bluuebunny/crossref_metadata_2025 huggingface dataset:
Wells ancient and modern—an historical review
Authors: Hardcastle B. J.
Published: November 2007

The practices of locating, digging and boring wells, raising water from them, providing well-head protection and speculating about the source of groundwater, are of great antiquity. Methods and ideas changed little until the Industrial Revolution. Steam power facilitated increased abstractions, and wells, adits and boreholes constructed by development of traditional methods, peaked by the end of the 19th century. By then, the scientific understanding of geology and of seepage towards wells had been founded. Thereafter, drilling and pumping technology and ground-water theory progressed rapidly. Awareness of the need for conservation by comprehensive management of resources grew, resulting in legislation which led to accelerated understanding and new modes of operation.
The development of crystalline basement aquifers in a tropical environment
Authors: Acworth R. I.
Published: November 2007

Chemical weathering is the dominant process in the development of a weathering profile on crystalline basement rocks. In the saturated lower part of the weathering profile, groundwater is the principal chemical reagent and the rate of groundwater flow determines the rate of weathering reactions.

The search for successful borehole sites in this environment also depends upon finding locations where the rate of groundwater flow is at an optimum. This search could therefore be facilitated by an appreciation of the part which groundwater flow plays in the chemical weathering process.

The principal factors which control the quantity of groundwater flow through a unit cross sectional area of the weathering system are the availability of recharge, the permeability of the weathered material and the hydraulic gradient between the recharge and discharge areas. Of these three, the importance of recharge is clear as this determines the input to the groundwater system. The permeability of the weathered material is a function of the extent of chemical weathering and is therefore intrinsically linked to the history of groundwater flow through the system. The remaining independent variable is the hydraulic gradient. This is normally developed in what is generally a relatively thin weathered layer which closely follows the surface morphology. The hydraulic gradient is therefore a function of the average surface slope over the groundwater flow path and therefore related to the surface morphology.

A plot of recharge against surface morphology therefore becomes a valid projection upon which the various groundwater provinces can be plotted and provides a useful means of classifying the various occurrences of groundwater within the weathered profile.
Pilot study of an aggregate abrasion test for breakwater armourstone
Authors: Latham J.-P. , Poole A. B.
Published: November 2007

The long-term performance of the materials out of which breakwaters and coastal protection works are constructed depends not only on physico-chemical degradation processes but also on the mechanical abrasion resistance of the rock or concrete used. The abrasion of breakwater armourstone affects the armour layer stability directly by causing weight loss from the rock blocks. Another important though unquantified source of stability reduction in the armour layer is the progressive rounding of armour by abrasion leading to poor interlocking between individual blocks and their neighbours (see the discussion of this phenomenon by Dibb
et al.
1983).
Gupta (1985) and others have demonstrated that there is a relative decrease in aggregate (macro)porosity for rounded compared with angular fragments. Such a decrease in an armour layer porosity due to the rounding of blocks may have a deleterious effect on energy absorbing properties of the layer. The assessment of abrasion resistance is therefore of great interest to the engineer concerned with in-service deterioration of armour layer performance. New quantitative methods for measuring the effects of abrasion on the entire profile of the breakwater armour layer were reported by Latham & Poole (1986).
Several standard engineering tests and analytical procedures have been recommended for the assessment of suitability of a particular rock for breakwater core and armour material (Fookes & Poole 1981; Allsop
et al.
1985). The test values recommended for acceptance by Allsop
et al.
are drawn from a list of tests which does not include an abrasion resistance test, although several abrasion
Indexing the engineering properties of residual soil
Authors: Vaughan P. R. , Maccarini M. , Mokhtar S. M.
Published: November 2007

The geological study of the formation and structure of
in situ
residual soils is well advanced; the study of the engineering properties of these soils much less so. In particular, no methods exist whereby mechanical properties can be related to geological descriptions, or to simple index tests, as is done for sedimentary soils. The methods for sedimentary soils are inappropriate for residual soils, yet no alternatives have been developed.

