Keuper Marl Research Articles

Relationship between California Bearing Ratio and elastic stiffness for compacted clays : Brown, S F; O'Reilly, M P; Loach, S C Ground EngngV23, N8, Oct 1990, P27–31

This paper reports data emphasising the nonlinear response of three compacted commonly occurring British clays, and examines the relationship between resilient stiffness and the Californian Bearing Ratio (CBR). The three soils tested were: (1) Keuper Marl, more properly known as Mercia Mudstone; (2) Gault Clay; (3) London Clay. Independent series of repeated load triaxial tests and CBR tests, under conditions appropriate to pavement subgrades, were performed on remoulded samples of these clays; the results of the triaxial tests were related to those of the CBR test by means of soil moisture contents. The experiments demonstrated that: (1) resilient Young's Modulus depends on the soil suction, the magnitude of the applied deviator stress pulse, and the soil type; (2) there is not a unique relationship between resilient Young's Modulus and CBR, because of the influence of deviator stress; (3) for soils compacted at water contents greater than the plastic limit, the relationship between resilient Young's Modulus and CBR, for a given deviator stress pulse magnitude, has the same type as that proposed by the Transport and Road Research Laboratory; (4) even though this equation takes no account of soil type, it is better than a simpler relationship often used previously. (TRRL)

Use of the standard penetration test for the design of bored piles in the Keuper Marl of Cardiff : Kilborn, N S; Treharne, G; Zarifian, V Proc Conference on Penetration Testing in the UK, Birmingham, 6–8 July 1988P87–92. Publ London: Thomas Telford, 1989

Use of the standard penetration test for the design of bored piles in the Keuper Marl of Cardiff : Kilborn, N S; Treharne, G; Zarifian, V Proc Conference on Penetration Testing in the UK, Birmingham, 6–8 July 1988P87–92. Publ London: Thomas Telford, 1989

Experience with a new high pressure self boring pressuremeter in weak rock. Part II : Ground EngngV22, N6, Sept 1989, P45–52

This article describes the development of a new high pressure self-boring pressuremeter (rsbp), which allows the in situ direct measurement of strength and deformation characteristics of keuper marl for foundation design beneath a new United Kingdom power station site. A specific weathering scheme for the keuper marl at this site grades the material a to d according to the proportion of clay and condition of the joints; this is shown in table 1. The authors first establish the need for a self-boring pressuremeter which could be used in weak weathered rock, overcoming the problems of predrilling, allowing horizontal stress to be assessed directly and giving more reproducible values of modulus, less affected by membrane compression. The new instrument is designed to operate through h casing or in nx boreholes. It is 73.6 mm in diameter and 450 mm long; it can be expanded up to 12% cavity strain or 20 mpa. It uses a 2 rod drilling system but can be operated with a rotary rig. Rock cuttings are flushed to the surface using water or liquid polymer mud. Oil pressure is used to expand the pressuremeter; the thin composite membrane is made of nylon and neoprene. Transformer oil and power for electronics and transducer signal readings is supplied via 2 hydraulic hoses. Full details are given of the calibration tests used. The second part of this article is published in the September 1989 issue of ground engineering.

Calibration and its effect on the results of pressuremeter tests in weak rocks

Abstract The paper describes in situ testing recently carried out in Keuper Marl using the Hughes high-pressure dilatometer for which an extensive study into calibration and its effects on results was made. The various calibrations performed are described followed by discussion of the effects of calibration corrections on the results obtained. The findings illustrate the importance of proper calibrations before and during a pressuremeter testing programme. In particular, the significance of membrane compression calibrations when testing mudstones classified as weak to moderately weak or stronger is highlighted.

