Based on a series of large scale shaking table model test, dynamic response and failure mechanism of steep slope reinforced with ground anchors are discussed in this paper. Shaking table model test with slope height of 2.6 m revealed that the tensile force of ground anchors increased during the displacement accumulation of the slope. It was also found from the model test that the staged loss of the tensile force of the anchors, which occurred after the tensile force reached to the ultimate value, resulted into the failure of the slope. Relevant deformation analyses using the Newmark method were also carried out so as to examine the applicability of the Newmark method for the displacement evaluation of the slope reinforced with the anchors subjected to large seismic load. Evaluated displacement was much smaller than the model test result possibly because the staged increase and loss of the tensile force of the anchors were not considered in the current simulation.
The purpose of this study is to develop a new earth reinforcement technology using spiral bladed drain pipes called “SDPR method”, which has both functions of an earth reinforcement to increase a pulling resistance with the spiral shape blades and a drainage pipe to lower a ground water level in the embankment. This paper summarizes the field test results of pull-out test and the observation of water retention characteristics for the expressway embankment with SDPRs. The pull-out test confirms that the friction resistance between the single SDPR and ground can be provided for the stability design of the embankment with SDPRs. The field observation of suction and volumetric water content in the embankment with/without SDPRs confirms the effectiveness of the SDPR method about the drainage performance, lowering of the ground water level and the quick restoration of the suction.
Currently, at the calculation of the earth pressure in the design of the retaining wall, a formula based on the theory of Coulomb or Rankine assuming straight slip is used. However, there is a limit to the scope of application of Rankine's formula (formula assuming two straight slips.) at present. For example, in the case of calculating the earth pressure that is considering cohesion, Rankine's formula is applicable only to a case with a simple horizontal plane at the ground surface on the back of the retaining wall. In this paper, in order to solve this issue, a new earth pressure calculation method assuming straight slip by drawing method is proposed, which is a different approach from the conventional method. Also, a new earth pressure calculation formula derived from this new method is proposed. In addition, in order to verify the validity of this proposed formula, the calculation results obtained according to conventional formula and Trial Wedge Method were compared with the results from this new formula.
In this study, the variation of stress-strain relationships of anisotropic tuff due to the condition of end restraint were investigated by consolidated drained triaxial compression test. For ordinary method of evaluating triaxial test results, the normal strains and the volumetric strains of specimens with the ratio of height to diameter, h / d = 2.0, was not influenced whether with or without sliding mechanism and Teflon sheets on the end of specimen, and Young's moduli and Poisson's ratio were not influenced by the end conditions. On the other hand, for evaluating strain tensor, shear strains were actually occurred and directions of principal strains were inclined due to end restraints. These phenomena indicated the possibility of inaccurate anisotropic stiffnesses obtained by the proposed method of determining anisotropic elastic properties by a single triaxial test.
Bentonite based buffer will change its condition from unsaturated state to saturation by groundwater seepage in high level radioactive waste disposal facility. This study has investigated water migration and swelling pressure characteristics in bentonite based buffer from unsaturated state to saturation from the viewpoint of material specifications such as kinds of bentonite and dry density. From the experimental results in this study, water migration behaviors in various powder bentonites as buffer have an analogy to water-diffusion from initial water content to around 90% saturation. Furthermore, the inflection points have appeared at around 90% saturation in the relationships between swelling-pressure and elapsed time. Therefore, the factor dominating water migration in buffer will change according to alternation of micro-structure in bentonite based buffers by swelling.
Pre-excavation grouting of shafts and galleries had been conducted during the construction of Mizunami Underground Research Laboratory in the aspect of reducing water inflow into shafts and galleries. After excavating GL. -500m gallery, a post-excavation grouting was performed on section of the pre-excavation grouting area under high water pressure condition (maximum water pressure: 4MPa). The post-excavation grouting experiment was performed outside of the pre-excavation grouting zone with designs, applying colloidal silica grouting material and complex dynamic grouting. It was estimated that the inflow after post-excavation grouting was reduced by 1/100 of the case that pre- and post-excavation grouting were not performed. In addition, a new theoretical formulation considering relationship between reduction of hydraulic conductivity and the grouting zone was derived. This paper states the theoretical evaluation is very convenient and useful for grouting design and estimate of water inflow on these results.
This paper shows the fundamental physico-chemical properties of base resin and reactant used for chemical grout. In this study, three types of grout materials including non-alkaline sodium silicate, activated colloidal silica and active composite silica were selected, and a plurality of experiments changing type of grout material, silica concentration and curing time were carried out to measure the volume shrinkage and the unconfined compression strength of plain gel and sand specimen improved by the grout. In conclusion, it was revealed that the volume shrinkage of plain grout gel depended on the type of grout material and the degree of silica concentration. Even though the volume shrinkage of plain grout gel occurred, it appeared that the unconfined compression strength of the sand specimen improved by the grout material did not deteriorate.
Concrete blocks are commonly installed at bend sections of buried pipe for resistance of thrust force. However, it is concerned that the stability of the concrete block might not be kept in the liquefied ground. In this study, new thrust protection method with gabion, made of geogrid and gravel is proposed to replace the concrete block method. The effect of the proposed method was evaluated by model tests which buried pipe model was loaded laterally in saturated ground model with controlled effective stress. As the results, the lateral displacement of the pipe model with gabion was nearly one-quarter of that of the buried pipe model without countermeasure. These test results showed the availability of new thrust protection method with gabion for resistance of thrust force.
Reinforced chain walls have two features that improve their seismic performance: (1) The chain has a larger pullout resistance than other reinforcing materials. (2) Combined resistance by friction of the chain and the end-bearing resistance of the anchor plate. While the pullout resistance of the chain-anchor plate assembly has been evaluated in previous studies, the seismic behavior of the reinforced chain wall as a whole is not well understood. In addition, due to the 2012 revision of the retaining wall guidelines, the theoretical design load acting on the reinforced earth walls during earthquakes has changed. In typical reinforced earth walls, seismic design is carried out with a reduced design seismic coefficient. In this study, dynamic centrifuge model tests of reinforced chain walls were conducted to evaluate the dynamic behavior and the applicability of the seismic design method. From the experimental results, it was confirmed that the reinforced chain wall has high earthquake resistance and can be designed using a reduced seismic design coefficient.