Most residual soils are weakly bonded, and they may have widely varying void ratios. A laboratory study of how these two features influence engineering behaviour is being conducted, based mainly on the testing of an artificial material in which both can be varied under control. Initial results from this study show that engineering behaviour depends on the void ratio of the soil related to that which the soil can have in the un-bonded ‘de-structured’ state. This indicates that it is useful to index the
in situ
void ratio of residual soils in relation to void ratio in the de-structured state, in a manner similar to the indexing of sands by relative density or of sedimentary clays by liquidity index. Simple methods whereby this may be done are suggested and discussed.
Causes of non-linear step pumping test responses
Authors: Rushton K. R. , Rathod K. S.
Published: November 2007

Step pumping tests are frequently used to examine the performance of wells. It is usually assumed that the drawdown in a pumped well due to a discharge
Q
can be divided into two parts, the formation loss
BQ
and a non-linear loss

CQ
n

which depends on the conditions in the vicinity of the well. This paper demonstrates that the actual response due to step pumping tests is often more complex.

As an aid to understanding the complexity of step tests, the effect of various conditions in the vicinity of the pumped well and in the aquifer are represented by a radial and vertical flow numerical model. Conditions which are represented include changes in hydraulic conductivity with discharge rate, a seepage face forming in the well, zones of lower hydraulic conductivity or higher hydraulic conductivity within the aquifer, the aquifer changing from the confined to unconfined state in the vicinity of the well and a reduction in the effective depth of penetration due to the collection of sediment in the well. Results from numerical model simulations indicate that there are distinctive discharge-drawdown relationships for each situation. Field examples are presented which illustrate how certain of these responses can be observed in practical situations.
Rehabilitation of clogged discharge wells in the Netherlands
Authors: van Beek C. G. E. M.
Published: November 2007

During the last ten years much research has been conducted by KIWA, in close cooperation with various waterworks, into the rehabilitation of clogged production wells. During this research it became apparent that various types of clogging could be distinguished. One type of clogging is caused by the mixing of groundwaters with incompatible chemical compositions in the well itself, due to the vertical chemical heterogeneity of groundwater in the aquifer. Another type of clogging is caused by the increased velocity of groundwater flow near the borehole, which increases the intensity of various biological and chemical processes. The selection of the correct method of rehabilitation, the rehabilitation results, and the costs, all depend on the type of cloging that has occurred.
Attenuation from seismic refraction surveying as a ground investigation aid
Authors: Murphy B. J. , Rosenbaum M. S.
Published: November 2007

Ground investigation applications of the seismic refraction technique are briefly reviewed and the rock mass parameters which may be obtained from seismic velocity discussed. The phenomenon of seismic attenuation is explained and techniques for its measurement described. The pulse broadening technique is found to give the best measure of seismic attenuation.
The use of soil fabric studies in evaluating the strengths of clays in a North Sea site investigation
Authors: Marsland A. , Love M. , Løken T. , Lunne T.
Published: November 2007

Soil fabric features influence both the large-scale engineering properties and measurements made in laboratory and field tests. The effects on the large-scale parameters and different types of tests can vary appreciably. In the absence of relevant full-scale test data from the site being investigated, fabric studies can play a vital role in the evaluation of design parameters from laboratory and small in situ tests. This is especially the case where relationships between test and large scale behaviour have previously been obtained in soils with similar fabric features and stress histories. The potential value of fabric studies is particularly important in offshore investigations where large-scale in situ tests are not feasible and even the data from laboratory and small in situ tests are severely limited. During a major investigation for a gravity platform in the Norwegian sector of the North Sea in 1981 it was found that the relationships between the results obtained from the different types of tests did not fit into the patterns previously found at other North Sea sites. The need to explain these anomalous results and the availability of adequate numbers of good quality samples provided an excellent opportunity to make extensive observations and measurements of the soil fabric features and to use them in the interpretation of the test data and the evaluation of design parameters. This paper describes the detailed macro-and micro-fabric studies which were made and their role in explaining the anomalies in the test data and in the evaluation of the design parameters.
Drilling fluid invasion and permeability impairment in granular formations
Authors: Howsam P. , Hollamby R.
Published: November 2007

In water well drilling the clogging of the formation due to drilling fluid invasion is a process of which most engineers/ geologists are aware but may not fully understand. Some simple laboratory test rigs are described. These were used to examine the damage mechanisms and damage potential of several drilling fluids. This work did not include a study of damage removal. The results show that solids content and rheology are the main factors influencing the type and degree of damage, as defined by the location and amount of permeability reduction. Whilst skin damage is the most obvious and occurs with many fluids, internal damage is equally significant and could be the most difficult to remove. With internal damage it is important to remember that the fluid which introduces the damage is not usually the same as that used to try and remove it.
Field trial of an ejector well dewatering system at Conwy, North Wales
Authors: Powrie W. , Roberts T. O. L.
Published: November 2007

