50 results found
Zangana HA, Rashid F, Hussein D, et al., 2022, Reservoir characterisation of unconventional rock units in the middle jurassic Sargelu Formation, atrush field, zagros folded belt, Journal of African Earth Sciences, Vol: 196, Pages: 1-11, ISSN: 1464-343X
The heterogeneous lithological components of the Middle Jurassic Sargelu Formation in the Atrush field of the high folded zone were examined using rock samples, conventional wireline logs, mud logs and well test results throughout two wells. The Sargelu Formation is 45 m thick and has been divided into three units based on lithological characteristics and shale volume. The upper unit of the Sargelu Formation is composed of argillaceous limestone with intercalation of dolostone and anhydrite beds. The middle unit of the Sargelu Formation is composed of organic rich laminated shales, which contain residual bitumen, whilst the lower unit of the formation is dominated by argillaceous limestones. Lithological variation, mineralogy and organic matter contents are shown to be essential factors in controlling the reservoir matrix porosity and permeability. The maximum matrix porosity and permeability were observed within the dolomite plug samples (13.40%, 10.40 mD) and the lowest values were recorded in the anhydrite samples, both found in the upper unit of the Sargelu Formation. The fracture permeability is three orders of magnitude higher than the matrix permeability and the hydrocarbon production is predominately derived from the fractured intervals throughout the Sargelu Formation. The interconnected fracture pathways are influenced by the lithological variation and mineralogical components of the formation along with the tectonic position of the field. It was found that as the confining pressure increased the fracture permeability reduced. The different lithologies were also found to be sensitive to increases in the confining pressure. The clastic shale rich rocks are most sensitive to increases in confining pressure, whilst the more carbonate rich rocks showed the lowest variation as a function of confining pressure.
Scoular J, Ghail R, Mason P, et al., 2022, Are measured InSAR displacements a function of the chosen processing method?, Quarterly Journal of Engineering Geology and Hydrogeology, Vol: 55, Pages: 1-10, ISSN: 1470-9236
The benefits of InSAR to the civil engineering industry have been demonstrated on many occasions, however there is still a limited uptake by end-users, due to perceived differences between data providers and uncertainty around how to interpret results. This paper critically compares three datasets for London: Radarsat-2 (RS2) from 2011 to 2015, TerraSAR-X (TSX) from 2011 to 2017, and Sentinel-1 (STL1) from 2015 to 2017. Two of the datasets (TSX & RS2) were processed by commercial data providers, while the STL1 data were processed using ENVI® SARscape® by the authors. The results show an inverse relationship between the Pearson Correlation Coefficient and absolute total displacement of Persistent Scatterers (PS). There is a strong correlation between datasets for total displacement greater than 5 mm, but a weak or no correlation in the 0–3 mm range. Consequently, standard commercial InSAR datasets, processed with no a priori knowledge of the area of interest, have error margins below 3–5 mm but correctly detect all deformation phenomena exceeding this threshold. RS2-TSX both capture the spatial extent of the investigated area of dewatering induced subsidence, however STL1 measures a much broader, less pronounced zone of heave than TSX.
Wang Z, Lawrence J, Ghail R, et al., 2022, Characterizing micro-displacements on active faults in the Gobi Desert with time-series InSAR, Applied Sciences-Basel, Vol: 12, Pages: 1-24, ISSN: 2076-3417
This research investigates small-scale tectonic activity in the Jiujing region in Beishan, northwest China through the application of persistent scatterer (PS) Interferometric synthetic aperture radar (InSAR). PS InSAR is an effective monitoring tool in this unpopulated, arid, and unvegetated rural area, whose surface geology is dominated by a single large granitic intrusion, and which represents a candidate site for a geological disposal facility (GDF) for high-level radioactive waste (HLW) in China. This research demonstrates that faults F16-2, F17, F18, and F20-2 are still active, producing dip-slip motions along the fault planes. The lithological variations in weathering and erosion can be discounted as the cause for these small-scale displacement variations. The work has also identified 11 previously unknown faults, characterising them from vertical (DU) and eastward horizontal (DE) displacements along and across the faults. These newly discovered structures demonstrate how PS InSAR can be used to monitor and measure micro-scale movements on regional-scale faults, which, in many cases, were previously considered to be inactive. Thus, this also improves our understanding of local stress regimes in this area. The Jiujing region is part of a convergent fault zone dominated by NE-SW compression, leading to NE-SW crustal shortening and NW-SE elongation. Through determination of the sense of ground movement measured at irregularly distributed PS points, some faults are reverse and trending NW-SE, while others are normal and trending NE-SW, highlighting how InSAR can be used to resolve fault type and relative movements to monitor tectonic fault blocks at a regional scale.
