Effects Of Sample Disturbance Research Articles

The distribution and engineering properties of interglacial deposits in Cork city and harbour

Abstract: A reassessment of existing data and additional testing on sediment core samples from one site was used to study the extent, nature, composition and engineering properties of the Quaternary interglacial deposits in an area of Cork city and harbour where many future developments are planned. A clear link is apparent between rockhead elevation and the presence of the interglacial deposits. Well-defined pockets of the deposit were proven. These are found mostly on the southern side of the Cork buried valley axis and increase in thickness to the north. The base of the interglacial deposits appears to mirror that of the rock-head and the western extent of the former coincides with a steep drop off in the latter. Much of the deposit encountered in commercial investigations is a thick relatively uniform silt/clay consistent with that described in previous studies. The sediment is predominantly silt sized, but its behaviour and engineering properties are consistent with those of a stiff clay. Sample disturbance effects were found to be significant and these likely result in an underestimation of the preconsolidation stress and the undrained shear strength of the material. Future work would benefit from the use of in-situ site investigation and geophysical techniques.

The Distribution and Engineering Properties of Interglacial Deposits in Cork City and Harbour

A reassessment of existing data and additional testing on sediment core samples from one site was used to study the extent, nature, composition and engineering properties of the Quaternary interglacial deposits in an area of Cork city and harbour where many future developments are planned. A clear link is apparent between rockhead elevation and the presence of the interglacial deposits. Well-defined pockets of the deposit were proven. These are found mostly on the southern side of the Cork buried valley axis and increase in thickness to the north. The base of the interglacial deposits appears to mirror that of the rockhead and the western extent of the former coincides with a steep drop off in the latter. Much of the deposit encountered in commercial investigations is a thick relatively uniform silt/clay consistent with that described in previous studies. The sediment is predominantly silt sized, but its behaviour and engineering properties are consistent with those of a stiff clay. Sample disturbance effects were found to be significant and these likely result in an underestimation of the preconsolidation stress and the undrained shear strength of the material. Future work would benefit from the use of in-situ site investigation and geophysical techniques.

A novel short pile foundation system bonded to highly cemented layers for settlement control

While design methods of deep foundations are mainly developed for homogenous soil deposits, the presence of highly cemented layers could lead to underestimation of resistance and overestimation of settlement of pile foundations. This study presents a novel approach using competent caliche layers bonded to the top and bottom of a continuous flight auger (CFA) pile as a new composite foundation system named caliche stiffened pile (CSP). The key objective is to optimize the required pile length in a cost-effective approach without ameliorating soil properties. Settlements of the CSP foundation for a high-rise building were monitored and full-scale tests were conducted to measure piles’ capacity. Finite element back analyses were performed to avoid adverse effect of sample disturbance in settlement calculations. A back calculation of a test fill embankment was performed to determine soil stiffness parameters by simulating an unscheduled imposed load to the structure. Impacts of the CSP on controlling the settlement of pile foundation and optimizing the required pile length are investigated using finite element analysis and a parametric study. The proposed CSP foundation can reduce the CFA pile settlement significantly in the presence of caliche layers with thickness equal or greater than a pile diameter at CFA pile head and toe, where the CSP is located.

Numune Örselenmesinin Geleneksel Ödometre Deneyleri ile Belirlenen Konsolidasyon Parametrelerine Olan Etkilerinin İncelenmesi

This study explores the effects of sample disturbance on the compression curves obtained from oedometer tests and the inferred effective preconsolidation stress (sp'). The samples were systematically disturbed by removing different fractions of the soil ranging from 10%, 20%, 30%, 40%, and 50% and remolding them back into place to reach the same initial void ratio. It was found that when the rate of disturbance was increased, it became more difficult to determine the sp' values on the compression curve; the typical bending point on the compression curve became increasingly indistinct, and negligible changes occurred in the sp' values of the disturbed soil samples up to a disturbance rate of 40%. If the soil samples whose consolidation parameters such as preconsolidation stress can’t be determined are subjected to disturbances greater than 40%, it is recommended that no consolidation parameter of such samples be specified.

