bluuebunny/crossref_metadata_2025 huggingface dataset:
Discussion on ‘The analysis and planning of step drawndown test’ by
Authors: Milne-Home W. A.
Published: November 2007

Dr Clark has presented an excellent review of the theory of the step drawdown test and its applications. The purpose of this communication is to comment on the use of the recovery portion of a step drawdown test to calculate aquifer transmissivity. The Theis method may be applied if the variable discharge rate is replaced by the average of the pumping rates. This average may be expressed as:

where Q̄ = mean pumping rate, V = total volume pumped, t = total pumping time.

Equation (1) is equivalent to Clark's formulation. Although it is a useful working approximation, more accurate results would be obtained if Q̄ were calculated by weighting each discharge rate by the time elapsed since that rate began. Sternberg (1967) has described such a method which can be modified slightly to determine transmissivity from the recovery portion of a step drawdown test. The transmissivity T, of an infinite, confined aquifer is shown to be:

where t
e
= 2{t-(ʃ10Q(γ)γ dγ /V)}, γ = time from start of pumping to time t, ť = time since pumping stopped, Q
e
= V/t,
e
, Q(γ) = variable pumping rate, sW' = residual drawdown in the pumped well (replacing the residual drawdown at any point radially distant r from the well in Sternberg's derivation).

For short step drawdown tests with steps of equal length, t
c
may be approximated by: where n = number of steps, Δt = length of each step, t
e
= time intervals since pumping started, Q
ti
+
ti+1
=
Discussion on ‘An experimental scheme for the disposal of micaceous residues from the China Clay Industry’ by
Authors: Taylor R. K.
Published: November 2007

Liquefaction phenomena are of great importance to those concerned with the impounding of mining and quarrying wastes, especially when the waste materials themselves are used for embankment construction. In this respect the effect of particle shape reported by the Authors is of much interest.

At Durham University we have been investigating the liquefaction potential of both fine and coarse colliery discards during the past three years, using controlled load and cyclic triaxial tests (Taylor
et al
. 1978a,
b
).

The examples of stress paths shown in Fig. 1 relate to controlled load tests carried out on coarse discards and other weak-rock aggregates, together with a fine discard test result conducted in the same effective confining pressure range. Two different coarse discard types are represented: (
a
) strong, coal-rich, platey material from west Wales (path 1), and (
b
) much weaker material from Nottinghamshire with a high seatearth content (path 2). Non-slaked shale from above the Harvey seam in Co. Durham was made up to the same nominal grading as the west Wales discard; this rock aggregate is represented by stress paths 3 and 4. Stress path 5 is a seatearth specimen from below the Harvey Coal, its particle size distribution being similar to the Nottinghamshire discard. Also shown on Fig. 1 is a test result (path 6) for shaly (non-plastic) tailings from a lagoon at the same west Wales colliery location as material 1. For these tests the stress paths are drawn such that:
P̄ =1/2(σ′
1
+ σ′
3
) and q =1/2(σ
1
-σ
3
); where σ
1
Ground water quality in weathered Deccan Basalt of Malwa Plateau, India
Authors: Lunkad S. K. , Raymahashay B. C.
Published: November 2007

Selected samples of well and spring waters from the weathered profiles of a typical Deccan Basalt outcrop reveal strong controls of soil mineralogy. Calcium plagioclase, augite and volcanic glass in the bed rock weather to montmorilloniterich black soils in the foothills. Soils at higher slopes are lateritic. Lime concretions are common and quartz is ubiquitous.

The HCO
3
/SiO
2
mole ratio in the waters is in the range predicted for alteration of plagioclase to montmorillonite and augite to kaolinite. The silica level is above quartz solubility and generally below solubility of amorphous silica. Montmorillonite and calcite are thermodynamically stable in the ground water environment. Geochemical mobility of elements during weathering decreases in the order Na, Mg, Ca, K, Si and Fe.
Discussion on ‘Drift deposit influences on the Triassic Sandstone aquifer of NW Lancashire as inferred by hydrochemistry’ by
Authors: Worthington P. F.
Published: November 2007

The authors are to be congratulated on this interesting paper, the implications of which extend beyond purely local considerations. The evident agreement between the hydrochemical data and the earlier geophysical interpretation of the glacial sands (Worthington 1972) supports the integrated use of these diverse techniques in hydrogeological evaluation. Although surface geophysical methods are well proven, they are not universally regarded as established within the framework of hydrogeological practice. If this paper encourages a more general acceptance of hydrogeophysics, it will have served an additional useful purpose.

One or two specific points do call for comment. The statement ‘Worthington (1977) records that the aquifer has a predominant intergranular permeability’ is not strictly correct and it therefore seems somewhat inappropriate to label the alleged proposition as ‘contentious’. The basic assertion of the paper cited is immediately evident from the abstract:

‘... the intergranular component of groundwater flow (within the Triassic Sandstone) can vary markedly from place to place and is apparently the predominant mechanism within a sizable area. Elsewhere intergranular flow is supplemented by fissure drainage, and is sometimes relatively insignificant. It is concluded that intergranular permeability exerts a basic control upon abstraction well productivity, with maximum benefits being derived where a comparatively strong intergranular flow is augmented by a well-developed, localized fissure network’.

