Abstract
The results of FLAC3D-based numerical evaluation of the bearing capacity shape factor s? are presented for square and rectangular footings on granular soils. The results confirm a peculiar effect found earlier by Zhu and Michalowski (2005), where for large values of internal friction angle, s? exhibits a peak at some aspect ratio of the footing, and then decreases towards unity at large aspect
ratio of the footing, and then decreases towards unity at large aspect ratios. The Zhu and Michalowski�
Key Words
footings; bearing capacity; shape factors; finite element method; three-dimensional analysis; numerical methods.
Address
Viktor Puzakov: Department of Civil Engineering, University of Minnesota, Minneapolis, MN 55455, U.S.A.
Andrew Drescher: Department of Civil Engineering, University of Minnesota, 500 Pillsbury, Minneapolis, MN 55455, U.S.A.
Radoslaw L. Michalowski: Department of Civil and Environmental Engineering, University of Michigan, MI 48109, U.S.A.
Abstract
The paper deals with the applications of spectral finite element method to the dynamic analysis of framed foundations supporting high speed machines. Comparative performance of approximate dynamic stiffness methods formulated using static stiffness and lumped or consistent or average mass matrices with the exact spectral finite element for a three dimensional Euler-Bernoulli beam element is presented. The convergence of response computed using mode superposition method with the appropriate dynamic stiffness method as the number of modes increase is illustrated. Frequency proportional discretisation level required for mode superposition and approximate dynamic stiffness methods is outlined. It is reiterated that the results of exact dynamic stiffness method are invariant with reference to the discretisation level. The Eigen-frequencies of the system are evaluated using William-Wittrick algorithm and Sturm number generation in the LDLT decomposition of the real part of the dynamic stiffness matrix, as they cannot be explicitly evaluated. Major
Key Words
machine foundations; dynamic stiffness method; spectral finite element; wittrick-william\'s algorithm; sturm number; major
Address
N. Lakshmanan: Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai-600113, India
N. Gopalakrishnan: Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai-600113, India
G.V. Rama Rao: Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai-600113, India
K. Sathish kumar: Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai-600113, India
Abstract
Many factors influence occurrences of rock burst in coal mines, such as mining methods, control methods of the coal roof, lithological characteristics of the roof and floor, tectonic stress, groundwater and so on. Among those factors, lithological characteristics in the roof are the intrinsic controlling factors that affect rock burst during coal mining. Tangshan colliery is one of the coal mines that have suffered seriously from rock bursts in China. In this paper, based on the investigating the
lithological characteristics of coal roofs and occurrence of rock bursts in Tangshan colliery, a numerical method is used to study the influence of roof lithological characteristics on rock burst potential. The results show that the lithological characteristics in the roof have an important impact on the distributions of stresses and elastic strain energy in coal seams and their surrounding rocks. Occurrences of rock bursts in this colliery have a close correlation with the thick-bedded, medium- to fine-grained sandstones in the roof. Such strata can easily cause severe stress concentration and accumulate enough energy to trigger rock bursts in the working face during mining operations.
Key Words
lithological characteristics; bursting potential; rock burst; numerical study; elastic strain energy.
Address
Pan Jienan: Institute of Resources & Environment, Henan Polytechnic University, Jiaozuo 454000, China
College of Earth Sciences, Graduate University of Chinese Academy of Sciences, Beijing 100049, China
Meng Zhaoping: Department of Resources and Geoscience, China University of Mining and Technology, Beijing 100083, China
Hou Quanlin: College of Earth Sciences, Graduate University of Chinese Academy of Sciences, Beijing 100049, China
Ju Yiwen: College of Earth Sciences, Graduate University of Chinese Academy of Sciences, Beijing 100049, China
Li Guofu: College of Earth Sciences, Graduate University of Chinese Academy of Sciences, Beijing 100049, China
Abstract
Breakdown pressures obtained from the classic, linear elastic breakdown model are compared with the corresponding pressures obtained using a nonlinear material model. Compression test results obtained on sandstone and siltstone are used for that purpose together with previously formulated nonlinear model which introduces elasticity functions to address nonlinear stress-strain behaviour of rocks exhibiting stress-dependent mechanical properties. Linear and nonlinear collapse pressures are also compared and it is shown that material nonlinearities have significant effect on both breakdown and collapse pressures and on tangential stresses which control breakdown pressure around a borehole. This means that the estimates of
Key Words
borehole; stress analysis; critical well pressures; material nonlinearities.
Address
Pawel A. Nawrocki: The Petroleum Institute, Department of Petroleum Engineering, P.O. Box 2533, Abu Dhabi, United Arab Emirates
Abstract
Due to the enormous amount of fills required, broken rock-fine grain soil mixtures have been increasingly used in the construction of high-fill foundations for airports, railways and highways in the mountain areas of western China. However, the compressibility behavior of those broken rock-fine grain soil mixtures remains unknown, which impose great uncertainties for the performance of those high-fill foundations. In this research, the mixture of broken limestone and a fine grain soil, Douposi soil, is
studied. Large oedometer tests have been performed on specimens with different soil content. This research reveals the significant influence of fine grains on the compressibility of the mixture, including immediate settlement, creep, as well as wetting deformation.
Key Words
compressibility; high-fill foundation; long term settlement; wetting deformation
Address
Ming Xu: Department of Civil Engineering, Tsinghua University, Beijing 100084, China
Erxiang Song: Department of Civil Engineering, Tsinghua University, Beijing 100084, China
Guangxu Cao: Department of Civil Engineering, Tsinghua University, Beijing 100084, China