Rashid F, Hussein D, Glover PWJ, et al., 2022, Quantitative diagenesis: methods for studying the evolution of the physical properties of tight carbonate reservoir rocks, Marine and Petroleum Geology, Vol: 139, Pages: 105603-105603, ISSN: 0264-8172
Conventionally, diagenesis has been studied by making qualitative morphological observations which have been organised into complex classification schemes. Petrophysics, with its many quantitative measurements, now gives us the ability to quantify the effects of the type, degree and timing of complex diagenetic process. The aim of this paper is to examine how different diagenetic processes affect the petrophysical properties of carbonate rocks and to develop quantitative methodologies to describe the results of diagenetic processes. A large number of petrophysical measurements have been made on a suite of 172 core plugs to provide a test data set. Diagenetic modification of the primary depositional fabric was observed in a wide range of measured petrophysical parameters, and that porosity and pore connectedness exert dominant control on all of the electrical and hydraulic rock parameters. This observation has been used to propose a new theoretical framework linking the effect of diagenetic process to petrophysical measureables. Cementation exponent was found to increase with permeability and pore size, especially in recrystallized rocks, and is explained by smaller porosity samples having a better connected pore network. Electrical connectedness was also found to correlate extremely well with hydraulic permeability, showing that these phenomena are linked closely in tight carbonate reservoir rocks. A method for calculating pre- and post-dolomitisation porosity and the degree of dolomitisation from the measured petrophysical and compositional data has also been developed and tested. All electrical and hydraulic properties are related to pore type, allowing cementation exponent to be obtained from optical microscopy/SEM studies or NMR measurements, providing a new approach to estimating cementation exponent in carbonate rocks. This paper also provides a powerful new approach allowing petrophysical changes associated with the type, degree and timing of different diagen
Vinck K, Liu T, Jardine RJ, et al., 2022, Advanced in-situ and laboratory characterisation of the ALPACA chalk research site, Géotechnique, ISSN: 0016-8505
Low-to-medium density chalk at St Nicholas at Wade, UK, is characterised by intensive testing to inform the interpretation of axial and lateral tests on driven piles. The chalk de-structures when taken to large strains, especially under dynamic loading, leading to remarkably high pore pressures beneath penetrating CPT and driven pile tips, weak putty annuli around their shafts and degraded responses in full-displacement pressuremeter tests. Laboratory tests on carefully formed specimens explore the chalk's unstable structure and markedly time and rate-dependent mechanical behaviour. A clear hierarchy is found between profiles of peak strength with depth of Brazilian tension (BT), drained and undrained triaxial and direct simple shear (DSS) tests conducted from in-situ stress conditions. Highly instrumented triaxial tests reveal the chalk's unusual effective stress paths, markedly brittle failure behaviour from small strains and the effects of consolidating to higher than in-situ stresses. The chalk's mainly sub-vertical jointing and micro-fissuring leads to properties depending on specimen scale, with in-situ mass stiffnesses falling significantly below high-quality laboratory measurements and vertical Young's moduli exceeding horizontal stiffnesses. While compressive strength and stiffness appear relatively insensitive to effective stress levels, consolidation to higher pressures closes micro-fissures, increases stiffness and reduces anisotropy.
Edgar J, Ghail R, Lawrence J, et al., 2022, The impact of facies variability within the Harwich Formation on ground engineering in the London area, UK, Quarterly Journal of Engineering Geology and Hydrogeology, Vol: 55, ISSN: 1470-9236
The Eocene Harwich Formation, underlying the Greater London (UK) area, presents many construction problems for design and location of tunnels, pipelines, and other engineering infrastructure projects. Variable deposits make up the sequence of the Harwich Formation. These include cemented fault zones, hard grounds, loose gravel and sand that, when unexpectedly encountered, can cause construction delays and increase costs. Here, we interpret borehole cores and logs, in-situ observations coupled with borehole derived samples, and calculate particle-size distributions to develop a general facies model that accounts for the lithological distribution within the Harwich Formation. This provides an improved geological framework for proposed subsurface construction that can reduce inherent engineering uncertainties, not only in the London region, but potentially in other similar geological environments.
