Dezi F.,University of San Marino |
Poulos H.,Coffey Geotechnics
International Journal of Geomechanics | Year: 2017
This paper describes kinematic seismic interaction analysis of square pile groups in homogeneous soil deposits, focusing on bending moments induced by the transient motion. Analyses were performed by means of a three-dimensional (3D) numerical procedure able to account for both pile-soil-pile interaction and radiation damping. The seismic motion was defined by an artificial accelerogram at the outcropping bedrock, and one-dimensional (1D) propagation analyses were performed to define the free-field motion within the deposits. An extensive parametric study was conducted to determine the effects of different variables, such as the soil properties, the bedrock location, the number of piles, and the pile spacing, on the dynamic response of pile-group foundations. Bending moments obtained from the analyses of the pile group, both at the pile head and at the interface separating soil layers, were normalized with respect to the single-pile bending moments, allowing for the proposal of a new design formula for the estimation of the kinematic bending moments in the most stressed pile of the group, starting from the knowledge of the single-pile response. The proposed formula was used, in conjunction with some simplified approaches that allow estimation of the single-pile response, to evaluate bending moments in the analyzed pile groups. The adequacy of the formula for design purposes is demonstrated. © 2016 American Society of Civil Engineers.
Trani L.D.O.,Coffey Geotechnics |
Indraratna B.,University of Wollongong
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2010
This paper presents an investigation into the seepage hydraulics of a layer of subballast filter subjected to cyclic loading in a fully saturated environment. A multilayer mathematical approach was used to predict the time-dependent permeability of this filter, with a reduction in porosity as a function of compression under cyclic loading, and the amount of base soil (<150 μm) trapped within the filter voids being the two main aspects of this proposed model. Laboratory test results conducted on a novel cyclic loading permeameter apparatus were used to validate the proposed model. The family of equations that are an integral part of the proposed model are then presented in the form of compact visual guidelines anticipated to provide a more practical tool for railway design practitioners. © 2010 ASCE.
Indraratna B.,University of Wollongong |
Rujikiatkamjorn C.,University of Wollongong |
Ameratunga J.,Coffey Geotechnics |
Boyle P.,Port of Brisbane Corporation
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2011
During the past decade, the application of vacuum preloading for stabilizing soft coastal clay and other low-lying estuarine soils has become popular in Australia. The cost-effectiveness is a major factor in most projects in view of the significantly reduced time for achieving a relatively high degree of consolidation. Resulting from an increase in trade activities at the Port of Brisbane, new facilities on Fisherman Islands at the mouth of the Brisbane River will be constructed on the new outer area (235 ha) adjacent to the existing port facilities through land reclamation. A vacuum-assisted surcharge load and conventional surcharge scheme in conjunction with prefabricated vertical drains was selected to reduce the required consolidation time through the deeper subsoil layers. The design of the combined vacuum and surcharge fill system and the construction of the embankment are described in this paper. A comparison of the performance of the vacuum combined surcharge loading system with a standard surcharge fill highlights the clear benefits of vacuum consolidation. Field monitoring data are presented to demonstrate how the embankment performed during construction. An analytical solution for radial consolidation considering both time-dependent surcharge loading and vacuum pressure is proposed to predict the settlements and associated excess pore pressures of the soft Holocene clay deposits. © 2011 American Society of Civil Engineers.
Liyanapathirana D.S.,University of Western Sydney |
Poulos H.G.,Coffey Geotechnics
Computers and Geotechnics | Year: 2010
In this paper, a numerical procedure based on the finite element method is outlined to investigate pile behaviour in sloping ground, which involves two main steps. First a free-field ground response analysis is carried out using an effective stress based stress path model to obtain the ground displacements, and the degraded soil stiffness and strength over the depth of the soil deposit. Next a dynamic analysis is carried out for the pile. The interaction coefficients and ultimate lateral pressure of soil at the pile-soil interface are calculated using degraded soil stiffness and strength due to build-up of pore pressures, and the soil in the far field is represented by the displacements calculated from the free-field ground response analysis. Pore pressure generation and liquefaction strength of the soil predicted by the stress path model used in the free-field ground response analysis are compared with a series of simple shear tests performed on loose sand with and without an initial static shear stress simulating sloping and level ground conditions, respectively. Also the numerical procedure utilised for the analysis of pile behaviour has been verified using centrifuge data, where soil liquefaction has been observed in laterally spreading sloping ground. It is demonstrated that the new method gives good estimate of pile behaviour, despite its relative simplicity. © 2009 Elsevier Ltd. All rights reserved.
Tammetta P.,Coffey Geotechnics
Groundwater | Year: 2013
The height of complete groundwater drainage above subsided longwall panels (referred to as H) at underground mines is determined using a data base of hydraulic head measurements made with multiple devices down the depth profile at each of a number of sites worldwide. H is shown to be relatively independent of most parameters except the geometry of the mined void and the overburden thickness. An empirical equation linking H to these parameters is developed using hydraulic head data, and confirmed using an independent data base of ground movement. H is shown to be the same as the height of the zone of major ground movement above a panel. H for special cases (above longwall chain pillars, above pillar extraction panels, and underneath significant water bodies) is invariably smaller than H above center panel for ordinary cases. A new caving model, from a groundwater perspective, is proposed for continuously sheared longwall panels at ordinary locations. It removes complexity and reduces the uncertainty in estimating H. The derived equation for H applies to a variety of strata types. © 2012, The Author(s) © 2012, National GroundWater Association.
