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The hinge type of precast concrete arch culvert was introduced to Japan from France in the 1990s in consideration of the saving of labor, shortening of the construction period, and high quality control of the concrete members. However, due to the 2011 off the Pacific Coast of Tohoku Earthquake (March 11, 2011), the three-hinged precast arch culverts that had been constructed in Japan at the beginning of the period when precast arch culverts were firstly introduced, suffered damage, which spoiled their serviceability. According to the extent of the damage and the type of culverts that were damaged, the longitudinal structural connectivity of the culverts was assumed to be one of the possible reasons for the reported damage mechanism. Therefore, the objective of this paper was to clarify how strongly the longitudinal structural connectivity influenced the longitudinal seismic behavior of the three-hinged arch culverts. To achieve this objective, an elasto-plastic finite element analysis was conducted with an analytical model that could capture the characteristics of the damaged culverts. Simultaneously, a penalty method with the bi-linear spring model was applied as a solution to the contact-impact problems of the precast segmental arch members. As a result, it was found that the weaker longitudinal structural connectivity in the damaged culverts allowed the torsional displacements of the arch members to induce critical damage to the arch members, namely, edge defects in the arch crown and concrete foundation. The numerical results proved the unignorable influence of the longitudinal structural connection on the possible damage to three-hinged arch culverts. [ABSTRACT FROM AUTHOR]

This paper presents a new method for analyzing the nonlinear response of a single, vertical pile with the circular cross-section under torque in layered soils. The nonlinear stress-strain relationships of both soil-pile interface and soil are approximated by the hyperbolic model, whereas the pile material is elastic. The torsional spring stiffness of the soil-pile interface and the soil are determined by traditionally available methods. A four-node finite element model for the soil-pile interface is proposed to represent nonlinear behaviors of the soil-pile interface and the soil, separately. A new iterative scheme for nonlinear analysis of a single pile under torque is also developed that avoids having to solve a large number of simultaneous equations found in traditional solution schemes. The new solution method is based on the tangential stiffness of the soil-pile interface and soil springs, which are determined at each load step. From this solution scheme, an equivalent stiffness of the soil-pile-interface system of each pile element is calculated from the bottom element to the top element while torque and angle of twist are calculated from the top to the bottom elements. The solution gives the distribution of the angle of twist and torque along the pile, and the equivalent stiffness of the soil-pile system and torque-angle of twist curves at any depth. The solution method can be easily applied to the practice field in nonlinear analysis and in designing a single pile under torque in layered soils. The analysis results using the new solution scheme compared well with the results from other analytical methods studied by previous researchers. The proposed method is also used to predict the behavior of two full-scale piles under torques. The predictions are in good to excellent agreement with measurements. [ABSTRACT FROM AUTHOR]

An underground structure buried in a soft ground located in a seismic-active region may experience intolerable deformation due to earthquake loading. The collapse of Daikai Station of the Kobe subway line during the 1995 Hyogoken-Nambu Earthquake demonstrated that underground structures may also sometimes be at high risk for failure in a huge earthquake. In particular, box culverts constructed in a soft ground with a thin overburden are vulnerable to earthquakes. Some previously constructed box culverts do not meet the present requirements of seismic design standards. In this paper, numerical analyses and 1-g shaking table tests are conducted to evaluate the effect of partial ground improvement (PGI) as a seismic countermeasure for the above-mentioned existing box culverts. Particular attention is paid to the optimum pattern of PGI that can most efficiently reduce the impact of an earthquake on a box culvert. The underground structure of Daikai Station is taken as an example and its physical and geometric conditions are used to model the box culvert in the analyses and the tests. In order to accurately consider the influence of the soil-structure interaction (SSI) on the underground structures, both the soil and the box culvert are considered in the analyses and the shaking table tests. Four different patterns of PGI are considered. Based on the analyses and the tests, an optimum pattern for the PGI of existing box culverts is proposed. [ABSTRACT FROM AUTHOR]