Shear wave velocity as a tool for characterising undrained shear strength of Nordic clays

There has been increasing recent use of shear wave velocity (Vs) measurements in geotechnical engineering practice. This has been driven by advances in cost effective and efficient methods of determination of Vs. Traditionally Vs measurements were used for seismic hazard assessment or dynamic analyses. However, they are being increasingly used for general site characterization studies, determination of strength and compressibility parameters by empirical correlation, assessment of sample disturbance effects and in the quality control of ground improvement schemes. This paper will briefly present the methods used to determine Vs and give some examples of Vs measurements in clays from Finland, Norway and Sweden. Despite similar depositional environments the range of Vs profiles for these three countries is significantly different. Differences in the profiles appear to be consistent with differences in basic clay properties, e.g. water content, density or plasticity. Nevertheless, the relationship between Vs and undrained shear strength (su) of clays appears to follow a similar trend for clays from Sweden, Finland and Norway. Correlations between Vs and su exist in the literature for Norwegian clays based on DSS tests. This paper studies the relationship between Vs and su from field vane test, which is commonly used in Finnish geotechnical practice. The proposed correlation is based on data from Sweden and Finland and is meant to be used for preliminary estimate of su from Vs in absence of test data or for validation of available test data.

Reply to the discussion by Koutsoftas on “Effects of sampling disturbance in geotechnical design”

Reply to the discussion by Koutsoftas on “Effects of sampling disturbance in geotechnical design”

Discussion of “Effects of sample disturbance in geotechnical design”

Discussion of “Effects of sample disturbance in geotechnical design”

Effects of sampling disturbance in geotechnical design

This paper describes an experimental study of the effects of sampling disturbance in an Australian natural soft clay and the consequences of different sample quality on the representativeness of soil parameters used in geotechnical designs. The paper is divided into three sections. Laboratory test results obtained from specimens retrieved using three different tube samplers as well as the Sherbrooke (block) sampler are first described. Then, the sample quality assessment, using available indices proposed for soft soils, is presented. It is shown that sample quality varies with the stress paths and boundary conditions applied in laboratory tests. Finally, mechanical soil properties derived from specimens retrieved using the different samplers are used in the prediction of two classical problems in soil mechanics: the settlement and excess pore pressure response underneath an embankment as well as the settlement and bearing capacity of a shallow footing. These two examples are used here to highlight the consequences of poor sampling in practice.

Site characterisation and some examples from large scale testing at the Klett quick clay research site

The Klett research site was developed in conjunction with the new E6 developments south of Trondheim, Norway. The site comprises non-sensitive clay to about 6 m to 8 m and quick clay with significant silt lenses below this down to at least 30 m. The materials encountered are typical of the marine clays found in Scandinavia and North America. Classical geophysical and geotechnical techniques such as total soundings, rotary pressure soundings and ERT proved very useful in characterising the quick clay. The material is particularly susceptible to sample disturbance effects and the work showed that it is important to test any samples as soon as possible after sampling. CPTU data proved particularly useful for the determination of some soil properties as well as general soil classification. Several full-scale experiments have been performed at the site. Pile capacity tests showed that significant ageing effects occurred. Lime-cement column tests, as well as laboratory trials, allowed considerable savings to be made in the amount of binder required for foundations and slope improvement. A full-scale embankment test provided very useful data for the calibration of soil constitutive models.

Effect of sample disturbance on cyclic shear strength of normally to lightly OC clays

Tests on Onsøy clay (Ip = 24–27%) were performed to study the effect of sample disturbance on undrained static and cyclic shear strength. Samples with different degree of disturbance from sampling were used and parallel sets of monotonic and cyclic undrained laboratory tests were performed on block and 54 mm composite piston samples. A silty Drammen clay (Ip = 19%) which was studied earlier was included in the study. Test results indicated that there are significant effects of sample disturbance on both static and cyclic undrained shear strengths for both Onsøy and silty Drammen clays.

Effects of sample disturbance and heterogeneity on the triaxial behaviour of a Canadian oil sand at ambient and high temperatures

The present paper investigates the mechanical behaviour of oil sand specimens in triaxial compression tests at both ambient and elevated temperatures. The emphasis is particularly on core sample disturbance and on the multiphase/strongly heterogeneous nature of the material that introduces difficulties in achieving an objective characterization of its shear behaviour. First, the effect of sample disturbance on the behaviour of the oil sand is studied. Tests are performed on both disturbed and recompressed specimens. Recompression to large stress prior to shearing improves evaluation of the initial stiffness and associated volumetric changes of the oil sand, strongly affected by sample disturbance. A method for the correction of test results obtained from disturbed specimens is also proposed. The corrected results are in good agreement with those pertaining to recompressed specimens. Furthermore, a general classification of the tested oil sands into lean and rich in bitumen, where the former shows much softer and weaker behaviour, is considered to help in addressing the variability in sample composition. As for thermal aspects, the experimental results indicate that both strength and stiffness exhibit a limited temperature dependency. The temperature does not affect lean oil sand specimens, whereas heating considerably increases deformability of rich specimens.

