Three-hinge precast arch culvert is a flexible structure due to hinge functions in the main body and is based on the different design concept of conventional culverts. Therefore, the conventional design method which does not consider the earthquake behavior cannot be applied. So far, the authors had conducted large-scale shaking table tests targeted for the culvert of 1/5 scales to confirm the damage morphology by using a strong earthquake response simulator. In this study, two types of analyses, dynamic analysis and static analysis, for the shaking table test were carried out to investigate the numerical analytical approach relating to aseismic design of the culvert. From results, the static analysis would be an effective aseismic design method because the analysis reproduced the damage progression of the culvert.
An alternative three-dimensional lattice spring numerical model, in which matter is discretised into a system of mass points, is developed for the study of rock-like materials. The model includes a normal spring and a shear spring for each pair of lattice points. The deformation of the shear spring is evaluated by using the local strain. In this method, to obtain the local strain, the rotation-related term in the relative displacement vector is calculated by the Euler equation for the rotation of imaginal rigid sphere. Relationships between the stiffness of the springs and the macro material elastic constants of the matter, e.g. the Young modulus and the Poisson's ration, are derived. The explicit-finite difference scheme is adopted to solve the system of equation of motion. Numerical examples are presented to show the abilities and properties of this method in modeling for simulation of deformation and failure of rocks and concrete.
In this study, investigations were carried out on soft rock slopes with the aim of evaluating the stability of slopes, including post-earthquake residual displacement. First, the strength and deformation characteristics of the post-peak process were determined through triaxial tests in order to consider the effect of failure of soft rock masses in the modeling of the time history response analysis. Furthermore, for the evaluation of the amount of post-earthquake residual displacement of the soft rock slopes, the dynamic centrifugal model test and time history response analysis were carried out. As a result, the residual displacement of the analysis nearly matched that of the model test.
Slope stability problem is one of the classical problems, while it is still in research and development to reveal complex dynamic response characteristic and failure behavior. Especially, it is difficult to estimate the stability of natural slope due to complex geology, strata, geotechnical property with large variability. In this research, two large slope models were constructed and a series of shaking table tests was carried out to reveal the dynamic response characteristic and failure behavior of natural slopes using a large shaking table. As a result, the dynamic response of the slope model was changed due to phase difference between the horizontal and vertical accelerations. Moreover, generation of a slip surface in the slope could be successfully measured so that the failure behavior of the slope model was clearly shown.
The Press-in Method is a piling technique where a static jacking force is used to install a prefabricated pile. It offers a wall of piles efficiently, as the press-in machine gains a reaction force form the previously installed piles. The structures constituted by the wall of piles are named as Implant Structures by the authors, exemplified by self-retaining walls, coastal levees and cell foundations, where appropriate embedment depths are assured to resist to the external loads on themselves. The performance of two types of these structures - the self-retaining wall with inclination and the novel type of self-retaining wall intended to reduce the deformation during its service period - have been investigated through model tests and field tests, which is reported in this paper. The latter self-retaining wall is the structure constructed by applying a horizontal load on its head after excavation, and was confirmed to be effective in reducing the deformation of the wall due to the backside surcharge. Finally, methods to estimate the deformation of the wall due to the excavation, the horizontal load and the backside surcharge are discussed.
The objective of the paper is to make the strengthening effect and the collapse mechanism in the slope reinforced with anchor works clear. Response characteristics of the slope model were analized based on the results obtained by the shaking table tests under 1G field for the slope models reinforced by anchor works. Furthermore, the effect was verified by using MPM which is possible to evaluate the behavior from large deformation to collapse. Among the slope models which carried out the shaking table tests, the slope models for not only small scale but also medium scale were used. It is found that the collapse of the reinforced slope model is caused by the following process. First of all, the static tensile force of anchor decreased after the weak layer became soft by the nonlinear behavior of the soil . Then the dynamic response of tensile force became larger due to the rise of vibration in the ground over the weak layer. Finally the tensile force of the anchor reached to the failure strength. Based on MPM analysis, it is found that the tightening effect is lager as the strengthening effect of anchor work, and that the collapse behavior is possible to reappear.
