Advanced Materials Research Vols. 261-263

Abstract: In order to explore the proper modified materials of the raw-soil building in mountain area, the raw-soil modified materials now being used commonly are analyzed effectively at first, and the natural reborn starch resource is thought which has a promising application prospect. In the end, experiments on compressive properties and shear properties of raw-soil material modified by quicklime, slaked lime and starch with different incorporation rates are carried out, and the tests show starch is applicable to modify raw-soil in mountain area.

Abstract: Near-field ground shock features are analyzed according to the seismological record of the May 12 Wenchuan earthquake made at the Wolong observation station. A numerical analysis model is established by taking the record as the input seismic load and a real high and steep rock slope on the bank of the Zipingpu Reservoir. The acceleration response and shear strain increment distribution features at different locations of the slope under horizontal seismic force are analyzed using Plaxis software. The moment when the widest plastic zone occurs for the slope is obtained by time history analysis. The corresponding stability factor of the slope at that moment is calculated using the strength reduction method (including shear strength and tensile strength). The above is the Time History Analysis–Strength Reduction Method presented in this article. In addition, the stability factor of the slope can be calculated using the pseudostatic method by taking the seismic force as the external load. This is the Time History Analysis–Pseudostatic method put forward in this paper. Analysis results demonstrate that, as far as the studied high and steep slope is concerned, at 31.89 s, the stability factor calculated with the Time History Analysis–Strength Reduction Method is 1.004, which is slightly larger than the 0.833 obtained using the Time History Analysis–Pseudostatic Method (Spencer method). Both results demonstrate that there is collapse and sliding failure of the localized rock mass at the top of the slope at that moment because of joint fracture. Field investigation after the earthquake further verified the calculation result, proving to a certain degree the rationality of the analysis method presented.

Abstract: According to past experiences, the collapse of tunneling work always triggered a chain reaction of collateral damage and caused a considerable urban impact. Therefore, while the tunnel disasters occur, the timely response is important to prevent the expansion of the disaster and the subsequent restoration work is equally important to shorten the impact duration and ensure the ultimate success of the project. This study used the restoration works of a tunneling failure that occurred in Kaohsiung MRT project as a research subject to identify those works, which are critical to the success in the process of the restoration. The research results suggest that an accurate site investigation, and a thorough analysis of possible alternatives and the selection of restoration methods with comprehensive consideration of various factors are the critical factors for the success of the restoration works.

Abstract: Constructing a metro station by enlarging an existing large-diameter shield tunnel can be considered as an attempt to build metro engineering efficiently, safely and economically. To Take the Gaojiayuan station of Beijing metro line 14 as an object of study, two-dimensional finite element models are used to simulate metro station construction by enlarging a large-diameter shield tunnel with an outer diameter of 10 m, based on the soil-tunnel-pipeline-building interaction. According to the theory of orthogonal experimental design, four different supplementary construction measures are considered to study the influence of whether or not adopting the measures on deformation of adjacent structures during enlarging construction. The deformation of adjacent structures is predicted on the basis of adopting four supplementary construction measures. The numerical results can be regarded as a reference for the design and construction of metro station by enlarging large-diameter shield tunnel.

Abstract: Grout flow pattern and rheological parameters determine grouting pressure transfer process in annular tail void and filling rate for shield tail void. However, cemented mortar is a mixture of cement, fly ash, sand, bentonite and water, which lead to grout rheological properties and rheological parameters are difficultly determined. Based on orthogonal experimental design method, grout rheological properties were tested by rotational viscometer. Utilizing variance and poly-nonlinear regression analysis, the qualitative and quantitative relationships between mix ratios and rheological parameters were obtained respectively. It is shown that cemented mortar flow pattern commonly agree with Bingham fluid type, and plastic viscosity varies between 1 and 4Pa•s, and shear yield stress varies between 10 to 40Pa respectively. Water-binder ratio and bentonite-water ratio are key influencing factors for grout rheological parameters. With the water-binder ratio increasing and bentonite-water ratio decreasing, plastic viscosity and shear yield stress present reducing tendency.

Abstract: Pit foundation excavation leads both settlement and uneven settlement in the building foundation. It has settlement cracks in masonry and concrete structure; these damages lie on the basis of the instability in neighboring buildings. In this paper, by the use of FLAC3D, it establish three-dimensional numerical analysis mode of interaction between foundation pit excavation and raft foundation, the change patterns of the soil deformation, pore water pressure and the uneven settlements of raft foundation are analyzed. The results indicate that the maximum value of the raft foundation settlement appears on the maximum pit free surface on the foundation pit, and the lesser value of the raft foundation settlement is away from the foundation pit, these indicate that the laws of the uneven settlement.

Abstract: The total porosity of high performance concrete specimens after different level uniaxial tensile loading were measured to reflect the damage degree of mechanical load to the microstructure of the concrete. Meanwhile, considering the environmental characteristics of the ocean tidal zone, chloride penetration tests of the concrete were carried out with salt solution capillary absorption method. Based on the profile of chloride measured from specimens, chloride diffusion coefficients of the concrete under uniaxial tensile load with different levels are determined further by Fick’s second law. Results show that both of total porosity and chloride diffusion coefficient of the concrete are increased significantly after short-term tensile loading. And the evolutions of the porosity and chloride diffusion coefficient are similar with the development of micro-cracks under uniaxial tensile load.

Abstract: Based on the framework of the FEM, the three-dimensional numerical analysis for evaluating the efficiency of pile groups of large diameter bored cast-in-place pile is conducted in this paper. The effect of the pile numbers and pile spacing on the efficiency of pile groups is obtained by studying the ultimate bearing capacity behavior of different arrangements of pile groups under vertical loading. Then they are compared with the calculated results gained by the formula of the efficiency factor of the pile groups based on superimposed stresses. The findings can serve as a reference for the design of large diameter bored cast-in-place pile.

Abstract: At present, the new Austrian tunneling method is basically used as the theoretical guidance for domestic tunnel design, which shows that the primary support is not progressed by durability design in the light of service life in the practical work generally acting as the temporary support structure during the period of construction. After the long-term tunnel operation, owing to the erosion of groundwater and the changes of internal stress and external load of surrounding rock, the reinforced of primary support system will be rusted; the bolt, grille arch frame and I-beam will be partially invalidated; the stress of tunnel structure system will be readjusted gradually from the original load-bearing state with dominant position of primary support into the load-bearing state by secondary lining. The Long-term safety analysis refers to the analysis of secondary lining internal force and safety coefficient by load structure model, and the long-term safety analysis of Qingshashan tunnel which is in season frozen zone with complex geological conditions is very necessary.

Abstract: Deep excavations release stresses in the earth and redistribute these stresses causing deformation. The pressure loss due to excavation may result in a base instability, where the soil flow beneath the sheeting into the excavation, producing a rise in the base elevation commonly termed as heave. The heave can lead the foundation piles casted before excavation to floating and being in tension, and even induce the tensile failure of pile in severe case. The characters of foundation piles in different excavation conditions, different location have been analyzed by a case study. The calculation results show that the deeper excavation, the larger vertical force acted on the foundation pile and the heave could induce the tensile failure of the foundation piles. So it is recommended that the tensile capacity of the foundation piles should be verified when the excavation is very deep.