An ejector or water jet pump is particularly suitable for pore water pressure relief applications in fine soils since it can operate at relatively low pumped flowrates, creating a vacuum at depth inside the well. A field trial of an ejector well dewatering system was carried out in laminated glacial lake deposits at Conwy, North Wales, in connection with the construction of the A55 Conwy Crossing. During the trial groundwater extraction flow rates and pore water pressures were monitored. Some of the ejector wells terminated in the bedrock underlying the lake deposits: in many of these, the groundwater extraction flow rates were high and the drawdowns achieved were relatively low. Back-analysis using conventional methods modelled closely the observed response of near-by piezometers. On the other hand, wells terminating in the lake deposits yielded low groundwater extraction flow rates and vacuums at about 500 millibar developed. In this case, conventional analysis substantially overpredicted both the rate and magnitude of drawdown in the surrounding ground. The reasons for this are as yet uncertain: nonetheless, the results of the trial demonstrate clearly the influence of the hydraulic boundary conditions on the performance of a dewatering system.
The passivity of steel in concrete
Authors: Leek Darrell S.
Published: November 2007

This paper describes the chemical nature of concrete and the internal environment in which the steel reinforcement is situated. The electrochemical basis for passivity of iron in aqueous solution is discussed and the anodic and cathodic reactions which occur are detailed in relation to pH-potential (Pourbaix) and current-potential (Evans) diagrams. The observed behaviour of iron in solution is compared to the behaviour of reinforcement in concrete. The breakdown of the passive film is discussed in relation to the commonly observed causes of deterioration of reinforced concrete i.e. carbonation of concrete, the presence of chloride ions at the steel surface and sulphate attack. Results of an SEM-EDS study of chloride-induced breakdown of the passive film are presented. The effects of the surface condition of the reinforcement prior to its inclusion in concrete and the use of latent hydraulic binders and thermosetting plastic coatings (fusion bonded epoxy) in relation to passivity and corrosion behaviour are discussed.
Discussion on ‘Modification of the formula used in the determination of the ten per cent fines value of aggregate’
Authors: Gribble C. D.
Published: November 2007

C. D. G
ribble
writes: I read the technical note by J. C. Bullas with interest. He discusses the value of
K
used to estimate the value of force (in kN) which must be applied to a sample of aggregate to obtain ten per cent fines in the expression:

Force (kN) =
K
/AIV.

The reduction he suggests in the value of
K
from 4000 to 2800 is based upon samples of crushed rock aggregates, i.e. all the samples were obtained from aggregates produced by crushing various types of hard rock. I and other workers have found that the previous value of
K
= 4000 works quite well when testing aggregate from sand and gravel sources. I plotted the 10 0.000000ines values and AIV data from samples of gravel, given in various
Mineral Assessment Reports
(1981-1986), in a graph similar to the one used by Mr Bullas. On to this graph (
Fig. 1
) I superimposed a nest of hyperbolic curves with
K
= 2000, 3000, 4000 and 5000. From this graph the best fit curve is one with
K
= 4250.

I would therefore suggest that two values of
K
are needed:

(i)
K
= 2800 for aggregate from crushed rock sources which is the one proposed by Mr Bullas in his paper;

(ii)
K
= 4000 for aggregate from sand and gravel sources, which is the value of
K
previously used in this type of calculation
Chemical reaction between concrete and natural groundwaters and its implications for the commissioning of observation boreholes in chalk
Authors: Song Lin-Hua , Atkinson T.C.
Published: November 2007

Four purpose-constructed observation boreholes in chalk were found to contain water with pH of 10-11.5 and abnormal chemistry within fourteen months of commissioning. Experiments show that this was due to contamination by alkaline porewater solutions from the concrete grout used in construction. Contamination was still detectable nearly three years after construction but was cleared by pumping. A six-hour pumping test is recommended as standard procedure during commissioning of observation boreholes.
Some observations on a comparative aerial photography interpretation of a landslipped area
Authors: Fookes P. G. , Dale S. G. , Land J. M.
Published: November 2007

All aerial photography interpretation must be used with caution. When well done and supported by ground truth exercises they can be a valuable aid to site investigation, depending on the quality and scale of the aerial photographs and the skill and background of the interpreter.

