Pile Settlement Research Articles

Analisis Daya Dukung Fondasi Bored Pile Pada Rumah Sakit Sultan Imanuddin Pangkalan Bun

This study intended to analyze the bearing capacity of single bored pile, the bearing capacity of the bored pile group, the load carried, the safety factor, and the settlement that occurs. The first calculation method is Schmertmann and Nottingham method, and the second calculation method is Meyerhof method. Based on the calculation of the bearing capacity of a single bored pile using the Schmertmann and Nottingham method obtained a value Qu = 49005,88 kN, while the Meyerhof method obtained a value Qu = 1633.71 kN. The calculation results for bearing capacity of the pile group using the Schmertmann and Nottingham method obtained a value Qg = 164169,70 kN and the Meyerhof method obtained a value Qg = 5472.93 kN. The results of the load carried by the bored pile group using Schmertmann and Nottingham method is Qi = 353.98 kN ≤ Qg = 164169.70 kN which means it’s still within safe limits. Using the Meyerhof method is Qi = 353.98 kN ≤ Qg = 5472.93 kN which means it is still within safe limits. The safety factor using the Schmertmann and Nottingham method obtained SF = 463.78 and using the Meyerhof method obtained SF = 15.46 which means it is very safe. Total settlement of a single bored pile is S = 0.0142 m ≤ 0.04 m which means it is safe. And the settlement of the bored pile group is Sg = 0.03 m ≤ 0.08 m which also means it is safe

Investigation on thermo-mechanical response of energy piles in saturated clay

In recent years, energy piles have been widely used in the collection of shallow geothermal energy. However, the engineering characteristics of the soil and the mechanical behaviour of the pile are affected by temperature, particularly in clay. To explore the influence of heating–cooling cycles on the thermo-mechanical response of an energy pile in saturated clay, a laboratory model test was designed. The energy pile in saturated clay was subjected to ten heating–cooling cycles. A fibre Bragg grating (FBG) system was adopted to monitor the pile strain. Meanwhile, pile and soil temperature, pore water pressure and pile top displacement data were collected using a dynamic acquisition instrument. The results show that FBG sensors can achieve good results in measuring the axial strain of a pile. The distribution and transmission of thermally induced axial force and stress are affected by soil properties and pile constraints. Temperature cycling will lead to the thermal consolidation of saturated clay, improving the bearing performance of energy piles, and to an irreversible settlement of the energy pile.

Experimental Study on the Negative Skin Friction of Piles in Collapsible Loess

The collapsible loess is widely distributed in western China. The special structure and water sensitivity of loess lead to the complex negative skin friction mechanism in pile foundations. Previous studies mainly focused on the negative skin friction of pile foundations and treatment measures, such as casing and coating methods. However, few studies have focused on the influence of the negative skin friction on the settlement and bearing capacity of piles in collapsible loess, especially environmentally friendly methods that can reduce the negative skin friction. In this study, a series of non-immersion and immersion experiments was conducted to investigate the settlement, axial force, and side friction resistance of piles in loess soil under controlled conditions. The results showed that under the non-immersion condition, the settlement of model piles increased with the increasing pile top load. The axial force gradually decreased along the pile length for piles without casing. The axial force attenuation of the casing section of casing piles was almost negligible due to the isolating frictional resistance effect of casing. The settlement of each soil layer increased with the increase in immersion time, and the process was divided into an initial gradual stage, rapid drop stage, and later gradual stage. Both negative and positive skin friction increased with the increasing immersion time and pile top load, and there was a neutral point. The maximum axial force of piles without casing exceeded the peak load at the pile top. The presence of steel casing reduced the failure of pile foundation in collapsible loess. The research results of this paper provide theoretical support for the application of piles in loess areas.