Hussein D, Rashid F, Lawrence JA, et al., 2022, Influence of fractures on the reservoir quality of Lower Miocene carbonates in Northern Iraq, Arabian Journal of Geosciences, Vol: 15, ISSN: 1866-7511
The Zagros Fold and Thrust Belt of the Kurdistan region of northern Iraq host major volumes of hydrocarbons in multiple fractured carbonate reservoirs throughout the Jurassic, Cretaceous, Palaeogene and Neogene. Limited research has been undertaken to characterize these recently discovered carbonate reservoir rocks. Here, the reservoir quality of the Neogene Euphrates and Jeribe Formations is investigated. Samples from five outcrops along the Azhdagh and Mamlaha anticlines and from four nearby wells (North Oil Company wells JM37, KM3, SAR1 and KU1) have been analysed to understand better their reservoir properties. In both formations very low matrix porosities (< 12 ± 0.5%) were measured and no visible pore connectivity was observed in thin sections. Matrix permeability was less than 0.10 ± 0.008 mD. The low porosity of the Euphrates and Jeribe Formation carbonates is related to diagenetic modifications including intense cementation and compaction. Given the low matrix porosity and permeability, the effect of fractures on fluid flow was investigated as a possible mechanism for enhanced reservoir quality. Naturally fractured core samples and highly fractured outcrops for both formations demonstrated enhanced flow of more than three orders of magnitude compared to matrix permeability. Lateral heterogeneities were observed in the area under investigation with lower fracture porosity and permeability in the North East compared to the South West of the region. Outcrop fractures were investigated near the wells on the flanks of the basin. The fracture network was found to be composed of two sets of sub-vertical, perpendicular fracture sets and sub-horizontal bedding. The fractures were closely spaced, persistent, with wide apertures rough surfaces and very well interconnected. The permeability data combined with field fracture survey information provides evidence that the reservoir quality in the drilled wells must in pa
Marsh AI, Williams OBE, FREng LG, et al., 2021, A sensitivity study of the factors affecting the risks associated with the disposal of spent nuclear fuel in a geological disposal facility in a clay environment, Progress in Nuclear Energy, Vol: 140, Pages: 1-17, ISSN: 0149-1970
The disposal route for the UK's inventory of spent nuclear fuel has yet to be decided upon, however if the UK follows the approach taken by many nations, its spent nuclear fuel will be destined for geological disposal. This paper provides a simplified, approach to the calculation of radiological risk posed to members of the public, associated with the disposal of spent advanced gas-cooled reactor (AGR) nuclear fuel in a geological disposal facility (GDF) located in a hypothetical clay geological setting. Simulating the release of radionuclides at differing levels of complexity shall aid in the development of aspects of the design, construction, operation, decommissioning and post-closure phases of geological disposal and the development of a safety case for geological disposal. This paper presents a high-level, 1-D model built in GoldSim, to provide an initial indication of the radiological risks to the public, the nature of which would require further development into a complex total system model in order to facilitate risk evaluation supplementary to a safety case. The model was validated against benchmark calculations provided by Radioactive Waste Management Ltd. The base case calculations suggest that the predicted risks to the potential exposed groups are well below, approximately 2 orders, the recommended risk guidance level of 1 × 10−6 per year. A number of sensitivity studies were carried out to identify the importance of various factors that could influence the predicted risks. Sensitivity analysis indicated that the most influential sensitivities on the annual risk posed by geological disposal were the depth and rate at which spent nuclear fuel dissolved in contact with groundwater. The pathways available for groundwater flow to the biosphere were also noted to significantly alter the peak risk observed; crucially almost all sensitivities did not increase the peak risk to within 1 order of magnitude below the recommended risk guidance level. Va
Mider G, O'Connor W, Lawrence J, et al., 2021, An investigation into ground movement on the Ventnor landslide complex, UK using Persistent Scatterer Interferometry, Remote Sensing, Vol: 13, Pages: 1-20, ISSN: 2072-4292
Analysis of ground movement rates along the coastline and upper sections of the Ventnor landslide complex was carried out utilizing Persistent Scatterer Interferometric Synthetic Aperture Radar methods using Sentinel-1 SAR data from 2015 to 2019 (four years). Results were compared with rainfall data, historical ground investigation records and monitoring surveys carried out at Ventnor to relate observations to geology, geomorphology and rainfall. Decomposition of InSAR viewing geometries to vertical and horizontal aligned well with previous ground-based studies. Subsidence of −9.8 mm a−1 at the Lowtherville Graben and heave of +8.5 mm a−1 along the coastline south of Ventnor Park were observed. Decomposition to east-west geometry results showed an eastward displacement of approximately 12.4 mm a−1 along the coastline south of Ventnor Park, and a westward displacement of −3.7 mm a−1 throughout built up sections of Ventnor town, indicating the landslide was displacing more in an eastern direction than vertically. The cause of this movement was investigated by using publicly available intrusive boreholes paired with Persistent Scatterer Interferometry, and a new ground model spanning east-west parallel to the coastline was presented. No evidence of significant ground movement was observed along heavily protected sections of the coastline, suggesting coastal defences comprised of concrete aprons and rip rap appear to be an effective coastal management/landslide stabilisation tool when compared to rip rap alone. The mechanism of this increased stability is likely due to the combination of toe weighting and reduced toe erosion. A lag of approximately 13–20 days was observed between high rainfall events and subsequent peaks in ground displacement, which was shorter than a 29 day lag observed in a previous study. Similar observations of prolonged rainfall resulting in prolonged displacements were also observed. The study demonstrate
