scholarly journals Estimating the Small Strain Stiffness of Peat Soil Using Geophysical Methods

2021 ◽  
Vol 7 (1) ◽  
pp. 44-54
Author(s):  
Kasbi Basri ◽  
Adnan Zainorabidin ◽  
Mohd Khaidir Abu Talib ◽  
Norhaliza Wahab
Keyword(s):  
Peat Soil ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Small Strain ◽  
In Situ Stress ◽  
Design Parameters ◽  
Small Strain Stiffness ◽  
Geotechnical Design ◽  
Sample Disturbance

Geotechnical design commonly requires that the in-situ stiffness, strength and permeability of the ground be obtained. Laboratory based investigation often related with risk of sample disturbance and difficulties to replicate the in-situ stress condition which results in overestimation or underestimation. Application of geophysical methods in geotechnical investigation previously was limited to targeting and dimensioning sub-surface features due to lack of resolution. However, rapid developments of geophysical methods result in the application of these methods in providing geotechnical design parameters. Multichannel analysis of surface waves (MASW) and seismic refraction were among the geophysical methods capable of obtaining stiffness parameters including the maximum shear modulus (Gmax) and maximum elastic modulus (Emax). The study revealed the efficiency of these methods to measure the small strain stiffness of peat soil with high accuracy as the results obtained were found to be similar to those obtained by previous researchers. Overall, the Gmax and Emax values of peat soil obtained range from 0.49 to 1.72 MPa and 1.46 to 5.15 MPa respectively. The Gmax and Emax values obtained shows significant increase with depth governed primarily by the effective stress. Other parameters such as degree of decomposition and peat thickness also shows potential influence on the Gmax and Emax values obtained.

scholarly journals Rock Mass Behavior under Tunnel Widening in Asymmetric and Symmetric Modes Considering Different Shapes and Parametric Conditions

Geosciences ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 518
Author(s):  
Babar Khan ◽  
Syed Muhammad Jamil ◽  
Jung Joo Kim ◽  
Turab H. Jafri ◽  
Jonguk Kim
Keyword(s):  
Rock Mass ◽  
In Situ Stress ◽  
Design Parameters ◽  
Tunnel Widening ◽  
Tunnel Support ◽  
Mass Behavior ◽  
Rock Types ◽  
The Difference ◽  
Support Conditions

To accommodate traffic volume on roads due to ever-increasing population growth, the widening of highways and motorways is in high demand. Nevertheless, the widening of tunnels on these road networks is quite complex due to the presence of numerous rock types, in situ stress, and different widening modes. To overcome these complexities, eight different tunnel shapes were simulated under varying support conditions for asymmetric and symmetric widening. It was found that the tunnels with a round shape, such as horseshoe and semicircular with flatbed, are more effective for asymmetric widening, whereas the provision of a rounded invert in these shapes can reverse the widening option to symmetric. Furthermore, an insignificant effect of the difference in asymmetric and symmetric widening of regular tunnel shapes, such as box, rectangular, and semi-elliptical, was found. A full factorial design statistical analysis confirmed the decrease in tunnel deformation by using various tunnel support systems and showed a significant deformation difference according to monitoring locations at the tunnel periphery. The deformation difference in the case of both tunnel widening modes was also analyzed according to different design parameters. This study provides a comprehensive understanding of rock mass behavior when the widening of any underground opening is carried out.

Effects of sample disturbance on the stress-induced microfracturing characteristics of brittle rock

1999 ◽  
Vol 36 (2) ◽  
pp. 239-250 ◽  
Author(s):  
E Eberhardt ◽  
D Stead ◽  
B Stimpson
Keyword(s):  
Crack Initiation ◽  
Elastic Stiffness ◽  
In Situ Stress ◽  
Brittle Rock ◽  
Stress Threshold ◽  
Fracture Crack ◽  
Sample Disturbance ◽  
Underground Research Laboratory ◽  
Stress Domains

