Abstract:With the rapid development of highway and railway construction in mountainous areas in China，the phenomenon of bridge pile foundations built in sloping ground is growing daily，but the bearing mechanism of bridge pile foundations in sloping ground is complex. Therefore，the design and calculation of bridge pile foundations in sloping ground has gradually attracted wide attention and become one of the current research hotspots. In the engi? neering design of bridge pile foundation，the inclined and eccentric load transmitted from the bridge superstructure， the extra earth pressure caused by the pile-slope asymmetry system，and the reduction effect of lateral soil resistance should be considered simultaneously. Based on the comprehensive analysis of related literature at home and abroad， in this paper，the current research status of the bridge pile foundation is elaborated detailedly in four aspects：the bearing mechanism，the field and the model test method，the stress deformation analysis and design method，the construction technology，safety assessment method and strengthening processing measures. Furthermore，future re? search directions in this field are pointed out.

Abstract:As the construction of highways extend to the mountainous areas in the central and western regions in China，a large number of high-steep slopes have been generated. The construction process not only broke the geo? logical and ecological balance of the original mountains，but also easily to induce geological disasters such as land? slides，collapses and debris flows，which seriously threaten people’s lives and property safety. Therefore，some problems of high-steep slopes in mountainous areas have always been the key and difficult points in geotechnical en? gineering，including stability analysis，design，treatment and monitoring. However，due to the characteristics of high uncertainty，strong nonlinearity and dynamic evolution of high-steep slopes，it is difficult to obtain reasonable answers to the above problems based on analysis and calculation methods of classical theory. Artificial intelligence technology has the unique advantage of dealing with nonlinear complex systems，and it has become an effective means to solve slope engineering problems in highway. Therefore，this paper summarizes the main research progress in several fields of slope engineering of highway in mountainous areas in the past 10 years，including intelligent analysis calculation and evaluation method of slope stability，calculation method for intelligent design of slope pro? tection and reinforcement，intelligent monitoring technology of slope，intelligent identification and prediction of landslides，intelligent inversion of rock and soil parameters，intelligent identification of rock slope structural planes，and so on. Furthermore，the further development direction of intelligent construction of slope engineering in highway is briefly explained in the fields of slope stability analysis and reinforcement design，on-site monitoring and landslide prediction.

Abstract:Based on the bag-sealed pile formation test and four sets of indoor static load tests，combined with seven sets of numerical models，the feasibility of pile formation，pile load transfer characteristics and load-bearing mechanism of bag-sealed piles were studied. The research results show that：1）The bag-sealed pile has the charac teristics of good pile quality and predictable pile shape while solving the problem of slurry leakage during pile forma? tion in karst areas. Under the conditions of equal pile diameter and equal loading，the ultimate bearing capacity of the bag-sealed pile is more than 1.15 times that of the traditional pile，the settlement of the pile top is much smaller than that of the traditional pile；and the settlement of the pile top is much smaller than that of the latter. 2）When the bag-sealed pile is loaded，each pile section plays in turn from top to bottom and carries the load alternately. The en? hancement of the end-bearing effect of the branched section on the load bearing capacity is greater than the weaken? ing of the bag on the side friction resistance，which is the load-bearing characteristics of the bag-sealed pile. 3）The branched section enhances the pile-rock bonding capacity，in which the lower part of the branched section plays the main bearing role and the upper part only plays the structural role. 4）The asymmetric distribution of the branched sections is one of the unfavorable factors for load bearing，which puts forward a requirement for the design of the bending resistance of the bag-sealed pile. The experimental and numerical simulation results demonstrate the pile formation process of the bag-sealed pile，reveal its unique bearing mechanism and verify its superiority of bearing performance. The research findings can provide ideas and bases for the application of bag-sealed piles in karst areas.

