Leighton Buzzard Sand Research Articles

Applications of the oedometer, triaxial and resonant column tests to the study of micaceous sands

Intergranular void ratio, e s, can be used as an alternative indicator to assess the mechanical and dynamic properties of composite matrix of coarse and fine grains. In this paper, an intensive laboratory study of saturated coarse rotund sand (i.e., Leighton Buzzard Sand) and fine (i.e., mica) mixtures with various mix ratios is performed by a series of oedometer, triaxial and resonant column tests. Oedometer tests performed on coarse rotund sand–fine mixtures show that initial conditions, fines percentages, and stress conditions affect the compression behaviours. Tests indicated that, up to a fraction of mica, which is named as transition fines content (FC t), compression behaviour of the mixture is mainly governed by the sand grains. As the percentage of mica exceeds FC t, mica governs the compression. In the triaxial tests, deviatoric stress ( q), pore pressure ( u), and undrained Young's modulus (Eu) have been obtained in a triaxial testing apparatus. Results revealed that there is a close relationship between the FC t and q, u, and Eu values. In the resonant column tests, a study of dynamic properties of saturated mixtures was investigated by measuring its shear modulus ( G) and damping ratio ( D), which is harmonic with the oedometer test results.

Some observations of the effects of pore fluids on the triaxial behaviour of a sand

This paper describes unusual stress–strain behaviour, involving deviatoric stress, axial strain and pore pressure jumps, observed during undrained triaxial compression testing of Leighton Buzzard sand when using syrup and silicon oil pore fluids. The materials, pore fluids, specimen preparation and test methods are described, as are the results of a suite of triaxial tests in a temperature controlled cell in which deviatoric stress, pore pressure and local strain were measured. The results are compared with the some existing data showing similar effects, and possible causes of the strain jumps are postulated. The results suggest that specimen formation in the way used here, in a viscous fluid, could suppress dilatancy.

Constitutive modeling of Leighton Buzzard Sands using genetic programming

This paper investigates the results of laboratory experiments and numerical simulations conducted to examine the behavior of mixtures composed of coarse (i.e. Leighton Buzzard Sand fraction B) and fine (i.e. Leighton Buzzard Sand fraction E) sand particles. Emphasis was placed on assessing the role of fines content in mixture and strain level on the deviatoric stress and pore water pressure generation using experimental (i.e. Triaxial testing) and numerical approaches (i.e. genetic programming, GP). The experimental database used for GP modeling is based on a laboratory study of the properties of saturated coarse and fine sand mixtures with various mix ratios under a 100 kPa effective stresses in a 100 mm diameter conventional triaxial testing apparatus. Experimental results show that coarse–fine sand mixtures exhibit clay-like behavior due to particle–particle effects with the increase in fines content. It is shown that GP modeling of coarse–fine sand mixtures is observed to be quite satisfactory. The results have implications in the design of compressible particulate systems and in the development of prediction tools for the field performance coarse–fine sands.

Neuro-fuzzy based constitutive modeling of undrained response of Leighton Buzzard Sand mixtures

This study aims to develop neuro-fuzzy (NF) based constitutive model for Leighton Buzzard Sand fraction B and Leighton Buzzard Sand fraction E mixtures using experimental data. The experimental database used for NF modeling is based on a laboratory study of saturated mixtures with various mix ratios under a 100 kPa effective stress. Emphasis was placed on assessing the role of fines content in mixture and strain level on the deviatoric stress and pore water pressure generation in a 100 mm diameter triaxial testing apparatus. The input variables in the developed rule based NF models are the Leighton Buzzard Sand fraction E content, and strain, and the outputs are deviatoric stress, pore water pressure generation and undrained Young’s modulus. Experimental results show that Leighton Buzzard Sand fraction B and Leighton Buzzard Sand fraction E mixtures exhibits clay-like behavior due to particle–particle effects with the increase in Leighton Buzzard Sand fraction E content. It is also shown that the performance of capacities of proposed NF models are quite satisfactory.

