It has been shown after mathematical and mechanical investigation that Limit Equilibrium Method (LEM) can be considered as a method to obtain the necessary condition of Slip Line Method (SLM), and that the solution can be obtained under the condition that F_s=1 and ∂F_s/∂θ=O, where F_s is the safety factor and θ is the inclination of the plane on which the safety factor is defined. Next, the generalized LEM (GLEM) is proposed, dealing with the following points : (1) Triangular or quadrangular blocks can be treated; (2) Safety factors are defined also on interblock planes; and (3) All types of plastic problems, slope stability, bearing capacity, and earth pressure are identically formulated. Two situations regarding treatment of the moment equilibrium condition are discussed. GLEM is applied to well-known problems. The results agree well with those obtained by theoretical methods. GLEM can be used to obtain the distribution of earth pressure or bearing capacity. GLEM, Iike ordinary LEM, is very effective for the practical problems, but GLEM is more theoretical and it can result in more accurate solutions.

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Stress wave theory is applied to open-ended pipe piles to clarify the effects of soil plug on the behaviour of piles during driving and static loading. Measured field data and various numerical models are reviewed ; methods are presented to calculate wave propagation in both the pile and the soil plug ; modelling is presented which takes into account the interaction between the soil plug and the pile ; also presented is simplified method to estimate the loadsettlement relation of the pipe pile in static loading. By correlating observed and calculated values in two analytical cases, the authors demonstrate that incorporation of the soil plug (modelled as a series of masses and springs) is required to correctly predict pile behaviour during driving and static loading.

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Anchors are being extensively used in foundations for the structures subjected to both compressive and tensile forces. An attempt has been made to develop screw piles as anchors in clayey soils. The screw piles are made of hollow galvanized iron pipes (dia. 25mm, 44mm, 60mm and length 640mm and 1000mm) to which helical plates (dia. 75mm, 100mm, 150mm) are welded. Number of plates are varied from 2 to 4 and there are different spacings of these plates adopted. These piles are screwed into soft to medium stiff clay bed prepared in a test tank. Standard type of loading frames have been made for effecting both compressive and tensile forces. In all about 40 Nos. of tests have been conducted in three soils. The behaviour of these piles has been studied through the load deformation curves. Decrease in the moisture contents leads to significant increases in the capacity of the piles. By keeping the ratio of the spacing of the helical plates to diameter of the helical plates between 1.0 and 1.5, optimum capacities of the piles could be obtained. The test results indicate that theoretical predictions for the load carrying capacities can be made by making use of the measured shear strength of the soils.

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A finite element model capable of taking into account nonlinear hysteretic soil behavior is presented to study earthquake induced retaining wall movement. The model also accounts for increase in lateral stresses and settlement associated with grain slip caused by cyclic loads. The predictive capability of the proposed method is verified by comparing responses given by the model with those computed by another existing finite element model and also with responses recorded at the Cambridge centrifuge facility. The study reveals that the wall displacement can be substantially affected, among other factors, by the increase in lateral stresses due to grain slip and wall-soil friction. Care should be taken when selecting a constant value of wall-soil friction angle for the entire duration of excitation since structural changes can occur in the soil adjacent to the wall.

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For piezocone penetration in clays, cavity expansion theory describes both the point resistance and induced excess pore water pressure in terms of the undrained shear strength (C_u) and rigidity index (I_r=G/C_u). Modified Cam Clay provides a simple effective stress representation of undrained behavior in terms of stress history. Therefore, the two theories may be combined to provide an approximate determination of the in-situ overconsolidation ratio (OCR = σ_p'/σ_υo') in terms of the effective stress friction angle (φ') and normalized piezocone parameter (q_T - u_m)/σ_υo', in which q_T=corrected cone resistance and u_m=measured pore water pressure. The approach distinguishes between piezocones which measure pore water pressures on the cone tip/face (u_t) and those which measure just behind the tip (u_bt). Specific examples are presented to show the general applicability of this simple effective stress model for estimating the in-situ stress history of clay deposits with 1<0CRs<60 and 20°<φ'<40.