Marsh AI, Williams LG, Lawrence JA, 2021, The important role and performance of engineered barriers in a UK geological disposal facility for higher activity radioactive waste, Progress in Nuclear Energy, Vol: 137, ISSN: 0149-1970
The effective management of radioactive waste is a necessary prerequisite to the use of nuclear energy. The UK's policy for the long-term management of higher activity radioactive waste (HAW), and potentially spent nuclear fuel (SNF), is disposal in a deep underground geological disposal facility (GDF). A GDF will isolate HAW from mankind until the radioactivity has decayed to levels where any risk to future generations is acceptably low. It is likely, therefore, that a GDF will need to safely contain radioactive materials for hundreds of thousands of years. The necessary isolation will be provided by a combination of natural (geological) and engineered barriers. A multi-layered engineered barrier system will provide the defence-in-depth that is required to give the public confidence in the long-term performance of the GDF. This paper identifies the significant role each engineered barrier or “layer” plays in ensuring that long-lived radionuclides remain isolated from the biosphere and receptors within the vicinity of a GDF. Receptors include human and animal populations, and the natural environment. The paper also explores the characteristics and performance of a number of suitable candidate materials for use in the UK GDF engineered barriers. An indication of the lifetime of potential barriers under conditions pertinent to each of the UKs proposed geological settings is given. As the performance of the engineered barriers will be vital to the GDF post-closure safety case, several areas for further work are proposed.
Rashid F, Hussein D, Lawrence JA, et al., 2021, Fluid flow and permeability analysis of tight gas carbonate reservoir rocks using fractures and dynamic data, Journal of Natural Gas Science and Engineering, Vol: 90, Pages: 1-18, ISSN: 1875-5100
The porosity, permeability, rock material and fracture networks of the newly discovered tight carbonate reservoir rock, the Early Cretaceous Sarmord Formation in Zagros basin are examined. The methods used to investigate the formation are rock cores, micro-resistivity image logs, drill stem tests, drilling fluid data, petrophysical wireline data and drilled cutting samples.The analysed data show that the Sarmord Formation is characterized by extensive open and partially open macro-fractures formed by the local stress from fault and fold propagation. These fractures are sub-vertical with an average dip of 73°, fracture aperture of 0.44 mm and persistence (length) of 11.0 cm. The dominant strike of the fractures is NE-SW, parallel to the observed faults and perpendicular to the main Miran West structure.The vast majority of reservoir porosity was found to be in the rock matrix, with the fractures having very limited impact (average fracture porosity is 0.032%) on porosity. In contrast the fracture permeability averages 240 mD which is four orders of magnitude greater than the matrix permeability. As a result, the inter-connected fractures create effective fluid flow pathways and enhanced hydrocarbon migration perpendicular to the fold structure. Faulting associated with the field structure led to fault damaged zones which act as zones of inter-connected fractures with higher permeability and preferential fluid flow pathways. It is demonstrated that the fracture permeability is driven by the fracture aperture and spacing, whilst the fracture persistence has limited control on permeability.The findings of this study highlight that the importance of fractures and faults on reservoir's quality in tight gas bearing rocks. The network of inter-connected fractures, provide the fluid flow which control the permeability. In contrast the matrix controls the pore spaces and the hydrocarbon storage. This work emphasizes the importance of understanding the impact of structural
Mider G, Lawrence J, Mason P, et al., 2020, Monitoring Littoral Platform Downwearing using Differential SAR Interferometry, Remote Sensing, Vol: 12, ISSN: 2072-4292
A methodology for the remotely sensed monitoring, measurement and quantification of littoral zone platform downwearing has been developed and is demonstrated, using Persistent Scatterer Interferometric Synthetic Aperture Radar data and analysis. The research area is a 30 km section of coast in East Sussex, UK. This area combines a range of coastal environments and is characterised by the exposure of chalk along the cliffs and coastal platform. Persistent Scatterer Interferometry (PSI) has been employed, using 3.5 years of Sentinel-1 SAR data. The results demonstrate an average ground level change of −0.36 mm a−1 across the research area, caused by platform downwearing. Protected sections of coast are downwearing at an average of −0.33 mm a−1 compared to unprotected sections, which are downwearing more rapidly at an average rate of −1.10 mm a−1. The material properties of the chalk formations in the platform were considered, and in unprotected areas the weakest chalk types eroded at higher rates (−0.66 mm a−1) than the more resistant formations (−0.53 mm a−1). At a local scale, results were achieved in three studies to demonstrate variations between urban and rural environments. Individual persistent scatterer point values provided a near-continuous sequence of measurements, which allowed the effects of processes to be evaluated. The results of this investigation show an effective way of retrospective and ongoing monitoring of platform downwearing, erosion and other littoral zone processes, at regional, local and point-specific scales.
