Showing papers in "Quarterly Journal of Engineering Geology and Hydrogeology in 1999"
TL;DR: In this paper, the authors explore the processes used to make some of these guesses and describe how the results are then applied to engineering design, showing that rational engineering decisions can be made in spite of the limitations of the input data.
Abstract: Assigning numbers to geology requires a delicate balance between the commonly held opinion that geology cannot be quantified and the over-optimistic view that every physical quantity can be described in precise mathematical terms. In reality, many geological characteristics cannot be quantified precisely and intelligent guesses based upon experience and logical arguments are the best that can be hoped for. This paper explores the processes used to make some of these guesses and describes how the results are then applied to engineering design. It is shown that, with care, rational engineering decisions can be made in spite of the limitations of the input data. In recent years the development of computer hardware and software has made it much easier to investigate the influence of ranges of values for each of the input parameters. However, care has to be taken that the design is driven by sound geological reasoning and rigorous engineering logic rather than by the very attractive images that appear on the computer screen.
127 citations
TL;DR: In this paper, long-term trends of changes in the quality of water discharging from abandoned coal mines have been studied for 32 long-established discharges in the Midland Valley of Scotland.
Abstract: Long-term trends of changes in the quality of water discharging from abandoned coal mines have been studied for 32 long-established discharges in the Midland Valley of Scotland. Six discharges have been studied in greater detail, providing insights into discharge quality evolution over more than a century. It has been found that minewater pollution is most severe in the first few decades after a discharge begins (the ‘first flush’), and that even the largest systems settle down to a lower level of pollution (particularly in terms of iron concentration) within 40 years. Long-term iron concentrations of less than 30 mg/1 are typical, and many are less than 10 mg/1. Low pH values (which might justify the over-used term ‘acid mine drainage’) do not generally persist, due to the rapid buffering of localized acidic waters by carbonates (both natural carbonates, and those introduced as rock powder for fire precautions during mining). This is corroborated by alkalinity concentrations, which tend to be highest in the early years of a discharge. While the pyrite content of the worked sequence strongly influences initial water quality (in terms of pH, iron and sulphate) during the ‘first flush’, there appears to be no correlation between long-term iron concentrations of discharges and pyrite content of local strata. Rather, higher levels are found in any sequence where there is scope for fluctuations of the water table in worked ground near to the discharge. A scientific approach to minewater remediation should allow for active treatment of discharges for the first decade or two, followed by long-term passive treatment after asymptotic pollutant concentrations are attained.
88 citations
TL;DR: A model for weathering of volcanic rocks, particularly those of pyroclastic origin, is presented in this article, where modifications, similar to those recently proposed for granites by Irfan, are proposed to the material and mass weathering schemes commonly adopted in Hong Kong for the characterization of weathered volcanic rocks in engineering use.
Abstract: The mineralogical and fabric characteristics of weathered volcanic rocks, which are widespread in Hong Kong, are poorly documented. Consequently, the significant variations commonly observed, even at the same locality, in engineering properties and in situ behaviour of these rocks and the resulting soils cannot be adequately related to their basic mineralogical and fabric characteristics. A model for weathering of volcanic rocks, particularly those of pyroclastic origin, is presented in this paper. Modifications, similar to those recently proposed for granites by Irfan, are proposed to the material and mass weathering schemes commonly adopted in Hong Kong for the characterization of weathered volcanic rocks in engineering use. The appropriateness of various proposed petrographic and chemical weathering indices to generally fine-grained volcanic rocks is examined. A number of modifications are proposed to the standard soil preparation and testing methods for the soils formed from tropical weathering of volcanic rocks in order to obtain meaningful and more repeatable results.
78 citations
TL;DR: In this article, a detailed glacial hazard assessment has been undertaken through to the development of a full remediation scheme in Nepal and represents the first time that such detailed hazard assessment and mitigation have been undertaken.
