| With the country to vigorously promote the urbanization process, the rapid expansion of the urban population, the city has brought traffic to a lot of pressure. To solve this problem, a new transport came into being-the subway. With the subway construction, the emergence of the large number of deep excavation, underground deep pit to ultra-deep, ultra-large-scale development, to engineering design, construction workers brought unprecedented challenges.In recent years, the theoretical and computational methods of deep foundation pit structure, although greatly improved, but because of the many factors that affect the supporting structure of the soil physical and mechanical properties, the calculation assumes that earthwork excavation, precipitation quality, climate so its influence factors, so that the calculated and measured values of the deformation and internal forces there is often a gap, the theoretical calculation of deep excavation has brought great difficulties. Variation of axial force deformation and support research in the process of deep excavation supporting structure has important guiding significance for the design and construction of deep foundation.In this paper, Jinan West Railway Station Metro Line1as the basis of deep excavation carried out relevant analysis; first type of deep foundation support, the deformation mechanism and calculation methods were analyzed deep foundation systems for deep foundation research laid the theoretical foundation pit; combined Jinan West Railway Station Metro Line1deep foundation Bracing System, developed a detailed on-site monitoring program; through on-site monitoring data collation, specifically on Metro Line1deep excavation pile top horizontal displacement, displacement piles, steel support axial forces conducted in-depth analysis of a comprehensive system, the corresponding variation obtained for the study of similar deep foundation construction monitoring provides some lessons.Finally, through the ANSYS finite element software on the1st line of deep foundation for three-dimensional nonlinear physical simulation, the " birth and death " for the protection of deep foundation excavation and support were simulated under different conditions, and analyzes the different working under conditions of displacement piles, bracing variation of axial force, and with the on-site monitoring data were analyzed, further evidence of the finite element software simulation of deep excavation supporting the usefulness and reliability of deep foundation for the future study has some practical significanceIn this paper, the following main conclusions:(1) the horizontal displacement of pile head, with the increase of excavation depth increases; Pile top central maximum deformation from north and south ends of foundation pit excavation also increased gradually; The first line of support (0.1H) can effectively control the displacement of supporting pile top; In deep foundation pit subject during the period of construction, the changing rate of displacement of pile top is small, the main structure was described, medium plate, roof had expected supporting effect; By above can draw deformation of foundation pit supporting pile cap has obvious effect of space and time; Short pile top horizontal deformation in foundation pit edge point S, N and long edge points (W1, W9, El, E9) monitoring value between6.5mm to14.1mm, and the long side of central point (W2-project.it, E2-E8) monitoring value between16.3mm to28.6mm, while the pile top horizontal displacement monitoring value is less than the standard stipulated by the alert value30mm, and0.2H%(37.2mm), but the short edge and corner point of foundation pit monitoring value is far less than the alert code value, if the alert value stipulated in the codes (30mm or0.2H%) on the deformation control, is too conservative, response of pile top deformation control index for piecewise control, in order to reduce unnecessary waste, therefore, suggest that similar to the engineering geological conditions of the strip type (length, width, depth=10:1:1) short edge and corner cap deformation of deep foundation pit of the alert value is16mm or0.1H%for foundation pit excavation depth (H).(2) with the increase of excavation depth, pile deformation curve change rule approximation shows\"bow\" form, with maximum horizontal displacement will be down, the maximum deformation generally occur in deep foundation pit near12.7m, the maximum deformation appeared in the vicinity of0.684H; Supporting pile horizontal displacement occurs mainly in the foundation pit excavation supporting stage (excavation to18.58m), which is1h, maximum deformation in this period accounted for about75%of the overall biggest pile deformation, and the underground engineering subject construction stage the largest pile deformation accounted for about25%of the overall biggest pile deformation.(3) by the field measured data analysis:for similar geological jinan region and the deep foundation pit supporting conditions, when the first line of the steel support (every6m) installed in the vicinity of0.1H, the first line of the steel support axial force design values should be multiplied by1.175correction coefficient; When the second steel support (each3m) installed in the vicinity of0.45H, the name of the second steel support axial force design values should be multiplied by1.075correction coefficient, when the third steel support (each3m) installed in the vicinity of0.8H, the third steel support axial force design values should be multiplied by the correction coefficient of0.863.(4) the deep foundation pit of three-dimensional numerical simulation results and field monitoring results although there are some differences, but its deformation, axial force of the development trend is consistent, proved that the use of the principle of equivalent stiffness will pile supporting structure into underground continuous wall supporting structure of the simulation method is correct, have certain reference significance. |
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