Viscous effects observed in tests on an anisotropically normally consolidated silty clay: technical note : O'Reilly, M P; Brown, S F; Overy, R F GeotechniqueV39, N1, March 1989, P153–158

Research is reported that provides quantitative evidence, for a silty clay, that the undrained shear behavior of cohesive soils is rate-dependent. A method, in qualitative terms, is suggested for modelling the general viscoelastic behavior of soils. Undrained triaxial tests were performed at a range of strain rates on specimens of an anisotropically normally consolidated silty clay derived from keuper marl. The results from these tests were used to formulate a simple model based on critical state soil mechanics concepts. The study found that the strength of K sub o anisotropically consolidated triaxial specimens of silty clay was dependent on the rate at which the test was performed. The concept of a viscous yield locus was postulated. This surface exists simulataneously with the static yield locus. The concept of viscous plasticity is found to be useful in understanding the behavior of fine-grained soils during cyclic loading in which viscous effects are important.

Long term measurements of forest soil exposure and creep in Luxembourg

The main theme of this article is the influence of biotic activity on the processes of splash and creep. Since 1980 forest floor exposure to splash and its agents (worms, moles, game and stemflow) has been recorded yearly along 5 transects across three materials in the Lias cuesta area: Lias sandstone, Psilonoten marls and Keuper marls. Measurement of tree vitality as a factor of leaf production was added in 1985. There is a decline in tree vitality since 1985. Main biotic component for exposure are worms which are particularly abundant in Keuper soils. Consequently, Keuper soils are more exposed to splash than the Psilonoten soils, whereas the soils of the Lias sandstone remain protected by a litter layer throughout the year. Creep in the surface soil of Keuper soils could be demonstrated with sand columns buried in 1981 which showed bending after one year but had largely disappeared by bioturbation six years later. Another form of creep involving the subsoil is due to the vertic properties of the weathering mantle and leaves slickensides in micromorphological sections.

Lost & Found: 161. Denstone College Collection

Tom Sharpe (Dept. of Geology, National Museum of Wales, Cathays Park, Cardiff CFl 3NP) writes: Tt may be of interest to record that the NMW acquired several specimens from the Cyril Brett mentioned in connection with Denstone College (see also Fig.3). The first acquisition in 1923 from *Prof. Cyril Brett, Denstone College Museum, Staffs.* comprised six fossils from the Trias and six specimens of salt pseudomorphs from the Keuper Marl of Staffordshire, and the second in 1934 from *Cyril Brett MA, 23 Lon-y-dail, Rhiwbina', comprised gem gravel (sapphire and garnet) from Butte, Montana, USA.* Fig.3. Some Denstone College fossils; from Smith, W.B. 1915, Cambridge count\ geographies: Staffordshire, p.34. Cambridge University Press. (Walter Bernard Smith was the Senior Science Master at...

Keuper Marl as a road foundation - predicting its strength : Turner, A J; Seago, K L Proc Symposium on Failures in Earthworks, London, 6–7 March 1985 P243–252. Publ London: Thomas Telford, 1985

A road constructed on a subgrade of Keuper marl experienced failure in areas of cut following the trafficking of the road base by construction traffic. Laboratory tests carried out on the subgrade material subsequent to failure showed the material strength to be very sensitive to moisture content. This paper attempts to relate strength in terms of CBR to a non-dimensional condition index, based upon moisture content and plasticity index, so that comparison with similar materials can be made. For the covering abstract of the symposium see IRRD 286603. (Author/TRRL)

The effect of cyclic loading on the undrained shear strength of a silty clay

Abstract The strength of saturated clays subjected to low‐frequency cyclic loading is of considerable importance in the design of offshore structures. A series of postcyclic undrained triaxial strength tests were carried out on samples of a silty clay (Keuper Marl), which had not failed under cyclic loading, to investigate the effect of this loading on the postcyclic monotonie effective stress path and strength of the soil. Undrained cyclic loading of normally consolidated and lightly overconsolidated samples by generating positive pore pressures caused the apparent degree of overconsolidation to increase. Samples subsequently subjected to monotonie testing followed effective stress paths commensurate with this apparent overconsolidation and failed on the “Hvorslev” surface on the “dry” side of the stable state boundary surface rather than on the critical state as would be expected of samples of this initial stress history. Samples which were initially heavily overconsolidated did not generate large pore ...

