Accumulative Deformation Research Articles

Investigation on Strain Characteristics and Fatigue Constitutive Model of Limestone under Osmotic Pressure and Cyclic Disturbance Coupling

The existing fatigue models are not sensitive to load cycles and do not consider the effect of osmotic pressure. To study the strain characteristics and fatigue constitutive model of limestone under osmotic pressure and cyclic disturbance coupling, 300 cycles of loading and unloading tests under different osmotic pressures were carried out and the evolution characteristics of irreversible accumulative deformation curve were analyzed. Then, an improved Nishihara fatigue model was established based on the theoretical results of rheological model by introducing the nonlinear function into Nishihara model. The results show that the irreversible cumulative deformation under different osmotic pressures experiences three evolutionary processes of initial deformation stage, stable deformation stage, and accelerated deformation stage with increasing cycle indexes, showing the typical fatigue deformation characteristics. The axial deformation at initial deformation stage increases significantly, the stable deformation stage shows approximately linear growth and accounts for 40% to 73% of total cycle indexes, and the accelerated deformation stage shows a sudden increase indicating the overall instability of limestone. The nonlinear function is introduced into the Nishihara fatigue model based on rheological theory, and a fatigue deformation model that can reflect the entire process of irreversible accumulative deformation curve is established. The physical meanings of model parameters are discussed, and the relationships between model parameters and cycle indexes are inverted. The model parameters have good convergence and verify the rationality and applicability of the fatigue constitutive model based on experimental data. The results have reference value for revealing the fatigue characteristics of rock under osmotic-cyclic stress coupling.

A Modified Triaxial Apparatus for Soils under High-Frequency, Low-Amplitude Vibrations

Abstract A modified triaxial apparatus was developed to explore the behavior of cohesionless soil subjected to high-frequency, low-amplitude vibrations, such as those induced by high-speed trains. It was based on a conventional Bishop-type triaxial apparatus to utilize its existing static loading module. The major modification was an added dynamic loading module with a low-inertia linear voice coil actuator mounted coaxially with the vertical loading rod. Through a signal generator and an amplifier connected to the voice coil actuator, a vibration input with wide range of frequencies and amplitudes could be superimposed to a monotonic loading process. A series of tests under different conditions were performed to demonstrate the effectiveness and performance of the modified triaxial apparatus, with the focus being placed on the reduction of shear resistance and accumulative deformation of sand induced by high-frequency, low-amplitude vibrations.

The effect of overconsolidation on monotonic and cyclic behaviours of frozen subgrade soil

This paper presents an experimental investigation on the monotonic and cyclic behaviours of the overconsolidated subgrade soil used in the Lanzhou-Urumchi high-speed railway at the temperature of -3°C. The important mechanical parameters of the overconsolidated soil, i.e., failure strength, initial elastic modulus, accumulative permanent strain and resilientmodulus were experimentally studied by using triaxial tests. Testing results indicate that the failure strength, initial elastic modulus, dilatancy and stress–strain relationship of frozen sample are all dependent to the overconsolidation ratio (OCR). The failure strength is slightly more susceptible to the overconsolidation ratio than the initial elastic modulus. The anisotropically consolidated path (k0=0.5-1) has a negligibleimpact on the stress–strain-strength behaviors. The development characteristics of accumulative permanent strain and resilient modulus are collectively dominated by the overconsolidation ratio and shear stress amplitude. Axial permanent strain acceleratedly accumulates with the decrease of the overconsolidation ratio at the same shear stress amplitude. According to the shakedown theory, allowable cyclic stress ratio was introduced to analyze accumulative deformation characteristics of frozen sample. The overconsolidation ratio and loading cycle number have negligible influences on the allowable cyclic stress ratio of frozen subgrade soil. Four cyclic stress-paths with the same shear stress amplitude were adopted in triaxial cyclic tests with aim to investigate the path-dependent deformation behaviors of frozen subgrade soil. The relationships of axial permanent strain under different cyclic stress-paths are roughly proportional, regardless of the cyclic stress ratio (CRS) and loading cycle number. Those quantitativerelationships can be completely determined by the overconsolidation ratio and cyclic stress-path parameter. The effect of cyclic stress-path on resilient modulus is more than the effect of overconsolidation ratio and less than the effect of shear stress amplitude. Several empiricalmodelswere proposed for the overconsolidated subgrade soil at the negative temperature to characterize the evolution laws of the above-mentioned engineering properties. Those empiricalmodels are capable of giving well descriptions of the development of those engineering parameters for frozen subgrade soil over a wide range of the oveconsolidation ratio.

