Sample Disturbance Research Articles

An attempt to monitor pore pressure changes in a block sample during and after sampling

A soil sample goes through stress changes during and after sampling. Sensitive clays are affected by sample disturbance and stress changes have a great effect on the quality. The reduction of in-situ total stresses to zero causes the soil sample to develop a negative pore pressure, which is also referred to as residual effective stresses. In an ideal situation, a block sample shall retain its residual effective stress during sampling and storage, which prevents it from swelling. To study this, an attempt was made to monitor the pore pressure variations inside a block sample of soft, sensitive, low-plasticity clay during and after sampling. The pore pressure was measured continuously during the storage period of 3 days and the results were compared with a similar work. The findings suggest that the residual effective stress in block samples may be reduced in a matter of minutes after sampling. Testing performed on reference samples corroborate these storage effects.

Influence of friction on sampling disturbance of lunar surface in direct push sampling method based on DEM

The direct push sampling method is one of the most commonly used sampling methods in lunar regolith exploration. However, the disturbance of in situ bedding information during the sampling process has remained an unresolved problem. In this paper, the discrete element method is used to establish a numerical lunar soil simulant basing on the Hertz-Mindlin contact model. The result of simulated triaxial test shows that the macro mechanical parameters of the simulant accurately simulate most known lunar soil samples. The friction coefficient between the simulant and the wall of the sampling tube is also tested and used as the key variable in the following simulation and study. The disturbance phenomenon is evaluated by the displacement of marked layers, and a swirling structure is observed. The changing trend of the friction coefficient on the soil simulant void ratio and stress distribution is also determined.

Closure to “Influence of Sample Disturbance on Estimated Side Resistance of Driven Piles in Cohesive Soils” by Steven R. Saye, Alan J. Lutenegger, Dan A. Brown, and Bryan P. Kumm

Closure to “Influence of Sample Disturbance on Estimated Side Resistance of Driven Piles in Cohesive Soils” by Steven R. Saye, Alan J. Lutenegger, Dan A. Brown, and Bryan P. Kumm

Discussion of “Influence of Sample Disturbance on Estimated Side Resistance of Driven Piles in Cohesive Soils” by Steven R. Saye, Alan J. Lutenegger, Dan A. Brown, and Bryan P. Kumm

Discussion of “Influence of Sample Disturbance on Estimated Side Resistance of Driven Piles in Cohesive Soils” by Steven R. Saye, Alan J. Lutenegger, Dan A. Brown, and Bryan P. Kumm

Influence of Soil Properties and Composition, and Applied Hydraulic Pressures on Sample Quality of Pusan Clays

Obtaining good quality samples from soft marine clay deposits is a challenge and it is being seen that the sample disturbance is inevitable even though lot of research has suggested using more sophisticated samplers, sampling methods, and special care being taken while handling and transportation of the samples. Hence, author doubt that apart from the above, there could also be other parameters playing critical role on the sample quality. Therefore, in the current study, sampling tube geometry is maintained same, especially angle of cutting edge and area ratio which are found to be key influencing factors and hence its impact on the current study is ignored. In the current study in order to assess the other contributing factors behind the additional sample disturbance, a special attention is given to find out other possible parameters that could also influence the sample quality. As a result of this study, it is found that the soil properties such as; silt and sand content in the soil, clay fraction, hydraulic pressure applied to penetrate the sampler, rigidity index of the soil, initial void ratio, plasticity index, and unit weight of the soil also contribute to sample disturbance. Since these properties, except hydraulic pressure, are soil inherent properties, there is always a certain minimum degree of sample disturbance associated with these soil inherent properties depending on the magnitude of these parameters. Unfortunately, the soil properties cannot be changed and thus a minimum sample disturbance is inevitable.

Influence of Soil Properties and Composition, and Applied Hydraulic Pressures on Sample Quality of Pusan Clays

Obtaining good quality samples from soft marine clay deposits is a challenge and it is being seen that the sample disturbance is inevitable even though lot of research has suggested using more sophisticated samplers, sampling methods, and special care being taken while handling and transportation of the samples. Hence, author doubt that apart from the above, there could also be other parameters playing critical role on the sample quality. Therefore, in the current study, sampling tube geometry is maintained same, especially angle of cutting edge and area ratio which are found to be key influencing factors and hence its impact on the current study is ignored. In the current study in order to assess the other contributing factors behind the additional sample disturbance, a special attention is given to find out other possible parameters that could also influence the sample quality. As a result of this study, it is found that the soil properties such as; silt and sand content in the soil, clay fraction, hydraulic pressure applied to penetrate the sampler, rigidity index of the soil, initial void ratio, plasticity index, and unit weight of the soil also contribute to sample disturbance. Since these properties, except hydraulic pressure, are soil inherent properties, there is always a certain minimum degree of sample disturbance associated with these soil inherent properties depending on the magnitude of these parameters. Unfortunately, the soil properties cannot be changed and thus a minimum sample disturbance is inevitable.