The major point to emerge here is that it is intergranular permeability which appears to exert a fundamental control upon the hydraulic conductivity of the Triassic Sandstone. It is therefore especiallv encouraging to note the agreement between,
A proposal for quantitative terrain evaluation for highway construction
Authors: Rodriguez Ortiz J. M. , Prieto C.
Published: November 2007

From the analysis of several highway projects throughout Spain the relative importance of various engineering geological factors have been evaluated. The following relevant factors are selected: bearing capacity, slope stability, quality of borrow material, problems of excavation, geomorphology, climatic conditions, and drainage conditions.

These factors are combined to define a feasibility index ranging from 0 to 2, evaluating the terrain according to its suitability for new highway projects, indicating the intensity and type of problems which can be expected. The evaluation is usually represented on maps at a scale of 1:25 000.
Remote sensing for the location and mapping of engineering construction materials in developing countries
Authors: Beaumont T. E.
Published: November 2007

Multispectral satellite imagery and other remote sensing techniques may now be employed to carry out surveys over large land areas so that fuller use can be made of locally available materials in order to reduce the costs of road construction. In many developing countries local resources are often not used as extensively as would be possible, due to the adaptation of specifications for road building materials that have been derived in industrialized countries with temperate climates and different geology.

These specifications are often inappropriate for natural gravels, weathered rock, and concretionary materials found in the tropics, many of which can be used successfully for constructing lightly-trafficked roads. The value of using recent technological developments in remote sensing methods and techniques of image analysis to locate and map the occurrence of such indigenous engineering materials are discussed with reference to a survey undertaken in Botswana to locate calcrete for low-cost road construction in the Kalahari Desert.
The littoral sediment budget between Selsey Bill and Gilkicker Point, and its relevance to coast protection works on Hayling Island
Authors: Harlow D. A.
Published: November 2007

The sediment distribution pattern on the beach and near-shore seabed has been established with the aid of a sampling programme and diving inspection. The littoral sediment budget has been established and quantified for the coastal unit, and a method of estimating historical rates of littoral drift from coastal changes has been developed. The effect of sediment reservoirs in regulating the budget, and the effect of dredging has also been considered.

Neither groynes nor seawalls have entirely succeeded in preventing erosion on Hayling Island, where the basic problem is a reducing feed of beach material to maintain the littoral drift. Beach replenishment proposals conclude the paper.
The contribution made to cliff instability by Head deposits in the west Dorset coastal area
Authors: Conway B. W.
Published: November 2007

In the west Dorset coastal area superficial materials include Head deposits which, by the nature of their origin, are variable in structure and composition. Two broad types are recognized depending on the provenance of the predominant constituent: Cretaceous Head and Lias Head. The Cretaceous Head was probably formed near to or at the end of the Devensian stage of the Late Pleistocene. Where the two types of Head deposit are superimposed, Cretaceous Head always lies above Lias Head.

On many slopes Lias Head has topographic expression as lobate sheet forms which are frequently masked by a blanket of Cretaceous Head. The high permeability of Cretaceous Head together with the low strength of Lias Head produce slopes presenting potentially unstable conditions to depths of up to 4 m below ground surface.

Three minor types of instability are generated in the Head deposits themselves: shallow translational movements, block slides, and shallow rotational slides. In addition, the high permeability of Cretaceous Head permits water to be introduced to undercliff areas, thus facilitating the development of instabilities in the solid formations below. This results in a mechanism of cliff-top retreat which is quite independent of cliff-toe erosion.

The events at sites in Lyme Regis and Charmouth are summarized to illustrate the hazard presented by Head deposits in cliff-top areas.
Factors affecting the transition between the various types of mass movement in coastal cliffs consisting largely of overconsolidated clay with special reference to Southern England
Authors: Bromhead E. N.
Published: November 2007

At present, the most widely accepted hypothesis for the transition from mudsliding to deep-seated rotational slipping as the dominant agent of mass transport in actively eroding clay cliffs is that the transition depends on the rate of marine erosion at the toe of the slope. This paper explores an alternative theory, that the transition from one type of behaviour to another depends largely on the nature of the materials at the crest of the slope and to a lesser, but still important, extent on the groundwater hydrology.

The main argument behind this alternative theory is that the presence of stronger soil strata at the crest of the slope inhibits the mudslide behaviour that would otherwise occur and hence form a toe-protecting ‘mudslide barrier’. This allows marine action to erode the toe of the slope directly, causing it to be oversteepened, and ultimately precipitates a deep-seated rotational landslide. Where the coastal cliffs are capped with thick, hard and jointed caprock the slides tend to be of the multiple rotational kind.
The application of wave refraction diagrams to shoreline protection problems: with particular reference to Poole and Christchurch Bays
Authors: Henderson G. , Webber N. B.
Published: November 2007

Wave refraction has an important role in the evolution and day-to-day behaviour of shorelines and beaches. It is often the major factor in dictating the magnitude and direction of the littoral drift.

