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In previous studies, the dynamic characteristics of a base-isolated structure on non-liquefied soil foundation have been investigated by some model tests. However, soil liquefaction can change the seismic responses of the base-isolated structure. In particular, due to the soil-structure interaction, the seismic-isolation layer of the structure is also bound to change the seismic responses of the pile foundation under the isolation layer, and then this also affect inversely the isolation performance of the isolated layer. However, this scientific problem has not been effectively studied. To investigate the seismic responses of a complex soil-pile-isolated structure interaction (SPISI) system after the soil foundation liquefied, a new shaking-table model test was designed. The test results were analyzed and compared with a series of previous model tests on isolated structures with different non-liquefied soil foundations. As results, after the soil foundation liquefied, severe swing responses of the isolated structure and pile cap were observed. Then, the seismic responses of the pile were also changed evidently by the SPISI and severely aggravated by the strong swing responses of the isolated structure. Meanwhile, the foundation liquefaction also significantly weakened the isolation performance of the lead-rubber bearing and even amplified the horizontal acceleration response of the isolated structure. Because of the above SPISI effects, the dynamic characteristics and response laws of the isolated structure on a liquefied soil foundation are not consistent with those of base-isolated structures on non-liquefied soil foundations. On the contrary, they are similar to those of a non-isolated structure on the general soil foundation. [ABSTRACT FROM AUTHOR]

Three-dimensional numerical simulation for clarifying the seismic response characteristics of an underground structure considering the influences of dynamic interaction with the surrounding liquefied soil is still a huge challenge. Using the proposed generic loosely coupled nonlinear effective stress method for site response of liquefiable soil, the authors developed an effective stress seismic response analysis of the underground subway station structure. Based on the effective stress method, the responses of the model underground subway station with three floors and three spans in model liquefiable foundation in the shaking table test are simulated. The comparison between the measured and simulated results proves that the developed method can effectively capture the response characteristics of the liquefiable foundation，by which the generation of residual excess pore water pressure and the effect of cyclic stiffness softening and degradation can be taken into good consideration, and the measured responses of model underground structure can be well reproduced. The results also demonstrate the availability of the shaking table test simulating the dynamic interaction between the underground structure and the surrounding liquefied soil. [ABSTRACT FROM AUTHOR]

This paper systematically investigates the dynamic behavior of sandy soils mixed with recycled tire rubber over a wide strain range in the order of 10 − 5 –10 − 2 , using combined resonant column and cyclic triaxial tests for measurement of the shear modulus and damping ratio. The experiment integrates small-strain tests using a resonant column apparatus and large-strain tests using a cyclic triaxial apparatus. The results demonstrated that the addition of rubber particles significantly enhances the linear elastic properties of the host sandy soils and improves the critical shear strain from which the rubber–sand mixtures change from linear to nonlinear stress–strain behavior. The critical shear strain is therefore introduced as the function of rubber content (RC), to identify the influence of RC on the strain-dependent dynamic properties of the host sandy soils. Then, a well-calibrated prediction formula is applied in conjunction with the concept of binary packing material to describe the behavior of the host sandy soils with various RC. Remarkably, the obtained normalized shear modulus and damping ratio vs. shear strain relationships address the limitations of existing testing methods to simultaneously capture the soil dynamic properties at low-strain (stiffness) and the large-strain (energy dissipation) regimes. The model constants can be simply determined through a unique set of explicit expressions which incorporate some basic index properties of the host sand and recycled tire rubber. In this regard, the proposed procedure provides a significant advantage in the evaluation of strain-dependent dynamic properties of rubber–sand mixtures in practice. [ABSTRACT FROM AUTHOR]

With the soil constitutive model developed for the dynamic large deformation of soft soil, a finite element model was constructed to simulate the soil–underground structure static and dynamic coupling interaction system, in which the dynamic contact between soil and underground structure and the dynamic damage of reinforced concrete were considered. The seismic performance and damage mechanism of the large underground subway station in different soil foundations were investigated and evaluated in detail. It was proven that the interaction mechanism between the soil and underground structure would change with the type of soil foundation and the peak acceleration of input ground motion, which can be evaluated by the interaction coefficient between the soils and underground structure. At the same time, some regulations on the seismic performance of underground structure in China code are already unsuitable for evaluating the seismic performance of a large underground subway station in the soft soil foundation or subjected to a strong earthquake, which should be investigate by the specialized time–history analysis method instead. In this study, five seismic performance levels were firstly defined by the inter-storey drift angle of underground structure and corresponding earthquake damage states. [ABSTRACT FROM AUTHOR]

In view of the seismic weak component of the single-frame-type subway station structure, the three-dimensional (3D) time-domain nonlinear finite element static-dynamic coupling analysis model of interaction between soil and subway station structure is established by, respectively, using rectangular reinforced concrete (RRC) columns, circular reinforced concrete (CRC) columns, and prefabricated concrete-filled steel tube (CFST) columns with a quick-connection device proposed in this article. This analysis model is further used to investigate the influence of different types of middle columns on the seismic response characteristics of the underground structure, such as the interstory displacement angle, seismic damage, and dynamic response. The results show that, compared with the rectangular columns, the circular columns with the equal moment of inertia suffer less damage in the earthquake and have better seismic performance. The prefabricated CFST columns can effectively ensure that the middle columns of the station structure are not severely damaged and can be replaced quickly after the earthquake, which improves the overall seismic performance of the subway station structure and the rapid recovery ability of the structural function after the earthquake. [ABSTRACT FROM AUTHOR]

More and more underground infrastructures have been built in special soil in recent years, especially in the loess area of western China. The loess, as a special soft soil, can have particular influence on the seismic characteristics of underground structures. Therefore, the seismic performance and safety evaluation of underground structures in loess area should be concerned. A series of large-scale shaking table tests were performed to investigate the damage mechanisms of a frame-type subway station structure in a loess site. The test results showed that the model soil softening and the stiffness degradation of the soil-structure system were more serious under stronger input motions. The acceleration response of the soil-structure interaction system in a loess site was more like that of a free-field when input PGA is lower. However, the soil-structure interaction phenomenon was more remarkable both in horizontal and vertical direction when higher PGA was input. The dominant frequency of the input motion had an inverse effect on the lateral soil deformation. The direct-force action mode of the dynamic earth pressure acting on underground structures presents a trumpet-type distribution. Meanwhile, the soil-structure interaction exhibited complex mechanical behavior, and slipping or gapping in test cases with higher PGA may occur. The strain measured in the center pillar and middle slab of the subway station was larger than that in other components. The results provide an insight into how strong ground motion might induce the influence and a possible way to describe quantitatively the damage of subway structure in loess ground. •A series of shaking table tests of subway model structure in a loess soil were conducted. • The dynamic characteristics of the loess soil under different ground motions were analyzed. • The seismic behavior of the subway station structure was obtained and analyzed through the test. [ABSTRACT FROM AUTHOR]