Biodiversity of shallow subtidal, under-rock invertebrates in Europe's first marine reserve: Effects of physical factors and scientific sampling

At Lough Hyne Marine Reserve in SW Ireland, shallow subtidal, under-rock biodiversity was investigated to assess (i) any deleterious effects of scientific sampling and (ii) quantitative baseline community patterns. Comparisons were made between 10 sites with annual rock-turning disturbance and 10 with multi-decadal (historical) disturbance. At each site, shallow subtidal rocks (N = 1289 total) were lifted, organisms recorded, and rocks replaced in their original position. Biodiversity indices were calculated to evaluate how diversity varied with location within the lough, frequency of sampling disturbance, degree of hypoxia/anoxia, dissolved oxygen (DO) concentration, and number of rocks turned. The richness of solitary invertebrates surveyed in situ averaged 21 taxa per site with significantly more in the South Basin (near the lough's connection to the ocean) than in the North Basin. The Shannon-Wiener Index did not differ significantly with variables investigated. However, evenness was higher at annually disturbed sites than at historical ones where anemones with algal symbionts often dominated. Several sites were hypoxic to anoxic under the shallow subtidal rocks. Cup corals were most abundant in the South Basin; DO was a crucial explanatory variable of these sensitive species. Solitary ascidians were most abundant at South-Basin annual sites with DO levels being a highly significant explanatory variable.

Consequences of sample disturbance when predicting long-term settlements in soft clay

An approach for assessing the effects of sample quality is presented. Soil samples were taken using a 50 mm Swedish STII piston sampler and the Norwegian University of Science and Technology (NTNU) mini-block sampler from a soft clay test site. Differences in laboratory test results are identified for several stress paths, assisted by simulations made using an advanced constitutive model. Hitherto such comparisons have focused on differences in basic engineering properties such as strength and stiffness. The effect of choosing alternative model parameters from piston and block samples is demonstrated through the analysis of the long-term settlement of an embankment. The simulations show that substantially larger settlements and lateral displacements are predicted using parameters obtained from the piston samples. Furthermore, the magnitude of the differences is larger than expected. This demonstrates that for this application, relatively small differences in the assessed sample quality, using traditional laboratory data interpretation methods, are amplified when applied to a prototype boundary value problem. It is suggested that a little more care in sampling and testing can result in large cost savings as a result of the more reliable model parameters that can be extracted, particularly when the improved sampling is combined with the use of an advanced constitutive model.

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.

Validity Criteria of Oedometric and Triaxial Test Results

Oedometric and triaxial tests are very much used in soil mechanics. However, in spite of their frequency in the world, these tests present some limitations related to remolding due to sampling process and to implemented experimental procedures. These limitations contribute to decreasing the resistance and deformability mechanical properties of soils, which condition their limit and critical states behavior. This paper proposes four validity criteria of oedometric and triaxial test results (compressibility criterion based on the oedometric test results; consolidation, resistance and rigidity criteria based on the triaxial test results) to appreciate the disturbance of test specimens. Impact of the sample disturbance on the yield envelope of clayey soils according to these validity criteria is then analyzed.

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.

Fractional-Order Embedding Supervised Canonical Correlations Analysis with Applications to Feature Extraction and Recognition

Due to the noise disturbance and limited number of training samples, within-set and between-set sample covariance matrices in canonical correlations analysis (CCA) based methods usually deviate from the true ones. In this paper, we re-estimate the covariance matrices by embedding fractional order and incorporate the class label information. First, we illustrate the effectiveness of the fractional-order embedding model through theory analysis and experiments. Then, we quote fractional-order within-set and between-set scatter matrices, which can significantly reduce the deviation of sample covariance matrices. Finally, we incorporate the supervised information, novel generalized CCA and discriminative CCA are presented for multi-view dimensionality reduction and recognition, called fractional-order embedding generalized canonical correlations analysis and fractional-order embedding discriminative canonical correlations analysis. Extensive experimental results on various handwritten numeral, face and object recognition problems show that the proposed methods are very effective and obviously outperform the existing methods in terms of classification accuracy.

Parameters inversion of high central core rockfill dams based on a novel genetic algorithm

Parameters identification of rockfill materials is a crucial issue for high rockfill dams. Because of the scale effect, random sampling and sample disturbance, it is difficult to obtain the actual mechanical properties of rockfill from laboratory tests. Parameters inversion based on in situ monitoring data has been proven to be an efficient method for identifying the exact parameters of the rockfill. In this paper, we propose a modified genetic algorithm to solve the high-dimension multimodal and nonlinear optimal parameters inversion problem. A novel crossover operator based on the sum of differences in gene fragments (SoDX) is proposed, inspired by the cloning of superior genes in genetic engineering. The crossover points are selected according to the difference in the gene fragments, defining the adaptive length. The crossover operator increases the speed and accuracy of algorithm convergence by reducing the inbreeding and enhancing the global search capability of the genetic algorithm. This algorithm is compared with two existing crossover operators. The modified genetic algorithm is then used in combination with radial basis function neural networks (RBFNN) to perform the parameters back analysis of a high central earth core rockfill dam. The settlements simulated using the identified parameters show good agreement with the monitoring data, illustrating that the back analysis is reasonable and accurate. The proposed genetic algorithm has considerable superiority for nonlinear multimodal parameter identification problems.