Morgan T, Ghail R, Lawrence J, 2020, Major faulting in London: evidence for inherited basement faults in the London Basin, Quarterly Journal of Engineering Geology and Hydrogeology, Vol: 54, Pages: 1-14, ISSN: 1470-9236
The near-surface of London is faulted, although the locations, architecture and tectonic origins of the faults are broadly unknown. This presents serious issues for geotechnical engineering in London and has implications for our structural understanding of the London Basin. The region is a product of Alpine compression, yet it is unclear whether these major faults are new Alpine shears or reactivated basement faults. We assess the plausibility of Alpine reactivation and inheritance of basement faults in London through three investigations: analysing structures in the near-surface; mechanically assessing the feasibility of basement fault reactivation under Alpine stress conditions; and comparing inheritance mechanisms with observations in London and the Thames Estuary. Three major en echelon fault sets are identified. These appear to have compartmentalized London's near-surface geology and are all interpreted to be products of Alpine reactivation of the underlying basement faults. Fault interaction and linkage is evidenced by complex zones of intense faulting identified by tunnelling projects. The role of new structural development in accommodating Alpine compression is considered to have been comparatively minor. The lack of major faulting in the basin's interior may reflect the competence of the underlying Anglo–Brabant Massif in restricting Alpine strains to its margins.
Scoular J, Ghail R, Lawrence J, et al., 2020, Retrospective InSAR analysis of East London during the construction of the Lee Tunnel, Remote Sensing, Vol: 12, Pages: 1-19, ISSN: 2072-4292
The Lee Tunnel was constructed as the first part of the Thames Tideway Improvement scheme, between 2010 and 2016. With tunnelling for the East section of the main Thames Tideway Tunnel, which joins the Lee Tunnel at Abbey Mills Pumping Station, beginning in early 2020, this paper investigates patterns of deformation in East London during construction of the Lee Tunnel. An unexpected geological feature, later identified as a drift filled hollow, was discovered during tunnelling. This study demonstrates that had eight years of ERS Persistent Scatterer Interferometry (PSI) data been analysed prior to tunnelling, the unusual pattern of displacement may have been recognised and further targeted borehole investigations taken place before the launch of the tunnel boring machine. Results also show how areas of different land use, including cemeteries and historic landfill, exhibit differences in settlement behaviour, compared with surrounding terraced housing. This research highlights the challenges in interpreting PSI results in an urban area with ongoing construction and the value of a long archive of data, which now spans almost three decades in London, that can be used to establish a baseline prior to construction.
Rashid F, Hussein D, Lawrence JA, et al., 2020, Characterization and impact on reservoir quality of fractures in the Cretaceous Qamchuqa Formation, Zagros folded belt, Marine and Petroleum Geology, Vol: 113, Pages: 1-22, ISSN: 0264-8172
Reservoir quality in tight fractured carbonate rocks is controlled by the fracture properties, the tectonic origin of fractures, the relationship of fractures to other sedimentary features within the rockmass and diagenesis. In this study fracture analysis, porosity and permeability of the Qamchuqa Formation in the Miran West block of the Zagros folded belt in Kurdistan has been studied. This was undertaken using core analysis, micro-resistivity image logs, drill stem tests (DST), mud logging data, Repeat Formation Test (RFT), drilled cutting samples and wireline log data.The integrated analysis shows that the Qamchuqa Formation is characterized by heterogeneous sedimentary and tectonic features. The sedimentary features include burial stylolites, dissolution seams and some fractures which formed at early stages of burial and diagenesis (Phase 1). Open fractures, partially open mineralized fractures, veins and tectonic stylolites were formed by later tectonic activity (Phase 2).The finding of this study highlight that the fracture properties including aperture, length, frequency and origin, play an important role in controlling the reservoir's quality. The open fractures and partially open mineralized fractures enhance permeability providing an inter-connected fracture network, leading to a high fracture permeability that controls fluid flow in this tight carbonate reservoir rock. The fracture network had little impact on the volume of hydrocarbon storage which is controlled by the pore matrix. In contrast, structures including stylolites, dissolution seams and veins generally have a negative impact on the reservoir quality by blocking the fluid flow.This work emphasizes the importance of understanding the regional geological history and the role of sedimentary and tectonic features when investigating in tight carbonate reservoirs.