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The performance of single pitch and multi pitch screw anchors during the application of installation torque is presented. An experimental testing program was conducted using five models of screw anchors with different geometry. The effect of the shape of the screw element, sand properties, and installation depth on the required installation torque value was examined. A theoretical model was developed from which the required installation torque value can be calculated in terms of the influencing factors. The required installation torque can be determined in terms of the ultimate uplift resistance calculated from any of the available theories. Based on the actual installation torque value measured in the field, the anticipated pullout capacity can be back calculated from the present theory. A comparison between theoretical and experimental results showed good agreement. Also, good agreement was observed when the present theoretical results were compared with the available field results reported in the literature.

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This paper discusses the consolidation behaviour of a diatomaceous mudstone, which is best featured as a naturally cemented material having a highly porous skeleton. Part I of the paper presents the results of isotropic consolidation tests as well as falling-head permeability tests, all of which were performed on undisturbed specimens of the mudstone by using a high-pressure triaxial cell. The principal findings include : (1) the mudstone exhibits distinct yielding when it straddles the pre-consolidation pressure ; (2) the secondary compression is negligibly small before the initial yielding, but becomes very pronounced when loaded sensibly above the pre-consolidation pressure ; and (3) the logarithm of the coefficient of permeability decreases linearly with decreasing void ratio. In part II of the paper, an associated series of coupled-stress flow analyses of the consolidation tests is performed in terms of the method of finite elements. An adapted version of the elasto-viscoplastic coustitutive model (Sekiguchi, 1977) is implemented into the analysis procedure. The procedure of determining the constitutive parameters is described. It is then shown that the predicted performances compare favourably with the measured performances of consolidation in a consistent manner, thus validating the relevance of the elasto-viscoplastic formulation adopted.

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Takadate loam and Hachinohe pumice, which are two typical volcanic soils distributed widely in the Hachinohe district of Japan, were selected for this investigation. The materials were used in laboratory compaction tests with a rammer under various methods of sample preparation and a given compactive effort. Unconfined compression tests were performed on the compacted soils. The sample preparation methods were categorized into the following four : Method-A (a process which adds moisture and reuses material), Method-B (a process which adds moisture and uses new material), Method-C (uses a drying process and reuses material) and Method-D (uses a drying process and uses new material). Method-D presented the most reasonable results in the laboratory for the real nature in-situ. Different sample preparations produced different curves for the relations of q_u, &isins;_f, E₅₀ and the moisture content. The relations for q_u, &isins;_f, E₅₀ and air void e_a, however, proved to be unique, irrespective of the method of sample preparation used for both types of soils. Thus, application of the air void in place of the moisture content was recommended as a reasonable parameter for quality control of the rolled fill in this district. It was also clarified that the relation of E₅₀/q_u and &isins;_f could always normalize the uni-axial characteristics of the two tested materials, irrespective of the method of sample preparation or soil type.

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The effects of desiccation on deterioration and the decay of strength are investigated using an unweathered diatomaceous mudstone. Unconfined compressive strength and splitting tensile strength are measured for 333 specimens prepared as follows ; (1) drying from an unweathered state, (2) wetting from a dried state, (3) applying the repetition of a certain type of drying-wetting process, and (4) applying the repetition of various types of drying-wetting process. Experimental results show that the strength reduction caused by the drying-wetting process depends on the degree of desiccation. The final strength is found to be a function only of the highest degree of desiccation that the specimen has ever experienced during the past drying-wetting process.

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Based on an experimental observation by Haung and Tatsuoka (1988) a mathematical technique first proposed by the Author, Poorooshasb (1982), is employed in the development of an analytical procedure to achieve the solution to a certain class of problems associated with the performance of heavily reinforced mats supported by weak subgrades. The class of problems that can be handled by the present analysis include ; (i) mats supporting point loads, uniformly or symmetrically distribute loads, (ii) mats bridging over voids appearing in the subgrade after construction and (iii) mats placed over nonuniform forms of ground subsidence. The analysis presented is essentially an engineer's approach and compares, in simplicity, to a similar approach used in the analysis and design of shallow beams.