Cyclic settlement of ballast layer due to train passages at high speed and its reduction by asphalt trackbed

Ballasted track has been widely adopted in railway lines, even in high-speed railways. As the train speed increases, ballast layer has to undertake excessive settlement or severe degradation. To preserve rail network safety and ride quality more optimally, it is vital to get further insight into the cyclic accumulative deformation of ballast layer. This study concentrates on investigating cyclic settlement of railway ballast with an emphasis on the inside particle-scale interactions in conventional ballasted trackbed, and further in asphalt trackbed, a promising structural form of the granular track. The entire transversal cross-section of granular trackbed is modeled based on discrete element method with realistic polygon elements. The numerical model is validated with the measurements from full-scale model tests and then used to study the deformation behavior of railway ballast. Subsequently, the trackbed model with insertion of asphalt layer is established to investigate the reduction of permanent deformation in asphalt trackbed. The granular trackbeds under different train loading are analyzed in the end. Results indicate that the inter-particle structure in the ballast is stabilizing with an increasing number of loading cycles, contributing to less particle migration, so the growth rate of permanent deformation appears a slowing trend. Besides, the asphalt layer optimizes the distribution of contact chains in the ballast and reduces the intensities of contact forces, leading to a remarkable decrease in permanent deformation. Moreover, the higher train speed results in more active ballast particles so that the trackbed becomes hard to stabilize especially when the shakedown threshold is reached. The adverse impact derived from the train speed can be weakened effectively by the asphalt layer. This paper discusses the cyclic settlement of railway ballast and its reduction induced by the asphalt layer. These conclusions will guide the potential methods to alleviate the permanent deformation in high-speed railways, such as employing the asphalt trackbed or controlling the train speed.

Critical Dynamic Stress and Accumulative Deformation Evolution of Embankment Silty Clay Subjected to Cyclic Freeze-Thaw

In cold regions, the permanent settlement of embankment is mainly caused by the repeated freeze-thaw process and long-term repeated train loads. Meanwhile, the critical dynamic stress (σdcr) is an important parameter index for determining embankment stability. Therefore, the accumulative permanent deformation evolution and critical dynamic stress of embankment soil subjected to cyclic freeze-thaw were studied using dynamic triaxial tests. Firstly, a numerical model for calculating critical dynamic stress considering the repeated freeze-thaw process was proposed, which shows that the critical dynamic stress of embankment soil rapidly decreases in the first two repeated freeze-thaw cycles, whereas it tends to be stable after the subsequent freeze-thaw process. Next, based on the normalization of the critical dynamic stress, an explicit model for predicting accumulative plastic strain (εp) of embankment soil was established. The above model considers freeze-thaw times, repeated dynamic stress amplitude (σd), and loading times, in which all material parameters of Qinghai-Tibet silty clay were presented. Thus, the critical dynamic stress and accumulative plastic strain models established in this paper can be applied to judge the embankment stability and predict the embankment settlement induced by train loads in cold regions.

Refinement of Ti18Zr15Nb alloy structure exposed to accumulative high-pressure torsion deformation

The strain γ processing at high-pressure torsion (HPT) deformation for many hard materials is really much smaller than expected. This is a result of slippage of sample surface and surface of anvils. In this context, the authors develop a new method- “accumulative high-pressure torsion” (ACC HPT). This method enables producing much higher true strains in metallic and alloys than the traditional HPT method. HPT and ACC HPT were applied to β-Ti-alloys Ti-18Zr-15Nb. As TEM studies showed, the size of grains after HPT n = 10 revolutions is about 40 nm while the size of grains after ACC HPT with n = 10 revolutions (in total) is about 20 nm.