A rare situation has arisen where eight interpretations of a landslip complex in gently folded Tertiary marine sediments overlain by young colluvium and covered by dense equatorial rainforest were made by different professional interpreters. This is used as an opportunity to illustrate the potential difficulty in obtaining a reliable interpretation.

Five of the interpretations were made without knowledge of a major new landslip which occurred in an area of existing landslips and three were made with knowledge of the new landslip, all using the same pre-major new landslip aerial photographs. Of the five made without knowledge of the new landslip, two did not identify existing landslips at the site and three partially identified landslips but each in a different configuration. With knowledge of the new landslip the interpreters identified old features in the aerial photographs similar to the features produced or exposed by the new landslip.
Hydrogeology of the Saq Formation east of Hail, northern Saudi Arabia
Authors: Hussein M. T. , Bazuhair A. G. , Ageeb A. E.
Published: November 2007

The study area lies about 120 km to the east of Hail in northern Saudi Arabia, covering a surface area of some 350 km2. The paper considers its general hydrogeological situation including information on groundwater occurrence and movements within the Saq Formation, aquifer parameters, groundwater composition and variation. Heavy pumping from 186 deep wells with an average discharge of 1800 gallons/min has resulted in a continuous drop in the groundwater level since 1982 and its effects on major ionic composition for the period 1982–1989 are discussed.
Sensitivity of sandstone strength and deformability to changes in moisture content
Authors: Hawkins A. B. , McConnell B. J.
Published: November 2007

The loss in uniaxial compressive strength between UCS
dry
and UCS
sat
for 35 British sandstone types is discussed. The difference between UCS
dry
and UCS
sat
for the clay-rich Cretaceous Greensand was 78% while for the Siliceous Sandstone the strength decreased by only 8%. Over the whole range of sandstones, however, the view that the weaker varieties are more sensitive to moisture content is not supported. The degree of sensitivity to moisture content is controlled primarily by the proportions of quartz and clay minerals present and to a lesser extent by the rock microfabric. Research indicates that the development of pore pressure during loading is negligible especially in pure sandstones and hence does not play a significant role in moisture related strength reduction.

The work has demonstrated a large variation in sensitivity to moisture content throughout the range of sandstones studied and has shown that an increase in moisture content of as little as 1 0.000000rom the dry state can have a marked effect on both strength and deformability. A classification scheme for moisture content sensitivity is proposed.
Application of shallow reflection techniques in hydrogeology
Authors: Davies K. , Barker R. D. , King R. F.
Published: November 2007

Shallow seismic reflection surveys have a range of application in groundwater investigations particularly where a precise solution to a subsurface problem is required. Recent surveys have mapped depth to bedrock, depth to water table, structure within alluvial deposits and the positions of old mineworkings. Example surveys from Down Ampney illustrate the application of shallow reflection surveys in the precise location of structural faults.
Automated monitoring and interactive data evaluation for a gravel aquifer in central London
Authors: Evans Neil A.
Published: November 2007

Scott Wilson Kirkpatrick was commissioned by CIRIA in 1990 to undertake an investigation into the impact of urbanization on the Thames Gravel Aquifer of central London. As a part of this investigation, a computerized approach to data handling was adopted. This paper describes the approach, from the use of downhole data loggers for monitoring groundwater and hydrological parameters, through to the analysis of field data using a lumped parameter model constructed on a spreadsheet and a geographical information system developed in-house. The advantages and disadvantages of this particular combination of computer hardware and software for aquifer monitoring studies are discussed.
A review of the attenuation of trichloroethylene in soils and aquifers
Authors: Bourg Alain C. , Mouvet Christophe , Lerner David N.
Published: November 2007

The transport, transformation, sorption and volatilization of trichloroethylene (TCE) as a non-aqueous phase liquid (NAPL) and as a dissolved aqueous constituent, under both laboratory and field conditions, are reviewed.