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An improved version of steady state Rayleigh wave method is presented for the determination of shear wave velocity (V_s) Profiles of a horizontally stratified soil deposit. A dispersion curve and particle orbits of Rayleigh waves can readily be determined in the field through measurements of ground motions induced by an exciter using sensors placed on the ground surface. To determine V_s-profile from the dispersion curve, an inverse analysis which can take into account higher modes of Rayleigh waves is presented and used. To increase the effectiveness of the proposed method, desirable distances among the exciter and sensors are indicated, and the measured particle orbits are used to validate the inverted V_s-profile. Comparative field tests are made at two sites using the proposed method and the conventional down hole method. The V_s-profiles from the two methods are in good agreement with each other, indicating the effectiveness of the proposed method.

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The concepts of two characteristic states and their representation as characteristic state lines in the stress space are introduced to describe volumetric behavior of cohesionless soil during shearing. The first characteristic state line represents the state of cohesionless soil at failure, while the second characteristic line represents the state at which the rate of volumetric strain momentarily vanishes as the soil passes from the compressive mode of deformation to the dilative mode of deformation during shearing. Explicit forms of the two characteristic state lines in the stress space are proposed and used to develop a constitutive model based on the framework of plasticity theory. The general forms of the characteristic state lines are verified using drained shear test data for a fine sand. Stress-strain and volumetric-axial strain responses are predicted using the proposed model and good correlations are observed with experimental data.

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If one is to deal with experimental analysis of soil-foundation interactions, the first problem to consider is that of reconstituting soil models. This paper presents the results obtained by using a sand-spreader which was designed and built by the author for this purpose. The paper also looks at design criteria and the calibration of the assembly. The dimensions of the sand sample, which is sprinkled into and contained inside an iron caisson, are 1.60 meters in width, 2.50 meters in length, and 1.70 meters in height, giving a total volume of 6.80 cubic meters. The preparation of sand beds can be accomplished with relative densities ranging from 25% to 70% and can be repeated within an error margin of ±1% ; the relative density inside the bed itself is fairly constant, having a mean standard deviation equal to 1.47%.

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The choice of reference stress state as datum for zero lateral strain is identified as a problem inherent in the determination of K₀ of sand by laboratory tests. A new, but simple, test method based on strain path testing is presented. This new test method enables a systematic investigation into the influence of a non-zero isotropic reference stress on the measured K₀ value. The results of such a study introduces the concept of a threshold reference stress, p'₀₀, the maximum reference effective stress that can be used to ensure the correct determination of K₀ value for a normally consolidated condition. p'₀₀ is dependent on the effective axial stress, σ'_a, at which K₀ is to be measured. The value of σ'_a/p'₀₀, however, lies within a narrow range. For an over-consolidated condition, K₀ appears to be independent of p'₀ Provided the preconsolidation stress is significantly higher than p'₀₀.

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In order to obtain practically a correction factor of the liquefaction resistance of saturated soils for the reduction of membrane penetration during cyclic triaxial test, LR_m, the relationships between LR_m and uniformity coefficient U_c are investigated. Here LR_m={(σ_d/2 σ'₃₀)_nc-(σ_d/2 σ'₃₀)_c}/(σ_d/2 σ'₃₀)_nc×100, in which (σ_d/2 σ'₃₀)_nc and (σ_d/2 σ'₃0)_c denote the stress ratios before and after the correction for the reduction of membrane penetration, respectively. Samples used are two kinds of sands and two kinds of decomposed granite soils, having uniformity coefficients of l.68, 1.83, 6.40, and 28.92 respectively. Membranes are three kinds of latex rubber ones with thicknesses of O.18mm, O.25mm, and O.60mm respectively. From the tests it was found that our correction method (Ohara and Yamamoto, 1981, 1982) is valid, and LR_m increases with the value of logarithm of U_c for the cases when the number of cycles required to cause liquefaction N_L is in the region of 10∼50. In the case, for example, of N_L=10, the values of LR_m are 8%, 16%, and 28% respectively for U_c= 2, 5, and 25. Furthermore, it was found that the strength effect of membrane on the liquefaction resistance of the soils can be ignored.

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