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AGS WA Symposium 2022
Engineering Geology and Geotechnics of Western Australia
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Landslides on the Bellarine and Nepean Pensinulas, Victoria
This paper provides a brief overview of landslides on the Bellarine and Nepean Peninsulas. The main types of landslides are discussed and selected brief case studies are presented to illustrate the types of slope instability. This paper follows a brief paper outlining the extent and nature of the landslides in and around the Greater Melbourne metropolis that was presented in the Engineering Geology of Melbourne (Wilson, 1992 in Peck et al., 1992).
The Bellarine and Nepean Peninsulas lie at the southern end of Port Phillip Bay about 30 km SSW of the Melbourne (Figure 1). The Bellarine Peninsula is about 30 km long (east–west) by about 15 km wide. Relief on the Bellarine Peninsula is typically low with the exception being the prominent 20 m high cliffs that extend along the north side of the peninsula (Figure 2). The highest point on the peninsula is Mt Bellarine (RL 137 m AHD). The Nepean Peninsula is about 20 km long (east-west) by up to 2 km wide (Figure 8). The highest point on the Nepean Peninsula is Cheviot Hill (RL 40 m AHD).
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Engineering geology of Fremantle Harbour (An historical perspective)
Prior to the construction of the Inner Harbour in Fremantle in the closing years of the nineteenth century, the body of water that is now the Inner Harbour comprised a broad estuary, and the Swan River flowed in to the sea across a shallow rock bar between two rocky headlands.
The history of construction of the Inner Harbour is described to illustrate the complexity of the geology in this part of Fremantle. The geology includes a deep sediment filled palaeochannel associated with a former course of the Swan River during the Quaternary when the sea level was considerably lower than its current level. The construction of the harbour involved blasting of the rock bar, major dredging and land reclamation and extensive piling. The distribution and impact of the various geological units on the harbour and a number of the geotechnical issues that have lead to construction difficulties in the past are detailed.
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Geophysical properties of soils
Low energy perturbations used in geophysical methods provide insightful information about constant-fabric soil properties and their spatial variability. There are causal links between soil type, index properties, elastic wave velocity, electromagnetic wave parameters and thermal properties. Soil type relates to the stress-dependent S-wave velocity, thermal and electrical conductivity and permittivity. The small strain stiffness reflects the state of stress, the extent of diagenetic cementation and/or freezing. Pore fluid chemistry, fluid phase and changes in either fluid chemistry or phase manifest through electromagnetic measurements. The volumetric water content measured with electromagnetic techniques is the best predictor of porosity if the water saturation is 100%. Changes in water saturation alter the P-wave velocity when SrĂ 100%, the S-wave velocity at intermediate saturations, and the thermal conductivity when the saturation is low SrĂ 0%. Finally, tabulated values suffice to estimate heat capacity and latent heat for engineering design, however thermal conductivity requires measurements under proper field conditions.
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Utilisation Of Deep Groundwater Barrier Walls Using Soil Bentonite And Biopolymer Slurries In Geotechnical And Environmental Applications
Menard Bachy has carried out over the last 15 years a large number of groundwater containment structures utilising a wide range of techniques. One particular technique is the Soil Bentonite (SB) wall which is one of the most efficient, cost effective and environmentally friendly solution to implement in-situ cut off (low permeability) walls. SB walls have been utilised historically for a wide range of applications including confinement of contaminated ground water around landfills, toxic tailing ponds but also for the improvement of performance of dams and other types of water retention structures. In the delivery of complex projects SB walls have also been utilised in combination with other mechanical and hydraulic structures such as PVC membranes, hydraulic gates, leachate collection trenches, and sumps but also sheet piles and other retention systems.
For the particular case of sites presenting environmental challenges, involving soil and groundwater pollution, a strategy requiring both removal and treatment of the source of the contamination as well as control of the contaminated groundwater plume acting as the pollution carrier is required. In the case of urban excavations where treatment is complicated by access and impact on community contamination confinement is often preferred. In any case, the adopted strategy needs to take into account the future use of the site, combined solutions involving both the reduction of the source of pollution and control of the pollution carrier generally offer the most sustainable outcome.
This paper presents a range of projects performed in Australia and overseas utilising different forms of SB walls. A particular focus is given on project methodology, site validation and trial testing but also production and quality control. The paper also provide a comparison of the environmental impact that different cut off wall techniques have and how they compare with SB type walls.
