The various stress change with rotating principal axes act on soil in actual ground. The distribution of the interparticle contact normals, meanwhile, gradually tends to concentrate towards the direction of the major principal stress σ₁ when that of anisotropic stress acts on soil skeleton. And then, the stiffness of soil in the direction of major principal stress relatively increases. In ordinary model, such an induced anisotropy is considered by applying kinematic / rotational hardening rule in ordinary stress space. On the other hand, a new method, in which the induced anisotropy of soil is described simple and general isotropic hardening model by applying the modified stress which reflects the fabric change due to the variations of the intermediate principal stress and the stress histories, is developed in this study. The validity of the proposed model is verified by comparison with the experimental results of true triaxial tests on medium dense sand. It is shown that the proposed model, which obeys isotropic hardening rule and follows associated flow rule in t_ij^* space, suitably considers the influence of the intermediate principal stress and the past stress history simultaneously and properly reproduces the test results under various complicated three-dimensional stress path.

View full abstract

One-third or one second of volume capacity in a landfill was filled with cover soils layers. Concerning about the increase of volume capacity in the landfill against the shortage of the place to construct the landfill, it is necessary to develop new cover soil with thin and low permeable functions. In this study, it was focused that calcium ions in the leachate reacted CO₂ obtained from micro metabolism under the pH of 8.0 and CaCO₃ should be precipitated. Hence, the objective of this study was to develop the new cover soil material called Bio-cover soil filled with CaCO₃ to reduce the total volume of cover soil in the landfill. Formation condition and hydraulic property of bio-cover soil were clarified in this paper and finally, calcium concentration of 80% was reduced in the source of calcium after forming bio-cover soil in this study.

View full abstract

Dynamic load test methods of single piles in vertical direction have been developed. In a vertical dynamic load test, signal matching analysis is carried out to identify appropriate soil resistance parameters. A static load-settlement curve of the tested pile is then calculated using the identified soil parameters. The dynamic pile load test method requires less time and cost compared with the conventional static pile load test. Hence, the authors have been developing a dynamic pile load test method of single piles in the horizontal direction. In this paper, the method of dynamic horizontal pile load test including loading and measuring systems and an analytical method is described first. Then, the validity of the proposed horizontal dynamic load test is examined and discussed through three case studies where dynamic horizontal load test and static horizontal load test were carried. It is concluded that although the proposed method still has a room for improvement, the proposed dynamic horizontal load test method is a promising approach to estimate static horizontal load vs horizontal displacement of a tested single pile.

View full abstract

Liquefaction countermeasure that prevents the ground from liquefying along the whole area of the long channel is estimated hugely expensive and impractical. Therefore, reasonable liquefaction countermeasure which can satisfy the performance requirements of the channel is expected, and proposal of an accurate method to predict the response behavior of channel is important. A study on the application of the countermeasure using sheet-pile with drain to the flume channel has been conducted in order to reduce the influence of liquefaction to the channel. Good reproducibility for dynamic effective stress FEM analysis (LIQCA code) with respect to the results of several shaking table tests (1G) is confirmed, and this analysis method can be applied to predict the response behaviors of the channel.

View full abstract

A laboratory compaction test method using a rammer to predict the effect of soil compaction in the fill work is proposed. This method can be performed using instruments as same as the ordinary tamping test. In this test, the progress of compaction according to the frequency of pass of a machine such as vibratory roller or bulldozer is represented by accumulation of tamping energy in a specimen. This method, different from other methods proposed so far, deals with the compaction effect during not only rolling but also spreading and leveling using a bulldozer. Comparing with the field compaction, we have confirmed that the relationship between the number of roller pass and the dry density of the fill is predictable using this technique, as long as the work conditions including machines and layer thickness are constant, even if water content and grain size characteristic of the fill material changes significantly. This technique can be used, as a substitution of the real fill compaction test, to confirm the validity of the prescribed requirement for number of roller pass, in a case that the compaction characteristic of the material may change.

View full abstract

A method for measuring the permeability coefficient of frozen soils in which generalized Clausius-Clapeyron equation is applicable has been proposed. In this method, in order to acquire continuous water flow, soil’s ice segregation phenomena have been prevented by applying axial stress. The top and bottom of the specimen were kept at normal temperature and the center of the specimen was controlled at minus temperature. Flow rate have been measured by applying differential head and the permeability coefficients were calculated by water flow in steady state. In this study, a test apparatus was newly developed using this measurement method and permeability coefficients at various temperatures were measured. As a result, the permeability coefficient of frozen soil has been shown to have a temperature dependency and the coefficient decreased rapidly around 0 °C.

View full abstract

Prebored piling method using nodular pile (precast concrete pile) consists of pitching the nodular pile into soil cement formed by mixing and agitating cement slurry and soil. Formulae for estimating vertical bearing capacity determined from the ground around the pile have been proposed based on the results of many loading tests. For vertical bearing capacity to develop, the soil cement has to transmit the load acting on the nodular pile to the ground; thus, the quality of soil cement (finished work quality, strength, etc) is a factor that affects the development of bearing capacity. However, examples that directly verify the quality of the soil cement after the loading tests are few in number, and many uncertain factors, such as the damage status of soil cement at ultimate bearing capacity, have not been clarified. In order to clarify such uncertainties, investigations were carried out on two excavated piles after conducting loading tests and confirming the bearing capacity. The results of the investigations showed that the soil cement around the excavated piles was formed satisfactorily and was sound with no crack or damage even at the ultimate bearing capacity.

View full abstract