In the general design problems, all information needed for design is collected in advance and the design is completed before the construction. However, since many kinds of uncertainties are inevitably involved in the results of design, it is far better from both view points of costs and safety in construction that we proceed with construction changing the previous design by using new information which can be obtained during construction. This advantage is specifically large in the earthwork problems because the change of design is comparatively easy. In the present paper, the process in which the previous design is changed by new information and the optimal design can be always led is called the "Dynamic Design Procedure" and formulated based on the Bayesian reliability prediction. The stability problem of an embankment constructed on a soft ground is taken as a concrete example.

抄録全体を表示

The writers have previously proposed equations to predict pore-pressure rise under uniform and non-uniform dynamic shear stresses for a saturated Ottawa sand based on the results obtained from undrained cyclic shear experiments in the Torsional Simple Shear Device. In this paper, they extend those previous studies to earthquake-type loadings and to saturated Ottawa sand at different densities and propose equations that predict the pore-pressure rise during earthquake-type loadings.The predicted and the measured pore pressures under earthquake-type shear stresses are compared, and a good correlation between the two is obtained.A diagram and a table are presented from which the four material parameters, C₁, C₂, C₃ and α, used in the above pore-pressure prediction equations can be readily obtained for any given void ratio or soil density.

抄録全体を表示

To investigate the possible effects of preshearing on the cyclic behavior of saturated sand, two series of cyclic static triaxial tests were performed. In the first series of tests, saturated samples were first subjected to small cyclic stresses having equal amplitudes on both sides of triaxial compression and extension until the pore water pressures increased to values less than the initial effective confining stress. The excess pore water pressures were then allowed to dissipate under the initial confining stress. This part of the stress changes represents the application of stress history to the sample. The samples were further subjected to cyclic stresses in order to observe the pore water pressure and shear strain behaviors as influenced by the previous stress cycle. It was found that the samples subjected to small preshearing developed less pore water pressures and shear strains on both sides of triaxial compression and extension. The second series of the tests were identical to the first series except for the application of a large shear stress to the sample on either sides of triaxial compression or extension during the preshearing. It was discovered that the sample subjected to large preshear on one side of triaxial loading, compression or extension, became stiffer on that side, but softer on the opposite side.

抄録全体を表示

There is much uncertainty to estimate the ground settlement associated with shield tunnelling due to the complicatedly interacted conditions between tunnelling methods and soil characteristics. Accordingly, if the shape of the ground settlement could be quantitatively predicted, it would be very effective for the assessment of its influence on the existing structures.It is presented that the shape of the ground settlement trough can be expressed as the product of the normal distribution function and the error function by introducing the mathematical model. The field observations were also carried out at the four sites of the shield tunnel construction in the Metropolitan areas. Besides, the model test was done, in which the settlements of sand layers were measured by the X-ray techniques.The following conclusions are obtained.(1) The lateral and longitudinal profiles of the ground settlement trough are well fitted with the normal distribution curve and the error function curve, respectively.(2) The parameter which represents the width of settlement is roughly proportional to depth of tunnel and its proportional constant depends upon soil characteristics.(3) In clay the ratio of lost ground is positively correlated with OFS(Simple Overload Factor) defined by construction conditions and soil characteristics.(4) Consequently the maximum settlement can be calculated by using these relationships.

抄録全体を表示

At a site near the Shinano river in the city of Niigata, Japan, where signs of liquefaction were conspicuous following the 1964 Niigata earthquake, a sand sampling program was carried out using a large diameter sampler to obtain undisturbed sand specimens for laboratory cyclic triaxial testing. The specimens were drained and frozen at the test site and brought back to the laboratory where they were again saturated and consolidated in the triaxial chamber to reproduce the in situ state of stress without destroying the fabric of the sand. Cyclic loading tests were then performed and the resistance to liquefaction was determined for specimens obtained from depths 2.5 m through 11.5 m deep. The result of these tests showed that the cyclic strengths of undisturbed loose sands from the test site were somewhat lower than would be anticipated from the similar cyclic triaxial tests performed on reconstituted specimens of the similar clean sands.

抄録全体を表示

In order to build an elastic-plastic model of soil behaviour it is necessary to define a yield function and a plastic potential. It is often assumed that these coincide and the so-called normality rule is obeyed. There is, however, much evidence that for soils the assumption of normality will not permit satisfactory predictions of soil behaviour to be made.Whereas the determination of the plastic potential from experimental studies is not difficult it is less easy to determine the form of the yield function. The indefinite yield points that are observed render the use of stress probe experiments somewhat inaccurate for this purpose.Here an alternative approach is proposed based on theoretical considerations. The form of the yield function is deduced for one set of experimental data for sand and also for one set of data for clay.

抄録全体を表示

The use of analytical solution of consolidation equation for settlement prediction is not always effective since such conditions as an initial distribution of excess pore water pressure, drain length, final vertical strain of soils and the coefficient of consolidation are sometimes quite uncertain in practical engineering problems. For this reason, an observational settlement prediction is freshly presented. First, the linear ordinary differential equation derived is demonstrated to give a settlement-time relationship. After that, by using the difference form of the equation (an autoregressive equation), observational procedure of settlement prediction is proposed. Two kinds of practical methods are presented. One is a graphical method, the advantage of which is its simplicity. The other is the method based on the Bayesian inference of the non stationary stochastic process, which can give a predictive probability distribution of future settlement and then also provide a preliminary theory for reliability-based design of settlement problems.The proposed methodology is demonstrated to be also applicable for some other special problems including settlement due to drainage from sand piles.

抄録全体を表示