There are many classifications of soil in the field of soil mechanics. However, most of them are related to materials of earth constructions such as embankments, roads, dikes etc.. In the application of soil stabilizations to a soft ground, it is required to know the natural state of its ground in addition to its soil classification since soil stabilizations as an artificial action are applied to a soft ground in its natural state. Several methods to represent the natural state of ground are discussed in this paper, namely, (1) area coordinates, (2) indication by pF-scale and (3) indication by consistency index. By analyzing various soil stabilizations done in situ on the basis of both the conventional classifications and the proposed methods, it was found that there were significant correlations among the characteristics of stabilized ground, the stabilizing method, the kind of soil and the natural state of the ground. On the basis of the relationships obtained, it seems possible to select an optimum soil stabilization suitable for a ground by primary survey of the ground.
The ground condition of the Kongo-gawa Tunnel from its entrance to the 100m-depth is severe, i.e., the earth covering is thin (15m), the upper layer of the ground consists of talus, and besides the clay layer under the tunnel is short of bearing power. To cope with this site condition, the silot tunnel method, the chemical grouting method, and the shotcrete method were adopted. As a large amount of settlement arose after excavation of silot tunnels, it was feared that the settlement would increase much more in excavating the upper half section. But by using the shotcrete method in excavating the upper half section, the settlement could be held down to a comparatively little amount. This paper reports the construction outline. Furthermore, the results of elastic FEM analysis for the upper half section excavation showed that the settlement of ground surface using the shotcrete method model became half as large as that of using the conventional method model.
The quicklime pile method has been adopted to improve weak soil foundations, especially those consisting of high moisture cohesive soil. When the method is applied to peat foundation which has organic soil with 1000-1500% moisture content, it is necessary that the quicklime maintains its hydraulic characteristic as a stabilizing material without losing its water absorbing and expanding effects. In the present study, a new hydraulic quicklime consisting of 71.3% CaO, 13.9% SiO2, 6.0% R2O3, 2.5% MgO etc., was used instead of a usual quicklime consisting of 82.9% CaO, 7.8% SiO2, 2.5% R2O3, 1.1% MgO etc., and the improvement of peat foundation by this new hydraulic quicklime was examined mainly by plate loading tests, N value, chemical durability etc.. The results were satisfactory.
In the recent years the shield method has been greatly improved and thus reliable back-filling become a very important problem for successful construction. The back-filling metarials currently used, however, have such undesirable tendencies as run-off into natural ground, flow-out to the face, dilution by water, etc.. In order to overcome these weaknesses, a new grouting material and a new injecting system with it have been developed. The main component of new grouting material is one type of silica-gel which is formed mixing silica-sol, particular cement and aggregates. In the new grouting method, a small amount of new grouting material is added to the back-filling slurry during its transmission by adopting a new mixing system, 1.5 shot of proportion type. Through this mixing process, the liquid material becomes a solid state of thixotropical-gel; in the state the material does not flow by its own-weight but easily flow by the action of pumping pressure. In order to compare effectiveness of the new grout and grouting system with that of the grouts and systems currently used, outdoor grouting tests were carried out use of a large-scale model mold. The results showed its great resistances against dilution by water, bleeding, segregation, flow-out and run-off.
The injection engineering has been making a rapid innovation during the past few years, specifically from the point of the high efficiency and anti-pollution measures. The conventional method utilizes the gelling characteristics of water glass in its alkaline range. Our new injection material utilizes the gelling characteristics of non-alkaline silica sol which is obtainable by removing alkali from water glass. In this paper, the principle of gelation, the results of various laboratory tests, the toxic test by using rats and killi fish, and the germination test of rice seeds were described. Furthermore, the examples of practical application in the cable buried works in the ground consisting of fine sand or complex soil layer were demonstrated where the efficiency of using this new injection material was found to be satisfactory.
Hydrophobic polyisocyanate grout is often applied in such places as subbases of railway tracks and roads, where dynamic loads predominate. Furthermore, dynamic loads will act on foundations of structures during earthquakes. In order to investigate the dynamic characteristics of soil solidified with hydrophobic polyisocyanate type grout (trade name is TACSS), the following studies were performed: (1) Influence of repetitive stresses during early strength gain. (2) High speed compression test. (3) Behavior of the displacement under one million cycles of repetitive loads. (4) Dynamic triaxial test to investigate the shear modulus and damping ratio. The results obtained from these studies are as follows: (1) There was no difference in compressive strength between the cases with and without repetitive stresses. (2) When the loading speed was about 900 times of the normal speed, the compressive strength became 43% higher and the maximum strain was 28% less than the normal case. (3) The solidified soil did not break even under one million cycles of repetitive loads whose stress amplitude was 10 to 90% of compressive strength. (4) As the results of the dynamic triaxial test, 3000∼7000kg/cm2 of equivalent shear modulus (Geq) and 1∼10 of equivalent damping ratio (heq) were obtained, and they were independent of the repeated number (N). These results show that the solidified soil (Toyoura standard sand) by TACSS looses the properties of sandy soil and exhibits the similar charcteristics of mud stone which has compressive strength of above 100kg/cm2.