Abstract:This study simulates the soils with spatial variability by random field theory and Karhunen-Loeve ex? pansion. Reliability analysis of strip footing lying on karst area is carried out based on finite element limit analysis and Monte Carlo simulation. The emphasis of this study is performing the parametric analysis through finite element modeling，in order to explore the effect of karst cave parameters（including depth and horizontal offset distance of karst caves）and spatial variability parameters（including correlation length and coefficient of variation）on the ulti? mate bearing capacity and failure probability of footings. Then，combined with the visualization of failure patterns of cave-footing system，the variation mechanism of footing failure probability is revealed. Finally，the finite element analysis results are compared with the existing research results to verify the accuracy of the numerical model and the reliability of the research conclusions. The results indicate that the higher the disperse degree of failure curve is，the more failure paths may develop under external loads，which leads to a higher failure probability of the footing. Fur? thermore，the footing failure probability increases with the increase of distance between the karst cave and the footing. The higher spatially variability of soils also leads to a higher failure probability of the footing. And the failure probability decreases significantly with the increasing factor of safety. If the method proposed in this paper is used for reliability analysis in the advanced design，the safety factor should be larger than 2 as far as possible and the lower limit theory should be used for analysis，in order to guarantee the safety.

Abstract:Whether the bridge pile structures adjacent to the slopes can support the threats of the landslides im? pact determines that the bridge can provide safe service. Therefore，the research on the slope instability mechanism and the law of sliding mass impact on bridge pile structure under earthquake and rainfall is an urgent need for bridge engineering design and construction. Based on the advantages of Smoothed Particle Hydrodynamics method，such as tracking the time change of particle characteristics and simulating large deformation，a parallelized Smoothed Particle Hydrodynamics algorithm was proposed to simulate the process of earthquake-induced landslides impact on bridge pile structure. The effects of seismic acceleration amplitude，frequency spectrum，duration on analyzing law of impact by rainfall-induced landslide and earthquake-induced landslide on bridge pile structure were analyzed， and the effect of different number of threads on the efficiency of parallel computing were studied. The results showed that the increase of seismic acceleration amplitude can accelerate the soil sliding impact on bridge pile structure and increase the impact volume. There was a seismic acceleration critical value for the increase of soil sliding impact vol? ume. If it was greater than the critical value，the increase of soil sliding volume was larger. In a certain frequency range，the sliding velocity and impact volume of soil increased with the increase of the peak frequency of seismic re? sponse spectrum，and the impact of sliding soil on bridge pile structure was accelerated. With the increasing propor? tion of the earthquake duration，the displacement of the middle and rear edge of the slope increased obviously，and the impact volume of the sliding soil on the bridge pile structure also increased. The optimization algorithm can make full use of threads and greatly improve the computing efficiency.

Abstract:As the pile foundations in slope areas near rivers are increasingly adopted，the problem of pile-soil horizontal coupling vibration of piles in slope foundations has also received mounting attention. Based on the existing theory of horizontal dynamic response of foundation piles in level ground，this paper proposes an analytical solution for the horizontal vibration response of foundation piles in sloped ground considering the slope effect. Firstly，by means of differential transformation，Helmholtz decomposition and separation of variables method，the threedimensional wave equation of soil is decoupled，and the continuous condition of the pile-soil boundary is introduced to solve the horizontal dynamic resistance of the surrounding soil of the foundation pile in the level ground. On this basis，the horizontal dynamic resistance of the soil around the foundation pile in the sloped ground can then be de? duced by introducing a reduction factor to consider the weakening effect of the sloped ground on the soil resistance on the side of the free surface and ignore the horizontal dynamic resistance provided by the shallow soils within a certain depth；in addition，governing equations for the horizontal vibration of the free section and the submerged section of the foundation pile in the sloped ground is deduced based on Euler beam model；the analytical solutions of the hori? zontal vibration response of the foundation pile can then be obtained by the transfer matrix method，including the dy? namic resistance of the foundation pile and the internal force and deformation of the pile shaft. The proposed solu? tions are verified by comparing with those existing analytical solutions of dynamic cases in the level ground and nu? merical simulations for static cases in the sloped ground in terms of internal force and deformation of the founda? tion pile.

