We are lining up some of our best experts at ANZ Geomechanics Conference
Check out the program at ANZ Geomechanics to see our experts who will be presenting on an exciting range of industry hot topics from our recent projects all over Australia. Don’t miss the opportunity for a personal discussion for more information by stopping by our Booth #1.
Click below for more information about our presentations.
Koolan Island – The Design and Construction of a Major New Seawall
Co-Authors: P. Petropulos
Following the major collapse in 2014 of the seawall at the existing open cut high grade iron mine on Koolan Island, a remote island off the Kimberley coast in WA, a new seawall solution was developed by the project team. This presentation will provide information on the overall scope of the works, geotechnical conditions and onerous working environment. During the construction phase the project team faced a number of significant challenges which will be discussed together with the on-going monitoring of the works allowing the safe commencement of the mining operations
Ground modifications using mass soil mixing technique in geotechnical engineering
Co-Authors: M. Lai
Mass Soil Mixing (MSM) is a specialized ground improvement technique to improve soft fine-grained soils and mud deposits, including dredged material. By mechanically blending a dry or wet cement binder with the soil, mass soil mixing can also be used to neutralize and contain contaminated soils as in-situ or ex-situ treatment. The method im-proves mechanical characteristics of soils to stabilize and control settlement of soft soils beneath road and rail em-bankments, residential developments and warehouses and to create working platforms for construction equip-ment. MSM can also be used to strengthen soils before excavation and to stabilize excavation bases. The method can be used over water or on land. This paper presents case study of MSM for 4.5m deep pump station excavation works within soft estuarine clays and very loose sands with high water table. The ground treatment was required down to of 6.5m depth and suffi-cient width to ensure stability during excavation for the pump stations. The required MSM shear strength of 250kPa (minimum) was determined by finite element modelling in Plaxis program.
This paper presents the design methodology, laboratory testing, construction works and post treatment verification of mass soil mixing works for excavation works and ground improvement.
Base Cleanliness of Bored Piles Revisited – A Case Study
Co-Authors: X. Le & S. Rex
Bored piles are commonly used as a foundation solution for civil engineering applications such as bridges and high-rise structures due to its distinct versatilities such as the ability to carry large magnitude loads and the flexibility in installation in almost all ground conditions. For bored piles designed to rely on its base resistance to carry part of the applied loads, the cleanliness of the base is critical to ensure the transfer of loads to the pile base is not hindered by the presence of debris or impurities that may compromise the performance of the pile. The degree of base cleanliness can be highly variable dependent on the piling contractor’s experience, tooling and construction methodology for a particular geological setting. With the advancement in the industry experience over the years, drilling tools and technology available in the market, this paper studies the base cleanliness of a bored piling project in Melbourne CBD where 900mm and 2500mm diameter piles were constructed in weathered siltstone below the groundwater table. A specialised cleaning bucket developed by the company and an air-flushing technique of the pile bore were carried out to compare the degree of cleanliness after each procedure. To verify the cleanliness of the base, a down hole camera was used for visual inspection. In addition to that, a device called the Shaft Quantitative Inspection Device (SQUID) consisting of three penetrometers attached to the rig Kelly bar was utilised to measure the thickness of any soft materials/debris at the pile base and generate real-time force vs displacement curves to assess the cleanliness of the base. This paper compares the difference and the effectiveness in the base cleanliness using the different cleaning techniques and highlights recommendations and further improvements for the future.
Lateral soil displacement resulting from the installation of CFA piles in soft marine clays
Co-Author: J. Fetherston, Dr W.L Chong
The Continuous Flight Auger (CFA) piling technique is commonly used where the presence of groundwater or potentially collapsible material reduces the cost-effectiveness of bored piling techniques. Whilst generally considered a soil replacement technique, the process of pumping concrete under pressure during the pile installation can result in significant lateral displacement of the surrounding ground, particularly in low strength soil conditions. If protection measures are not adopted, this displacement can lead to damage of adja- cent underground structures and may compromise the integrity of previously installed piles nearby, due to the lateral stresses imparted. This paper reviews the results of ground movement monitoring performed during the installation of CFA piles in soft thixotropic marine clays known as the Coode Island Silt (CIS) in the Yarra Delta geological area of Melbourne. The monitoring data was collected from two sites in the Melbourne Dock- lands area where multiple inclinometers with electronic data loggers were installed in the ground at varying distances from the pile installation locations, to depths of up to 25m. The purpose of the monitoring was to determine the impact of the CFA pile installation on the surrounding ground and nearby structures along with the impact of pile installation on previously installed piles in the vicinity. The results of the monitoring were back-analysed using Finite Element software PLAXIS 2D to establish benchmark models based on the actual pile installation sequence, concreting pressures and as-built pile details. The effect of varying the distance be- tween a point of interest and the pile installation location and different pile diameter were studied. The paper also makes recommendations for future field monitoring and analysis of pile group effects.
Wide Range of Application of Ground Reinforcement By Means of Rigid Inclusions in Foundation Works
Rigid Inclusions (RI) are usually installed in weak compressible soils to increase ground bearing capacity, reduce ground settlement and to control differential settlement across structure. The technique was initially developed in Europe during 1990’s to support road and railway embankments. Rapid development, technical and commercial success of this ground improvement method has increased the applications to a wider range of structures. Recently, the technique has been used to support low to medium height industrial and residential buildings, large footprint warehouses, storage tanks and foundations for wind turbines and solar panels.
The rapid development of this new technique requires that the design, construction and testing to be developed in the form of national standards or guidelines. The existing piling standards are not applicable to ground improvement works. British standard BS 8006 is applicable to reinforced-soil structures. The research carried out in France between 2005 and 2011, has resulted in the publication titled “Recommendation for the design, construction and control of rigid inclusion ground improvement” commonly known as ASIRI recommendations. The document presents three distinctive design approaches for rigid inclusions design. The first case is where RIs are used to reduce settlement, the second is where RIs are required to increase bearing capacity and the third is the special case for embankments on rigid inclusions. These recommendations are presented, discussed and compared with the Australian Standards and road authority specifications.
This paper demonstrates the design approach to ground reinforcement by means of rigid inclusions using case studies of storage tanks and industrial building applications. The design is performed following ASIRI recommendations and validated using two computer programs: Plaxis and Keller Improvement Designer (KID). This paper also shows the methodology of ground improvement selection, design calculations, verification and testing of the design assumptions on site.