Abstract: Recession of glaciers throughout the Himalayas is resulting in the development of a growing number of high-altitude proglacial lakes that are retained behind natural moraine dams. Some of these have failed catastrophically and the consequential Glacier Lake Outburst Floods (GLOFs) have resulted in substantial damage and loss of life downstream. With growing populations in remote valleys coupled with the demand for substantial growth in the capacity for hydro-electric power for export, the risk of further disasters is increasing. Accordingly, His Majesty9s Government of Nepal has undertaken a series of studies since 1985 to investigate the risks associated with such glacial lakes. This photofeature encapsulates aspects of the work undertaken between 1994 and 1997 at Tsho Rolpa, which is thought generally to be the largest and most dangerous glacial lake in Nepal. The present project at Tsho Rolpa is the first of its kind in Nepal and represents the first time that such detailed glacial hazard assessment has been undertaken through to the development of a full remediation scheme in Nepal. Tsho Rolpa lies about 110 km north east of Kathmandu at the eastern end of the Rolwaling Valley (Fig. 1) and immediately south of Gauri Sankar (7146 m). The lake (Fig. 2) is about 3.5 km long by 0.5 km wide and is up to 135 m deep. It is fed by Trakarding Glacier (Fig. 3) to the southeast which is itself a composite glacier supplied by several glaciers from among the peaks to the east and south east of
52 citations
TL;DR: The former Department of the Environment has published 35 applied geological mapping studies dealing with land-use planning in a range of geological and planning environments as mentioned in this paper, which were carried out in England and Wales between 1983 and 1996.
Abstract: The former Department of the Environment has commissioned 35 applied geological mapping studies dealing with land-use planning in a range of geological and planning environments. These were carried out in England and Wales between 1983 and 1996. Using geological maps as a base these studies have developed two types of applied geological maps: thematic maps dealing with particular topics and summary maps bringing together many of the earth science factors relevant to planners and developers. The recommendations made by Geomorphological Services Limited (GSL) in 1985 in a previous review of these studies are summarized. The output, type and range of information, and its potential users are compared. Each study is assessed, with respect to the GSL recommendations, in terms of its content and usefulness, based in part on how it has been received by users. The main types of summary and thematic maps are described and guidance given on their content and presentation. The importance of maps in providing the key interface between earth scientists and planners is discussed, in particular the significance of map scale, use of colour and accuracy of the geological lines. Good practise is illustrated by reference to examples.
50 citations
TL;DR: In this article, the geomorphological factors influencing debris flow paths and deposition zones were assessed from a geomorphology study of the catchment to define criteria for preliminary hazard zoning of downslope developments.
Abstract: The north part of Lantau Island is undergoing rapid development following construction of the new airport at Chek Lap Kok. This development, primarily on reclaimed land, is adjacent to a range of steeply sloping hills that experience levels of annual rain in excess of 2500 mm. Rainfall induced landslides on this steeply sloping natural terrain are potential hazards to developments down slope. Landslides on these natural slopes resulting from two major rainstorms in 1992 and 1993 were studied to determine their characteristics and define the geomorphological factors influencing their debris trails. These data were compared with the aerial photographic record of landslide scars within the same catchment over the period 1945-1995 to determine the potential hazard from natural terrain landslides to downslope development. The limited data set indicates that channelized debris flows which produce long debris trails pose the greatest hazard potential to downslope development. Factors influencing debris flow paths and deposition zones were assessed from a geomorphological study of the catchment to define criteria for preliminary hazard zoning of downslope developments.
49 citations
TL;DR: In the afternoon of Wednesday 23 April 1997, a large subsidence crater opened up in front of a house on Ure Bank Terrace, on the northern outskirts of Ripon in North Yorkshire as mentioned in this paper.
Abstract: In the afternoon of Wednesday 23 April 1997, a large subsidence crater opened up in front of a house on Ure Bank Terrace, on the northern outskirts of Ripon in North Yorkshire. Overnight its sides collapsed inwards, so that the hole had doubled in size by the next morning (Fig. 1). The subsidence crater was then 10 m in diam- eter, and 5.5 m deep to a choke of debris overlain by water 1 m deep. Its sudden appearance was the cause of considerable concern to the occupants of the adjacent house, and the event was widely reported in the national press and media. A subsidence hollow was mapped at this site by the 1856 Ordnance Survey and documented by Cooper (1986). More subsidence had occurred at the Ure Bank site in previous years, but this latest collapse had rather more impact. Creeping movement of the soil towards the new hole meant that the adjacent house was destined for demolition. The event was the latest of a series of ground collapses that have occurred, at an average rate of about one per year, in and around the city of Ripon. While they are little more than an inconvenience in farmland, they have the potential to cause serious damage when they occur in built-up areas. The immediate cause of the Ure Bank subsidence was the downward movement of soil, drift and recent fill into actively expanding voids within the ground. Ultimately, it was caused by the partial collapse of a cave
48 citations
TL;DR: In this article, the effect of long-term soaking on the California Bearing Ratio (CBR) of compacted gypsiferous soil containing about 64 0ypsum was studied.
