post-grouting at the pile base. This study introduced a novel method to test the effect of base post-grouting of three 88 m long piles. A total of three test piles were grouted at the bottom of the piles. The grouting amount of the No. 1 pile was 500 kg, the No. 2 pile was 250 kg, and the No. 3 pile was 0 kg. The transmitted wave method in the pile and dynamic penetration method were used in combination to quantitatively evaluate the effect of base post-grouting on the soil below the pile base. The influencing range of base post-grouting was firstly evaluated by the transmitted wave method in the pile, and the strength of the soil before and after grouting under the same pile base was measured by the dynamic penetration method. The test results showed that: the depth of the pile base reinforcement was 2 m for No. 1 pile, and 1 m for No. 2 pile, which was consistent with the grouting amount; the elastic modulus of the soil below the pile base after base post-grouting was about twice that of the soil before base post-grouting; the strength of the soil below pile base was largely improved after grouting; and the bearing capacity of the base soil layer increased from 35.5% to 41.7% when the grouting amount increased from 250 kg to 500 kg.

Efficacy of Design Methods for Predicting the Capacity of Large-Diameter Open-Ended Piles

Large-diameter open-ended piles (LDOEPs) are increasingly being used for support of infrastructure projects. Yet, many of the methods in current use for predicting their capacity are based on studies involving small-diameter piles. The efficacy of eight commonly used pile design methods was explored using a database of 64 load tests on full-scale LDOEPs. Capacities were computed using eight commonly used design methods based on both the standard penetration test (SPT) and cone penetration test (CPT). The calculated capacities were compared with capacities interpreted from load tests using several failure interpretation criteria. The study demonstrated that cone penetration test (CPT)-based methods are somewhat superior to SPT methods, but all methods exhibited scatter between measured and predicted capacities, with the computed capacity off by a factor of two in many load tests. Several plugging conditions were compared for each of these methods. Seven of the eight design methods better predicted pile capacity considering that the piles are unplugged, ignoring contributions of the soil internal friction on the pile inner diameter. These findings suggest that (1) LDOEPs do not plug during static loading, with little contribution of interior skin friction to pile capacity; and (2) LDOEPs do not develop significant end bearing.

Age estimation at puberty, avoiding extrapolation using a non-invasive easily applicable method

Age determination in children and adolescents of unknown age is often based on the degree of bone development (Greulich and Pile method). However, the variability of development at puberty, extrapolation to other populations and the use of invasive means make the reliability and feasibility of this method uncertain. Using pubertal criteria that are simple to identify and easily applicable to any population, we distributed a sample of Tunisian adolescents aged 11 to 16 years into pubertal stages. A nonlinear model between pubertal stages and chronological age was obtained by weighted line square procedures using quantile-quantile plots. Tunisian adolescents have an advanced onset of puberty of slightly more than 13 months compared to French adolescents. The use of our model allowed us to estimate with good accuracy the age of Tunisian adolescents based on their biological maturation. The mean differences between estimated age and actual age from these values were 0.12 ± 0.66 years. In 60% of the cases, the differences between chronological age and estimated age are between ± 6 months. The procedure followed uses simple pubertal criteria. This allows the development of a model for age attribution easily applicable to any population and thus avoids the drawbacks observed in other methods.