This paper outlines a mathematical description of the stress dilatancy behaviour of granular materials which accounts for stress level and void ratio dependencies. The consideration of these aspects has important implications in the modelling of granular material behaviour. In fact, granular material mechanical response is largely dominated by the evolution of dilatancy, fabric and void ratio histories. The starting point in this study is the well established Rowe's theory which is revisited and ultimately modified by introducing a factor linked to governing state parameters in order to describe the complete behaviour of granular materials during deformation. Numerical simulations of triaxial tests on granular materials at different void ratios and stress levels are herein presented to illustrate the model.

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It is widely known that shear strength of clay continues to increase after the end of primary consolidation. Some reports show that the strength gain is remarkable especially for marine clays near surface of natural deposits. However, not much is understood on this subject. An attempt has been made to reveal the phenomenon of strength gain with time. The developing mechanism of shear strength is characterized by assuming that shear strength gain during the secondary process can be understood as two contributing components : secondary compression and effect of cementation. The increase rate of shear strength for a sedimentary from clay slurry is investigated. It is found that a remarkable increase in shear strength is obtained during the secondary process, though little change takes place in water content. Based on experimental data, the authors suggest that cementation effect on shear strength gain is in relation with overburdened pressure p₀. The increasing rate can be expressed simply by Δc_u/Δlog t=0.3√(p₀). This relation is verified as nearly valid when overburdened pressure is extended to p₀=0.01-1000 kPa.

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A variational approach for the analysis of rectangular rafts on an elastic half-space under vertical loading is presented. The deflected shape of a raft is represented by a function with a set of undetermined constants. The response of the raft is determined by the use of the principle of minimum potential energy. The results based on the present method compare well with available published solutions.

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Resilient modulus (M_r) is one of the most important parameters in the design of highway pavements, and it is an indicator of the behavior of material as a component of the pavement system which is subjected to vehicular loading. To improve on the quality of the aggregate, cement kiln dust (CKD) is being proposed as an additive to an aggregate intended for base/subbase construction of highway pavements. A series of triaxial cyclic loading tests were performed in accordance with the AASHTO T294-921 procedure to investigate effects of CKD amounts and curing time on the resilient modulus of the aggregate. It is found that the M_r values increase with the CKD amount and with curing time within a certain period. The aggregate stabilized with 15% CKD is found to be best suited for base/and subbase with regard to the M_r value. For 7-day and 28-day curing periods, the increase in M_r values with respect to the raw aggregate can be up to 70% and 120%, respectively ; however, the difference between the 28-day and 90-day stabilized aggregate is minimal. Scanning Electronic Microscopy (SEM) tests and X-ray diffraction (XRD) tests were performed to reveal the mechanism of stabilization. It is found that the increase in resilient modulus is the result of hydration of the CKD and filling of the intracluster voids of the fine particles of the aggregate.

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This paper presents a comprehensive analysis of the effects induced by drained and undrained preshear and, in general, by preloading history on the undrained behaviour of loose sand prepared by moist tamping. The results are interpreted from the point of view of understanding the evolution of elastic anisotropy and the shape of the yield surface. The undrained behaviour of loose sand is shown to be a powerful and expeditious means for analysing the effects of stress-induced anisotropy. At first the reliability of this approach is evaluated through a comparison of the undrained effective stress paths with the stress states corresponding to a stiffness change along drained stress paths of samples subjected to the same preloading history. Subsequently the effects induced by isotropic preconsolidation, by drained preshear at different maximum stress ratios and along different stress paths, by undrained preshear and, finally, by drained cyclic preshear are analysed in detail on samples with similar void ratios at the beginning of the undrained loading phase ; the results are discussed in terms of the evolution of the yield surface and elastic anisotropy. This paper is consequently both a further development in the analysis of the effects of preloading history on the undrained behaviour of saturated loose sand and another step towards a better understanding of the mechanisms governing the evolution of mechanical anisotropy in loose sands along triaxial stress paths.

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This study shows that calcium carbonate plays an important role as a cementing agent of soils. The vane shear strength and unconfined compressive strength of sedimentary soils are shown to vary with depth and are strongly dependent on the calcium carbonate content. It was found that an increase in calcium carbonate content caused an increase in soil strength, and that a decrease in soil strength was attributed to the decrease in carbonate content. The cementing effects due to calcium carbonate are quantitatively evaluated in this study. The results show that the increase in soil strength due to calcium carbonate is very high, depending on the type and age of the soils. For example, some alluvial sedimentary soils show an increase in unconfined compressive strength of 64 kPa by an increase of one percent in calcium carbonate.