Load-Bearing Characteristics of PHC Piles Constructed by the Inner Digging Method Based on Ultimate Load Testing and Numerical Simulation

This paper studies the load-bearing characteristics of two prestressed high-strength concrete (PHC) pipe piles constructed by the medium mid-digging and hammering methods. The ultimate load tests and numerical simulations of the pipe piles constructed by both methods were carried out to analyze the ultimate lateral resistance, and ultimate resistance performance characteristics of the two pipe piles and the influence of the wall thickness of the pipe piles on the bearing performance. The test results show that the pipe pile constructed by the middle inner digging method has a higher pile quality. The single pile bearing capacity of the pipe pile constructed by the middle inner digging method is 50% higher than that of the common hammering method. The enlarged part of the pile end has an obvious effect on improving the bearing capacity. The settlement of the pipe pile constructed by the middle inner digging method is smaller than that of the hammering method. The large diameter pipe pile constructed by the middle inner digging method usually shows characteristics of the end-bearing pile. The resistance of the pile end accounts for 40–50% of the top load. The numerical simulation results agree with the field test and are compared and discussed. The simulation results show that when the bearing capacity of the pile is provided by the pile side frictional resistance, the influence of the pile wall thickness on the bearing capacity is insignificant. When the top pile load is close to the bearing capacity of the pipe pile, the influence of the pipe pile wall thickness on the bearing capacity is greater.

Evaluation of fitting to hyperbolic functions of load transfer curves for piles in granular soil profiles

ABSTRACT Load–transfer methods are important tools to analyse and predict pile settlements. Several studies on single piles and pile groups used experimental data from instrumentation, in order to evaluate the load–transfer mechanism to the foundation soil, by obtaining skin friction and toe resistance. For single piles, the load–transfer curves can be approximated by hyperbolic models, and for pile groups, by models in which the interaction between nearby piles is added to the hyperbolic curve of each individual pile through analytical formulations. By collecting experimental data from 68 piles executed in granular soils that were instrumented and subjected to static load tests, this study evaluated the fitting of load–transfer curves to hyperbolic functions for single piles and pile groups. Remarkable fitting to hyperbolic functions was found for single piles, and very good agreement was also obtained for pile groups (adjusted R 2 around 0.96). The deformation parameters (M s and M b) by Bohn et al. for single piles were reassessed, and new reference values that led to more convergent predictions were proposed. Lastly, the use of the parameters M s and M b was also extended to pile groups and new preliminary reference values were suggested.

The Effects of Branch Spacing and Number on the Uplift Bearing Capacity of a New Squeezed Multiple-Branch Pile: A Numerical Simulation Analysis

The squeezed multiple-branch pile is a variable section pile that was built by adding a bearing branch cavity to a constant section pile using expansion and extrusion equipment. It is widely used in engineering practice for its high bearing capacity, small settlement deformation, high economic benefits, strong adaptability, and simple pile forming process. In this paper, a new type of squeezed multiple-branch pile is proposed and its forming tool is invented. The forming tool of the pile has applied for an invention patent and is authorized by the China National Intellectual Property Administration. Multiple groups of comparison models of the new squeezed multiple-branch piles are established by using FLAC3D numerical simulation software to investigate the influence of the number and spacing of branches on the bearing mechanism in response to uplift load. The results indicated that the number and spacing of branches have a significant effect on the uplift bearing capacity, load–displacement curves, side friction resistance, and stress distribution law in the new pile and soil around the pile. The suitable number and spacing of branches maximize the uplift bearing capacity and minimize the settlement of a single pile.

Capacity of piles subject to downdrag: a comparison of North American bridge design codes and observations from a full-scale test pile program

Negative skin friction caused by ground settlement is an important consideration for deep foundations in limit states design. However, there are inconsistencies in the methodology whereby negative skin friction and associated drag force are considered in assessing the geotechnical capacity or geotechnical ultimate limit state (ULS) in various design codes. This includes two current North American bridge design codes, the Canadian Highway Bridge Design Code, and AASHTO LRFD Bridge Design Specifications. A test pile program was developed to observe effects of ground settlement on pile settlement, capacity, and drag force. Two instrumented steel H-piles were driven through a compressible clay layer to a hard end-bearing stratum, subjected to ground settlement by constructing a 1.5 m high embankment, followed by static load testing. A load-transfer model was calibrated from the test pile program observations. Test results and the calibrated model were used to compare geotechnical ULS requirements of the two bridge design codes. It is demonstrated that drag force did not detrimentally impact pile capacity. The results showed that for conditions of the test pile program, assessing the geotechnical ULS can be more conservative when adhering to the current AASHTO LRFD Bridge Design Specifications than the Canadian Highway Bridge Design Code.