The development of a wave refraction model for a particular site, (Poole/Christchurch Bays in the central south coast of England), is described. The computational technique is very powerful and an area of 2500 km
2
of sea bed has been reproduced with the refraction behaviour superimposed for various wave directions and periods in deep water. In assessing the results, regard must be paid to the simplifying assumptions and the effects of offshore shoals.
Additional observations on the Folkestone Warren landslides
Authors: Hutchinson J. N. , Bromhead E. N. , Lupini J. F.
Published: November 2007

The Folkestone Warren landslides are first compared to the landslides at geologically related sites on the northern coast of France and the southern coast of England. Additional historical data is then presented on the Warren landslides, particularly that of 1915, and the influence on these of the interruption of littoral drift produced by the Folkestone Harbour works is examined. An indication is also given of other considerable mass shiftings which have taken place in the Warren since the early nineteenth century. A preliminary morphological study is made, the features being linked, where possible, with the historical data. The degree to which the frequent Chalk falls from the High Cliff are controlled by the joint pattern is briefly examined and the recent subsurface investigations in the Horse's Head area are reviewed and discussed.

The existing back-analyses of the slips are critically re-examined in the light of the fresh historical and morphological data and additional back-analyses are carried out. Measurements of the residual strengths of the high and low liquid limit Gault are made, in two different ring shear machines, and compared with the combined results of the back-analyses.
Discussion on ‘Large landslides in London Clay at Herne Bay, Kent’ by E.N. Bromhead
Authors: Hutchinson J.N.
Published: November 2007

Bromhead's paper provides useful information, derived from the back-analysis of existing slips in the Herne Bay area, on the values of residual strength of the London Clay mobilized in the field. As the slips treated are generally rather deep-seated, the data extend our knowledge of the field residual failure envelope for the London Clay into a higher range of normal effective stress.

In his summary plot (Fig. 10) of this envelope, however, the author does not make use of some existing data in the low and medium normal effective stress range. Field residual strengths derived from the back-analysis of shallower slips in the London Clay are available from sites at Guildford, Hadleigh, Sud-bury Hill and Dawes Road. These data, plotted with Bromhead's values in Fig. 1a, permit the construction of a well substantiated field residual envelope for the London Clay up to a value of normal effective stress of about 160kN/m
2
. The shape of the residual failure envelope in the vicinity of the origin of the Mohr diagram and the magnitude of any small intercept on the shear strength axis remain, of course, uncertain. The field residual envelope shown in Fig. la can be approximated, up to a normal effective stress of about 70 kN/m
2
, by the parameters c′
r
= o, φ′r = 13.3° (Hutchinson & Gostelow 1976) or by c′
r
= 0.5 kN/m
2
, φ′
r
= 12.9°. The envelope thus defined lies slightly lower than that shown by the author for this stress range. At higher normal
A brief review of foundation construction in the Western Canadian Arctic
Authors: Thomson S.
Published: November 2007

Introduction

The design and construction of foundations in permafrost imposes problems that are in addition to those encountered in temperate regions. The additional problems are brought about by a subsurface that has a temperature below freezing all year round. Therefore, consideration must be given to the temperature profile in the subsurface, its variation with time and any changes imposed on it, as well as to strength and deformation properties of the frozen soils.

Extent of permafrost

Before dealing with foundation design, a review of the location of the perennially frozen ground both areally and vertically is necessary. The permafrost map of Canada (Fig. 1) shows the general areal distribution. The permafrost is divided into two zones by a line trending northwesterly from the south edge of Hudson's Bay. North of this line is the Continuous Zone in which, as the name implies, permafrost is virtually everywhere. South of this line is the Discontinuous Zone in which localized areas of unfrozen ground appear and which gradually increase in areal extent until the temperate areas are reached.

Figure 2 shows schematically the distribution of permafrost in a vertical section as one proceeds in a northerly direction (
Brown 1970
). Note that the active layer (defined by
Brown & Kupsch (1974)
as the top layer of ground above the permafrost table that thaws each summer and refreezes each fall) decreases in thickness but the thickness of the permanently frozen mass increases northwards. The junction between the Discontinuous and Continuous Zones
Permeability of three compacted tropical soils
Authors: Ola S. A.
Published: November 2007

This paper presents studies of permeabilities of three soil samples of widely differing properties at various degrees of saturation, various compactive efforts and various thixotropic strength ratios. The soils studied consist of a soft clay shale–attapulgite, a black cotton soil, and a lateritic kaolinitic soil. The results indicate the attapulgite to be the most structure sensitive and the lateritic soil the least structure sensitive. The permeabilities reflect these structural behaviours of the soils. Based on the test results, a practical back pressure is recommended for complete saturation of these compacted soils. The influence of moulding moisture contents on permeabilities are presented and values of thixotropic strength ratios for the three soils are also recommended.
Coastal engineering problems at Clacton-on-Sea, Essex
Authors: Harris W. B. , Ralph K. J.
Published: November 2007