Study of the yielding of sand under generalized stress conditions using a versatile hollow cylinder torsional apparatus

The hollow cylinder torsional apparatus (HCTA) is particularly suited to studying the mechanical behavior of cross-anisotropic test specimens since both the magnitudes of the three principal stresses and the orientation of the major–minor principal stress axes can be independently controlled. Novel features of the University College Dublin HCTA, particularly the instrumentation and calibration procedures necessary to achieve accurate generalized stress path testing, are presented. The plastic yield behavior of fully saturated Leighton Buzzard sand was studied under generalized stress conditions. Physically identical test-specimens (35.5 mm inner radius, 50.0 mm outer radius and 200 mm in length) were prepared using a water-pluviation technique that reproduced the inherent cross-anisotropic fabric of many natural sand deposits. A series of stress path tests systematically probed the stress space in order to locate segments of yield loci. The deviator stress at yield was found to vary in a well-defined pattern that depended on the magnitude of the intermediate principal stress parameter. However, the deviator stress at yield was largely independent of reorientations of the major principal stress that had occurred during the initial anisotropic consolidation stage of the tests. The experimental yield data was used to show that the Matsuoka–Nakai and Lade yield criteria provide satisfactory predictions of the onset of plastic yielding in sand deposits under generalized stress conditions for routine geotechnical engineering design.

The Direct Shear Strength and Dilatancy of Sand–gravel Mixtures

A total of 87 direct shear tests in a large direct shear-box apparatus have been used to investigate the strength and dilatancy of sand–gravel mixtures. This paper focuses on the differences in behaviour between a silica sand (yellow Leighton Buzzard sand) and sand–gravel mixtures obtained by adding fractions of two kinds of gravel to the sand. The purpose is to find a relation between the grain-size characteristics of the materials and the shearing resistance. Experimental results are analysed in terms of the frictional and dilatant contributions to the strength of mixtures as a function of their relative density, and are compared with dilatancy theories and empirical equations. The addition of gravel to the mixtures, even at low fractions (less than 0.1 by volume), causes an increase in peak friction angle (Φ ′peak) which results both from higher dilatancy at failure (ψ max) and higher constant volume friction angle (Φ ′cv). Use of the minimum voids ratio (e min) of the materials allows the data for the two families of mixtures to be normalized and interpreted in terms of Φ ′cv and the ratio (Φ ′peak − Φ ′cv)/ψ max. The relationships between relative density (D r ), ψ max and Φ ′peak − Φ ′cv are only partly explained on a physical basis, so we develop empirical equations to predict the peak shear resistance of sand–gravel mixtures (up to gravel contents of 0.5) on the basis of easily measurable quantities. Such equations constitute a practical tool to overcome the problems arising from the impracticality of testing coarse material in the standard shear-box apparatus.

Controls on quartz silt formation by crystalline defects

Silt composed predominately of quartz occurs abundantly in the sedimentary material found in deposits worldwide. Its origin is still the subject of many debates, but one acknowledged source is due to glacial grinding. To examine this problem and test the apparent contradictory evidence in the literature, a series of experiments were performed. In these experiments, the Bromhead ring shear apparatus was used as it can simulate glacial grinding due to its uninterrupted shearing action; hence, it provides an effective reproduction of glacial grinding. Experiments conducted on unweathered sand-sized vein quartz produced little silt, while use of sand from a sedimentary deposit, Leighton Buzzard sand, produced plentiful silt. Experimental results suggest that there is an internal mineralogical control on the formation of quartz silt particles. It is argued that the processes involved in the formation of quartz introduce defects (Moss defects) into the low-quartz crystal structure, demonstrated by the presence of peaks in the particle size curve around 20 microm. This indicates that there is a lithological control for the silt yielded under weathering, and this could explain why a pronounced mode at around 20-60 micirom is commonly observed in silts, such as loess.

