Showing papers in "Quarterly Journal of Engineering Geology and Hydrogeology in 1980"

Rebound, its nature and effect on engineering works

Abstract: Summary 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.

Design of foundations of dams containing soluble rocks and soils

Abstract: Summary Four major classes of soluble rocks or soils have been found on dam sites. They are represented by the minerals gypsum, anhydrite, calcium carbonate and halite. Dissolution of these materials can constitute a risk in terms of potential settlements and leakage paths within the foundations of dams. Engineering solutions depend on the solubility and specific rate of solution of the minerals; also upon hydraulic conditions imposed on the foundations. This paper demonstrates a quantitative basis for the design of safe structures which contain these soluble minerals within their foundations. Site investigation procedures are described so that potential estimates of relevant ground parameters may be obtained and used in engineering design.

Additional observations on the Folkestone Warren landslides

Abstract: Summary 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 Horse9s 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.

An introduction to the influence of natural aggregates on the performance and durability of concrete

Abstract: Summary The production of aggregates for construction is the largest of the extractive industries in Britain. Natural aggregates form the main component, by volume, in the manufacture of concrete but the part played by aggregates in the durability and performance aspects of concrete is still relatively little understood. The paper summarizes the main physical and chemical considerations of aggregate in concrete, especially those leading to cracking and deterioration. It broadly considers the British specification of aggregates, which has largely been built up from decades of local experience, and emphasizes the need in many locations overseas for more specific requirements on use of aggregates in different climatic and geological settings. The strong influence on aggregate performance by the use of geologically weathered rock is little recognized even in good concrete practice and is highlighted in the paper. In conclusion, suggestions are given for all-purpose aggregate testing programmes.

P-wave velocity measurements in a machine-bored, chalk tunnel

Abstract: Summary During tunnelling trials in the Lower Chalk at Chin-nor, Oxfordshire, two techniques for assessing rock quality based on measurement of P-wave velocity were evaluated. Ultrasonic pulse velocity measurements at 54 kHz were made over 0.2 m path lengths at the tunnel face and the conventional hammer seismograph method was used over 10 m path lengths along the tunnel side wall. The ultrasonic measurements were obtained by placing transducers on the flat surfaces of circular grooves cut by the tunnel boring machine picks and provided an excellent method for in-situ evaluation of local variations in the mechanical characteristics of the chalk. In order to obtain the relation between acoustic velocity and geotechnical properties of the chalk in this region of complex fissuring, it was necessary to compare average values of velocity and chalk properties for successive readings over a distance of 1.6 m which is equivalent to ten times the mean distance between fissures. Linear relations were found for acoustic velocity versus both chalk strength and discontinuity spacing for the range of chalk variability that was encountered. P-wave velocities from the hammer seismograph observations over 10 m path lengths showed considerably less scatter than the ultrasonic velocities because such a large number of discontinuities was included in each path length but a significant change in values from the range 1.08-1.27 km/s to the range 1.45-1.64 km/s occurred some 35-40 m from the tunnel portal. This increase is directly associated with the change in ground surface level and consequent increase in overburden stress. Moreover, the velocity ceased to increase significantly at an overburden stress of 0.4 MN/m 2 , a level that corresponds well with the stress at which a discontinuity became acoustically closed in laboratory tests. The measurements emphasize the fact that, when the P-wave velocity is used as an indicator of rock quality near the ground surface, it is important to take the effect of overburden stress into account.

Empirical relationship between Los Angeles abrasion and Schmidt hammer strength tests with application to aggregates around Jeddah

Abstract: Summary A study has been made of the Los Angeles abrasion test in relation to the compressive strength of a wide variety of rocks being quarried to meet the growing demand for aggregates around Jeddah. It was found that the results of compressive strength as determined by the Schmidt rebound hammer could be used to predict the Los Angeles abrasion test results. The aggregates tested are of volcanic and plutonic origins and are basic to acidic in composition. A rock material strength map of the Jeddah area illustrates that most of the coarse-grained plutonic rocks are of low strength and the corresponding Los Angeles abrasion values for these rocks are high, rendering them unsuitable, — especially when the aggregate is to be used in road or building construction or is to be subjected to high wear.

Development of piping erosion conditions in the Benson area, Arizona, U.S.A.

Abstract: Summary Piping is a subsurface form of erosion which involves the removal of subsurface soils in pipe-like erosional channels to a free or escape exit. Although it develops in different types of soils and under a wide range of physico-chemical conditions, piping materials are commonly highly erodible. The present study in the Benson area, Arizona shows that piping commonly develops in alluvial deposits in the vicinity of arroyo-cuts and deeply incised gullies actively trenching in the flood plain deposits. It shows also that soils susceptible to piping usually comprise silts and silty sands with a low clay content, and that they are generally of low dry density, high void ratio, and have collapsing properties. It was found that overgrazing the area of study in the past and misuse of the land, combined with the climatic conditions of long dry summers with intermittent short rain storms, have contributed to the initiation and development of piping erosion. Gully erosion and badland topography are quite extensive in the area of study due mainly to the collapse of the pipes at an advanced stage of their development.