Erosion along the frontage at Clacton has necessitated the progressive protection of the cliff and foreshore during the last 100 years. The cliffs consist of Pleistocene gravels overlying London Clay and reach a level of 20 m above Ordnance Datum (Newlyn). The top of the clay is irregular and incised by buried channels which allow water to drain to the front of the cliff and weaken the clay forming the cliff base. On the foreshore the stability of the existing sea walls protecting the cliff base was endangered by erosion on the downdrift side of the two large groynes constructed a few years previously.

Remedial measures included the relief of perched water tables and drainage of the cliff by vertical and inclined bored drains; the protection of the toe by constructing stepped aprons and sea walls of pre-cast concrete components; the installation of a new groyne system and replenishment of foreshore material.
Contamination of a Chalk aquifer by mine drainage at Tilmanstone, East Kent, U.K.
Authors: Headworth H. G. , Puri S. , Rampling B. H.
Published: November 2007

Arising from the discharge at the surface of minewater drainage pumped from a mine in the Kent Coalfield, which underlies the Chalk of East Kent, U.K., an area of some 27 km
2
of the Chalk aquifer has become contaminated with saline water having concentrations of chloride between 200 and 5000 mg/l. Between 1907, when the first shaft was sunk, until 1974, when the discharge onto the Chalk ceased, it is estimated that 318 000 tonnes of chloride were discharged, and only about 15% has so far been dissipated by stream flows. An investigation has been carried out to determine the size and shape of the plume of contamination, and to examine possibilities for rehabilitation of the aquifer. The work has shown that the top 40-50 m of Chalk has become saturated with highly saline water, but at greater depths the contaminant is localized around well-developed fissures. The results of fifteen months pumping of a production borehole located near the centre of the pollution plume suggests that a long period would be required for the contamination to be cleared, and this has been supported by the results of a mathematical model.
Rebound, its nature and effect on engineering works
Authors: Nichols T. C.
Published: November 2007

Rebound of rock masses, defined as the expansive recovery of surficial crustal material, either instantaneously, time-dependently, or both, initiated by the removal or relaxation of superincumbent loads, is found in most geological terrains. The applied loads resulting from past or present geological processes are removed or relaxed by (1) natural processes such as valley erosion (long term) or (2) artificial processes such as excavations (short term). Rebound features are most pronounced if the time period of load removal is short compared to the relaxation time of the material, assuming that relaxation time is a material property.

Some factors that affect rebound and its intensity are:

Initial fabric, lithology, crack density, anisotropy, density and moisture content.

Magnitudes of deviatoric stresses (stress differences, stress ratios) operating at the time of load removal, their orientation with respect to the free surface and their rate of unloading.

Initial strength and time-dependent strength.

Environmental conditions, such as moisture, temperature and other weathering agents.

The near-surface stress distribution and time-dependent strain release measured within different geological terrains suggest that the redistribution and/or release of stored-strain energy within rock masses may be a major factor contributing to rebound. Strains, stored in the rocks as a result of past and present geological loads, can be released by excavation processes. As new surfaces are formed, the rock mass changes volume, creating physical property changes that include increased void space and higher permeabilities, thus allowing more rapid access for chemical agents that accelerate the weathering process. Rebound is a rate-dependent process that is manifested differently in various geological terrains.

Long-term stability is dependent on changing fracture density and the rate at which strength decreases within near-surface rock material. The strength reduction may be, among other things, a function of the internal decay of cohesion due to the development or propagation of fractures. The time-dependent processes of rebound and the ambient stress fields are important in the development of criteria for the long-term design of engineering installations that are placed within or on disturbed rock masses.
Fault control of groundwater flow and hydrochemistry in the aquifer system of the Castlecomer Plateau, Ireland
Authors: Daly D. , Lloyd J. W. , Misstear B. D. R. , Daly E. D
Published: November 2007

The Westphalian strata of the Castlecomer Plateau contain two main sandstone aquifers that are in variable hydraulic continuity due to major fault displacements. The faulting separates the plateau into three effectively independent groundwater blocks. A hydrochemical study shows that carbonate dissolution and ion exchange are the two dominant chemical processes active in the aquifer and that the degree to which they occur is a function of the ability of the aquifer to transmit water which is controlled by fault displacement.
Cement hydrate development at opal-cement interfaces and alkali-silica reactivity
Authors: Baker A. F. , Poole A. B.
Published: November 2007