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Bearing capacity of footings in layered clay by the punching shear method
The undrained bearing capacity of shallow and deep square and circular footings and piles by the punching shear model in layered clay consisting of a stronger layer cs overlying a softer layer cw is examined. It is shown that for a footing founded in the stronger clay layer an important concept is the critical depth, defined as the footing depth when the softer clay first affects the bearing capacity. Equations for both the bearing capacity and the critical depth based on the punching shear model are derived. These are compared to solutions by the computer program FLAC for surface and deep footings, published computer solutions for circular footings and spudcans and experimental test results on model footings, to confirm the validity of the punching shear model. The critical depth ratio H/B is a function of cs/cw and the equation relating H/B and cs/cw derived for surface footings is also valid for deep footings. The maximum H/B is 1.55. Pile design methods that use H/B = 10 are therefore significantly conservative for a layered clay soil profile. The application of these concepts to a variety of geotechnical problems is illustrated by eight worked examples. Good agreement was found with computer derived solutions, and the punching shear model is free of the computational inconsistencies that affect some existing finite element methods. The equations derived from the punching shear model provide a very rapid and convenient means of obtaining the bearing capacity of footings in layered clay in a sufficiently accurate manner, suitable for routine geotechnical practice.
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Slope stabilisation techniques at Khao Laem Dam, River Kwae, Thailand
The Khao Laem Multipurpose Project is on the River Kwae Noi in Kanchanaburi Province, Western Thailand. The infamous Death Railway was constructed along this river valley during the Second World War. This paper has been prepared as part of the 20 years since impoundment reunion.
The Project comprised a 92 m high, concrete faced, rockfill dam embankment with a crest length of 1019 m and a left abutment spillway and power station of 300 MW capacity. Water released from the Khao Laem and adjacent Srinagarind reservoirs in the dry season irrigate 400 000 ha in the Mae Klong Irrigation Area.
Preliminary investigations of the Quae Noi Basin were commenced by the Electricity Generating Authority of Thailand (EGAT) in 1968. The Snowy Mountains Engineering Corporation (SMEC) became involved in 1973 and completed geotechnical investigations, detailed design and tender documents by 1979. Construction commenced in January 1980 with SMEC retained as Consultant Engineers during construction. Technical representatives of the World Bank (the main Project funding organisation) considered this scheme to be one of the most difficult ever attempted in the world. Reservoir impoundment commenced in 1984.
As well as having major, karstic foundation, cut-off issues, a number of slope stability problems occurred during construction. These were related to extreme differential weathering, karstic features and penetrative weathering along adversely dipping geological structures. Various remedial measures were needed.
Major rotational failures in soil batters of the diversion channel were recut at flatter batter angles, without regularly spaced berms. On soil slopes, saturated berms appear to facilitate slope failure by allowing initial slumping, which progressively continues upwards to form large slip circles.
Sudden, partial failure of the right abutment cliff occurred during access blasting to install rock anchors. To maintain a safe working environment during excavation down the overhanging cliff to the dam plinth, microseismic monitoring was required during and after every blast to ensure an acceptable acoustic emission threshold, prior to access.
Support for the upstream and downstream diversion tunnel portals included 15 m long rock bolts and dowels, shotcrete lining and concrete retaining walls. At the upstream portal, 20 m long drainage holes were drilled to dewater an elevated water table. Maximum recorded flow from these pre-drainage holes was 180 litres/sec.
An excavation of 100 m vertical depth in erosive soil was required to reach sound foundation rock for the dam plinth and upstream rockfill in Area 2. Resistivity depth sounding and systematic diamond drilling were used to determine the depth and extent of differential weathering.
Significant translational movements, which occurred in the spillway crest and intake structure excavations, were related to wedge sliding on adversely dipping clay seams. Stabilising techniques included recutting the upper part of the spillway crest excavation and installing rock bolts, dowels, rock anchors and a concrete toe block.
The spillway chute and stilling basin excavations were redesigned to be excavated parallel to bedding planes. Only spot bolting and local dental concrete were required.
Prior to the excavation of the power station, pseudo elastic, blocky, computer modelling was completed to determine support requirements. Extensive pre-dowelling and rock bolting were required in areas of adversely dipping geological structures. Monitored movements during construction were consistent with normal stress relief.