Semple R.,Coffey Geotechnics
Australian Geomechanics Journal | Year: 2013
In many parts of the world, including Australia, the state of practice in assessing if liquefaction will occur is based on the recommendations of Youd et al. (2001) which arose from workshops convened in the United States by NCEER (now MCEER). In some regards, the final publication did not so much represent a consensus view as a compromise between differing opinions within the expert group. Since then, disagreements over key aspects of liquefaction assessment in North America have increased to the point of chaos (Youd, 2011). There is little awareness in Australia of this situation nor appreciation of the NCEER limitations in applying these recommendations. Poorly informed decisions are increasing costs and causing project delays. This paper presents no original research but is an attempt by a practising geotechnical engineer to point out some problematic aspect of the NCEER liquefaction criteria, and of current recommendations in the literature and in so doing to encourage other practitioners and regulators to consider reasonable adjustments or alternatives.
Whiteley R.J.,Coffey Geotechnics
Harmonising Rock Engineering and the Environment - Proceedings of the 12th ISRM International Congress on Rock Mechanics | Year: 2012
Systematic underground coal mining began in eastern Australia in 1802. Coal is now Australia's largest commodity export. With continuing expansion of this industry and population growth over the last 209 years many abandoned mines now lie within the precincts of large Australian cities, towns or high priority growth areas and are now adversely impacting surface developments due to fear of mine subsidence. Many of these old mines were operated with the room-and-pillar mining method and represent a major subsidence risk where standing and/or partially collapsed workings lie within 100m of the ground surface. Among the key issues hampering urban and infrastructure development are the lack of reliable data on the location and likely stability of these old workings and the costs of traditional investigative geotechnical technologies, principally drilling, that attempt to provide this information. It is widely accepted that P-wave borehole seismic imaging can greatly increase the cost-effectiveness of drilling by expanding the effective radius of investigation of a borehole and can locate regions of lower seismic velocity associated with collapsed workings and voids. However, it is less well recognised that regions of increased stress within the roof-pillar system, indicative of high risk standing workings, can also be seismically imaged as regions of higher seismic velocity. Demonstrations of this approach are provided by two case studies from Australian coalfields. The first study applies direct underground seismic imaging of a coal pillar in the Eastern Coalfields before and after it was split. This shows that approximately doubling the stress on the load-bearing regions of the split pillar increases P-wave seismic velocities by about forty percent. The second study, near the margins of old workings in the Western Coalfields, uses crosshole and surface-to-borehole seismic imaging to identify unexpected mine voids that were not intersected in the boreholes and observes the high velocity signature typical of a high risk, standing pillar. It is concluded that using P-wave borehole seismic imaging technologies with increased focus on the regions of increased stress can greatly improve the assessment of high risk mine subsidence areas. © 2012 Taylor & Francis Group, London.
Poulos H.G.,Coffey Geotechnics
Geotechnique Letters | Year: 2011
Comparisons are made between the measured and computed axial and lateral responses of piles supporting a viaduct bridge in Singapore. The computed values were obtained from programs that use simplified boundary-element analyses for axial and lateral pile response, combined with input free-field ground movements obtained from approximate closed-form solutions. Parallel twin tunnels were constructed adjacent to the piles and measurements of axial force and bending moment in two of the piles that were instrumented have been reported. The agreement between measured and computed behaviour is generally good.
Walker R.T.,Coffey Geotechnics
Computers and Geotechnics | Year: 2011
A new method, the η or 'eta' method, for modeling consolidation by vertical and horizontal drains is presented. The approach is applicable in one, two and three dimensional as well as axisymmetric cases. Material and geometry properties are familiar from unit cell vertical drain analysis and are consistent across dimensions. An uncoupled finite element method (FEM) program is used to test the efficacy of the new approach. Because drains are not explicitly modeled in the finite element mesh, mesh complexity and computational time are greatly reduced. Unlike existing plane strain matching methods there is no special transformation of permeability or drain properties. The analyses conducted indicate that the η method provides an efficient and consistent means of modeling drains in any dimension. © 2011 Elsevier Ltd.
Mitchell J.K.,Virginia Polytechnic Institute and State University |
Kelly R.,Coffey Geotechnics
Proceedings of the Institution of Civil Engineers: Ground Improvement | Year: 2013
Ground improvement will be critically important in future geotechnical practice to achieve reductions in quantities of material used, reduction in carbon footprint, prevention and mitigation of natural disasters, treatment and recycling of industrial wastes, remediation of polluted soils, development of brownfield sites and maintenance and rehabilitation of existing structures. Challenges exist in providing cost-effective sustainable ground improvement under current economic conditions. These issues are addressed under categories of reduce, reuse and recycle in the first part of the paper. Selection processes for ground improvement methodologies, improved analysis, knowledge of long-term performance and understanding of effects of variability are required to develop more efficient designs. These issues are addressed in the second part of the paper.