Highlights • Shaking table tests are conducted to estimate SSI effect on an isolated structure. • Isolation ability of isolation layer should be weaken by the softening soil layer. • Rotation response laws of isolator on different soil foundations are different. • Isolation of softening soil can compensate for the lost isolation ability of isolator. Abstract Soil-structure interaction (SSI) has a significant effect on the earthquake response of a base-isolated structure, particularly on the rotation response of the SSI system and the isolation performance of the isolation layer, as demonstrated by previous shaking table tests (Zhuang et al., 2014). On a softer soil foundation, the SSI should have a greater influence on the seismic response of an isolated structure. To this end, a new shaking table test is conducted to estimate the effect of SSI on the dynamic characteristics of a base-isolated structure on a multi-layered soil foundation including a soft clay layer. As expected, the isolation efficiency of the isolation layer is reduced by the SSI effects, especially with increasing peak ground acceleration (PGA) of the input motion. Compared with the test results for an isolated structure on a harder soil foundation, the rotation responses of the pile cap and the isolation layer in this study are stronger. Additionally, the rotation responses of the pile cap are significantly amplified by the isolation layer. This type of amplification effect can become stronger with increasing PGA of the input motion, which differs from the results for previous tests with a base-isolated structure on a harder sand foundation. Meanwhile, when the natural isolation property of the softening soil layer is considered, the seismic responses of a base-isolated structure are reduced by the SSI effects because the natural isolation of the soft soil layer can compensate for the lost isolation ability of the isolation layer. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the effect of concrete diaphragm wall on the seismic response of underground structures using numerical simulation. The seismic response of a two-story subway station supported by concrete diaphragm walls located in Nanjing, southeast China was analyzed. A finite element model was developed to simulate the soil-diaphragm wall-underground structure interaction during earthquakes. This model simulated the nonlinear dynamic behavior of soils using a visco-plastic model and concrete damage using a plastic-damage constitutive model. The effect of the diaphragm wall was explored related to the burial depth of the subway station. The simulation results showed that during a strong earthquake, the diaphragm wall reduced the lateral deformation of the lower story of the structure. However, the effect was very limited to the upper story of the structure. In contrast, during a small earthquake, the diaphragm wall increased the lateral deformation of the upper story of a deeply buried structure. The concrete diaphragm wall also increased the settlement of a deeply buried structure. The earthquake damage to the underground structure increased with the increase of the burial depth. The seismic tensile damage to the diaphragm wall was found adjacent to the invert of the structure. The damage to the diaphragm wall increased the uplift potential of a shallowly buried structure during earthquakes. Findings from this paper provide guidance to the seismic design of large underground structures buried in similar grounds. Highlights • FE model is developed to simulate dynamic soil-diaphragm wall-structure interaction. • The effect of concrete diaphragm wall (CDW) is related to burial depth of structures. • The CDW may increase earthquake induced deformation of underground structures. • The CDW may aggregate damage to underground structures in certain parts. • The CDW is vulnerable to earthquake damage adjacent to the invert of structures. [ABSTRACT FROM AUTHOR]

Nanjing sand as a typical kind of natural schistous quartz sand is extensively deposited along the middle and lower Yangtze River valley in China. The engineering properties of the schistous sand are quite different from those of siliceous sands. Several cyclic torsional shear tests are completed in this research to investigate the shear modulus reduction of post-liquefaction Nanjing sand under different loading states. In these tests, the maximum double-amplitude shear strain should reach 100% for each soil specimen. The effect of rubber membrane force on the strength of the soil sample is demonstrated and studied by a special water sample. The results show that the shear stress–strain curves should be corrected on the strength of post-liquefaction sand in a cyclic torsional shear test to alleviate the effect of the rubber membrane. The effective confining pressure, initial static shear stress, and cyclic shear stress have a remarkably small effect on the shear modulus reduction of saturated post-liquefaction Nanjing sand in the “zero effective stress” and dilative stage after the phase transformation. However, these factors considerably affect the shear modulus reduction of saturated Nanjing sand in the reversal contractive stage. Meanwhile, the shear modulus and single-amplitude shear strain amplitude have a better correlation than that between the shear modulus and the double-amplitude shear strain. Accordingly, the modulus decay functions for post-liquefaction Nanjing sand in different loading stages are formulated by the test results. [ABSTRACT FROM AUTHOR]

The model test method is crucial for studying the seismic performance of underground structures. Presently, model tests for the seismic response of underground structures are primarily performed with 1-g and N-g centrifuge shaking table. The 1-g shaking table model test is limited by the stress similarity in the soil-structure interaction system and cannot reproduce the seismic damage process and extent of the underground structure. The small table size of the N-g centrifuge model test makes it difficult to reflect the spatial effects of the seismic response of large underground structures. Seeking a large-scale model test method that can directly simulate the seismic damage process is essential for investigating the seismic performance of underground structures. Herein, based on the seismic response characteristics of underground structures, a quasi-static pushover test device applicable to underground structures was designed, and the corresponding tests and numerical model calculations were executed using the Daikai subway station as a prototype. Based on the macroscopic phenomena of structural damage development of the subway station in the test, the damage mechanism of the station structure was analyzed and compared with the numerical model. The strain amplitudes, displacements, and digital scatter strain color maps were analyzed to verify the reliability of the cyclic pushover loading test simulating the seismic performance level and damage process of the underground structure. Simultaneously, the rationality of the proposed quantification system for classifying the seismic performance level of single-story underground structures was verified. • A large-scale quasi-static pushover model test considering the soil-underground structure interaction was proposed. • The reliability and feasibility of the new model test were verified by numerical simulation. • The seismic performance level and amplitude of the drift ratio can be accurately reflected by the model test. [ABSTRACT FROM AUTHOR]

• New concept was defined to evaluate the damages of the underground structure (US). • New model was firstly used to predict the seismic performance levels of US. • A quantification system for the seismic damage of shallow buried US was advanced. • IDR was suitable to describe the seismic damage of shallow-buried US. • PGV was found more suitable for the seismic intensity measure of US in soft soil. This paper proposes a new method for evaluating the seismic performance and fragility of large underground structures. A typical underground subway station consisting of a two-story and three-span structure was used as the research subject. Considering the variation of sites and the uncertainty of input ground motions, we developed a finite element model of a nonlinear dynamic soil-underground structure interaction system. Based on the incremental dynamic analysis method, the nonlinear seismic responses of the subway station structure were calculated for 900 cases. Python (software) was used to accelerate the processing of the large number of numerical simulation data. Based on the seismic damage characteristics of an underground structure, this paper proposes a new concept of average seismic damage value to evaluate the damage condition of the underground structure to overcome the inadequacies induced by an expert's intuitive judgment. Meanwhile, the random forest prediction model was adopted to predict the seismic performance levels (SPLs) of the underground structure, and a non-parametric test was performed to verify the correlation between the degree of seismic damage and the inter-story drift ratios (IDR) of the large underground structure. This proved that the IDR could describe the seismic damage of shallow-buried underground structures; we advanced a precise quantification system of the SPL for shallow-buried subway station structures with two-story and three-span using probability statistics. The peak ground velocity (PGV) is more suitable than the peak ground acceleration (PGA) for use as the seismic intensity measure (IM) for large underground structures when the stiffness of the soil foundation becomes soft. In addition, the seismic fragility curves of the shallow-buried subway station structure were constructed and analyzed using the developed quantification system for the SPL. [ABSTRACT FROM AUTHOR]