The Application of Ground Conductivity and Offset Wenner Resistivity Soundings to Optimise the Investigation of a 300 ha Site in the West Midlands

Abstract In order to evaluate quickly and cost effectively the detailed shallow sub-surface geology of a 300 ha area in the West Midlands, geophysical techniques were used in conjunction with shell and auger drilling. Since the area contains one of the largest landfill sites of its type in Europe and is crossed by a river which is abstracted for drinking water within a short distance downstream, it was important to determine the geology and hydrogeology in some detail. Previous geological surveys of the area, which included the drilling of over 80 boreholes for sand and gravel extraction, indicated the presence of up to 5 m of highly variable sandy overburden overlying Keuper Marl. It was apparent from an initial desk study that despite the large number of boreholes the geology had been completely misinterpreted. A ground conductivity map was produced using a Geonics EM-31 which rapidly gave a picture of the general structure and identified targets for drilling and Offset Wenner resistivity soundings. The geophysics revealed the presence of a major buried channel cutting deeply into the marl, which was later confirmed in several places by drilling. Surface outcrops of clay or marl could be identified using the ground conductivity values alone. The use of the geophysical techniques has considerably reduced the cost and time of the investigation and has allowed the major effort to be concentrated in problem areas.

A Pore pressure and stability model for a silty clay under repeated loading

The behaviour of saturated clays subjected to low frequency cyclic loading is of considerable importance in the design of offshore structures. Monotonie strain-controlled and low frequency (0·1 Hz) repeated load triaxial tests have been carried out on reconstituted samples of Keuper Marl, a silty clay, under undrained conditions. The strain-controlled tests were carried out at overconsolidation ratios of 1, 4, 10 and 20 and the data from these tests were used to establish the stable state boundary surface. Results from repeated load tests on samples with overconsolidation ratios of 1 and 4 were compared with this boundary surface. Previous investigations have shown that the dry side of the state boundary surface for clays, sometimes known as the Hvorslev surface, forms an empirically determined stability criterion for cyclic effective stress paths of samples of all stress histories. Normally consolidated and lightly overconsolidated soils subjected to undrained cyclic loading become heavily overconsolidated, the movement of the effective stress path being governed by the build-up of porewater pressure. It has been shown that the rate of pore pressure development is a function of the number of cycles, the applied stress and the sample stress history. The combination of the stability criterion with the pore pressure relationship allows the prediction of the number of cycles to failure in terms of fundamental critical state constants and two further easily determined pore pressure parameters. Le comportement des argiles saturées soumises à des chargements cycliques de basse fréquence a une grande importance pour la construction en mer. Des essais triaxiaux monotones à chargement répétés ont été effectués avec déformations contrôlées et à basse fréquence (0·1 Hz) sous des conditions non-drainées sur des échantillons reconstitués de la marne Keuper (une argile limoneuse). Les essais à déformation contrôlée ont été effectués avec des rapports de surconsolidation de 1, 4, 10 et 20 et les résultats obtenues à partir de ces essais ont été utilisés pour établir la surface limite d'état stable. On a comparé les résultats des essais à chargements répétés sur des échantillons ayant des rapports de surconsolidation de 1 et 4 avec cette surface limite. Des recherches antérieures ont montré que le côté sec de la surface limite d'état dans le cas des argiles, auquel on donne parfois le nom de surface de Hvorslev, constitue un critère de stabilité déterminé de façon empirique pour les chemins de contraintes efficaces cycliques des échantillons soumis aux contraintes de façon quelconque dans le passé. Des sols normalement consolidés, ou légèrement surconsolidés, qui sont soumis au chargement cyclique dans des conditions non-drainées deviennent très surconsolidés, le mouvement du chemin de contrainte efficace étant régi par l'accroissement de la pression de l'eau interstitielle. On a démontré que la vitesse de développement de la pression interstitielle dépend du nombre de cycles, de la contrainte appliquée et de la contrainte à laquelle l'échantillon a été soumis dans le passé. La combinaison du critère de stabilité et du rapport de pression interstitielle permet la prévision du nombre de cycles jusqu'à la rupture en fonction de constantes d'état critiques fondamentales et de deux autres paramètres de pression interstitielle qui sont facilement déterminés.

