This paper shows the short history and the prospect in future on the development of the vacuum consolidation method in Japan. The vacuum consolidation method has the similar history of development of plastic board drain method. Both methods which are currently used for the soft ground improvement constitute of three phases of development. The first phase of the vacuum consolidation method is the introduction stage started in 1970s. But it was soon disappeared in the construction market without proved its efficiency. But after the stagnation of about 10 years was passed, the vacuum system revived to apply the road fill on the soft ground again. Because its superiority of acceleration of consolidation was recognized that is attained not considering failure of ground caused by fill as pre-loading. This paper reviews the development, stagnation and revival of this method focusing on why the vacuum consolidation method revived. It leads the current assessment and future perspective of the vacuum consolidation method.
In March, 2000, the circular notice of Ministry of Construction decided that the elusion test of hexavalent chromium (Cr6+) had to be carried out when cement or cement stabilizer was used or improved soil was reused on particular ground improvements such as the Deep Mixing Ground Improving Method. In November, 2007, the Ministry of Land, Infrastructure, Transport and Tourism instructed that the elusion test of Cr6+ was carried out for the recycled sand from used cement-concrete. Kansai Geotechnology & Environment Research Center was accredited as the certified testing laboratories of the elusion test of Cr6+ under ISO/IEC 17025 by JAB, in 2007. In this report, the analyses of amount and secular change of elution of Cr6+, kinds and area of construction, etc. are done by the elusion test data of 3 years in the past. Then it becomes clear that 87% of samples achieve the soil environmental quality standards for elution of Cr6+ and the elution of Cr6+ is controlled by addition of the stabilizer coped with Cr6+.
The lime and the cement treated soil have been regarded as stable for a long time due to hydrate generated by pozzolanic reaction. As the treated soil is exposed to natural conditions, its strength would decrease by calcium leaching. In lowland having the thick alluvial clay deposit, the chemical soil treated method is often applied to improve the strength of soft clay ground. The lime treated soil applied to the base of a tidal river dike is deteriorating. It had been constructed in about twenty years ago and now appears to be muddy and leakage of river water. The treated soil is exposed to seawater in this area. This study considered mechanism of calcium leaching from the lime treated soil when it was immersed in seawater. Leaching tests were carried out to clear influences of the component of seawater on calcium leaching. Artificial seawater, NaCl, MgCl2, MgSO4 solutions were used in the test. Influence of NaCl on calcium leaching was very small. Magnesium containing in seawater reduced pH value of the solution-treated soil mixture. Calcium leaching was accelerated when magnesium concentration was higher. Magnesium was founded to be a main component to cause calcium leaching.
There are many famous quarries that produced good quality stone in Japan. These stoneworks are produced much stone sludge as by-product. Most of the stone sludge is disposed as wastes, and creating environmental problems. It is necessary to research on methodology for large volume management of stone sludge. Authors have investigated fundamental physical properties of stone sludge for beneficial use. The authors found that the stone sludge can yield much silicate under high-alkaline condition. The Silicate can advance a pozzolanic reaction of cement. This paper describes evaluation of improved soil physical property when stone sludge and cement are mixed with pond sludge. Strength characteristics of the experimental results in uniaxial compression tests and cone penetration test. In addition, the strength development mechanism, field emission scanning electron microscope (hereinafter “FE-SEM” and so on) texture and structure, energy dispersive X-ray spectroscopy (the “EDS” and so on) is described from a quantitative analysis by.
