Advanced Materials Research Vols. 168-170

Abstract: Lots of primary or secondary structural planes in similar soil surrounding rock are the main difference with Quaternary soil surrounding rock, but the particularity isn’t considered in the analysis of tunnel stability. The fact, which similar soil surrounding rock has most weak structural planes, is testified by engineering examples. The influence of structural plane in similar soil surrounding rock on excavation stability was analyzed through combining theory with disintegration test and numerical calculation. The research results show that there are a lot of structural planes in similar soil surrounding rock. The angle between structural planes and tunnel axes and shearing strength of structural planes control the stability of tunnel. Disintegration time of soil is shortened due to structural planes. On a certain condition, structural planes can induce local collapse in soil surrounding rock while excavating.

Abstract: This paper investigates the mechanical properties (compressive strength, splitting tensile strength and flexural toughness) of polypropylene fiber reinforced self-compacting concrete (PFRSCC). The effect of the incorporation of polypropylene fiber on the mechanical properties of PFRSCC is determined. Four point bending tests on beam specimens were performed to evaluate the flexural properties of PFRSCC. Test results indicate that flexural toughness and ductility are remarkably improved by the addition of polypropylene fiber.

Abstract: Fiber reinforced polymer (FRP) tube-encased concrete columns represent a formwork-free, steel-free, and corrosion-resistant alternative for a construction of a new infrastructure. In this study, a total of nine square concrete columns with cross-section of 200mm×200mm and height of 600mm including six confined concrete encased in CFRP tubes and three unconfined concrete as control specimens are prepared. The tubes with fibers oriented at 90° from axial direction are manufactured to have 3 or 5 plies of CFRP with 10mm, 20mm, or 40mm rounding corner radius. To ensure proper bond, a 100mm overlap is provided in the direction of fibers. Uniaxial compressive tests are conducted to investigate the axial strength, compressive behavior, stress-strain relationship, and ductility of them throughout the loading history until the CFRP tubes rupture. It is evident that in all cases, the CFRP tube confinement can improve the behavior of unconfined concrete, in terms of axial compressive strength or axial deformability. Test results have shown that the stress-strain behavior of confined specimens vary with different confinement parameters, such as the level of confinement (3-ply and 5-ply), corner radius at vertical edges (10, 20 and 40 mm).

Abstract: The application of FRP materials in civil engineering is now a hot spot in the research and development of the international civil engineering field. To conclude on the basis of previous experience, this paper summarizes and reviews current state about the research and use of FRP, while the prospect of using outlook FRP reinforcement to promote the construction in civil engineering application is also given.

Abstract: The advanced Temperature and Stress Test Machine was introduced to evaluate the cracking resistance of concrete with inclusion of light-burnt MgO under full restraint by tracking thermal and deformation development. Results showed that light-burnt MgO being incorporated ranging between 4 per cent and 6 per cent by mass of cementitious materials was beneficial to increase the maximum compressive stress and cracking stress of concrete by 0.37MPa and 0.2MPa on average respectively. The maximum temperature was slightly reduced from 59.8°C to 66.2°C while cracking temperature was significantly decreased from 0.8°C to minus 5.6°C. Sensitive anti-cracking coefficient F was forwarded to assess the early cracking tendency of concrete and in general, inclusion of 4 per cent light-burnt MgO with activity of 109s was rated the best in crack resistance.

Abstract: Fiber reinforced polymer (FRP), particularly those incorporating carbon fiber (CFRP), has high strength, high stiffness-to-weight ratio and high resistance to corrosion, which shows potential for use as prestressing tendons in corrosive environment. However, concrete beams prestressed with FRP tendons have showed brittle flexural failure due to the elastic rupture of FRP tendons. In order to improve the ductility, a combination of bonded and/or unbonded prestressing tendons was used. Nine prestressed concrete beams were tested up to failure to study the effect of bonded and unbonded FRP tendons on their flexural capacity. Three factors were taken into consideration; the bonding condition of CFRP tendons, the location of CFRP tendons and the prestressing ratio. Also an analytical investigation was carried out to extend some flexural capacity calculation equations to this beam type. The results of the experimental showed that under the same condition, the carrying capacity of concrete beam prestressed with bonded FRP tendons was 20% higher than that of internal unbonded prestressed beam, and was 40% higher than that of external unbonded prestressed beam without deviators. By combination of bonded and unbonded FRP tendons, the ductility of prestressed concrete beams can be improved.

Abstract: In the underground repositories, the microstructure change of surrounding rock mass under the chemical reaction will cause the porosity change in medium. Aiming at the chemical reaction effect on the environment medium, the porosity of sandstone specimens, along with Ca2+ concentration of solution were tested. Based on the analysis of test results and the theory of chemical thermodynamics, the chemical action mechanism was concluded for absorption of Ca2+. With the combination of the theories of chemical kinetics, chemical thermodynamics, and solute transportation, a reactive-transport model to describe porosity change under chemical reaction was established. Finally a simplified chemical model was advised to describe microstructure change of rock under chemical reaction. And the numerical simulation analysis was performed. The simulation result indicates that with the reaction time increasing, the porosity reduces firstly and then is driven to stabilization in the end. The study results can be used as a valuable reference to understand the mechanism of the chemical reaction effect on the microstructure change of sand rock.

Abstract: Estimating passive earth pressure accurately is very important when designing retaining wall. Based on the unified strength theory and plane strain assumption, an analytical solution has been developed to determine the passive lateral earth pressure distribution on a retaining structure when the backfill is cohesive and inclined considering the effect of the intermediate principal stress. The solution derived encompasses both Bell’s equation (for cohesive or cohesionless backfill with a horizontal ground surface) and Rankine’s solution (for cohesionless backfill with an inclined ground surface).

Abstract: In this article, the notion of orthogonal nonseparable four-dimensional wavelet packets which is the generalizaion of orthogonal univariate wavelet packets is introduced. A new approach for constructing them is presented by iteration method. The orthogonality properties of five-dimensional wavelet packets are discussed. Three orthogonality formulas concerning these wavelet packets are estabished.