Considering the complexity of the soil-structure dynamic interaction mechanism, underground structures are restrained and influenced by the surrounding soil in earthquakes, and their seismic damage under strong earthquakes is different from that of above-ground structures. The seismic response of underground structures is influenced by several coupling factors, including structural form, ground motion parameters, and soil properties, etc. In addition, the burial depth of the underground structure is also one of the critical parameters affecting its seismic response. In this study, the computational model of soil-structure dynamic interaction at different burial depths was established by using the finite element software ABAQUS with a single-story, double-span Daikai subway station as the prototype. The influence laws of different burial depth conditions on the seismic response characteristics such as inter-story drift ratio, internal force of critical sections, and seismic damage of subway stations are systematically studied. Meanwhile, this paper compares the correlation and applicability of PGA (peak ground acceleration), PSSRD (peak site soil relative displacement), and SSSRD (structural side soil relative displacement) with the seismic response of underground structures under different burial depths by applying the principle of vulnerability analysis. The results show that PGA and SSSRD are relatively better IMs (intensity measure) in shallowly buried structures, while the relative superiority of PSSRD gradually increases with increasing burial depth, and PSSRD is a more reasonable IM in deeply buried underground structures. • There is a most unfavorable buried depth for the seismic performance of underground structures. • The maximum inter-story drift ratio is a good indicator to quantify the seismic damage state of underground structures. • The seismic intensity measures are different for the underground structures with different buried depth. [ABSTRACT FROM AUTHOR]

In this work, several shaking table tests are conducted to investigate the seismic responses of a large subway station in various liquefied soil conditions. Different liquefaction states are modeled for the soil foundation by inputting different earthquake intensities. According to the test results, when the lateral soil layer surrounding the underground structure is partly liquefied, the cumulative residual deformations of the subway station are much greater than those in either non-liquefied or completely liquefied ground, which is mainly as a result of the large unrecoverable lateral deformation of the partially liquefied ground. Additionally, when the surrounding lateral soil layer is completely liquefied, the subway station structure experiences significant uplift. When only the soil layer near the upper wall is liquefied, large residual dynamic soil pressures on the sidewall are observed at the end of the test. In addition, the strain distribution rules of the underground structure are clearly altered in the presence of different states of soil liquefaction. These new findings can be used as a basis for evaluating the seismic risk of large underground structures in liquefiable ground. [ABSTRACT FROM AUTHOR]

A large underground subway structure could be severely damaged in a strong earthquake, such as the seismic damages of Daikai subway station in the 1995 Kobe earthquake. After the 1995 Kobe earthquake, the effects of earthquakes on underground structure became a hot topic. According to the seismic damage characteristics of the pipelines buried in the liquefiable soils, a large underground structure may be damaged ever more severely by the liquefaction. To examine the dynamic properties of saturated liquefiable soil, an existed constitutive model is revised and implanted into the commercial FEM software. Then the nonlinear seismic responses of large underground subway structures built in liquefiable soils are analyzed by a numerical modeling. The results of the comprehensive numerical analysis indicate that the existing subway station has a significant effect on the liquefaction of the nearby soils that are likely to be liquefied. The around sand soils under the suggested depth 20 m may be also liquefied under the influence of the large subway station, which should be non-liquefiable sand in many related codes of China. The subway station floats up as soon as the nearby soils are liquefied, and the soils accordingly flow from the lateral foundation to the bottom foundation of the subway station. It is also found that the floating of the subway station is completely out of sync in the main vibration stage of the inputted ground motions and the rising stage of the pore pressure, and it also lags behind in the main vibration stage for a considerable time and begins to stabilize only when the vibration weakens sharply and is close to zero. Generally, the dynamic softening soils under the subway station also have great effect on the seismic response of the large subway station. [ABSTRACT FROM AUTHOR]

To estimate the earthquake damages of a large subway station built in soft ground, a soil-underground structure static and dynamic coupling interaction model is advanced with the strong nonlinear properties of soil modeled by a developed viscous-plastic constitutive model. The numerical modeling results show that the large underground structure in soft site has a large vertical relative deformation during the horizontal earthquake, which could be larger than its horizontal relative deformation. The dynamic deformation responses of the components near to the middle span of the underground structure are obviously larger those of the other components at the side spans, which means that these components near to the middle span are more apt to be damaged in horizontal earthquake. According to the horizontal relative deformation and the seismic damage process of the large underground structure, which limited elastic working state and the limited elastic-plastic working state are determined, and the maximal interlayer displacement angles are suggested to be 1/430 for the limited elastic working state and 1/185 for the limited elastic-plastic working state. In addition, the seismic soil pressure coefficients on the upper side wall have significant changes. To the large underground structure shown in this paper, the seismic soil pressure coefficients on the top half of the upper side wall should be defined alone in its seismic design. [ABSTRACT FROM AUTHOR]

• The soil–underground structure interaction model was developed and verified simply. • A method for determining seismic performance and fragility of underground structure was established. • A comparative evaluation of the different IMs for underground structures was carried out. Currently, research on the underground structures seismic fragility is still in its infancy state. In this study, we carried out numerical simulation on soil-underground structure system (SUSI) by taking the Daikai metro station damaged in the Kobe earthquake as analysis object. Considering input ground motion characteristics, based on incremental dynamic analysis (IDA method), a statistical numerical modeling method was established to classify underground structure seismic damage status and its seismic performance level. The analysis results showed that the input ground motions had a significant effect on the IDA curves. The rationality and randomness of the selected ground motions were important influencing factors to ensure the underground structures seismic fragility curves. In relation to the damage that occurred to the Daikai station in 1995, the peak ground acceleration (PGA) and peak relative lateral displacement (PRLD) of the site were suitable for estimating the seismic performance of the shallow buried structure constructed. Finally, the seismic fragility curves were compared with the existing research results, and a seismic damage assessment was carried out, which verified the effectiveness of the statistical numerical modeling method developed in this study. [ABSTRACT FROM AUTHOR]

To investigate the static and dynamic characteristics of rubber–sand composite soil (RS soil) reinforced with cement, a series of triaxial compression tests and resonant column tests was performed by considering the influence of rubber content (10%, 20%, 30%, 40%, and 50%), cement content (0, 1.5, 2.5, 3.5 and 4.0 g/100 mL), and effective consolidation confining pressure (50, 100, and 150 kPa). Compared with the RS soil, the addition of cement significantly improved the shear strength of a cement–rubber–sand composite soil (RCS soil), based on an undrained shear test. The increase in cement content not only makes the elastic modulus and cohesion of the RCS soil increase but also reduces the internal friction angle of the RCS soil. With the increase in rubber content, the failure of the RCS soil samples changes from strain-softening to hardening, and the prediction equation of the initial elastic modulus of the RCS soil is given herein when the recommended cement content is 3.5 g/100 mL. The effects of rubber content, cement content, and effective confining pressure on the dynamic shear modulus and damping ratio of the RCS soil were studied via the resonant column test. The test results show that the increase in rubber content slows down the modulus attenuation of the RCS soil, but increases its damping ratio. The test results also show that the increase in cement content makes the bonding force between particles greater so that the modulus attenuation of the RCS soil becomes slower and the damping ratio is reduced. At the same time, according to the change rule of the maximum dynamic shear modulus of the RCS soil with the rubber content, when the recommended cement content is 3.5 g/100 mL, an empirical formula and recommended value of the shear modulus Gmax of the RCS soil are proposed. [ABSTRACT FROM AUTHOR]