Evaluation of the structural and waterproof performance of a precast and assembly underpass under long-term surface dynamic loads

With the development of rapid underground construction, precast assembly underpass (PAU) has been used as an alternative way to replace the traditional cast-in-place underpass. However, only limited research was conducted to investigate the behaviour of longitudinal joints on the ultra-shallow buried structure under long-term surface dynamic loads. Although the underpass segments may not be damaged under dynamic loads, the unexpected deformation of longitudinal joints can lead to the safety risk of connecting bolts and waterproofing. This paper aims to evaluate the mechanical behaviour and waterproof performance of PAU under dynamic loads. Firstly, the full-scale numerical model was carried out, and a relative circumferential deformation index of longitudinal joints is proposed on the basis of the yield strength of connecting bolts. Then, a 1/10 scaled physical model test is designed to evaluate the long-term accumulative deformation by simplifying the ground surface vehicle loads into a simple cosine wave. Moreover, based on the results of the scaled model test, a relative radial deformation index is suggested by conducting the waterproof strip shear tests. The relative circumferential and radial deformation values at the longitudinal joints are recommended less than 15 and 30 mm, respectively, which is to satisfy the standards of both structural safety and waterproof. The results were also applied successfully to a tunnelling project.

Mechanical Response of Granite Residual Soil Subjected to Impact Loading

When constructing subway tunnels, blasting is commonly used to deal with granite boulders in weathered granite formations. It is, therefore, crucial to evaluate how the blasting-induced impact loading affects surrounding granite residual soil. By means of laboratory impact tests at different conditions, this paper presents the mechanical responses of granite residual soil. High-speed impact loading affects the soil in two ways, namely, (1) increasing the shear resistance; and (2) damaging the soil structure. Cyclic impact tests reveal the critical peak stress Acr, which approaches soil apparent preconsolidation pressure. When the peak stress exceeds Acr, the soil is severely damaged and the accumulative deformation increases sharply, indicating that the cementation of soil is destroyed. Besides, the soil is most resistant to impact loading at a threshold value of the loading frequency fth and exhibits better resistance under high confining pressures. A framework was proposed that reflects soil structural damage and within which the failure mechanism under impact loading is explained. The damage to the soil structure generated with energy dissipation is the decisive factor in soil failure, and the accumulation of permanent deformation is the direct reason why soil fails. Three response modes were proposed for studied soil under impact loading. This research provides parameters for subway tunnel construction and enhances the understanding of granite residual soil under impact loading.

Influence of HPT and Accumulative High-Pressure Torsion on the Structure and Hv of a Zirconium Alloy

The authors previously used the accumulative high-pressure torsion (ACC HPT) method for the first time on steel 316, β-Ti alloy, and bulk metallic glass vit105. On low-alloyed alloys, in particular, the zirconium alloy Zr-1%Nb, the new method was not used. This alloy has a tendency to α → ω phase transformations at using simple HPT. When using ACC HPT, the α → ω transformation can be influenced to a greater extent. This article studies the sliding effect and accumulation of shear strain in Zr-1%Nb alloy at various stages of high-pressure torsion (HPT). The degree of shear deformation at different stages of HPT was estimated. The influence of various high-pressure torsion conditions on the micro-hardness and phase composition by X-ray diffraction (XRD) of Zr-1%Nb was analyzed. It is shown that at high-pressure torsion revolutions of n = 2, anvils and the specimen significantly slip, which is a result of material strengthening. It was found that despite sliding, regular high-pressure torsion resulted in the high strengthening of Zr-1%Nb alloy (micro-hardness more than doubled), and after high-pressure torsion n = 10, up to 97% of the high-pressure ω-phase was formed in it (as in papers of other researchers). Accumulative high-pressure torsion deformation leads to the strongest transformation of the Zr-1%Nb structure and Hv and, therefore, to a higher real strain of the material due to composition by upsetting and torsion in strain cycles.