In the case of structural construction of sheathing and cut-off wall within the city limit, the soil mixing wall engineering method is being employed because of least noise and vibration characteristics. In this method, multi-shaft mixing auger machine are used to excavate the ground, mixing the soil with the blown cement milk from the auger axial, while the rectangular cement pile are continuously driven in. By using multi-shaft mixing auger, continuous soil cementing is possible, consequently raising its reliance as a sub-surface wall compared to that of the single auger. The strength of the soil cemented sub-surface wall weakens depending upon the kinds of soil encountered, and in the case of deep excavation, it cannot resist the soil pressure by itself, and thus the reinforcement by the H type steels at suitable intervals becomes necessary in actual practice. The important role of soil cement in this case are considered to be sheathing, rigidity and adherence to the H type steel. The soil cement may be efficient partially to improve bending rigidity, although it is usually neglected in design. In order to clarify this point, an experimental study was performed on the effect of reinforcement for bending rigidity of the soil cement to the H type steel. It was found that this effect contributed about 20% to 30%.
The soft clays, alluvial deposits, are widely distributed over several coastal regions in Japan. The inferiority of these kinds of soils is the main obstacle for using them as construction and foundation materials. Furthermore, the inferior clay soils floating and accumulating on the sea bed, the so-called“Hedoro”, disturb the navigation and decrease the ability of port functions. Thus, in recent years a very difficult social problem of coastal pollution has arisen. The purpose of this study was to investigate the influences of microorganisms on engineering properties of soft clays in order to solve the above problems as well as to use them as engineering materials, such as in reclamation work and embankments. The growth of microorganisms was obtained by adding trace amounts of microbial nutrients and inocula into the clay soils and the properties of these treated soils were improved.
In this paper, the first part discusses the engineering characteristics of granulated slag as a soil material and the second deals with some applications of it in the fields. (1) The weight per unit volume of this slag is 1.2∼1.4(g/cm3), which is about 70% as compared with that of a natural soil. The low density depends on the slag particle which has many pores inside. (2) The coefficient of permeability of the slag is 1.0×10-1∼10-2(cm/sec), so that the slag can be used as a soil material with high drainage. (3) The angle of internal friction is more than 35°, which depends on the degree of compaction. The slag particles are normally angular and grip well each other. (4) The slag has the character of self-hardening with time and it is promoted easily by the help of alkali as a lime. Thus the slag can be used as a cohesive sandy material. The granulated slag, which has the above characteristics, can be used for the materials of embankment on soft clay ground, basement of road, stabilization of slope, back-filling of retaining wall and so on. Some examples of the site uses and designs of the granulated slag were also given.
Special Solidificants have often been used in recent years for treatment of Hedoro (bottom sediment mud) and soft soil. However, the conditions for application and the effects of such special solidificants are not yet thoroughly understood. Comparison tests of 14 varieties of cement-type solidificants were therefore performed. (1) The solidificants were found to contain CaO, SiO2, Al2O3 and SO3, and were divided into six groups according to the amounts of these components contained. (2) A solidificant having a large content of SO3 (11∼13%) produced the highest strength. On the other hand, ordinary portland cement and solidificants of similar composition produced low strengths. (3) It was observed by means of an X-ray diffractometer and a scanning electron microscope that the formation of ettringite in solidified soil contributed greatly to strength gain.
Deep Mixing Method of soil stabilization using cement as a hardening agent has been widely applied at actual construction sites in recent years. In this method, the effect of cement treatment is generally judged by the unconfined compression test. This report gives a description of size effect as one of various factors that influence the unconfined compressive strength of cement treated soil. To investigate the size effect, unconfined compression tests were performed on the specimens of various volume with constant slenderness ratio (H/D=2.0) and those of various slenderness ratio with constant diameter (D=40mm). The effect of tamping methods that influence the unconfined compressive strength was also examined. As the result, it was found that the unconfined compressive strength, qu, decreased with increasing diameter of specimen under constant slenderness ratio. qu decreased little with increasing slenderness ratio, H/D. E50, the tangent modulus at stress level equal to one-half of qu increased from 200qu kgf/cm2 to 380qu kgf/cm2 for qu with increasing diameter. The unconfined compressive strength, qu2, obtained by tamping a rod bar decreased with decreasing strength, qu1, obtained by dropping on the concrete base. For qu1 less than 15kgf/cm2, qu2/qu1=(0.8∼1.0), and for qu1 greater than 15kgf/cm2, qu2/qu1=1.0 were found.
There are many soil stabilization methods which have been applied to improve inferior ground. This paper deals with a new method, called“partial-drain method”, in which high permeable and discontinuous materials were uniformly added into the clay to accelerate the consolidation. The results of laboratory tests by this method showed that there were many fragments which had a remarkably good influence on the consolidation and the shearing resistance of the improved clay. Some material properties of fragments, such as their absorpting characteristics, their specific gravities and their states of distribution in the clay were also discussed. The main results obtained are as follows. (1) The coefficients of consolidation and permeability of the improved clay were about 2.0∼4.0 times as much as that of the unimproved clay. (2) The shearing resistance of improved clay was about 1.6∼1.7 times as much as that of the unimproved clay. (3) The dispersing characteristics of fragments in the clay was improved by adding carboxymethyl cellulose (panfloc).