Sand liquefaction is considered to be one of the main causes of severe earthquake damage. The seismic response of large-scale underground structures is mainly controlled by the deformation of surrounding soils, and the large liquefaction-induced lateral displacement poses a serious threat to large underground structures. In this paper, a large-scale shaking table test is performed to simulate the dynamic interaction between liquefiable foundation, diaphragm wall and underground subway station. The results indicate that the interaction mode between soil and underground structure changes significantly with the different liquefaction states of surrounding soil. The underground structure improves the liquefaction resistance of adjacent lateral soils, but significantly reduces the liquefaction resistance of soils located directly below the structure. The development of dynamic pore pressure is related to the seismic intensity, and a significant dissipation of dynamic pore pressure usually occurs after the end of a strong seismic excitation. Moreover, the acceleration response law along the vertical direction has changed significantly within the buried depth of the underground structure. Specifically, the acceleration response of the lateral foundation is inhibited in the absence of liquefaction, but is enhanced in the complete liquefaction. In addition, the liquefaction states of model site also affect the spatial strain response of the underground structure. [ABSTRACT FROM AUTHOR]

• Designed elastic sliding bearings installed on the top of columns of underground structure. • Seismic response and damage mechanism of an isolated underground structure is simulated. • Some findings were made on the seismic performance of underground structure with sliding bearing. Existing studies on earthquake damage have shown that the center column of a shallow-covered underground structure is more prone to be damaged by a strong earthquake than other parts, as seen by the damage induced during the Kobe earthquake in 1995. In this study, in regard to the seismic damage process of an underground structure, elastic sliding base-isolated bearings are installed on the top of its columns. It is found that the seismic damage to the center columns and the medium plate of the underground structure is effectively alleviated by the sliding bearing. Consequently, the axial stress responses of the center columns are remarkably reduced and completely in a compressive state during a strong earthquake, which can effectively improve the overall seismic performance of the underground station structure. However, the mechanical transfer properties between a column and a longitudinal beam are also significantly changed by the elastic sliding bearings. Thus, the seismic damage to the slabs near the side walls of the underground structure is slightly aggravated following the elastic sliding bearing installation on the top of the columns. [ABSTRACT FROM AUTHOR]

Sand liquefaction is one of the leading causes of severe earthquake damage. In this study, shaking table tests were carried out to investigate the dynamic interaction between the saturated sand and the irregular subway stations. In this test, a method for the preparation of a liquefiable foundation based on a flexible sensing chain combined with water sedimentation was proposed. Typical test results were interpreted, including the development and spatial distribution of pore pressure, surface subsidence, acceleration, deformation, and dynamic earth pressure. Results show that the spatial distribution of excess pore water pressure is changed by the irregular underground structure, and the liquefiable soil below the bottom plate of the structure can be divided into I, II, and III areas based on the degree of liquefication. The surface subsidence is significantly related to Arias intensity and is concentrated within the range of 5 %–95 % of the intensity. The structural floating is synchronized with the liquefaction of the saturated sand, and the uneven floating and inclination of the underground structure are remarkable, anti-flotation design of underground structures should take into account differences in section forms. During the liquefaction of saturated sand, the foundation soil has conspicuous lateral deformation, especially in the deep soil layer. The shape of the dynamic earth pressure increments turns from triangular to linear, when the foundation soil changes from non-liquefied to liquefied. Compared with the limiting values of the elastic inter-story drift ratio, the maximum inter-story drift ratio of the structure is smaller. The tensile strain responses on the columns, particularly in the lower layer, are more prominent than those at the slabs and side walls. • Shaking table model test is designed on the saturated sand-underground structure interaction system. • Dynamic interaction between irregular-section underground structures and saturated sand is researched, including the different liquefaction states for saturated sand. • A method for the preparation of a liquefiable foundation based on a flexible sensing chain combined with water sedimentation was proposed. • The liquefiable soil below the bottom plate of the structure can be divided into three areas based on the degree of liquefaction. • Differences in cross-section forms should be considered in the anti-floating design of underground structures. [ABSTRACT FROM AUTHOR]

Sand liquefaction-induced lateral flow has caused the destruction of a large number of buildings. In this work, an overall time-history numerical simulation is conducted to study the nonlinear dynamic interaction of soil with an underground structure buried in a slightly sloping liquefied foundation. Firstly, the consistency between the numerical simulation and model test results is verified. Then, the influence law of the ground inclination angle on the liquefaction distribution of the foundation around an underground structure reveals that the soil liquefaction at the lateral side of the underground structure is alleviated but is aggravated severely in the soils under the subway station. Additionally, the dynamic uplifting behavior and the seismic damage of the underground structure are different from those in a horizontally layered liquefied foundation. The rotation response and asymmetrical seismic damage of an underground structure in a slightly sloping liquefied foundation need attention. [ABSTRACT FROM AUTHOR]

The response displacement method (RDM) is recommended for the seismic analysis of underground structures in the transverse direction for many codes, including bases for design of structures-seismic actions for designing geotechnical works (ISO 23469) and code for seismic design of urban rail transit structures (GB 50909-2014). However, there are some obvious limitations in the application of RDM. Springs and the shear stress of the soil could be approximately evaluated for the structures having a simple cross section, such as rectangular and circular structures. It is necessary to propose simplified seismic analysis methods for structures with complex cross sections. This paper refers to the idea of RDM and proposes three generalized response displacement methods (GRDM). In GRDM1, a part of the soil surrounding a structure is selected to generate a generalized underground structure with a rectangular cross section, and the same analysis model as RDM is applied to analyze the responses of the structure. In GRDM2, a hollow soil model without a generalized structure is used to compute the equivalent load caused by the relative displacement of the soil, and the soil-structure interaction model is applied to calculate the responses of the structure. In GRDM3, a continuous soil model is applied to compute the equivalent load caused by the relative displacement and shear stress of the soil, and the soil-structure interaction model is applied to analyze the responses of the structure, which is the same as the model used in GRDM2. The time-history analysis method (THAM) is used to evaluate the accuracy of the proposed simplified methods. Results show that the error of GRDM1 is about 20%, while the error is only 5% for GRDM2 and GRDM3. Among the three proposed methods, GRDM3 has obvious advantages regarding calculation efficiency and accuracy. Therefore, it is recommended to use GRDM3 for the seismic response analysis of underground structures that have conventional simple or complex cross sections. [ABSTRACT FROM AUTHOR]

