For in-situ containment, the conventional techniques such as soil-cement walls or steel sheet pile walls are utilized to vertical cut-off wall installed around contaminated sites or illegal waste dumping sites, to prevent contaminants transport to aquifer. However, when subsurface waste or special stratum exists at the place of soil-cement walls constructing, the quality of soil-cement for hydraulic barrier may not be provided. In such a case, the construction process of soil-cement wall is thought that the ground is excavated with casing tube (by all-casing method) in order to take out wastes and wrong soils, and after that, soil-cement placement and casing tube removal is carried out. Vertical cut-off wall with continuous overlapped soil-cement columns can be built by repeating this cycle. We investigated mixture proportion of soil-cement with high density, high liquidity and high quality for hydraulic barrier material of vertical cut-off wall. As a result, applying the high liquefied soil-cement technique which we developed in the past, high liquefied and no separation soil-cement based on sand and bentonite was realized, and high compressive strength excess 1N/mm2 and low hydraulic conductivity range from 10-8 to 10-9 cm/s were obtained.
Vertical cutoff walls using low-permeable materials are often constructed at contaminated sites to contain the contaminants and to prevent their migration in the aquifer. Although soil-bentonite cutoff walls can be expected not to lead shear failure even against ground motion due to its softness, cutoff walls are possible to be hydraulically damaged with slip failure or crack. In this study, laboratory-scale hydraulic conductivity tests were conducted with a flexible-wall permeameter, with emphasis on the self-sealing capability of soil-bentonite with hydraulic defects. In order to simulate cutoff walls with defects, specimens with a crack or hole were subjected to permeation. We found as a result that hydraulic conductivity values decreased with time due to the self-sealing capability of soil-bentonite regardless of CaCl2 concentration of base soil. After 4-day permeation, the average hydraulic conductivity of specimens with hydraulic defects was up to 2.2 times that without the defects, while leakage along the cracks were relatively higher with higher initial CaCl2 concentration of base soil. It can be assumed that the self-recovery of soil-bentonite in hydraulic conductivity can be attributed to both the re-swelling of bentonite to non-cations permeant and to shrinkage of crack face and hole due to the softness of soil-bentonite. Thus, even when hydraulic defects occur in cutoff walls, soil-bentonite can recover its hydraulic barrier performance within several times of original hydraulic conductivity with time.
Due to the 2011 off the Pacific Coast of Tohoku of March 11, 2011, a large scale tsunami hit the Pacific coast area of the Tohoku and North-Kanto Regions, Japan. As a result of the earthquake and subsequent tsunami, approximately 900,000 tons of the tsunami-related deposits were left in the flooded area in Kesennuma city, Miyagi Prefecture. Since they were expected to be certainly recycled as embankment or backfilling materials in the prospective restoration and reconstruction works, proper treatment and management were essentially required for the tsunami-related deposits. Additionally, rapid completion of the treatment project was also important for the local residents to preserve living environment and improving public health. Thorough our laboratory experiments and a field demonstration to select soil modification materials for the tsunami-related deposits, both gypsum-based and lime-based materials were effectively accelerating dry sieving process. A part of the tsunami-related deposits contained naturally occurring heavy metals and required an additional treatment for immobilization. Elution concentration of arsenic and fluorine could be controlled stably below their criteria by using magnesia-based material. This paper summarizes the outline of the treatment of tsunami-related deposits and describes the geotechnical properties of recycled geomaterials in Kesennuma treatment area.
In Japan, damage to the forest by the propagation of bamboo is reported. Therefore periodical felling and effective inflection of bamboo are required. Currently, the bamboo is crushed to chips, and these materials have been promoted in various field. Bamboo chips are material which contains a lot of fiber. Therefore it has water absorption ability. The very soft dredged soil which has high water content is required to make improvements preliminarily such as stabilization and dehydration process for conveyance and effective utilization. In general, the cement solidification usually used a predominant improvement method. However, it requires a large amount of cement about dredged soil having high water content and the increase of pH due to the addition of cement is also concerned. The purpose of this study is to improve the very soft dredged soil which has high water content inexpensively and effective by the addition of shredded waste bamboo. As a result, in the water-absorption property of bamboo chips, the method of crushed bamboo have different capacities to water-absorption ability of bamboo chips. In the improvement effect of bamboo chips, the bamboo chips having high water absorption potential is possible to improve to the conveyable material, with less additive rate. In the mechanical characteristic of improved soil using cement and bamboo chips, soil strength is increased by adding the bamboo chips.
