In this study, attempts were made to use sandy soil as the main raw material in making unfired bricks. e sprayed-cured brick specimens were tested for compressive and flexural strength, rate of water absorption, percentage of voids, bulk density, freezing/thawing, and water immersion resistance. In addition, the microstructures of the specimens were also studied using scanning electron microscope (SEM) and X-ray diffraction (XRD) technique. e test results show that unfired brick specimens with the addition of ground-granulated blast-furnace slag (GGBS) tend to achieve better mechanical properties when compared with the specimens that added cement alone, with GGBS correcting particle size distribution and contributing to the pozzolanic reactions and the pore-filling effects. e test specimens with the appropriate addition of cement, GGBS, quicklime, and gypsum are dense and show a low water absorption rate, a low percentage of voids, and an excellent freezing/thawing and water immersion resistance. e SEM observation and XRD analysis verify the formation of hydrate products C-S-H and ettringite, providing a better explanation of the mechanical and physical behavior and durability of the derived unfired bricks. e results obtained suggest that there is a technical approach for the high-efficient comprehensive utilization of sandy soil and provide increased economic and environmental benefits.
The riverbanks in the Lower Jingjiang Reach are mostly composite ones with fine sand overlain by cohesive clay, thus when the sandy layer is undermined due to rapid erosion, the cohesive upper layer generates a cantilever and is prone to beam failure. In this study, the formula of critical width of cantilever failure was improved considering the hydraulic effects. The formula of accumulated width of failed blocks at bank foot was deduced. A collapse analysis model of composite banks was subsequently proposed, and the collapse process of a typical bank slope was simulated using the model. The conclusions include: The cantilever failure of composite riverbanks is more prone to occur during the period of water level decline than that of water level rise. The critical width of cantilever decreases with the dropping of river level, the weakening of the supporting role of river water and the enhancement of the overturning effect of groundwater. The thicker the cohesive layer is, the greater the decrement of its critical overhang width is as river level decline. The protective effect of failed blocks accumulated at bank foot reduces its erosion distance, the more times the bank collapse takes place, the greater the impact is.
Using superfine sand as the main raw material and the superfine sand concrete without coarse aggregate was made by method of semi-dry moulding in this paper. The compressive, splitting tensile and immersion strength of the concrete material was studied to determine the influence of mix proportion of the binding materials. The results show that the optimal mixing ratio for materials used is 70% superfine sand, 15% cement, 9% ground granlated blastfurnace slag( GGBS), 2% gypsum and 4% lime. The compressive, tensile and immersion strength of this concrete at 28 days is 20MPa, 2.5 MPa and 20 MPa respectively, meeting the demand of civil engineering .In areas with an abundance of superfine sand but a shortage of ordinary aggregate, the material mentioned will have prominent economic value as well as promising application prospects. 1.InstructionSuperfine sand is a kind of fine sand with 0.7~1.5 fineness modulus. Its void content, soakage and silt content are relative high. Numerous researches have been taken on application of superfine sand. Shouchang Deng [1] made concrete with superfine sand and found that the best dosage of this material is about 20%. He also strictly controlled the water content for fear of segregation of concrete and decrease of its strength. Canyun Yi [2] tried to improve the fine aggregate gradation by adding aggregate chips into superfine sand, which increased its fineness modulus. When the dosage of aggregate is half of the amount of fine aggregate, superfine sand concrete with high compressive strength (22.3MPa) can be produced. TU Er-hong·TU Er [3] added superplasticizer, air entraining agent and fly ash to superfine sand concrete, by lowering the water-binder ratio and sand ratio, he finally prepared normal concrete with different strength levels as well as C20 pump concrete with high fluidity, good permeability and freezing resistance. Therefore, researches that using superfine sand as fine aggregate have been mature. However, there are few studies on using superfine sand to produce concrete without coarse aggregate at present. Baochang Sun [4] made some exploratory researches on this area. He produced such concrete by mixing cement, superfine sand and water. When the content of water is 420kg/m 3 , the compressive strength of such a concrete at 28 days peaked at 13.4 MPa. He also pointed that this kind of concrete is a new material in need of deeper researches. In China, there are large areas in short of medium and coarse sand. On the contrary, fine sand is widely distributed, mainly over Chongqing [5] , Liaohe and Northern Shaanxi [6] regions. For areas like this, to prepare superfine sand concrete without coarse aggregate will have prominent economic value as well as promising application prospects.In this paper, different ratios of cement, GGBS, gypsum and lime were mixed by semi-dry moulding with same dosage of superfine sand to produce concrete without coarse aggregate. Then the compressive, tensile and immersion strength of specimens at 28 days were tested and the optima...
Abstract.To study the influence of pile-soil interaction on the seismic behavior of PHC piles, this paper takes the PHC pile in the soft clay as the research object, which is simulated by fiber beam element, and the pile-soil interaction is simulated by using equivalent embedded method and p-y soft clay soil spring which is under cyclic load, respectively. The seismic behavior index of pile foundation under limit state is obtained through applying the horizontal cyclic load on the pile top. The research shows that, with the different depth of pile, the hysteretic energy dissipation index and the displacement ductility factor obtained by the equivalent embedded model are about 2.2~2.5 times and 1.1~1.4 times of the p-y curve model respectively. While the yield strength and ultimate strength obtained by the p-y curve model are larger than those obtained by equivalent embedded method.
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