Coral reefs thrive in complex marine geological environments and are likely to suffer from dynamic marine disasters. The liquefaction characteristics of saturated marine coral sand subjected to dynamic loading, such as ocean waves, submarine earthquakes, storm tides, volcanic activities, and hurricanes, are key factors affecting the safety of coral reefs. A systematic study is conducted through a series of hollow-cylinder torsional shear experiments on the undrained response of saturated marine coral sand with different non-plastic fines contents (FC s) under cyclic linear stress paths with various cyclic loading direction angles (α d). An interesting discovery is that the cyclic linear stress paths with angles α d and 90°− α d have the same stress effect on liquefaction characteristics under isotropic consolidation condition. The test results show that if the near-zero effective stress state is defined as the criterion for initial liquefaction, then the liquefaction resistance of saturated coral sand decreases with increasing α d or FC. The generation of excess pore water pressure (EPWP) presents three modes: (1) "rapid–stable–fast," (2) "rapid–stable," and (3) "fast linear-like." Moreover, an energy-based EPWP prediction method is established. A novel discovery is that the generalized shear strain amplitude (γ ga) is uniquely related to the EPWP ratio of coral sand for a given relative density and FC. In addition, by introducing unit cyclic stress ratio (USR) as a new index of liquefaction resistance, a common correlation between equivalent skeleton void ratio e sk * and USR 15 (required for initial liquefaction in 15 cycles) is established for all test cases considered. This is confirmed by the experimental data of five types of terrestrial siliceous sands reported in the literature. • The cyclic linear stress paths with α d and 90°− α d have the same stress effect on liquefaction characteristics, and differ only in the direction of the initial dynamic shear stress. • The excess pore water pressure generation of marine coral sand present three mode: (1) "rapid - stable - fast", "rapid - stable", and "fast linear-like". • An energy-based excess pore water pressure prediction method was established, and there is a unique tangent relationship between γ ga and R u of marine coral sand. • Based on binary packing theory, a unified expression for the liquefaction strength of saturated coral sand was established, and the applicability was verified. [ABSTRACT FROM AUTHOR]

In current practice, the analysis of progressive collapse in building structures widely employs the alternate load path method. However, there are very few collapse tests that can be utilized under blast loads, especially for investigating the degradation mechanism of progressive collapse resistance in post-blast building structures. In this study, the degradation mechanisms and methods for damage assessment of reinforced concrete structures under blast loads were investigated through numerical analysis. A substructure model derived from explosion loads based on a drop-hammer testing machine was validated by comparing with test results, and the established model accurately captured three typical failure modes in the substructure columns and confirmed the axial tensile effects of the columns on the adjacent components. A substructure damage assessment method was used to assess the degree of damage in a 5-story reinforced concrete frame structure under different explosion scenarios. The results show that the degree of damage distribution of the reinforced concrete frame structure exhibited an S-shaped distribution under corner column blast scenarios while an arch-shaped distribution was observed for middle column blast scenarios. Furthermore, empirical formulas based on the explosive mass and distance (M-R) curves were established. These empirical formulas can help to rapidly predict the damage levels of RC frame structures for a given explosion scenario within a certain scope. [ABSTRACT FROM AUTHOR]

With the increasing utilization of fiber-reinforced polymer (FRP) bars in concrete structures, the issue of retrofitting damaged FRP-reinforced concrete (FRP-RC) structures will emerge. However, limited research is available on the seismic performance of damaged FRP-RC structures after retrofitting. In this study, cyclic tests were conducted to evaluate the efficiency of precast ultra-high performance concrete (UHPC) plates in retrofitting the seismic performance of GFRP-RC columns with continuous or lap-spliced GFRP bars. Three GFRP-RC columns, among which one column with lap-spliced details was strengthened with precast UHPC plates, and the other two columns were retrofitted with precast UHPC plates combined with NSM after simulated seismic damage testing. To compare the retrofitting efficiency of this method for GFRP-RC and steel-RC columns, a previous study on steel-RC columns retrofitted with UHPC was incorporated. For the pre-damaged GFRP-RC columns after retrofitting with precast UHPC plates combined with NSM, the peak load experienced an increase of 76 %–79 %, and the ductility was complete restored. The failure modes of strengthened or retrofitted GFRP-RC columns differ from those of strengthened or retrofitted steel-RC columns. Further, the flexural strength of GFRP-RC columns and beams after being strengthened or retrofitted by UHPC can be predicted well based on the cross-section analysis model. • Cyclic behavior of pre-damaged GFRP-RC columns retrofitted with UHPC was investigated. • The seismic performance of GFRP-RC columns was significantly improved after retrofitting with precast UHPC plates. • The design method accurately predicts the flexural strength of GFRP-RC columns and beams strengthened with UHPC. [ABSTRACT FROM AUTHOR]

Cement polystyrene shell mold (CPSM) grid concrete walls have been widely applied in the construction of low and mid-rise buildings with higher load-bearing and insulation properties. A star-type grid concrete wall was constructed based on the infill wall simplified to an equivalent diagonal bracing model. To investigate the seismic responses and behavior of a star-type grid concrete wall structure, an overall time-history numerical simulation was carried out in this paper. Typical results, including acceleration, deformation, hysteresis curve and failure pattern of this novel construction system, were interpreted. Results indicate that the star-type grid concrete wall structure has satisfactory seismic performance, including energy dissipation capacity. The structure has higher lateral stiffness and can work in an elastic state under major earthquakes. Accordingly, it is more sensitive to near-fault ground motion with higher frequency components. Meanwhile, the structural inter-story drift angle is less than the limit value of lighter damage when subjected to a super-major earthquake, and the structure presents shear deformation. The openings significantly affect the failure mode, the star-type grid concrete wall with a window (a small aspect ratio less than 1.11) conforms to shear failure, and the wall with a door (aspect ratio of 2.5) conforms to bending-shear failure. The diagonal bracing can distribute the stress in the wall, especially the concrete lattice beam, and effectively resist the lateral forces via the concrete lattice column, improving the ductility and integrity of the structural system. [ABSTRACT FROM AUTHOR]

Incorporating ceramic waste into concrete aggregates and combining it with the steel tube to form recycled ceramic concrete-filled steel tube (RCCFST) is an innovative method that not only considers the concept of sustainable development but also effectively treats ceramic waste. In order to popularize the application of RCCFST in practical engineering, it is necessary to study its creep behavior. In this study, for the first time, the replacement rate of recycled ceramic coarse (fine) aggregates was systematically used as the main research parameter in a creep test. A novel, rigorous creep test was designed and implemented to thoroughly analyze its creep behavior in concrete-filled steel tubular (CFST) short columns. The influence of the recycled ceramic coarse (fine) aggregate on the creep deformation, creep coefficient, and specific creep of the specimens was analysed using the 156-day creep curves obtained in the tests. Using a scanning electron microscope, the microstructural causes for the influence of recycled ceramic aggregates on creep were revealed. Research has shown that the creep deformation of recycled ceramic concrete-filled steel tube increased by 2.73 %–18.45 % compared with ordinary concrete-filled steel tubes after the 156 days of loading. The influence of coarse and fine aggregates of recycled ceramics on the creep coefficient and specific creep of the specimen showed different laws with the change in replacement rate. When the replacement rate of recycled ceramic coarse (fine) aggregates is 100 %, the creep coefficient and specific creep of the specimen are greater than that of the ordinary concrete-filled steel tube specimen. According to the test results, the applicability of the four recycled concrete creep models to recycled ceramic concrete was compared using a step-by-step integration method. The comparison results show that the creep calculation curve of the ACI-W model is closest to the test curve. 68 examples are compared and analyzed by using this model to explore the influence of various factors. • Creep test of RCCFST structure is carried out. • The influence of RCCA and RCFA on the creep of RCCFST structure is different. • Revealing the influence of RCA on creep from microstructure. • An improved creep model of RCCFST structure based on the existing model. • The effects of aggregate water absorption on creep coefficient are explored. [ABSTRACT FROM AUTHOR]

