Soils excavated in construction works often contain non-anthropogenic heavy metals and metalloids due to their geologic histories. Evaluation of their leaching behaviors is essential to predict the groundwater contamination risk and achieve an effective remediation design when reusing such soils as construction materials. This paper addresses the leaching behaviors of arsenic (As) and other inorganic constituents contained in a marine sediment by employing two different-size column percolation tests (50 mm in diameter × 300 mm in height and 150 mm in diameter × 700 mm in height) with saturated/unsaturated flow conditions. Long-term leaching profiles were analyzed to assess the effects of both physical and chemical factors affecting the leaching behaviors such as pH, ORP, specimen size and flow conditions. At the middle of the unsaturated larger column, higher As leaching concentrations were observed even under neutral condition. However, As leaching was limited at the bottom, probably due to pH dependent leaching behavior and precipitation of As with co-precipitation of aluminum compounds. As a result, there was no significant difference in both As leaching amount and leaching processes obtained in two column percolation tests, particularly in the early stage of the tests.

Energy-Based Method (EBM) for liquefaction potential evaluation was previously proposed, wherein the total energy demand at a site is determined by upward wave energy. To make the most of the EBM already developed (the first stage evaluation), additional steps have been proposed to evaluate the liquefaction-induced strain and associated soil settlement using given earthquake wave energy by introducing a simple assumption that the wave energy is equally shared among the liquefied layers already selected in the first stage. By applying this to a uniform sand layer as well as case history sites, it has been found that the two-stage evaluation tends to calculate much higher liquefaction-induced strains than 7.5% in a smaller number of layers than the first stage. Furthermore, soil subsidence at the case history site has been calculated using a robust correlation of volumetric strain versus shear strain based on database of various intact soils. The ground surface subsidence thus calculated is found to be agreeable with post-earthquake observation at the same site. Thus, the newly developed two-stage EBM of liquefaction evaluation can predict not only the possibility of liquefaction but also the maximum induced strain in individual liquefied layers, and associated surface settlement without resorting to complicated nonlinear effective stress dynamic response analyses.

Due to a lowering of water table and a man-made fill with urban development, subsidence of soft clayey ground occurs in Taira, Iwaki City, Fukushima Prefecture, Japan. Subsidence also occurred in the area as a result of the 2011 Tohoku earthquake that occurred off the Pacific Coast. In this study, the change in the subsidence was measured by leveling, and it was revealed that 8 cm of subsidence occurred for two years after the earthquake struck, and subsequently, a little less than 1 cm of subsidence per year continues to occur. From the geotechnical investigation and laboratory tests conducted at this site, it was found that the subsidence occurred on a normally consolidated slit layer. Furthermore, undrained cyclic shear tests were performed for clay blending specimens, and reconsolidation tests were carried out following the shearing. It is concluded that the subsidence decreases with an increase in the overconsolidation ratio. Additionally, the subsidence increases with excess pore-water pressure ratio and shear strain amplitude.

Accelerated curing method is intended to determine if strength is gained in only 1 day for the laboratory mixing test, quality control, and work progress control. In this paper, a fundamental study was conducted on the accelerated curing method for kaolin and bentonite as the standard soil. After that, an experimental study was conducted to observe the strength development characteristics during improvement of the bottom sediments in the creek by accelerated curing method and normal curing method. From the fundamental study results with standard soils, it was found that a linear relationship is obtained between the unconfined compression strength from 1 day of accelerated curing method (q_u1) and 28 days of the normal curing method (q_u28). With the bottom sediments in the creek, q_u1 was observed to be lower than q_u28. In addition, the strength ratio (q_u28/q_u1) showed almost constant value regardless of the dosage of cementitious solidified material. However, there was a difference depending on the type of cementitious solidified material and the water cement ratio. These results show that the accelerated curing method is useful for presuming q_u28.

