Effects Of Sample Disturbance Research Articles

原位置における砂の動的変形特性の推定法 : 地盤の動的変形特性の評価法に関する研究(II)

In this paper, the authors proposed the prediction method on the in situ dynamic deformation properties of sands for the earthquake response analysis of the ground. This method is based on the hyperbolic stress-strain relationship, which is called "the Hardin-Drnevich model", and in addition takes the effects of sample disturbance into consideration. The results estimated by the proposed method were in good agreement with the test results by the cyclic triaxial tests, which were performed to investigate the effects of void ratios, confining pressures and sample disturbance on the dynamic deformation properties of sands. Finally, the application of this method to the in situ dynamic deformation properties was given and at the same time the strain-dependency curves of shear moduli and damping ratios predicted by the proposed method were compared with those by the correction methods of other investigators.

Effect of simulated sampling disturbance on creep behaviour of rock salt

This article presents the results of an experimental study of creep behaviour of a rock salt under uniaxial compression as a function of prestrain, simulating sampling disturbance. The prestrain was produced by radial compressive loading of the specimens prior to creep testing. The tests were conducted on an artifical salt to avoid excessive scattering of the results.

Effects of sample disturbance on dynamic properties of sand : Tokimatsu, K; Hosaka, Y Soils Found V26, N1, March 1986, P53–64

Effects of sample disturbance on dynamic properties of sand : Tokimatsu, K; Hosaka, Y Soils Found V26, N1, March 1986, P53–64

Effects of Sample Disturbance on Dynamic Properties of Sand

ABSTRACT Laboratory tests were conducted on sand samples obtained by two different methods: in situ radial freezing which is likely to preserve the in situ dynamic soil properties, and conventional coring with a triple tube sampler. The results show that: (1) despite a relatively small difference in the drained shear strength, the undrained cyclic shear strength of the tube sample is considerably lower than that of the sample by freezing; and (2) the possible cause of this difference is a change in negative dilatancy characteristics due to sampling disturbance. Samples having dynamic characteristics similar to those of the sand by freezing were formed and tests were run on the samples to study major factors influencing sample disturbance. The test results imply that: (1) the shear stress history occurring during sampling is the primary factor reducing the undrained cyclic shear strength and modulus, whereas the reduction of confining pressure alone has negligible influence: (2) the deterioration of undrained cyclic shear strength due to sample disturbance is well correlated with a change in the elastic shear modulus ; and hence (3) the degree of sample disturbance can be assessed to some extent by comparing the two elastic shear moduli measured in the laboratory and the field.

Liquefaction Resistance of Two Alluvial Volcanic Soils Sampled by in Situ Freezing

Two new improved-efficiency techniques for soil sampling by in situ freezing were used to obtain undisturbed samples of saturated alluvial volcanic soils, locally termed “Shirasu”, from Kagoshima city, Japan. Undrained cyclic triaxial tests were conducted on the undisturbed alluvial Shirasu samples obtained from a depth of 5.4 to 6.0 m at site A, and from a depth of 8.4 to 10.5 m at site B, after they had been thawed. For studying the effects of sample disturbance, undrained cyclic triaxial tests were also conducted on the reconstituted specimens. The liquefaction resistance in the field was estimated based on the laboratory tests. Based on the above studies it was shown that (1) two new developments in the technique of sampling by in situ freezing were successfully achieved in the field, and (2) compared with the liquefaction resistance of the undisturbed samples, that of the reconstituted samples from site A, all of which had about the same density, was about 45 to 50% of the value for undisturbed samples, and that of the reconstituted samples from site B, with relative density 13 to 20 percentage points higher than that of undisturbed samples was about 62 to 67%.

Strain Path Method

The Strain Path Method provides an integrated and systematic framework for elucidating and predicting pile foundation behavior, interpreting in situ tests, assessing sampling disturbance effects and, in general, approaching “deep geotechnical problems” in a consistent and rational manner. This article describes the fundamentals of the method and presents solutions for the effects of quasi‐static undrained penetration of piles, cones and samplers on the deformations and strains in saturated isotropic clays. Procedures to determine penetration stresses and pore pressures and extensions of these solutions in an approximate form to more realistic conditions (e.g., anisotropic clays and drained penetration in sands) by means of the Strain Path Method are outlined. Estimates of undrained soil distortions due to sampler penetration indicate the necessity of reevaluating standard sampling and laboratory testing procedures utilized at present to estimate the in situ behavior of foundation soils, especially in the cases of soft clay deposits.

