Results of non-uniform cyclic triaxial tests on Monterey #0 sand are presented. Two series of tests are performed in which the number and magnitude of stress cycles are unchanged but the order in which the cycles are applied varies. Results of these tests show that pore pressure generation depends upon the order as well as the magnitude of the non-uniform stress cycles. To account for this dependence, a pore pressure generation model which accounts for the influence of cyclic shear stress ratio upon the shape of the pore pressure generation curve is developed. Pore pressures calculated using the stress ratio dependent model show good agreement with laboratory test results except when some of the applied stress cycles are below the threshold stress level causing liquefaction in uniform cyclic loading.

抄録全体を表示

A study on the effects of four organic fluids on permeability of compacted kaolinite is presented. A flexible wall permeameter set up was designed and constructed. Permeation fluids were 0.1% and 100% nitrobenzene, acetone, phenol and benzene, each mixed with 0.01 N CaSO₄ as reference solution. Full saturation permeabilities (k_h) were obtained under continuous backpressure at hydraulic gradients (i_h) of less than 100 and effective stress of 69 kN/m². All tests with chemicals at low concentrations resulted in slight decrease of k_h. With pure solutions, however, the value slightly increased with acetone and phenol and significantly decreased with benzene and nitrobenzene. These results together with fabric studies indicated that changes in k_h with organic fluids can be explained by the variations in the surface forces of interaction on clay particles affecting the flow characteristics. In order to assess the effect of the testing scheme, acetone permeabilities were obtained in both rigid and flexible wall permeameters. Excessive increases in permeability were observed with the rigid wall permeameters. The possibility of the effective stresses in flexible wall permeameters veiling the permeability changes due to organic fluid permeation was investigated. The results indicate that the observed increases in permeability with rigid wall permeameters can only be explained by the side leakages due to shrinking of the compacted clay when permeated with organic solvents.

抄録全体を表示

Lack of information about the spatial distribution of the modulus of subgrade reaction results in significant uncertainty with respect to the true value of the calculated displacements, shear forces and moments in the analysis of "beams on elastic support". In order to incorporate this uncertainty into the analysis, the spatial distribution of the modulus of subgrade reaction is modeled here as a homogeneous low pass Normal random function of the space coordinate along the beam, and an approximate solution of the resulting random differential equation is derived. The paper considers the case of an infinite bean acted upon by a single concentrated load. For this case explicit solutions are presented for the spatial distributions of standard deviations of displacements, moments, and shear forces at every point along the beam. In addition the correlation coefficient between displacement at different points is evaluated. This information is sufficient for the determination of probability distributions of settlements, differential settlements, shear forces, and moments, at every point along the beam, thus making it possible to carry out a complete probabilistic design of such beams.

抄録全体を表示

The available empirical relationships for maximum dynamic shear modulus (G_max) and dynamic shear damping (D_s) at low strain amplitudes for sands are reviewed. Based on tests with Monterey No.0 sand in resonant column device, new relations for G_max and D_s are proposed. In addition, based on test data in longitudinal mode of vibration, relations for dynamic Young's modulus (E_max) and dynamic longitudinal damping (D_l) are developed for the first time. The developed relations are convenient to use as they are dimensionally correct and are applicable for any system of units. The observed experimental data and proposed relations are in good agreement. The proposed relations for G_max and D_s are compared with reported relations and a difference of approximately 20% and 100% is observed in some cases for dynamic shear modulus and shear damping, respectively. More field and experimental results are warranted to put the developed relations for dynamic Young's modulus and longitudinal damping on firm foundation.

抄録全体を表示

A criterion is presented for assessing liquefaction potential of a soil deposit to earthquake motions. The criterion, originally developed in 1970 by one of the authors, used three basic factors ; (1) soil type, (2) SPT N-value around water table, and (3) maximum acceleration at the ground surface. By replacing the second and third factors with normalised SPT N-value (i.e. SPT N-value corrected for the specified effective vertical stress) and shear stress ratio (i.e. earthquake induced shear stress divided by vertical effective stress), an extended criterion is obtained. Applicability of the extended criterion is examined with the field performance data obtained at and within 5 km from the strong-motion observation stations. The results indicate the extended criterion has reasonable applicability. The extended criterion also shows good agreement with the criteria developed by Tokimatsu and Yoshimi (1983) and Seed et al. (1985).

抄録全体を表示

The objective of this paper is to describe the characteristics of the mechanical behavior of improved sandy soil under monotonic loading. The improved sandy soil is a new soil material which is stabilized with cement. The salient features of the proposed constitutive model are summarized as follows. (i) A failure criterion is proposed which is easily incorporated in stress-strain relationships. (ii) A non-associative flow rule is used in the incremental constitutive equation. (iii) A generalized form of the Modified Cam clay model is applied to plastic potential. (iv) The isotropic hardening involves plastic work related not only to volumetric change but also to deviatoric deformation. (v) The double hardening model is adopted to take account of the influence of the two yield functions on plastic behavior. To investigate the effective stress paths and stress-strain relationships, several triaxial tests of the improved sandy soil are performed under monotonic loadings. The model simulation is compared with the experimental data and qualitative correspondence is satisfactory.