Contamination of a Chalk aquifer by mine drainage at Tilmanstone, East Kent, U.K.

Abstract: Summary 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.

Reactions between aggregates and cement paste—an interpretation of the pessimum

Abstract: Summary This paper is concerned with the reaction between the alkalies present in the pore fluids of the cementitious phases of concrete and certain siliceous aggregates. The reaction may be expansive and consequently deleterious. Maximum expansion occurs at some definite or ‘pessimum’ concentration of reactive aggregate for any given mortar. The nature of the reaction is discussed and formulae are given which describe the curve of expansion against proportion of reactive aggregate. The magnitude and significance of the coefficients of these expressions are discussed and suggestions are made for the limits to be set on the allowable expansion and other design parameters if the effects of the reaction are to be minimized.

Properties of aggregates affecting concrete in North America

Abstract: Summary 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.

Permeability of three compacted tropical soils

Abstract: Summary 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.

Reactions between dolomitic aggregate and alkali pore fluids in concrete

Abstract: Summary Carbonate aggregates will react with alkalies from the cement paste in concretes under certain conditions. Several types of reaction are possible, and one involving dolomitic aggregates which contain intergranular clays can lead to disruptive expansion in the concrete. This reaction of dolomite with cement alkalies is essentially one of dedolomitization, a complex reaction rim containing three recognizable zones develops at the interface between the cement paste and aggregate. The details of the reaction processes and of ionic migration with time have been followed using electron probe microanalysis. The effect of the presence of additional alkalies and of sodium chloride on the reaction processes and speed are also discussed on the basis of microanalytical data.

The use of a numerical model in the management of the Chalk aquifer in the Upper Thames Basin

Abstract: Summary A non-linear groundwater model has been developed as an aid in the management of the Chalk aquifer in the Upper Thames Basin. The area of investigation includes Stage I of the Thames Groundwater Scheme, and the model has been used to assess the performance of the aquifer during the severe drought of 1975-76 when river flow was augmented by pumping groundwater into the river. Results indicate that the main loss of water during this period was caused by stream-bed leakage and evaporation from the riparian zone, but that these losses were relatively small. The aquifer is shown to have considerable potential for further development as a major source of water, provided that use is made of denser networks of production boreholes located in the middle and lower slopes of the valleys in the area of Chalk outcrop.

Itacolumites: the flexible sandstones

Abstract: Summary Itacolumites (flexible sandstones) display a bimodal stress-strain behaviour resulting from an unusual inter-digitated grain-to-grain fabric. The sandstone can move freely over a limited arc, then locks, and displays only elastic behaviour. Grain contacts are all open about 5 μm, thereby permitting some free movement. Each quartz grain is interdigitated with its surrounding neighbours, therefore the specimen has appreciable fabric cohesion despite a lack of true mineral cement. Fabric cohesion, as opposed to cementitious cohesion, is strongly stress dependent, and itacolumites can be expected to have highly curvilinear failure criteria.

Frost heave of roads

Abstract: Summary The mechanism by which frost heave occurs when freezing temperatures, frost-susceptible materials and an adequate supply of water occur simultaneously is outlined. Index tests for identifying frost-susceptible materials (particularly sub-base aggregates) are discussed and emphasis is given to improvements in the Transport and Road Research Laboratory (TRRL) test and the role of suction/permeability relationships. Analysis of the design procedure to prevent frost heave damage highlights the importance of material and environmental factors. Results from homogeneous and composite specimens support this conclusion. A quantitative model has been developed and reasonable agreement obtained between its predictions and the heave observed in a Precise Freezing Cell. The work described is relevant to the improvement of empirical design procedures in the near future as well as the possible introduction of analytical design methods at a later stage.

Experimental assessment of pollutant migration in the unsaturated zone of the Lower Greensand

Abstract: Summary In Britain most groundwater resources are held in bedrock aquifers and the unsaturated zone forms an important buffer between landfill disposal sites and the water table. The processes which control the transfer of (1) persistent organic compounds, (2) inorganic anions and (3) heavy metals, in the unsaturated zone have been evaluated using experimental lysimeters constructed in the Lower Greensand at a site near Uffington, Oxfordshire. Complementary monolith and column experiments were conducted. Biodegradation is the primary mechanism for the attenuation of the inorganic anions and the organic species, but the migration of heavy metals is limited by interactions with the sediment. Sequential, selective chemical extraction indicates that the stability of the geochemical phases retaining heavy metals controls their rate of movement. Although the processes which regulate the partition of the heavy metals are complex, uptake by sesquioxides and clay minerals are particularly important.