Electron probe microanalysis data indicates that sodium, potassium, and calcium ions migrate into opal aggregate from the cement paste in experimental alkali-silica reactive concretes. The reaction also modifies the development of cement phases at the interface with the opal and these modifications are reflected in modifications of the tensile strength of the opal/cement bond. It is suggested that the calcium silicate hydrates which develop in the cement at the interface with opal may control the migration of alkali ions into the opal. With high alkali concentration in the cement pore fluids this hydrate layer at the interface may not develop completely allowing high concentrations of alkali ions to reach the reacting opal causing a change in the composition and properties of the alkali-silica gel reaction product.
Properties of aggregates affecting concrete in North America
Authors: Gillott J. E.
Published: November 2007

Aggregates compose the largest single component in concrete and significantly affect its strength, durability and appearance. The mechanical properties of concrete are affected by the strength of the cement-aggregate bond and by other factors such as texture and soundness of the rock. External agencies attack concrete and reduce its durability by both physical and chemical processes. Physical mechanisms include cyclical freezing and thawing, wetting and drying. Chemical deterioration results from reaction with sulphate-bearing waters, acids, a marine environment, industrial effluents and similar corrosives. Internal compatibility is essential, as deleterious interaction between concrete constituents may cause poor durability, as in the case of expansive alkali-aggregate reactions. Deliberate exposure of aggregates, sometimes used architecturally, may give concrete a pleasing appearance, but localized stains from weathering of aggregate particles lead to an unsightly appearance. Relatively few attempts have been made to improve aggregate properties artificially and ‘unsound’ aggregate is simply rejected. Depletion of good quality supplies near major centres of construction suggests that more pre-treatment of marginal aggregates may become economically attractive in the future.
Discussion of papers in this issue
Authors: Sims I.
Published: November 2007

The potential for alkali-reactivity of an aggregate and its actual reactivity as seen in practice can often be detected by a detailed petrographic examination where the standard chemical and physical tests provide ambiguous results.

French (this volume) comments that the standard mortar bar tests (ASTM-C227-71) may not always lead to accurate diagnosis of the likely performance of an aggregate. In practice, misunderstandings often arise over the application of the test to carbonate or impure carbonate aggregates or to other rocks lacking the specifically alkali-silica reactive minerals. Problems in interpretation also arise where the mortar bar results show progressive expansions that are close to or below the failure criteria suggested by ASTM C227-71. Silicate rocks showing slow expansion rates are now recognized, including Gillott's (1975) Type III reactions and marginal results of the mortar bar test cannot therefore be regarded as unimportant. The consideration of both these problems can be greatly assisted by petrographic examination which may allow proper diagnosis of the type of reaction that is likely to occur even though the rate may not be predictable.

Sometimes a petrographic examination identifies the principal cause of deterioration or failure of concrete. In one British example, unreinforced concrete bases were subject to cracking, and alkali-silica reactivity was established by petrographic analysis as the major mechanism involved (Fig. 1A and B). The coarse aggregate was an inert limestone, the cement was a high-alkali variety, and the sand was mostly quartz except for alkali-reactive chert which occurred in the coarsest sand fraction. The
The hydrogeochemistry of the Jurassic limestones in Gloucestershire, England
Authors: Morgan-Jones M. , Eggboro M. D.
Published: November 2007

This study is a review of the major and minor chemical constituents in groundwater in the Jurassic limestones of Gloucestershire, England. Particular emphasis has been placed on the identification of hydrogeochemical processes.

Groundwaters in the limestones of the Great Oolite Series and the Inferior Oolite Series, where they are unconfined, are of the Ca, HCO
3
type. In areas where both limestone series are confined beneath clays there is a gradual change in the chemistry to a Na, HCO
3
type. Deep within the confined limestones, particularly in the Great Oolite series, an Na, Cl component has been identified. Natural heavy metal concentrations are generally very low except where old pipework has influenced the Pb or Zn content.

Significant down-dip chemical changes in terms of redox conditions, pH, dissolved oxygen content, ion-exchange and the concentrations of minor constituents are exhibited by groundwaters in the limestones of both series. An oxidation-reduction zone has been defined in each limestone unit. In the Inferior Oolite the zone occurs some 8 km down-gradient from the onset of confined conditions. In the Great Oolite a similar zone occurs 1–2 km into the confined area. The delay in the onset of reducing conditions in the Inferior Oolite is tentatively attributed to leakage of Great Oolite water through the intervening Fullers Earth.
The development and geotechnical problems of sabkha, with preliminary experiments on the static penetration resistance of cemented sands
Authors: Akili W. , Torrance J. K.
Published: November 2007

The sedimentary and evaporative environment that has prevailed on the southern shores of the Arabian (Persian) Gulf region, has produced salt encrusted flat areas known as ‘sabkha’, along the coast and in some nearby depressions.

In this paper the morphology, development, mineralogy and hydrology of coastal sabkhas have been briefly reviewed. Geotechnical properties and problems associated with sabkha deposits have been described.

The authors' general view of sabkha as cemented and uncemented layers of varying thickness and properties has been confirmed by a limited field study in terms of pits and boreholes carried out near Dhahran, Saudi Arabia. Calcium carbonate and more recent diagenetic minerals such as gyp-sum serve as the primary cementing agents.