Abstract:The horizontal bearing characteristics and reliability of the bridge foundation piles in the sloping ground are affected by the slope effect and parameter uncertainty. Considering the slope effect，a simplified model of the pile was first established and the finite difference solution of internal force analysis was derived. Based on the sto? chastic response surface method，the limit state function was proposed to analyze the horizontal bearing reliability of piles in sloping ground. The first order second-moment calculation method was used to solve the reliability index and failure probability，and the calculation results were compared with the Monte Carlo method and quadratic function re? sponse surface method to verify the rationality of the solution method and program. Finally，the influences of pile di? ameter，proportional coefficient of foundation resistance，elastic modulus of pile body and horizontal load on the hori? zontal bearing reliability of piles were discussed with the engineering example. The results show that the variability of pile diameter has the greatest influence on the horizontal bearing reliability of piles under the failure mode of horizon? tal displacement. The failure probability of foundation piles increases with the increase of slope effect reduction fac? tor. The slope effect and parameter variability have little influence on the failure probability of piles under the failure mode of materials yield. For bridge high pier pile located in the sloping ground，the deformation safety should be in? creased to ensure the reliability of the pile.

Abstract:Pile in karst areas often impales the caves with different height and often bears the vertical load on pile top or unilateral overload，but worst of all，the working mechanism of the pile impaling cave is not well under? stood. Due to this problem，the lever loading device was designed，the strain of pile when impaling the caves of different height with applied vertical load on the top of the pile was tested，the strain of pile body，the earth pressure and horizontal displacement under unilateral overload were tested when the top of the pile is free，and the transfer law of axial force and the response under unilateral overload of pile impaling the cave of different height were ob? tained. The results show that：1）When the vertical load is applied on the top of the pile bears，before the pile enters the rock layer from the soil layer or the cave，the axial force-depth curve is of obvious interface effect，that is the pile′s axial force at the bottom of the soil layer or the cave grows，and the growth rate increases with the increase of load. The axial force-depth curve of the cave is "concave"，its magnitude of the concave increases with the increase of the load on the top of pile and the height of the cave. 2）When unilateral overload is applied on the pile，all of the horizontal displacement of pile，earth pressure，elastic resistance and bending moment increases with the increase of overload and the height of cave. When the pressure at the top of the pile is zero，the lateral displacement of the pile decreases with the increasing depth，and it is maximal at the top of the pile. Both of the earth pressure and elastic re? sistance increase first and then decrease along the depth in the soil section. The bending moment of the embedded pile and pile impaling cave increase with depth，and it is maximal at the bottom of the soil layer. But it decreases af? ter entering the rock layer and cave. 3）Both of the vertical and horizontal bearing capacity of pile decreases with the increase of the height of the cave impaled by the pile. The pile section inside the cave formed by percussion drilling is not easily damaged by vertical compression and bend. Under the unilateral overload，the pile impaling cave is most likely to rotate around the soil-rock interface and bends at the bottom of the soil layer. In engineering，it is rec? ommended to increase the diameter and reinforcement rate of the upper pile in the soil layer and to embed the ex? panded section to an enough depth so as to improve the horizontal bearing capacity of the pile impaling cave.

Abstract:Due to the perennial freezing and thawing cycles，the soil structure in plateau mountainous area dete? riorates continuously，which adversely affects the pile-soil interface and the stability of structures. In this paper，the indoor laboratory tests and numerical simulation were carried out，a freezing-thawing cycle degradation model of soil structure was established，a coupled mathematical model of water-thermal-mechanics considering soil structure deg? radation was then established，and its reliability was also verified. Based on this，the stability of pile-soil system in plateau mountainous area during service period was numerically analyzed. The experimental results show that the soil permeability coefficient and pore ratio increase logarithmically with the number of freezing-thawing cycles，the soil cohesion decreases exponentially with the number of freezing-thawing cycles，and the internal friction angle in? creases logarithmically with the number of freezing-thawing cycles. During service period，the maximum frost heave displacement around soil gradually decreases with the increase of service life，and the maximum thaw settlement dis? placement also decreases. As a whole，the around soil shows a thaw settlement trend. The frost heave displacement of pile decreases gradually with time，the thaw settlement displacement increases as well，and the growth rate of frost heave and thaw settlement continuously decreases. However，the thaw settlement displacement of pile is larger than its frost heave displacement. Test results can supply some technical support and theoretical guidance for the design of pile foundation in plateau mountainous areas.