When simulating the vertical drain method using a soil–water coupled finite element analysis, a macro-element method can be used as a means of approximately applying the water absorption function of drains to individual elements. In this paper, the discharge function of vertical drains was added to the method by treating the water pressure in the drain as an unknown and adding a continuity equation for the drains to the governing equations. By extending the method in this way, the analytical results came to exhibit the well-resistance phenomenon automatically, depending on the analytical conditions. Numerical analyses were conducted after incorporating the proposed macro-element method into a quasi-static soil–water coupled elasto-plastic finite element method based on the finite deformation theory. The main conclusions are as follows: (1) the proposed method enables highly accurate approximations for problems involving material and/or geometrical nonlinearity and multilayered grounds; (2) the proposed macro-element method is capable of reproducing various phenomena that occur when the vacuum consolidation method is applied to a clayey ground containing a middle sand layer; (3) by following the formulation used in this paper, it is unnecessary to match the mesh division width to the drain arrangement and spacing. In addition, it is possible to obtain solutions that are minimally affected by the mesh size. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical study on the evaluation of thermal response test (TRT) results observed in a precast high-strength concrete (PHC) pile and a general conventional vertical type borehole with spiral coil type ground heat exchangers (GHEs). Field TRTs were carried out on a PHC energy pile and a general vertical type borehole, and an equivalent ground thermal conductivity was estimated using the spiral coil source model. The PHC energy pile and conventional vertical type borehole were numerically modeled using a three dimensional finite element method for the estimation of borehole thermal resistance and the comparison with the TRT results. Based on the results, this paper suggested a method to evaluate the ground thermal conductivity using the infinite line source model and the results were compared with those of the spiral coil source model. [ABSTRACT FROM AUTHOR]

Underground coal gasification (UCG) is an efficient method for the conversion of the deep coal resources into energy. This paper is concerned with a feasibility study of the potential of deeply lying coal seams (>1200 m) for the application of UCG combined with subsequent storage of CO 2 for a site located in Bulgaria. A thermal–mechanical coupled model was developed using the ABAQUS software package to predict the heat transfer, the stress distributions around the UCG and the consequent surface subsidence. Material properties of rocks and coal were obtained from existing literature and geomechanical tests which were carried out on samples derived from the demonstration site in Bulgaria. Three days of gasification has been simulated by assigning a moving heat flux on a cell of 2 m × 2 m × 2 m at a velocity of 2 m/day. Results of temperature and stress distribution showed that the developed numerical model was able to simulate the heat propagation and the stress distribution around cavities under a thermal–mechanical coupled loading during the UCG process. Also, the surface subsidence was found to be 0.08 mm after three days of gasification for the case studied. It is anticipated that the results of this paper can be used for the prediction and optimization of the UCG process in deep coal seams. [ABSTRACT FROM AUTHOR]

Landslide dams (LDs) are usually composed of natural debris materials and normally exhibit heterogeneous strata along both the depth and run-out directions. In addition, LDs usually have weaker structures than undisturbed ground and are more vulnerable to seepage loading. Considering that the surface layer of naturally packed LD materials is mostly in an unsaturated state, it is undoubtedly important to investigate the hydraulic/mechanical behavior of LDs with heterogeneous strata subjected to seepage loading. In this paper, a systematic flume test program was firstly conducted, in which the Tangjiashan LD was carefully referenced for its model design. Three different water level rising rates and two different stratal arrangements were considered in the flume tests. Then, soil-water-air coupled finite element analyses were conducted to simulate the flume tests, and all the material parameters of the LD materials were carefully determined based on the results of element tests. A comparison of the test and calculated results showed the possibility of using the proposed numerical method to predict the occurrence of dam breaching and to estimate the risk of LD failure. Moreover, the hydraulic/mechanical behavior of the LD materials and the heterogeneous strata of the LD were proven to be very important to the stability of the LD. Finally, from an engineering viewpoint, the possibility of utilizing a naturally formed LD, and not destroying it after its formation, is also discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a steel pipe sheet pile (SPSP) reinforcement method for existing caisson foundations in water. The technique involves driving SPSPs around the caisson foundation and connecting them to it with reinforcing footing. To support the rational design of reinforcements using this method, the following factors influencing the technique׳s effectiveness and related mechanical behavior should be considered: (1) the conditions of the caisson/SPSP reinforcement footing connection; (2) the caisson/SPSP flexural rigidity ratio; (3) the distance between the caisson and the SPSP wall; and (4) the pile length. However, as the influence of these factors on the reinforcement effect and mechanical behavior has not yet been clarified, the current method has no standardization for the concept of the load transfer mechanism in reinforced foundation systems, and the ultimate lateral bearing capacity of existing caissons has been largely ignored in previous construction. This paper describes centrifuge model tests and three-dimensional elasto-plastic finite element total stress analysis conducted in relation to real cases in order to identify a more effective and rational reinforcement structure. The static lateral bearing capacity and seismic performance of reinforced foundations were investigated, and the following factors were considered: (1) the conditions of the caisson/SPSP reinforcement footing connection; (2) the caisson/SPSP flexural rigidity ratio; and (3) the pile length. Finally, a structural design flow is proposed based on the experimental and numerical simulation results. A chart to facilitate determination of appropriate reinforcement structures is also presented. [Copyright &y& Elsevier]

