Soil-water characteristic curves for paper sludge (PS) and construction sludge (CS), applied as landfill barrier materials, are examined to estimate the unsaturated infiltration parameters. A prediction of water interception, based on the unsaturated infiltration characteristics of each type of the compacted sludge constituting the cover systems, is made using the UNSAT-H model. The data obtained from soil-water retention tests are identified by representative fitting models such as the van Genuchten and the Brooks-Corey models. From the soil-water characteristic curves and the fitting parameters, the effects of molding water content of the compacted sludge on the soil-water characteristic curves are clarified. It is found that PS compacted at a higher water content retains water greatly, because α and n (fitting parameters for the van Genuchten model) of PS decrease with an increase in the molding water content of the specimen. In the case of CS, macroscopic pore space forms when the compacted CS has a lower level of molding water content, while the CS at a higher water content can be compacted without the formation of clod structures. Such formation of clod structures contributes to the water retentiveness of CS. The results of an evaluation of the water interception performance of the cover systems, using a sludge barrier, show that the cumulative quantity of percolation water through the cover systems is less than 15 cm, which is approximately 1% of the total rainfall during the three-year analyzing period. Although the occurrence of leakage depends on the molding water content and rainfall condition at each site, over 99% of the rainfall can be intercepted by the installation of a cover system, even under a heavy raining condition such as that at Owase, Kyoto, and Tokyo in Japan.

View full abstract

Based on a series of cyclic cavity expansion tests carried out on a thick hollow cylinder apparatus (HCC) and on mini-pressuremeter tests performed in a calibration chamber, a method is proposed to establish a reliable correlation between the result of a "reference" cyclic expansion test carried out in a sand, in terms of cavity volume accumulation after a certain number of cycles, and the elementary behaviour of the same sand as observed upon undrained cyclic triaxial tests, in terms of number of cycles necessary to reach cyclic mobility or true liquefaction. The strong similarities observed between drained cyclic expansion test (non homogeneous test) and undrained triaxial test (homogeneous test) allow valuable correlations to be obtained between the results of both types of tests. A first validation of the method proposed is performed by comparing the liquefaction properties of two different sands with same initial conditions, and shows a good discriminating power of the method. Finally, the necessity of further validation of the method, in particular, a validation based on the performance of real in situ pressuremeter tests on sandy sites is mentioned.

View full abstract

A series of laboratory model shaking table tests were performed to evaluate improvement of the dynamic performance of mechanically reinforced soil structures that are vertically preloaded and prestressed by using a ratchet connection for the tie rods. The preloading and prestressing (PLPS) procedure was originally developed to substantially decrease the residual settlement at the top of backfill subjected to long-term live load such as traffic load. It is shown that the maintenance of high prestress in the backfill is also essential to substantially reduce the shear and bending deformation as well as vertical compression of reinforced backfill subjected to dynamic load. For relatively slender reinforced backfill structures, the maintenance of high prestress is particularly important to restrain the occurrence of large bending deformation of backfill. For these purposes, it is proposed that the top end of the tie rods be fixed to the crest of the structure by using a ratchet connection, which allows free compression of backfill at nearly constant prestress while mechanically not allowing any expansion of backfill. It is suggested that, to avoid a resonant or nearresonant state during seismic loading, the initial value of the natural frequency f_n of a given structure be designed to be sufficiently higher than the anticipated predominant frequency f_p of given seismic load, while the f_n value during dynamic loadine is maintained at a higher valve than the f_p value by using a ratchet connection.

View full abstract

A new devise is developed for conducting a strain-path controlled test with a conventional triaxial test apparatus. By controlling lateral stress during axial strain controlled test, this devise can keep the principal strain increment ratio, R_ε, defined as a ratio between axial and lateral strain increments, constant. Toyoura sand specimens at relative densities of 55% and 80%, consolidated under four different initial confining stresses, are axially loaded with a R_ε-value between -0.5 and 1.0. The specimens are then unloaded to the initial stress states and reloaded with different R_ε-values. The test results during compression show that the principal stress ratio, K, converges at a constant value. The converged K-value is strongly dependent on the Rε-value but insensitive to the strain history and the initial stress state. There is a well-defined relationship between the principal stress ratio K and the total strain ratio R_{ε, τ} where the K-value decreases with decreasing R_{ε, τ}-value. The K-R_{ε, τ} relation is independent of its strain path and uniquely expressed in terms of the internal friction angle and the dilatancy angle of the sand. Based on the K-R_{ε, τ} relationship, a simple equivalent linear constitutive model for axisymmetric condition is developed. Two series of stress-controlled drained triaxial compression tests are performed, and the results are compared with those simulated by the model. The computed results show excellent agreements with the test results, indicating that the proposed constitutive model, although based on the equivalent linear concept, is promising for simulating a stress-strain relation including dilatancy behavior of sand in the stress-controlled triaxial test.

View full abstract

The soil-structure interaction of underground structure was studied considering soil liquefaction of the backfill soil. A series of 1G shaking table tests was conducted on an aluminum fixed base structure model embedded in saturated cohesionless soil. A special attempt was made to experimentally build a stress-strain relationship as well as an effective stress path of soil around the embedded structure by installing a variety of transducers for acceleration, displacement, pore pressure and earth pressure. Moreover, earth pressure and bending strain of the flexible wall of the embedded structure model were measured. The time histories of shear modulus of liquefied soil, amplification of shaking, and the phase difference between displacement and earth pressures on the structure's side face were recorded. It was observed that the natural period of the ground along with structure and the dilative nature of the soil significantly affect the type of soil-structure interaction around the studied embedded structure. The problem of the determination of dynamic pressures on a flexible wall during liquefaction is solved analytically considering the dynamic feature of embedded structure observed in a series of shaking table tests. Finally, a comparison is made between measured and calculated dynamic pressure for several test results in order to show that the proposed solution of dynamic pressure on flexible wall gives good results.