Numerical study on the effect of protective wall depth in reducing structure deformations caused by tunnelling

To reduce tunnelling induced damage of buildings, a ‘protective wall’ is sometimes constructed between the location of the new tunnel and existing foundations. One of the key design questions relates to the optimal wall depth, where further increase has a limited benefit in reducing structural distortions. This paper presents the results from finite element analyses used to study how protective walls reduce tunnelling induced damage to adjacent structures. A scenario where the protective is located very close to a tunnel is studied, which is considered to be of practical interest and a critical case concerning potential for building damage. The analyses consider a tunnel with a row of 4 piles (in sand) supporting a 5-storey steel frame running transverse to the tunnel direction, with a wall located between the tunnel and the first pile. Results show that the protective wall’s depth affects soil and pile settlements, the redistribution of loads applied to the piles (due to structure stiffness), and ultimately structural deformations and building damage. For the case considered, the optimal depth of the wall is approximately 1.25 times the tunnel axis depth; marginal reductions in pile settlements and building damage are obtained as wall depth is increased further.

Behavior of Pile Group Constructed on Clayey Soil under El-Centro Seismic

Over the past decades, pile foundations used to support buildings through a transfer of superstructure loads into more stable soil strata than surface soil layers. Buildings are exposed to seismic force, pile undergoes more stress through the significant vibration of the surrounding soil in addition to the static stresses of buildings. The investigation of the behavior of pile foundations under the influence of earthquakes is still limited or not well described. Further, this paper presents a theoretical study to evaluate the vertical settlement and horizontal displacement of piles embedded in clay and silty soil of Baqubah soil under the effect of the acceleration time history of the 1940 El-Centro earthquake. The study was carried out by using the commercial finite element software PLAXIS 3D. A three-dimensional analysis of the soil-pile foundation for four multi-story buildings is performed with different diameters (0.5, 0.7, and 1) m for the corner, exterior, and interior pile, respectively. The linear elastic model for pile foundation and the Mohr-Coulomb model for soil layers were used in this numerical analysis. The research showed that vertical settlement and horizontal displacement increase as the duration of the earthquake increases, and horizontal displacement with values smaller than vertical displacement. Also, the results showed the vertical settlement is similar for different diameters, in contrast to the horizontal displacement, which was of different values with a range between (3% to 22%) when the diameter increased from 0.5m, 0.7m, and 1m. Also, it can be observed that values increased with the direction of the earthquake from the right to the left side of the pile-soil system with a range of (12% to 32%).

Three-Stage Analysis Method for Calculating the Settlement of Large-Diameter Extralong Piles

In terms of safety, large-diameter extralong piles require highly accurate settlement prediction because of their high load-bearing capacity. According to the bearing mechanism of the large-diameter extralong pile, in this paper, a novel and scientifically accurate three-stage analysis method is proposed for predicting pile settlement based on Randolph’s study of pile forces in homogeneous soils, in view of the limitation that the accuracy of the conventional settlement calculation method is only applicable to the pile in the end-bearing frictional bearing condition. The three-stage analysis method fully considers the deformation characteristics of the pile in three different bearing states: pure friction bearing stage, end-bearing friction bearing stage, and damage stage. The critical load of TP4-1 in this paper is 9620.89 kN, and the ultimate compressive bearing capacity is 19279.09 kN, as calculated using the three-stage analysis method, and thus the three bearing states are clearly defined. The settlement under all levels of load obtained using this method can be very close to the real-case settlement, and the maximum error of the TP4-1 pile is only 0.52 mm, as observed by numerical simulation, static load test of TP4-1, and experiments on the other three test piles.

Analysis of Settlement of Group Pile Foundation in Linear Viscoelastic Soil

The settlement of a group pile foundation is the result of elastic-plastic settlement of the pile and rheological settlement of the soil. Unfortunately, most research only considers elasto-plasticity settlement of piles or rheological settlement of soils. Classical theories like the Poynting-Thompson model only provide some prediction for the elasto-plasticity behavior of pile groups, which cannot satisfactorily reflect the total settlement characteristics of pile group foundation. In the current paper, we presented a method to study settlement behaviors of pile group foundation in linear viscoelastic soil based on the pile-pile interaction factors, the calculated equation of settlement of single piles and pile groups under vertical loads that are derived, the influence law of pile end resistance, pile spacing, slenderness ratio, elastic modulus ratio, and Poisson ratio on pile end load ratio, and the interaction factors that have been presented. Finally, some typical predictive examples have been presented for a 2 × 2, 3 × 3 group pile showing settlement from a field test. It is found that the pile-pile interaction factors increase with the increase of the pile-soil elastic modulus ratio and length-to-diameter ratio but decrease with the increase of the ratio of distance to diameter, and the ratio of distance to diameter has little effect on the interaction factor when pile spacing is more than 10 d (d is the diameter of the pile). The error between the field test results and computed data is 14.9%, the settlement calculated by the present method shows good agreement with the reported results, and the correlativity coefficients R2 are greater than 0.9223, which signifies that the present method is suitable for the theoretical calculation and prediction of the composite foundation settlement of linear viscoelastic soil when piles are used to strengthen the foundation. The method would provide a unique view to quantitative prediction of the settlement characteristic of group pile foundation.

