Lateral Resistance Of Piles Research Articles

Effect of Soil Degree of Saturation on Pile Lateral Resistance at Different L/D Ratios

Effect of Soil Degree of Saturation on Pile Lateral Resistance at Different L/D Ratios

Physical Modelling of High Stiffness Large Diameter Steel Tubular Pile Subjected to One-Way Horizontal Cyclic Loading

Two centrifuge model tests were conducted, each with three large diameter steel tubular piles installed under similar conditions, i.e., diameter (Φ) = 2 m; thickness (t) = 25 mm; loading height from the rock surface (HL) = 6.5 m, but different rock socketing depths (dr), i.e., 2 m, 3 m, and 4 m, respectively, in prototype scale. Two additional 1 g model tests were conducted using the same model pile and ground. The results indicate that the pile lateral resistance increased with an increase in the rock socketing depth to diameter ratio (dr/Φ) in both 1 g and 50 g models. However, the difference between the two gravitational acceleration levels became visible in the non-linear behaviour as the imposed displacement increased. Specifically, the 1 g models showed larger residual displacement and less stiffness in reloading than the 50 g models, particularly under cyclic loading. Two types of ultimate failure modes were observed, i.e., rock failure and pile structural failure with local buckling just above the rock surface. The latter failure mode was only attained in the pile with a dr/Φ ratio of 2 in a 50 g models among the test conditions adopted in the models, but not in the 1 g model.

EVALUATION OF LATERAL RESISTANCE OF STEEL PIPE PILE WITH WINGS IN COHESIVE SOIL BASED ON THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS

Simulation analyses for in-situ cyclic loading tests in cohesive soil were conducted to indicate that finite element models considering nonlinearity of soil material , pile-soil separation , and a loosened soil layer were valid for evaluating lateral resistance of steel pipe piles with wings driven by rotational penetration. The results of analytical studies demonstrated that pile head load of piles with a loosened soil layer approached that of piles without a loosened soil layer when pile head displacement progressed. Linear finite element models were proposed to evaluate reduction of lateral resistance of piles due to a loosened soil layer.

Insights from in-situ pore pressure monitoring around a wind turbine monopile

Offshore wind turbine monopiles transfer large bending moments into the soil. Due to the large diameter of the foundation, a significant volume of soil is mobilised to absorb the incoming forces from wind, waves and current. If excess pore pressures are generated during load cycles, the long drainage path length could lead to accumulation of pore pressures and loss of strength and stiffness in the soil. During monopile design, undrained behaviour of the soil during cyclic loading is often assumed to conservatively assess the lateral pile resistance during storms. In-situ monitoring of pore pressures in the soil surrounding a monopile foundation allows the assumption of undrained behaviour to be checked for several episodes during the operational life of the foundation. A 3-year period of monitoring data was analysed for a North Sea monopile which included normal operation, storm episodes and rotor stops. Pore pressure and earth pressure sensors were positioned on the pile at two different depths in the most intensely loaded layer of surface sand. The data provides insight into the amount of excess pore pressure accumulation with storm loading not leading to significant accumulation of excess pore pressure. The only episodes showing a significant development of excess pore pressures were rotor stops with suction pressures being developed on the unloaded side of the monopile. The observed response suggests that significant pile-soil stiffness reductions in the top layer due to cyclic loading are not expected for the monitored location. The study shows the value of monitoring pore pressures in the soil mass surrounding offshore foundations for checking design assumptions.