View full abstract

Undrained anisotropy, together with the undrained response to monotonic as well as cyclic rotation of principal stress directions, of an isotropically consolidated loose Ham River sand has been investigated by performing three series of hollow cylinder tests. The initial anisotropy of the sand when subjected to a single consolidation pressure was successfully established in the first series of tests, each using different, but fixed in each test, values of α (i. e., the direction of major principal stress relative to the vertical deposition direction) at different b values (i. e., the relative magnitude of intermediate principal stress). The response against monotonic principal stress rotation was also examined in the second series of tests, in which the total stress path defined using the shear stress, t, and α was varied in various manner with b fixed at 0.5. In the third series of tests, the response to cyclic changes of both α and b was examined, and the results were interpreted with the comparative behaviour of the monotonic loading tests with different combinations of α and b. It was found that the sand's undrained anisotropy and cyclic response could be interpreted by invoking the concept of undrained local boundary surface (LBS). The four-dimensional LBS could be visualized in (t, p', α) space as a family of superimposed three-dimensional shapes with different b values.

View full abstract

The prospect of reusing sludge treated by solidification/stabilization prompts this technique and makes it attractive. However, the reuse of solidified/stabilized sludge must deal with the increasing concern of environmental impact in terms of heavy metals leaching, alkaline migration control and acid neutralization. This paper presents the results of an experimental study to investigate the suitability of a new low alkalinity additive (mainly gypsum and polymer). Assessment of two types of treated sludge was conducted through unconfined compression strength (UC) test, microstructure analysis (X-ray diffraction, scanning electron microscopy), pH test, acid neutralization capacity (ANC) test and chemical analysis for Pb leaching. Results of UC test and microstructural analysis show a solidification effect on the treated sludge with the development of new components, mainly hydrated gypsum, and to a lesser extent, hydrated cement products. pH variation measured during 28 days indicates the effectiveness of treatment by a low alkalinity additive. pH values were found tobe lower than 9 and influenced by the type of sludge and curing conditions (with and without air contact). ANC was found to be different for raw sludge and was enhanced by the treatment especially in the case of sludge treated with the highest amount of additives. ANC appears to involve dissolution of Ca, Mg, Al, Na and Si containing components. Although an increase of Pb release was observed with the increase of acid addition due to matrix dissolution and pH drop, measured concentrations were seriously reduced after treatment by the additive in treated sludge.

View full abstract

The failure criterion represented by matric suction is proposed on unsaturated soils. Although there is plenty of unsaturated ground under low confining pressure (lower than 100 kPa) near the surface of the earth, the application of the failure criterion under low confining pressure has not been confirmed. To achieve this objective, strength and deformation characteristics of an unsaturated cohesive soil were studied, with close attention paid to tensile stress using a hollow cylinder torsional shear apparatus. Experimentation was carried out under the conditions of constant suction, where it is easy to estimate the effect of matric suction. The difference between the failure mechanism under compressive stress and under tensile stress is investigated in this study. Then, the application range of the existing failure criterion is discussed with a focus on low confining stress range. Finally, new failure criterion on unsaturated soil considering tensile stress is proposed on the basis of the experimental results.

View full abstract

Composite reinforcements achieve the desired performance with a synergetic action from two components. In this paper, development of a composite reinforcement system, made of high tensile steel wire, encased in a cement mortar as a viable system for soil reinforcement applications is proposed. The high tensile steel wire takes care of the tensile strength requirement, whereas the interfacial friction between the backfill and the cement mortar takes care of adequate frictional capacity requirement. Both requirements can be independently controlled, enabling an optimum design of the composite reinforcement from both the considerations for a given situation. The paper presents the development of the technique, behavior and analysis of failure mechanisms of composite reinforcement from pullout test results. The results demonstrate that pullout failure of the composite reinforcement, tensile failure of the steel wire and bond failure arising from the proportioning of cement mortar mix needs to be considered in the analysis.

View full abstract

When a mudflow moves down a slope, the gravity induced shear stress, τ, is opposed by the combined effect of the undrained shear strength, c_u, of the mud, and its viscosity, η, which is associated with the velocity gradient in the mudflow, dv/dy. In equation form this can be expressed as : τ= c_u+η(dv/dy). The resistance provided by the mud involves the contribution of both c_u and η. For an understanding of the mobilization mechanics of mudflows, one needs then these two parameters. This study describes two methods that can be used to determine these parameters. The c_u of the muds is measured using a cylinder-strength meter devise. The technique associated with this devise consists in lowering a cylinder of known dimension and weight into a mud sample, measuring the depth of penetration of the cylinder into the mud, and calculating the strength, c_u, of the mud required to support the solid cylinder at that depth. The c_u of the mud is calculated using Sokolovski's theory designed to calculate the indentation pressures developed by a Tresca plastic when a cylinder penetrates it. The determination of the viscosity, η, of the mud is obtained from either the velocity measurements of the free surface of the mudflow, or from the difference between the velocity of the free surface of the mudflow and its velocity at the interface between the mudflow and the surface on which it moves. The viscosity η is obtained from a relationship that relates these velocities with η.

View full abstract

[in Japanese]

View full abstract