抄録全体を表示

A conventional and practically useful analytical method of bearing capacity is presented, assuming that sliding surface in the ground is composed of single log-spiral. Emphasis is placed on some advantages of the method, showing that bearing capacity factors can be expressed to some extent in analytical closed forms and that the method can readily be developed for evaluating bearing capacity of foundations under eccentric and inclined loads and that of deep foundations. Numerical results are compared with those from other theoretical and empirical formulae as well as experimental results, drawing some remarks ; 1) log-spiral solutions of bearing capacity factors are comparable to other theoretical values so far presented, 2) the present analysis confirms validity of superposition in the calculation of bearing capacity, 3) it also substantiates Meyerhof's hypothesis of the effective width of foundation for eccentric loading, and 4) log-spiral solutions for inclined loading show relatively good correspondence with practical formulae as well as experimental results.

抄録全体を表示

Evaluation of soil parameters used in routine design work is presented for soft clay deposits as related to their geological stress history. A classification method of soft clay from this point of view is first proposed and then design parameters such as K₀, undrained strength including strength anisotropy and deformation characteristics are discussed in detail. It is demonstrated that proper understanding of geological stress history is the first and essential requirement in evaluating these parameters. Further, determining procedure of consolidation yielding stress, which is also an important parameter, is presented with support of field and laboratory test results.

抄録全体を表示

A new procedure for predicting the ultimate bearing capacity of an embankment foundation is discussed, and its applicability to construction safety control is reviewed in connection with observational construction. The procedure developed in this paper consists of the following three processes : (1) An elastic consolidation back-analysis is performed by using the values monitored in the field. (2) Elastic-plastic soil parameters, for a constitutive model proposed by Sekiguchi and Ohta, are estimated by interpreting the elastic soil parameters obtained from the back-analysis of process (1). (3) Ultimate height of an embankment is computed by the coupled elastic-plastic deformation-water flow finite element analysis using the imaginary viscosity method. The procedure is applied to actual embankments, around which displacements are monitored, and is verified to be able to predict the subsequent settlement, as well as the safety factor of embankment foundation which periodically changes as construction progresses. An easy-to-understand diagram for safety control of embankment foundations is summarized in the form of a flow chart, so that engineers may apply it in engineering practice.

抄録全体を表示

A series of torsion shear tests was performed along various stress-paths on hollow cylinder specimens of K₀-consolidated clay to investigate the influence of rotation of principal stresses on the stress-strain and strength characteristics. The effects of stress-paths and reorientation of principal stresses were mainly observed in the prefailure stress-strain behavior. The experimentally obtained failure surface from torsion shear tests could practically be modeled by an isotropic failure criterion. Coupling effects between stresses and strains were observed when torsion shear and vertical normal stresses were applied. The work-space for torsion shear tests was illustrated, and the relation between stresses and strain increments was also studied in the work-space.

抄録全体を表示

This research note examines fixed and deforming finite difference grid approaches for solving problems involving moving boundaries. In order to make comparisons between the solutions effected by each approach, emphasis is placed on the prediction of deficient pore pressures which develop within a clay stratum which is being excavated. It is assumed that the linear partial differential equation which describes consolidation is applicable. In the deforming grid approach, the distribution of deficient pore pressures is defined by a set of nodal degrees of freedom (u₁, u₂, ···u_n) which are allowed to move as the excavation front advances, thereby maintaining a constant number of unknowns at all times. In order to account for the influence of moving reference points, the rate of pore pressure change at a material point ∂u/∂t is replaced by du/dt-v∂u/∂x. In order to avoid spurious oscillations in the nodal degrees of freedom, which move with the reference points, upwinding is introduced. For the fixed grid approach, the influence of material removal at a boundary is taken into account by removing the nodes above the excavation level at discrete times. Owing to the loss of nodal degrees of freedom as excavation advances, a much greater number of nodes is required to complete the analysis when compared with the deforming grid approach. A comparison of the solutions from each model showed that the deforming grid approach performed better, as anticipated. Both models underestimated the deficient pore pressure dissipation when compared with the solutions provided by Koppula and Morgenstern (1984).

抄録全体を表示

This paper concerns the effect of using the different in-situ vane types performed in the same site. The first equipment is the VANE TYPE I which conducted without casing and preboring, and the other is the VANE TYPE II carried out in preboring type hole. The results indicate that the undrained shear strength from the VANE TYPE I is higher than the other about 20-30%. In addition, the unconfined compression tests yield approximately the same undrained strengths with those from VANE TYPE II. The difference in strengths between these tests are believed partly dependent upon the effects of disturbance during sampling. Despite the large variation of plasticity index in Bangkok area, the normalized corrected VANE TYPE I strength based on Bjerrum (1972) and the measured VANE TYPE II strength (C_u/σ'_v0) show the unique curve when they are plotted versus OCR.

抄録全体を表示