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Using a suction-controlled triaxial apparatus for unsaturated soils, a series of tests on a compacted clay was performed to investigate the influences of stress states, water content, void ratio, and matric suction on the collapse behavior. The triaxial tests were carried out under the conditions of (1) different stress ratios and mean stresses, (2) triaxial compression and extension, (3) different initial void ratios of specimens with the same water content, (4) different initial water contents with the same degree of compaction, and (5) different controlled matric suctions. The main conclusions were obtained as follows: (1) The volume change induced by the collapse mainly depends on the initial void ratio and mean net stress under which the collapse occurs, irrespective of imposed matric suction; (2) the amount of collapse is small at both low and high confining stresses, and there exists a maximum value of collapse at a particular mean stress; (3) the shear strain increment induced by collapse depends on stress ratio, triaxial compression, or extension stress; (4) when imposed suction is decreased, large collapse deformation takes place in the samples compacted dry-of-optimum, while little collapse deformation takes place in the samples compacted wet-of-optimum; and (5) the collapse behavior can be explained by the elastoplastic theory for unsaturated soils.

In this experiment, silica sol was used as raw material, the mixture of ammonium chloride and ammonia was used as coagulant. After replacing the solvent with n-hexane, silica aerogel was obtained under the condition of normal pressure. The influence of sol pH and coagulating temperature on the gel time was studied. According to the SEM photographs, the influence of drying temperature from 30 °C to 60 °C on the microstructure of silica aerogel was analyzed. This study showed that when sol pH was 6.5, coagulating temperature was 80 °C and the concentration of ammonia was 0.4 mol/L, the gel time was the shortest. The average size of silica aerogel particles was 10-20 nm, the average size of apertures was 20-50 nm. When the drying temperature was 40 °C, the specific surface area was 402.41 m2/g, the pore volume was 2.33 cm3/g, the density was 0.18 g/cm3.

In order to enhance the photocatalytic activity of BiVO4, the Ag2O loaded on BiVO4is studied. In this study, Ag2O loaded on BiVO4was prepared with Bi(NO3)3, NH4VO3and C6H8O7as raw materials by sol-gel method. Influences of the sintering temperature and sintering time were studied on photocatalytic activity, crystal composition and molecular structure. The molecules of matter were characterized by FTIR. Both the phase transition in the sintering process and the influence of Ag2O loaded on crystal structure and size of the BiVO4powder were studied by XRD. The structure of the obtained samples were studied using transmission electron microscopy. The photocatalytic activity Ag2O loaded on BiVO4in different calcination time and different calcination temperature had been studied through the degradation methyl orange solution. It is found that the BiVO4photocatalytic efficiency of methyl orange is about 20% when the samples calcined for 4h and calcined at 500°C, the Ag2O loaded on BiVO4photocatalytic efficiency of methyl orange is doubled.