An improved soft-kill BESO algorithm for optimal distribution of single or multiple material phases

Finding the optimum distribution of material phases in a multi-material structure is a frequent and important problem in structural engineering which involves topology optimization. The Bi-directional Evolutionary Structural Optimization (BESO) method is now a well-known topology optimization method. In this paper an improved soft-kill BESO algorithm is introduced which can handle both single and multiple material distribution problems. A new filtering scheme and a gradual procedure inspired by the continuation approach are used in this algorithm. Capabilities of the proposed method are demonstrated using different examples. It is shown that the proposed method can result in considerable improvements compared to the normal BESO algorithm particularly when solving problems involving very soft material or void phase

Study of rock truss bolt mechanism and its application in severe ground conditions

Instability of underground excavations is an ever-present potential threat to safety of personnel and equipment. Further to safety concerns, in the event of failure, profitability may reduce significantly because of loss of time and dilution of the ore, raising the importance of support and reinforcement design in underground excavations both in civil and mining engineering. The truss bolt reinforcement system has been used in controlling the stability of underground excavations in severe ground conditions and preventing cutter roof failure in layered rocks especially in coal mines. In spite of good application reports, working mechanism of this system is largely unknown and truss bolts are predominantly designed based on past experience and engineering judgement. In this study, the reinforcing effect of the truss bolt system on an underground excavation in layered rock is studied using non-linear finite element analysis and software package ABAQUS. The behaviour of the rock after installing reinforcement needs to be measured via defining some performance indicators. These indicators would be able to evaluate the effects of a reinforcing system on deformations, loosened area above the roof, failure prevention, horizontal movement of the immediate layer, shear crack propagation, and cutter roof failure of underground excavations. To understand the mechanism of truss bolt system, a comparative study is conducted between three different truss bolt designs. Effects of several design parameters on the performance of the truss bolt are studied. Also, a comparison between the effects of truss bolt and systematic rock bolt on different stability indicators is made to highlight the different mechanism of these two systems. In practice, site conditions play a vital role in achieving an optimum design for the reinforcement system. To study the effects of position of the bedding planes and thickness of the rock layers, several model configurations have been simulated. By changing the design parameters of truss bolt, effects of thickness of the roof layers are investigated and a number of optimum truss bolt designs for each model configuration are presented

Exploring topology and shape optimisation techniques in underground excavations

Topology optimisation techniques help designers to nd the best layout of structural members. When followed by shape and sizing optimisation, these techniques result in far greater savings than shape and sizing optimisation alone. During the last three decades extensive research has been carried out in the topology optimisation area. Consequently topology optimisation techniques have been considerably improved and successfully applied to a range of physical problems. These techniques are now regarded as invaluable tools in mechanical, aerostructural and structural design. In spite of great potential in geomechanical problems, however, the application of topology optimisation techniques in this field has not been studied thoroughly. This thesis explores the state-of-the-art topology and shape optimisation methods in excavation design. The main problems of concern in this thesis are to find the optimum shape of an underground opening and to optimise the reinforcement distribution around it. To tackle these problems, new formulations for some topology optimisation techniques are proposed in this thesis to match the requirements in excavation problems. Although linear elastic material models have limited applications in excavation design, these models are used in the first part of this thesis to introduce the proposed optimisation technique and to verify it. Simultaneous shape and reinforcement optimisation is considered as well. Using the proposed optimisation techniques, it is shown that the computational effort needed for this mixed optimisation problem is almost the same as the effort required to solve each of shape or reinforcement optimisation problems alone. In the next part of this thesis, reinforcement optimisation of tunnels in massive rocks is addressed where the behaviour of the rock mass is in uenced by few major discontinuities. Although discontinuities exist in the majority of rock masses, due to its complexities, optimising the excavations in these types of rocks has not been considered by any other researcher before. A method for reinforcement optimisation of tunnels in such rock masses is proposed in this thesis and its capability is demonstrated by means of numerical examples. Lastly, shape optimisation of excavations in elasto-plastic soil is addressed. In this problem the excavation sequence is also taken into account. A stressbased parameter is dened to evaluate the efficiency of the soil elements assuming Mohr-Coulomb material model. Some examples are solved to illustrate and verify the application of the proposed technique. Being one of the first theses on the topic, this work concentrates on the theoretical background and the possibility of applying topology optimisation techniques in excavation designs. It has been demonstrated that a properly tailored topology optimisation technique can be applied to find both the optimum shape and the optimum reinforcement design of openings. Optimising the excavations in various types of grounds including elastic homogeneous rock masses, massive rocks, and elasto-plastic soil and rock media have been considered. Different objective functions, namely, mean compliance, oor heave, and tunnel convergence have been selected and successfully minimised using the proposed techniques. The results obtained in this thesis illustrate that the proposed topology optimisation techniques are very useful for improving excavation designs