This paper presents a fully coupled flow deformation model to characterize the nonlinear seismic site response of liquefiable marine sediments, considering the ocean wave environment. Emphasis is placed on extending a simplified soil hysteresis model for the effective stress analysis of nonlinear site seismic response. The proposed model addresses the limitations of existing one-dimensional (1D) hyperbolic soil models to simultaneously capture the 3D hysteretic stress–strain behavior and the accumulated volumetric deformation of soil skeleton. The volume strain formulation of soil skeleton is included in the Biot's volumetric compatibility equation as the source term for excess pore water pressure buildup. The proposed method is implemented into an explicit time matching finite difference analysis platform, and validated against the recordings of the KSRH10 site for North–South (NS) direction of KiK-net borehole arrays in Japan. Finally, the influences of ocean wave loading upon the seismic wave propagation behavior in liquefiable marine sediments are examined with reference to the Bohai Strait site condition, China. The obtained results indicate that the ocean wave environment has significant effect on the nonlinear seismic site response of liquefiable seabed at shallow depth. • A fully coupled flow deformation model is presented for the simulation of seabed liquefaction. • A simplified soil hysteresis model is extended for the fully coupled seismic site response analysis. • Model calibrations are carried out against the recordings of the KSRH10 site from the KiK-net. • Influences of ocean wave on the seismic response of liquefiable marine sediments are investigated. [ABSTRACT FROM AUTHOR]

A finite element method (FEM) for simulating seismic wave fields of three-dimensional (3D) local irregular topography is proposed in this article. The author begins by developing a program to solve the seismic response of 3D layered foundations using the frequency-domain stiffness matrix method. This enables the user to easily obtain the input of ground motion for the finite element model, as well as conduct finite element simulations of the seismic wave field of incident P-, SH-, SV-, and Rayleigh waves coming in from any direction. This method solves the problem that previous 3D finite element modeling methods couldn't handle SV waves when the angle of incidence is greater than the critical angle. Furthermore, it effortlessly accounts for the dispersion properties inherent in layered foundations. A series of 3D seismic wave field simulation examples are employed to validate the method's accuracy. In the end, this method is subsequently applied to further investigate the seismic response of frame structures in sedimentary valleys, and the significance of soil nonlinearity and topographic effects on the seismic response of structures is presented. • A two-step FEM is proposed to study the seismic response of irregular terrain. • It is capable of simulating seismic waves coming in at any angle. • It works for body and surface waves and can consider wave dispersion. • It also applies to soil-structure interactions and nonlinearities. • Good accuracy of the method is presented, and topographic effects are verified. [ABSTRACT FROM AUTHOR]

Ensuring the safety of undersea shield tunnels constructed in soft marine deposits that are subject to strong seismic motion represents a major engineering challenge. An example of one such undersea shield tunnel is the 2.70 km-long subsea highway tunnel crossing under the Gulf of Suai in the Rongjiang River Estuary in Shantou, China. Using the generalized response displacement method, the authors developed a nonlinear seismic response analysis of the segmental lining for the 2.7 km-long Suai tunnel. In the proposed longitudinal seismic response analysis, the engineering geology characteristics and nonlinear dynamic behavior of the Suai seabed soil, the nonuniform mesh layout of the free-field site, the artificial boundary conditions and nonuniform seismic input, simulation model, and the parameters of soil-tunnel interaction systems, are considered in detail. Special emphasis is given to the irregular unloading-reloading rules for the stress-strain hysteresis loop, the seismic input at artificial boundary nodes, and the spatial incoherency of ground motions in the seabed site. The opening width at the ring intersegment under simultaneous actions of longitudinal, transversal, and vertical seismic motions is critical for seismic safety. The proposed methodology was deemed conservative, as demonstrated by a comparison with dynamic transient analysis using the three-dimensional finite element method. The results of this pilot study should be of use in the construction of future long subsea shield tunnels in the high seismic intensity region. [ABSTRACT FROM AUTHOR]

Ground liquefaction is one of the severest threats that ensue subsequent damage to the subway underground structure during and after strong earthquakes. However, few studies on the seismic response of large-scale subway underground structures in liquefiable site, especially for complex subway stations, have been reported. Existing researches that consider the diaphragm wall as safety reserve for the seismic design of subway stations are oblivious of the influence of the diaphragm wall on the deformation and uplift of underground structures. Contradictory to the original intention, the diaphragm wall may have adverse effects on the overall deformation behavior and force redistribution of the structure. Thus comprehensive exploration of the interaction between the diaphragm wall and the subway station in liquefiable site during and after earthquake should be carried out to rationalize the design of the underground structure. Numerical simulations of the seismic response of different soil-structure interaction systems are implemented and discussed in the present study. In the numerical simulation, the constitutive model for saturated sand and the Arbitrary Lagrange-Euler (ALE) method to prevent mesh distortion are applied to constitute the static and dynamic coupling finite-element model. Earthquake responses of the soil and the complicated underground subway station are then investigated. Modeling results are analyzed in respect of earthquake responses yielding the liquefaction distribution of the site, the uplift feature of the unequal-span subway station, the dynamic settlement and vector characteristics of the surrounding soil, the lateral deformation and the earthquake-induced damage of the underground structure. It is found that the uplift of the unequal-span subway station is featured by uneven uplift across the spans. When the diaphragm wall is installed, the tension damage degree of the bottom plate of the subway station are intensified, while the components of cantilever span in the upper layer suffer the less. The resulted new findings from this study shed light on the seismic performance and seismic design method for the unequal-span subway stations at a liquefaction site. [ABSTRACT FROM AUTHOR]

A novel and efficient method for simulation of spatially correlated earthquake ground motions (SCEGMs), named as improved Hilbert spectral representation method, was presented. By using Hilbert–Huang transform (HHT), the known record can be decomposed into a series of intrinsic mode functions (IMFs) and a residual function. Targeting on each IMF, simulated IMFs for every field point were derived through a spatial correlation model. The frequency dependence of the spatial correlation structure was simplified such that only the correlation at the predominant frequency of each target IMF was considered. SCEGMs can then be obtained by superposition of simulated IMFs and the original residual function. Taking the Suai shield tunnel project in China as reference, the intersegment opening width response of shield tunnel under multiple support excitation (MSE) and identical support excitation (ISE) were investigated and compared. First, numerous accelerograms, including horizontal and vertical components, were generated based on selected real records and artificial acceleration time histories on bedrock to realize MSE. The generalized response displacement method (GRDM) in combination with a large-scale FEM model was then utilized to proceed with the study. Results showed that the MSE can lead to a higher opening width of tunnel in general. The distribution of longitudinal opening width under MSE is also different from that under ISE. The sharp variation of soil layer stiffness along the longitudinal direction of tunnel may lead to extremely large intersegment opening width or severe damage. [ABSTRACT FROM AUTHOR]