The influence of serpentinite and other rocks on the stability of concretes in the Middle East

Abstract: Summary It has been suggested that the expansive serpentinization of olivine can occur in concretes which contain ultrabasic aggregates. This process could lead to the deterioration of concretes and has been blamed for the poor performance of some concretes in the Middle East. This paper reviews the petrology of serpentinite-bearing concretes and mortars made with aggregates collected in the United Arab Emirates. It shows that most, if not all, of the deleterious changes observed in the field can be explained by other mechanisms involving contaminant lithologies and factors not connected with the aggregates; and that olivine has remained unaltered in concretes of up to 40 years in age.

Cement hydrate development at opal-cement interfaces and alkali-silica reactivity

Abstract: Summary 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.

Coastal engineering problems at Clacton-on-Sea, Essex

Abstract: Summary 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.

A brief review of foundation construction in the Western Canadian Arctic

Abstract: 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 Hudson9s 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

Fault control of groundwater flow and hydrochemistry in the aquifer system of the Castlecomer Plateau, Ireland

Abstract: Summary 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.

The suitability of aggregates from weathered Peterhead granites

Abstract: Summary Concrete has traditionally been made using sand and gravel filler. Concretes have been compared using two variably weathered granites from north east Scotland as aggregates. This study investigates the differences produced in concrete made from different grades of weathered aggregate. As the intensity of weathering increases, the bond between mineral grains weakens and therefore the durability of the aggregate is diminished. The intensity of weathering can be shown by the loss of certain oxides in the rock mass. Some of the major requirements for concretes are the impact and abrasion values of the aggregates used, and the shrinkage and compressive strength of the concrete produced. It can be shown that these values are all dependent on the mineralogy, geochemistry and petrology of the aggregate.

Discussion on ‘Large landslides in London Clay at Herne Bay, Kent’ by E.N. Bromhead: J. N. Hutchinson writes

Abstract: Bromhead9s 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 Bromhead9s 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

Applied petrology—the stability of concrete aggregates

Abstract: The papers in this issue were presented at an Ordinary General Meeting of the Society in February 1979. They illustrate some of the aggregate problems that can arise in modern concrete and the value of petrological and geochemical techniques in the study of potentially deleterious systems. It is common to regard concrete aggregates as inert filler. Perhaps in Britain this is fair, although in recent years several examples of damage due to aggregate instability have been described. Internationally, the difficulties of finding good aggregate are more profound; British flint may make good concrete but Danish and German flint is often reactive and extremely deleterious. The problems are particularly acute in extreme climatic zones and where hard rock and good gravel is scarce or must be transported for great distances. The Chairman of the first session, Mr A. D. Robertson of Sir William Halcrow and Partners, referred to the very great interest created by the problem of the behaviour of concrete in the Middle East and recalled that one of the first occasions on which this had been aired was in the Society9s meeting room, as recently as 1975. Since the first signs of trouble had manifested themselves in Bahrain the scale of construction in the Middle East had increased dramatically and the earlier problems had been exacerbated by the need to find sources of aggregate in quantities far in excess of earlier demands for use in more elaborate forms of construction capable of sustaining higher stresses. Early considerations of concrete

Discussion on ‘Large landslides in London Clay at Herne Bay, Kent’ by E.N. Bromhead: M. Dunbaven writes

Abstract: M. Dunbaven writes: The geometrical forms of the slips described in the paper bear many similarities to failures in mining waste dumps reported by Blight (1969). The important feature of the slides is the coincidence of the lower parts of the slip surfaces with a weaker layer of soil; in this case the Oldhaven Beds of silty fine sand. The example chosen for discussion is the Mirmar landslide where the weak layer forms the base of a simple slope. A careful study of some similar landslides has shown that the graben block and the en masse movement of the lower slope are common characteristics. Recent research at James Cook University has reproduced such failures in a small physical model. A slope made from a well graded cohesionless silica sand was built over a layer of bentonite saturated to give low yield strength. Overall dimensions of the slope were: height 400 mm, width 750 mm, base length 1100 mm. The kinematics of the failure have been determined by photography which revealed basically a movement of two ‘rigid’ wedges. A computer study based on a wedge analysis was conducted using both force balance and energy balance equations, with the condition that one slip-plane pass through the base material. The situation which created the highest force or energy imbalance was calculated by numerical optimization. For both methods, the predicted slip-planes closely followed those observed in the laboratory, however, different answers would be expected for a material which exhibited significant dilatancy.

Discussion of papers in this issue

Abstract: 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 Gillott9s (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