The effects of sampling disturbance on the laboratory-derived mechanical properties of brittle rock were measured on cored samples of Lac du Bonnet granite taken from three different in situ stress domains at the Underground Research Laboratory of Atomic Energy of Canada Limited. A variety of independent measurements and scanning electron microscope observations demonstrate that stress-induced sampling disturbance increased with increasing in situ stresses. The degree of damage was reflected in laboratory measurements of acoustic velocity and elastic stiffness. Examination of the stress-induced microfracturing characteristics during uniaxial compression of the samples revealed that the degree of sampling disturbance had only minor effects on the stress levels at which new cracks were generated (i.e., the crack initiation stress threshold). Crack-coalescence and crack-damage thresholds, on the other hand, significantly decreased with increased sampling disturbance. The presence of numerous stress-relief cracks in the samples retrieved from the highest in situ stress domains was seen to weaken the rock by providing an increased number of planes of weakness for active cracks to propagate along. A 36% strength decrease was seen in samples retrieved from the highest in situ stress domain (sigma1 - sigma3 approximate 40 MPa) as compared with those taken from the lowest in situ stress domain (sigma1 - sigma3 approximate 10 MPa).Key words: sample disturbance, brittle fracture, crack initiation, crack propagation, material properties, rock failure.

Effect of cementation on the small-strain parameters of sands

2001 ◽  
Vol 38 (1) ◽  
pp. 191-199 ◽  
Author(s):  
A L Fernandez ◽  
J C Santamarina
Keyword(s):  
Laboratory Test ◽  
Experimental Studies ◽  
Small Strain ◽  
Test Results ◽  
Loading History ◽  
Viscous Losses ◽  
Laboratory Test Results ◽  
Geotechnical Design ◽  
Selection Of

Natural cementation affects the properties of soils, the interpretation of in situ and laboratory test results, and the selection of criteria for geotechnical design. In this paper, published experimental studies are reviewed, a microscale analysis is presented of the effect of cementation on small-strain stiffness for distinct stress-cementation histories, and the effect of cementation on small-strain velocity and damping is experimentally studied. Observations include the prevailing effects of cementation over effective stress, the coexistence of frictional and viscous losses, and the effects of decementation when the medium is unloaded from the level of confinement prevailing during cementation.Key words: wave velocity, seismic response, stiffness, damping, sampling effects, loading history.

Potential improvements of design parameters by taking block samples of soft marine Norwegian clays

2007 ◽  
Vol 44 (6) ◽  
pp. 698-716 ◽  
Author(s):  
Toralv Berre ◽  
Tom Lunne ◽  
Knut H Andersen ◽  
Stein Strandvik ◽  
Morten Sjursen
Keyword(s):  
Undrained Shear Strength ◽  
Design Parameters ◽  
Shear Tests ◽  
High Quality ◽  
Soft Clays ◽  
Direct Simple Shear ◽  
Sample Disturbance ◽  
Marine Clays ◽  
Oedometer Tests

Undrained triaxial and direct simple shear tests on samples reconsolidated to the in situ effective stresses and oedometer tests have been carried out on standard piston tube and on high quality block samples from 12 deposits of soft Norwegian marine clays. Based on the results of a selected number of these tests, empirical procedures for estimating the effect of sample disturbance have been developed. These procedures can be used to show the potential increase that may be achieved in undrained shear strength and apparent preconsolidation stress by taking high quality block samples. Suggestions are also given regarding corrections for rate of loading and temperature effects; as well, examples are given regarding possible consequences for design if higher strengths are utilized.Key words: soft clays, sample disturbance, consolidation procedures, stress–strain–strength behaviour.

scholarly journals A comparison of small strain stiffness in till as measured by seismic refraction and barometric loading response

2018 ◽  
Vol 51 (4) ◽  
pp. 493-502
Author(s):  
R. M. G. Kelly ◽  
P. Bergamo ◽  
D. A. B. Hughes ◽  
S. Donohue ◽  
S. L. Barbour ◽  
...  
Keyword(s):  
Seismic Refraction ◽  
Small Strain ◽  
Small Strain Stiffness

scholarly journals Optimization Analysis of Excavation Procedure Design of Underground Powerhouses under High In Situ Stress in China

2021 ◽  
Vol 11 (21) ◽  
pp. 10252
Author(s):  
Xiao Liu ◽  
Peng Yan ◽  
Ming Chen ◽  
Sheng Luo ◽  
Ang Lu ◽  
...  
Keyword(s):  
Stress Level ◽  
In Situ Stress ◽  
Complex Stress ◽  
Design Parameters ◽  
Rock Classification ◽  
Underground Powerhouse ◽  
High In Situ Stress ◽  
Blasting Excavation ◽  
Stress Levels

