Anchored gabion reinforced soil wall is considered to be more structurally stable than steel-frame-faced reinforced soil wall. In previous studies, apparent cohesive strengths of earth-retaining structures with horizontal reinforcement as well as soilbags which have similar reinforcement effects as gabions were evaluated. However, the effect of the different type of wall facing has not been fully estimated. A series of multi-stage loading tests were done on earth-retaining structure with anchored gabion-faced structure and steel-frame-faced structure. As a result of the tests, it was confirmed that the anchored gabion-faced structure recorded higher performance to withstand horizontal load exerted by the earth pressure. Moreover, the amount of contribution given by the anchored gabion-faced structure to the apparent cohesive strength was evaluated by Mohr-Coulomb failure criterion. When FEM analysis was conducted, it was concluded that further investigation on analytical parameters are needed to accurately replicate the test results.
It is important to examine the frictional resistance between a reinforcement and backfill soil used for steel strips-reinforced soil walls, because it is one of the main parameters regulating the wall design. The fine content of soil has generally been evaluated to determine availability of backfill soil. However, it has not been possible to evaluate the actual frictional characteristic of reinforced soil walls with different backfill soil materials on each construction site. In this study, we developed a small and simplified pull-out test apparatus that can be used to evaluate the friction characteristic of steel strips-reinforced soil walls for the use of construction site. We also confirmed the reliability of our developed testing as compared with the field pull-out tests. Furthermore, we propose a method for evaluating the friction characteristics of backfill materials on site before construction, in order to ensure required quality.
Evaluation method of the montmorillonite content of the bentonite was investigated based on methylene blue (MB) adsorption tests. The accuracy of simple MB adsorption test, so-called the spot method, was investigated by a blind-prediction test using montomorillonite-sand mixtures. As results, the standard error of the spot method was within 2 mmol/100g when same experimental tools were used. Furthermore, the amount of MB adsorbed obtained by the spot method was corresponding to the saturated amount of MB adsorbed obtained by the spectrometry method, which is a precise measurement method. These results suggest that the saturated amount of MB adsorbed can be determined by the spot method. The saturated amount of MB adsorbed on the collected montmorillonite of Ca-type bentonite, the particle diameter under 0.2 μm, was determined as 150.5 – 151.2 mmol/100g. The montmorillonite content of the bentonite was 75.7 – 76.7 %. This was different from the calculated value using 140 mmol/100g as the saturated amount of MB adsorbed on pure montmorillonite, which was commonly used for evaluating the montmorillonite content in many previous studies. These results imply that it is necessary to use the saturated amount of MB adsorbed on the montmorillonite collected from each bentonites in order to accurately evaluate the montmorillonite content for estimation of the permeability and swelling pressure of the bentonite.
Road embankments where the embankment material has become highly hydrated, caused by ground water and the like flowing in, may become unstable by rainfall or earthquakes. In general, such embankments are reinforced by constructing the highly permeable basket-crib works at the toe of slope and placing pipes to drain the seepage water from the embankment. But since ground water distributions inside embankments are generally complicated, drainage pipes may not be placed appropriately along water channels and may not drain the water sufficiently. This paper describes our verification of the effects of the measure to drain seepage water by building a crushed-stone ground improvement body in the embankment and connecting it with drainage pipes. The paper also presents an analysis of water-level changes at application site was constructed and gives points to note when applying the work method at the site.
The authors have tried to estimate the seepage analysis models based on field measurement data of volumetric water content using the merging particle filter which is one of the data assimilation methods. In the previous studies, one-dimensional seepage analysis models were assumed, and unsaturated seepage behaviors were simulated by setting the free drainage boundary condition at the bottom of the one-dimensional models. However, in the case of heavy rain, because of the observation rising groundwater level at a field slope, the simulation setting the free drainage boundary condition could not reproduce the field measurement data. In this study, the authors proposed a new method estimating the seepage analysis model including the boundary condition at the bottom of the one-dimensional model using merging particle filter, and the applicability of the proposed method was verified. As a result, the estimated seepage analysis model by data assimilation could reproduce the measurement data of not only numerical experiments but also field slope. Therefore, the availability of the proposed method simulating from the unsaturated condition to the saturated condition was verified.
In this paper, in order to clarify the mechanical characteristics of “Tataki”, or artificial stone, made from waste of the siliceous tuff, a series of laboratory tests are carried out. The experiments involve unconfined compression test, bending test and needle penetration test. From the experimental results, the in-situ applicability of Tataki as geomaterials or civil engineering materials is discussed. The following conclusions are obtained from the present study: (1) Unconfined compressive strength of Tataki made from waste of siliceous tuff increases remarkably by extending the curing period. Also the higher the density of Tataki is, the higher strength development effect of that is due to pozzolanic reaction. (2) Unconfined compressive strength of Tataki can be estimated by two parameters of dried density and curing period. (3) By compacting Tataki densely, the stiffness of Tataki becomes higher. (4) Sandy soil is unsuitable for base material of Tataki. (5) Even though the flexural strength of Tataki is not as high as that of mortar, its strength increases remarkably by extending the curing period. (6) Higher the density of Tataki is, its durability is high against repeated action of freezing, drying and soaking.
As has been reported since old times, a berm ditch installed in a cut slope in a snowy cold region is deformed due to frost heaving. The purpose of this research is to elucidate the rotating mechanism of the berm ditch by frost heaving. We constructed a 1/10 scale model of an actual berm to conduct an indoor model experiment for reproducing the frost heaving, thawing, and settlement behavior of a berm ditch. Meanwhile, we used a U-shaped ditch installed in the berm of a road slope in service and conducted onsite measurements of the temperatures and displacements of the ground around the ditch. The results show that the berm ditch moves up due to adfreeze and frost heave occurring in the extreme surface layer of the flat part of the berm and turns to the mountain side due to nonuniform frost heave occurring in the transverse direction. In addition, results of a simple water transmission test confirm that the water transmission performance of the berm ditch three years after the installation was significantly degraded by accumulation of sediment and fallen leaves, which had been promoted by the step of the joint caused by the rotation.
Regarding embankment collapses due to earthquakes, there are various shapes. Therefore, it is essential to predict failure patterns of the embankment collapses to determine effective countermeasures. In addition, a result of prediction of failure patterns of the embankment collapses is applicable to a risk evaluation model, which determines priorities and countermeasure methods of disaster prevention for existing railway embankments. Accordingly, we analyzed using Hayashi’s quantification methods to previous data of the railway embankment collapses due to earthquakes, and developed a method capable of predicting failure patterns of the embankment collapses from various embankment conditions.
The purpose of this paper is to develop a new earth reinforcement technology called “The SDPR method” having both functions of a single earth reinforcement to increase the embankment strength and a drainage pipe to lower a ground water level in embankment at the same time. This paper summarizes the effectiveness of the SDPR method by means of unsaturated-saturated seepage analysis and slope stability analysis in terms of the drainage effect, reinforcement effect and unsaturation effect of SDPRs. The main conclusions are as follows: 1) SDPR is effective for improving the stability of embankment and particular recovering the safety factor just after rainfall. 2) From saturated-unsaturated seepage analysis, it is confirmed that the soil layer near SDPR becomes unsaturated condition and SDPR is also effective for lowering the groundwater level of the slope of embankment especially for the shallow area above the position of SDPRs. 3) Under current numerical conditions, it is proposed that the appropriate length of SDPR is 6m to 9m while the appropriate interval is 3m to 5m depending on the magnitude of rainfall and earthquake.