Abstract: The Bangkok metropolitan area, located on a thick river soft clay deposit, has recently started a construction project on a mass rapid transit underground railway (MRT). This paper presents a finite element study on the Bangkok MRT underground construction project. The excavation of Sukhumvit Station was selected as the case study for the FEM numerical modelling in this paper. The numerical study focuses on the initial input on the ground conditions and the constitutive soil models. The geotechnical parameters were selected based on the soil investigation reports carried out for the purpose of the construction. The parameters selected for the constitutive models used in the FEM analysis were calibrated against the laboratory testing results. Finally, all the FEM simulations were compared with the data from field investigations. [Copyright &y& Elsevier]

Abstract: In this paper, particular attention was paid to the seismic enhancement effect of group-pile foundation with partial ground improvement method that is used for existing pile foundations in practical engineering. A model test on a full system with a superstructure, a nine-pile foundation and a sandy ground was conducted with the shaking table test device. The model pile is made from aluminum and the model ground is made from Toyoura Sand. The shaking table test device is 120cm in width and 160cm in length. The maximum acceleration is 1g and the maximum displacement is 5cm. The maximum payload is 16kN and the highest frequency is 10Hz. The model ground is carefully prepared to obtain a ground with controllable unified density. Before the shaking table test, the pattern of the partial ground improvement for an existed group-pile foundation is carefully selected using numerical tests with a 3D elastoplastic static finite element analysis. In the analysis, the nonlinear behavior of ground and piles are described by the cyclic mobility model (Zhang et al., 2007) and the axial force dependent model (AFD model) proposed by Zhang and Kimura (2002) can take into consideration of axial-force dependency in the nonlinear moment–curvature relations. The applicability of the numerical analysis has been verified in previous works by comparing the numerical results with a real-scale field tests (Kosa et al., 1998). Based on the results from the numerical tests on seismic enhancement effect of group-pile foundation with ground improvement, an optimum pattern of partial ground improvement of an existing pile foundations has been picked out for shaking table test. A numerical analysis using the program DBLEAVES (Ye, 2007) is also conducted for the same optimum pattern for comparison purposes. The effectiveness of the partial ground improvement method has been proved by both the shaking table test and the numerical analysis. [Copyright &y& Elsevier]

Abstract: A comprehensive set of experimental data on Bangkok subsoils from oedometer and triaxial tests are analysed in this paper in order to determine the stiffness and strength parameters for Hardening Soil Model. The parameters determined are the Mohr–Coulomb effective stress strength parameters together with the stiffness parameters; tangent stiffness for primary oedometer loading, secant stiffness in undrained and drained triaxial tests, unloading/reloading stiffness and the power for stress level dependency of stiffness. The oedometer data are obtained from three different Bangkok soil layers: soft clay at 6–8m depths; medium clay at 12–14m depths; and stiff clay at 15.5–18m depths. The triaxial tests data are carried out for soft and stiff clays at depths of 5.5–6m and of 16–18m under both undrained and drained conditions, respectively. Finally, two sets of parameters for soft and stiff Bangkok clays are numerically calibrated against undrained and drained triaxial results using PLAXIS finite element software. [Copyright &y& Elsevier]