Abstract: The effect of long-term soaking on the California Bearing Ratio (CBR) of compacted gypsiferous soil containing about 64 0ypsum was studied. Sixteen CBR samples compacted at optimum moisture content and 950f the modified AASHTO dry density were prepared in accordance with ASTM (D 1883-87). Two samples each were soaked for periods of 0, 4, 7, 15, 30, 60, 120, and 180 days with a 20 lb (89 N) surcharge load. The water in the soaking tank was changed continuously to avoid full saturation with gypsum. The tests revealed a sharp drop in CBR with soaking period, especially within the first week. Thereafter, the loss in CBR took place at a smaller rate so that the soil strength became constant after about six months. The decrease of total soluble salt and gypsum content in soil with increasing soaking period is in full agreement with the loss in CBR with soaking period. The paper reveals that a soaking period of four days can lead to serious overestimation of soil strength for these soils.
42 citations
TL;DR: In this paper, a combination of resistivity imaging, core drilling and geophysical logging was found to provide a good overview of the variation in rock quality and detailed information on the engineering geological characteristics and genesis of the strata.
Abstract: Investigations over two major tectonic zones in the Hallandsas Horst, Southern Sweden were carried out in connection with a railway tunnelling project. A combination of resistivity imaging, core drilling and geophysical logging was found to provide a good overview of the variation in rock quality and detailed information on the engineering geological characteristics and genesis of the strata. Resistivity data, acquired along parallel lines over the zones using multi-electrode equipment, were processed by means of automatic inversion software to generate sections showing the variation of resistivity with depth. Wireline core drilling at selected points gave an almost complete core recovery, which revealed major sedimentary sequences and heavily weathered crystalline rocks that were previously unknown or only partially known despite conventional core drilling and percussion drilling. Geophysical borehole logging confirms the resistivity imaging results, and would be a particularly valuable complement to core logging in cases where significant core loss occurs.
36 citations
TL;DR: In this paper, the authors used PHREEQE to predict that unregulated minewater discharges from abandoned mines will have marked effects in the River Almond, with goethite being initially precipitated at a rate of up to 36 kg/day, dissolved sulphate concentrations ranging between 170 and 800 mg/l and pH being depressed to 6.5.
Abstract: Polluted discharges from abandoned mines are a major cause of freshwater pollution in central Scotland, often contributing high Fe, SO 4 2- and acidity to receiving streams. The Central coalfield has been extensively mined for over a century and Polkemmet was the last colliery to close in 1985. Recent monitoring indicates that the rate of groundwater recovery is approximately 0.15 to 0.2 m per week. Without intervention, this trend would result in complete recovery by 2000 and probable discharge into the River Almond. Geochemical modelling indicates that pyrite oxidation, calcite dissolution and goethite precipitation are primarily responsible for the evolution of groundwater chemistry currently observed at Polkemmet. Predictive modelling using PHREEQE suggests that unregulated minewater discharges will have marked effects in the River Almond, with goethite being initially precipitated at a rate of up to 36 kg/day, dissolved sulphate concentrations ranging between 170 and 800 mg/l and pH being depressed to 6.5. Combined active lime flocculation and passive aerobic wetlands may be the most effective means of treating the predicted minewater discharges. Keywords: abandoned mines, hydrochemistry, surface water, underground mining, water quality
30 citations
TL;DR: In this paper, the feasibility of using a stress path triaxial cell for evaluating the vertical swell of expansive soils under multi-dimensional loading conditions was examined, and the results of these tests were compared with the volume changes observed for samples tested under identical initial conditions in the oedometer.
Abstract: Preconstruction treatment or the selection and design of a foundation system both rely on accurate estimates of the potential heave of the supporting expansive soil. The majority of volume change testing of expansive soils has been performed under one-dimensional loading conditions in the oedometer. However, due to differences between laboratory test constraints and field conditions, the amount of volume change measured in various oedometer testing methods may differ dramatically from heave observed in the field. This paper presents the results of an experimental investigation in which the feasibility of using a stress path triaxial cell for evaluating the vertical swell of expansive soils under multi-dimensional loading conditions was examined. Several series of triaxial swell tests were conducted in which the influence of confinement on the predicted vertical swell was evaluated. The results of these tests were compared with the volume changes observed for samples tested under identical initial conditions in the oedometer. The applicability of the triaxial testing technique was further ascertained by predicting surface heaves observed in an instrumented field test. The triaxial swell tests provided reasonable estimates of the measured field heaves in comparison to the oedometer tests which yielded rather conservative predictions.