The authors have newly developed a geosynthetic system for surface soil stabilization, called “the Lattice-Frame-Reinforced (LFR) sheet”. The LFR sheet combines a geotextile and a lattice frame which is composed of “geojacket” formed by filling mortar into fabric hose called “jacket”. This geosynthetic system was applied to a surface soil stabilization for lifting works with 90t crawler crane which were accompanied with the bridge pier reinforcement project. In this paper, the design procedure of this geosynthetic system and the application result, are described firstly. Secondary, the results of the back analyses which were conducted since the first prediction result showed large difference with in-situ measurement data, are mentioned. Finally, design chart of this geosynthetic system, composed by conducting 3-D deformation analyses with using the procedure which was proved by back analyses, are also described.

Unsupported excavation for a horseshoe shaped tunnel with 5.0m height was carried out in sedimentary soft rock under 45m depth, and the ground deformation during the excavation was measured by high resolution equipment installed prior to the construction work. In order to simulate the ground deformation, soft rock samples retrieved from the same site and tested at a laboratory. Three-dimensional elasto-plastic FEM analysis was carried out to investigate the observed behavior, where the soil parameter values were assigned based on the results from laboratory tests and in-situ measurements. The FEM analysis showed that the absolute value of settlement at the tunnel crown caused by the unsupported tunnel excavation was only slightly influenced by the ground strength parameters. The majority of the influence was due to the deformation modulus in the elastic region. The settlement characteristic may have been also affected by non-uniformity, the confining pressure and creep.

We have been developed the repairing method for the seismic reinforcement and the leakage control of a fill-type dam embankment using the cement-mixed muddy soil. The needle penetration test (NPT) attached with a sewing needle of 0.84mm in diameter as standard equipment was applied to evaluate the strength of the cement-mixed muddy soil. However, the accuracy to estimate the strength of the cement-mixed muddy soil in NPT is not satisfactory causing that the strength level in cement-mixed soil which become the purpose of in this study is lower than the strength levels of cement-mixed soil in the ordinary soil improvement method and soft rock. Therefore, we investigated the applicability of the new-type NPT that replaced the sewing needle with the cone-shaped needle increasing the diameter to estimate the strength of the cement-mixed soil by laboratory testing program. The test results show the followings. The penetration resistance of a cement-mixed soil sample by the new-type NPT using the large-sized diameter needle is increasing in proportion to the side surface of needle into the sample in the second order curve. The unconfined compressive strength can be evaluated by the relationship between penetration resistance and the amount penetration by considering the needle penetration gradient.

The Japanese Geotechnical Society, has been continuously carrying out proficiency tests related to geomaterial tests. In this report, based on the proficiency test reports from 2012-2017, and the results of the questionnaire undertaken in accordance with this, we summarized the accuracy and dispersion in the geomaterial test, and the actual state of its execution. As a result, it was confirmed that 1) the number of test centers participating in the proficiency test transitioned between 50-70 test centers, and the number of participations from government and private research and test centers showed an upward trend, that 2) the check on purchase of test equipment, and execution rate of pre-usage inspections and calibrations / periodic inspections showed an improvement, whereas in regard to some of the test equipment, the calibration / periodic inspection execution rate was particularly low, and that 3) the test standards compliance rate generally showed an upward trend, whereas for some of the test standards, the compliance rate was below 30%.

Using the Geographic Information System, the earthquake damage information such as building damage, ground deformation, and sand boil was traced from the “Niigata Earthquake Ground Disaster Map”, and the area and length of each damage were extracted for each 50 m mesh section. Based on the amount of damage, we compared the damage occurrence rate and the damage scale of each mesh for some topographic conditions. As a result, the sand dune land basically had a low damage rate, but there was a large ground damage in the lowland area of the coastal dune. Earthquake damage occurred in whole area of reclaimed land belong in old river channel and that damage scale was considerably large, but the artificial ground between old sand dunes in the southern area had only little damage. In the hinterland and the natural levee area in the former river channel area of the early Edo period, the damage level was the same as the reclaimed land, while the most area originated from land area tended to have a little damage.