In nature, soils are often composed of varying amounts of clay, silt and sand. Variation of the percentage of these compositions can affect the final strength of the soils when stabilised with cement. In this study, focus was placed on clayey soils with different gradation of sand impurities up to 40% in mass. An extensive study of such clayey soils treated with cement was investigated. For the results, it is noted that water:cement ratio was a major influence of strength development of cement-treated clayey soils. In contrast, the soil:cement ratio was found to have minor effects on the strength development. The presence of sand impurities has a significant reduction on the strength development of the cement-treated clayey soil mixture due to more free water available for hydration. The use of free-water:cement ratio is adopted which was shown to be capable of adjusting for such change in amount of free water and water holding capacity of the clay which is determined with Atterberg’s liquid limit tests. The effects of gradation (fine, coarse and well-graded) of the sand impurities were found to affect strength development minimally, owing to similarities in their liquid limits when mixed with clay. Ordinary Portland cement (OPC)-treated clayey soils produced a more rapid gain in strength but lower final strength at 28 days of curing as compared with Portland blast furnace cement (PBFC). This is found to be persistent for different gradation of sand impurities. A linear correlation can be established based on the log of the unconfined compressive strengths developed at different curing age, with slopes of these linear trends found to be similar for PBFC and OPC-treated clayey soil specimens. Finally, a strength prediction model comprising of these findings is developed. The parameters adopted in this model coincide with values proposed by past studies, thereby validating the robustness of the model. The practical benefits from this study offer a quality control scheme to forecast long-term performance of cement-treated clayey soils as well as optimise cement dosage in cement stabilisation to produce a more cost-effective and less environmental-invasive usage of the technology in geotechnical applications.
Nonlinear frequency shift of space-charge waves in a relativistic electron or positron beam is analyzed. The frequency shift is shown to be a function of the wave amplitude. It is suggested that the frequency shift of beam space-charge waves may be a saturation mechanism for astrophysical free-electron lasers. 相似文献
In this paper, we used the more rigorous general relativistic viscous hydrodynamical equation to discuss and calculate the temperature profile in the accreting disk around a Kerr black hole. It is found that for an accreting disk around a Kerr black hole, the occurrence of extremum values in the temperature profile is indeed possible. Furthermore, the temperature profile is always the same—no matter what kind of viscous mechanism is adopted—if the radiative mechanism of the materials in the disk is black-body radiation. For free-free radiation, we adopted the so-called α-viscosity law model to get a solution analogous to that obtained earlier (Fanget al. 1980). The calculations show that there exists a fast cooling ring region lying just inside the temperature maximum. In this ring region, there are probably some pecularities which do not exist in the usual temperature profile calculation (Fang, 1981). 相似文献
There is increasing observational evidence of nonlinear wave–wave interactions in space and astrophysical plasmas. We first review a number of theoretical models of nonlinear wave–wave interactions which our group has developed in the past years. We next describe a nonlinear three-mode truncated model of Alfvén waves, involving resonant interactions of one linearly unstable mode and two linearly damped modes. We construct a bifurcation diagram for this three-wave model and investigate the phenomenon of intermittent chaos. The theoretical results presented in this paper can improve our understanding of intermittent time series frequently observed in space and astrophysical plasmas. 相似文献
On March 11th 2011 a Mw9.0 mega-thrust interface subduction earthquake, the Great East Japan Earthquake, occurred 130 km off the northeast coast of Japan in the Pacific Ocean at the Japan Trench, triggering tsunami which caused damage along 600 km of coastline. Observations of damage to buildings (including vertical evacuation facilities) and coastal defences in Tōhoku are presented following investigation by the Earthquake Engineering Field Investigation Team (EEFIT) at 10 locations in Iwate and Miyagi Prefectures. Observations are presented in the context of the coastal setting and tsunami characteristics experienced at each location. Damage surveys were carried out in Kamaishi City and Kesennuma City using a damage scale for reinforced concrete (RC), timber and steel frame buildings adapted from an earlier EEFIT tsunami damage scale. Observations show that many sea walls and breakwaters were overtopped, overturned, or broken up, but provided some degree of protection. We show the extreme variability of damage in a local area due to inundation depth, flow direction, velocity variations and sheltering. Survival of many RC shear wall structures shows their high potential to withstand local earthquake and significant tsunami inundation but further research is required into mitigation of scour, liquefaction, debris impact, and the prevention of overturning failure. Damage to steel and timber buildings are also discussed. These observations are intended to contribute to mitigation of future earthquake and tsunami damage by highlighting the key features which influence damage level and local variability of damage sustained by urban coastal infrastructure when subjected to extreme tsunami inundation depths. 相似文献
An increasing number of rapidly growing urban areas in Asia are becoming more vulnerable to seismic hazards in their development process. However, local authorities rarely integrate seismic risk into the procedure of emergency and land-use planning. This article explores the question of whether seismic risks for urban areas are increasing or diminishing over time, while trends such as population growth and land development in hazard-prone areas increase the potential for loss in disasters. The net effects of such urbanization factors are examined through the use of simulation models that estimate building inventory and seismic loss changes. Seismic losses are modeled for a comparative analysis under the same hypothetical earthquake events hitting at different points in a city area’s long-term development. A case study of seismic risk assessments is illustrated by the Hsinchu City, Taiwan. Results of a prospective analysis indicate that, for the same seismic events, overall risk is expected to increase due to a forecast 2.9 % growth in building inventory. This increment in loss is largely attributed to a large amount of initial buildings predicted to be developed into commercial and industrial uses. However, the spatial pattern of risk would change slightly; particularly, the southeastern, eastern, and some older core areas would be the most vulnerable and risky both at current and future time periods. The approach here enables city planners to incorporate seismic risk analysis into predisaster emergency and land-use planning to encourage risk-reduction strategies. 相似文献
On 30 September 2009 at 05:16?pm local time (10:16 am UTC), a major earthquake registering a magnitude Mw 7.6 occurred off the coast of Padang in West Sumatra. This paper presents the observations from a reconnaissance mission that investigated the performance of structures, infrastructure and geotechnical structures within the affected region. As well as presenting the detailed observations made on the mission, insights as to why structures failed and deficiencies in the construction practices of the region are also presented. Considering the high seismic risk of this area and that seismic gaps suggest another earthquake with a magnitude greater than 8.7 may occur, these observations are particularly significant. One of the vital features of this earthquake was a number of very large and devastating landslides that occurred in the district of Pariaman. These landslides were not only extensive, but had an extremely high lethality. Another key feature of the earthquake was the surprisingly high number of government buildings that collapsed. The paper concludes by presenting a number of recommendations for both the rebuilding of failed structures as well as for hazard assessments of existing structures and geotechnical features. 相似文献