Sample Disturbance Effects in Silt

AbstractThis paper presents results of testing good-quality piston tube samples and parallel block samples from three silt sites in Ireland and Norway. Theoretical work and laboratory strain damage...

Investigating the effect of sample disturbance, compaction and stabilization on the collapse index of soils

Collapsible soils are problematic soils, which support heavy loads at their natural water content, but as their water content increases, they undergo a considerable reduction in volume. This research presents results of single oedometer tests for determining the collapse index of undisturbed and remolded soil samples. The alteration in this index was investigated by applying disturbance to samples. Samples were remolded by different dry unit weights and water contents. Additionally, some samples were stabilized with cement kiln dust, lime, ammonium sulfate and potassium chloride to investigate their effect on the collapse index. The results indicated a greater collapse index for undisturbed samples compared to that of remolded ones. It was also found that increasing water content and dry unit weight contribute to collapsibility reduction and stabilization, making it possible to minimize the collapse index to the degree of non-collapsible soil. Reduction procedure is affected by amount of additives, dry unit weight and water content of samples. In addition, curing time of samples was another effective factor for cement kiln dust and lime.

Influence of Sample Disturbance on Estimated Side Resistance of Driven Piles in Cohesive Soils

AbstractThis paper describes the influence of sample disturbance on laboratory undrained shear strength tests used for pile capacity calculations of driven close-end pipe piles, referencing an approach based on the stress history and normalized soil engineering properties (SHANSEP) for estimating the side resistance of pipe piles in cohesive soils. The SHANSEP technique provides a rational basis for relating the soil overconsolidation ratio (OCR) to the normalized side resistance overcoming the problems related to sample disturbance. Sample disturbance of soils with OCR<2 is identified as a significant factor affecting the selection of values of side resistance for pile design. The empirical record of load test sites was modified to remove test data that were likely affected by sample disturbance effects from the current database referencing the SHANSEP-based approach to provide a reliable set of reference undrained strengths and measured side resistance values, which produces an equivalent new undrained ...

Geotechnical Parameters for the Variegated Soils of São Paulo Formation by Means of In Situ Tests

The purpose of this paper is to present geotechnical parameters of the variegated soils from the São Paulo Formation, aiming in particular to establish correlations between stress history parameters, earth pressure coefficients at rest, deformability modules and resistance obtained through piezocone and dilatometer tests. The performance of in situ tests has, as the major advantage over laboratory tests for obtaining soil parameters of the project site, minimization of sample disturbance effects. Using data from geotechnical investigation carried out during the basic design of the Green Line expansion for the Metrô – SP it was possible to obtain preconsolidation pressure (σ’p), over consolidation ratio (OCR), earth pressure coefficients at rest (K0), Young’s module (Ei), initial shear module (G0), constrained module (M) and undrained shear strength (su) for the variegated soils of the São Paulo Formation. These soils are characterized by interlayered levels of clays and sands, constituting a characteristic with different geotechnical parameters and perched water tables. These characteristics explain some of the knowledge gaps on these soils. Nevertheless, it was possible to validate the correlations between earth pressure coefficients at rest (K0), over consolidation ratio (OCR), Young’s module (Ei), undrained shear strength (su) and preconsolidation pressure (σ’p) through field tests and the results of laboratory testing conducted by other authors.