Abstract:The mechanical and deformation of the transmission tower foundation are related to the safety and cost of the transmission project. Large-angle corner towers often need to be constructed in the stratum of thick soil overlying bedrock in mountainous areas，therefore，the required uplift and horizontal loads are large. The proposed new cable anchored platform foundation shows good applicability for the above-mentioned conditions. In order to study the bearing capacity of this foundation，the mechanical and deformation characteristics of the foundation under combined uplift and horizontal loads were investigated via theoretical analysis，numerical simulation and in-situ ex? periments. The results show that the uplift and horizontal resistance can be guaranteed by the inclined arrangement of the cable and the applied pre-stress in cables. The deformation of the foundation can be effectively controlled when the pre-stress value of the cable is set to 90% of the design uplift load. The numerical simulation and in-situ experi? ment results show that the foundation deformation and cable axial force meet the design requirements when the ap? plied load is equal to the design load，indicating the feasibility and applicability of the foundation scheme. The de? structive experiment shows that the failure mode of the foundation is the concrete cracking caused by insufficient punching shear strength of the platform concrete. This research provides a reference for the design and calculation of the cable anchored platform foundation and its further application in the transmission tower.

Abstract:In this paper，a method for calculating the side friction of gravel pile interface in gravel stratum un? der the influence of particle shape is proposed. The side friction of a single pile is calculated by using the interface shear function which can describe stress-strain hardening and softening. In order to consider the influence of gravel particle shape on interfacial shear stress-strain behavior，eight kinds of gravel are prepared in this paper. The shape parameters（slenderness ratio，convexity and sphericity）of gravel are obtained by the image processing method. Con? sidering the weight of three shape parameters，an improved calculation method of overall particle regularity is pro? posed. The discrete element model of irregular gravel pile interface shear is established to explore the relationship be? tween the overall regularity of particles and the critical friction angle of interface and the critical state of interface shear. The results show that there is a strong linear relationship between the overall regularity of particles and the critical friction angle，and the overall regularity only changes the intercept of the critical state line. The influence of particle shape is considered in the pile side friction function，and the pile side friction of pile foundation at different depths under vertical load in gravel stratum is solved. The indoor test results are compared with the results obtained by the pile side friction calculation method considering particle shape proposed in this paper，which verifies the ap? plicability and accuracy of the method proposed in this paper.

Abstract:This paper put forward the corresponding calculation method of bearing capacity to investigate the failure mode of the foundation near slope crest. Firstly，a model of bilateral failure mode for foundation near slope crest was established by considering the asymmetry of geometric size and shape of each slide block. Next，a simpli? fied analysis method for the bearing capacity of the foundation adjacent to the slope was proposed based on the upper limit theorem of limit analysis and virtual power equation，and introducing the soil strength mobilization coefficient to characterize the strength mobilization of soil far from the slope. Then，the rationality of the theoretical analysis model and calculation method was verified by the numerical calculation results of an engineering example，and the reasonable value of the soil strength mobilization coefficient was determined by comparing the results under different working conditions. The aforementioned analysis method can consider the bilateral failure mode for the foundation near slope crest and the influence of the distance between the foundation and slope crest on the bearing capacity of the foundation. Meanwhile，it can also be degenerated to that for analyzing the bearing capacity of the ground founda? tion，which can provide a certain reference for the design and calculation of road engineering in mountainous areas，and has certain theoretical and engineering application value.

Abstract:To investigate the cyclic lateral response characteristics of bridge pile foundations in sloping ground， model experiments of piles in sloping ground under different cycle numbers，load amplitudes and slope angles were carried out. The accuracy of measurement results was validated by the comparisons between the measured subgrade reaction profiles and those derived by measured bending moment profiles，and then the evolutions of pile head de? flection，rotation at the pile head，bending moment and subgrade reaction profiles were revealed. The measurement results show that the pile head deflection is composed of elastic deformation and plastic deformation，in which the elastic deformation almost remains unchanged and the plastic deformation nonlinearly increases with cycle numbers at a decreasing rate，that is the plastic shakedown. The dimensionless pile head deflection and rotation atop the pile nonlinearly increase with cycle numbers，and the upper envelopes of the former can be fitted by power functions y0/D =An0.11. The one-way cyclic lateral responses of piles in sloping ground are mainly affected by the first 100 cyclic lateral loadings. The maximum bending moment and subgrade reaction increase with the load amplitude and slope angle，and their locations fall with the increase of slope angle but are rarely affected by the load amplitude.