Because the present rainfall traffic regulation standard of expressways against rainfall-induced surface failure does not consider rainwater infiltration and deformation of a slope, appropriate decisions for road closure and its deregulation are sometimes difficult. To propose a new index aimed at the advancement of the present rainfall regulation standard, laboratory scale experiments as a fundamental study are conducted. Through a preliminary experiment, a possible mechanism of water infiltration and slope deformation was identified. According to this, slope deformation starts when the volumetric water content exceeds a quasi-saturation state, which is not a fully saturated state but a saturated state with entrapped air. After implementing laboratory experiments to confirm repeatability of the quasi-saturation phenomenon, two phenomena were confirmed. One is the repeatability of the quasi-saturation state in these model slope experiments. The other is that a process from a quasi-saturation state to slope failure is manifested in order of the quasi-saturation state, the saturation state, and the slope failure. When the relation between the variation of volumetric water content and the deformation was evaluated using an image sensing technology called template matching, it was confirmed that the slope displacement begins to extend after the volumetric water content exceeds the quasi-saturation state. The volumetric water content increases after the quasi-saturation state is exceeded because the increase in soil porosity due to variations in soil structure caused by seepage force. This indicates that there is no deformation when the volumetric water content does not exceed the quasi-saturation state. In addition, the quasi-saturation state is a possible index for predicting rainfall-induced surface failure. However, to apply real slope monitoring for practical use along expressways, additional laboratory scale experiments utilizing medium and large-scale slope models are required, in addition to the continuation of the on-site slope monitoring test.
This paper focused on inducement of landslide and performed two types of stress control tests by reducing normal stress (effective mean stress) under controlling shear stress constant in both triaxial compression and ring shear tests to simulate landslide behavior. In both tests, yield and failure stresses were properly obtained as a threshold of displacement generation and a breaking point. As a result, the thresholds of displacement generation were especially shown to be expressed by the strength line described by the shear resistance angle of cohesive soil. In case of incipient sliding type landslide, the threshold of displacement generation was shown to be indicated by the peak strength line determined by displacement control ring shear test. On the other hand, it was described by the residual strength line in case of re-sliding type landslide. The shear resistance angle that represents the threshold of displacement generation revealed the shearing history of cohesive soil. In re-sliding type landslides, the displacement of landslide is repeatedly proceeded, but it is generally limited. The design work of landslide with use of strength constants was newly interpreted as aiming at the threshold for displacement increase in landslide. In re-sliding type stress control test, displacement behavior was found to be brittle different from that of incipient sliding type landslide. Since consolidation effect in re-sliding type landslide seems great, the effect of consolidation on yield stresses was systematically investigated by both stress control and displacement control tests. The yield stress clearly increased with overconsolidation ratio and was consistent in both tests.
It has been reported that tsunami deposits generated by the Great East Japan Earthquake are causing soil contamination. Unsaturated seepage flow in contaminated soil can cause groundwater contamination. Unsaturated hydraulic conductivity is an important indicator that can be used to predict groundwater contamination. This paper proposes an in-situ unsaturated permeability test method. The proposed method makes it possible to estimate the unsaturation characteristic parameters and saturated hydraulic conductivity in the van Genuchten equation through simple measurements. In the proposed test method, the volumetric water content of the soil is measured by infiltrating water from the ground surface, and the water pressure can be changed arbitrarily. Since the water pressure can be set at up to 100 kPa, efficient testing of low-permeability ground is possible. By increasing water pressure incrementally, unsaturation characteristic parameters can be estimated with higher accuracy. These parameters can also be estimated easily by measuring the initial suction and volumetric water content of the soil because parameter n in the van Genuchten equation represents the curvature of the unsaturated characteristic curve and parameter α represents a point of inflection of the curve. Measurement by this test method, however, is difficult if the volumetric water content of the soil being measured is close to that of saturated soil.