The Geotechnical Laboratory is engaged in research to protect geo-infrastructure and geo-environment from natural disaster and environmental pollution. Specifically, the keywords are ground improvement, foundation structure, barrier structure of waste landfill site, containment structure of ground and groundwater pollution, and recycling society. The Geotechnical Laboratory are developing geotechnical research activities effectively linking related issues on the upstream and downstream sides and further further collaborating with other countries.
Influence of Pulling-out Existing Piles on the Surrounding Ground
The tear down of infrastructures has been increasing in recent years due these infrastructures have aged and their utilization has decreased along with the decrease in population. The number of pile foundations being pulled out is now far greater than that being newly installed pile foundations.
This study considers the influence of a pull-out hole on the static and dynamic characteristics of the surrounding ground using two-dimensional dynamic finite-element analysis. The special qualities required by fillers injected into such holes are being also clarified.
Evaluation of Ground Improvement by DEM
The technology (method) for ground improvement aimed at securing the stability of the ground achieves the desired geotechnical conditions by artificially improving the soft ground. Although many technologies for ground improvement are proposed at present, there are few methods to confirm whether the designed ground improvement is actually carried out, and a method for evaluating the technology for ground improvement is necessary.
Therefore, a granules analysis based on distinct element method (DEM) for various technologies for ground improvement is being conducted, and being examined the method of more effective ground improvement.
Development of Real-Time Visualization for Ground Improvement
In ground improvements as well as pile constructions, it is important to effectively utilize various information obtained during the construction to ensure their qualities and shape forms.
Therefore, in parallel with the ground improvement and the pile construction, an innovative system that can measure some characteristic of surrounding ground with real time, visualize the measured values in three dimensions and facilitate construction management is being developed.
This system promotes i-Construction being promoted by Ministry of Land, Infrastructure and Transport, and Construction Information Modeling (CIM), contributing to improvement and efficiency of construction production system.
Real-time Checking for Ground Improvement Works
In contrast to the mechanical stirring method in which the ground soil and the modifying material are mixed and stirred by stirring blades and the improved body is formed in the ground, the high pressure injection stirring method is a method in which the improved diameter is changed due to soil condition and so on. There is a possibility that it can be changed with, and a method for easily confirming the shape, particularly the improved diameter, is highly desired.
Therefore, a technology that can make “visualization” of the situation of ground improvement and confirm such as the improved diameter in real time is being proposed and developed.
Influence of Ground Uncertainties on Ground Improvement
Chemical grouting is one of ground improvement methods to inject liquid chemicals into the void of soft sandy ground. It is used mainly to prevent liquefaction and increase in strength for the sandy ground. However, due the sandy ground involves uncertainties, it is difficult to determine the penetration range of chemicals. Existing research has analyzed under homogeneous ground conditions, but in fact it is a heterogeneous ground with uncertainty.
Therefore, a seepage flow analysis for chemical solutions against the ground requiring ground improvement in uncertainty ground is being carried out and it is being compared the behavior of chemical solution with homogeneous ground.
Impermeable Coating on Contaminated Soils and Wastes
The impermeable coating treatment is a technology which coats solid wastes and soils by a particle unit with the impermeable material containing water-absorbing polymers. The elution of attached substances on the surface of soil particles such as heavy metals will be suppressed, because each particle of soils is coated with impermeable materials uniformly.
In order to utilize solid wastes and soils, it has been evaluating the basic properties by laboratory experiments.
Silica-based Solidifying Material Made from Inorganic Solid Wastes
It has been developing a powdery silica-based solidification material that heat treated inorganic solid wastes including much silica ingredient, such as a waste grass and a waste fly ash, mixed with alkali aids.
A solidification mechanism of the mixture with silica-base solidification material, blast furnace slag and water is clarified based on the viewpoints of chemistry and mineralogy.
It has been clarified that the silica-based solidification material has the efficiency of delay by laboratory blended test and field test.
Evaluation of Fluidization Treated Soils Based on MPS Method
Recently, fluidization treated soils have come to be used as landfill materials or fillers in such landfill of underground space in Japan. However, the design and construction of the fluidization treated soils at present is based only on empirical knowledge.
Therefore, it has been evaluating the flow-ability of the fluidization treated soils based on the flow analysis by the MPS method and the experimental evaluation. Favorable results have been obtained in the numerical flow analysis by using the Bingham model to the MPS method.
Gypsum Hemihydrate Content in Recycled Gypsum Boards
This study reviews in detail the thermal behavior of recycled and reagent gypsum from the viewpoint of recycled gypsum utilization as geo-material. It has been discussing the methods to determine the content of the gypsum hemihydrate from the viewpoint of density as a simple quality judgment method of the recycled gypsum.