TL;DR: In this article, an electrical resistivity imaging of field-scale solute transport in the unsaturated zone of the Chalk in East Yorkshire is described, where an electrically conductive tracer is applied to the surface of an 18 m 2 plot at a rate of 49 mmd -1 for two days (representative of very heavy rainfall).
Abstract: Electrical resistivity imaging of field-scale solute transport in the unsaturated zone of the Chalk in East Yorkshire is described. The study involved application of an electrically conductive tracer to the surface of an 18 m 2 plot at a rate of 49 mmd -1 for two days (representative of very heavy rainfall). The resistivity response of the upper 25 m over the following ten months is reported. These results are interpreted together with geological and hydrological data. The hydrogeological interpretation is that rapid bypass flow occurs along steeply inclined joints during high intensity rainfall in autumn and winter, but not usually during the summer. Joint saturation occurs locally, progressing upwards from horizons rich in thin marl layers.
TL;DR: The Folkestone Beds formation is a marine shallow-water deposit of Cretaceous age as mentioned in this paper, which consists mostly of poorly lithified sands which classify onto the sand/sandstone borderline, having properties neither akin to the classical concept of an engineering soil nor being strong enough to be labelled a rock.
Abstract: The Folkestone Beds formation is a marine shallow-water deposit of Cretaceous age. It consists mostly of poorly lithified sands which classify onto the sand/sandstone borderline, having properties neither akin to the classical concept of an engineering soil nor being strong enough to be labelled a rock . Intact samples were obtained by block sampling at 17 locations. Studies of the microfabric were made from thin sections prepared after epoxy resin impregnation. Although predominantly quartzose, the samples have a very wide range of grain sizes, size distributions, porosity and grain contact relations. The random inter-relationships amongst the microfabric parameters suggest that shelf sands, such as this formation, do not fit the patterns reported for deeply buried, and hence more diagenetically altered, sandstones. The majority are weakly cemented but samples from two locations possess negligible binding cement and are classed as locked sands . Measurements of the peak shear strength were carried out on air-dry samples of the intact sand using a 60 mm square, direct shear box. The peak shear strengths were strongly influenced by the intensity of interlocking: this factor being more significant than either porosity or total cement content. The samples possess a tensile strength, uniaxial compressive strengths up to 725 kPa and a cohesion intercept at zero normal stress in the shear box. The fabric cohesion reduces with increasing content of coarse sand and is very poorly developed in coarse sands.
TL;DR: Using the Dar Zarrouk parameters, a constant can be found which will simply translate resistivity to transmissivity, provided that either clay content or porosity is the primary control on resistivity and permeability.
Abstract: Surface electrical soundings can be used to extrapolate pumping test results over an area. Using the Dar Zarrouk parameters, a constant can be found which will simply translate resistivity to transmissivity, provided that either clay content or porosity is the primary control on resistivity and permeability. The applicability of the technique is tested on the gravel aquifer at Desborough Island, UK.
TL;DR: In this article, the degree of induration of Palaeogene limestones in Denmark has been measured by gamma-transmission measurements on whole cores, which are used both as a sampling guide in the core laboratory, and for assessing the degree in which the Limestone limestones are indurated.
Abstract: Density scanning by gamma transmission measurements on whole cores is here demonstrated to be valuable both as a sampling guide in the core laboratory, and for assessing the degree of induration of Palaeogene limestones in Denmark. Fracture intensity is also indicated. Moduli of elasticity calculated from acoustic velocities are systematically related to density (and thus porosity), so we have attempted to relate the degree of induration to the dynamic moduli of elasticity. The dynamic moduli of elasticity fall, as is commonly observed, above those measured from uniaxial compression tests. P-wave as well as S-wave velocities are anisotropic in the entire porosity interval (12%–44%). This is reflected in a significant anisotropy of the dynamic shear modulus at high densities, whereas the anisotropy for lower densities and for the dynamic Young9s modulus and dynamic bulk modulus remain below the level of significance. The anisotropy probably reflects minor horizontal fractures formed during exhumation of the limestone and unloading of the cores. The density scanning tool thus proves a useful method for determination of geophysical and geotechnical parameters.
