Construction of tunnels in urban areas requires assessment of the impact of tunneling on the stability and integrity of existing pile foundations. We have focused our attention to the analysis of the carrying capacity...Construction of tunnels in urban areas requires assessment of the impact of tunneling on the stability and integrity of existing pile foundations. We have focused our attention to the analysis of the carrying capacity of pile foundations provided by the impact of construction of urban tunnels on adjacent pile foundations, under the engineering background of the construction of the # 2 Line of the Guangzhou subway. It is carried out using a fast Lagrangian analysis of a continuum in a 3D numerical code, which is an elastoplastic three-dimensional finite difference model, to simulate the response of piles under the entire process of metro tunneling （deactivation of soil element and activation of the lining）. The adjacent stratum around the tunnel is classified into three regions： Zone Ⅰ （upper adjacent stratum of tunnel）, Zone Ⅱ （45°-upper-lateral adjacent stratum of tunnel） and Zone Ⅲ （lateral adjacent stratum of tunnel）. In each region one typical pile is chosen to be calculated and analyzed in detail. Numerical simulations are mainly conducted at three points of each pile shaft： the side-friction force of the pile, the tip resistance of the pile and the axial loading of the pile. A contrasting analysis has been conducted both in the response of typical piles in different regions and from computer calculated values with site monitoring values. The results of numerical simulations show that the impact on carrying capacity of the piles lies mainly in the impact of construction of urban tunnels on the side-friction forces and the tip resistance of piles. The impact differs considerably among the different strata zones where the pile tips are located. The complicated rules of side-friction force and tip resistance of piles has resulted in complicated rules of pile axial loading thus, in the end, it impacts the carrying capacity of pile-foundations. It is necessary to take positive measures, such as stratum grouting stabilization or foundation underpinning, etc, to deal with the carrying capacity and the settlement of pile-foundations. The results are of value to similar engineering projects.展开更多
Instead of most existing postprocessing schemes, a new preprocessing approach, called multi- neighboring grids （MNG）, is proposed for solving PDE eigen-problems on an existing grid G（A）. The linear or multi-linear...Instead of most existing postprocessing schemes, a new preprocessing approach, called multi- neighboring grids （MNG）, is proposed for solving PDE eigen-problems on an existing grid G（A）. The linear or multi-linear element, based on box-splines, are taken as the first stage Khuh -λh/1Mh/1Uh. In this paper, the j-th stage neighboring-grid scheme is defined as Khuh λh/j Mh/j Uh = λh/j Mh/j Uh , where gh ：- Mh/j-1 Kh/1 and Mhuh is to be found as a better mass distribution over the j-th stage neighboring-grid G（/k）, and Kh/1 can be seen as an expansion of Kh on the j-th neighboring-grid with respect to the （j - 1）-th mass distribution Mh_l. It is shown that for an ODE model eigen-problem, the j-th stage scheme with 2j-th order B-spline basis can reach 2j-th order accuracy and even （2j ＋ 2）-th order accuracy by perturbing the mass matrix. The argument can be extended to high dimensions with separable variable cases. For Laplace eigen-problems with some 2-D and 3-D structured uniform grids, some 2j-th order schemes are presented for j ≤ 3.展开更多
文摘Construction of tunnels in urban areas requires assessment of the impact of tunneling on the stability and integrity of existing pile foundations. We have focused our attention to the analysis of the carrying capacity of pile foundations provided by the impact of construction of urban tunnels on adjacent pile foundations, under the engineering background of the construction of the # 2 Line of the Guangzhou subway. It is carried out using a fast Lagrangian analysis of a continuum in a 3D numerical code, which is an elastoplastic three-dimensional finite difference model, to simulate the response of piles under the entire process of metro tunneling （deactivation of soil element and activation of the lining）. The adjacent stratum around the tunnel is classified into three regions： Zone Ⅰ （upper adjacent stratum of tunnel）, Zone Ⅱ （45°-upper-lateral adjacent stratum of tunnel） and Zone Ⅲ （lateral adjacent stratum of tunnel）. In each region one typical pile is chosen to be calculated and analyzed in detail. Numerical simulations are mainly conducted at three points of each pile shaft： the side-friction force of the pile, the tip resistance of the pile and the axial loading of the pile. A contrasting analysis has been conducted both in the response of typical piles in different regions and from computer calculated values with site monitoring values. The results of numerical simulations show that the impact on carrying capacity of the piles lies mainly in the impact of construction of urban tunnels on the side-friction forces and the tip resistance of piles. The impact differs considerably among the different strata zones where the pile tips are located. The complicated rules of side-friction force and tip resistance of piles has resulted in complicated rules of pile axial loading thus, in the end, it impacts the carrying capacity of pile-foundations. It is necessary to take positive measures, such as stratum grouting stabilization or foundation underpinning, etc, to deal with the carrying capacity and the settlement of pile-foundations. The results are of value to similar engineering projects.
基金supported by National Natural Science Foundation of China(Grant Nos.6097008961170075 and 91230109)
文摘Instead of most existing postprocessing schemes, a new preprocessing approach, called multi- neighboring grids （MNG）, is proposed for solving PDE eigen-problems on an existing grid G（A）. The linear or multi-linear element, based on box-splines, are taken as the first stage Khuh -λh/1Mh/1Uh. In this paper, the j-th stage neighboring-grid scheme is defined as Khuh λh/j Mh/j Uh = λh/j Mh/j Uh , where gh ：- Mh/j-1 Kh/1 and Mhuh is to be found as a better mass distribution over the j-th stage neighboring-grid G（/k）, and Kh/1 can be seen as an expansion of Kh on the j-th neighboring-grid with respect to the （j - 1）-th mass distribution Mh_l. It is shown that for an ODE model eigen-problem, the j-th stage scheme with 2j-th order B-spline basis can reach 2j-th order accuracy and even （2j ＋ 2）-th order accuracy by perturbing the mass matrix. The argument can be extended to high dimensions with separable variable cases. For Laplace eigen-problems with some 2-D and 3-D structured uniform grids, some 2j-th order schemes are presented for j ≤ 3.