Research of jacked pile penetration test based on airbag loading

In view of the problem that the model test of pile jacking cannot reproduce the soil's self-gravity and thus cannot truly reflect the pile jacking force, this paper developed an airbag loading system. The airbag is used to pressurize and simulate the overburden soil weight. The method of subsection pile jacking and coupling is ingenuously adopted to achieve long pile penetration. Because the airbag and pressure can be controlled well, it is convenient to simulate the cohesive soil foundation. The size of the model pile used in the test is larger than that of the usual centrifugal model test pile, so it belongs to large scale model test. The experimental results using this system show that the pile jacking force increases with the increase of penetration depth. The degradation of pile lateral resistance has little impact on pile jacking force. After modification based on the degradation theory of pile lateral resistance, the overall variation law of pile lateral resistance is good, and the difference value generated at the joint of pile segments is basically 0. With the increasing of pile depth, the pile lateral resistance is gradually exerted. The pile end resistance fluctuates with the depth, and accounts for a relatively high proportion of pile jacked force, which is maintained above 50%. The method of pile jacking with airbag loading in this paper provides a new idea for the study of the penetration characteristics of jacked pile.

Predicting Lateral Resistance of Piles in Cohesive Soils

The ultimate lateral resistance of free- and fixed-headed piles in cohesive soil is examined in this paper using the three-dimensional finite element limit analysis with upper and lower bound theorems. A special concern, and that is the novelty of this study, is devoted to the combined effect of the three important dimensionless parameters; namely, the overburden stress factor (n), the pile length-diameter ratio (L/D), and the ratio of eccentric length to diameter (e/D). Numerical results are expressed by using Broms’s horizontal load factor, and comparisons are made with several published solutions. In addition, the associated failure mechanisms are investigated with respect to the three parametric effects. The adopted new technique has been successfully used to study a number of different geo-stability problems. It is thus the aim of this paper to produce accurate and practical results with design equations and charts that can be used by practitioners to predict the undrained lateral capacity of fixed- and free-headed piles.

Dynamic Response of Cement–Fly Ash Mixed Pile Composite Foundation Under Wave Load

CFMPs (cement and fly ash mixing piles) are used to reinforce fly ash foundation to solve the problem of a large amount of fly ash accumulation in coastal areas. CFMP-fly ash composite foundation is used as the foundation of coastal and coastal engineering. Through the indoor model test, the bearing characteristics and load transfer mechanism of CFMP-fly ash composite foundation under wave load were investigated. The results show that with the increase of wave load, the horizontal resistance of the fly ash stratum increases gradually, the soil resistance moves down, and the level of resistance shows nonlinear characteristics. The pile bending moment, pile displacement, and horizontal resistance of the CFMP composite foundation are concentrated in the upper pile and fly ash stratum, which can improve the ability of the composite foundation to resist horizontal load by improving the physical and mechanical properties of the upper fly ash stratum. Through the calculation of the load–displacement curve, it is found that the measured displacement value is closer to that obtained using the p–y curve method (a method for solving nonlinear lateral resistance of piles). The hysteretic curve area of cyclic loading decreases with the increase of cyclic number. The accumulation of elastoplastic deformation of pile shows that the properties of fly ash gradually change to elastic stage, cyclic loading can reduce the horizontal deformation modulus of composite foundation CFMP caused pile—fly ash system of weakening, in peak load reaches level under the critical state displacement curve showed a trend of the rapid growth of nonlinear, cyclic cumulative failure occurs, and the cyclic load limit state is reached, which affects the service performance of the whole structure.

A Numerical Analysis on Lateral Resistance of Pile–Bucket Foundation for Offshore Wind Turbines

The large-diameter single pile has been widely used in marine wind turbine foundations. In order to improve its lateral bearing capacity, the suction bucket foundation (BF) can be used as a reinforcement method, which surrounds the periphery of the monopile foundation (PF), forming a new wind turbine foundation, i.e., pile–bucket foundation (P–BF). By using the general finite element software ABAQUS, in this paper, several numerical models are established to investigate the influence of pile diameter and bucket diameter on the lateral bearing capacity of large-diameter monopiles. The numerical results show that the internal force distribution along the pile shaft for the case of P–BF is similar to the case of PF. Compared to bucket height, bucket diameter has more of an effect on lateral capacity and the p-y curve in the P–BF. In the combined P–BF, the buckets can provide lateral bearing capacity, and the piles can provide anti-overturning moments, resulting in higher lateral bearing capacity. In this paper, the p-y curve in the API specification is modified based on the results from the finite element simulation. The modified p-y curve fits well with the results of the finite element calculation and can be used as a reference for the design of the P–BF in actual engineering.