TL;DR: In this article, a common orientation has been established between traced groundwater flow routes and the dominant northwest-southeast fracture trend within the Ulster White Limestone Formation, suggesting poor fracture connectivity and thus extreme aquifer heterogeneity.
Abstract: The Cretaceous Chalk in Northern Ireland (Ulster White Limestone Formation) is a locally important aquifer for both public and private supply, yet little is known about its groundwater flow regime. This issue is important for the protection of existing groundwater abstractions and for the development of new sources as it will help determine groundwater vulnerability and resource potential in the Chalk. The subject has been addressed using hydrochemical variations from individual springs, together with artificial and natural water tracing techniques employed from river-sinks located at outcrop. A common orientation has been established between traced groundwater flow routes and the dominant northwest-southeast fracture trend within the Ulster White Limestone Formation. Hydraulic gradient has also been shown to have little significance in controlling the flow direction, suggesting poor fracture connectivity and thus extreme aquifer heterogeneity. Tracer breakthrough curve characteristics and velocities (up to 2838 metres per day) are indicative of conduit rather than fracture flow. In addition, the highly variable water chemistry associated with all the proven river-sink supplied springs has been independently classified to meet conduit flow criteria. Conversely, the much less variable water chemistry associated with springs draining Chalk subcrop areas (with no influence from river-sinks) is consistent with a less active karstic regime.
TL;DR: In this paper, the combined use of cross-borehole electrical imaging and borehole television (CCTV) as methods for focusing the packer test was applied to a limestone aquifer.
Abstract: Double packer testing is a commonly used technique in hydrogeology for assessing vertical spatial variations of permeability in a borehole. In fractured rock systems, spatially continuous fractures are typically major transmissive features that control groundwater flow and solute transport. Efficient, cost-effective packer testing of fractured rock aquifers can be conducted by focusing the packer test on hydraulically conductive zones, defined using borehole geophysical techniques. The combined use of cross-borehole electrical imaging and borehole television (CCTV) as methods for focusing the packer test was applied to a limestone aquifer. CCTV identified features exposed in the borehole whereas Electrical Resistivity Tomography (ERT) revealed their spatial continuity and probable hydraulic significance. Whole borehole pumping tests were conducted to provide a check on the effectiveness of these methods as tools for guiding the packer test. Results from a set of boreholes in a fissured aquifer revealed the transmissivity estimates obtained from the whole borehole pumping test to be close to the sum of transmissivities obtained from focused packer testing of features identified using CCTV and ERT. The hydraulic properties of the aquifer were hence defined whilst avoiding intensive packer testing of the entire length of the boreholes.
TL;DR: In this article, a study of the hydrogeological controls on the Pleistocene Crag aquifer in northeast Norfolk is reported, where a laterally continuous clay horizon is identified at around -25 mOD and is mapped as far as the coast.
Abstract: A study of the hydrogeological controls on the Pleistocene Crag aquifer in northeast Norfolk is reported. Geophysical methods, in particular multichannel seismic reflection profiling, have provided useful information on the internal structure of the aquifer. The Crag represents a layered aquifer, with horizons of clay and silt strata able to limit the overall vertical permeability of the aquifer. A laterally continuous clay horizon is identified at around -25 mOD and is mapped as far as the coast. Shallow wells and borehotes in the Crag are prone to contamination. Nitrate is widely recorded, with concentrations of typically up to 150 mg l -1 in shallow wells, derived from mainly agricultural sources, although deeper boreholes are less affected given the restricted downward movement of ground-water. The land drainage systems within this lowland area dominate the hydrology and hydrogeology of the catchment. Surface flows into the River Thurne are controlled by the operation of drainage pumps and a catchment water balance demonstrates that groundwater principally discharges to the drainage ditches within the extensive arable and grazing marshes in the catchment.
TL;DR: A review of the catchment of the Lincolnshire Limestone aquifer and its associated models was carried out by as mentioned in this paper, which led to the development of improved methods of estimating the recharge due to runoff, identifying locations such as inliers of the Limestone in the river valleys where runoff can enter the aquifer system and representing leakage through the overlying strata in the east of the study area.