Development of a New Hollow Cylinder Apparatus for Stress Path Measurements over a Wide Strain Range

Abstract The development and operation of a new, automated hollow cylinder apparatus that facilitates accurate stress path measurements from the pseudo elastic domain to failure strain levels are described. Innovative sample loading mechanisms of 19.3 kN axial and 103 N · m torsional capacities facilitate rapid, precise (of the order of 10−5 % strain) displacement and rotation of the sample loading piston, with negligible compliance in the mechanisms on reversing the direction of piston motion. Both internal and external instrumentation are used to record the deformational response of the test specimen to better than 10−2 % strain. Significant differences were found between the strain values measured using the internal and external instrumentation, with the external instrumentation underestimating the true stiffness of the specimen. A series of drained stress-path tests on Leighton Buzzard sand specimens showed that predefined stress paths can be followed to an accuracy of 0.5 kPa using the new apparatus.

An improved direct shear apparatus for sand

A conventional direct shear apparatus (DSA) has been modified to improve its articulation by moving the point of shear load application to the sample centre. Jewell's symmetrical arrangement has been adopted for a 100 mm square shearbox, resulting in increased dilation rate and reduced rotation. Testing using coarse Leighton Buzzard sand has enabled the performance of the modified DSA to be optimised by exploring different test configurations. Optimum results were obtained with a substantial initial gap between the shearbox frames of 5D50, the use of thin rubber edging strips to contain the sand, and the omission of grid plates at the sample boundaries. Upper-frame rotations persist during testing, but have almost no effect on measured parameters. A framework of relationships between parameters measured in a direct shear test ((ϕ′ds)p, ψp and (ϕ′ds)Id) and relevant plane strain parameters ((ϕ′ps)p and ϕ′crit) is set out, based on Rowe's flow rule and Davis's (1968) relation. Stroud's simple shear apparatu...

An improved direct shear apparatus for sand

A conventional direct shear apparatus (DSA) has been modified to improve its articulation by moving the point of shear load application to the sample centre. Jewell's symmetrical arrangement has been adopted for a 100 mm square shearbox, resulting in increased dilation rate and reduced rotation. Testing using coarse Leighton Buzzard sand has enabled the performance of the modified DSA to be optimised by exploring different test configurations. Optimum results were obtained with a substantial initial gap between the shearbox frames of 5D50, the use of thin rubber edging strips to contain the sand, and the omission of grid plates at the sample boundaries. Upper-frame rotations persist during testing, but have almost no effect on measured parameters. A framework of relationships between parameters measured in a direct shear test ((ϕ′ds)p, ψp and (ϕ′ds)Id) and relevant plane strain parameters ((ϕ′ps)p and ϕ′crit) is set out, based on Rowe's flow rule and Davis's (1968) relation. Stroud's simple shear apparatus (SSA) data for coarse Leighton Buzzard sand have been examined and shown to fit Rowe's flow rule. The output from the modified DSA also fits these relationships well, and shows good internal consistency. A simple relationship enables modified DSA peak direct shear friction angles to be converted into plane strain friction angles. Large displacement direct shear friction angles for the modified DSA are related to critical state friction angles by tan(ϕ′ds)Id = sin ϕ′crit.

Influence Of Input Motion Characteristics On Dynamic Soil-structureInteraction By Shaking Table Test

The present paper deals with shaking table tests performed at the EERC laboratory of the University of Bristol, involving a 1:6 scaled steel model of a one-storey frame structure located over a Leighton Buzzard sand deposit. The tests were conducted by settling the soil in a flexible larninar box, which allows the reproduction of boundary conditions similar to a free field. The deposition procedure led to an almost uniform soil relative density. Dynamic characterisation of the soil-structure model was achieved by means of exploratory tests performed using a low-level-random input. Each shaking table test was performed by applying a sine-dwell displacement time-history, increasing, run by run, the amplitude and maintaining a constant value of the input frequency. In this paper the attention is focused on the effect of the input motion characteristics and on the model response in terms of coupled andfor uncoupled soil-structure behaviour.

