A study was conducted on a method of increasing the horizontal resistance and improving the seismic performance of pile foundation by conducting ground improvement mainly by means of the consolidation method around piles in peaty soft ground. However, internal and external stability is a technical concern regarding this method, as it is necessary to ensure the performance requirements for pile foundation and evaluate the soundness of solidified improved columns. Therefore, the mechanical behavior and critical state of the pile foundation were verified by means of a full-scale experiment by changing the specifications of solidified improved columns and re-examining the specifications using non-linear finite element analysis. As a result, in order to establish a pile design method for composite ground it was confirmed necessary to set the depth of solidified improved columns based on the characteristic length of piles 1/β, and the improvement strength to within the standard values required on an engineering basis. In addition, verification of horizontal subgrade reaction at normal times and setting of a reduced permissible horizontal displacement during earthquakes were confirmed to be necessary as verification indexes to ensure the soundness of solidified improved columns and simultaneously adapt the pile design method.
Embankment including precast arch culverts is generally thought to give non-uniform load distribution to ground due to the void space of precast arch culverts. So when such a structure is constructed on soft ground, various subsidences on soft ground and remarkable bending moments in the arch culvert will be observed. Therfore, it is necessary that the soft soil in which such structures are founded be stabilized to improve the overall stability of the structure. In this study, centrifuge model test and its numerical analysis were carried out, and the stability of the embankment set up on soft ground is evaluated. Based on the analytical results, it is confirmed that soil stabilization greatly contributes to the stability of the multi units arch culverts embankment.
We propose a novel discrete crack propagation analysis method for clastic sedimentary rocks. In this method, the structures of the rocks are assumed as various kinds of polygons, and the cracks occur at the interface of each polygon. This method is constructed by both the Enriched free mesh method (EFMM) and the Multi-dimensional moving least squares method with constraint condition (C-MultiMLSM). In the proposed approach the EFMM provides high accuracy stress distributions in continuous area, and the C-MultiMLSM provides high accurate interpolation in discontinuous area. The feature of this method is that we can carry out robustness simulations for the brittle materials with pre-existing cracks in elasticity and fractured condition. In this paper, the accuracy of proposed method in elastic condition and fractured condition is verified. Furthermore, we discuss the fracture diversity in fractured rocks as one of applications of the proposed method.
These days, slope disasters occur due to unexpected heavy rains. Expressways that play an important role as a main lifeline for emergency basis should be protected from the disasters. The purpose of this project is to develop multipoint monitoring system for the slope disaster prevention using wireless sensor network. It is the future that the system can perform not only disaster detection but also hazard assessment by three steps, that is "safe", "caution necessary" and "dangerous". In addition, long-term operation without battery exchange is possible and there is no limitation of a slope size for the monitoring. Here we focus on the evaluation of wireless communication performance of the wireless sensor network called mesh-network by primary experiments and demonstration experiments on the slopes. It is confirmed that time required for constructing the network is sharply shortened when two or more sensor nodes can communicate with the base-station. Battery life can maintain for three years by using the developed battery pack. The visibilities among the sensor nodes strongly affect the data recovery rate compared with the effect of the distance among the sensor nodes. To solve the problem, the communication cost can save by installing relay nodes among the sensor nodes. On the other hand, when the visibility between sensor nodes is high, not less than 100m communication distance is possible, and the data recovery rate of 90% is realized. The tolerance to a data deficit rate is dependent on a slope condition and policy of the road administrator. Therefore, the design of the optimal mesh network system in each slope is a future subject.
Drinking water sludge discharged during water purification contains a lot of organic matter. The generation process of drinking water sludge is quite different from that of general soils, so the influence of organic matter decomposition on the engineering properties is not interpreted enough. Therefore, it is important to investigate the decomposition characteristics of organic matter of drinking water sludge, and to discuss the relation between the organic matter decomposition and shear strength. First, this study isolated fulvic acid and humic acid, and observed the organic matter decomposition and soil respirations. The humic acid content of drinking water sludge was relatively high, and 44% of humic acid was decomposed during 6 month in aerobic condition. Second, triaxial compression tests were executed using the sludge that organic matter has been decomposed by hydroperoxide solutions. Approximately 1.38% of organic matter decomposition showed decrease in the internal friction angle from 39.7°-40.4° to around 37.9°.
A series of undrained cyclic triaxial tests was performed on reconstituted decomposed granite soil Masado sampled from two sites. The liquefaction strengths of these Masado were almost constant when the relative density was less than 80% and they increased markedly when the relative density exceeded 100%. This was believed to be due to the fact that the relative densities were calculated based on conventional minimum and maximum density tests specified for clean dry sands whereas Masado contains non-plastic fines and volume reduction occurred during saturation. In the present study, minimum and maximum density tests were carried out using wet samples and the results were used to re-define the new relative density of the material. The relationship between liquefaction strength and the re-defined new relative density showed good correlation, with Masado showing similar trend in behavior with relative density as Toyoura sand. With the proposed method of using a re-defined relative density, a better understanding of the relation between liquefaction strength and relative density of decomposed granite soil containing fines was obtained.