In recent years, the generation of coal ashes from many thermal power stations and various kinds of industries has been increasing. And also soft dredged soils annually disposed in marine area have become a serious geo-environmental problem of various countries. It is difficult to reuse as construction materials due to the fine grain size and flying dust, and the disposal sites of these materials have been decreasing. Therefore, it is very important to reuse these materials. Granulation technique is a method which converts coal ashes and soft cohesive soils into high-strength particles. This is one of the soil improvement methods to make efficient use of these materials. In this study, the granulation technique of these materials was examined. And the geo-material properties of granulated materials were investigated. (1) As making the granulated materials, they were sensitive to the addition volume of water and the best volume of water exists. The grain diameter became uniform by lengthening the granulation time and the uniformity coefficient became small. (2) The aspect ratio Ar of the granulated materials was lower and roundness coefficient Rc was higher than those of natural sands. In other words, the particles of granulated materials were closer to sphere than those of natural sands but their surfaces were rougher. It was clear that single particle crushing strength of granulated materials was lower than that of natural sands though it depends on being low the additive rate for cement. (3) Shear behaviour of granulated materials was similar one of sand with particle breakage. In each granulated material to which the coefficient of curvature is similar, it was also shown that the particle strength correlated well with the secant angle obtained from shear tests and it was possible to estimate the shear strength of granulated materials.
The reuse of waste plasterboard must be promoted more to maintain the residual capacity of the controlled type landfill sites because it is predicted that the amount of plasterboard retrieved with demolition works of building continues increasing for the time being. However, mixing the board comminuted while separating base paper namely the powdery dihydrate gypsum into ground, the leaching concentration of fluoride which has been contained in plasterboard since inception by coming from raw materials might exceed the environmental quality standards for soil pollution. The light burned magnesite has been early used for not only the improvement of soft ground but also the insoluble treatment of heavy metal pollution soil. Referring to such on-site achievements, we have made the samples which consist of powdery dihydrate gypsum, light burned magnesite and distilled water. Having added magnesite of 10% and water of 50% for the mass of gypsum, fluoride leaching concentration satisfied a target level (hereafter referred to as “insolubilization treated powder”). Moreover, regarding clay and sand mixed the insolubilization treated powder of which content was up to 30%, it was guessed that those might not re-leach fluoride under the stirring with an acid or alkaline water solution. Successively we performed the CBR test, box shear test and unconfined compression test to clarify a stabilization effect brought by mixing the insolubilization treated powder into clay. According to the results obtained from these tests, clay stabilized with the insolubilization treated powder surely indicated a tendency to increase bearing capacity and to develop strength as compared with clay in which only lime or cement was added. Judging from the novel findings mentioned above, it is possible to utilize the insolubilization treated powder as part of the soil materials.
Necessity to promote a recycle of waste plaster board is mounting, since the waste plaster board has been legally prohibited to dispose into inert landfill site. However, it is concerned that the recycled waste plaster board (recycled gypsum) produces hydrogen sulfide gas, so that it is one of the interference with the recycling. There is a possibility to control the hydrogen sulfide gas production from the recycled gypsum by artificially changing into alkaline condition or adding iron oxide. In this study, we discussed the hydrogen sulfide gas production from a ground improvement with the recycled gypsum, quick lime, and/or iron oxide powder. In addition, unconfined compression strength of the ground improvement is evaluated in order to obtain an incentive of the recycling. Adding only the recycled gypsum cannot improve strength of a soft ground having much amount of fine particles. Quick lime was required for strength improvement. If pH of the ground improvement is greater than 9, it was observed that the hydrogen sulfide gas production potential is negligible. Increasing pH by adding the quick lime is able to more effectively control the production of the hydrogen sulfide gas than adding the iron oxide powder. The production of the hydrogen sulfide gas is able to be controlled by adding the quick lime more than half of the amount of gypsum addition.
In the civil engineering field, water-swelling materials are often used as joint sealing materials to improve water cut-off performance in the joints of the steel (pipe) sheet pile. In short, water-swelling materials are extremely effective as water sealing materials. However, many characteristics of water-swelling materials have not yet been proved, and one of the unproven characteristics is the swelling pressure. Solving the issue of the swelling pressure will contribute to improving water sealing in the joints of the steel (pipe) sheet pile. At the same time, it is also expected to greatly contribute to the application of water-swelling materials for other purposes, or the new development and improvement of water-swelling materials. The purpose of this paper is to prove the characteristics of swelling pressure of water-swelling materials which are applied to joint sealing materials, e.g., a steel (pipe) sheet pile, etc., and to experimentally evaluate the swelling pressure of water-swelling materials. The results we obtained are : (1) the swelling pressure depends on the membrane thickness of the water-swelling materials. The thicker a membrane becomes, the bigger the pressure tends to be. (2) While the swelling pressure is not much influenced by the temperature of the water to be immersed, it is influenced by the quality of water to be immersed. Similar to the traits of the swelling rate, the swelling pressure when immersed in artificial sea water is lower compared with that when immersed in freshwater. (3) For example, water-swelling materials 1 mm thick achieve a swelling pressure of 6.7MPa when immersed in fresh water, and 4.2MPa when immersed in artificial sea water, respectively. Accordingly, we assume they should fully perform the swelling functions under a restricted environment as well.