Retention and Solute Transport Properties in Disturbed and Undisturbed Soil Samples

Solute transport parameters can be determined in miscible displacement experiments, usually performed in columns with disturbed (sieved) soil samples. Experiments with undisturbed samples are uncommon, due to the difficulty of taking undisturbed samples at the size required for these experiments. Structural alteration of the disturbed material implies modifications in the pore geometry that determines hydraulic properties, including hydraulic conductivity and retention and properties related to miscible displacement. An existing model for prediction of breakthrough curves based on retention properties was tested using material from a medium-textured Ferralsol, and alterations caused by sample disturbance were investigated. Soil water retention curves and miscible displacement parameters were determined in breakthrough experiments with nitrate salts in columns filled with undisturbed and disturbed soil samples. Data obtained from the undisturbed samples showed a higher dispersion, suggesting homogenization of pore geometry and a reduction in the representative elementary volume by the disaggregation and sieving of the soil material. The transport parameters for nitrate determined in disturbed and undisturbed samples were significantly different and the model was able to simulate the observed breakthrough curves after fitting the pore connectivity parameter.

Estimation and Separation of Preconsolidation Stress Using Triaxial,- and Oedometer Test in Kiscelli Clay

The study is about the estimation of preconsolidation stress using a correlation method. Disturbance of soil samples can result in the yield point of void ratio-log vertical stress data from oedometer test being unreadable. Therefore, correlations were calculated to estimate preconsolidation stress using effective vertical stress ( σ ′ v 0 ), oedometer modulus ( E oed ) from oedometer tests and unloading-reloading modulus ( E ur ) from triaxial tests. Profile of stress history: Overconsolidation ratio ( OCR ), overconsolidation difference ( OCD ) and overconsolidation gradient ( OCG ) were determined in Kiscelli Clay based on new equations. An additional new parameter, ratio of mechanical preloading component of overconsolidation is defined and analysed.

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.

An analytical investigation of soil disturbance due to sampling penetration

It is well known that the quality of sample significantly determines the accuracy of soil parameters for laboratory testing. Although sampling disturbance has been studied over the last few decades, the theoretical investigation of soil disturbance due to sampling penetration has been rarely reported. In this paper, an analytical solution for estimating the soil disturbance due to sampling penetration was presented using cavity expansion method. Analytical results in several cases reveal that the soil at different location along the sample centerline experiences distinct phases of strain during the process of sampling penetration. The magnitude of induced strain is dependent on the position of the soil element within the sampler and the sampler geometry expressed as diameter-thickness ratio D/t and length-diameter ratio L/D. Effects of sampler features on soil disturbance were also studied. It is found that the induced maximum strain decreases exponentially with increasing diameter-thickness ratio, indicating that the sampling disturbance will reduce with increasing diameter or decreasing wall thickness of sampler. It is also found that a large length-diameter ratio does not necessarily reduce the disturbance. An optimal length-diameter ratio is suggested for the further design of improved sampler in this study.

Pore pressure response to barometric pressure change in Champlain clay: Prediction of the clay elastic properties

Champlain Sea clay deposits play a crucial role in limiting contaminant migration to underlying aquifers in the Saint Lawrence River Valley. Champlain Sea clays are well known as being prone to landslide and sample disturbance. Estimation of their elastic properties using their in situ loading efficiency would provide mechanical properties for the soil dynamic analyses and immediate settlement calculations encountered in geotechnical projects. Determination of loading efficiency can be envisioned as a very small strain test. In this paper we describe a detailed monitoring program for 10 vibrating wire piezometers installed within sealed boreholes on 5 study sites near Montreal in Quebec, Canada. The pore pressure response to barometric pressure variation was analyzed with three methods: linear regression, visual inspection, and multiple regression, which gave loading efficiencies between 0.7 and 0.95. These values were then used to estimate the elastic properties of the clay formation. Vertical compressibility and specific storage on the order of 1×10−6kPa−1 and 1×10−5m−1 were respectively obtained for most of the monitoring sites. A comparison of compressibility values derived from the in situ loading efficiency method, with those obtained with pressuremeter, oedometer, and pulse tests confirmed that clay compressibility is strain dependent. The pore pressures measured on the study sites have been corrected by applying the multiple regression and visual inspection methods. For most piezometers, both methods provided nearly identical results. However, for deep piezometers, the multiple regression method provided smoother pore pressure time series than the visual inspection method. The vertical hydraulic gradient obtained with corrected pressure data was shown to change significantly on some test sites during the monitoring period.