Application of 3D laser scanner, optical transducers and digital image processing techniques in physical modelling of mining-related strata movement

A physical testing protocol for modelling mining-related problems has been presented. • A new method for monitoring fracture propagation pattern has been introduced. • Laser based and optical devices have been used for physical modelling of subsidence. • Multiple-seam subsidence has been measured by photogrammetry, DIC analysis, optoNCDT and 3D TLS

Tunnel reinforcement optimisation for nonlinear material

In this paper, topology optimization is applied in optimizing tunnel reinforcement. Nonlinear behavior of geotechnical material is considered to illustrate the practical material behavior under working condition. The adjoint method is used to derive the nonlinear sensitivities. A revised bi-directional evolutionary optimization (BESO) is used to maximize the structural stiffness of reinforced tunnel with a prescribed volume of reinforcement. The developed BESO method is illustrated in a simple example of tunnel reinforcement design to verify the proposed approach

Shape optimization of metallic yielding devices for passive mitigation of seismic energy

Bi-directional Evolutionary Structural Optimization (BESO) is a well established topology optimization technique. This method is used in this paper to optimize the shape of a passive energy dissipater designed for earthquake risk mitigation. A previously proposed shape design of a steel slit damper (SSD) device is taken as the initial design and its shape is optimized using a slightly modified BESO algorithm. Some restrictions are imposed to maintain simplicity and to reduce fabrication cost. The optimized shape shows increased energy dissipation capacity and even stress distribution. Experimental verification has been carried out and proved that the optimized shape is more resistant to low-cycle fatigue

Effects of thickness of roof layers on optimum design of truss bolt system using finite element modeling techniques

In underground excavations, optimum design of reinforcement systems is largely based on geological features of the surrounding rock such as in-situ stress distribution, rock strength properties, thickness of the layers, etc. In current design of truss bolt systems these parameters are yet to be considered. In this study, effects of changing thickness of roof layers on optimum design of truss bolt have been investigated using three stability indicators, namely reduction in the loosened area above the roof, number of plastic points and horizontal movement on the first bedding plane. Total of 7 different bedding configurations have been generated and 100 different truss bolt designs have been tested on each bedding configuration. Results showed that by changing the thickness of the roof layers, the optimum design of truss bolt changes drastically. In highly laminated formations, it has been demonstrated that a gently inclined bolt angle is more effective, while by increasing the thickness of roof layers, truss bolt systems with a higher bolt angle and longer bolts, i.e. similar to systematic rock bolt systems, responds better

Applications of topology optimization techniques in seismic design of structure

During the last two decades, topology optimization techniques have been successfully applied to a wide range of problems including seismic design of structures. This chapter aims to provide an introduction to the topology optimization methods and a review of the applications of these methods in earthquake engineering. Two well-established topology optimization techniques will be introduced. Several problems including eigenfrequency control of structures, compliance minimization under periodic loading, and maximizing energy absorption of passive dampers will be addressed. Numerical instabilities and approaches to overcome them will be discussed. The application of the presented approaches and methods will be illustrated using numerical examples. It will be shown that in seismic design of structures, topology optimization methods can be useful in providing conceptual design for structural systems as well as detailed design of structural members