The soil clays of Great Britain: I. England and Wales

AbstractThe mineralogy of the clay fractions (<2 µm) of the major soils of England and Wales is reviewed, and the data presented in terms of the 1:250 000 National Soil Map. Most soils developed in pre-Rhaetic sediments are dominated by mica with lesser amounts of chlorite and kaolin. Exceptions are soils developed in calcareous Coal Measure shales which have significant smectite contents, and freely drained soils in Keuper Marl which contain swelling chlorite, sepiolite and palygorskite. Soils developed in post-Triassic sediments are dominated generally by expansible minerals, except for those developed in Lower Lias and Estuarine Series rocks (Jurassic) which are dominated by mica and kaolin respectively. The presence of loess in soils seems to be associated with the occurrence of a complex interstratified mineral with X-ray diffraction properties akin to vermiculite. Weathering of soil clays is most marked in the wetter uplands, but over most of lowland England is detectable only by slight changes in non-exchangeable potassium content and cation-exchange capacity towards the soil surface. Applications of soil clay mineralogy in the fields of plant nutrition and soil mechanics are discussed, in particular the production of maps showing mineralogical provinces.

Sediment source and storage in small watersheds on the Keuper marls in Luxembourg, as indicated by soil profile truncation and the deposition of colluvium

Soil survey reports and soil maps of 11 second-order watersheds on the Keuper marls in Luxembourg were used to establish the extent to which soils were modified by accelerated erosion and colluviation, and to calculate the volume of colluvium. The amount of truncation of the soil profiles in the eroded area is on average 55 cm, of which the equivalent of 36 cm remains in the watersheds as colluvium. The 34% of the eroded soil material that has left the watersheds represents the longterm sediment-delivery ratio. Landuse exerted a more powerful control on the production of colluvium than geomorphology. The area occupied by colluvial soils (C, ha) which offer good quality land can be predicted from the area under agriculture (L, ha) with the equation C= .74L− 56. Comparison with palynologically dated colluvium produced figures for sediment yield of the source areas in the range between 700 and 1800 kg/ha · year.

Soil water regimes of soils developed on Keuper Marl

SUMMARYThe deeper horizons of soils developed on Keuper Marl (Worcester Series) often remain unsaturated during the winter, with corresponding high tensions, even when the surface layers are waterlogged. Re‐wetting of the deeper layers is restricted because of the inherent low volume of coarse pores in the Bt horizon and because the small volume of desiccation cracks formed during the summer soon disappear on re‐swelling. It is suggested that this unexpected water regime may not be uncommon in soils developed on clay‐shale sediments and that the soil drainage (wetness) classes recognized in England and Wales may need to be modified.

Behaviour of a bridge abutment foundation on Keuper marl during and after construction : Marsland, A; Butcher, A P; Taffs, F H Inst Civ Engr ProcV74, Nov 1983, P917–944

Behaviour of a bridge abutment foundation on Keuper marl during and after construction : Marsland, A; Butcher, A P; Taffs, F H Inst Civ Engr ProcV74, Nov 1983, P917–944

Sediment source and storage in small watersheds on the Keuper marls in Luxembourg: As indicated by soil profile truncation and the deposition of colluvium

Soil survey reports and soil maps of 11 second-order watersheds on the Keuper marls in Luxembourg were used to establish the extent to which soils were modified by accelerated erosion and colluviation, and to calculate the volume of colluvium. The amount of truncation of the soil profiles in the eroded area is on average 55 cm, of which the equivalent of 36 cm remains in the watersheds as colluvium. The 34% of the eroded soil material that has left the watersheds represents the longterm sediment-delivery ratio. Landuse exerted a more powerful control on the production of colluvium than geomorphology. The area occupied by colluvial soils (C, ha) which offer good quality land can be predicted from the area under agriculture (L, ha) with the equation C = .74 L − 56. Comparison with palynologically dated colluvium produced figures for sediment yield of the source areas in the range between 700 and 1800 kg/ha·year.

