摘要:

Results of an investigation into the behavior of a fine-grained clayey soil at Moss Landing during the 1989 Loma Prieta earthquake are presented. A deposit of this soil underlies portions of the Moss Landing Marine Laboratory that experienced up to 1.3 m of lateral spreading deformations during this magnitude 7 earthquake. Silty clay from the deposit erupted to the surface in a "soil boil" characteristic of liquefaction, during and immediately after the earthquake. A sample from the silty clay boil had a liquid limit of 38, a plasticity index of 17, and a <5 µm fraction of 24%, and thus would be considered nonliquefiable according to commonly used criteria. Analysis of cyclic triaxial test data suggests that portions of the silty clay deposit likely developed high residual excess pore pressures (ru,rapprox 80-90%) and significant shear strains during the earthquake and thus likely contributed to the observed lateral deformations. The field and laboratory data show that commonly used criteria for identifying "liquefiable" clayey soils should be applied with caution and should not be indiscriminately viewed as a substitute for detailed laboratory and in situ testing of low plasticity fine-grained soils.Key words: liquefaction, cyclic loading, silt, clay, earthquake, case history.

ISSN:0008-3674    

DOI:10.1139/t97-078

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This paper presents the surface settlement performance induced by the foamed type of earth pressure balance shield in contract CH218 of the Hsintien Line of the Taipei Rapid Transit System. The surface settlement characteristics caused by the single tunnel and by twin tunnels with reference to two sections spaced at 87 m are studied. Field observations indicate that the surface settlement trough due to the single tunnel can be represented by the normal distribution. The distance of the inflection point to the tunnel center and maximum surface settlement value are consistent with those found in the literature. The characteristics of the surface settlement trough are related to the type of the soil, particularly where the crown of the tunnel is located in a layered soil deposit. The ground surface settlement induced by twin tunnels was found to be larger than estimated using the principle of superposition.Key words: shield tunnelling, surface settlement, field observation.

ISSN:0008-3674    

DOI:10.1139/t97-073

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Test results reported on several natural sensitive soils show significant anisotropy of the yield curves, which are generally oriented along the coefficient of earth pressure at rest (K0) axis. An attempt is made in this paper to explain the anisotropy in yielding from microstructural considerations. An elliptic pore, with particle domains aligned along the periphery of the pore, and with the major axis of the pore being oriented along the direction of the in situ major principal stress, is chosen as the unit of microstructure. An analysis of forces at the interdomain contacts around the ellipse is carried out with reference to experimentally determined yield stress conditions of one soil, and a yield criteria is defined. The analysis, with the proposed yield criteria, enables one to define the complete yield curve for any other soil from the results of only two tests (one constant eta compression test with eta close to eta sub K0, where eta is the stress ratio (=q/p)and eta sub K0is the stress ratio corresponding to anisotropicK0compression, and another undrained shear test). Predicted yield curves are compared with experimental yield curves of several soils reported in the literature.Key words: sensitive clays, yield criteria, anisotropy, microstructure.

ISSN:0008-3674    

DOI:10.1139/t97-072

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A comparison is made between several limit states design methods for the bearing capacity of shallow foundations. It is found that the main reason for the difference between the methods is the variation in the load factors.Key words:limit states design, shallow foundations, sand, clay.

ISSN:0008-3674    

DOI:10.1139/t97-075

出版商:NRC Research Press    

年代:1998

数据来源: NRC