A Method for Correcting Undrained Shear Strength for Sample Disturbance

In order to find out an appropriate method for correcting the undrained shear strength for sample disturbance, a series of triaxial compression tests is performed on mixed soil samples having wide range of plasticity index. Conditions of the ideal and perfect samples are brought to by the K 0 consolidation and the shear stress release after the consolidation, then further disturbance is given to specimens by cyclic loadings. Model sampling is made for obtaining the “undisturbed” samples, and unconsolidated undrained triaxial compression tests are performed on these “undisturbed” samples. In these compression tests, the pore pressure is measured for assessing the residual effective stress in the ideal, perfect and “undisturbed” samples respectively. Results of the compression tests show that the pore pressure can increase on shear stress release for soils of low plasticity index, and that the effect of sample disturbance is similar to the effect caused by cyclic loadings. By combining the concepts of strength reduction due to rebound and reduction in effective stress due to sample disturbance, a comprehensive way for correcting the measured value of the undrained shear strength for sample disturbance is proposed.

Preparation Techniques for Oil-Sand Testing

Abstract Evaluation of technologies for oil-sand mining and enhanced oil recovery in oil sands and other uncemented sandstone reservoirs requires high-quality undisturbed samples and special sampling, preparation, and testing techniques to minimize the effects of sample disturbance by expansion. This paper presents some methods developed for storage, preparation, and laboratory testing of the geomechanical properties of oil sands. These techniques have application to the handling of other earth materials that are difficult to prepare for testing.

841030 Some effects of sample disturbance on soft clay : Atkinson, J H; Kubba, L M Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981V2, P423–426. Publ Rotterdam: A. A. Balkema, 1981

841030 Some effects of sample disturbance on soft clay : Atkinson, J H; Kubba, L M Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981V2, P423–426. Publ Rotterdam: A. A. Balkema, 1981

Considerations in the Undisturbed Sampling of Sands

The effect of sampling disturbance on the cyclic strength characteristics of sands is investigated by sampling from deposits of known dynamic characteristics prepared in the laboratory. Push-tube (Hvorslev fixed piston) sampling caused density changes (densification) of Monterey 0 sand with a relative density about 60 percent. A relatively larger relative density increase (about 10 percent) was noticed in the case of virgin samples as compared with about 6 percent increase for samples having a prior strain history. A combination of advance trimming and block sampling techniques caused little, if any, change in density. Some disturbance, resulting in only a partial loss of the resistance gained due to previous seismic effects, did take place. Based on the experimental results, an estimation of sampling disturbance effects for natural deposits is presented.

Modulus values for weathered rock from plate load tests : Douglas, D J Proc International Conference on Structural Foundations on Rock, Sydney, 7–9 May 1980, P17–22. Publ Rotterdam: A A Balkema, 1980

This paper summarises the data obtained from plate bearing tests on eight sites in act and Queensland where testing of highly weathered or decomposed rock has been carried out to obtain modulus or strength values for use in foundation analysis or design. In situations where relatively heavy foundation loadings are proposed over very weak or weak rocks, the plate load test has proved a valuable means of assessing strength and/or deformation properties which can be used with confidence in subsequent foundation design. In most of the cases reported here, it has been possible to upgrade the design, with the use of higher bearing pressures and more reliable prediction of maximum settlements than would have been possible without the test information. Most of the materials tested have not been suitable for conventional sampling, and on those which could be sampled, the effects of sampling disturbance substantially lowered the apparent shear strength and modulus. The results of pressuremeter tests on one site have indicated modulus values in reasonable agreement with those from the plate load tests on a second site, the agreement between the two test methods was relatively poor but both techniques indicated a similar range of results.

