Accurate and continuous data accumulation of deformation measurement of dam body is important for proper dam safety management. Regarding the improvement of the accuracy of rock-fill dam deformation survey, there are problems that the measurement frequency is low and the accuracy may be affected by slight differences in measurement techniques and by observer. In recent years, Global Positioning System (GPS) measurement system which enables us to measure the exterior deformation of rock-fill dam bodies continuously, accurately and three-dimensionally have been developed. The authors, based on the approximate expressions corresponding to the long-term settlement of the embankment, have proposed approximate expressions of horizontal displacement by using the GPS measurement data in Agigawa Dam. As a result, predicted deformation by using the approximate expressions well matched to the value measured by GPS measurement system. Based on the research results in Agigawa dam, it is possible to monitor other dams by proposing approximate expressions using the same method that utilizes the features of the GPS of high precision and continuous observation data.
Based on the existing cascading experiment of collapsed soil using large scale slope model, characteristics of flow behavior was analyzed as well as that of impulsive behavior. Moreover, applicability of particle method (MPM) to evaluate impulsive action was conducted a study as well as the method to evaluate fluid force. As soil model, sandy soil and crushed stone were used. As a result, it is found that difference of flow behavior according to soil properties is caused by the difference of flow behavior such as either sliding or rolling depending on friction coefficient and inclination of slope, and that the analysis using MPM can reproduce flow behavior, sedimentation behavior and the impulsive action well by setting the realistic value based on the material tests resulting as an analysis parameter, and that the method to evaluate impulsive load by the fluid force might become the evaluation of the dangerous side depending on soil properties.
Vibration caused by trains traveling on viaduct propagates to the ground and this vibration sometimes give rise to vibration problems against people who live near the route. Especially, for speeding up of the Shinkansen, elucidation of this kind of wave propagation and countermeasures to damp the vibration become urgent matters. Vibration-isolating wall set in the ground is one of well-known countermeasures. Although studies through theory, experiments and analyses have been carried out, unified opinions for design have not been obtained yet. Therefore, model tests were conducted to confirm the effect of the vibration-isolating wall and to examine plane distribution of the vibration. The method of the model test and results obtained are reported in the paper. The effectiveness of the rigid vibration-isolating wall according to distance between the exciter and the edge of the wall was confirmed from the experiment. As a result, the effective length of the vibration-isolating wall to reduce the ground vibration are demonstrated.
Landslide disasters have occurred frequently due to heavy rain in the last decade. Some disasters at road embankments were considered to occur due to the inflow of groundwater connected through fault zones. This study verified the effectiveness of a groundwater-drainage facility for road embankments, and measured the groundwater flow entering through fault zones. An in-situ investigation was carried out at a highway embankment which collapsed in 2007, to measure the surface water and groundwater flows. It was found that a stone filled net (gabion) placed at the toe of the slope has a higher drain capacity for more intense rain. Also, the collected data indicated credible inflow of groundwater through a fault zone from the adjacent basin. The inflow amount was calculated as a percentage of groundwater flow without inflow. In the calculation, it was effective way to suppose whether the adjacent basin was connected by the fault zone or not. Design of a drainage countermeasure and maintenance technique for inflow of groundwater were also described in detail.
In this study, the effect of curing on the strength characteristics of PS ash-based improved soil was examined together with the mechanism inducing the effect. As a result, it was found that the liquid index of improved soil decreases with curing time so that the soil become hardened, despite the fact the water absorption performance of the PS ash-based improving material does not change over time. It was also found that the cone index gradually increases with time and it has a unique relationship with the liquid index. On the other hand, it was observed that the component composition of PS ash-based improving material was qualitatively similar to that of ordinary Portland cement. Then the formation of ettringite in the improved soil along with curing was confirmed by XRD analysis. Increase of constrained water due to the ettringite formation is considered to be a factor of the change in properties of the improved soil. The time-dependent change of constrained water was calculated based on water contents obtained under 40 degree-heating temperatures. It was found that the change of constrained water has a good correlation with the change in the liquidity index. Furthermore, the cone index of the improved soil can be predicted based on the constrained water.