The subway shield tunnel of Sanyang Road in Wuhan, China, is a Yangtze River-crossing tunnel project with a mega diameter of 15.7 m, which crosses several soil layers with sharply different properties. To investigate the seismic characteristics of this special subway tunnel under spatially varying earthquake ground motions (SVEGMs) with high efficiency, the concept of response displacement method was utilized and realized with a refined free-field model and a simplified soil-tunnel model. Two sets of borehole accelerograms, denoting near-field and far-field ground motions, respectively, were selected and taken as the reference to generate fully non-stationary SVEGMs. A lot of responses along the longitudinal direction under multi-support excitation (MSE), including intersegment opening width, inner forces, and acceleration, were observed and compared with those under identical support excitation (ISE). The comparative results showed that the responses of subway shield tunnel under MSE are generally higher than those under ISE. The longitudinal distributions of intersegment opening width and bending moment response of lining are dominantly affected by the site conditions. Excitation methods, spectral characteristic and PGA of input earthquake can also have effect on the longitudinal distribution of tunnel response. The results can contribute to revealing the difference between seismic response characteristics of shield tunnel under MSE and those under ISE and predicting the underlying location of seepage or severe damage of shield tunnel. The analysis procedure established in this paper possesses highly potential for application to the aseismic design of practical shield tunnel project. [ABSTRACT FROM AUTHOR]

The paper presents a robust modeling method for a fully coupled effective stress analysis of the wave-induced liquefaction scenarios, based on the Biot consolidation theory. In this context, emphasis is placed on the implementation of a well-calibrated cyclic soil model and an empirical shear-volume coupling equation, which links the increment of volumetric strain per cycle of wave with the shear strain occurring during that particular cycle. Unlike most of the previous investigations using the amplitude of shear stress over the wave period (or the phase-resolved oscillatory shear stresses) as the source term for calculating the residual pore pressure, in this study, the source term is related to the rate of plastic volumetric deformation and implemented into the Biot consolidation equation to consider both generation and partial dissipation of excess pore pressure during wave propagation. Then, the proposed modeling method is incorporated into a dynamic finite difference analysis procedure. Model calibrations are carried out in terms of individual soil element behavior and seabed response under progressive waves, respectively. Overall good agreement demonstrates the reliability of the modeling method for the prediction of wave-induced seabed response. Finally, the paper highlights the potentials of proposed modeling framework to simulate the basic features of wave-induced seabed response (i.e., the coupling of progressive buildup of pore pressure and cyclic softening of soil skeleton), by means of numerical examples. The obtained results show that the cyclic behavior of liquefiable seabed under wave actions can be well captured by the proposed model. [ABSTRACT FROM AUTHOR]

• Effective stress characterization is present for the seismically induced seabed-tunnel interactions. • A new source term is defined in the Biot's coupled solid–fluid formulation for the residual EPWP. • Model calibrations are carried out by retrospective simulations of cyclic axial–torsional tests. • Effect of ocean environmental loads on the seismic response of immersed tunnel are interpreted. Unlike the terrigenous site condition, the seabed site is characterized by complex hydrodynamics in the ocean environment (i.e. ocean waves and currents). This paper investigates the significance of the ocean environmental loads on the seismic interactions between the buried immersed tunnel and the surrounding soil undergoing buildup of excess pore water pressure (EPWP) and residual liquefaction. A fully coupled nonlinear effective stress analysis framework is proposed, integrating liquefaction/solidification analysis procedure with consideration of cyclic plasticity, of partial drainage, of finite soil deformation and of soil-structure interaction. A new source term is defined in the Biot's coupled solid–fluid formulation for the residual EPWP, as the phase-resolved plastic volume strain of soil skeleton. The proposed model is calibrated against the benchmarking data of undrained stress-controlled cyclic axial–torsional test. The numerical results reveal that the continuous disturbance of ocean wave and current has major consequences for the seismic soil-structure interactions such as EPWP response, liquefaction pattern of seabed over the contact areas and uplift/settlement of immersed tunnel, especially at the post-liquefaction stage. It is concluded that ignoring the environmental loads caused by ocean wave and current in seismic design practice of immersed tunnels can be misleading. [ABSTRACT FROM AUTHOR]

• Focusing on nonlinear static-dynamic structure-soil-structure interaction (SSSI). • SSSI is dominated by ground motion, structure spacing and number of structures. • SSSI significantly changes seismic response of inter-story drift. • SSSI increases the seismic response near the second natural period of the building. • SSSI significantly changes the peak shear force at the top of the pile foundation. Based on the 1–3 identical high-rise buildings with pile-raft foundation, a series of building-site two-dimensional finite element analysis models with different building spacings is established. Then, considering the nonlinear characteristics of soil and structure, the static-dynamic coupled numerical simulations are conducted to study the structure-soil-structure interaction (SSSI) under different ground motion. The results show that: 1) Adjacent high-rise buildings have the most unfavorable impact on the peak acceleration of the 1/4–1/2 height floors of the middle building, and increase the normalized response acceleration spectra value of acceleration near the second natural period of the structure; 2) Adjacent high-rise buildings have the most significant impact on the inter-story drift of the top, bottom and basement of the middle building; 3) Adjacent high-rise buildings redistribute the total horizontal shear force of the pile top of the middle building among the pile foundations, so that the peak value of the pile top shear force of each pile changes significantly, which is extremely unfavorable to the seismic safety of the structure. It should be taken seriously in the seismic design of structures. In addition, the structure spacing that results in favorable or unfavorable effects is discussed, and the reasons for the impact are analyzed. [ABSTRACT FROM AUTHOR]

In this paper, an elastoplastic modeling method is presented for dynamic consolidation of liquefiable seabed around a pipeline subjected to ocean environmental loadings (i.e. wave and current). Special attention is given to the cyclic plasticity modeling of liquefiable marine sediments and the evolving soil-pipeline interactions, in association with the Biot's dynamic consolidation theory. Motivated by the experimental findings, this paper extends a Masing-type model to the liquefaction-induced deformation regime of marine sediments within the cyclic plasticity framework. A novel plastic flow rule is developed to capture the cyclic-shearing-induced volumetric strain and hence exercise direct control over the response pattern of excessive pore water pressure (EPWP). Then, a model calibration procedure is outlined, with respect to cyclic laboratory sample tests under various loading paths. Finally, the combined actions of current on the wave-induced dynamics of liquefiable seabed around a buried pipeline are studied by numerical examples. The results demonstrate that the propagation of ocean current has major consequences for the wave-induced soil-structure interactions such as EPWP response, liquefaction pattern of seabed over the contact areas and uplift of pipeline. The liquefaction triggering of seabed and the consequence for the dynamic response of pipeline in the wave and current environment are also investigated. • The cyclic plasticity of liquefiable seabed around pipeline under wave and current is modeled. • A newly-observed cyclic shear-volume coupling model is incorporated into the plastic flow rule. • Model calibrations are carried out by element simulation of liquefaction against laboratory tests. • Influences of current on the wave-induced liquefaction and uplift of pipeline are investigated. [ABSTRACT FROM AUTHOR]