Laboratory experiments aimed at simulating the development of cementation in sabkha material, by chemically precipitating calcium carbonate and calcium sulphate within pluviated sand samples, have shown that marked increase in static penetration resistance is exhibited with the addition of 2-5% precipitate (by weight of sand) as compared to uncemented sands. The results also demonstrate the potential advantages of using static cone pentrometers in the field to assess the strength and layering of sabkha.
Discussion on ‘Geotechnical, mineralogical and chemical interrelationships in weathering profiles of an over-consolidated clay’ by D. J. Russell and A. Parker
Authors: Robinson D.
Published: November 2007

D. Robinson writes: The authors have clearly demonstrated in their Fig. 3
a
the change in shape of the illite basal 10 Å reflection with depth in a weathering profile of the Oxford Clay. They attributed this change to a decrease in crystallinity caused by weathering which results in a progressive loss of interlayer potassium and leads to an increased shoulder on the low 2θ side of the 10 Å peak. Quantification of the shape factor, as the authors suggest, has been widely attempted in clay mineral studies. In the examples quoted (Gill
et al.
1977; Weaver 1960) the ratio of the peak-minus-background intensity at 10 Å to that at 10.5 Å is utilized in the examination of crystallinity changes through diagenesis into low-grade metamorphism. This ratio therefore is a measure of the similarity to an ideal 10 Å peak rather than reflecting the importance of the 11 Å
d
-spacing as in the shape-factor chosen by the authors.

The changes demonstrated in peak-shape, however, could also be caused by the presence of varying proportions of random mixed-layer components in the illite (Thorez 1975). The authors will be aware that there are various pretreatment methods that allow the recognition and semi-quantification of interlayer components (Hower & Mowatt 1966; Weaver 1956). It may be that the various geotechnical parameters could be better understood if there is a varying proportion of interlayer component in the illite, especially if it is of a swelling character.

It is obvious that the authors have many more data
An analysis of secondary toppling rock failures—the stress redistribution method
Authors: Evans R. S.
Published: November 2007

Following the terminology of
Goodman & Bray (1976)
, several examples of secondary toppling failures are presented. Six possible failure mechanisms are considered; bearing capacity failure or differential settlement due to weathering and creep with associated stress redistribution are concluded to be the most likely failure mechanisms; however, the former is not supported by field evidence. The differential settlement mechanism involves stress relaxation in the basal softer rocks (claystones) whereby the overburden load is redistributed to the fresher materials, thus reducing the amount of differential settlement likely to occur. The lateral constraints provided by horizontal stresses may temporarily inhibit this mechanism.
The El Asnam (Algeria) earthquake of 10 October 1980; conclusions drawn from a field study
Authors: Ambraseys N. N.
Published: November 2007

The El Asnam earthquake (M
LH
= 7.2; M
LV
= 7.3; M
PV
= 6.5) occurred at 12:24:24 G.M.T. on 10 October 1980 in the central part of the Chelif valley in Algeria affecting a rather densely populated region of about 900 000 within 7000 km
2
. (
Ambraseys 1980
). It destroyed at least 25 000 housing units and rendered 300 000 people homeless. The main shock, which killed about 2500 and injured more than 7000 people, was felt as far away as Spain 550 km distant. It was followed by a damaging aftershock 3 hr later (M
LV
= 6.1; M
PV
= 5.9). No foreshocks were recorded, but other phenomena have been reported which could have been premonitory (Fig. 1a).

The El Asnam earthquake is the largest event in the Atlas since 1790, and in the Chelif valley since 1716. For the Atlas as a whole, the moment rate calculated from long-term observations is only 10
25
dyn-cm/year. This corresponds to a slip rate of only 0.7 mm/year which is a small fraction of the value calculated from plate motions, implying that much of the deformation of the Atlas occurs aseismically and that the tectonic activity of the region is not fully reflected by its short-term seismicity. This is a serious handicap in the assessment of the earthquake hazard in the Atlas. The frequency distribution of events above magnitude 4 3/4 was found to be
f(M)
= 2.2 exp(-2.2
M
), with a probable cut-off at about
M
= 7 1/4 to which corresponds a return period
Engineering Group of the Geological Society
Authors: Chandler R. J.
Published: November 2007

The Annual Regional Meeting of the Engineering Group of the Geological Society in 1980 was held at Kingston Polytechnic from 8th to the 12th September. Kingston proved a happy choice as a location for the meeting; a pleasant campus provided accommodation and lecture theatre facilities in close proximity, and, though close to London, was at the same time far enough from the metroplis to discourage all but a tiny handful of delegates from ‘commuting’ daily. And so the informal, and friendly communal atmosphere familiar to all who have attended Engineering Group Regional Meetings in the past was very evident too at Kingston.