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Geotechnical and chemical characteristics of ETP and WTP biosolids
Stricter regulations on the quality of wastewater treatment by-products are giving rise to an increasing volume of stockpiled biosolids. The annual production of biosolids in Australia is approximately 300,000 dry tonnes, which involves a biosolids management cost of about $A90 million. Biosolids are the end product and the main solid component collected from the wastewater treatment process. This paper presents some of the geotechnical and chemical properties of two samples of biosolids collected from Melbourne Water’s Eastern Wastewater Treatment Plant (ETP) stockpile No. 22 and the Western Wastewater Treatment Plant (WTP) stockpile No. 10. Various geotechnical tests – liquid limit, plastic limit, particle density, particle size distribution, organic content, and linear shrinkage – were undertaken. In addition, chemical tests comprising leachate analysis for heavy metals and chemical composition were conducted on the samples of biosolids. From an environmental perspective, all the samples of biosolids were found to be safe in terms of leaching for use as a landfill application material. The experimental results showed that the ETP biosolids have about 7% of organic content with some of the geotechnical and chemical properties similar to a conventional soil with similar particle size distribution. In addition, empirical relationships were obtained for the compaction behaviour of the ETP biosolids and a comparison soil used in this study. The results obtained in this study can be used as a guide for the use of ETP and WTP biosolids in different civil engineering applications.
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Applications Of Large Scale Direct Shear Testing
Direct shear testing is a common and well-established method for determining the strength of geomaterials. In particular, it is ideally suited to measuring the strength of interfaces between geomaterials and structures, e.g. at the rock-concrete interfaces of concrete dams and concrete piles drilled into rock; and within geomaterials, e.g. natural rock joints.
One area that has been of significant interest to researchers at Monash University since about 1980 has been the behaviour of the interface formed between a concrete pile and the surrounding rock. The performance (capacity and displacement response) of the pile is dominated by the behaviour of this interface. Axial loading of the pile produces slip displacement at the rock-concrete interface, in much the same way as shearing of a rough rock joint. In order to investigate the behaviour of this interface, a large direct shear testing apparatus was designed and constructed. Design criteria for the shear apparatus and associated split shear box were:
- To have the capability of testing large samples so that scale effects could be investigated
- To be as rigid as possible to prevent sample rotation and minimise compliance while keeping friction losses to a minimum
- To be able to replicate in-situ boundary conditions such as normal stress and stiffness as accurately as possible
- To be able to apply any loading pattern (stress and displacement control) so that both cyclic and monotonic loading conditions could be investigated
The construction of the shear rig was completed in 1991 and has since been used almost continuously on a number of research and consulting projects. A photograph of the shear rig is shown in Figure 1. These projects have included the testing of rock-concrete interfaces and rock-rock interfaces, jointed rock masses, base coarse and rock fill material and the dynamic testing of pile-soil interfaces. The rocks used to date have varied in uniaxial strength from 1 MPa to 200 MPa and included siltstone, Johnstone (a synthetic siltstone), sandstone, calcarenite, basalt and granite.
A short description of the capabilities of the direct shear rig and some of the applications for which it has been used are presented in this article.
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Lithological Character and Structural Geology of the Cooks River Area with Focus on the M8 Tunnels
The M8 is a 9 km long dual road tunnel excavated south of Sydney connecting the M5 at Kingsgrove to the future M4- M5 link and Sydney Gateway at St Peters. The tunnel traverses beneath the Cooks River, one of the main sources of sediment for the Botany Basin. The Cooks River has been reconfigured by land reclamation, so the palaeotopography is no longer reflected. A 40 km2 palaeotopographic surface was developed during the M8 design phase to assist in understanding the sub-surface soil and rock mass, and locations faults may be intersected. The mainline and access ramp tunnels for the M8 also spanned the stratigraphic profile from the top of the Ashfield Shale to 80 m into the Hawkesbury Sandstone, allowing a detailed understanding of the facies profile for this part of the Sydney Basin to be formed. During excavation, several fault zones were confirmed with data collected providing geological insight to the fault character in various lithologies. One of these faults is inferred to correlate with the regional fault zones/joint swarms of Och, Pells and Braybroke, 2004 in the CBD, with a further three inferred to continue to the south based on the palaeotopographic surface generated for the M8 project. Several dyke systems were also intersected, correlatable eastwards to the coast, inland (westwards) using the palaeotopographic surface and one correlatable via the palaeotopography to a diatreme located to the north.