Shaking table test of failure of a shallow foundation subjected to an eccentric load

Many models have been developed to solve geotechnical problems, but their validation is only possible by a parallel experimental analysis on real works. In this sense, a well controlled experiment was carried out on a shallow foundation resting on a dry coarse Leighton Buzzard sand. A flexible shear stack was filled with a uniform relative density Leighton Buzzard sand. The foundation was subjected to a vertical eccentric load and to a sine dwell-type acceleration transmitted from a shaking table over which the shear stack was located. The dynamic response of both the soil and the foundation was checked by means of a complex network of accelerometers and displacement transducers. To have a detailed description of the behaviour of the footing under the seismic motion, four coloured layers of sand were introduced into the deposit at different depths. By measuring the displacements of the coloured layers, carefully excavated after the test, it was possible to investigate the experimental failure mechanism. It was then compared with the theoretical failure mechanism and the seismic bearing capacity was evaluated.

The bearing capacity of footings on a sand layer overlying soft clay

The bearing capacity of foundations can be improved by superimposing a layer of compacted sand or gravel. Although it is difficult to calculate exactly the bearing capacity of such inhomogeneous soil profiles, approximate solutions have recently been presented for several of the more frequently encountered profiles, in an attempt to provide acceptable design data. This technical note makes recommendations about the practical use of currently available solutions of this problem, which are based on data obtained from recent laboratory model bearing-capacity testing. It first outlines an approximate method for calculating bearing capacity for sand overlying clay, but is mainly concerned with the results of a test programme. The experimental set-up used a strip footing 0.12m wide, and a 2.0m long, 1.4m high 0.3m wide test tank with parallel glass sides, containing Glyben artificial clay overlaid by Leighton Buzzard sand. Stress-settlement relationships were obtained for clay subgrade alone, sand alone, and sand overlying clay. Experimental measurements of bearing capacity were compared with those predicted by the methods of Terzaghi and Peck, Vesic, and Hanna and Meyerhof. Agreement was found to be closer when allowance was made for the local shear failure of the clay.

Effect of incremental loading on the creep behaviour of chemically grouted sand

This paper describes the results of a study on the stress-strain time dependent (creep) behaviour of silicate-Hardener 600B grouted Leighton Buzzard sand specimens when subjected to incremental loading at certain time intervals. Unconfined and confined multi-stage creep tests were conducted on sand specimens injected with different silicate content grouts which cover the range generally used in engineering practice. The laboratory results showed that creep movements increase with the increase in stress ratio causing a rise in strain rate which ultimately leads to creep rupture (complete failure). However, an increase in the stress ratio does not affect the linear relationship between logarithm of strain rate and the logarithm of time suggesting that the three parameter phenomenological relationship of Singh and Mitchell (1968) may be suitable to describe the multi-stage creep behaviour of silicate-Hardener 600B grouted sand.

Centrifuge Model Tests of Nailed Soil Slopes

This paper presents the results of 24 centrifuge model tests of nailed soil slopes and vertical walls, constructed out of dry Leighton buzzard sand. The walls were initially supported by fluid pressure from flexible rubber bags against the face, and excavation was modelled by gradually draining the fluid from the bags. The finished model walls were 200 mm high and were initially tested at 30 g acceleration to correspond to a prototype structure 6.0 m high. If failure was not obtained, the acceleration was increased progressively to a maximum of 80 g. No surcharges were applied. The main parameters varied in the tests were the wall slope, nail length, nail surface roughness, nail inclination, facing stiffness and facing roughness. Observations were made of the mechanism of failure when it occurred, of soil pressures on the facing, and of pre-failure deformations. Failure was always by pull-out rather than breakage of the nails, and a series of pull-out tests of the model nails was conducted to aid interpretation of the results. Failure surfaces were seen to have the shape of logarithmic spirals, and limit equilibrium analyses based on these surfaces agreed well with experimental observations. Prior to failure, earth pressures on the facing compared reasonably well with those calculated by Coulomb’s method, except at the base of the wall. One test set out to model a full-scale trial wall, and although the construction process could not be exactly modelled in the small-scale centrifuge tests, comparisons were sufficiently good to give confidence in the model test results.

