Deep excavations in water-bearing gravels in Cork

Long, Michael; Murphy, Martin J.; Roberts, T. O. L.; O’Brien, Joanna; Clancy, Noel

doi:10.1144/qjegh2014-098

“…SPT tests for the Curragh gravels show average N values of close to 50 blows/300mm, indicating the material is dense to very dense, similar to the Dublin City deposits. Long et al (2015) present a detailed characterisation of the fluvio-glacial gravels in Cork City and their particle size distribution data, again, show the material is very similar to that found in Dublin City. However, SPT 'N' values for Cork are much more variable, with frequently loose or loose to medium dense layers being encountered.…”

Section: Discussion and Analysis Of Datamentioning

confidence: 55%

Characterisation of gravel deposits in the pre-glacial channel, Central Dublin

Kealy¹,

Long²,

McCarron³

et al. 2021

Irish Journal of Earth Sciences

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This paper reports on the production of an interactive 3-dimensional model over a key section of a pre-glacial channel feature in Dublin City. Significant infrastructural developments, most importantly the Dublin MetroLink project, are planned in the study area. The model presented here represents a complex depositional environment produced by several discrete phases of glaciation and deglaciation during the Quaternary and is consistent with previous published reports on the area. The geology in the study area typically consists of a Quaternary channel cut into the Carboniferous limestone bedrock, an intermittent lower glacial till, a large fluvio-glacial sand and gravel deposit and an intermittent upper glacial till.The digital software used to manage and create a 3-dimensional ground model is described and is comprised of several commercially available modules. The digital 3-dimensional ground models are particularly useful as a single data repository which can easily be updated as new data becomes available. Interpretation of a large body of geotechnical tests confirmed the fluvio-glacial sand and gravel deposit is relatively non-homogenous but can be broadly characterised as a medium to very dense slightly sandy to sandy gravel. Simple index tests, such as particle size distribution analyses and standard penetration testing, are very useful for both material characterisation and interpretation of profiles, albeit the latter test results can be influenced by the presence of cobbles or boulders. Geophysical testing, especially shear wave velocity profiling, was shown to be a very useful characterisation tool in these deposits. The findings of this work are consistent with the overall understanding of the erosional features, pattern of glacial deposition and general geological history of the study area in Dublin.

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“…It is approximately 4.5km in the east-west direction and 1.2km north-south. The eastern part of the Central Island area of Cork city was chosen as the western limit of the study area as it is well known from ground investigation data that no interglacial deposits exist west of this point (Long et al 2015). The focus was on the general eastern city centre area together with the upper part of Cork harbour.…”

Section: Identification Of Study Areamentioning

confidence: 99%

“…The distribution and engineering characteristics of the fluvio-glacial gravels beneath Cork city have been well established. Detailed reports have been published on the design of piled foundations in these materials (Collins and Mitchell 1990), on the construction of deep basements, with a particular emphasis on dewatering of the gravels (Long et al 2015), on their economic potential for production of geothermal energy (Allen and Milenic 2003;Hemmingway and Long 2011) and on their general distribution within the Cork city syncline (Davis et al 2006). However, the stiff interglacial clays found sporadically within the thick gravel sequences of the Cork city syncline are poorly characterised and are often overlooked at the desk study stage of site investigation.…”

Section: Introductionmentioning

confidence: 99%

The distribution and engineering properties of interglacial deposits in Cork city and harbour

Curtis,

Long

2024

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A reassessment of existing data and additional testing on sediment core samples from one site was used to study the extent, nature, composition and engineering properties of the Quaternary interglacial deposits in an area of Cork city and harbour where many future developments are planned. A clear link is apparent between rockhead elevation and the presence of the interglacial deposits. Well-defined pockets of the deposit were proven. These are found mostly on the southern side of the Cork buried valley axis and increase in thickness to the north. The base of the interglacial deposits appears to mirror that of the rock-head and the western extent of the former coincides with a steep drop off in the latter. Much of the deposit encountered in commercial investigations is a thick relatively uniform silt/clay consistent with that described in previous studies. The sediment is predominantly silt sized, but its behaviour and engineering properties are consistent with those of a stiff clay. Sample disturbance effects were found to be significant and these likely result in an underestimation of the preconsolidation stress and the undrained shear strength of the material. Future work would benefit from the use of in-situ site investigation and geophysical techniques.

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“…It is approximately 4.5km in the east-west direction and 1.2km north-south. The eastern part of the Central Island area of Cork city was chosen as the western limit of the study area as it is well known from ground investigation data that no interglacial deposits exist west of this point (Long et al 2015). The focus was on the general eastern city centre area together with the upper part of Cork harbour.…”

Section: Identification Of Study Areamentioning

confidence: 99%

“…The distribution and engineering characteristics of the fluvio-glacial gravels beneath Cork city have been well established. Detailed reports have been published on the design of piled foundations in these materials (Collins and Mitchell 1990), on the construction of deep basements, with a particular emphasis on dewatering of the gravels (Long et al 2015), on their economic potential for production of geothermal energy (Allen and Milenic 2003;Hemmingway and Long 2011) and on their general distribution within the Cork city syncline (Davis et al 2006). However, the stiff interglacial clays found sporadically within the thick gravel sequences of the Cork city syncline are poorly characterised and are often overlooked at the desk study stage of site investigation.…”

Section: Introductionmentioning

confidence: 99%

The Distribution and Engineering Properties of Interglacial Deposits in Cork City and Harbour

Curtis,

Long

2023

ijes

0

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A reassessment of existing data and additional testing on sediment core samples from one site was used to study the extent, nature, composition and engineering properties of the Quaternary interglacial deposits in an area of Cork city and harbour where many future developments are planned. A clear link is apparent between rockhead elevation and the presence of the interglacial deposits. Well-defined pockets of the deposit were proven. These are found mostly on the southern side of the Cork buried valley axis and increase in thickness to the north. The base of the interglacial deposits appears to mirror that of the rockhead and the western extent of the former coincides with a steep drop off in the latter. Much of the deposit encountered in commercial investigations is a thick relatively uniform silt/clay consistent with that described in previous studies. The sediment is predominantly silt sized, but its behaviour and engineering properties are consistent with those of a stiff clay. Sample disturbance effects were found to be significant and these likely result in an underestimation of the preconsolidation stress and the undrained shear strength of the material. Future work would benefit from the use of in-situ site investigation and geophysical techniques.

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Deep excavations in water-bearing gravels in Cork

Cited by 8 publications

References 8 publications

Characterisation of gravel deposits in the pre-glacial channel, Central Dublin

Characterisation of gravel deposits in the pre-glacial channel, Central Dublin

The distribution and engineering properties of interglacial deposits in Cork city and harbour

The Distribution and Engineering Properties of Interglacial Deposits in Cork City and Harbour

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