A novel short pile foundation system bonded to highly cemented layers for settlement control

While design methods of deep foundations are mainly developed for homogenous soil deposits, the presence of highly cemented layers could lead to underestimation of resistance and overestimation of settlement of pile foundations. This study presents a novel approach using competent caliche layers bonded to the top and bottom of a continuous flight auger (CFA) pile as a new composite foundation system named caliche stiffened pile (CSP). The key objective is to optimize the required pile length in a cost-effective approach without ameliorating soil properties. Settlements of the CSP foundation for a high-rise building were monitored and full-scale tests were conducted to measure piles’ capacity. Finite element back analyses were performed to avoid adverse effect of sample disturbance in settlement calculations. A back calculation of a test fill embankment was performed to determine soil stiffness parameters by simulating an unscheduled imposed load to the structure. Impacts of the CSP on controlling the settlement of pile foundation and optimizing the required pile length are investigated using finite element analysis and a parametric study. The proposed CSP foundation can reduce the CFA pile settlement significantly in the presence of caliche layers with thickness equal or greater than a pile diameter at CFA pile head and toe, where the CSP is located.

Evaluation of bearing capacity of PHC pipe piles via the dynamic and static loading test

Due to its faster implementation and potential cost savings for estimating the bearing capacity of PHC pipe piles, the High Strain Dynamic Test (HSDT) offers an alternative approach to Static Load Test (SLT). The report presents a bearing capacity study via those methods with a sliding micrometer. And a Pile Driving Analyzer (PDA) imported from the United States is employed, to determine the design parameters of pile foundation engineering and provide the error sources of bearing capacity. Sliding micrometers with cone-shaped rings are embedded in the inner side of the pile piles every 1 m for measuring the strain. The law of stress and strain at various depths during loading is presented in this paper. As a new concept, the “inflection point” is proposed by the relationship between shaft resistance and relative displacement of pile-soil. By comparing the SLT and HSDT, the relationship between toe resistance and settlement of pile is demonstrated. This paper analyses the reliability and precision, and explore the error source so as to provide theoretical evidence for trail-pile testing in future. And the error of bearing capacity between SLT and HSDT with CAPWAP studies shows that the HSDT could provide adequate results for assessing the bearing capacity of PHC pipe piles.

Perencanaan Pondasi Borepile Pada Jembatan, Studi Kasus : Jembatan Utama Cisadane

The most important part in a bridge construction is the foundation. Bore pile foundation is planned for 2 abutments and 5 piers. The entire foundation uses a diameter of 1 meter with a depth of 20-30 meters. Calculation of axial bearing capacity using the reese and wright method produces a single pile axial bearing capacity of 268.090 - 470.697 tons. The efficiency of the pile group using the Converse-Labarre method and the axial bearing capacity of the pile group is 5870,246 - 33176,233 tons. Single pile settlement using a semi-empirical method and resulted in a decrease of 50,100 - 59,490 mm. The settlement of the pile group used the vesic method and resulted in a decrease of 6,627 - 13,302 cm. consolidation decrease using the coefficient of volume change and resulted in a decrease of 104,024-576.047 mm with a time of 5,694-26,731 years. The calculation of lateral bearing capacity and pile deflection using the Broms method resulted in the lateral bearing capacity of the pile group of 3024-20580 tons and deflection of 1.485-5.888 mm. foundation reinforcement using the reference of SNI 2847-2019. Longitudinal reinforcement using 10D32 and stirrup reinforcement D16-50 and D16-75. Pile cap planning refers to SNI 2847-2019, resulting in a pile cap thickness of 1.5-4 meters. The X direction and Y direction reinforcement used are D32-150 for the pier and D32-150 and D25-150 for the abutment. The calculation of the cost budget plan uses the unit price analysis method and the resulting total cost is 73.574.031.053.