Lateral Pile Resistance, Wall Displacement, and Induced Reinforcement Force for Laterally Loaded Single Piles Near Mechanically Stabilized Earth Walls

Lateral Pile Resistance, Wall Displacement, and Induced Reinforcement Force for Laterally Loaded Single Piles Near Mechanically Stabilized Earth Walls

Numerical Investigation into Lateral Behavior of Monopile Due to Scour Enhanced: Role of State-Dependent Dilatancy

The removal of soil during scouring is crucial to the lateral resistance of piles in bridges of railways or highways. In this process, dilatancy of the interface soil induces variation in normal stress, which in turn influences the interface soil lateral resistance. Due to the lack of analysis in previous studies in terms of cohesionless soil state (i.e., relative density and stress level) in remaining soil after scouring, it is difficult to simulate the properties and behavior of interface soil. The objective of this study is to explain the change of the sand state at the compression interface after scouring, quantify the stress-strain characteristics of the pile during this period and eventually present the prediction p-y curves of the lateral service capacity. The state-dependent constitutive model for saturated sand is employed, combined with the 3D finite element simulation, and the state development of the remaining soil is exhibited. The enhancement of dilation and stress relief of the remaining shallow horizon eventually gives rise to the reduction of the lateral resistance. In addition, the remaining overburden soil surrounding the pile restricts the interface soil, enlarging the normal stress and strengthening the deep horizon. Then, the friction angle considered the influence of state-dependent changes is used to quantify the hyperbolic p-y curves.

Enhancement of Tabular Pile lateral resistance with external wings addition

Enhancement of Tabular Pile lateral resistance with external wings addition

Effect of the Slenderness Ratio of Piles on Ultimate Lateral Resistance in Sandy Soil

This research presents the results of 14 tests, where the pile is subjected to static lateral loads. The tests are carried out on pile models with different length / diameter ratios embedded in sand with different relative densities. The influence of embedment length to diameter ratios (L/D), relative density and mode of failure of the pile on the ultimate lateral resistance of piles are investigated. A series of different ratios of embedded length to constant diameter ranging from 12 to 30 was used to perform this study. From the results of the experimental models, it is found that, the length to diameter ratio is a significant variable that influences the ultimate resistance of the piles, where lateral static loads were employed to the single pile by a static lateral load using a device designed for this purpose, and due to the static lateral load the pile was deflected. The ultimate lateral resistance of a pile is investigated to specify the behavior of the pile under the effect of lateral loads as a rigid or flexible pile.

Analysis of Under-Reamed Piles Subjected to Different Types of Load in Clayey Soil

Underreamed piles with one or more bulbs have been widely used in almost all types of soil to support a range of structures. In some cases, in addition to vertical compressive or uplift loads, piles must withstand a considerable lateral load. A 3-D finite element study using ABAQUS software was conducted to examine the behavior of underreamed piles in clay soil under pure lateral, pure uplift, and combined uplift and lateral loads. In this study, pile (L/D) ratios of 11.66, 15, 20, and 25 were considered by adjusting the pile length to simulate the behavior of rigid and flexible piles. The piles were modeled as a linear elastic material, and the soil behavior was simulated using the Drucker-Prager constitutive model. The findings show that the lateral resistance of piles with (L/D) ratios of 11.66 and 15 increased slightly when underreamed piles were used. However, no change in lateral resistance was observed for underreamed piles with (L/D) ratios of 20 and 25 compared with straight piles. The uplift capacity of underreamed piles was significantly greater than that of a straight pile. The lateral capacity was marginally influenced by the prior uplift loading, such that it decreased for a rigid underreamed pile, and increased for a flexible underreamed pile.

