Based on the soil-water coupled finite element analysis incorporated the modified macro-element method, the improvement of soft ground by the vacuum and surcharge preloading method is investigated systematically. SYS Cam-clay model is employed for the constitutive model of soft soils and the soil parameters are determined by the curve fitting of the one-dimensional compression result. The results show that: 1) the settlement at the ground surface is as large as 3.5m which is very close to the design value; 2) the long-term settlement is also predicted and the degree of consolidation at 180d is over 98%; 3) Negative and positive horizontal displacement appears due to the vacuum preloading and surcharge preloading respectively and it is necessary to control the rate of surcharge to avoid the instability of the ground; 4) There is significant oscillation in the pore pressure inside the ground due to the construction of embankment and the following consolidation under vacuum pressure.

抄録全体を表示

The acid silica sol grouting material has been frequently used in the chemical grouting method. Recently, it has been recognized that the ground can contain high amounts of calcium carbonate (CaCO₃), which are formed by deposits of shell and corals (high CaCO₃ ground/soil). When using acid silica sol grout with a typical pH value of 2 to 4 in this type of ground, the chemical reaction of the excess acid in the grout reacts with the CaCO₃ in the ground to produce carbon dioxide gas with foaming. Consequently, this chemical reaction reduces the strength and permeability of the ground. On the other hand, alkaline-based grout does not produce CO₂ bubbles when there high levels of CaCO₃ are present in the ground, because there is no excess acid in the grout. However, the used of alkaline-based grout cannot be expected to improve durability after gelation because of the large amount of alkali components. Therefore, it is neseccary to develop a grout that is more durable and does not cause CO₂ foaming in the high CaCO₃ ground. In this study, we investigated the physical properties of chemical grout agents mixed with a sodium silicate solution and acid carboxylic ester, controlling the duration of the gel time and CO₂ foaming. We compared the strength characteristics of sand-gel with sand-gel specimens using two sample soils: Tohoku silica sand No.6 and high CaCO₃ soil. Shrinkage and leaching tests were conducted to assess the durability of homo-gel.

抄録全体を表示

In situ soil-cement mixing is frequently used to minimize soil liquefaction, enhance soil strength and reduce soil permeability. For quality assurance purposes, drill core samples are taken from the soil-cement mixtures and unconfined compressive strength tests are carried out 28 days after mixing and placement, which may delay construction works. Clearly, there is a need to accurately predict the strength of soil-cement mixtures early. In this study, we prepared soil-cement mixtures with different proportions of clay, silt, sand, cement and water. The as-prepared specimens were subsequently cured at standard and various temperature, pressure and time conditions. We then compared the strength characteristics of the as-prepared soil-cement specimens. Unconfined compressive strength increases between 24 h and 48 h of accelerated curing; however, increasing the curing temperature does not lead to increases in strength. Compressive strength slightly increases with the curing pressure. Finally, the compressive strength depends on the cement and fines content and W_Total/C of the soil-cement mixtures.

抄録全体を表示

Soil nailing has been used to reinforce the unstable ground such as slope stability and face bolting in the bored tunnels. In these civil engineering projects, the slender steel bars as reinforcement elements have been mainly used for axial tension load transfer. Alternatively, the usage of steel tubular pipes is highlighted for constructability reasons and an extra bend/shear resistance of pipes. However, commercially available steel pipes have smooth surface so that the bond strength is not enough to resist the pull-out tension loads. Therefore, the fabrication such as shear keys on the outer surface of the pipe is essential to obtain the bond strength between the pipe and the grout filling. The dimpled pipes using on-line depression forming method has been developed to improve the bond strength, which has small depressions regularly arranged on the outer surface. This paper presents the introduction of the dimpled pipe briefly, and a particular emphasis is given to the evaluation of the high bond strength by the pull-out tests and the mechanism.

抄録全体を表示

Basic engineering properties including fluidity, breeding characteristics, unconfined compression strength and hydraulic conductivity are evaluated for soil-cement mixtures for diaphragm wall construction. The specific objective is to assess the effects of 1) adding three different recycled fine additives including foundry dust, concrete powder and gypsum-rich slag, and 2) mixing with seawater on these engineering properties. Although addition of these fine additives decreased the fluidity of soil-cement slurry, adding the appropriate amount of fine additives increased the unconfined compression strength and decreased the hydraulic conductivity of soil-cement mixture after 28 days aging. Furthermore, using seawater instead of fresh water can also improve the strength and hydraulic barrier performances of soil-cement mixture. These results verify the applicability of these recycled fine additives and seawater to soil-cement diaphragm wall construction.

抄録全体を表示

In order to recycle dredged soil, our research group developed interlocking blocks from dredged soil. Dredged soil interlocking blocks (350mm in width, 350mm in depth and 100mm - 150mm in height) were made from soft clay dredged at the Kanmon run. They were produced with the constant dehydration pressure 5MPa and cement content of 15%, 20% and 25% per the dry weight of clay. The unconfined compression test and bending test were carried out to investigate material characteristics of dredged soil interlocking blocks in the water for six months. On the other hand, in order to check the effect of interlocking blocks, a road was constructed by using interlocking blocks on the surface and, as a roadbed material, dredged and dehydrated soil and crushed stone for mechanical stabilization were used. Characteristics of dispersion of traffic load and settlement were evaluated by running experiments. Stress was measured by four earth pressure gauges and settlement was measured by surveying. The following conclusions are obtained: (1) There was close relationship between unconfined compressive strength and water-cement ratio. Therefore, it is concluded that unconfined compressive strength of dredged soil blocks are controlled by water-cement ratio. (2) Dredged and dehydrated soil can disperse traffic load effectively. (3) Soil-concrete blocks can’t disperse traffic load effectively, but have sinking suppressing effect when using dredged and dehydrated soil as roadbed material.

抄録全体を表示