Experimental investigations and modeling of nonlinear elasticity of fiber-reinforced soil under cyclic loading at small strain are conducted in this paper. The investigations include three aspects. First, cyclic shear tests are conducted using conventional triaxial apparatus. Twenty-seven specimens with three different fiber contents are employed to conduct triaxial cyclic shear tests under different confining pressure and loading repetition. Effects of geofiber, confining pressure and loading repetition on elastic shear modulus of reinforced soil are studied and analyzed. Second, a hyperbolic function is introduced to describe the nonlinear stress–strain skeletal curve under cyclic loading. Nonlinear elastic modulus is expressed as a function of shear strain and two variables A and B that are related to the initial tangential modulus and ultimate cyclic loading stress, respectively. In the present paper, variables A and B both are further assumed to be functions of geofiber content, confining pressure and loading repetition. Finally, eight constitutive coefficients of the nonlinear elastic model are calibrated using stress–strain curves from cyclic triaxial shear tests. The calibration of parameters is conducted using the technique of the linear regression for multiple variables. Impacts and effects of geofiber, confining pressure and loading repetitions on soil nonlinear elastic behavior are discussed. 相似文献
A series of effective stress analyses is carried out on the seismic performance of river dikes based on the case histories during the 1993 Hokkaido-Nansei-oki and 1995 Hyogoken-Nambu earthquakes in Japan. Seven case histories selected for the analyses involve a crest settlement ranging from none to 2.7 m in the dikes 3–6 m high with evidence of liquefaction at foundation soil. The effective stress model used is based on a multiple shear mechanism and was developed by one of the authors. The soil parameters are evaluated based on the site investigation and laboratory test results. The results of the analyses are basically consistent with the observed performance of the river dikes. In particular, the effective stress model shows a reasonable capability to reproduce the varying degree of settlements depending on the geotechnical conditions of foundation soils beneath the dikes. The analyses also indicate that the effect of a cohesive soil layer mixed with the liquefiable sand layers beneath the dikes can be a primary factor for reducing the liquefaction-induced deformation of dikes. 相似文献
Shallow seismicity and available source mechanisms in the Andaman–westSunda arc and Andaman sea region suggest distinct variation in stressdistribution pattern both along and across the arc in the overriding plate.Seismotectonic regionalisation indicates that the region could be dividedinto eight broad seismogenic sources of relatively homogeneousdeformation. Crustal deformation rates have been determined for each oneof these sources based on the summation of moment tensors. The analysisshowed that the entire fore arc region is dominated by compressive stresseswith compression in a mean direction of N23°, and the rates ofseismic deformation velocities in this belt decrease northward from 5.2± 0.65 mm/yr near Nias island off Sumatra and 1.12 ±0.13 mm/yr near Great Nicobar islands to as much as 0.4 ±0.04 mm/yr north of 8°N along Andaman–Nicobar islandsregion. The deformation velocities indicate, extension of 0.83 ±0.05 mm/yr along N343° and compression of 0.19 ±0.01 mm/yr along N73° in the Andaman back arc spreadingregion, extension of 0.18 ± 0.01 mm/yr along N125° andcompression of 0.16 ± 0.01 mm/yr along N35° in NicobarDeep and west Andaman fault zone, compression of 0.84 ±0.12 mm/yr N341° and extension of 0.77 ± 0.11 mm/yralong N72° within the transverse tectonic zone in the Andamantrench, N-S compression of 3.19 ± 0.29 mm/yr and an E-Wextension of 1.24 ± 0.11 mm/yr in the Semangko fault zone ofnorth Sumatra. The vertical deformation suggests crustal thinning in theAndaman sea and crustal thickening in the fore arc and Semangko faultzones. The apparent stresses calculated for all major events range between0.1–10 bars and the values increase with increasing seismic moment.However, the apparent stress estimates neither indicate any significantvariation with faulting type nor display any variation across the arc, incontrast to the general observation that the fore arc thrust events showhigher stress levels in the shallow subduction zones. It is inferred that theoblique plate convergence, partial subduction of 90°E Ridge innorth below the Andaman trench and the active back arc spreading are themain contributing factors for the observed stress field within the overridingplate in this region. 相似文献
The speedv, especially the problem whether super S-wave velocity in the classical model (linear elasticity fracture mechanics) exists,
of spontaneous propagation of a shear fault is investigated theoretically. An in-plane shear crack propagating in the crack
plane is taken as the model of the shear fault. The results obtained firstly by Kostrov (1975) is extended from sub-Rayleigh
wave velocity to super S-wave velocity, and the analytical expression for the stress intensity factorK2 in the case ofα>v>β is derived. It is proved that for Poisson mediumK2 is positive and real in the velocity range (β, 1.70β). This demonstrates that (β, 1.70β) is the velocity range which fulfils the conditions for spontaneous crack propagation. The existence, convergence and positiveness
or negativeness ofK2 forv in individual sections are examined, and it is found that for an in-plane shear crack: 1. There are three sections forv, i.e., [0.vR], (β, 1.70β), andα, respectively, and 2. There are two physically reasonable sections forv, the first is [vR, β], and the second is [1.70β, α]. These two forbidden sections behave as barriers to fault propagation.
The analytical expressions derived in this paper are not only suitable to classical model, but also to the other derivative
models (e. g., the slip-weakening model and the renomalization model etc.). The model considered in this paper is more realistic
than the static model employed by previous authors.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica, 15, 9–14, 1993. 相似文献