In order to clarify the behavior of the occurrence of nonuniform settlement caused by liquefaction, the surface wave explorer method and 2-dimensional effective stress were performed, aimed to the field damaged in the 2011 off the Pacific coast of Tohoku earthquake. First, the surface wave explorer method was applied to several sections which shows different degree of damages. These results showed that the thickness and the resistance of liquefiable layer were largely different at each part and had some relationship with the degree of settlement. Furthermore, 2-dimensional effective stress analyses were carried out by used of the ground model with consideration of the result of the investigation. The simulated results verified that the nonuniform settlement was caused by the special distribution of the thickness and the resistance of liquefiable layer. Moreover, the possibility of the use of surface wave explorer method for prediction of liquefaction was confirmed.
Buried pipes have been damaged due to soil liquefaction during past earthquakes. To estimate the mechanism of pipe uplift due to liquefaction, shaking model tests were conducted for pipes buried at a relatively shallow depth in loose clean sand. The effect of the apparent specific gravity of the pipe and upward seepage were studied in the tests. As the apparent specific gravity of the pipe decreased, the rising speed increased. The fluctuations in the pipe rising was within narrow limits, and was synchronized with the response of excess pore water pressure. It was concluded that dilatancy affects the uplift of buried pipe. When the estimated viscosity coefficient of the liquefied soil decreased due to upward seepage, the pipe rose 1.7 times faster. This test result contributes to our understanding of pipe uplift damage due to pore water pressure migration from the surrounding ground.
Since a major portion of ground anchors (hereinafter anchor) installed on slopes is embedded in the ground, it is difficult to directly check tension members. Although lift-off tests of anchors are generally carried out to confirm the residual tensile force, the load-displacement curve derived from the tests could be a clue to estimating the condition of the anchor. However, there are still many factors that need to be clarified; for instance, tensile load applied to anchors using hydraulic jacks show a different transmitting status depending on how the anchor body is fixed, and the shape of the graph is influenced by the method used to fix the anchor head. This study assesses the characteristics of the load-displacement curve by analyzing the results of lift-off tests using a full-size test anchor.
Tumulus mounds have been damaged by natural processes and human actions. Earthquakes particularly give serious damage such as failures in tumulus mounds and rock falls in burial chambers. In the present study, seismic behavior and damage mechanism of tumulus mounds are studied by centrifugal model test and numerical analysis. Dynamic tests were conducted on a 1/50 scale cross-section model of a tumulus mound. Cracks were observed in the surface of the crest and slope. The fracture modes of the stone chamber were controlled by the friction between resin boards that constitute the simulated stone chamber. The resin boards with smaller friction slid and the backfill fell. On the other hand, the burial chamber consisting of the resin boards with larger friction did not deform but cracks were observed extended from the corners of the burial chamber. Numerical analysis showed that the cracks are induced by tensile stress. It was also found that the friction between the chamber stones do not affect the stress distribution in the mound but the friction plays an important role in controlling the failure of the backfill and protecting the stone chamber.
The relationship between the work period and the cost of construction to remediate soft ground generally involves a tradeoff between the two. Curbing the costs of peaty ground consolidation, which is work that is done in a relatively short period, is a technical challenge. To clarify the effectiveness of low-improvement-rate soil improvement combined with gravel foundation reinforcement, which is a soft-ground improvement technique with excellent construction properties, the experimental construction of an embankment was done and long-term measurements were performed. This paper reports on the stability of this embankment and the soundness of the geotextile used in it. A parametric study, in which the improvement ratio, the embankment height and the tensile rigidity of geotextile were used as the parameters, was done by using the results of a reproduction based on two-dimensional elastic-plastic FEM analysis of the observation data of the experimental construction. This parametric study examined the effectiveness of the construction technique in controlling differential settlement. Based on the results of the above examination, a design method for implementing this construction technique was proposed.
In seepage flow analyses employing the finite element method, recharge or pumping wells are generally approximated by point sources, since the wells are extremely small compared to the analysis region or other subsurface structures. However, such wells, when modeled as point sources, often yield inaccurate results. The authors have developed a new well model using point sources that improves the solution accuracy. This well model calibrates the permeability of finite elements surrounding the point sources based on theoretical solutions. The performance of the well model has been presented by Code Verification via several numerical experiments in Verification and Validation (V&V) terms. This paper reports the experimental outcomes of spatial discretization error as Solution Verification on the present well model.