Mapping and classifying large deformation from digital imagery: application to analogue models of lithosphere deformation

SUMMARY Particle image velocimetry (PIV), a method based on image cross-correlation, is widely used for obtaining velocity fields from time-series of images of deforming objects. Rather than instantaneous velocities, we are interested in reconstructing cumulative deformation, and use PIV-derived incremental displacements for this purpose. Our focus is on analogue models of tectonic processes, which can accumulate large deformation. Importantly, PIV provides incremental displacements during analogue model evolution in a spatial reference (Eulerian) frame, without the need for explicit markers in a model. We integrate the displacements in a material reference (Lagrangian) frame, such that displacements can be integrated to track the spatial accumulative deformation field as a function of time. To describe cumulative, finite deformation, various strain tensors have been developed, and we discuss what strain measure best describes large shape changes, as standard infinitesimal strain tensors no longer apply for large deformation. PIV or comparable techniques have become a common method to determine strain in analogue models. However, the qualitative interpretation of observed strain has remained problematic for complex settings. Hence, PIV-derived displacements have not been fully exploited before, as methods to qualitatively characterize cumulative, large strain have been lacking. Notably, in tectonic settings, different types of deformation—extension, shortening, strike-slip—can be superimposed. We demonstrate that when shape changes are described in terms of Hencky strains, a logarithmic strain measure, finite deformation can be qualitatively described based on the relative magnitude of the two principal Hencky strains. Thereby, our method introduces a physically meaningful classification of large 2-D strains. We show that our strain type classification method allows for accurate mapping of tectonic structures in analogue models of lithospheric deformation, and complements visual inspection of fault geometries. Our method can easily discern complex strike-slip shear zones, thrust faults and extensional structures and its evolution in time. Our newly developed software to compute deformation is freely available and can be used to post-process incremental displacements from PIV or similar autocorrelation methods.

Accumulative Deformation Characteristics and Microstructure of Saturated Soft Clay under Cross-River Subway Loading.

The cross-river subway in the Hangzhou Bay area often passes through deep, thick, soft soil at the bottom of the river. At the same time, overlying erosion, siltation, and changes in water levels adversely affect the deformation of the subway, thereby causing hidden dangers to its safe operation. Using two-way dynamic triaxial testing, the effects of cyclic loading of the cross-river subway on the soft clay foundation were investigated for the first time, using simulation methodology as the prime objective of the present study. A strain development curve for the soft clay was obtained as a result. Considering the effects of effective confining pressure (p′) and radial cyclic stress ratio (τr), an explicit model of accumulative strain on soft clay under cyclic loading of the cross-river subway was established. The results showed that the accumulative axial strain (εd) was closely related to p′ and τr. Under certain conditions, as p′ and τr increased, the εd produced by the soil tended to decrease. Furthermore, through non-destructive testing based on nuclear magnetic resonance (NMR), pore distribution and pore size changes in soft clay during cyclic loading were analyzed. It was observed that under the action of the cross-river loading, the large internal soft clay pores were transformed into small pores, which manifested as a significant decrease in the number of large pores and an increase in the proportion of small pores. Lastly, the macroscopic dynamic soil characteristics observed during triaxial testing closely correlated with the microscopic pore size of the soil obtained in the NMR test, which indicated that using pore distribution and pore size changes to describe microscopic changes was a valid method.

