Lower Lias Clay Research Articles

Laboratory study of the long-term durability of buried concrete exposed to Lower Lias Clay

This paper describes a long-term investigation into chemical degradation vulnerability of four different types of concrete that were exposed to pyrite rich clay. In this, four 100mm square by 1.2m long concrete columns made from Portland cement (PC), Portland limestone cement (PLC), sulfate resisting Portland cement (SRPC) and Portland cement blended with 25% pulverised fuel ash (PC–PFA) were buried for 9years in slightly weathered Lower Lias Clay of water soluble sulfate class DS-2. One face of each concrete column was coated with bitumen to test the performance of this method of protection. The temperature was controlled at 4.5±0.5°C using a cold water circulation system. The performance of the different concretes was assessed by means of visual observation supported by X-ray diffraction (XRD), Infra-red Scanning (IR) and Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM-EDX) to identify the deterioration products.It was found that deterioration due to the thaumasite form of sulfate attack occurred in all four concretes with PLC concrete being the worst affected. The thickness of thaumasite deterioration into the concretes over the 9-year exposure was as follows: PLC=47; PC=33; SRPC=22 and PC–PFA=10mm. The study affirmed the susceptibility to Thaumasite Sulfate Attack (TSA) of both PC–25% PFA replacement and SRPC concretes. It was also found that, the amount of concrete deterioration decreased with increasing burial depth, which was probably due to reduced access to air. The bitumen coating, even if damaged, was an effective barrier at preventing deterioration in all concretes.

Investigation of concrete–clay interaction with regards to the thaumasite form of sulfate attack

The influence of clay composition on the severity of attack due to thaumasite sulfate attack (TSA) on concrete made with CEM I and CEM I blended with 10% Limestone Filler (LF) was investigated. Concrete specimens were exposed to weathered Lower Lias Clay (LLC), for which the water soluble sulfate corresponded to the BRE sulfate class of DS-2, for 12months at 5 and 20°C. A parallel study was carried out in which specimens of the same concretes were placed in sulfate solutions equivalent to DS-2 and DS-4 at the same temperatures. It was found that concrete exposed to clay with sulfate design class DS-2 deteriorated at a faster rate than corresponding specimens in DS-2 solution and at a similar or greater rate to those exposed to the DS-4 sulfate solution. This suggests that the aggressively of clay and resulting concrete deterioration could exceed what might be observed in concrete exposed to equivalent standard test solutions.

Effect of an oak tree on seasonal ground movements in the Lower Lias Clay, Bristol, UK

Changes in ground elevation were monitored between 1990 and 1997 at depths of 0.4, 0.8, 1.2 and 1.6 m and distances of 1, 2.5, 5, 10, 15, 20, 25 and 50 m from a mature oak tree on the Lias Clay of Lower Jurassic age. Whilst movement was evident at all monitoring points, it was most pronounced within 5 m of the tree where in 1995 a maximum seasonal difference of 63 mm was recorded at 0.4 m depth, compared with only 14 mm at the same depth but 10 m from the tree. The influence of the tree on the geotechnical properties of the Liassic clays is reported.

An experimental study of combined acid and sulfate attack of concrete

Abstract There is disagreement about the role of sulfuric acid in the thaumasite form of sulfate attack (TSA) of concrete. Some researchers suggest that thaumasite is formed only at pH above 10.5, whereas others report that the primary cause of deterioration in the affected M5 bridge foundations was sulfuric acid attack followed by neutral TSA. The aim of this work is to reconcile these conflicting views by undertaking parallel studies of concrete exposed to aggressive acid and sulfate solutions and concrete/clay interface work using weathered Lower Lias clay. Concrete specimens have been exposed to BRE Digest 363 sulfate class solutions and acidic and acidic-sulfate solutions at 4.5 ± 0.5 °C. Selected samples are being characterised at intervals up to 5 years. At this stage, results are reported for 5-month samples. Various binders including Portland cement, Portland–limestone cement, blastfurnace slag cement, pulverized-fuel ash cement and sulfate-resisting Portland cement at water/binder ratios (w/b) from 0.35 to 0.5 have been studied. Initial visual observations and X-ray diffraction analyses have identified thaumasite in some of the systems after 5 months immersion in solution. An overview of the ongoing parallel concrete/clay interaction work is also presented to contextualise the concrete work.