THE BEHAVIOUR OF A BRIDGE ABUTMENT FOUNDATION ON KEUPER MARL DURING AN -D AFTER CONSTRUCTION.

Site investigation, including large-diameter deep in-situ plate loading tests and pressure-meter tests on Keuper Marl in Cheshire, is described. Details of the instrumentation and measurements made on a bridge foundation during and after construction are given. These included measurements of the bearing pressures acting on a 1 M wide strip across the foundation as well as measurements of pore-water pressures and settlements at and below foundation level. The total pressures measured across the base clearly reflected the construction sequence and gave overall pressures close to the estimated values. However, the distribution of pressure across the base differed significantly from that estimated. The pore-water pressures dissipated quickly and most of the settlement occurred during construction. The deformation parameters back-analysed from the differential settlements measured under the bridge are compared with those obtained from the plate and pressuremeter tests. (Author/TRRL)

A stable isotope study of the Mercia Mudstones (Keuper Marl) and associated sulphate horizons in the English Midlands

ABSTRACT Widespread evaporitic sulphate horizons occur in the frequently dolomitic Mercia Mudstones (Upper Triassic) of the English Midlands. The mudstones were deposited on an extensive peneplain which had areas of upstanding minor relief (Charnwood Massif, Derbyshire—Pennines, London Platform). Horst and graben structures formed during the early and middle Triassic, controlled late Triassic sedimentation rates and peneplain slope directions. A stable isotope study (S,C,O) of the sulphates and dolomites of the Trent Formation indicates that during the deposition of the lower Fauld Member grabens such as the Need wood Basin in Staffordshire and areas marginal to a graben such as Newark in Nottinghamshire had a marine brine regime with minor continental input. Using constraints applied by sulphate concentrations of modern waters in arid environments, the ratio of volume of marine input to volume of continental input lay between 3:1 and 4:1. The horst area (East Leake, Nottinghamshire) was strongly influenced by continental brines which derived sulphate from the exposed Carboniferous Hathern Anhydrite Series. A predominantly continental brine regime existed across the whole area during deposition of the overlying Hawton Member. Periodic marine influxes gave rise to thin sulphate horizons whilst continental run‐off was occasionally sufficient to form temporary lakes. The Blue Anchor Formation (Rhaetian) was deposited in a lacustrine environment with waters of mixed marine and continental origin. Salinities were lower than those of the preceding Trent Formation brines.

The Formation of the Lias Cuesta (Luxembourg) in the Light of Present-Day Erosion Processes Operating on Forest Soils

The escarpment of the Lias cueasta in the southern part of Luxembourg is formed by the Lias sandstone. The lowland in front is underlain by poorly consolidated Keuper marls. In several places the equally weak Psilonoten marls form a secondary step between the main escarpment and the lowland. As this relief configuration cannot be accounted for by lithological differences between the underlying rock types, the hypothesis is tested here that it is due to differential erosion of the soil under natural conditions, i.e. deciduous woodland. It is shown that this hypothesis can be accepted when the erosion processes are viewed in their ecological context. Today, erosion by splash is one of the major processes responsible for lowering the forest floor in Luxembourg. It was found that, other conditions being equal, the efficacy of this process is determined more by the absence of a protective litter cover than by the erodibility of the soil material. Due to a much larger exposed surface area, especially during the summer months, the Keuper soils are indeed more subject to splash than the Psilonoten soils, whereas the soils of the Lias sandstone remain protected by a litter layer virtually throughout the year. Leaf consumption by earthworm, mainly Lumbricus terrestris, is the principal cause of the observed differences. The ecological conditions of the poorly drained Keuper soils are most favourable for this earthworm species.

Strength tests on large diameter cores of Keuper Marl and application to a slope failure (In German) : Wichter, L Publ Inst Soil Mech, Rock Mech, Univ Fridericiana, Karlsruhe, N84, 1980, 177P

Strength tests on large diameter cores of Keuper Marl and application to a slope failure (In German) : Wichter, L Publ Inst Soil Mech, Rock Mech, Univ Fridericiana, Karlsruhe, N84, 1980, 177P