NAPL-TCE is expected to migrate quite rapidly in soils and other water-unsaturated conditions, leaving droplets of organic liquid in the pore spaces. At the water table level, TCE may stop its downward movement and diffuse laterally, together with a slow migration downwards. From there on NAPL-TCE will slowly dissolve in groundwater. However, some specific hydraulic characteristics may induce rapid transport downwards away from the water table.

TCE may appear in soils and aquifers as a result of its wide industrial use and also, possibly, as a degradation by-product of other chlorinated hydrocarbon solvents. TCE can undergo abiotic and (mostly) biotic, aerobic and (mostly) anaerobic transformations leading to less chlorinated ethenes. A half-life of 300 days was observed under field conditions.

Batch and column experiments show that TCE is weakly sorbed on soil and aquifer solids with linear partition coefficients. Retardation factors in the range of l to 9 are reported from laboratory and field investigations. The adsorption is almost fully reversible.

Gaseous TCE is more adsorbed than aqueous TCE, the extent of uptake being greatly influenced by the moisture content of the solid. Soil gas surveys appear as a promising technique for the study of soil and groundwater contamination by TCE.

NAPL-TCE contamination should be quite effectively removed by steam injection. Because of its low adsorption and weak degradation under aerobic conditions, the diffuse contamination of aquifers by dissolved TCE can be extensive. In the case of localized and more severe pollution, approaches for the restoration of aquifers based on pumping followed by treatment at the surface may be effective but they usually are not economical. In situ treatment by stimulating the biotrans-formation is considered as a favourable alternative.
Great Man-Made River Project, Libya, Phase I: a case study on the influence of climate and geology on concrete technology
Authors: Fookes P. G. , Stoner J. R. , Mackintosh J.
Published: November 2007

The paper discusses the principal climatic and geological features influencing the design and manufacture of the large (1.6 to 4m) prestressed concrete cylinder pipes used in the 1900 km of the wellfield collector and main conveyance lines of Phase I of the Libyan Great Man-Made River Project.

Pipe design and manufacturing processes are outlined and the winning and processing of aggregates are discussed. Particular reference is made to the extremely aggressive climatic and geological conditions and to the methods employed to overcome them successfully.
Simple generalized methods for estimating aquifer storage parameters
Authors: Younger P. L.
Published: November 2007

In many practical applications, hydrogeologists are called upon to predict aquifer behaviour in areas devoid of pumping test data. Estimations of transmissivity may sometimes be made from specific capacity records, but in general storage parameters (specific yield and storativity) are not readily obtainable. Existing methods for estimating these parameters are few and inaccurate, especially for storativity (
S
). By returning to the basic definition of confined aquifer storage, a simple method has been developed for estimating
S
as a function of aquifer lithology and thickness alone. Variations in aquifer porosity (which are often difficult to quantify) are neglected in this formulation and numerical experiments have shown that the errors introduced by this assumption are negligible except for indurated aquifers of low compressibility (α < 10-
10
ms
2
/kg). Porosity can be more easily determined for these aquifers than for unconsolidated aquifers of higher compressibility and a more accurate calculation of
S
can thus be made. This method has been tested against storativities derived from pumping test data for wells in the Altiplano of Bolivia and a good correlation between estimates and field values was found. The importance of obtaining good estimates for
S
is illustrated by reference to a typical problem encountered in a development project in the Altiplano, where the increased accuracy obtained using the new method (instead of older less rigorous methods) has beneficial consequences for the local community.
Geotechnical assessment of some charnockites from Nigeria as construction materials
Authors: Eze E. O.
Published: November 2007

Charnockites are a distinctive type of granite characterized by coarse-grained texture and the presence of pleochroic hypersthene and perthitic feldspars. They occur worldwide mainly in the Precambrian shield areas but are not as abundant as other rocks of granitic affinity.

Laboratory test results for three charnockites from Nigeria indicate good quality materials that are fairly comparable in many aspects with the more tried and tested granites. However, the coarse-grained texture, the relatively high percentage loss values in the aggregate crushing value test as well as the Los Angeles abrasion and sulphate soundness values, which only just meet acceptance limits seem to indicate possible poor performance, particularly where they are to be subjected to significant impact, cavitation and scour. The compressive strengths of the samples fall below 200 MPa, which is generally considered a good average value for aggregate for most civil engineering works. However, the disparity between test results and performance records of some rocks, local availability of a rock and the high ratio of transportation to production costs of crushed stone all militate against any disadvantage these somewhat poor test results may indicate charnockites have when compared with more established rocks.
Hydrogeochemistry of Millstone Grit and Coal Measures groundwaters, south Yorkshire and north Derbyshire, UK
Authors: Banks David
Published: November 2007