The results of strengthening the foundation with a bored pile with an enlarged pile base

The article presents the results of static tests of a strip foundation fragment, strengthened with a bored pile, which has an enlarged pile base at its lower end. To evaluate the results obtained, tests were also carried out for the static load of a strip foundation fragment without strengthening with a bored pile with an enlarged pile base and a separately located bored pile with an enlarged pile base. According to the data obtained during tests for static load, dependence graphs were constructed: settlements of a strip foundation fragment without strengthening with a pile with an enlarged pile base from the pressure under its toe and settlement of a bored pile with an enlarged pile base from the static indentation load. As a result, it was found that the use of a bored pile with an enlarged pile base as strengthening of a strip foundation fragment made it possible to increase the maximum allowable pressure under the toe of a strip foundation fragment on the ground by an average of 25% and reduce the settlement of a strip foundation fragment by an average of 43%.

New Foundation Treatment Technology Using Cement Soil Composite Tubular Piles Supported by Optical Fiber Sensing Technology

The purpose is to optimize the foundation’s treatment process and improve the foundation’s construction effect to better apply the cement soil composite tubular piles. This exploration is to study the cement composite tubular piles. First, the principle and application of optical fiber sensing technology are discussed. Then, the application design and conditions of the cement composite tubular pile are discussed. Finally, a new foundation treatment technology supported by optical fiber sensing technology is proposed and comprehensively evaluated based on the application of cement soil composite tubular piles. The research results show that: (1) the new foundation treatment technology reflects the optimization of the optical fiber sensing technology for the foundation treatment. Moreover, it is further optimized through the application of cement soil composite tubular piles. (2) When subjected to the same load, the longer the core pile is, the smaller the cement soil composite pile’s settlement is. When the inner core pile is 20 m ~24 m long, the settlement of the cement soil composite pile is small. When the length of the inner core pipe pile is 16 m ~20 m, the settlement range of cement soil composite pile becomes larger. (3) With the increase of friction coefficient, the settlement distance of cement soil composite tubular pile will decrease. The above data show that compared with the traditional foundation treatment technology, the new foundation treatment technology designed based on the application of composite tubular piles, supported by optical fiber sensing technology, can well solve the foundation construction problems, avoid pavement settlement, cracking, and other phenomena, and ensure the overall safety of the road. This exploration fully reflects the advantages of the new technology of foundation treatment and ensures the quality of road engineering. It provides a reference for the development of foundation treatment technology of construction projects and contributes to the development of the construction industry.

An Analytical Method Evaluating the Evolution of Group Effect for Vertically Loaded Pile Groups Subjected to Tunnel Excavation

Tunnel excavations near existing vertically loaded pile groups are frequently encountered in urban areas, and most available studies have focused on the additional deformation and stress induced in the pile group, lacking in consideration of the variation in the pile-soil interaction (PSI) in the process, which plays an important role in pile group behavior with close pile spacing. In addition, for vertically loaded pile groups subjected to excavations in their proximity, the combined actions of the overlapping stress and shielding effect can lead to complicated variations in the group effect, which in turn results in difficulty in evaluating the PSI relationship and the pile group response. Thus, the modified Poulos method is extended in this paper to account for the effects of tunneling, and the variations in the group effect, load redistributions and pile settlements are also investigated. The validity of the proposed method is firstly verified by an available centrifuge model test with tunneling near a 2 × 2 fixed-head pile group. Further, the influences of the pile spacing and relative distance between the pile group and the tunnel are analyzed, and the most unfavorable working condition could be a tunnel excavated near the soil surface, close to a pile group with a small pile spacing.