Abstract:Based on the centrifuge shaking table test on high-cap vertical pile group and high-cap inclined pile group in dry and saturated sandy soil site，the dynamic characteristic parameters of the dry and saturated sand foun? dation soil as well as the high-cap straight and inclined pile group foundation are all analyzed，and the effects of ground motion intensity on the dynamic response of foundation soil and high-cap pile group in the dry and saturated sand fields are studied. The result shows：1）The saturated sand foundation contains more long-period components； the damping ratio of the saturated sand foundation with the same relative density is twice that of the dry sand founda? tion；The periodic characteristics of the soil-pile group model are mainly affected by the foundation characteristics， and the damping ratio characteristics of the soil-pile group model are more affected by the pile type and site characteristics；2）The straight group piles have one dominant frequency，and the inclined group piles have two dominant frequencies；3）With the increase of the input ground motion intensity，the characteristic period of the foundation soil increases，the non-linearity of the dry sand foundation increases，the saturated sand pore pressure ratio in? creases，and the acceleration response of the foundation and pile group foundation cap decreases；4）The intensity of the input ground motion increases，and the bending moment of the pile body increases. The unfavorable positions of the bending moment of pile are at the pile top connecting with cap，at the foundation buried depth of 1 times pile diameter，and at the half buried depth of the pile foundation.

Abstract:Aiming at the ultimate bearing capacity of pile end rock in the single row pile foundation of underly? ing cavity bridge，based on the punching shear failure theory of pile end rock of single row pile foundation for under? lying cavity bridge，the failure mode of pile end rock of single row pile foundation of underlying cavity bridge is as? sumed. The calculation method of the side area of the overlap part of the punching shear under each pile is obtained by using the spatial surface integral. Further considering the relationship between the overlap area and the reduction of the bearing capacity of the pile end rock，a calculation method of the ultimate bearing capacity of the pile end rock of the single row double pile and the single row three pile foundation of the underlying cavity bridge is proposed. The rationality of the method is verified by experiments. And the influence of pile spacing L on the ultimate bearing capacity of rock strata at the pile tip of single-row double-pile and single-row three-pile foundation of the underlying cav? ity bridge is analyzed by the theoretical method and numerical simulation. The results show that：（1）when the pile spacing L is small，the local overlap of punching shear occurs；（2）when the pile spacing L is twice the pile diam? eter，the total bearing capacity of single row double piles and three piles of the bridge is 75 % and 67 % of the total bearing capacity without considering the superposition effect，respectively. With the gradual increase of pile spacing L，the total bearing capacity of the pile end rock of double piles and three piles increases gradually. When the pile spacing L reaches five times the pile diameter，the bearing capacity reaches more than 99 % of the total bearing ca? pacity without considering the superposition effect.

Abstract:To investigate the vertical vibration characteristic of a large-diameter floating pile，a threedimensional fictitious soil pile model（TFSP）is presented by introducing a three-dimensional visco-elastic con? tinuum theory and considering the three-dimensional wave propagation effect of the pile and pile end soil. First，the fundamental solutions of pile shaft and fictitious soil pile are derived by using Laplace transform and variables sepa? ration methods. Then，combining the compatibility conditions at the interfaces of pile-soil and pile-TFSP，the ana? lytical solution of dynamic impedance at the head of a large-diameter pile is obtained. The rationality and accuracy of the proposed model and corresponding analytical solutions are verified by comparing them with existing research.Finally，the numerical examples are performed to investigate the effect of the radial location of the pile cross-section and parameters of TFSP on the dynamic impedance of a large-diameter floating pile. The results indicate that the dy? namic stiffness and damping of the pile head decrease from the pile center to the pile edge，and the smaller the length diameter ratio of the pile，the more obvious the radial heterogeneity of the dynamic impedance of the pile. For large-diameter piles，ignoring the radial wave effect of the pile shaft can overestimate the amplitude and frequency of the dynamic impedance at the pile head，which is not conducive to the anti-vibration design of the pile shaft. The proposed three-dimensional fictitious soil pile model not only has better applicability for the vertical vibration of the large-diameter floating pile but also can be used to analyze the dynamic characteristics of the end-bearing pile by ad? justing the parameters of the fictitious soil pile.