Contribution of construction activity to aggressive ground conditions causing the thaumasite form of sulfate attack to concrete in pyritic ground

Abstract Historically, the potential for sulfate concentration to be increased as a result of disturbance of pyrite-bearing ground during construction has not been taken into account in UK guidance documents for concrete specification such as BRE Digest 363. This omission was found in 1998 to have contributed to the occurrence sulfate attack in the foundations to several bridges on the M5 motorway founded on pyrite-bearing Lower Lias Clay. The concrete for these was specified to meet the maximum Sulfate Class 2 natural sulfate levels measured during site investigation, however, Sulfate Class 3 and Class 4 levels were generated subsequently by oxidation of pyrite in backfill. In response to the M5 cases, new UK guidance has been issued for assessing pyrite-bearing ground which may be disturbed by construction activity, this being based on the newly defined parameter total potential sulfate.

Pyrite oxidation in Lower Lias Clay at concrete highway structures affected by thaumasite, Gloucestershire, UK

The process of pyrite oxidation with the resulting formation of sulfates in disturbed pyrite-rich mudstone is recognised in the UK as a potential engineering hazard. This paper describes and quantifies the extent of pyrite oxidation in Lower Lias Clay in Gloucestershire using a large data set collected in 1998 and 1999 during the investigation of twenty-eight, approximately 30-year old highway structures affected by the thaumasite form of sulfate attack. Most of the structures have concrete spread footings founded on undisturbed and relatively unweathered Lower Lias Clay, and are surrounded by backfill of reworked Lower Lias Clay. Chemical, X-ray diffraction and X-ray fluorescence analyses are used to determine the composition of the soils. Differences are identified in the sulfides, sulfates and total sulfur concentrations between unweathered and weathered Lower Lias Clay and the backfill. The work is supported by pyrite oxidation trials in the laboratory on clay samples stored in bags and sealed tubes. The results indicate that pyrite oxidation, sulfate formation and leaching have occurred as the Lower Lias Clay weathers in situ and also during and following disturbance and reworking for highway construction. The amount and rate of pyrite oxidation are estimated, and comparison is made with the concentration of sulfate in the surrounding groundwater, and the extent of thaumasite sulfate attack measured at adjacent structures.

A summary of the Highways Agency Thaumasite Investigation in Gloucestershire: the scope of work and main findings

Abstract A summary of the scope of work, the interpretation approach and some of the main findings of the Thaumasite Investigation carried out on behalf of the Highways Agency on the trunk roads in Gloucestershire is given. The reinforced concrete structures investigated were approximately 30 years old and had been cast in situ using predominantly Grade C35-C40 concrete made using Portland cement with limestone coarse aggregates. All of the backfill surrounding the buried concrete at each structure predominantly comprises reworked Lower Lias Clay, occasionally mixed with some alluvium. There was found to be an decrease in pyrite content and an increase in acid-soluble sulfate as the Lower Lias Clay weathered. The amount of pyrite lost in the Made Ground was generally found to be in the range 50–75%. There was no evidence of acidic ground conditions at the time of the investigations. No significant relationships were found between chemical, mineralogical or physical soil parameters and distance from concrete or degree of thaumasite attack. Groundwater characterisation by means of Piper plots indicated that the groundwater in the Made Ground classifies as a sulfate-type and in the Lower Lias Clay as a sulfate/chloride-type. Sulfate levels in the groundwater extracted from the backfill showed a good correlation with the amount of TSA at a structure. The extent of thaumasite attack was found to be strongly related to groundwater level. Where there was no attack, the concrete was usually above the maximum water level (i.e. permanently dry, except for percolating water) and where there was full attack, the concrete was usually below the minimum water level (i.e. permanently wet). It was found that the process of thaumasite formation leading to TSA creates four zones within structural quality concrete with a sharp reaction front. In the most severe cases of attack, the surface had a white pulpy appearance and often there was expansion. The typical pattern of attack to the buried vertical members was: no attack within 1 m of ground level; local patches of softening or blistering at mid-height; increasingly severe and more widespread attack towards the base. The maximum depth of softening was found to be approximately 45 mm and the maximum amount of expansion of the face of the concrete was 33 mm. Bituminous coatings appeared to have provided partial protection to some structures.

A comparison of classification systems for aggressive ground with thaumasite sulfate attack measured at highway structures in Gloucestershire, UK

Part one of the BRE Special Digest 1 ‘Concrete in aggressive ground’ (2001) provides UK guidelines on assessing aggressive ground conditions with respect to the specification of concrete and protective measures required for concrete structures in contact with the ground. This supersedes the guidelines of BRE Digest 363 (1996) and the Thaumasite Expert Group Report (1999). All three publications rely in part on classifying the ground based on the chemical composition of the soil, backfill and groundwater at the location of the proposed structure. This paper provides an empirical assessment of the three classification schemes that was made possible following an extensive investigation into the thaumasite form of sulfate attack (TSA) in buried concrete highway structures in Gloucestershire. Ground classifications were made at 21 of the sites. The results of this study confirmed that whenever possible, the sulfate concentration in groundwater should be measured, and that as noted in SD1, the potential sulfate classification can be too conservative. The conclusions are limited geologically to the Lower Lias Clay Formation and to Recent Alluvium. The current classification system needs to be developed further by undertaking and reporting similar case studies from a variety of ground conditions.