Mathematical analysis and its experimental comparisons for the accumulative roll bonding (ARB) process with different superimposed layers

Based on the traditional two-layer accumulative roll bonding (TARB), the geometrical variations and mathematical relationship during the four-layer accumulative roll bonding (FARB) were derived and summarized. Furthermore, the multi-layer accumulative roll bonding (MARB) technology was proposed and the geometrical variations and mathematical relationship of MARB were simultaneously derived and summarized. Experimentally, Mg-14Li-3Al-2Gd (LAGd1432) sheets were fabricated by TARB and FARB, respectively. Compared with the TARB, the FARB has a higher accumulative efficiency in terms of accumulative layers, total number of interfaces, interface spacing, total deformation and equivalent strain. Therefore, the FARB-processed sheets in lower cycles have the similar microstructure and mechanical properties of the TARB-processed sheets in higher cycles. In addition, FARB process can further break through the deformation limit of TARB process in a single cycle through adopting two-step rolling in one cycle with 50% deformation in one pass and 75% accumulative deformation in one cycle, which can effectively solve the problem of poor interface bonding of the latest interface brought by the last cycle, and thus significantly improve the phenomenon of unstable performance of the ARB-processed sheets.

An analytical model for predicting compressive behaviour of composite helical Structures: Considering geometric nonlinearity effect

Composite helical structures (CHS) can store and release strain energy through elastic deformation, which has a good application prospect in automobile, aerospace and other fields, such as shock-absorbing spring, deployable antenna, etc. Compressive behaviour (i.e. stiffness, strength and load–displacement relationship) is one of the most important basic mechanical properties of CHS. In order to accurately predict the compressive behaviour of CHS, this paper proposes a new analytical model considering geometric nonlinearity effect. In the geometric model, the geometric parameters of CHS change continuously with the increase of compressive load. The load–displacement relationship considering geometric nonlinearity is deduced by accumulative compressive load increment and accumulative compressive deformation increment. The compressive stiffness of CHS is obtained using linear fitting with least square method. On this basis, the analytical expression of compressive strength of CHS is derived. The predicted results are compared with experimental data from literatures. It is shown that predictions using the new analytical model correlated well with experimental results. Considering geometric nonlinearity effect in the analytical model can predict the compressive behaviour of CHS more accurately. The analytical model is used to further analyze influences of helix angle and helix diameter on the compressive behaviour of CHS.

A novel evaluation method for accumulative plastic deformation of granular materials subjected to cyclic loading: Taking frozen subgrade soil as an example

This paper presents multi-stage cyclic loading tests with three confining pressures and eight dynamic stress amplitudes on frozen subgrade soil at the negative temperature − 2 °C to experimentally study accumulative and resilient deformation properties under different cyclic loadings. The coupled effects of the confining pressure and dynamic stress amplitude on accumulative and resilient deformation properties of frozen sample are analyzed in detail. Accumulative and resilient deformation behaviors of frozen samples at each stage of multi-stage cyclic loading tests exhibit similar patterns as that observed in the single-stage cyclic loading tests. Two-stage evolution feature for resilient modulus of frozen subgrade soil is experimentally determinated. Critical cyclic number is defined as the turning point of two-stage feature for resilient modulus to further distinguish the post-compaction compression stage and secondary cyclic compression stage of frozen subgrade soil. The influence of confining pressure on critical cyclic number is negligible. With the increase of dynamic stress amplitude, critical cyclic number approximately increases. Dynamic stress amplitude, rather than confining pressure, is main influencing factor for critical cyclic number in this investigation range of confining pressure. A new evaluation criterion for three typical deformation areas of granular materials subjected to cyclic loading is proposed based on the shakedown theory. The devlopment features of accumulative permanant strain at the multi-stage cyclic loading tests are studied and judged by two published shakedown criteria and presented new criterion. Two published shakedown criteria's applicability and limitation for frozen subgrade soils are further investigated and discussed. The assessment capacity of this new criterion is validated by all testing results for frozen subgrade soils. The evaluation results based on this new criterion are in approximate agreement to those according to Chen's shakedown criterion (Chen et al., 2019).

