Search

An elasto-plastic constitutive model was established in order to describe the stress-strain behavior of normally and over-consolidated sand for static loading in a wide stress region. The fundamental concept herein is based on the assumption that sand can be regarded as an isotropic material. The proposed model which involves eight parameters consists of two set of the yield, plastic potential and hardening functions. These functions are expressed based on a few basic assumptions and experimental evidences obtained from the multi-step stress path tests under 0.1MPa-10MPa confining pressure. This model can give good qualitative prediction of shear and volumetric strains for triaxial compression tests with various stress paths on normally and over-consolidated sand in a wide stress region.

In order to investigate the compressive and shear characteristics of undisturbed Hiroshima type decomposed granite soils, the isotropic compression and triaxial compression tests were carried out using the undisturbed specimens made up by the new core bit. Test results were discussed paying attention to the degrees of weathering of samples.The results obtained can be summaraized as follows.1) The irreversible change of void ratio under isotropic compression is due to the particle breakage and the vanishing of structure effect.2) The stress-strain behavior, stress-dilatancy relation and shear constant φ' depend on the degrees of weathering.3) Failure criterion is expressed in terms of coefficient of the exponent.4) The decrease in strength due to submergence is remarkable in a low confining pressure and in moderately weathered sample.

The triaxial compression tests along various stress paths were carried out in order to investigate the yield characteristics of dense sand in low and high pressure regions. The yield characteristics were discussed in particular reference to the pressure regions and stress paths. The results were summarized as follows: 1) The shapes of yield curves in low and high pressure regions are somewhat different each other, but they have very similar properties. 2) Based on the properties of the yield curves, a yield function is derived. The yield function was confirmed to have a comformability for the granular materials in a wide stress region. 3) The shape of yield curves can be determined approximately using the state parameter proposed by Moroto.

A detailed paleomagnetic and rock-magnetic investigation on the early and middle Matuyama loess-paleosol sediments has been carried out at the Baoji section, Shaanxi province, southern Chinese Loess Plateau. Our new magnetostatigraphy revises the position of the lower Olduvai boundary from L27 to S26. Seven shortlived geomagnetic excursions, tentatively named as E1, E2, E3, E4, E5, E6, and E7, have been recognized in the L13, S22, L26, L27, S29, and upper and middle parts of L32, respectively. Results of the anisotropy of low-field magnetic susceptibility (AMS) show that the studied loess-paleosol sediments retain the primary sedimentary fabric. Rock magnetic experiments reveal that the sediments from the excursional and polarity transitional intervals have the same magnetic characteristics as those from the surrounding normal and reversed polarity intervals. Assuming a constant accumulation rate between polarity boundaries, these seven excursions are estimated to be at about 1.11 Ma (E1), 1.58 Ma (E2), 1.92 Ma (E3), 2.11 Ma (E4), 2.25 Ma (E5), 2.35 Ma (E6), and 2.42 Ma (E7) Ma. The E1 and E2 in the middle Matuyama Chron can be correlated with the Punaruu and Stage 54 (Gilsa) excursions, respectively. The E4, E5, and E7 in the early Matuyama Chron can be correlated with the Réunion II, Réunion I, and cryptochron C2r.2r-1 (X-subchron), respectively. The E3 in the lower Olduvai subchron and E6 in the early Matuyama Chron have no comparable events. At present they can only be correlated with the anomalous directions observed in the Osaka Bay core (Biswas et al., 1999). Therefore, further investigations are necessary to support their global occurrences. The present result together with the two late Matuyama excursions dated at about 0.89 Ma and 0.92 Ma (Yang et al., 2004) show that the Baoji section yields at least nine Matuyama excursions which, along with the results of the study, suggests that eight excursions occur at 0.9–2.2 Ma (Channell et al., 2002), thereby providing evidence that the short-lived geomagnetic excursions may also be a basic characteristic of the geomagnetic field during the Matuyama Chron.

The method for determining the blood level of ethosuximide was first described by Hansen in 1963. Referring to his method, we determined the plasma level of ethosuximide by the method for measuring phenytoin and phenobarbital proposed by Saitoh and others. This method proved to be much reproducible. In the test, 2ml of phosphoric acid buffer and 11 ml of dichloroethane were added to 0.5ml of plasma. The solution was well shaken and centrifuged at 2500 rpm. After 3ml of 1N-NaOH was added to 9ml of dichloroethane layer, the mixed solution was well shaken and centrifuged at 2500 rpm. The 1N-NaOH layer was transferred to a microcell and its absorbancy at 218 nm was measured.The standard curve showed a straight line passing through the origin of the coordinate axes. The average recovery rate was 97.8±1.4%. Thus, by the method of Saitoh and others it became possible to measure at the same time the levels of phenytoin, phenobarbital and ethosuximide.