In general, in cases when the shallow ground is soft, a method of surface soil stabilization is adopted. However, problems regarding surface soil stabilization often arise. There are a lack of guaranty regarding construction quality, dispersion of the solidification material, prolonging of the curing time, operating efficiency at the time of disassembly and anxiety concerning the workability of clear and leaching of hexavalent chromium. We've developed an alternative method of surface soil stabilization in which the recycled plastic piles are driven under the foundation in fixed intervals. The piles are manufactured from material recovered by The Containers and Packaging Recycling Law and the remnants from a plastic factory. The main ingredients are polypropylene and polystyrene. The end of the pile is cone-shaped, and the axis is not hollow but filled with plastic. To verify the reinforcement effect on the composite ground by the pile, two loading tests were executed. They consisted of pushing and pulling tests of the pile, and pushing tests of the plate. In order to verify the durability of the recycled plastic piles under the ground, age acceleration tests in the laboratory and aging degradation tests of the exposed specimens were performed. The main findings of the loading tests and the durability tests are as follows : (1) The bearing capacity of the ground driven piles was more than matched that of the separate ground and piles. (2) The bearing capacity of the pile was calculated from The Swedish Weight Sounding Test and the bearing capacity of the ground driven piles were able to be evaluated by a reinforcement coefficient of 1.6. (3) The recycled plastic piles satisfied all criteria on durability tests, and no deterioration on the molecular level was confirmed.
Maizuru-Wakasa expressway was constructed on the soft ground area consisting a thick layer of peat and soft clay. In trial embankment construction, a large lateral displacement and settlement due to embankment load were observed. Therefore, vacuum consolidation (air-water separation system type) was selected to apply to another trial area nearby the previous one to improve the ground for embankment construction. It was found that the vacuum pressure could maintain at high level even after a successive consolidation settlement up to about 10m, A significantly incremental soil strength after consolidation settlement were observed. The analysis of soil strength increment induced by vacuum consolidation compared to another case history was analyzed and described in this paper
Grouting is an important part of construction in rock and soil for such as controlling the flow of water, filling voids in the ground and strengthening grounds. Grouting method has advantages over other soil improvement methods of not discharging slimes and requiring large spaces. However, conventional cement grout was difficult to permeate into fine sand. Chemical solution grout shows high permeability ; on the other hand, the solidified ground is not strong and durable enough. The purpose of our work is to develop grouting methods with ultrafine cement (the average particle size 1.5μm) grout. The authors conducted both laboratory and field grouting tests. As a result, the grout permeated into a one-meter long artificial ground composed of fine sand, where conventional superfine cement grout was not able to permeate. Furthermore, unconfined compressive strength of the solidified ground was 10 times as large as that of solidified ground with chemical solution grout. As for the field test, the ball-shaped solidified ground was observed in the grouted area, and its diameter was 190cm as designed. It is concluded from the tests that ultrafine cement grout showed a great permeability and high solidified strength.
In a case of applying the soil-cement columns to small buildings, the diameter of soil-cement column might become larger than the width of a base because strength of soil-cement column is low. To cancel this problem, and to decrease the cost and the environmental load, method of soil-cement column reinforced with wooden core (SCWC) was developed. The compression tests of the cement-treated soil and wood core were conducted, and describes that the strength of SCWC is simply addition of the strength of cement-treated soil and the strength of wood core. The vertical loading tests on actual size SCWC were conducted, and the bearing capacity factors were obtained. The bearing capacity factors are based on N-value of the ground estimated from Swedish weight sounding test (SST). The allowable bearing capacity calculation table is proposed. This calculation table is made by the strength of SCWC and the bearing capacity factors led based on N-value of the ground estimated from SST.
