The rapid development of high-speed transportation infrastructure such as highway and high-speed railway has resulted in the advancement of soft soil improvement techniques. Vacuum preloading combined with vertical dr...The rapid development of high-speed transportation infrastructure such as highway and high-speed railway has resulted in the advancement of soft soil improvement techniques. Vacuum preloading combined with vertical drains has been proved to be an effective method in the treatment of soft foundation. A three-dimensional numerical analysis of the coupled methods was presented, in which the smear zone and the well resistance were taken into account. The variations of the basic soil parameters including the permeability coefficient and the coefficient of volume compressibility were considered in the numerical model. The result of the numerical model was then compared to the measured value. The results indicate that the decrease of coefficient of volume compressibility accelerates the consolidation of the soil while the influence of hydraulic conductivity is insignificant. A cube drain presents the closest result to the real situation compared to the other equivalent methods of prefabricated vertical drain (PVD). The case study indicates that the numerical model with variation of soil parameters is closer to the measured value than the numerical model without variation of soil parameters.展开更多
The main objective of this study is to verify, through compression tests on different prisms, the vertical and horizontal deformability and the failure modes of the components of concrete blocks under compression. In ...The main objective of this study is to verify, through compression tests on different prisms, the vertical and horizontal deformability and the failure modes of the components of concrete blocks under compression. In this study two mortar mixes were tested, along with two types of prism, with and without the presence of a vertical joint. The conclusions were： the appearance of non-linearities of the masonry corresponds to an increase in the lateral strain due to extensive cracking of the material and a progressive increase in the Poisson ratio, the cracks in the three-block prisms built with the mortar type I were vertical, occurring symmetrically on both sides; the prisms built with mortar type II had, as a consequence of localized crushing, an association with vertical cracks due to the concentrations of stresses at some points, the presence of a vertical joint led to the appearance of separation cracks between the middle block and the vertical mortar joint, when the stress reached approximately 30% of the compressive strength of the set; the prisms with two whole blocks and one vertical joint （B） built with the mortars of mixes I and II had a compressive strength of the order of 42% and 66% of the prisms with three whole blocks （A）, respectively.展开更多
The properties of two types of fly ash geopolymers made from class F fly ashes produced in wet bottom and dry bottom boilers were investigated in the present study. The source material used in the geopolymer concrete ...The properties of two types of fly ash geopolymers made from class F fly ashes produced in wet bottom and dry bottom boilers were investigated in the present study. The source material used in the geopolymer concrete was activated with sodium hydroxide and sodium silicate solution. The results revealed that the geopolymer produced with wet bottom boiler fly ash(CZ-FA)hardened quickly, and had higher early-age strength and lower shrinkage than the geopolymer produced with dry bottom boiler fly ash(SX-FA). The compressive strength of the two geopolymers made from CZ-FA and SX-FA was 45 MPa and 15 MPa respectively when cured at 60 ℃ and delayed for 14 d. However, after 90 days' delay, the compressive strength of both the samples is almost the same, up to 80 MPa. Nearly 20% volume shrinkage of the samples made from SX-FA was much higher than that made from CZ-FA, which was almost zero. XRD, SEM/EDS and FT-IR were used to analyze the main reason of the differences.展开更多
基金Project(2010THZ021)supported by Tsinghua University,ChinaProject(50978139)supported by the National Natural Science Foundation of ChinaProject(2012CB719804)supported by the National Basic Research Program of China
文摘The rapid development of high-speed transportation infrastructure such as highway and high-speed railway has resulted in the advancement of soft soil improvement techniques. Vacuum preloading combined with vertical drains has been proved to be an effective method in the treatment of soft foundation. A three-dimensional numerical analysis of the coupled methods was presented, in which the smear zone and the well resistance were taken into account. The variations of the basic soil parameters including the permeability coefficient and the coefficient of volume compressibility were considered in the numerical model. The result of the numerical model was then compared to the measured value. The results indicate that the decrease of coefficient of volume compressibility accelerates the consolidation of the soil while the influence of hydraulic conductivity is insignificant. A cube drain presents the closest result to the real situation compared to the other equivalent methods of prefabricated vertical drain (PVD). The case study indicates that the numerical model with variation of soil parameters is closer to the measured value than the numerical model without variation of soil parameters.
文摘The main objective of this study is to verify, through compression tests on different prisms, the vertical and horizontal deformability and the failure modes of the components of concrete blocks under compression. In this study two mortar mixes were tested, along with two types of prism, with and without the presence of a vertical joint. The conclusions were： the appearance of non-linearities of the masonry corresponds to an increase in the lateral strain due to extensive cracking of the material and a progressive increase in the Poisson ratio, the cracks in the three-block prisms built with the mortar type I were vertical, occurring symmetrically on both sides; the prisms built with mortar type II had, as a consequence of localized crushing, an association with vertical cracks due to the concentrations of stresses at some points, the presence of a vertical joint led to the appearance of separation cracks between the middle block and the vertical mortar joint, when the stress reached approximately 30% of the compressive strength of the set; the prisms with two whole blocks and one vertical joint （B） built with the mortars of mixes I and II had a compressive strength of the order of 42% and 66% of the prisms with three whole blocks （A）, respectively.
文摘The properties of two types of fly ash geopolymers made from class F fly ashes produced in wet bottom and dry bottom boilers were investigated in the present study. The source material used in the geopolymer concrete was activated with sodium hydroxide and sodium silicate solution. The results revealed that the geopolymer produced with wet bottom boiler fly ash(CZ-FA)hardened quickly, and had higher early-age strength and lower shrinkage than the geopolymer produced with dry bottom boiler fly ash(SX-FA). The compressive strength of the two geopolymers made from CZ-FA and SX-FA was 45 MPa and 15 MPa respectively when cured at 60 ℃ and delayed for 14 d. However, after 90 days' delay, the compressive strength of both the samples is almost the same, up to 80 MPa. Nearly 20% volume shrinkage of the samples made from SX-FA was much higher than that made from CZ-FA, which was almost zero. XRD, SEM/EDS and FT-IR were used to analyze the main reason of the differences.