Centrifuge modelling of a tetrapod jacket foundation under lateral cyclic and monotonic loading in soft soil

The tetrapod jacket foundation is one of the most common types of foundations used for offshore structures. Although the static bearing capacity of the jacket foundation is important, a safe design must be taken into consideration for accumulative deformation and stiffness degradation during cycling. To address this, a set of centrifuge model tests of a tetrapod jacket foundation subjected to cyclic and monotonic loading was conducted in kaolin. The test results mainly reveal (i) the influence of loading history on the lateral bearing capacity of the jacket foundation; (ii) the evolution of accumulative deformation of the jacket foundation during cycling; (iii) the stiffness degradation of soil–pile interaction under cyclic loading. Comparing typical “lateral soil resistance”–“pile lateral displacement” (p–y) curve approaches with test results, a hyperbolic tangent p–y curve method is adopted to calculate the soil–pile interaction of the jacket foundation. The values of the p-multipliers of leading-row and trailing-row piles in soft soils are clearly lower than that in sands. Finally, a cyclic p–y curve method related to cycles and embedded depths is developed for the jacket foundation in the hope of providing guidance for the design of the jacket foundation in soft soil.

Enhanced asphalt mixture behavior by using khawa clay to resist deformation

This paper aims to investigate the effect of adding bentonite (khawa clay) on the asphalt mixture response represented by reducing total accumulative deformation. Asphalt cement with penetration grade of (40-50) and optimum asphalt content of 4.9 was used. Bentonite with different percentages of (0%, 3%, 6%, and 9% by total weight of asphalt cement) was used. The asphalt mixtures were tested by uniaxial creep test under static load at two test temperature (40°C and,60°C) and the applied stress used 600 KPa. From the experimental result of rotational viscosity after and before the addition of bentonite at two temperatures 135°C and 165°C, it can be seen that the viscosity of the asphalt cement was enhanced when adding 9% of Khawa clay to around 126% percent of improvement in viscosity at 135°C and about 195% at 165°C. The improvement in the viscosity of asphalt leads to a decrease in the accumulative strain.

EXPERIMENTAL STUDY OF OBSERVABLE DEFORMATION PROCESS IN FAULT META-INSTABILITY STATE BEFORE EARTHQUAKE GENERATION

According to the steady state of fault and energy balance, we provided a new idea to observe the precursors for a stressed fault. The meta-instability (or sub-instability) state of a fault is defined as the transition phase from peak stress to critical stress of fast instability (earthquake generation) during a full period of slow loading and fast unloading. The accumulative deformation energy begins to release in this stage. Identifying its deformation before fast instability would be beneficial to obtain premonitory information, and to evaluate the seismic risks of tectonic regions. In this study, we emphasized to analyze deformation process of the meta-instable stage with stain tensor data from a straight precut fault in granite at a slow loading rate, and observed the tempo-spatial features during the full deformation process of the fault. Two types of tectonic zones and instabilities occur on the stick-slip fault. The low- and high-value segments in the volume strain component appear along the fault strike with a load increment. The former first weakens and then becomes initial energy release segments; the latter forms strong stress-interlocking areas and finally turns into the initial region of fast instability. And there are two stages in the entire instable process of the fault: the initial stage is associated with the release of the low volume strain segments, which means fault pre-slips, slow earthquakes or weak earthquakes. The second one characterizes a strong earthquake through the release of high volume strain parts. The rupture acceleration in the first stage promotes the generation of the second. Moreover, fault instability contains two types of strain adjustments along the fault: the front-like strain change along the transition segments from low- to high- strain portions with volume strain release, and the compressive strain pulse of fault instability after the volume strain release extends to a certain range with loading increment. In laboratory experiments, the front-type strain occurs about 12 seconds before fast fault instability; the compressive pulse initiates within less than 0.1 second, and then the fault turns quickly into a dynamic strain adjustment, which appears quasi-synchronously between different measurement points, and, finally, an earthquake is generated.

