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Numerical study of bearing capacity for a circular footing
The bearing capacity of a vertically loaded, shallow and strip footing is one of the problems that has been widely studied by various methods. However, most of these studies were carried out for two-dimensional configurations. This paper focuses on the bearing capacity of a three-dimensional circular footing. A series of numerical computations using the finite-difference code, FLAC3D, was carried out to evaluate the soil-bearing capacity for vertically loaded, rigid circular footing for both smooth and rough interfaces. The adopted approach involves a numerical solution of the equations governing elastic-plastic soils with an associative flow. The FLAC3D code is utilized to obtain the three bearing capacity factors for a wide range of values of the friction angle. The bearing capacity and included shape factors, which are presented in the form of graphs, are compared against existing expressions and numerical solutions.
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The Seventh James K. MitchelL Lecture: Characterization of silt/sand soils
The term silt/sand or M/S is proposed as an inclusive abbreviation of soils that can span from sand with very little silt, silty sand to pure silt. It is generally believed that sands with fines (particles passing #200 sieve) tend to be more compressible. Because of their low permeability, cone penetration tests (CPT) in sands with fines can be partially drained. High compressibility makes the soil more contractive and thus showing lower resistance in undrained shearing. Significant ground subsidence can also be associated with the high compressibility of M/S/ soils. For CPT in granular soils with similar density and stress states, the high compressibility and partial drainage can both contribute to lower cone tip resistance. Natural granular soils are more likely to contain fines than being clean (fines content < 5%). Studies on M/S soils are far less than those on clean sands. Because of the unique geological setting, the author had the opportunity to work with a local M/S deposit in Central Western Taiwan in the past 25 years. Procedures for laboratory soil element tests as well as CPT calibration tests using reconstituted specimens have been developed and a series of tests performed. Practical undisturbed sampling techniques in M/S soils were experimented and applied. Methods to correlate cyclic strength, fines contents and cone tip resistance in M/S deposit were proposed. The concepts of equivalent granular void ratio and state parameter were experimented in compiling the test data. The paper describes the new characterization techniques developed and lessons learned in the interpretation of test data for the studied M/S soils.
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Acid Sulfate Rock Management In Earthworks For Roads
Acid sulfate rocks (ASR) have elevated levels of reduced sulfur, usually as pyrite or other sulfide minerals, and in NSW occur in the lower Sydney Basin and other areas. When exposed to water and oxygen a series of chemical reactions lead to the formation of acid leachates and sulfate salts, and the acidic conditions can also produce high levels of metals in solution. These products can be damaging to both the environment and engineering elements of roads such as concrete and steel bridge foundations and culverts, geotechnical reinforcements such as reinforced soil wall straps and rockbolts, cut batters and pavement materials. This paper presents experiences with ASR in road projects including an overview of the basic science, investigation and test methods, ASR characterisation, design considerations, management plans and construction issues. The Conjola Mountain realignment project on the Princes Highway in southern NSW is presented as a case study together with some research work undertaken on this project.
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Geotechnical Challenges In Design And Construction Of Bridge Foundations And Approaches In Hilly Granite Formation
This paper presents a case study of geotechnical design and construction challenges of bridge foundations and approaches in a hilly granite formation in northern New South Wales, Australia. Firstly, the geological formation and existing cut slope conditions which have high risks of rock fall will be described. The original design was based on the available geotechnical information and assumed construction methodology. Reinforced concrete cantilever retaining walls founded on mass concrete were adopted for the bridge southern approach to resolve constructability issues over hilly terrain. The design considered retaining wall block sliding stability while overturning and internal stabilities were satisfied. Slope treatments using a rock fall fence together with individual boulder stabilisation or removal were also considered. It was found during construction that the actual ground conditions were different to that originally inferred and modifications to pad footing designs were deemed necessary. Additional investigations were undertaken, and the subsurface ground models updated to inform the revised design. For the northern bridge abutment foundation, a piled foundation was introduced to optimise the design with due consideration of temporary piling platform and access along a new geotextile reinforced approach embankment. The revised design was developed in close collaboration with the Contractor and the Principal. The foundation design of Pier 2 was revised using micro-piles to address the presence of a weak rock layer intrusion. In the end, key lessons learnt from this challenging project have been summarised for future project references.
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The Use Of Fractal Theory And Soil Index Properties To Infer The Soil Water Retention Curve For Low And High Plasticity Clays
Four fine-grained soils from South Australia containing differing particle size distributions were tested for their soil water retention properties. Despite their wide-ranging index properties, the samples from all four sites were confirmed to contain fractal particle size distributions (PSD) from sieve and hydrometer testing. Air entry values were obtained for each site from soil water retention curves (SWRC) that were generated using an unsaturated triaxial device with a pore air pressure/volume controller and a high air entry porous disk, which confirmed all sites contained fractal pore size distributions. The fractal dimensions of the particle and pore size distributions were not equal for any of the four sites tested in this paper. Using the four sites described in this paper, comparisons are presented between experimental SWRC results, theoretical results underpinned by fractal theory, and predictions derived from a curve fitting equation based solely on PSD and soil index properties. Lastly, this paper discusses the importance of understanding the unsaturated behaviour of fine-grained soils and some of the challenges associated with aligning current industry practice and advances in research within the field of unsaturated soil mechanics.