Scoular JM, Croft J, Ghail RC, et al., 2019, Limitations of persistent scatterer interferometry to measure small seasonal ground movements in an urban environment, Quarterly Journal of Engineering Geology and Hydrogeology, Vol: 53, Pages: 39-48, ISSN: 1470-9236
London Clay, which underlies the majority of Greater London, has a high shrink–swell potential that can result in damage to foundations and surface infrastructure due to seasonal expansion and contraction of the clay. Currently, surface movement as a result of shrink–swell is not monitored in London, meaning that the magnitude and cyclicity of these movements is poorly understood. Persistent Scatterer Interferometric (PSI) Synthetic Aperture Radar data provide high-precision line-of-sight displacement measurements at a high point density across urban areas, offering the possibility of routine shrink–swell monitoring across whole cities. To test this, PSI data derived from TerraSAR-X (TSX) observations for the period from May 2011 to April 2017 were analysed for shrink–swell patterns across three areas of London in Hammersmith, Muswell Hill and Islington. A consistent cyclicity and amplitude was detected at all sites and the number of cycles is comparable with those identified in rainfall data. The amplitude of these cycles is smaller than anticipated, most probably because of the resisting effect of roads and pavements. The Cranfield University Leakage Assessment from Corrosivity and Shrinkage (LEACS) database was used to subdivide the PSI data and the average velocity and amplitude of each class statistically tested for significant differences between classes. The results show that it is not possible to statistically isolate possible soil shrink–swell movement in TSX PSI data in London.
Aliyu MM, Shang J, Murphy W, et al., 2019, Assessing the uniaxial compressive strength of extremely hard cryptocrystalline flint, International Journal of Rock Mechanics and Mining Sciences, Vol: 113, Pages: 310-321, ISSN: 0020-7624
Cryptocrystalline flint is an extremely hard siliceous rock that is found in chalk formations. The chalk is frequently a prefered rock type, which in recent decades is often used as a host for underground rock caverns and tunnels in Europe and North America. A reliable estimation of the uniaxial compressive strength (UCS) of the extremely strong flint, with an average UCS of about 600 MPa will provide guidance for a proper engineering design, where flint is encountered, thereby avoiding project progress delay, litigation as well as economic consequences. Conventional UCS measurement using core samples is cumbersome for flint due to the extreme strength and hardness of the rock, for which the core sample preparation process is often extremely difficult. In this study, the UCS prediction models of flints collected from the North-West Europe were developed and the validity of the developed models was investigated. A series of laboratory index tests (comprising the three-point-bending, point load, ultrasonic velocity, density, Shore hardness and Cerchar Abrasivity tests) were perfomed. The index test results were correlated with the UCS values previously determined in the laboratory using both cylindrical and cuboidal specimens to develop the UCS prediction models. Regression analysis of the UCS and the index test results was then performed to evaluate for any potential correlations that can be applied to estimate the UCS of the cryptocrystalline flint. Intensive validity and comparison studies were performed to assess the performance of the proposed UCS prediction models. This study showed that UCS of the tested flint is linearly correlated with its point load strength index, tensile strength and compressional velocity, and is parabolically correlated with its density. The present study also demonstrated that only a couple of the previously developed empirical UCS models for estimating UCS are suitable for flint, which should be used with care.
Lawrence JA, Spence R, Mortimore RN, et al., 2018, Coastal cliff rock mass weakening of chalk and the impact of salt water, Proceedings of the Institution of Civil Engineers: Geotechnical Engineering, Vol: 171, Pages: 545-555, ISSN: 1353-2618
The relationship between salt water and the strength of Chalk forming the coastal cliffs of northwest Europe was investigated. Uniaxial compressive strength (UCS) tests on core samples from three horizontal boreholes drilled at the base of Chalk cliffs in East Sussex, UK, showed the weakest Chalk to be near the cliff face. The UCS nearly doubled over the length of the 9 m deep boreholes. The UCS results were close to values expected for Chalk of this intact dry density for samples farthest from the cliff face. High chloride concentrations (salt water) of up to 69 000 mg/l were found to be associated with the lowest UCS values closest to the cliff face. Lower chloride concentrations, with values of 1850 mg/l or less and often with a non-marine origin, were found in the stronger core samples. It can be concluded that the Chalk coastal cliffs in the areas tested became weaker towards the cliff face. This can, in part, be linked to salt water weakening although it is likely that other factors are also contributing to this phenomenon.
Lawrence JA, Preene M, Lawrence U, et al., 2018, Engineering in Chalk, Publisher: ICE Publishing, ISBN: 978-07277-6407-2
Agar S, Lawrence J, Ghail R, et al., 2018, PSInSAR remote sensing observations of deformation behaviour at Salisbury Plain, UK, Chalk 2018, Publisher: ICE Publishing, Pages: 269-274
PSInSAR is a radar remote sensing approach that offers measurements of ground deformation over large areas at sub-mm precision. The technique has significant potential for granting insight into ongoing geological processes. Data recovery in rural areas is challenging due to the highly inconsistent radar scattering behaviour exhibited by vegetated ground, and thus a rural area of the UK – Salisbury Plain - was used as a case study to examine the challenges and potential for PSInSAR techniques in rural areas. Results showed regional uplift of clay formations relative to the Chalk, which was attributed to clay shrink-swell correlated with seasonal increases in groundwater levels.