Abstract:Due to the long free section and the lack of soil resistance on the free surface of the foundation pile lo? cated on the steep slope，the deformation has an obvious P-Δ amplification effect. In this paper，introducing the en? ergy variational principle，considering the complexity of the pile bearing and pile-soil interaction in the steep slope section，and assuming that the soil displacement is a nonlinear attenuation mode along the radial direction of the foundation pile，the total energy control differential equation of the three-dimensional foundation pile-soil system in the steep slope section is established. On this basis，combined with different boundary conditions and the coordina? tion conditions of pile-soil displacement，the semi-analytical energy method solution for the deformation of the foun? dation piles on steep slopes under complex bearing conditions is obtained based on the finite difference method，and the solution can fully consider the P-Δ effect of the pile deformation in the steep slope section under various loads. Then，the indoor model loading verification test of the single pile under the axial and lateral load on the steep slope section was carried out，and the theoretical calculation value was compared with the measured value. The compari? son results show that the theoretical solution in this paper is in good agreement with the test results. Finally，a quanti? tative analysis of the influencing factors of the P-Δ amplification effect of foundation piles on steep slopes is carried out. The results show that the P-Δ amplification effect of bridge foundation piles on steep slopes increases signifi? cantly with the axial and lateral load ratio and the free length of the pile top but decreases with the increase of soil stiffness. At the same time，the slope gradient has a significant increase influence on the P-Δ effect.

Abstract:A typical four-span reinforced concrete continuous bridge is employed as examples in this paper， and a plane strain Finite Element（FE）analysis model is developed for three liquefaction pile-ground-bridge sys? tems. Considering the dynamic coupling effect between the pore water and soil particle in the saturated soil，the ef? fect of stone column as a liquefaction countermeasure on excess pore pressure buildup and overall bridge-ground sys? tem seismic response are systematically investigated. In addition，the influences of stone columns on the bridge’s seismic fragility and earthquake hazard curves are explored through constructon of the liquefaction ground–bridge structures. Based on the probability theory，the effect of reinforcement measure using the stone column on the seis? mic risk of the pile-ground-bridge system is established，and the results with/without stone column scenarios are compared. The results show that the stone column has a significant effect on the sand liquefaction. The use of stone columns can significantly reduce the excess pore pressure of soil，thus lowering the bridge-ground system’s overall deformation，seismic vulnerability，and earthquake risk.

Abstract:To solve the design problem of single pile crossing karst caves in practice，the bearing capacity of a single pile crossing unfilled karst cave was analyzed in this paper. Based on the field geophysical and laboratory test results，the distribution of the karst cave and the physical and mechanical parameters of rock and soil were deter? mined. Fourteen groups of numerical calculation models were established by using finite element software to capture the bearing characteristics of a single pile crossing an unfilled karst cave under different conditions of cave radius， cave position and pile diameter. The applicability of the BoxLucas1 load transfer model was verified by using numeri? cal results. A calculation method was then proposed to predict the response of a single pile crossing unfilled karst caves. The present study showed that the influence of karst caves on the bearing capacity of a single pile was weak? ened by increasing pile diameter and filling karst caves，and the radius and position of karst caves had a significant influence on the single pile bearing capacity. For practical purposes，the accurate exploration of karst cave distribu? tion should be paid attention to，which was beneficial to reducing the influence of karst caves on single pile bearing capacity. The proposed calculation method can provide a theoretical basis for parameter design and estimation of the bearing capacity of a single pile in the karst area.

Abstract:Based on the stress-bubble fictitious soil-pile model and the improved hyperbolic model considering the initial critical frictional resistance of the pile-soil interface，a simplified method for calculating the settlement of vertically loaded single pile is proposed，which can consider the effect of stress diffusion at the pile tip and the initial critical frictional resistance at the pile-soil interface. Firstly，the influence degree of the model parameters on the settlement of a single pile is analyzed and discussed by using the present calculation method，and the reasonable value ranges of model parameters are given. Then，the rationality of the present calculation method is verified by comparing the results obtained using the present calculation method with the field measured data. Furthermore，the proportion of pile compression and pile tip soil settlement，the distribution law of pile axial force and the characteris? tics of pile lateral friction resistance under different pile top loads are further analyzed and studied. The present calculation method has clear parameters and simple application，which can provide a more accurate settlement value for pile foundation design，thus having a wide engineering application prospect.