It is attempted to apply the improved soil using cement materials as the hardening agent to the foundation ground of the important buildings for electric power plants. The current design procedure of the improved ground is based on the static strength such as the unconfined compressive strength of the improved soil. However, it is not clear whether the static strength is relevant to seismic designs where the effects of the cyclic loading induced by the earthquake shall be considered. Hence, the authors studied the dynamic strength of the improved soil in comparison with the static strength, by executing a series of the cyclic triaxial tests with different loading frequencies and the consolidated-undrained triaxial compression tests (CUB tests) with different axial strain rates. The tested soil specimens which have the unconfined compressive strength of about 5 MPa were made in laboratory using the mixture of a dredged marine clayey soil, a B-type blast-furnace cement (300kg/m3) and water. Both of the CUB tests and the cyclic triaxial tests showed similar results with respect to the relationships between the strength and the strain rate. The larger the compressive strain rate was, the higher the strength became. It is concluded that the static strength could be used as a sufficiently safe value in seismic designs since the strain rate of the cyclic loading induced by the earthquake is much larger than that of the static test.
This thesis describes the effect of ground improvement due to Low-Replacement-Ratio SCP Method. In this method, the replacement ratio is 30 to 50 percent. Because 70 percent of the consolidation layer is composed of unimproved clay, it is designed with taking account of increase in strength of clay. Therefore, it is required to grasp strength of clay between the improved piles accurately which enables to compare the stress sharing of sand and clay. In addition, the factor of safety against slip failure can be obtained. This thesis studies a case about measurement of circular slide and stress sharing ratio by strength and void ratio of clay measured with RI-CPT and its analysis flow. The case is Haneda Air Port D-RUNWAY Project.
Economy and environmental safety have recently become very important factors in the construction of soil structures. A combined technology of shallow stabilization and floating-type cement treated columns has an advantage to reduce the construction cost of the soil structure on deep soft soil layers. In this paper, bearing capacity of this type improved ground were investigated. At first, in order to evaluate bearing capacity of this type improved ground, skin friction applied around surface of the floating type column was investigated. Secondly, loading model tests were conducted under the plane strain condition in different improvement conditions to investigate failure tendency of the improved ground. Finally in order to evaluate bearing capacity of this improved ground, equivalent conversion model is proposed with consideration of skin friction. It was confirmed that bearing capacity of the improved ground can be estimated by using this proposed model. By using this model, the embedded depth of an equivalent foundation can be related to the improvement parameters such as improvement ratio and improvement depth.
In the construction of the D-runway in Tokyo International Airport (Haneda Airport), “the settlement prediction and management system (HSAP)” which can efficiently evaluate the consolidation settlement of artificial reclamation was developed. The reclamation history data base which reflected the actual construction until July, 2009 and the reclamation plan after that was made. The actual measurement and the calculation value were compared and the various consolidation parameters were identified. Moreover, the long-term consolidation test and constant strain rate consolidation test were executed, and the secondary consolidation parameter was set based on the isotache model's concept. Based on the prediction result of the residual consolidation settlement, the filling height of the D-runway at the start of in-service period was decided to be 0.70m, which is required from the aviation operation.
It would be very convenient if the permeability of a fine-grained soil could be predicted by simple index properties such as a void ratio. The difficulty is considered to be the uniqueness of water's property in such a soil. In order to effectively evaluate the permeability of a fine-grained soil, a new definition of soil's void ratio was proposed as a result of a freezing test. In this study, the following conclusions are obtained : 1) A new index called “frozen void ratio” is defined as a ratio of the volume of frozen water at a certain temperature below a zero degree Celsius to the volume of soil particles and unfrozen water ; 2) It was shown that under the reported test condition the frozen void ratio at -1°C most closely related to the permeability of a soil ; and 3) It was demonstrated that the Kozeny-Carman equation may be applied to a fine grained soil if the frozen void ratio is used instead of the conventional void ratio.