Lawrence J, hussein D, Rashid F, et al., 2018, Developing pore size distribution models in heterogeneous carbonates using especially nuclear magnetic resonance, Engineering in Chalk
Lawrence J, mortimore R, Thrower A, 2018, Macro and micro fabrics in chalk identified using the Bushinsky Oil Technique: an updated method and new applications for an old experimental technique, Engineering in Chalk
Morgan T, Lawrence J, Ghail R, 2018, Fault damage zones: Implications for geotechnical engineering near faulting, 15th Young Geotechnical Engineer Symposium
Faulting not only produces a plane of weakness within the rockmass but can significantly weaken it locally by the development of a damage zone around the fault. The paper aims to highlight to the geotechnical community the potential impact of the fault damage zone by using GSI and Hoek-Brown assessments of the rockmass strength on a case study from Culver, SW England. Both assessments demonstrated that the rockmass within the damage zone is weaker than the unfaulted rock, weakening significantly towards the fault core.
Asoms SG, Stavrou A, Lawrence JA, 2018, Developing a GIS based methodology for coastal chalk cliff retreat using multiple datasets, Pages: 369-374
Topographical mapping survey data which covered a period from 1951 to 2000 was used as the main data set to develop a cliff recession analysis of the coastal cliffs at Birling Gap, East Sussex, UK. This a portion of the coast is dominated by the Seven Sisters chalk coastal cliffs and Birling Gap is characterized by the presence of a palaeo-valley which formed during the Devensian glaciation. The entire area is subject to high rates of erosion and frequently cliff collapses at all scales. Using a GIS platform, a database was created geo-referencing this detailed cartographic historical record. The cartographic information was translated into spatial linear elements within the GIS; each linear element defining the position of the cliff at a specific period. A spatial and statistical analysis of the georeferenced information provided a complete and comprehensive analysis of the shoreline recession, allowing spatial and temporal correlation of the coastal erosion occurring at this location. The cartographic information was then enhanced by using more recent data sets, mainly obtained by aerial photos, which allowed the analysis to be extended into the 21st century. This methodology was developed to demonstrate how different data sets can efficiently and effectively be combined to provide end users with a single referenceable tool to holistically investigate the processes, causes and impact of coastal erosion.
Mider G, Lawrence JA, 2018, Anisotropic permeability of chalk, Pages: 481-487
The consolidation history of chalk denotes that it has been subjected to different horizontal and vertical stresses throughout its geological history. A testing programme was developed to investigate whether this would mean that chalk exhibits anisotropic permeability. Three Southern Province Chalk formations in south east England were tested; West Melbury Marly Chalk, Seaford Chalk and Newhaven Chalk formations. All the specimens were collected in the field, orientations were recorded before the samples were cut and prepared for laboratory testing. The laboratory testing programme identified small anisotropics in permeability measurements in Seaford and Newhaven Chalk formations, and anisotropy in unconfined compressive strength measurements. Anisotropic permeability in the West Melbury Marly Chalk Formation is unresolved due to heterogeneity of the samples collected from the formation. All tested samples also had index properties measured, and they have also been presented in the paper. It can be concluded that vertical samples in the Seaford and Newhaven Chalk formations are more permeable and weaker than horizontally drilled samples.
Asoni SG, Stavrou A, Lawrence JA, 2018, Erosion of the chalk coastal cliffs at Birling Gap, Sussex, UK. Correlation between rate of coastal retreat, geotechnical rocks properties and precipitation, Pages: 361-367
Birling Gap forms part of the Seven Sister cliffs, East Sussex, UK. Geotechnically the area is characterized by the presence of a Devensian paleovalley developed in a shallow syncline within the Seaford Chalk Formation. It is a dynamic coast line which is subject to continual erosion. A detailed survey has been undertaken along the coast of Birling Gap from 1950 to 2000. Using these data, the spatial information is translated into geospatial elements of an ArcGIS platform. The geo-referencing process defines the position of the cliff in a specific period. Aerial photos and most recent mapping survey are used to extend and complete the temporal analysis to the 21 st century. The outputs show that mean rate of coast retreat is 0.54 m/y and circa 30 m of coast has been lost in the last 60 years. Analysing the pluviometry data, it is possible to establish a relation between peak precipitation and high rates of coastal retreat. Higher rates of retreat are measured on the central portion of the studied area which is characterized by the deeply weathered paleovalley, which differs geotechnically from the surrounding more competent, less weathered chalk. The study shows how an accurate mapping survey translated into a GIS database can be a useful tool to understand the temporal geodynamic and hydrodynamic evolution of coastal environments. This work quantifies rapid erosion along this part of our chalk coastline and identifies that erosion is higher during periods of prolonged increased precipitation.