A pilot study has been performed to ascertain the baseline hydrochemistry of both shallow (springs) and deep (borehole) groundwaters of the Millstone Grit and Coal Measures. In terms of major ion composition the majority of the shallow groundwaters in the two formations are rather similar (typically Ca/Mg-SO
4
2-
/HCO
3
-
). The deep groundwaters show more variability. In some boreholes, marked seasonal temperature fluctuations and chemical compositions similar to shallow groundwaters indicate short residence times. In contrast, several boreholes in the Coal Measures indicate highly reducing conditions, evidenced by sulphate reduction and spectacular methane exsolution at two sites in Sheffield. Some deep Coal Measures groundwaters show elevated chloride concentrations compared with shallow waters, which may indicate the influence of deep formation brines, while others yield sodium bicarbonate waters indicative of cation exchange. At the other extreme, highly oxidizing conditions, e.g. in broken ground at the Mam Tor landslip, promote pyrite oxidation and yield acidic, ferruginous waters with high contents of heavy metals including uranium and thorium. At three sites in the Coal Measures, sampling of radon was feasible, yielding values in the range 8–32 Bq/l.
Land drainage and saline intrusion in the coastal marshes of northeast Norfolk
Authors: Holman I. P. , Hiscock K. M.
Published: November 2007

Land drainage has caused a significant increase in surface water salinity in the River Thurne catchment of northeast Norfolk which is related to saline intrusion in the underlying Crag aquifer. A survey of surface water C1 concentration revealed values ranging from <100 mg 1
-1
to >12 000 mg 1
-1
, with C1 exceeding 10 000 mg 1
-1
at the centre of the coastal marshes. In the sub-surface, an electromagnetic induction survey demonstrated elevated apparent conductivities of 100–200 mS m
-1
at the greatest exploration depth, except for areas having higher topography where fresh, or slightly brackish water persists. An electrical resistivity survey identified a low true resistivity layer (typically <1 Ωm), assumed representative of saline water, at a depth of typically <10 m below sea level under the coastal marshes. Higher land associated with dunes and isolated blocks of elevated land within the marshes gave a saline interface at 10–15 m below sea level, and beneath the catchment watersheds at >20 m. Solute transport modelling of an artificial vertical section through the aquifer supports the field observation that the distribution of surface water salinity is primarily determined by the spatial distribution of water levels in the main drains, all of which are maintained below sea level by pumping.
Modelling the hydraulic relationship between the River Derwent and the Corallian Limestone aquifer
Authors: Carey M. A. , Chadha D.
Published: November 2007

The River Derwent in North Yorkshire has been identified by the Environment Agency as a river with a high priority for flow alleviation due to low flows during summer months. The river flows across the Corallian Limestone aquifer and loses flow to this aquifer, via a set of solution hollows in the stream bed. This loss in flow has been gauged, as of the order of 15 to 35 Ml/day, and in dry years the entire river flow can be lost to the aquifer. Groundwater abstraction from the Corallian Limestone aquifer varies seasonally, and is currently between 25 and 35 Ml/day, with the higher rates of pumping occurring during the summer months. One of the main groundwater abstractions is for public water supply, and this source is located about 1.5 km from the river. Abstraction from this source is largely sustained by the leakage from the river.

The Corallian Limestone aquifer and its hydraulic relationship with the River Derwent has been represented using the USGS modelling package MODFLOW, to improve the understanding of the flow regime and to provide a tool to assist in the evaluation of different water resource management options. This model has provided a good representation of the aquifer system, and in particular has shown that leakage from the River Derwent is a key factor in controlling the groundwater regime and in maintaining a water balance for the aquifer. The model has been used to examine different management options for the aquifer system, including the influence of reducing the volume of water available to leak through the river bed on the groundwater abstraction sources.

