With recent advancements in computer software and hardware, numerical simulation has become an important tool for analysis and design in gotechnical engineering. This review article surveys major problem types in geotechnical numerical simulation and the existing software appropriate for solving each problem type. Most engineering problems can be expressed as either a boundary-value problem or an initial-value problem. Major geotechnical numerical simulation problems, including load-deformation stress analysis, seepage, slope stability and bearing capacity, are discussed; and the existing commercial software packages for each problem type are recommended. This article also includes a discussion on the important considerations required in geotechnical numerical simulation and on the prospect of possible future developments in geotechnical numerical simulations.
It is imperative to keep adjacent structures intact for most urban excavations. To achieve this end, auxiliary measures, including buttress walls, cross walls, ground improvements, or strengthening of bracing systems, are often adopted in the excavation design. Numerical tools, simple or complex, can be used to assess the very complex 3D effects of these auxiliary measures. This paper delineates the use of a simple 1D FEM program, TORSA, to simulate the 3D effect of buttress walls for two deep excavations via a simplified approach. It is found that that good engineering judgment in conjunction with the appropriate use of this simplified approach can produce results that are close to field measurements.
Observations from earthquakes over the past 40 years have shown that local soil conditions can significantly influence the characteristics of ground shaking during earthquakes. These so-called site effects are typically quantified via site response analysis that involves the propagation of earthquake motions from the base rock, through the overlying soil layers, and to the ground surface. This article introduces the time domain nonlinear site response analysis program DEEPSOIL developed by Hashash’s research group at the University of Illinois, Urbana-Champaign. This latest version, DEEPSOIL 6.0, can perform both time domain nonlinear and frequency domain equivalent linear analysis (similar to SHAKE) and it also has a user-friendly interface. This article introduces the theoretical background of the program, highlights its features, and compares the time domain nonlinear analysis with frequency domain equivalent analysis.
Due to its advantages for operation, the MC model with the total stress concept is widely used for numerical analysis of deep excavations in Taiwan. However, the hardening soil model (HS model) is able to simulate the non-linear stress-strain relationships of soils, as well as the shear and cap yield surface (isotropic hardening) and stress-dependent soil stiffness at various conditions. It thus should be more reliable for deep excavation situations. Therefore, the drained and undrained analyses with both total and effective stress concept are evaluated by employing the PLAXIS program. Then characteristics of the MC model are reviewed and a brief introduction of the HS model and the proper parameters are presented. In addition, buttress and cross walls are commonly employed in deep excavation to reduce the lateral displacement of diaphragm walls and adjacent ground settlement. Accordingly, for reference we present the actual behaviors of 3D effects resulting from these measures, which were approximately simulated with the plane-strain methods.
The route of new shield tunnel project will pass through an existing MRT station, after which, a new MRT station will be constructed at the intersection of two MRT lines. Moreover, direct transfer service will be provided between the existing and new stations. The diaphragm wall of the new station has been completed adjacent to the existing station. Then the shield tunnel will ransversely drive through the existing station and connect with the new station. In order to mitigate the impact on the existing structures, a series of horizontal and vertical ground grouting treatments will be executed underneath the existing station before beginning TBM. In this research, a 3D numerical tool was utilized to analyze and evaluate the influence of tunnel excavation and grouting on the existing structures. This paper also introduces methods of modeling for ground grouting and shield tunnel construction.
Two cooling ponds were designed on a slope inside the power plant area. The higher cooling pond is referred to as "upper pond", and the pond below that is referred to as the "lower pond". Due to the construction errors, planar sliding failure occurred on the slope between the upper pond and lower pond.According to the geological survey, the bedrock consisted of sandstone and shale. The excavation face showed that the shale layer was about 20~30cm thick. It is assumed that the rock mass cracked along the existing joints of sandstone due to the excavation at the toe of the slope, and rainwater seeped through the cracks into the shale below the sandstone. The immersed shale decomposed to clay gouge, lost its bearing capacity, and as a result the slope planar sliding failure occured.For construction and operation safety, MIDAS-GTS was adopted for the slope stability analysis during excavaiton. The shale layer was simulated in the 3D geological model. The assessment of the impact of the lower pond excavation on the upper pond, and the impact of the lower pond construction on the backfill area beneath were also included in this study.
With recent advancements in software and hardware, the development of GIS technology has expanded from two dimensional to three dimensional applications, and the use of spatial GIS data has gradually included underground as well as surface issues. This article first introduces the recent evolution, data requirements, basic procedures and methods for building 3D-GIS data. It then provides application examples related to engineering geology, geotechnical engineering, and landslide estimation.
The two main advantages of using 3D-GIS data are for information exchange between different engineering interfaces of professional engineers and as and effective communication tool. Beyond introducing basic concepts of 3D-GIS data to geotechnical engineers, this article also points towards more applications in geotechnical fields, even that this technology could be combined with the BIM (Building Information Modeling) concept.
Today, with computer advancements applying CAD on engineering design is more convenient. Complex geotechnical engineering problems can be simplify and simulated in numerical model by CAD. In addition, the analysis results can be visualized in CAD to help engineer clear understanding influence of each parameter.
The market is flooded with different CAD software. In this article, how to apply ANSYS to deal with geotechnical engineering problem is demonstrated by mean of several practical case studies. Although applying numerical software already can solve most of cases, there are still some limitations and topics needed to be solved. Through the feedback of practical experience can be provided to advance these analysis tool and method.
The characteristics of stress wave propagation in pile foundations can be applied for pile integrity inspection. The traditional impulse response method is limited by its one-dimensional theoretical basis and its waveform generation method, so specific types of defects are unable to be either distinguished or identified. This restriction can be relieved by treating a pile foundation as a waveguide, and developing a three-dimensional frequency wave equation with appropriate boundary conditions. It is then possible to build new interpretation baselines in terms of wave modes, propagation velocities, attenuation coefficients, and modal shapes. The mathematical computation software Maple is used for deriving the numerical solutions for this specific problem. Advanced guided wave characteristics and experimental design concepts are further evaluated and exploited based on the derived computational results.