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The methods of Coulomb and Rankine are still the most widely used to compute earth active thrusts on walls. The former is prevalently used for gravity walls, the latter for cantilever walls. In contrast to Coulomb's method, which can be used in a wide range of conditions, Rankine's method has a very limited applicability and does not permit the solution of many practical problems concerning active thrusts on cantilever walls. This paper shows that the methods of Coulomb and Rankine, when used in the same conditions, give identical values of the active thrust coefficients. Then it proposes a new method, based on Coulomb's approach, for evaluating active thrusts on cantilever walls in general conditions, which can solve a large variety of problems involving backfill with irregular topographic profiles, lines and strips of charge and whatever pore pressure distribution.

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It is essential to predict or evaluate permeable flow for the safety of structures constructed in a cracked rock mass. The permeable flow analysis, however, is not easy due to the limitation of the in-situ measurement of geological and hydrological conditions. To overcome this difficulty, we propose a pair of analysis methods, the Monte-Carlo simulation of fracture networks to estimate probabilistic distributions of permeability and the bounding media analysis to provide upper and lower bounds for the expectation of the permeable flow. An example problem of an actual rock mass is solved by using these two analysis methods. It is shown that the predicted distribution of the effective permeability becomes log-normal, and that the computed upper and lower bounds actually bound the mean of the permeable flow which is computed from the Monte-Carlo simulation of randomly generating porous media. The validity and usefulness of the proposed analysis methods are discussed.

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A new stability analysis of rock mass is proposed by taking account of contact interaction along macroscopic discontinuous lines. The lower bound theorem in plasticity is employed with the finite element discretization technique. The joint element is introduced to describe the equilibrium equation in terms of stress in rock and contact traction along discontinuous line. The shearing behavior of joint as sliding and detachment is modeled as a rigid perfectly plastic one. The applicability of proposed method has been investigated in detail in comparison with the upper bound solutions by Tamura (1990). For every case, both computation results matched well indicating that both methods could be applicable to the stability estimation of a rock mass including macroscopic cracks inside. The ultimate bearing capacity of ground which includes discontinuous lines inside has been further assessed to investigate the effect of geometrical configuration and shearing property of discontinuous lines on the total stability. In particular, non-linear shearing property of discontinuous line against confining stress has been brought into the proposed method. The wide applicability of the proposed method to stability estimation of rock mass is clearly confirmed through some numerical studies.

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In the conventional approach of elastoplastic modeling, using the invariants of ordinary stresses and strain increments can not properly consider the effect of intermediate principal stress on the strength and dilatancy of soils. A previously introduced modeling approach using modified stress (t_ij) can express the strength and dilatancy behavior of normally consolidated clay under generalized three-dimensional stress conditions. It has been verified that this modified stress approach closely simulates soil behavior under monotonic loading conditions. To express stress induced anisotropy, a kinematic hardening (in the stress ratio space) model for clay using modified stress has been proposed, which over predicts volumetric strain and does not show stabilization of strain during cyclic loading. To rectify those problems the evolution rule of the rotational variable has been modified and a subloading surface has been introduced in the model proposed in this paper. The applicability of the proposed model on normally or overconsolidated clay under monotonic or cyclic loading conditions is verified using triaxial, true triaxial and torsional shear tests.

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Cast-in-place concrete piles are made by placing concrete into slurry that fills an excavated hole, and where appropriate control of the physical properties of slime and slurry is necessary. Electric resistivity of suspension generally depends on the content of the suspended substance, so that physical properties such as density, sand fraction and funnel viscosity of slurry and sand fraction of slime, are closely related to resistivity of slurry and slime. In order to control these physical properties, we must measure their depth distributions in excavated holes. Measurement of resistivity in excavated holes continuously by depth is relatively easy, so we attempted to obtain information on physical properties of slurry and slime by measuring vertical distributions of resistivity. Relationships between the resistivity and physical properties of slime and slurry were determined in the laboratory test, and the vertical resistivity distribution of the slime and the slurry in the hole of a cast-in-place pile at excavation was also studied with a sensor capable of recording in-situ resistivity continuously. As a result, it was found that changes of resistivity were widely affected by the bentonite content of slurry and the sedimentation thickness of slime can be estimated with satisfactory precision by the vertical resistivity distribution (depth profile of resistivity) in an excavated hole. The resistivity method can be an effective, promising control method for the physical properties of slurry when the relationship between resistivity and the properties is quantitatively determined.

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A problem which hinders 3-D seismic tomography using the crosshole technique is observed, identified, and theoretically explained. The problem relates to the phenomenon that the amplitude and phase of the shear wave are not consistent over a horizontal plane crossing the wavefront. These variations in amplitude and phase are explained based on the theory of shallow earthquakes, which confirms that this phenomenon is directly related to the n-value of the source used in the crosshole measurements. Polar diagrams are presented for sources with various n-values. Examples are also provided for the variation of time records due to the source orientation. Furthermore, a procedure is proposed for the determination of the n-value of the source.

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