This paper will describe how the model has been applied to this aquifer system, the benefits obtained and the problems encountered.
Determination of aquifer properties in northern Qatar for application to artificial recharge
Authors: Streetly M. J. , Kotoub S.
Published: November 2007

The aquifer system in Qatar has been heavily exploited for agricultural purposes for over 20 years, leading to a decline in groundwater quality. In 1992 the Ministry of Municipal Affairs and Agriculture appointed Entec to carry out a two-year study into the feasibility of using artificial recharge to restore the aquifer system. This study involved field testing and modelling of the Rus and Umm Er Radhuma (UER) aquifers at four sites. Step, constant rate and tracer injection/reabstraction tests were carried out on each aquifer at each site.

The step tests on boreholes in the UER indicated that non-Darcian behaviour occurred in the aquifer and extended a significant distance from the pumping boreholes. This was not observed during the step tests on boreholes in the Rus. A variety of techniques were used to analyse data from the constant rate tests and these provided a range of values for standard aquifer parameters as well as allowing a conceptual model of flow processes in the aquifer to be developed. This understanding was used in developing finite difference solute transport models to replicate the results from the tracer tests. Values of dispersivity of 0.5–5 m were derived for the Rus aquifer whilst values in the range 10–150 m were derived for the UER. Effective porosities were high at around 0.2 for both aquifers.
An introduction to stone colonizing micro-organisms and biodeterioration of building stone
Authors: Wakefield Rachael D. , Jones Melanie S.
Published: November 2007

Over the last decade, the concept of stone decay being caused solely by one or two processes has been revised in favour of a more holistic notion that many operate together, are synergistic and possibly cyclical or seasonal. Certain of these processes may become predominant over others at particular times of the year or at specific periods in the history of the stone. Many researchers from different disciplines now agree that biological deterioration is of significance, and cross disciplinary work is becoming the rule rather than the exception. This short introduction gives an overall view of the principal mechanisms important in stone biodeterioration. The main groups of micro-organisms found on stone and their role in stone biodeterioration are reviewed. The final section discusses decay processes which can be brought about by many different groups of micro-organisms living together as a complex microbial community at the stone surface.
Weathering of sandstone by alunogen and alum salts
Authors: Williams R. B. G. , Robinson D. A.
Published: November 2007

In many places in eastern Germany, the Czech Republic and southern Poland, outcrops of the Elbsandstein are undergoing rapid honeycomb weathering and scaling in the presence of gypsum, alunogen and alum salts. Laboratory experiments have been undertaken to test the relative efficacy of these salts as weathering agents. Cubes of Lower Cretaceous sandstone from West Sussex have been repeatedly soaked in salt solutions and then oven dried at 50°C. The experiments show that alunogen causes relatively little damage, but alum salts are highly destructive, especially if gypsum is present. The addition of gypsum reduces the damaging effects of alunogen, while gypsum on its own causes minimal weathering.
Putting numbers to geology—an engineer's viewpoint
Authors: Hoek Evert
Published: November 2007

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.
The Folkestone Bed sands: microfabric and strength
Authors: Richards N. P. , Barton M. E.
Published: November 2007

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.
Karstic groundwater flow characteristics in the Cretaceous Chalk aquifer, Northern Ireland
Authors: Barnes S.
Published: November 2007

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.
In situ
determination of
G
hh
at Bothkennar using a novel seismic method
Authors: Hope V. S. , Clayton C. R. I. , Butcher A. P.
Published: November 2007

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.
Use of electrical imaging in site investigations for a railway tunnel through the Hallandsås Horst, Sweden
Authors: Dahlin Torleif , Bjelm Leif , Svensson Conny
Published: November 2007

Investigations over two major tectonic zones in the Hallandsås 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.
Estimating transmissivity from surface resistivity soundings: an example from the Thames Gravels
Authors: MacDonald Alan M. , Burleigh James , Burgess William G.
Published: November 2007

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.
Glacial hazard assessment at Tsho Rolpa, Rolwaling, Central Nepal
Authors: Reynolds John M.
Published: November 2007

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 Majesty's 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
The role of calcium carbonate in the compressibility of Pliocene lacustrine deposits
Authors: Bozzano Francesca , Marcoccia Sabrina , Barbieri Maurizio
Published: November 2007

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.
Weathering simulation for durability assessment of the in-service performance of construction materials
Authors: Taylor-Firth A. , Laycock E. A.
Published: November 2007

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.
Subsidence caused by gypsum dissolution at Ripon, North Yorkshire
Authors: Cooper Anthony H. , Waltham Antony C.
Published: November 2007

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