Hadlow NW, Lawrence JA, Mortimore RN, 2018, Evaluation and prediction of anticipated depths of weathering (engineering rockhead) as a function of geomorphology in areas of chalk outcrop in southern England and northern France, Pages: 711-720
Conceptual models of weathering in areas of chalk outcrop in southern England indicate that the depth of weathering and engineering rockhead are variable with respect to geomorphology. This variation is typically demonstrated by the transition from interfluve to valley with the depth of weathering changing as result of elevation and aspect. Valley axes are shown to have the deepest weathering, inter-fluves the shallowest and valley slopes a transitional depth with slope gradients on north-west facing slopes generally greater than southeast facing slopes. The main processes considered to have formed the weathering profiles in the Chalk of southern England are periglacial processes associated with seasonal freeze-thaw and mass movement in the last ice-age. In this study, analysis of historical site investigation data, including geophysical surveys, has allowed these conceptual models to be reviewed. This analysis has suggested that two physical transitions occur within the near-surface chalk rock mass that relate to geomorphology. The first, and deepest, transition is considered to represent an opening of discontinuities in the rock mass as a consequence of relaxation in the near surface due to unloading. The second transition is considered to represent an increase in discontinuity frequency in the rock mass due to formation of new discontinuities which progressively intensifies towards the surface. The base of the second transition is generally considered to be engineering rockhead for most engineering situations. Using the data reviewed, a model was developed to estimate the approximate position of these transitions based on relative ground surface elevation within a geomorphological domain. This model may be used to estimate the depth of engineering rockhead based on topographical data, such as a digital terrain model (DTM), in the absence of site investigation data for a site. This has applications for preliminary design where piled foundations or shallow tunnelli
Aliyu MM, Murphy W, Lawrence JA, et al., 2018, Impact of tectonic faults on the morphology and mechanical properties of grey flints, Pages: 515-520
Grey flints of different morphologies (tabular and nodular) located proximally and distally to large tectonic faults were investigated. Different positions to tectonic faults were considered to examine the influence of geological structures on mechanical properties of flints. Different morphologies were considered to investigate the variation in mechanical properties of flints with morphology. Uniaxial compressive strength, point load strength, tensile strength, density and deformability of grey flints were tested. The results show grey flints are stronger, denser and more rigid than similar flints from zones of tectonic disturbance and faulting, but do not show any trend between flint morphology and mechanical properties. Understanding field variables such as the influence of proximity to tectonic faults and the variation in mechanical properties of flint may provide important input for the successful design of engineering projects and the behaviour of chalk oil reserviours.
, 2018, ENGINEERING IN CHALK., ISBN: 9780727764072
Hussein D, Collier R, Lawrence JA, et al., 2017, Stratigraphic correlation and paleoenvironmental analysis of the hydrocarbon-bearing Early Miocene Euphrates and Jeribe formations in the Zagros folded-thrust belt, Arabian Journal of Geosciences, Vol: 10, ISSN: 1866-7538
The Lower Miocene Euphrates and Jeribe formations are considered as the main targets of the Tertiary petroleum system in the western part of the Zagros Basin. The formations consist of carbonates with some evaporate intercalations of the Dhiban Formation. This study utilized data from a field investigation including newly described outcrop sections and newly discovered productive oil fields within the Kirkuk embayment zone of the Zagros fold and thrust belt such as Sarqala and Kurdamir wells. This work is the first to show a stratigraphic correlation and paleoenvironmental interpretation by investigating both well data and new outcrop data. Three depositional environments were identified, (1) an inner and outer ramp belts environment, (2) shoal environment, and (3) restricted lagoon environment. Within these 3 environments, 12 microfacies were identified, based on the distribution of fauna mainly benthonic foraminifera, rock textures, and sedimentary structures. The inferred shallow water depths and variable salinities in both the Euphrates Formation and Jeribe Formation carbonates are consistent with deposition on the inner ramp (restricted lagoon and shoal) environments. Those found in the Euphrates Formation constrained the depositional environment to the restricted lagoon and shoal environment, while the microfacies in the Jeribe Formation provided evidence for an inner ramp and middle to outer ramp belt environments. This study represents the first detailed research that focuses on the stratigraphic correlation and changes in carbonate facies with the main aim to provide a wider understanding of stratigraphy of these carbonate reservoirs throughout the northern part of Iraq.
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