A systematic experimental study has been conducted for dynamic properties of natural soft clay employing an improved cyclic triaxial apparatus. Undisturbed samples with various void ratios and plasticity indices picked up from a alluvial clayey layer have been tested to reveal the following important facts : (1) The rate of the time-dependent increase of the shear modulus of clay can be approximated by a simple experimental equation in which only plasticity index is used. (2) The damping ratio of clay remarkably decreases with time implying that in situ clay will exhibit smaller damping ratio than that measured in the laboratory. (3) The strain-dependent variation of the shear modulus ratio is very sensitive to the plasticity index of the cohesive soil. The higher the plasticity, the lower will be the rate of the strain-dependent decrease of the modulus. (4) Based on the experimental results on clays with different consolidation histories, the current practice of combining the in situ small strain modulus with the laboratory modulus ratio vs. strain curve to estimate the in situ large strain modulus to be used in dynamic response analyses of grounds may be justified for engineering purposes.

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An adequate determination of permeability and flow resistance law is one of the important tasks for the hydraulic analysis of ground water motion in fractured rocks. In this paper, the flow characters and resistance law are experimentally studied by three kinds of rock block media composed of triangular, parallelogrammic and rectangular unit blocks in laboratory. By a newly designed apparatus, the flow rate measurement and flow path observation are carried out with the porosity range of 2.62%∼16.21% for each medium. Experimental results are examined by the dimension analysis, and the permeability formula is proposed.

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With respect to the groundwater analysis involving tunnels and caverns in rock, most papers have presented the problems on the basis of the assumption that the porous media were undeformable. Because of the dynamic deformation between fissures and rock masses due to water pressure, the groundwater motion will be affected by the deformable medium in addition to the excavation of underground structures.This paper aims at an examination of hydraulic behavior and the analysis of groundwater flow by a rock block model which behaves as an elastic body affected by the dynamic change of fissure water pressure. A new equation, which takes the vertical distribution of permeability into consideration is proposed based on both theory and field investigations. By this equation, the groundwater movement around the cavern is analyzed by the rock block model in a confined stratum of fractured rock. Results obtained from the finite difference method are examined by some laboratory experiments, which were carried out by using a rock block model composed of a number of cubic blocks and a cavern. Comparing their numerical and experimental results, it is found that the seepage flow analysis of the underground cavern by means of the rock block model may be valid for not only the analysis of flow around the cavern but also the hydraulic modelling of seepage motion in rock masses.

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A practical method for estimating the settlement of soft grounds including secondary compression has been proposed in the former papers (1979, 1980). The theory can exclude the difficulty that the vertical strain at 100% primary consolidation increases with the thickness of clay layer, owing to the secondary compression involved in the process of excess pore-water pressure dissipation, that is, during primary consolidation.The basic postulates, which were employed in the proposed equation in the former papers, are firstly reexamined. Among them, it is attempted to make clear the physical meaning of the following basic equations Δe=f(σ_υ, t) (i)Δe=Δe_p+Δe_s (ii) where σ_υ; vertical pressure, t; elapsed time, Δe; change in void ratio, Δe_p, Δe_s; void ratio changes due to primary consolidation and secondary compression, respectively. Eq. (i) is common with primary consolidation and secondary compression. As a result of the formulation by means of the both relations (i) and (ii), it is confirmed that the method proposed herein is in good agreement with the new concept of settlement which Bjerrum (1973) had brought out in analysis of settlement of structures in Norway. In addition, numerical investigations on the influences of several factors on the settlement versus time relations are performed by incorporating the experimental finding by Mesri (1973) that the ratio of the coefficient of secondary compression to the compression index, C_a/C_e(=R) is kept constant depending on the soil type into the basic equation. In numerical investigations, special emphasis is laid on the influence of the thickness of clay layer on settlement versus time curves.Computed time-settlement curves are compared with observations of settlement by Aboshi (1973) which are most reliable so far regarding the scale effect of one-dimensional consolidation of clay soil. This comparison suggests that the present theory will be valid especially for settlement prediction of soft grounds which exhibits predominant secondary compression.

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This paper is concerned with the elasto-viscoplastic constitutive equation of normally consolidated clay. A three dimensional constitutive equation is derived based on the Perzyna's elasto-viscoplastic theory and Cambridge theory. Comparing the theoretical results with the experimental results by triaxial compression test, it becomes evident that the derived constitutive equation can explain the behavior not only such time-dependent behavior as creep, stress relaxation and strain rate effect, but also as secondary compression, aging and isotropic stress relaxation. The equation has eight material parameters which can be determined by two undrained strain rate constant triaxial compression tests with different strain rates, usual consolidation and swelling tests. The proposed theory has a feature to be able to determine the secondary consolidation rate from the results of strain rate controlled undrained triaxial compression test.