The engineering geology of the Lower Lias Clay at Blockley, Gloucestershire, UK : J. M. Coulthard & F. G. Bell, Geotechnical & Geological Engineering, 11(3), 1993, pp 185–201

The engineering geology of the Lower Lias Clay at Blockley, Gloucestershire, UK : J. M. Coulthard & F. G. Bell, Geotechnical & Geological Engineering, 11(3), 1993, pp 185–201

Influence of weathering on the engineering behavior of Lower Lias Clay : Coulthard, J M; Bell, F G Proc 26th Annual Conference of the Engineering Group of the Geological Society, The Engineering Geology of Weak Rock, Leeds, 9–13 September 1990P183–192. Publ Rotterdam: A A Balkema, 1993 (Engineering Geology Special Publication No. 8)

Influence of weathering on the engineering behavior of Lower Lias Clay : Coulthard, J M; Bell, F G Proc 26th Annual Conference of the Engineering Group of the Geological Society, The Engineering Geology of Weak Rock, Leeds, 9–13 September 1990P183–192. Publ Rotterdam: A A Balkema, 1993 (Engineering Geology Special Publication No. 8)

The engineering geology of the Lower Lias Clay at Blockley, Gloucestershire, UK

The Lower Lias Clay at Blockley, 20 km due south of Stratford-upon-Avon, UK, is thought to be representative of this clay formation over much of the Severn Basin. As far as the mineralogy of the clay is concerned, illite is the dominant clay mineral, kaolinite being subsidiary, with quartz, calcite, pyrite and chlorite/vermiculite present in subsidiary or accessory amounts. Weathering changes the mineralogy, with illite being degraded and calcite and pyrite being removed. Furthermore free iron oxide coatings become important as a result of weathering, with the maximum concentrations being present in the highly weathered material. The unweathered clay possesses a preferred orientation associated with turbostratic structures. At certain horizons microfolding and remoulding occurs in the unweathered clay and silty layers are displaced. Weathering has progressively destroyed the micro-structures present in the weathered clay horizons. The fissures in the Lower Lias Clay occur in five uniplanar sets. In the unweathered clay the intensity is fairly constant but it increases in a narrow zone just below the weathered horizons. The number of curved fissures also increases at this depth. This intense fissuring continues into the lowest zone of weathered clay where weathering is confined to the fissure surfaces. Fissures become less apparent in the more weathered horizons as more and more degradation has taken place. However, new smaller fissure systems are developed in the weathered clay, as are desiccation cracks. Engineering index properties and values of shear strength are given. Relationships between moisture content and strength, liquid limit and iron (Fe) content were observed, and a relationship between weathering zones and the shear strength-depth curve was established.

Influence of soil-extractable aluminium and pH on the uptake of aluminium from soil into the soybean plant (Glycine max)

The effects of soil pH and other soil properties on the uptake of AI by soybean plants have been investigated in a greenhouse experiment. Six soils were compared that were developed over six contrasting bedrock types ranging widely in their AI content and other chemical and physical characteristics, namely Oxford Clay, Chalk, Lower Lias Clay, Devonian Shale, Granite and Lower Greensand. Soil pH varied naturally between soil types and each soil was also amended to give two other pH levels using elemental sulphur and/or calcium carbonate. AI concentrations in various parts of the soybean plants were determined by ICP-AES after acid digestion. The AI solubility in the soils and hence its availability to the plants was estimated using a number of different reagents designed to extract different forms of AI.The AI concentration measured in the soybean leaves was found to be predicted most accurately by the 'available' AI extracted from soils by 0.02 M CaCl2. The relationship appears to the linear, with a correlation coefficient of 0.97 (p <0.01). The AI content of the leaves increases with decreasing soil pH. The relationship is non-linear with a marked increase in leaf AI for soils with pH <4.4. The amounts of 'plant-available' AI in the soils extracted with 0.02 M CaCl2 was much less than that extracted with 0.05 M EDTA, although both increased markedly with decreasing soil pH. The amount of AI measured in the soybean plants was directly related to both the 'available' forms of AI in the soils, and also to the pH of the soils. Soil pH was identified as a major factor that controls the uptake of Al from soil into the soybean plant.