Abstract: Hydrogeological studies of the Lincolnshire Limestone aquifer in south Lincolnshire combined with the development of mathematical models were reported in the 1970s. However, these studies concentrated on the aquifer and did not consider the total catchment conditions of both the groundwater and surface water systems. Greater importance is now placed on understanding total stream and river flows and preparing models which can predict the change in flows due to different abstraction scenarios; this has required a complete review of ‘the catchment’ of the Lincolnshire Limestone and the associated models. This review has led to the development of improved methods of estimating the recharge due to runoff, identifying locations such as inliers of the Lincolnshire Limestone in the river valleys where runoff can enter the aquifer system, improving the representation of wild bores (uncapped overflowing artesian boreholes) and representing leakage through the overlying strata in the east of the study area. These developments now allow the simulation of total river flows, especially low flows. A novel type of diagram has been devised for representing inflows, outflows and changing flow conditions along the streams and rivers.
TL;DR: In this paper, a facility is described which is capable of simulating climatic parameters and pollution activated effects, which can be induced simultaneously or individually and in real-time or cyclic mode.
Abstract: A facility is described which is capable of simulating climatic parameters and pollution activated effects. These can be induced simultaneously or individually and in real-time or cyclic mode. The behaviour of materials and associated construction technologies can be continuously monitored by visual inspection and computer controlled data acquisition and analysis systems, thus making possible realistic prediction of ‘in-service performance’ and probable durability.
TL;DR: In this article, a novel seismic method for determining the variation of velocity with depth of horizontally propagating, horizontally polarized shear waves (S h,h ) has been proposed, which exploits the curved paths of seismic waves in deposits with increasing velocity properties with depth.
Abstract: The paper describes a novel seismic method for determining the variation of velocity with depth of horizontally propagating, horizontally polarized shear waves ( S h,h ). The technique exploits the curved paths of seismic waves in deposits with increasing velocity properties with depth. The new method has been applied at the soft clay test site at Bothkennar, and the results of this survey are compared with S h,h and S v,h wave velocity profiles obtained using conventional crosshole survey techniques at the site. The seismic data are further compared with the results of recently reported bender element tests on unconfined samples from the bedded and mottled Bothkennar clay. It is shown that, at the site investigated, the new method presents results comparable to those from the established field survey techniques. Neither the seismic nor the bender element data indicate significant stiffness anisotropy at the site.
TL;DR: In this article, the authors compared actual yields from sand and gravel excavations with reserve calculations based on drilling and found that, in a majority of cases, the measurement of reserves using conventional techniques is accurately carried out.
Abstract: Little work has been published that compares actual yields from sand and gravel excavations with reserve calculations based on drilling. To do so sites must meet criteria of clear identification; in-house site investigation; full drilling; and properly recorded production. There are several potential sources of difference between calculated and actual figures. Twenty-six sites were investigated, yielding from 63.64% to 152.400f calculated reserves. The mean of the results is 104.37%, the median 104.31% and the mode group 107.0–109%. This analysis confirms that, in a majority of cases, the measurement of reserves using conventional techniques is accurately carried out. A variance of ± 5 0s suggested as the geologist9s target.
TL;DR: In this paper, the basic test and evaluation requirements necessary for a successful competency assessment of the contaminant attenuation capability of clay soils are discussed, and two clay soils from South Wales were chosen for study.
Abstract: This study focuses on the basic test and evaluation requirements necessary for a successful competency assessment of the contaminant attenuation capability of clay soils. Two clay soils from South Wales were chosen for study. Of particular interest is the problem of specification of ‘ necessary and sufficient tests ’ for proper assessments of competency. The tests and evaluation protocols leading towards confident competency assessment of the candidate clay soils are developed. Soil column leaching studies, together with results from analyses of the physicochemical and mineralogical characteristics of the soils, are used to determine clay soil contaminant attenuation capability. The results demonstrate that reliance on a limited amount of information can lead to some inappropriate premature interpretations that can prove to be harmful. In a situation where attenuation of dissolved metals is important, only one of the soils tested is considered to be an adequate clay soil for a clay engineered barrier.
TL;DR: In this paper, a study on the influence of calcium carbonate content on the physical characteristics and compressibility parameters of Pliocene lacustrine deposits is discussed, and it is shown that the yield stress for cemented materials corresponds to the partial disruption of the structure.