Degradation-induced evolution of particle roundness and its effect on the shear behaviour of railway ballast

Abstract Ballast degradation has a strong effect on railway track performance (including accumulative deformation, ballast resistance, and drainage). The main objective of this research is to determine the evolution of roundness during ballast degradation and investigate the mechanical properties of real ballast shape at different abrasion stages. To this end, the Los Angeles (LA) abrasion test is conducted on three groups of fresh ballast materials with different sizes (i.e., 25–30 mm, 40–50 mm, and 50–60 mm). Then, a homemade image-acquisition platform is used to extract ballast outlines from multiple projection directions. Next, the corner sharpness of the degraded ballast is quantified by particle roundness. The LA abrasion test shows that particle roundness gradually increases with increasing abrasion. Subsequently, biaxial shear tests are performed on ballasts with different roundness characteristics based on the discrete element method (DEM). The shear behaviours of degraded ballasts with different degrees of roundness are investigated through macroscopic (e.g., the shear strength and dilatancy response) to microscopic (e.g., the mean coordination number, the ratio of sliding contacts, and the mean particle contact moment) analyses. The results show that the shear strength slightly increases in the peak state, while a substantial reduction in shear strength is observed in the residual state with increasing roundness. Moreover, the microscopic analysis shows that greater roundness results in a smaller mean coordination number, as well as decreases in the ratio of sliding contacts and the mean particle contact moment.

Radial Joints Behavior of a Precast Asymmetric Underpass Induced by Long-Term Loads of Ground Vehicles

With the rapid development of the urbanization, many underpasses are designed and constructed in big cities to alleviate the huge traffic pressure. The construction method has been changed from traditional on-site concrete pouring technology to prefabricated assembly technology. However, this change will inevitably bring out some new problems to be studied such as the behaviour of the radial joints. In this study, the numerical simulation model of Moziqiao precast and assemble underpass with large asymmetric cross section was constructed by using the ABAQUS software to study the transient response of the underpass induced by ground surface dynamic load. Based on the similarity theory a 1/10 scaled model test was carried out to study the long-term radial joint behaviour of the underpass considering the prestress loss during the 2000 000 loading cycles. The results transient dynamic response from computed and tested was compared in terms of acceleration. The comparison showed that the transient response accelerations have good consistency. The results of the physical model test were analysed in terms of joint opening, closure, and slipping. The accumulative joint opening was closely correlated to the prestress level, and the joint opening at different prestress levels increased with the loss of the prestress. The joints closure decreased with the increase of the previous accumulative color value. The joint slipping mainly attributed to the slipping of the top segment. Both the opening and slipping of the joints at RJ 1 were larger than that of RJ3 due to the wider span of RJ1, which reflected an asymmetric effect. This study revealed the long-term accumulative behaviour of the radial joints, which convinced us that the long-term accumulative deformation of the joints should be taken into consideration during the design stage for similar projects.

Experiment on Interaction of Abutment, Steel H-Pile and Soil in Integral Abutment Jointless Bridges (IAJBs) under Low-Cycle Pseudo-Static Displacement Loads

Soil-abutment or soil-pile interactions under cyclic static loads have been widely studied in integral abutment jointless bridges (IAJBs). However, the IAJB has the combinational interaction of soil-abutment and soil-pile, and the soil-abutment-pile interaction is lack of comprehensively study. Therefore, a reciprocating low-cycle pseudo-static test was carried out under an cyclic horizontal displacement load (DL) to gain insight into the mechanical behavior of the soil-abutment-pile system. Test results indicate that the earth pressure of backfill behind abutment has the ratcheting effect, which induced a large earth pressure. The soil-abutment-pile system has a favorable energy dissipation capacity and seismic behavior with relatively large equivalent viscous damping. The accumulative horizontal deformation in pile will be occurred by the effect of abutment and unbalance soil pressure of backfill. The test shows that the maximum horizontal deformation of pile occurs in the pile depth of 1.0b~3.0b of pile body rather than at the pile head due to the accumulative deformation of pile, which is significantly different from those of previous test results of soil-pile interaction. The time-history curve for abutment is relatively symmetrical and its accumulative deformation is small. However, the time-history curve of pile is asymmetrical and its accumulative deformation is dramatically large. The traditional theory of deformation applies only to the calculation of noncumulative deformation of pile, and the influence of accumulative deformation should be considered in practical engineering. A significant difference of inclinations in the positive and negative directions increases when the displacement load is relatively large. The rotation of abutment when bridge expands is larger than that when bridge contracts due to earth pressure of backfill.