Sample Disturbance and Stress-Strain Behavior

Different effects of sample disturbance were simulated in a resonant column apparatus that clearly show the change in stress-strain behavior when the sample is subjected to swelling, reconsolidation, shear strain, or total stress changes. A new framework that applies the concept of “reference strain” is suggested for considering disturbance effects on stress-strain behavior, based on results of laboratory and field measurements. The normalized behavior of a soil can be determined with high accuracy in the laboratory. By also measuring the shear strength and initial tangent modulus in the field it is possible to accurately describe in situ stress-strain behavior.

Comparison of down-hole and laboratory shear wave velocities

The method of down-hole seismic surveying is described. This method was successfully used to a depth of 50 m in a cased borehole and these results are presented. The method may be used to find the in situ low strain shear modulus for use in theoretical response studies.Structural changes and changes in the stress state of samples usually result from sampling, handling, and testing procedures. Large changes in soil properties may result from these processes. An assessment of the change in soil properties is presented, which is of importance for the use of laboratory derived soil properties in theoretical in situ dynamic response studies.The magnitude of sample disturbance is assessed by comparing in situ and laboratory measured shear wave velocities. In situ down-hole shear wave velocities are compared with low strain (1 × 10−6) laboratory dynamic torsion test results. The large differences found may be correlated with the in situ shear wave velocity.A procedure is presented to correct the laboratory established shear modulus–strain relation–ship for the effects of sample disturbance. The adjusted laboratory curve is then suitable for use in theoretical response studies and will be a more accurate representation of the in situ deformation characteristics.

Significance of Deep Sea drilling project sediment physical property data

Sediment disturbance associated with the Deep Sea Drilling Project coring and core‐handling program are discussed along with the effects of sample disturbance on some measurements of physical properties. Information was obtained from shopboard observations and testing on Leg 43 and shore‐based testing of several sediment samples. Disturbance results from (1) remolding of the particle structure during coring, and (2) swelling induced by stress release and thermal expansion in the presence of excess water. Remolding is most significant to depth of 50–100 m, whereas swelling effects increase with coring depth. As a result, the shipboard data are not rep‐sentative of in situ sediment properties. The tendency is for porosity to increase and for bulk density to decrease with increased swelling. Strength is significantly reduced for swelled samples with further reductions from remolding. All observations and data suggest a need for improved coring capabilities and an in situ testing program.

The Vane Test in Organic Soils: Reply

Solving these two simultaneous equations, one can get Sv and S,. The vane inserted at 45 to the vertical may give the strength along that direction, but to determine the strengths along any other direction (say i to the vertical), a parallel test will have to be conducted in a perpendicular direction. The same equations as above can be used to compute the shear strengths in the i direction and at (90 i) direction, from the torques at failure in the two directions. The difference in strength, determined by the 45 in-situ vane and the vane inserted into the block sample at 45 may be due to the stress release effects and sample disturbance effects besides the other reasons mentioned by the authors. It is also possible due to the difference in the mechanism of failure in the two tests. The complexities involved in evaluating directional strengths by special vanes such as the 45 vane has been discussed by Bhaskaran (1971).

Effect of Sample Disturbance on the Strength of a Clay

Of the many variables that influence the laboratory-test shearing strength of saturated homogeneous clays, the effect of sample disturbance (partial remolding) has received little constructive analysis. It has generally been assumed that sample disturbance reduces the laboratory shearing strength and thereby results in an added factor of safety when the test results are applied to field design. It will be demonstrated herein for certain clay soils of the type tested that, due to sample disturbance, the actual field shear strength may be less than the laboratory-test shear strength. A method of analyzing strength data is described, in which is considered the effect of sample disturbance.

Discussion of “Effect of Sample Disturbance on the Strength of a Clay”

Discussion of “Effect of Sample Disturbance on the Strength of a Clay”

Closure to “Effect of Sample Disturbance on the Strength of a Clay”

Closure to “Effect of Sample Disturbance on the Strength of a Clay”

The Undisturbed Consolidation Behavior of Clay

Quantitative methods for correcting the results of the laboratory consolidation test for the effects of sample disturbance are presented. These methods are developed by attempting to answer several...