Interpretation of direct shear box testing of sands as quasi-simple shear

Interpretation of the direct shear box (DSB) test implicitly assumes a simple shear mode of deformation, but this assumption has not been fully verified, in particular in tests on sands. This paper describes a laboratory investigation, which was commissioned to find an optimum configuration of a DSB apparatus for measuring the strength and dilatancy characteristics in direct simple shear. The examination was made in a newly developed DSB apparatus using dry specimens of two standard sands: Toyoura sand and silver Leighton Buzzard sand. Boundary effects, such as the wall friction, the size of the opening between the two halves of the shear box and the constraint imposed by the loading platen, were each independently examined in pilot tests to determine their influence on the measurements of strength and angle of dilatancy. The optimum configuration was determined through careful examination of the boundary stresses and strains of rectangular specimens subjected to shearing under drained and constant-volume conditions, and also by comparing the results with those of comparative torsional simple shear and plane strain compression tests. On the basis of the test results obtained using an optimum configuration of the DSB device, the stress dilatancy of the sands was characterized by a non-associated rule based on a classical energy theory for the interrelationship between the angle of shearing resistance and the angle of dilatancy.

Varying temperature and creep of silicate grouted sand

This paper illustrates the impact of temperature variation on the creep behaviour of sodium silicate–600B ester permeated Leighton Buzzard sand, where the temperature of triaxial cell water in which the grouted sand samples is installed is raised and lowered between 20·C and 30·C at different time intervals during the constant loading tests. It has been found that creep strain is temperature sensitive at nominal silicate concentrations of 40% to 60% by volume and both the magnitude of creep strain and its rate increase with increase in temperature and vice versa. Also described is the temperature controlled apparatus developed for creep testing of grouted soils, where the temperature can be maintained at the specified temperature within ±1·C.

Relating Failure Tests Performed in Hollow Cylinder Apparatus to Inherent Anisotropy

Described are failure tests performed on a fine-grained Leighton Buzzard sand in the Nottingham hollow cylinder apparatus. These tests were conducted to characterize the inherent anisotropy of the material formed during the sample preparation procedure. An image analysis procedure for determining preferred particle orientation is introduced and its derivation discussed. An attempt is subsequently made to relate the statistically significant preferred orientation to the anisotropic shear strength properties of the Leighton Buzzard sand.

Relating Failure Tests Performed in Hollow Cylinder Apparatus to Inherent Anisotropy

Described are failure tests performed on a fine-grained Leighton Buzzard sand in the Nottingham hollow cylinder apparatus. These tests were conducted to characterize the inherent anisotropy of the material formed during the sample preparation procedure. An image analysis procedure for determining preferred particle orientation is introduced and its derivation discussed. An attempt is subsequently made to relate the statistically significant preferred orientation to the anisotropic shear strength properties of the Leighton Buzzard sand.

Quality of the Lubrication Layer used in Element Tests on Granular Materials

ABSTRACT In order to find the proper composition of lubrication layer to be used for element tests of granular materials in the laboratory, a series of direct shear tests between a granular material specimen and a lubrication layer was performed. The granular materials used ranged from a fine sand to a gravel with D50 = 0.16 mm ~ 1.85 mm. The lubrication layer consisted of a layer of silicone grease and a latex rubber disk, and its variations. Based on the test results, the following points are shown: (1) For Toyoura Sand (D50 = 0.16 mm), when a properly designed lubrication layer is used, the apparent frictional angle ϕμ can be as small as around 0.14 ~ 0.16 degrees when a normal stress is 2.0 ~ 6.0 kgf/cm2 (196 ~ 588 kN/m2). These values are independent of void ratio. (2) For Hime Gravel (D50 = 1.85 mm) and Silver Leighton Buzzard Sand (D50 = 0.62 mm), a proper amount of powder should be added to the original grease in order to improve the quality of lubrication by preventing the squeezing out of grease from the places of stress concentration in the proximity of particles indenting the lubrication layer. At the same time, the amount of powder should not be too much in order not to increase the shear resistance of a mixture of grease and powder. Fly ash is suggested as a proper type of powder. By this method, even for Hime gravel, a low value ϕμ of around 0.8 degrees at normal stresses of 1.5 ~ 7.0 kgf/cm2 (150 ~ 700 kN/m2) can be obtained.