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It has been indicated that the sensitivity of the marine sediment in Ariake Bay area varies between 8 and 50, and rarely is 100. Recently, however, extra quick clays with sensitivity greater than 50 and sometimes near 1000 were found in this area. In order to find the cause of the formation of extra quick clays, the sediment samples of slightly-very quick and extra quick clay obtained from two sites in Ariake Bay area were analyzed with respect to their mineralogical, chemical, and geotechnical properties. There was no appreciable difference in caly mineralogy between the sediment samples from two sites, and they contained smectite as the main mineral. The principal difference between the sediment samples of slightly-very quick and extra quick clay was in the salt concentration in the pore water which was in the range of 1.02∼10.4 g/l and 0.05∼1.08 g/l, respectively.The experiments of salt addition to extra quick clays and salt leaching from medium quick clays demonstrated that extra quick clays could be developed by leaching out of the salt in the pore water. The fact that extra quick clays can be developed in the sediment in Ariake Bay area, in spite of the presence of smectite as the main mineral, was interpreted by considering smectite in the clays to be of low-swelling type.

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This study has been carried out systematically and over a long period to clarify practical design problems for pile foundations to be constructed on a man-made island. Forty-one test piles in total were driven at six sites of the island. Of them, fifteen piles had their lower portions enlarged. The experiments conducted from 1977 to 1981 showed the following : (1) Settlement of the ground consisted of settlements of the fill, the alluvial clay and the diluvial layers. (2) A considerable number of blows was required to drive the piles through the sandy fill, although the dynamic stress during hammering was in any case below the allowable stress of pile materials. Pull-out tests of bitumen-coated piles showed little segregation of bitumen from the piles with enlarged lower portions. (3) Consolidation settlement of the alluvial clay layer caused settlement of the fill and, consequently, negative skin friction on piles. Frictional resistance of sandy soils was large. As generally known, negative skin friction was considerably reduced by the use of a bitumen-coated pile. (4) The bearing capacity of a pile driven into the bearing soil layer was attributed to the frictional resistance on the pile. (5) In case of a pile with enlarged lower portion, its lateral resistance could be maintained to a degree similar to that of a normal straight pile by filling the gap around the pile with sand.

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Geometrical property (fabric) of discontinuity in geological materials is discussed in terms of (1) position and density, (2) shape and dimension and (3) orientation of related discontinuities such as joint, fault and discrete particle. By taking into account these geometrical elements, a unique measure called fabric tensor F_ij is definitely introduced to embody the fabric concept without loss of generality.The first invariant of F_ij is important as an index measure to evaluate the crack intensity which is related to the number and dimension of cracks. Porosity of granite is shown to be an index measure equivalent to the first invariant of F_ij. According to uniaxial compressive tests on gypsum plaster samples with two-dimensionally oriented cracks and granite samples, the logarithm of the first invariant of F_ij is linearly related to their uniaxial compressive strength.A measure Γ which is related to the second invariant of the deviatoric part of F_ij shows a distance from an isotropic fabric. So, it is expected to be an index to measure the degree of anisotropy due to preferred alignment of discontinuity.The principal axes of F_ij are identical to the principal axes of fabric anisotropy. There is no doubt that Γ and the principal axes are important in the analysis of anisotropic-discontinuous geological materials.

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Experimental studies were conducted to investigate the effect of disturbance due to sample preparation on the shear strength of cohesive soils. The variation of the pore-water pressure was monitored during consolidation, extrusion and trimming with an embedded small porewater pressure transducer. The unconsolidated and undrained compression tests and unconfined compression tests were carried out on trimmed samples and the pore-water pressure during shearing was also observed with the probe.The negative pore-water pressure observed immediately after the removal of the consolidation pressure of 98 kN/m² compared well with the theoretical prediction. The negative pore-water pressure, the mean effective stress, decreased with the progress of sample preparation and remained at the constant value of about 30 and 20 kN/m² for soil with plasticity index equal to 50 and 30 respectively. This is equivalent to the overconsolidation ratio of 3 and 5. The stress paths for shearing tests are analogous to those of overconsolidated samples. The comparison of the strength of trimmed samples with that of ideal samples shows that the mechanical disturbance reduced the undrained strength more than swelling. Due to the sample preparation the undrained strength reduced by 15% and 30% for soil with plastcity index of 50 and 30 respectively.

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In this paper, the characteristics of dilatancy, i. e., the volumetric change which occurs when subjected to shear stress under the condition that the effective mean normal stress p is held constant, are examined performing p-constant stress-controlled drained triaxial compression tests on a clayey soil with various OCRs.For the understanding and interpretation of test results, the state paths on normalized state plane (q/p_e, p/p_e), where p_e is Hvorslev's parameter, and the relations between stress ratio and strain increment ratio are discussed using a few OCR dependent parameters which serve to specify the dilatancy characteristics. The sign of dilatancy volumetric strain is classified according to the degree of overconsolidation and the shear stress level.Additionally the non-linearity of swelling index κ is shown and the applicability of a relationship between κ and OCR, which has been proposed, is demonstrated for the clay used in this study and other cohesive soils appeared in literatures.

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