To recommend the excavation procedures and design parameters for underground powerhouses, excavation procedures of fifty-one underground powerhouses in China were summarized and analyzed based on in situ stress conditions. Firstly, the complex stress environment in China was introduced and fifty-one underground powerhouses with their engineering scale, size, lithology, rock classification and in situ stress level were listed in detail. Subsequently, to evaluate the influence of in situ stress levels on excavation procedure design, the correlation between excavation procedures and in situ stress level in three main excavation zones were analyzed accordingly. Moreover, to provide the excavation design recommendations, the strength–stress ratio (SSR) was promoted to analyze and recommend the design parameters, and the blasting excavation design based on the stress transient unloading control was also supplemented. The results show that excavation procedures have different priorities under different in situ stress levels, and the design parameters show an obvious relationship with in situ stress levels. Moreover, the excavation procedure parameters are suggested to adjust accordingly under different SSR. The discussion of influencing factors and specification ensures its rationality and accuracy. It is believed that the summary and recommendations can provide a good reference for excavation procedure optimization of underground powerhouse under high in situ stress.

Investigation of small- to large-strain moduli correlations of normally consolidated granular soils

2021 ◽  
Vol 58 (1) ◽  
pp. 1-22
Author(s):  
Ibrahim Lashin ◽  
Michael Ghali ◽  
Mahmoud N. Hussien ◽  
Mohamed Chekired ◽  
Mourad Karray
Keyword(s):  
Large Strain ◽  
Small Strain ◽  
In Situ Stress ◽  
Soil Parameters ◽  
Physical Parameters ◽  
Granular Soils ◽  
Shear Wave Velocities ◽  
Settlement Behavior ◽  
Constrained Modulus

The establishment of correlations between the small-strain shear modulus (Go) and other soil parameters (such as the oedometer constrained modulus, Moedo) at large deformations constitutes an important step toward more precise modeling of soil deformation behavior. In this study, the shear wave velocities (Vs) of 22 different granular soils of various physical characteristics were measured experimentally using the piezoelectric ring-actuator technique (P-RAT) incorporated in the conventional oedometer cell. For each sample tested, the development of Moedo with the development of relative density (Id), as well as the void ratio (e), was recorded. Then, the obtained Vs and Moedo/Go trends were correlated to the physical parameters of the tested granular soils with the development of e and Id. A practical application employing the achievements in geotechnical engineering design was also evaluated. Based on the proposed correlations, geotechnical designers can easily estimate in situ stress–settlement behavior from the predicted Moedo and Id values using simple in situ measurements.

The effect of sample disturbance on laboratory properties of Lac du Bonnet granite

1994 ◽  
Vol 31 (5) ◽  
pp. 692-702 ◽  
Author(s):  
C. Derek Martin ◽  
Brian Stimpson
Keyword(s):  
In Situ Stress ◽  
P Wave ◽  
Confining Stress ◽  
Near Surface ◽  
Brittle Rocks ◽  
Frictional Properties ◽  
Stress Dependent ◽  
Sample Disturbance ◽  
Core Discing

Laboratory properties of Lac du Bonnet granite samples collected at depths ranging from near-surface to 1000 m were established. The laboratory properties indicated that either the in situ properties were changing with depth or the samples were changing with depth. Comparison of P-wave velocities in the samples and in situ confirmed the latter, i.e., sample disturbance was affecting the laboratory properties. The strength of the damaged samples indicated that sample disturbance affected the cohesion of the material, not the frictional properties, and that the cohesion loss cannot be accounted for, by applying a confining stress. Sample disturbance started to affect the laboratory properties of Lac du Bonnet granite when the maximum far-field in situ stress exceeded about 10% of the unconfined compression strength. Key words : sample disturbance, core discing, cohesion, brittle rocks, damage, microcracks, stress-dependent Young's modulus.

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

2014 ◽  
Vol 51 (8) ◽  
pp. 896-910 ◽  
Author(s):  
Toralv Berre
Keyword(s):  
Shear Strength ◽  
Water Content ◽  
In Situ Stress ◽  
Undrained Shear Strength ◽  
Stress Strain ◽  
Effective Stresses ◽  
Sample Disturbance ◽  
Oedometer Tests ◽  
Undrained Shear

The tests in this investigation were performed on a natural soft clay with plasticity index around 32%, which was K0 consolidated to a vertical stress of 2942 kPa and then K0 unloaded 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 K0 loading (i.e., K0 triaxial 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.

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