Lime soil stabilization is widely adopted at construction works such as rail way embankment, subgrade, base course, port and harbor, airport, reclaimed area, recycle of surplus soils etc. When lime-stabilizer and soil are mixed, the ettringite reaction following water absorption and ion exchange reaction is caused within a few days. As a result, needle-shaped crystals, ettringites, make each other’s soil particles link chemically and the soil material is stabilized strongly. In this paper, in order to clarify the mechanical properties of lime-stabilized soil, a series of consolidated undrained compression (CU) tests at different mixture ratio of lime-stabilizer were carried out. The following conclusions are obtained in this study: (1) The shear strength of the lime-stabilized soil increases remarkably and the soil is shown large negative pore water pressure, positive dilatancy, during shear process. (2) Frictional resistance of soil particles of the lime-stabilized soil at the critical state becomes large gradually by increasing mixture ratio of lime-stabilizer. (3) The tendency of strength parameters, c' and Φ', of lime-stabilized soil is fluctuant with changes in mixture ratio of lime-stabilizer.
This paper discusses on strength and self-restorative capacity of GBFS (granulated blast furnace slag) under several conditions. In laboratory tests, GBFS specimens are cured in three types of solutions (plain water, seawater, and calcium hydroxide solution) and the change in unconfined compressive strength and hydration reaction of GBFS are investigated. It is confirmed that the strength of GBFS increases with curing duration due to hydration reaction regardless of its history of shear failure. When GBFS is once collapsed after curing, the shear strength increases up to 60% of those without shear failure. In addition, a prediction method of the strength of GBFS due to the self-restoration is proposed.
The authors have been studying how to make effective use of fly ash by-products from coal-fired power plants since 2004, and developed J-ash, an artificial ground material, based on the crushed solid soil by the Okinawa Electric Power Company, Incorporated. This paper describes the relationship between the unconfined compressive strength which made coal ash solidify by cement and soil mechanical properties of J-ash. As a result, it was indicated that J-ash is artificial ground materials with the performance beyond sandy soils. Examples of use of J-ash as a materials for earthquake restoration are also reported.
This paper reports the results of load and resistance factor design (LRFD) calibration for pullout limit states for geogrid reinforced soil walls owing to soil self-weight loading plus permanent uniform surcharge. The calibration method uses bias statistics to account for prediction accuracy of the deterministic models for reinforcement load and pullout capacity, and random variability in input parameters. New revised design models are proposed to improve load/resistance prediction accuracy based on current design manual established by Public Work Research Center of Japan. And load and resistance factors are proposed that give a uniform probability of failure of 1%.
The Yashima Castle remains were found recently in the Park of Yashima, Takamatsu City.The mansory wall of the castle is found to have greate historical value through archeological study.However,the castle wall was severly damaged due to sevier weather condition for long period of time. The Takamatsu City decided to restore the castle in orginal shape and structure and open to public uses. Through geotechnical survey, it is found that the foundation of the castle is unstable state and needs to stabilize through any kind of stabilizeing method.However, it is requred to sustain the original structure as using original materials.The method adopted is stabilization by MgO for upper portion of the fill behind the wall, and steel pipes for draining and reinfocemet of the lower portion of the wall.These methods were found to be effective throgh experiment and numerical analysis.The restoring works has been completed successfully using monitoring of deformations of the wall and strain mesurement of pipes.
A soil improvement of the low improved rate is effective for cost reduction of countermeasure for soft ground and shortening the construction period. Therefore we developed a new design method that could consider an arch action to occur in embankment. It is possible to evaluate embankment load carrying cement column and non-improved soft ground by the arch action. Therefore it is possible to distribute improved cement column distance bigger than a conventional construction method. It is complete and places an improved cement column under the embankment. So, it is possible to control settlement and differential settlement of the embankment, moreover it is becoming cost reduction of countermeasure for soft ground and shortening the construction period. In this report, we introduce the outline of the Arch Action Low Improvement Ratio Cement Column Method, and we clarify the effectiveness by comparing ALiCC method and conventional methods.
The authors have proposed a simple design method of the VD using PBD materials for horizontal drainage. This design method is based on the comparison of the required flow volume qA calculated from a Barron type equation and the drainable amount qV computed by solving simultaneous equation of the flow network. In order to prove the validity of proposed design method, the model experiment and site observation have been conducted. As the results of this research, the followings were obtained; 1) As a result of model experiment, it was shown that the consolidation characteristics of VD is similar to the predicted value by the proposed design method. 2) As a result of observation at the actual construction site, the measured value of the flow quantity in PBD was close to the predicted one especially for a vertical drain part. 3) However, the flow quantity in a horizontal drain was measured only immediately after the loading. This means the use of PBD material as a substitute of sand mat might be practical at least at the early stage of loading.