Many thanks are due to the organising committee, composed of E. N. Bromhead, I. R. Wood and G. Walton, who were responsible not only for the domestic arrangements of the Meeting, but for the organization of field visits and, of particular importance for readers of the
Quarterly Journal of Engineering Geology
, the programme of lectures of which some are now published in the following pages. Although it is always invidious to single out individuals for particular mention, the thanks of everyone who attended the Meeting must go to Dr Bromhead, who, as is always the fate of the Local Secretary, bore the brunt of the organization of all aspects of the Meeting.

The theme of the Meeting was ‘Engineering Geology Applied to Construction’. The 3 days set aside for the presentation of papers took general themes of (i) the investigation of slopes and site investigations for road schemes,
A building site on cambered ground at Radstock, Avon
Authors: Hawkins A. B. , Privett K. D.
Published: November 2007

This paper gives details of the foundation problems at a housing development on a 4–7° slope of Blue Lias limestone, overlying Rhaetic and Keuper Marl.

Cambering in the past has produced extension gulls with cavities up to 1 m wide and zones of disturbance over 5 m wide. These structures were not visible on the surface or on the aerial photographs and presented unforeseen problems when discovered in foundation trenches. Extensive site checks have been undertaken, the foundations for each building plot being inspected by one of the authors.

A simple classification of the extension gulls on this site, based on the mode of opening along joint and bedding surfaces and any subsequent collapse or infilling, is presented. The overall stability of the hillside is discussed with reference to the residual strength of the Rhaetic, which here is a highly plastic, montmorillonitic horizon containing well marked shear planes.

The presence of the gulls necessitated several changes of the site layout in an attempt to avoid the most highly disturbed ground. The developer suffered a 150ss in the proposed number of units.
Dalton By-pass: site investigation in an area of abandoned haematite mine workings
Authors: Arrowsmith E. J. , Rankilor P. R.
Published: November 2007

The choice of the public for a route for the Dalton By-pass lay through an extensive area of well-worked and abandoned haematite mine workings. The geology of the area and the method of mining are described, and the reasons are given for the selection of the preferred route.

The problems associated with the route are discussed, together with the detailed planning necessary to organize an extensive complex site investigation, involving almost 700 boreholes in a roadway length of 4½ km. A typical cutting is examined in some detail to illustrate the contractual and technical problems connected with the required excavation of a cutting slope directly over a major iron ore sop; these problems include the removal and treatment of the water-filled collapse cone over the rubble-filled cavern left by the ore extraction. The relative costing of an elevated structure and an embankment founded on collapsed workings are discussed.

Some engineering conclusions are drawn from the site investigation regarding the suitablty of embankment fill, the rate of settlement of embankments on alluvium, and the stability of a rock slope.
Mesozoic and Tertiary argillaceous units: distribution and composition
Authors: Sellwood B. W. , Sladen C. P.
Published: November 2007

The generalized distribution and mineralogy of major Mesozoic and Cenozoic mud formations in England can be illustrated using isopach maps and composite cross-sections.

Burial diagenesis has only affected the clay minerals in the deeper parts of the Wessex-Weald area onshore. Early diagenetic clay minerals are only significant in the Triassic where sepiolite, palygorskite and corrensite formed in strongly saline environments. Authigenic clays formed sporadically in the Jurassic, Lower Cretaceous and Tertiary when smectite formed by halmrolytic alteration of mafic volcanic ashes.

For most of the Mesozoic and Cenozoic the clay mineralogy reflects weathering in the source areas.
The engineering properties of mudrocks
Authors: Cripps J. C. , Taylor R. K.
Published: November 2007

The ‘rock’ and ‘soil-like’ properties of British mudrocks are shown to be influenced by: (a) their lithology; (b) their geological history of loading (especially during exhumation); (c) the type and method of testing; and (d) the degree of weathering. In particular, unloading and weathering leads ultimately to a normally-consolidated clay of much the same undrained shear strength, irrespective of age and origin of the parent material.

For this reason, the engineering properties of the unweathered mudrocks are illustrated separately in terms of classification indices, undrained and effective shear strengths and deformability in relation to geological age.
Thermal conductivities of mudrocks in the United Kingdoms
Authors: Bloomer J. R.
Published: November 2007

Any prediction of sub-surface temperatures, or evaluation of heat flow from measured temperatures, requires knowledge of the thermal conductivities of the rocks in the area under consideration. An accurate evaluation of the thermal conductivity of mudstones is particularly important, not only because of their widespread occurrence in sedimentary basins but also because of their relatively high insulating effect.

The difficulties in making thermal conductivity measurements of mudstones and the methods used are briefly discussed.

A simple expression for a relationship between thermal conductivity, density and lithology is derived from physical considerations and verified by experiment. The importance of this relationship for geothermal studies in uncored wells is discussed (mudstone sections are rarely cored in commercial holes).

Finally, a table of values of thermal conductivities of mudstones, of Triassic to Pleistocene age, from the Hampshire and Lincolnshire basins and from the Moray Firth, are presented. These values range from l.2 Wm
-1
K
-1
for the Pleistocene clays in the Moray Firth to 2.3 Wm
-1
K
-1
for the Keuper Marl in the Hampshire Basin.
Editorial
Authors: de Freitas M. H.
Published: November 2007

Volume 14 of the
Quarterly Journal of Engineering Geology
marked the end of the series edited by Dr R. J. Chandler.