The validity of the estimation method of gypsum hemihydrate content using the density was experimentally confirmed. Moreover, by calculating the gypsum hemihydrate content from the measurement result of the recycled gypsum density, the effectiveness of the quality control method based on the density was proven.
Transportation Behavior of Radioactive Substances in Soils
In 2011, a number of radioactive substances were released as a result of the accident at the Fukushima Daiichi Nuclear Power Plant that was caused by the Tohoku Region Pacific Coast Earthquake. The released radioactive substances fell onto the surrounding ground or into the sea. Therefore, decontamination measures for the ground have been conducted at the field site.
The advection-dispersion equation has been added to the radioactive half-life in order to evaluate transportation of radioactive substances.
Improvement of Insolubilization Materials on Contaminated Soils
In recent years, heavy metal ions, which are harmful substances irrelevant to artificial development, may exist in the soil, soil contamination due to soil and rock containing naturally derived heavy metals has become apparent.
Therefore, focusing on improvement of insolubilization treatment which is one of contaminated soil treatment methods, it has been developing new insolubilization materials. Specifically, it is conducting the tests on the insolubilization effect on heavy metals and elucidates insolubilization mechanism chemically and mineralogically as well as insolubilization effect on heavy metals.
Evaluation of Containment Performance on Coastal Landfill Sites
The containment performance of impervious structures is considered the most important performance, which the toxic substances are enclosed in coastal landfill sites. The containment performance is evaluated generally by the hydraulic conductivity and the thickness of impervious structures to focus on an advection. However, the leakage of toxic substances is affected by a diffusion and a dispersion.
The containment performance is evaluated from the viewpoint of the diffusion and the dispersion in this research. Concretely, the influence which the toxic substances leaks from impervious structures on the diffusion and the dispersion is evaluated by the infiltration and advection-dispersion analysis on steel-made side impervious walls.
Water Cut-off and Remediation Promotion Technologies at Waste Landfill Sites
It has been proposing the construction of steel pipe sheet pile (SPSP) cutoff walls for promoting remediation of water-soluble toxic substances and containment of water-soluble toxic substances at landfill sites in order to maintain and ensure the environmental safety of waste landfill sites over time.
It has been investigating environmental safety at coastal waste landfill sites by applying water cut-off and remediation promotion techniques to the joint sections of SPSP water cut-off walls that provide shore protection for waste landfills.
Development of H-joint Steel Pipe Sheet Piles in Construction of Foundations
It has been developing a new H-joint SPSPs technology from a simple idea in which two steel pipes are connected by H-steel section welded on them in order to improve the performance and widen application areas of SPSP technology.
It shows development and application potential of newly developed H-joint steel pipe sheet piles (SPSPs) in SPSP structures.The H-joint SPSP is expected to remediate problems of traditional joints in SPSPs.
Applicability of Geostatistical Methods to Ground Investigation
It has been predicting the cross-sectional distribution of the ground characteristics at unknown points and areas, where the converted N-values in the relevant ground are not clarified, using geostatistical methodology. In particular, it uses relevant-ground converted N-value data obtained through the improved type Swedish sounding test (Nippon Screw Weight System; hereinafter, referred to as the NSWS test) for the filling ground of certain detached houses, where ground subsidence was actually generated.
Thus, it has been validating the geostatistical method for the prediction of the cross-sectional distribution of ground characteristics, including physical properties, at narrow detached-house grounds.
Life Cycle Assessment on Recycling of Construction Sludges
It has been examined the evaluation method for social environmental efficiency to socially evaluate waste recycling, by incorporating environmental load as an environmental cost in addition to the direct cost.
The social environmental efficiency evaluation including consideration of uncertainties is conducted, because waste recycling involves various uncertain elements.
Necessity of Broad-based Disposal for Disaster Wastes
It quantified the environmental impact with respect to the tsunami debris generated by the Great East Japan Earthquake and further, by incorporating a time scale, we discussed the appropriate disposal flow from both environmental economics and time axis viewpoints.
It has been shown that the promotion of broad-based disposal and reuse of waste is important from the comprehensive aspect of environmental impact and time.
Environmental Accounting on Civil Infrastructures
It has been proposing the environmental burden and benefit assessment method, which contributes to the evaluation of public works, by considering a quantitative environmental impact.
The method developed is applied for the Bangkok subway construction project, so that the environmental impact following the Bangkok subway construction work is evaluated on the basis of environmental accounting.