Iron powder mixing is one of the methods of remediating soil contaminated with volatile organic compounds (VOCs). Iron powder dechlorinates VOCs by reduction. This method has been adopted widely because its can remediate with a relatively short time and can be applied to various type of soil. Iron powder is usually supplied into contaminated soil as slurry mixed iron powder with a thickener water solution，therefore there was a problem that ground foundation becomes weaker after work. In order to control ground strength after remediation，we have developed the new method which consists of highly-concentrated iron powder slurry using specific thickener and forming agent making bubbles which tend to broke after work. This new method reduces the water addition amount to 1/5 of conventional method，so make possible to restrain that the ground becomes weaker. Laboratory tests select the kind and contents of thickener and forming agent. Field experiments confirmed that the mixing and digging performance is secured and ground strength after work.
Granular solidification technique for soft mud have been studied using some original neutral conditioners in addition to solidification materials. The cone index has adopted to evaluate the improvement effect of the soils. In order to apply the treated muds as filling materials, mechanical properties of the compacted soils should be studied. The permeability test and the series of the unconsolidated undrained triaxial compression test have conducted for the soils. The target cone index were set between 400 kN/m2 and 800 kN/m2. The coefficients of permeability depended on the amount of added stabilizer and were between 1×10-4 m/s and 1×10-8 m/s. Under unconsolidated undrained condition, the friction angles were under 10 degree regardless of the sorts of original mud or stabilizing material, and the cohesion were under 60 kN/m2 depended on the cone index. The modules of deformation of the treated muds increased with the maximum deviator stress increased.
Nowadays the land subsidence and the liquefaction at residential grounds have been becoming more apparent. However, there are no particular investigation methods to determine their causes. This is because the grounds of detached residents where an investigation should be conducted are often very confined. In this study, a detailed analysis of N-value distribution at an embankment of a detached residence located on inclined bedrocks using improved Swedish weight sounding machine is conducted. The causes of land subsidence and the future tendency for the land subsidence are estimated. Also, a reinforcement method and material to fortify weak ground is proposed in this study.
In order to confirm the efficacy of the carbonate precipitation method based on an enzyme catalyst and microbial functions in increasing peat strength, we performed laboratory tests with the urease enzyme and a urease-producing bacterium from peat and measured ammonia-nitrogen and nitrate-nitrogen concentration, unconfined compressive strength, and diversity of the microbial community by using next generation DNA sequencing. We then investigated the influence of the conditions used during the addition of the urease enzyme and the subsequent increase in the population of the urease-producing bacterium during the test term. From the results obtained, it was found that the addition of the urease enzyme increased calcite precipitation and also increased the unconfined compressive strength(over 50kN/m2) and the production of ammonium ions; this increase in the concentration of ammonium ions increased the pH of the peat. We also found a change in the composition of the microbial community under the carbonate precipitation conditions.
In this study, an analysis was made of the causes of variations in the results of Particle size distribution test (sedimentation analysis), liquid limit test, plastic limit test and unconfined compression test in which the coefficient of variation was nearly 5% or higher during proficiency testing of geomaterial tests. The analysis was made based on the results of a questionnaire survey conducted at the same time as the proficiency testing. As a result, it was verified that not only the experience of test engineers but also complying with standards, and checking, inspecting and correcting test apparatuses and measuring instruments are important to the improvement of the accuracy of geomaterial tests. It was also revealed that the maximum and minimum weights measured by a balance scale affect test accuracy.
This study was carried out assuming the melt-solidified slag is used as a fine aggregate for mortar and concrete. Mortars were manufactured using two kinds of melt-solidified slags that produced in different sites for a fine aggregate. The influence that the replacement ratio of the melt-solidified slag to the natural aggregate gave to fresh properties and strength of mortar was examined. In addition, the effects of a grading control of the aggregate on the properties of the mortars were also investigated when the melt-solidified slag is grinding with the ball mill for the particle properties improvement. Furthermore exposure tests of concrete using melt-solidified slag fine aggregate sited on snowy and cold region were examined. Weight of the concrete, the dynamic modulus of elasticity and the brightness of concrete surface, was compared with the case of using natural sand. As a result, basic properties of mortar using the melt-solidified slag were clarified. Using the ground melt-solidified slag was effective in the performance improving of mortar.
Some existing post-tensioning prestressed concrete (hereinafter PC) members have PC wires insufficiently grouted in sheath. The exposure test for re-grouted PC wires with five grades in corrosion was carried out for a maximum of about 700days in order to examine the applicability of re-grouting technique to PC wires corroded and insufficiently grouted in sheath. The effect of re-grouting for the corroded PC wire was investigated in comparison of the residual diameters of PC wires with and without re-grouting. As a result, the partial corrosion in the border section between grouted and non-grouted portion was especially reduced by re-grouting for the corroded PC wire. Moreover, the greater restriction of corrosion by re-grouting was indicated in PC wires with the reduction by around 4% in diameter, while the corrosion was restrained even in those with the reduction by above 4%.