Determination of failure mechanism of very soft clay behind L-pile wall with physical model tests

This paper presents physical model tests to verify the failure mechanism of soil behind the gap of contiguous L-pile retaining wall used to support the excavation in soft clay. The ratio of pile gap to pile width (Sg /B) of 0.1, 0.3, 0.5, 0.7, 1.2, 1.6, 2.0, and 3.0 was used. The undisturbed soft clay samples were obtained from an open cut in Samutprakarn province. The physical model tests were conducted in the vanity of the soil sampling area to avoid the effect of sample disturbance. The pressures were applied to the physical model using screw jack until the failure of soil between the L-piles was observed. The digital photos of soil movement were recorded during the test to monitor the failure mechanism. The test results show that the normalized failure pressures reduce as the gap width ratio (Sg /B) increases. The failure pressure of L-pile is lower than that of circular pile proposed by Winit [9] due to soil arching size. The failure arches are clearly observed in the model with Sg /B of 0.1–1.2, but not with Sg /B of 1.6–3.0.

Back analyses for slope failures in rock

Some of the geotechnical parameters used in the analysis may not be accurately measured directly from laboratory tests due to effects of sample disturbance and errors of tests. The back analysis or the observational method are thus often applied to determine the representative and/or dominant strength parameters based on field observations in practice. Based on the Hoek-Brown failure criterion, it was known that the disturbance factor (D) should be determined with caution. The difficulty of measuring rock mass disturbance accurately has been shown. Three rock slope failures will be investigated in this paper using back-analysis technique. In addition, various rock mass strength parameters are taken into consideration.

Effect of Destructuration on the Compressibility of Perniö Clay in Incremental Loading Oedometer Tests

AbstractThe paper evaluates the destructuration and creep properties of soft sensitive Pernio clay during one-dimensional consolidation. Incremental loading oedometer tests presented herein were part of an extensive testing program performed on natural and reconstituted samples of Pernio clay. Given the experimental results, general stress–strain compression curves were investigated taking into consideration the effects of clay structure and sample quality. The effect of sample disturbance on preconsolidation pressure was quantitatively evaluated by an exponential relationship. Compression parameters accounted for the detailed stress-dependent behavior. The assumption that the Cae/Cc ratio would be constant in one-dimensional consolidation was proven wrong. Three new sensitivity approaches were developed and proved to be feasible in comparison with sensitivity determined by fall cone tests. The developed sensitivity indices were exponentially related to the initial void ratio e0. The stress–strain–strain ...

On the evaluation of pre-consolidation pressure of undisturbed saturated clays

The objective of this research was to show the effect of sample disturbance on the values of pre-consolidation pressure бc by using Schmertmann method. A prediction of бc form pocket penetrometer is also achieved. This was carried out by comparing the values of бc that were estimated from the results of consolidation tests, with the readings of pocket penetrometer for same samples. Pocket penetrometer is a simple tool that can be easily used in field and laboratory to initially predict unconfined compressive strength for clayey soils. Before carrying out the consolidation tests on undisturbed samples, pocket penetrometer readings were recorded. The correlation obtained between pocket reading and бc values that resulted from consolidation tests was found to be valid for a wide range of clay stiffness, ranging between medium stiff to very stiff clay. As for soft clay, this correlation was found not to be applicable where its behavior is believed to be greatly affected by the degree of disturbance occurring to samples during drilling.

Effect of sample disturbance on triaxial and oedometer behaviour of a stiff and heavily overconsolidated clay

The tests in this investigation were performed on a natural soft clay with plasticity index around 32%, which was K0consolidated to a vertical stress of 2942 kPa and then K0unloaded to a vertical stress of 74 kPa (i.e., to the “in situ” stress). The specimens so created were disturbed in various ways to study the effect of sample disturbance on the stress–strain relationships during undrained shearing and during drained K0loading (i.e., K0triaxial and oedometer tests). The results for two testing alternatives may be summarized as follows. Alternative 1: Allow the specimen to swell at the correct in situ effective stresses, but accept an initial water content that is higher than the in situ value. This alternative was found to give the best stress–strain relationships around the in situ effective stresses for undrained triaxial tests, but with undrained shear strength values up to about 20% too low, due to the swelling taking place during consolidation to the in situ effective stresses. Alternative 2: Prevent swelling by starting the test at effective stresses that are higher than the in situ stresses, but with a water content that is closer to the in situ value than if alternative 1 is chosen. Using only isotropic stresses prior to shearing, this alternative was found to give better undrained shear strength values (although up to about 14% too high) but strain values much too small around the in situ effective stresses. For oedometer tests, only alternative 2 was investigated. Also, for these tests, the strains around the in situ stress were too small, but preconsolidation stresses estimated from stress–strain curves were typically only around 60% of the true value.