Initial shear stress induced by nearby slopes, embankments and structures causes shear deformation in the ground, leading to sliding, tilting and uneven settlement of the structures due to liquefaction. In this study, a hollow torsional shear apparatus is used to study the effect of initial shear stress acting either on horizontal plane (θ0=0) or on inclined plane (θ0=45) on liquefaction behavior of medium to loose sand of relative density Dr≒30, 50% and fines content Fc=0 - 30%. A series of test results have revealed that the liquefaction failure is categorized into four types; Cyclic Failure for α=0, Cyclic Biased Failre for small α (θ0=0), Biased Gradual Failure and Biased Sudden Failure both for larger α. Among the 4 failure types, it is important to pay special attention to BSF type, which may develop abrupt strain increase due to initial stress in the process of pore-pressure build-up by cyclic loading. In comparing with undrained monotonic loading tests, the mechanism how the abrupt BSF type failure differs from the gradual BGF type failure has been clarified, in view of the difference in volume contractility of loose sand containing NP fines under initial shear stress.
A series of dynamic deformation tests was performed on tire chips and their mixtures with sand with various proportion of tire chips by hollow cylindrical torsional shear testing apparatus. The shear stiffness of the sand specimen decreased drastically by mixing with the tire chips. However, the degradation of the stiffness dependent on magnitude of shear strain did not appear up to large strain level reflecting the elastic characteristics of the tire chips. Based on the findings, the seismic response analyses were carried out on the mixtures and alternating layers of sand and tire chips. Both the equivalent linear response analysis 'SHAKE' and the on-line pseudo-dynamic response analysis were performed aimed at clarifying the earthquake response characteristics of tire chips and tire chips-sand mixtures. The analyses results confirmed the quake-absorbing excess pore water pressure control and seismic isolation effects of tire chips as a geomaterial.
Bentonite-based buffer materials for high-level radioactive waste (HLW) disposal are expected to fill up the space between buffer and a wall of the disposal pit, and/or between buffer and an waste-container called as overpack by its swelling deformation. That is called as self-sealing ability. This study performs the model tests simulated the relationship between buffer and space mentioned above. It also investigates the validity of the theoretical equations for evaluating the swelling characteristics of bentonite-based buffer and backfill material, which were proposed in Komine and Ogata (2003, 2004), by comparing the calculations and the experimental results.
A simple soil layer system which is composed of a finer soil layer underlain by a coarser soil layer provides an excellent property of capillary barrier. In order to realize the best performance of the capillary barrier function effectively, it is necessary to make larger the gap of particle diameter of sand and gravel material. The functional deterioration of capillary barriers in service for dozens of years is of concern because of the transport of sand particles to the lower gravel layer due to an earthquake et al. The authors found that using crushed shells instead of gravel in the lower layer greatly helps reduce the infiltration of sand particles into the lower layer as well as provides the function of capillary barriers. In this study, the diversion lengths are measured in the laboratory soil box tests using crushed shells instead of gravel in the lower layer, and compared well with the estimations calculated by the theoretical equation proposed by Steenhuis, et al. In addition, we compared it with the diversion lengths are measured in the laboratory soil box tests using a sand layer underlain by a gravel layer by Morii, et al. As the result, the authors make clear the applicability of the theoretical equation proposed by Steenhuis, et al.
Estimating the rockfall risk degree of boulders on slope has been intensively challenged by the agencies and business owners, such as railway companies. In the current practice, some experiential methods based on the statistical analysis of the past rockfall incidents are widely used, since the outbreak mechanism of rockfall is still not fully understood. In this study, an estimation method of the risk assessment for the boulder-type rockfall is proposed in order to meet the railway companies' needs for evaluating the rockfall risk in an objective/quantitative manner. The proposed method will enable us to reveal the in-soil penetration depth of the boulder on slope by vibration measurement and calculate the dynamic stability directly. By applying the proposed method to the field slope along the railway, the validity of this method has been confirmed.
Unsaturated triaxial tests of disturbed and undisturbed loam were carried out to reveal pore size changes that occur with volume changes using water retention properties, with simple shearing processes, under undrained and drained conditions. Initial matric suction was set as 0, 50, or 90 kPa. The confining pressure (net normal stress) was set as 100 kPa. This paper describes a method for estimating the pore size distribution using a capillary tube model of water retention curves obtained from triaxial tests. Results clarified a relation between the void ratio and pore size change ratio for each triaxial test condition. Furthermore, based on those results, we investigated the relation between soil structure and suction effects, which influence volume change properties.
According to the technical guide for grouting method for dam construction in Japan modified in the year 2003, one of the key issues for grouting is quality assurance and effectiveness by minimizing the amount of injected grout. Hence, the grouting management support system was newly developed by combining joint density diagram and geostatistical simulations. In this system, the joint density diagram was used to determine most effective direction for the grout injection boreholes and the hydraulic conductivity fields before/after grout injection were estimated by geostatistical simulations. In this paper, the newly developed system was introduced and applied to the actual dam construction site.