Nonlinear Stochastic Seismic Response Analysis of Three-Dimensional Reinforced Concrete Piles

A reliable assessment and design of engineering structures requires appropriate estimation and consideration of different sources of uncertainty. The randomness of seismic ground motion is one major uncertainty that needs to be considered from the perspective of performance-based earthquake engineering. To properly account for this uncertainty and its corresponding effect on pile foundations, a stochastic seismic response analytical framework based on a probability density evolution method and a stochastic ground motion model is proposed for the nonlinear stochastic seismic response analysis of pile foundations. A three-dimensional finite element model of a reinforced concrete pile with a large diameter embedded in the soil foundation is firstly established and calibrated using the full-scale lateral load test results from the literature, in which the nonlinear behavior of soil, the soil–pile interaction, the concrete damaged plasticity, and the steel yielding of the pile are properly modeled. Then, the calibrated three-dimensional numerical model is employed as an illustrative example for the stochastic seismic response analysis using the proposed framework. The mean, standard deviation, and probability density function of pile settlement and the dynamic reliabilities of the pile concerning various performance requirements are obtained in the present study. The settlements of the pile show great variability under the excitation of various stochastic ground motions, and the maximum mean value of the pile settlements is about 8 mm. The changing shape of the settlement probability density functions in every moment demonstrates that it is unreasonable to use assumed probabilistic distribution models to characterize the seismic responses of pile foundations during a seismic reliability analysis. Based on the proposed method, it is found that the dynamic reliabilities of the selected reinforced concrete pile concerning four different performance levels are 0, 0.1293, 0.8247, and 1, respectively. The proposed stochastic seismic response analytical method in the present study can provide a proper and comprehensive way to quantify various uncertainties and their corresponding effects on the seismic performance of pile foundations. It can also be used to estimate the actual reliability level of pile foundations that are designed by the current codes when they are subjected to seismic loads.

Settlement and long-term bearing capacity of the pile taking into account the rheological properties of soils

A large number of scientific works by both Russian and foreign authors are devoted to the interaction of a single pile with the surrounding and underlying soils. Based on experimental, numerical and theoretical studies, various methods, approaches and solutions have been obtained in scientific works, which make it possible to most correctly predict the settlement and bearing capacity of a single pile. Research in this area is relevant, since the determination of the settlement of the pile, as well as the study of the mechanism of distribution of the load transmitted to it, play an important role in the design of pile foundations. In this work, the boundary value problem of the interaction of a long and incompressible pile with the surrounding and underlying soils in an elastic-viscous formulation, taking into account soil strengthening, was solved, based on the Maxwell model, as well as on the basis of the rheological model of A.Z. Ter-Martirosyan. This study presents a detailed course of solving the boundary value problem, as well as the basic formulas for calculating the settlement and long-term bearing capacity of a single pile. The change in the curve of dependence σ R ( t ) at different values of soil viscosity is shown when solving the problem in an elastic-viscous formulation. An additional graph of σ R ( t ) dependence is presented showing the difference in the presented soil models. Based on the plotted graphs of the dependence of σ R ( t ) when solving the problem in an elastic-viscous formulation, it can be concluded that the time to reach the maximum value of the load under the foot of the pile is directly proportional to the value of the soil viscosity. When solving the problem on the basis of the rheological model A.Z. Ter-Martirosyan, the maximum value of the load under the foot of the pile is reached earlier than when solving the problem in an elastic-viscous formulation both with and without soil strengthening, which requires additional study.

Soil Heterogeneity Effects on Bridge Piles Deformation under Shield Tunnelling Disturbance

This research examines the impact of soil heterogeneity on the bridge piles beneath a nearby tunnel excavation using Monte-Carlo stochastic analysis. Sensitivity analysis is specifically used to the variation of stratum range, variation coefficient (COV), and fluctuation distance of the soil Young’s modulus. Meanwhile, the reliability evaluation approach is also applied to systematically examine the impact of COV on the likelihood of a pile failing. The findings suggest that more consideration should be given to the degree and range of geological parameter variations in the strata surrounding the tunnel. The horizontal and vertical fluctuation distances in this project are predicted to be around 18 m and 4.5 m, respectively. The fluctuation range influences the frequency of low stiffness zones in the soil. Additionally, the variation coefficient has a significant effect on the pile deformation, presenting a positive association. The pile deformation exhibits an increasing tendency in the wake of the growing variation coefficient. More significantly, the increase of the COV will directly lead to a rising failure probability of the pile settlement. According to extensive Monte-Carlo simulation calculations, the simulation results considering the variability of soil parameters have a certain deviation from the deterministic in the perspective of probability statistics. It is quite necessary to attach importance to the soil heterogeneity effects in the pile foundation stability under construction disturbance.