Abstract:In order to get the penetration effect of plum-blossom piles，a series of model tests of plum-blossom piles penetrating transparent soil was carried out. Combined with transparent soil and particle image velocimetry， based on the static pressure pile method，the displacement characteristics of soil around the plum-blossom pile in the process of jacked-pile penetration in different stages were studied. According to the cylindrical cavity expansion theory and the geometric characteristics of plum-shaped piles，a simple modified cavity expansion theory is pro? posed to compute the radial displacement induced by the pile penetration and the influence range of penetration effect of plum-shaped piles. At the same time，an analysis model of the penetration effect and cavity expansion of plum-shaped piles is proposed by using a numerical calculation method. By comparing the test results of the trans? parent soil test and the analysis results of the modified cavity expansion theory，the modified cavity expansion model is validated，and the penetrating process of plum-shaped piles and round piles with equal cross sections is com? pared. The results show that the soil compaction transition zone of a plum-blossom pile is about 1.5 times that of a circular pile with equal cross section，and the penetration effects of a plum-blossom pile are similar to those of tradi? tional equal section circular pile in cavity expansion area. The pile driving tip resistance，pile shaft and total resis? tance of tapered pile equal 1.0 times，1.38 times and 1.12 times of those of equal section circular pile respectively.

Abstract:A vertical loading test is carried out on one intact pile and eight necking piles through transparent soil technology，and the vertical capacity of the necking pile is studied. The speckle field of soil around the pile is processed using MatPIV software to obtain the soil displacement law. On this basis，the reasons for the change of ver? tical bearing capacity of piles are analyzed compared with the intact pile. The results show that the necking has a sig? nificant contribution to pile capacity. When the necking length is 10% of the pile length，the bearing capacity loss can be as high as 45%；When the necking diameter is 20%，the bearing capacity loss is 27.3%. The reason is that when the necking dimension is large，the soil around the necking develops inclined and downward displacement， causing the relative displacement of the pile shaft and the soil to reduce，and reducing the side shaft friction of the pile. Consequently，the necking makes the pile capacity reduce. For some necking piles，the pile capacity is insensitive to the necking because of the combined action of the resistance generated by the necking，the resistance at the pile end，and the shaft friction. However，its large settlement leads to the result that it is unsuitable for bearing. When the necking locates in the shallow or middle parts of pile shaft，the pile capacity is seriously lost. When the necking locates in the deep parts of the pile shaft，the soil at the necking position and at the end of the pile runs through each other，and its shear failure occurs. The research achievement can provide theoretical and technical ref? erences for the design and reinforcement of pile foundations.

Abstract:Based on the vertical load test on an indoor sand half-surface model pile，the VIC-3D non-contact full-field strain measurement system was used to record the dynamic development of the soil displacement field around the expanded body in real time. By using digital image correlation techniques，the entire process of the soil displacement field distribution characteristics and development under the load was observed. The failure state of soil around the expansion body was investigated. The influence of different expanded diameters on the bearing capacity， the distribution of displacement，the compression zone and the subsidence zone was explored. The main compression area and main subsidence area were quantitatively analyzed. The results show that with the increasing diameter of the expanded body，the bearing capacity of the drilled-expanded concrete pile gradually increases，and the loaddisplacement curve of single pile changes from steep drop type to slow change type. The vertical and horizontal dis? placements of soil around the expanded body increase with the increase of pile top displacement，but the increased amplitude is affected by the buried depth，the distance from the expanding body and the distance from the boundary of the compression zone. The horizontal displacement of soil at different buried depths shows a "C" shape. The influ? ence range of soil displacement around piles increases with the increasing diameter of the expanding body，and the subsidence zone and compression zone are formed above and below the expanding body，respectively. The area of the regions is positively correlated with the diameter of the expanding body and the displacement of the pile top. Through nonlinear surface fitting，the functional relationship between the area of main compression area，main subsidence area，the diameter of expansion body，and displacement of pile top is obtained，which can provide some reference for the prediction of the area of main compression area and main subsidence area.