The role of a soil × dietary sulphur interaction in the impairment of copper absorption by ingested soil in sheep

SummaryFour repletion experiments were carried out to clarify the roles of molybdenum, sulphur and iron in the inhibition of copper absorption by ingested soils. In each experiment, groups of four to six hypocupraemic Scottish Blackface ewes were repleted for 21 days with diets containing CuSO4 and/or soil Cu and the responses in plasma Cu used to assess the availability of the Cu supplied.In Expts 1 and 2, three soils varying in Mo but high in Fe content and derived from Lower Lias Clay, Namurian Shale and Weald loam were added at 100 g/kg D.M. to diets of low (1·0) and high (4·1 g/kg D.M.) S contents: they provided 3·1, 2·8 and 0·1 mg Mo/kg D.M. respectively. When compared with groups given no soil, each soil increased plasma Cu repletion in the low S experiment and decreased it in the high S experiment. Inhibition was thus not completely dependent on soil Mo but dependent upon dietary S.Soils varying in Fe content were compared in the manner of the above experiments in Expts 3 and 4. Two Fe-rich soils, developed from the Upper Chalk and a Barton Clay and providing 2·8 and 1·5 g Fe/kg D.M., impaired Cu repletion on the high S diet but not on the low S diet. A soil, developed on a sand from the Bagshot Beds and providing only 0·15 g Fe/kg D.M., did not impair repletion but FeSO4, providing 0·8 g Fe/kg D.M. did so, irrespective of dietary S content. Ingestion of Fe-rich soils in a high S diet caused three-fold increases in rumen sulphide concentrations 5 and 24 h after feeding. It is suggested that soil ingestion impairs Cu absorption in sheep by trapping S as heavy metal sulphides such as FeS and releasing sulphide in the acid abomasum.

The Romano-British Site at Brockworth, Glos

An area of about two acres (o'8I hectares) produced evidence for occupation, which included two native-type round hunts. A rectangular system of ditches, some with rows of post-holes alongside, conformed to Roman land-measurement. A study is made of this and other possible land-divisions between Brockworth and Gloucester. B ROCKWORTH is situated in the Severn Valley between Gloucester and the Cotswold escarpment. The parish is divided by the line of Ermin Street, with the church and Court lying to the north. The Horsebere Brook winds its way past the site from the slopes of the Cotswolds to reach the Severn about 8 km away near Gloucester. Three other westwardflowing streams cross the low-lying undulating country between Churchdown Hill, 45 km due east of Gloucester, and Robinswood Hill to the south, both outliers of the Jurassic escarpment. Over the Lower Lias clay are spreads of Superficial Deposit, here composed of gravel and sand intermingled with a yellow clay. The local pre-Roman background consists of occupation recorded on Churchdown Hill, the Birdlip burial on the escarpment, and pits and ditches noted at Barnwood on either side of

The geomorphology of the south-central Mendip Hills

The Hills, consisting mainly of cavernous Carboniferous Limestone, form a gently rolling plateau surface at 800 to 850 ft. (245–260 m.) O. D. Several monadnocks of Old Red Sandstone stand up to 200 ft. (60 m.) higher. The steep south flank of the plateau extends nearly down to sea-level and is basically a Triassic feature exhumed from beneath soft Mesozoic strata. The plateau, on the other hand, is thought to be largely a subaerial erosion surface of late Pliocene date. Six erosion benches are recognised on the south flank between 670 ft. (205 m.) and 70 ft. (21 m.) O.D. They reflect the intermittently falling Pleistocene sea-level, and may be correlated with Zenner's eustatic levels from the Calabrian to the Main Monastirian. A more irregular bench in the east is a structural feature developed at the base of the Lower Lias Clay. A system of dry valleys similar in pattern to normal river systems is entrenched into the plateau. The original drainage pattern on the plateau surface was directed southwest or south, probably superimposed from a Miocene dome of Chalk. Entrenchment at the start of the present erosion cycle soon brought adjustment to the Palaeozoic structure. The Cheddar proto-system, closest to the Bristol Channel, had base-level advantage and beheaded most of the others. The valleys debouch through gorges cut in the south flank. The size of the gorges varies according to the size of their fossil catchments. Changes of gradient in the thalwegs are due to a succession of knickpoints receding from the south flank baselevels. Valleys and gorges were incised by surface streams; the upper parts in the late Pliocene and early Pleistocene before drainage had gone underground, the lower parts when streams returned to the surface on Ice Age permafrost. Underground drainage gravitated toward the lowest limestone outcrops. The two main springs are located at the mouths of the two main gorges, Cheddar and Ebbor. Ancient water tables traced in the dry springhead caves can be correlated with the erosion benches. Most of the hundreds of closed depressions or dolines on the limestone plateau were created by solution working down from the surface. Also on the plateau are eighteen internally draining karst basins up to 50 ft. (15 m.) deep and 300 acres (1.2 km. 2) in area. They developed at various stages of the Pleistocene by desiccation of headwater valleys. The older examples have a complex history and supported lakes on permafrost during glacial periods. Most show one or more overspill channels.