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Geotechnical Engineering And Knowledge Transfer Through Academic-Industry Collaboration
There appears to be broad consensus among government, Academia and industry regarding the need to improve current low levels of academic-industry collaboration in Australia. In the authorsβ view these low levels of cooperation, and the flow-on detrimental effects to innovation in the industry, are intrinsically tied to many of the discussion points raised in recent ISSMGE CAPG facilitated forums. While the problems are complex and varied, one of the main obstacles to enabling academic-industry collaboration in the geoprofession remains the inertia of industry and perceptions that academic-industry research fails to deliver tangible benefits to the company. The authors have highlighted some key issues relating to the debate regarding academic-industry collaboration while also reflecting on their own collective experiences to highlight the importance, and benefits, of academic-industry partnership and the role that learned societies can play in enhancing this collaboration.
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Methods of investigation and repair of light construction on reactive soil not complying with expectations
Following the procedures of Australian Standard AS2870 does not always give correct, concise, or usable answers to determine why buildings fail. In fact, the answers can be misleading. Throughout the evolution of Australian Standard 2870, stump and bearer construction has been eliminated from reactive sites as has hold down screw piles; neither are in the current edition of Australian Standard 2870. Further, there is a lack of literature on the research that went into Australian Standard 2870 (1986) and why there are now beams for H2D sites (i.e. highly reactive) having an I value (uncracked stiffness) 2.7 that of the 1986 edition. Methods of investigation used today include relative level survey via a water level only, photographic record of cracks and distortion, and geotechnical investigations (bore logs) to determine soil moisture, free swell, and consistency index (Atterbergs Limits). This paper recommends, in necessary cases, that plumbing investigations utilising a newly developed methodology be implemented. This methodology has verified that water is flowing from trenches external to the site in close to 100% of the cases where heave was observed. Three example cases are used as points of discussion, including recycled sites, which have problems of abnormal moisture before construction starts, new construction on new subdivisions, and a case where abnormal moisture conditions happened well after construction. Ultimately the method of repair permanently is hold down screw piles retrofitted, or attempt to control moisture variations after the failure methodology has been corrected.
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Effect of depth on results from the Perth sand penetrometer test
The Perth Sand Penetrometer (PSP) is widely used in WA for compaction control, particularly for preparation of sand foundations for domestic and light commercial structures. The relevant Australian Standard (AS1289.6.3.3β1997) specifies that the test is to be performed by first inserting the penetrometer to a depth of 150 mm below the ground surface, and then counting the number of blows required to achieve a further 300 mm penetration (to a total penetration depth of 450 mm). In practice the test can be, and frequently is, continued to greater depths β typically for another 300 mm (to a depth of 750 mm), but sometimes to even greater depths. However, there is contradictory evidence of how the increase in test depth affects the measured blowcounts for a given constant relative density with depth. This paper presents the results of some studies into this effect. It is concluded that there is no definitive universal relationship between blowcounts and depth for any given relative density, and hence site-specific calibration would be required if the test was to be used in this manner for any important project.
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Some Inadequacies Of Common Design Procedures For Deep Foundations
This paper examines some aspects of common deep foundation design that the author considers may be inadequate. The following aspects are considered:
- Ignoring foundation interactions;
- Ignoring the beneficial effect of the raft;
- Assuming a rigid cap or raft;
- Over-simplification of the geotechnical profile;
- Ignoring the beneficial effects of basement walls;
- Ignoring the effects of ground movements;
- Ignoring kinematic effects in seismic design.
Each inadequate aspect will be considered in turn, with examples given of the possible consequences. Some aspects lead to conservative designs, while others tend to be unconservative. Suggestions will be offered for addressing the perceived inadequacies, some of which are likely to involve the application of innovative techniques.
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Simplified analysis of the strength of anchor plates in a cohesionless soil: Part 1 – Analytcial solutions
Two and three dimensional analytical solutions for the strength of anchor plates buried in a cohesionless soil are derived. Anchor plates that are oriented horizontally, vertically and inclined are considered. The aim of the paper is to present simple and understandable solutions based on geometrically defining the mass of soil mobilised by the movement of an anchor. The weight of this soil mass and the soil friction forces acting on it balance the maximum anchor pull which can thus be determined. Corroboration of the analytical solutions has been obtained by model tests of anchors buried in clean dry sand. The model tests and the experimental results that have been obtained are described in Part 2 of this two-part paper.