In ocean environments, wave usually propagates in association with a current. The paper presents a cyclic characterization framework for elastoplastic consolidating behavior of liquefiable seabed around the immersed tunnel under combined wave and current loading, based on the Biot dynamic consolidation theory. Special attention is placed on modeling the nonlinear wave-current interaction, the cyclic plasticity behavior of marine deposits and the soil-structure contact effect. The paper extends an existing Masing model to large strain regime (in the order of 10−2) in the framework of cyclic plasticity for capturing the liquefaction-induced nonlinear behavior of marine deposits. Then the proposed cyclic plasticity model is implanted into an explicit time matching finite difference analysis platform, permitting a comprehensive simulation of the intensive response of the immersed tunnel in the seabed experiencing the excess pore pressure accumulation and residual liquefaction. Retrospective simulation of a well-documented centrifuge test by the proposed framework indicates satisfactory agreement, validating the reliability for capturing the excess pore pressure accumulation and residual liquefaction during wave propagation. Finally, the influences of current on the wave-induced liquefaction in the vicinity of an immersed tunnel are investigated by a numerical example. The results indicate that the ocean current significantly changes the original characteristics of wave-induced liquefaction as well as the induced uplift of the immersed tunnel, especially with consideration of the cyclic plasticity behavior of marine deposits. The mechanisms of seabed liquefaction and the induced uplift of the immersed tunnel under wave and current actions are also interpreted • Elastoplastic characterization is presented for seabed-tunnel interactions under wave and current. • An existing Masing model is extended to large strain regime in the framework of cyclic plasticity. • Model calibrations are carried out by retrospective simulation of a well-documented centrifuge test. • Influences of current on the wave-induced liquefaction and uplift of tunnel are interpreted. [ABSTRACT FROM AUTHOR]

• The cyclic resistance of a saturated marine silt under non-proportional loading is studied. • The equivalent cyclic stress ratio ESR is applied to quantify the wave-induced cyclic stress paths. • A unique correlation between ESR and the liquefaction resistance N L can be established. • A closed-form expression is given to relate the pore pressure ratio and the generalized shear strain. The significance and complexity of cyclic behavior of saturated silt under non-proportional loading are still of great concern in practice, due to the highly inherent anisotropy of soil fabric. This paper presents an experimental investigation conducted in an automated hollow cylinder apparatus into the undrained anisotropy and cyclic resistance of a saturated marine silt under wave-induced non-proportional loading, which is replicated by simultaneous changeover in magnitudes and directions of the principal stress. Special attention is paid to the influence of cyclic shear mode and stress path, characterized by the cyclic stress ratio (CSR) and the ratio (δ) of the amplitude of deviatoric stress components (i.e. deviator stress and torsional shear stress), on the pore pressure response and deformation characteristics. The cyclic stress path is not a negligible factor for the cyclic resistance of saturated silt in the non-proportional loading, but had significant impact. The CSR can not properly characterize the resistance of silt to cyclic shearing, involving continuous rotation of the principal stress. This observation is considered to be directly associated with the soil fabric anisotropy. Remarkably, for all loading patterns investigated, the pore pressure ratio r u is uniquely correlated with the generalized shear strain γ g , rather than to the CSR. Consequently, a closed-form expression is proposed to relate γ g and r u , which can be used to predict the onset of failure as well as the pore pressure at a specific strain. By using the equivalent cyclic stress ratio (ESR) to characterize the cyclic undrained resistance of saturated marine silt (in terms of the number of cycles required to failure, N L), a virtually unique correlation between ESR and N L can be established for all the non-proportional loading investigated. [ABSTRACT FROM AUTHOR]

• Seismic response and damage mechanism of irregular-section underground structure in a soft site were researched. • Some advanced testing method were used to measure the deformation of the site and underground structure. • Soil Surface settlement is significantly correlated with Arias intensity. In this study, shaking table tests were performed to investigate the dynamic interaction of a silty-clay soil with an irregular-section subway station. During the tests, a shape acceleration array (SAA) was used to measure the lateral deformation of the model soil, and a non-contact dynamic displacement testing method was applied to visualize and digitalize the seismic damage process of the station structure. Typical test results, including the dynamic earth pressure, seismic settlement, deformation, and acceleration of different levels of the structure, were interpreted. The results indicated that the movement of the subway station was more controlled by the surrounding silty-clay soil in terms of phase and amplitude. SAA can effectively measure the soil deformation, and the relationship between the relative lateral displacement and soil depth can be well fitted in a cosine function, especially when subjected to strong earthquakes. Seismic settlement is significantly linked to Arias intensity, and the subway station experienced significant uneven settlement, resulting in soil-structure separation in the vertical direction. The multi-story irregular-section subway station deforms in a shear mode. The maximum inter-story drift ratio was approximately 1/171. The components in the lower layers of the shallow-buried subway station structure, particularly in the central columns, underwent cumulative damage. Hence, more robust forms of structural members and the ductility of central columns should be carefully considered in the seismic design of subway station structures. [ABSTRACT FROM AUTHOR]

This paper presents a robust modeling method for fully coupled effective stress analyses of wave–induced liquefaction scenarios around immersed tunnels. The method is based on the Biot consolidation theory, and special emphasis is placed on modeling the high–strain behavior of the liquefiable seabed and the evolving boundary conditions at the tunnel–seabed interface. Motivated by the experimental results, the existing Masing model is extended to the high–strain regime in the cyclic plasticity framework to capture the liquefaction–induced nonlinear behavior of the sand. In particular, a newly–observed shear–volume coupling model is implemented into plastic flow rule to realize volumetric compaction by cyclic shearing and exercise as the source term for residual excess pore pressure accumulation in the Biot's equation. Subsequently, the proposed cyclic plasticity model is implanted into an explicit time matching finite difference analysis platform, permitting a comprehensive simulation of the intensive response of the immersed tunnel in the seabed experiencing the excess pore pressure accumulation and residual liquefaction. Moreover, a model calibration procedure is presented based on the cyclic laboratory sample test data and prescribed loading paths. Finally, the liquefaction–induced uplift of an immersed tunnel under progressive wave action is studied numerically. The obtained results provide the cause of liquefaction and the resulting consequences for tunnel uplift in ocean wave environments. [ABSTRACT FROM AUTHOR]

A series of large-scale shaking table tests were performed to investigate the seismic response of an underground subway structure with irregular sections in adverse soil conditions (soft and liquefiable sites). Emphasis is placed on the influence of the adverse soil conditions on the response of the irregular underground structures and over areas of soil-structure interface, involving buildup of pore pressures and resulting large deformations. The results indicate that the seismic responses of the structure and the soil were sensitive to input motions with richer low-frequency components. The seismic damage of the underground structure was more significant in the soft site as compared with that in the liquefiable site. The liquefiable site worked as a natural seismic isolation system for the underground structure, significantly reducing the damage potential to the model structure. Under the action of a strong earthquake, the horizontal displacement response of the liquefiable site sharply increased compared with that of the soft site. With respect to the structure response, the interlayer displacement of the structure in the soft site was approximately twice that in the liquefiable site. The lateral deformation of the structure was greater in the soft site and the interior structure column was more prone to damage. Correspondently, the peak and the residual strains in the structural components in the soft site were higher than those in the liquefiable site were. The results provided insights into the site effects of adverse soil conditions on the seismic response of underground structures, especially on the seismic damage process and the failure mechanisms of the structure members. [ABSTRACT FROM AUTHOR]