Abstract: The results of a study on the influence of calcium carbonate content on the physical characteristics and compressibility parameters of Pliocene lacustrine deposits are discussed. The origin of CaCO 3 has been investigated and it is thought to have been precipitated, after consolidation, as cement which partially filled the void spaces between soil particles. Average CaCO 3 content was about 22% along a 116.5 m deep vertical profile. The CaCO 3 in the clay and silt fractions (CaCO 3 *) was considered the best available estimate of that acting as cement. The relationships reported in the literature between Atterberg limits and CaCO 3 content have been statistically confirmed by the tests performed on decalcified laboratory samples, but not by those performed on natural samples due to lithological heterogeneities. Yield stress, constrained modulus, swelling index and microstructure resistance were affected by CaCO 3 * content in the stress range lower than yield stress. In the stress range higher than σ′ vy , no relationship was observed between C c and CaCO 3 , while an inverse relationship between C s and CaCO 3 was observed in both the natural and remoulded samples and thus is thought to be due to the presence of inactive calcite. Moreover, the remoulded samples also show an increase in C s with respect to the natural ones. From these findings it follows that the yield stress for cemented materials corresponds to the partial disruption of the structure.
TL;DR: In this article, the authors applied four geophysical methods to characterize the spreading ground downstream of these sites and to guide drilling of test bores to guide the construction of recharge dams for temporarily impounding flood flows from the Northern Oman Mountains.
Abstract: Sites in the interior of the Sultanate of Oman have been considered for the construction of recharge dams for temporarily impounding flood flows from the Northern Oman Mountains. Impounded water would be discharged under control to infiltrate into downstream aquifers. Four geophysical methods were applied to characterization of the spreading ground downstream of these sites and to guide drilling of test bores. The main aquifers occur in permeable zones at the base of the alluvium and in the upper, weathered, bedrock. The alluvium is variably cemented and clay rich, and behaves as a confining layer between the shallow, unconsolidated surface infiltration zone and the aquifer. The thickness of the upper unconsolidated layer of boulders and gravels was most accurately mapped with seismic refraction or vertical electrical sounding (VES). These methods were slow to apply in the arid, bouldery ground conditions and surveying was in places constrained by the wadi walls. Gravity survey, with control provided by VES, was a rapid method of profiling the total thickness of alluvium and weathered zone overlying the denser and more resistive unweathered ophiolite bedrock. VES was usefully supplemented by simultaneously measured induced polarization (IP) soundings which respond to the distribution of clay minerals. Transient electromagnetic sounding (TEM) proved to be the most rapid method of survey as no ground contact was required. Alluvial thickness was interpreted by resistivity-depth modelling of TEM data and was most reliable over low-resistivity argillaceous mudstone or shale bedrock.
TL;DR: In this article, a program of high-resolution shallow seismic surveys are described, including 3 km of refraction and 1 km of shallow reflection profiling, showing that the Quaternary drift cover is variable in composition and thickness with a maximum thickness of 80 ± 8 m. The spatial distribution of refractor velocities is discussed.
Abstract: Porth Neigwl is a 6 km wide, drift-filled embayment, located on the Llyn Peninsula of northwest Wales, UK. The embayment is surrounded by hills formed of Lower Palaeozoic Rocks. Infilling the embayment is a 17 km 2 area of thick Quaternary deposits which are well exposed in the sea-cliff. These deposits have been studied intensely over the past century. However, previous workers have made little reference to the total extent or architecture of the Quaternary deposits that lie below present sea level and nothing is known about the rockhead geometry. A programme of high-resolution shallow seismic surveys are described, including 3 km of refraction and 1 km of shallow reflection profiling. Refraction results show that the Quaternary drift cover is variable in composition and thickness with a maximum thickness of 80 ± 8 m. However, results indicate that rockhead within the embayment lies consistently at an elevation of around - 32 m OD. The spatial distribution of refractor velocities is discussed. High-resolution shallow reflection surveys identify three major Quaternary sequences below present sea-level that are consistent across the area. This study demonstrates that combined seismic refraction and reflection studies are very useful in the rapid analysis of Quaternary stratigraphy and spatial depth to rockhead variations in areas of thick drift.
TL;DR: In this article, the authors presented the results of measurements made using these three methods on granular soils during investigations for the construction of the Nigg Bay fabrication yard, Cromarty Firth.
Abstract: Three methods are frequently adopted to measure the permeability of granular soils: determinations made on the basis of the soil9s particle size distribution; on the results of in situ rising or falling head tests; and on the results of in situ pumping tests. The paper presents the results of permeability tests made using these three methods on granular soils during investigations for the construction of the Nigg Bay fabrication yard, Cromarty Firth. Of the methods based on particle size distribution, the one due to Masch & Denny was found to give results closest to the pumping test values. Permeabilities calculated using Hazen9s rule were significantly higher than the pumping test results, while those calculated from the results of in situ falling head tests were significantly lower. On the basis of the results presented, there would appear to be a case for the adoption of a method such as Masch & Denny9s for permeability estimation of granular soils.