Ultimate lateral resistance of piles in sand based on the modified strain wedge model

This paper proposes a novel method for calculating the ultimate lateral resistance exerted by sandy soil against laterally loaded piles. The ultimate lateral resistance distribution of the pile on the front side of the pile above the rotation point is determined by a modified strain wedge model with the three-dimensional cone shape, while the ultimate lateral resistance on the back side of the pile below the rotation point is calculated according to the theory of the passive earth pressure. Using the proposed distribution form of the ultimate lateral resistance along the pile length, an explicit expression to calculate the ultimate bearing capacity is obtained based on the limit equilibrium principle. The rationality of the proposed method is verified by several laboratory and field tests from published literature, and the comparative analysis show that the prediction results coincide with the experimental results. The variations in the normalized modified strain wedge shape depth, radius and ultimate bearing capacity of the pile with the change in the relative stiffness are deeply explored by using the proposed method, and some fitted expressions to quickly determine the modified strain wedge shape and estimate the ultimate bearing capacity of different piles are obtained.

Bounding-surface-based p-y model for laterally loaded piles in undrained clay

Pile foundations supporting long-span bridges, offshore platforms and offshore wind turbines often suffer from repeated lateral loads due to wind, waves and currents. To predict the degradation of the pile's lateral resistance and cumulative lateral deformation through cyclic loading, a theoretical cyclic p-y model is derived for a laterally loaded pile in undrained clay, formulated within the framework of the bounding-surface elastoplastic theory. Unlike the conventional p-y curves which models the degradation of the pile's lateral resistance based on the cycle number and amplitude, bounding surface contraction is employed in this study to model the softening of the soil resistance during laterally cyclic loading. To ensure practicability, the softening model parameter can be easily calibrated by the in-situ T-bar testing technique. A series of verifications with centrifuge tests having various pile-head conditions, pile-soil relative stiffness and load amplitudes are performed. The good agreement demonstrates its ability to predict the degradation of pile lateral resistance.

Application of Miniature FBG-MEMS Pressure Sensor in Penetration Process of Jacked Pile.

In order to study the penetration mechanism of jacked piles in viscous soil foundation, the stress variation law of the pile–soil interface was obtained by installing silicon piezoresistive earth pressure and pore water pressure sensors, and fiber Bragg grating (FBG) sensors in a model pile body, and the penetration characteristics of jacked piles in homogeneous viscous soil were defined. The test results show that: Fiber Bragg grating and silicon piezoresistive sensing technology can better meet the requirements of testing the characteristics of jacked pile in viscous soil. The ratio of pile lateral resistance to pile end resistance varies when pile is jacked in homogeneous viscous soil. In the early stage of pile jacking, the ratio of pile lateral resistance is small, and in the later stage of pile jacking, the ratio of pile lateral resistance increases, but the ratio of pile end resistance is still higher than that of pile lateral resistance. The ratio of the effective stress to the total radial stress is high, and the variation law of the two is consistent with the depth. The total radial stress, pore water pressure, and effective radial stress all exhibit the degradation phenomenon, and the degradation degree decreases gradually with the increase in penetration depth at the same depth. The ratio of excess pore water pressure to overburden weight decreases with the increase in depth, and the maximum value is 87%. The research results can provide a reference for the engineering practice of jacked pile in viscous soil foundation.

Effect of torsion on the undrained limiting lateral resistance of piles in clay

The behaviour of piles subjected to lateral loads has been explored by a number of investigators over the past five decades. However, the vast majority of the previous literature has ignored the potential influence of additional torsional effects due to horizontal eccentricities of the applied lateral loads. In this paper, an upper bound mechanism and a lower bound stress field are presented for the calculation of the ultimate combined torsional and lateral loads on single piles in clay. The corresponding analytical upper and lower bound plasticity solutions are shown to be in excellent agreement, bracketing the theoretically exact failure loads with an error of less than 0·5%. Two-dimensional finite-element analyses are also presented and the computed ultimate loads and observed failure mechanisms are shown to compare very well with the plasticity solutions. Based on the numerical results and analytical solutions, failure load interaction diagrams and a simple empirical equation are presented that allow the calculation of the lateral bearing capacity factor for any level of applied torsion and pile–soil adhesion factor. It is demonstrated that the effect of torsion can be very significant, causing reduction in lateral bearing capacity of up to 50% and therefore should be considered in design.

