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In the internal support system of foundation pit engineering, concrete support has been widely used in foundation pit engineering due to its advantages of high bearing capacity, unrestricted layout, cast-in-place end nodes and good integrity. However, the disadvantages of concrete support in design and construction are also very obvious, with problems such as large design section, long construction time, heavy pollution, high cost and serious waste. Therefore, in view of the advantages and disadvantages of concrete support in foundation pit engineering and combined with the characteristics of deep foundation pit engineering of metro open cut station, the prefabricated composite concrete filled steel tube internal support is designed in this paper. From the perspective of improving the stiffness and strength of end joints and achieving fixed connection at the end, a fixed end composed of long bolts and mold bag concrete is proposed, which is suitable for the prefabricated composite steel tube concrete internal support of metro foundation pit. The design scheme, structural characteristics and working principle of the fixed end are explained and compared with the cast-in-place concrete support node, which shows that the fixed end plays the role of fixed support in the support system, which is composed of special components such as embedded steel plate, hollow flange, bag concrete and long bolt. In order to establish the theoretical basis for the design and check of the fixed end, the analytical method of the compression and bending load-bearing capacity of the fixed end is obtained by analyzing the mechanical mechanism, failure mode and evolution law of the fixed end. In order to verify the feasibility of the theoretical analysis method of the bearing capacity of the fixed end, the theoretical and numerical results are verified and analyzed by numerical simulation, and the main factors affecting the bearing capacity of the fixed end are parameterized. [ABSTRACT FROM AUTHOR]

The segment assembly problem of shield tunnel in the transition curve part is always a difficult problem in the construction process because of the complex shape of the transition curve and the changeable points of segment assembly. Based on the requirement of staggered assembling and wedge segment characteristics, this paper puts forward a method within the plane to complete every piece of assembling construction by calculating and judging the condition of error control with comprehensive comparison of standard ring and wedge ring combination, and fit out design and varification methods, which meets the specification and control index and guarantees ing uniform linear axis in segment assembling. According to the actual engineering needs, the maximum allowable deviation control method and the segment assembly optimization measures near the slow circle point are proposed, and the accuracy and applicability of the method are proved by the shield tunnel between Wanchai North Station and Wanchai station of Zhuhai Zhuhai-mechanical line, which provides a theoretical basis for the control of segment assembly quality on the transition curve. [ABSTRACT FROM AUTHOR]

Abstract: In the past decade, several molecular maps of cotton have been constructed using diverse DNA molecular markers and mapping populations. In this study, an interspecific linkage map of allotetraploid [...]

This paper aims at influence analysis of approaching excavation on adjacent segments for twin tunnels with variable clear spacing located in Beijing, China. A series of numerical simulations have been conducted to investigate the influence of approaching excavation on ground displacements and mechanical responses of segments. What's more, on-site monitoring was conducted at the position of the minimum spacing between the twin tunnels. It is found that the deformation of the measured segment presents a pronounced asymmetric ovalization when the second tunnel approaches the measured cross-section. During the approaching excavation of the second tunnel, the normal force increases gradually, whereas the bending moment first decreases and then increases. The maximum increments of internal forces in the measured segment are both located at the regions near the second tunnel, in which the springline and shoulder of the segment are mainly subject to the effect of the circumferential compression and axial tension. The approaching excavation reduces the horizontal displacements of the ground between twin tunnels and increases the ground settlements as well as the horizontal displacements of the ground on both sides. The actual tunneling case of first along the curved trajectory and then along the straight-line trajectory can reduce internal forces of the segment. [ABSTRACT FROM AUTHOR]

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