TL;DR: In this article, ground penetrating radar was used along a 350 m stretch of the highway to investigate the number and extent of scour holes beneath the carriageway, and the results provided a basis for prioritizing countermeasures designed to repair the highway foundations and ensure the public safety.
Abstract: At Nant-y-Garth Pass, the A525 Wrexham to Ruthin Road is susceptible to undermining due to the scouring action of an adjacent fast-flowing stream. Concealed scour cavities were suspected following manual probing but the full threat posed to the integrity of the carriageway and to the safety of road users remained uncertain. Ground penetrating radar was used along a 350 m stretch of the highway to investigate the number and extent of scour holes beneath the carriageway. The survey identified extensive subsurface voiding with distinct anomalies associated with shallow cavities measuring up to 9 m long by 0.2 m high and extending as far as the centre of the road. More subdued radar features were interpreted as scoured pockets where fine-grained debris had been washed out and the remaining material had been disturbed and loosened. The results provided a basis for prioritizing countermeasures designed to repair the highway foundations and ensure the public safety.
TL;DR: The A55 North Wales Coast Road between Chester and Holyhead forms a strategic part of Euroroute E22 (Sassnitz to Dublin) and provides a major artery to the British and European motorway network for traffic arising not only from North Wales but also from Ireland via the international ferry terminal at Holyhead.
Abstract: The A55 North Wales Coast Road between Chester and Holyhead forms a strategic part of Euroroute E22 (Sassnitz to Dublin) and provides a major artery to the British and European motorway network for traffic arising not only from North Wales but also from Ireland via the international ferry terminal at Holyhead (Fig. 1). The highway comprises 145km of modern dual carriageway. Unfortunately rockfall activity poses a significant geohazard in the vicinity of the mountainous headland at Pen-y-Clip and especially affects the westbound carriageway approaches to the road tunnel through the headland (Fig. 2). This area has a history of high rockfall frequency and, in 1984, a rock avalanche blocked the headland road and caused a two week closure (McWilliam 1991). At Pen-y-Clip, steep slopes and adverse geological factors combine to create potentially unsafe ground above the road. The Pen-y-Clip promontory constitutes a natural obstacle along the coastal plain and routes tend to converge towards the seaward point of the headland. The Pen-y-Clip road tunnel, opened to traffic in October 1993, was driven through the headland and a wide variety of rockfall protection measures including rockfall checkfences were incorporated into the design and construction of the project (Brady et al. 1994). The checkfences were installed in advance of construction to protect the workers on the scheme and to safeguard the headland road particularly against rockfall initiated by blasting during construction. Geologically, the headland at Pen-y-Clip comprises a core of igneous rocks associated with the Penmaenmawr intrusion (Fig. 3). The intrusion measures
TL;DR: The Claygate Beds and Bagshot Beds are the uppermost formations of Eocene age in south Essex, the former resting on the London Clay and the latter on the Bagshot Clay as discussed by the authors.
Abstract: The Claygate Beds and Bagshot Beds are the uppermost formations of Eocene age in south Essex, the former resting on the London Clay. The Claygate Beds consist primarily of silts and clays with subordinate sands, whilst sands are more common in the Bagshot Beds. The paper describes the geotechnical properties of these two sedimentary units. The results form part of a larger study of the engineering geology of south Essex. The sands, particularly in the Bagshot Beds, are fine grained. All the sands are uniformly sorted and negatively skewed. Quartz is the principal minerals in these beds and in the fine material, mica, montmorillonite, kaolinite and chlorite figure in that order of relative abundance. The geotechnical properties of the silts and clays of both formations are generally similar. However, the plasticity of the Claygate Beds tends to decrease somewhat from the lower to the upper division and the range of plasticity is greatest in the upper division. This may be due to the greater variation in quartz content and montmorillonite content in the latter division than in the two others. The clays in both formations tend to have normal activity whilst that of the silts is both normal and active. The values of the undrained shear strength parameters, especially in the sandy material, are influenced by the amount of cement present, and the degree of interlocking of grains and the degree of compaction. The undrained shear strength of the silts and clays suggests that they range from soft to very stiff.