Three-dimensional analysis of pile groups subject to torsion

A series of three-dimensional finite-element models was developed to investigate the non-linear behaviour of pile groups connected to rigid caps and subjected to torsion. Pile groups of sizes 1 × 2, 2 × 2 and 3 × 3 installed in sand were analysed to investigate group resistance as well as the variation of pile flexural and torsion deformation. Furthermore, the relative contributions of the pile cap, pile torsion resistance and pile lateral resistance to group torsion resistance were quantitatively evaluated. The influence of group size, pile spacing, pile length, cap condition and soil stiffness was thoroughly explored. Piles were assumed to behave in a linear elastic fashion, while soil was modelled by way of the non-linear hardening-soil model. The numerical results showed that the contribution of the torsion strength of individual piles to the group overall strength decreases with the increase in group size and pile spacing but increases with the increase in pile length and soil stiffness. Among these parameters, the torsion resisted by individual piles ranged from 20 to 45% of the external applied torque. Moreover, it is found that the pile cap contributes about 7% of group resistance for surface pile caps, while this contribution increases up to 53% for embedded pile caps.

Model study on the performance of single-finned piles in clay under lateral load

Generally, foundations of many structures, such as transmission towers, bridge abutments, ocean engineering structures, marine dolphins, dock-fendering systems, and moorings are subjected to different modes of lateral loading. This research aims to study an alternative and novel technique to improve the lateral pile capacity in clay using fins at the top of piles. Laboratory small-scale model tests were carried out to study the behavior of laterally loaded finned piles installed in clay soil for different undrained shear strengths (Cu = 11 and 15 kPa). The effects of different factors, such as pile type, stiffness, geometric dimensions, and shapes of fins, were studied. Moreover, the effects of the fin number and inclination angle were also investigated. Results emphasized that there is an increase in the lateral pile resistance against the lateral load after placing fins at the top of the pile head. It has been found that the optimum length of the adopted fins should equal 0.4 of the pile embedded length and the fin width should equal the pile diameter. The existence of fins improved the behavior of finned piles by 1.67 and 1.55 for piles of L/D = 10 in the case ofCu = 11 and 15 kPa, respectively, compared to regular normal piles in the same condition. Also, the improvement in L/D = 22 piles due to fins reached to 1.29 and 1.35 for the case of Cu = 11 and 15 kPa, respectively.

Ultimate Load Tests on Bearing Behavior of Large‐Diameter Bored Piles in Weathered Rock Foundation

Based on the vertical compressive static load test and pile mechanics test of three large diameter bored piles (one of the test piles was treated with postgrouting) in granite gneisses foundation, the bearing capacity, deformation characteristics, and influencing factors of the single pile under the limit state are analyzed and compared with the recommended values of survey report and the recommended values of current codes. By comparing the measured and theoretical values of pile axial force, the bearing capacity of cast‐in‐place pile under normal and limit conditions is analyzed. The experimental results show that the Q-s curve of large‐diameter rock‐socketed mud wall retaining bored pile with a length‐diameter ratio of 25–33 and rock‐socketed depth of 5–8 d shows a rapid growth. After grouting treatment, the ultimate compressive bearing capacity of single pile is improved, the maximum settlement is reduced by 6.6%, the rebound rate is reduced by 11.1%, and the settlement effect of controlling pile top is not significant. The bearing capacity and deformation characteristics of the three test piles are less affected by length‐diameter ratio and rock‐socketed depth. For postgrouting piles, the ratio of frictional resistance of rock‐socketed segment and the ratio of pile lateral resistance are less affected by length‐diameter ratio and rock‐socketed depth, while, for postgrouting piles, the ratio of pile lateral resistance is more affected by rock‐socketed depth. The pile end resistance ratio of the three test piles is significantly affected by the rock‐socketed depth, whether or not the pile side postgrouting treatment is carried out.