Many readers around the world will have good reason to be grateful to Dr Chandler for his editorship of the Quarterly Journal, and I am sure that they would wish me to thank him on their behalf for the excellent work he has done in maintaining the Quarterly Journal as a vehicle of international reputation for the publication of geotechnical and hydrogeological work. Dr Chandler assumed his responsibilities as editor in 1978 and the first issue under his charge was the very successful Proceedings of the Conference on Engineering Problems associated with Ground Conditions in the Middle East. In 1979 he guided the response of the Journal to the needs of the members of the Hydrogeological Group and since that time there has been a growing commitment to provide space for the publication of hydrogeological work. Since 1978 there has developed a tendency in the Society to sponsor thematic meetings, the proceedings of which have been accommodated by its Journals. These present the Editors with special problems and we are fortunate that Dr Chandler succeeded in providing us with the proceedings for the important meetings on Engineering Geological Mapping for Planning, Design and Construction; Coastal Engineering; Stability of Concrete Aggregates; Engineering Geology Applied to Construction; and Mudrocks of the UK. In addition he maintained a general mixture of subjects for other issues that sustains the broader interests of the
Shallow foundations on London Clay
Authors: Johnson P. B.
Published: November 2007

The drought period of 1975-76 was a stark reminder to the construction industry of the potential risks involved in placing shallow foundations on those clay sub-soils which are susceptible to the phenomena of swelling and shrinkage. Many of these clays are encountered in SE England and a fairly large outcrop of London Clay occurs in the Fareham area of Hampshire. A considerable number of foundation problems exist in this area and eight case histories are reviewed in this paper, with particular emphasis on the effect of trees and vegetation on soil moisture content. Four of these cases deal with damage to existing properties and four are concerned with new development. This study reinforces the view that piles may well provide the best technical solution for foundation construction in problem areas such as this.
The influence of shrinkage cracks on pore-water pressures within a clay embankment
Authors: Anderson M. G. , Hubbard M. G. , Kneale P. E.
Published: November 2007

For slope stability estimations, the soil pore-water conditions need to be accurately specified. The influence of cracks in clay was previously observed significantly to modify soil water response. In this study shrinkage cracks were monitored in a clay embankment where the soil water response to precipitation had been shown to be more rapid than the clay micro-permeability would predict. The cracks were shown to increase the hydraulic conductivity of the clay at all times of the year and to be the cause of the rapid soil water potential responses monitored. X-ray examinations of closed crack sites indicated that fractures at these sites formerly extended to greater depths.
Chloride ion concentrations as an aid to estimating recharge to the Woburn Sands
Authors: Irving W. M.
Published: November 2007

On the N side of the London basin the principal representative of the Lower Greensand is the Woburn Sands, which outcrops in Bedfordshire and Cambridgeshire.

Where the outcrop is covered with till, recharging waters contain higher concentrations of chloride than those recharged in drift-free areas. This is considered to be due to higher evapotranspiration rates where the soil is underlain by boulder clay. Indirect recharge from influent streams and mixing with old saline waters also cause localized increases in chloride concentrations.

Average, annual, natural direct recharge for till-free areas, calculated from average annual rainfall and average chloride concentrations in the recharge and rain waters, agrees closely with published figures calculated using Penman and Grind-ley's equations. Approximate values for recharge through boulder clay are calculated in this way and the merits and limitations of this method for estimating recharge are discussed. The amount of indirect recharge from influent streams is also estimated.
Least-squares fitting of the linear Mohr envelope
Authors: Lisle R. J. , Strom C. S.
Published: November 2007

Introduction

Mohr's hypothesis proposes that when shear failure along a plane takes place, the normal stress σ and the shear stress τ acting on that plane have a characteristic functional relationship. This function relating τ and σ, it is proposed, depends on the material and can be represented on the στ plane by a line defining the critical values of α and τ for shear failure.

In practice this critical line is constructed tangen-tially to Mohr circles representing different combinations of principal stresses applied to specimens of a particular material and is therefore referred to as the Mohr envelope.

For some materials a straight Mohr envelope with the equation τ =
c
+ μσ appears from the results of triaxial testing. Furthermore in the routine testing of some materials (e.g. soils) a straight line envelope is sometimes assumed a priori. In such tests small deviations of the Mohr circles from the envelope are attributed to errors and a best-fitting straight line is used to obtain the parameters (μ,
c
) necessary to characterize the properties of the material.

We describe here a procedure for calculating a best-fitting straight Mohr envelope from data consisting of the applied principal stresses (i.e. from the Mohr circles).

The concept of best-fit used

The criterion used for selecting the envelope of best fit is illustrated in Fig. 1. By means of a least-squares fit we represent the Mohr envelope by a straight line τ =
c
+ μσ- subject to the condition that
S