The elliptic structure composed of particles aligned in an elliptic circle in granular material is recognized as a unit of microstructure. The mechanical properties of this elliptic structure are examined in the two-dimensional condition. Based on the contact forces between the constituent particles calculated from equilibrium, stability is presented as a function of the shape of the elliptic structure and the stress condition surrounding the structure. The deformation behavior given as the compliance matrix is also examined, based on shell theory and the theory of micropolar elasticity. It was found that some characteristic mechanical properties of a granular material, such as deformation anisotropy, dilatancy and non-coaxiality, can be explained by the elliptic structure, where the rotation of the constituent particles plays an important role.
The basic objective of this research was to investigate the effectiveness of"bitumen"as a soil stabilizing agent. For this purpose, four different soils from Northern Jordan, which exhibit certain engineering problems, such as swelling and collapsibility, were selected. Two of these soils are swelling soils (Irbid and Ramtha), while the other two are collapsible (JUST and Mafraq). To conduct this work, soil-bitumen mixtures were prepared at 3%, 5%, 7% and 10% bitumen by dry weight of soil. Both natural and bitumen treated soils were subjected to similar laboratory tests to observe the influence bitumen on swelling and collapse potential. The test results showed that bitumen is effective in stabilizing the tested soils. Upon mixing with soils, bituminous materials act as a binding agent between soil particles. Additionally, test results showed that cutback bitumen percentages in excess of 7% do not show a substantial reduction in swelling and collapsibility potentials.
Physical modelling of soil deformation over a moving basement shows that localisation of deformation is an important feature of response. Different patterns of response are observed in model tests on clay and sand. Internal localisations which do not extend to the boundaries of the soil mass are observed in the sand tests. Numerical modelling of this problem, with finite elements, has used the tij models with parameters chosen to represent typical clays and dense sands. The nature of the analyses is such that localisation can be inferred but not observed. Although results are presented in terms of contours of proximity to failure and contours of shear strain, it is study of stress paths followed by individual soil elements that is most instructive in indicating likelihood of localisation and in revealing the differences in clay sand response that result from their significantly different volume change characteristics.
Physical modeling utilizing a centrifuge is often attempted in order to investigate short-term stability problems of soft clay deposits whose undrained shear strength generally varies with depth. Since accurate evaluation of the strength profile in model beds is essential for such studies, a cone penetration test (CPT) technique in the centrifuge has been developed to obtain geotechnical information continuously with depth. A series of CPTs in homogeneous clay beds was conducted in order to establish the correlation between cone resistance qc and undrained shear strength cu. This empirical relationship can take account of the influences of penetration rate, stress level and the error associated with the stress acting on the rear of the cone tip. In the end, this CPT technique in the centrifuge has proved itself to be useful in evaluating the undrained shear strength profile in non-homogeneous clay beds.
Liquefaction susceptibility is the measure of a soil's ability to liquefy during earthquakes. Conventionally, liquefaction susceptibility is determined from soil properties and a subjective knowledge of the geologic conditions. There are many uncertainties in this approach because of the subjectivity in evaluating many important factors. An expert is required if the evaluation is to be performed with confidence. The application of fuzzy set theory is proposed to improve this process. The intent was to develop a method of evaluating liquefaction susceptibility that included factors usually evaluated only by an expert. The method could then be used by engineers with little experience with liquefaction. This new approach incorporates expert opinion of the importance of the subjective factors known to affect liquefaction. The engineer inputs the soil profile using linguistic descriptions which are then processed using the theory of fuzzy sets. The resulting fuzzy sets are interpreted by defining the Fuzzy Liquefaction Susceptibility Index (FLSI), a number which can be plotted and contoured to produce a map of liquefaction susceptibility. The new approach was tested by mapping the liquefaction susceptibility of Charleston, South Carolina, and comparing with other published results generated from conventional analysis. The results were quite comparable, indicating the potential for the new method to evaluate liquefaction susceptibility. The new technique is useful in creating maps of relative liquefaction hazard that can be used in municipal planning.
The results of an experimental investigation on the drivability of helix-shaped units into submerged sand and sand subjected to upward seepage flow are presented. In this research study, the helical units are used as structural anchoring elements. A testing program is conducted to study the effect of water existence in a sand deposit on the driving moment (torque) required to install helix-shaped units, with reference to torque required to install the same in dry sands. Dense sand is used in this study with water conditions varying from hydrostatic pressure to upward seepage flow with three different velocities. Measurements are recorded for the installation torque versus depth of installation. Based on the results of this study, it is concluded that the existence of water in the sand bed material facilitates the installation and reduces the torque required to drive the helical units. It is also found that helix drivability improves with the increase of the velocity of seepage flow, however, this seepage flow negatively reflects on the resistibility of these units to pullout forces. It is recommended that the design of both the driving technique and the pullout resistance of helix-shaped foundation units be balanced in a way that the easiness of installation and the obtained pullout resistance are optimized. It is also recommended that pullout resistance of anchors should not be compromised to achieve higher drivability.
The undisturbed sand samples were obtained using both the in-situ freezing method (FS sample) and the rotary-type triple tube sampling method (TS sample) from four sites. The liquefaction strength of these samples was determined by conducting undrained cyclic triaxial tests. The liquefaction strength and the relative density of these samples were compared. Test results were also discussed with other researchers using the data presented from the point of view of sample disturbance during sampling. The following conclusions were made : (1) In the case of natural sand deposits, the liquefaction strength of the TS samples was about the same or lower than that of the FS samples. For artificial fill of loose sand, however, the liquefaction strength of the TS samples was higher than that of the FS samples. (2) In some cases, for the natural medium dense sand, the liquefaction strength of the TS samples was much lower than that of the FS samples even though both samples have almost the same relative density. This result means that, factors other than the relative density, such as changes in the micro-fabric during sampling and/or effects of aging on the extent of sample disturbance should be considered. (3) In the case of natural sand deposits, a strong correlation was seen between the liquefaction strength ratio (ratio of liquefaction strength between FS sample and TS sample) and the SPT N-value normalized by an effective overburden pressure of 98 kPa(=1 kgf/cm2), N1, such that the liquefaction strength ratio increases with increases in N1.
Two Methods (Method A and Method B) used to determine the in-situ horizontal stress of cohesionless soil are presented. Method A is a laboratory test. In test Method A, a high-quality undisturbed sample of cohesionless soil recovered by the in-situ freezing technique was thawed under no-lateral strain condition in a special cell under the in-situ vertical stress. The cell pressure at the time when the frozen sample was completely thawed indicates the in-situ horizontal stress. Method B is a field test. In Test Method B, a special measuring device was inserted into a frozen borehole below subsoil provided by in-situ freezing sampling. The pressure measured in the device when the surrounding subsoil was completely thawed indicates the in-situ horizontal stress. A series of comparative tests to confirm the reliability of these two proposed methods were performed in the laboratory. Sand specimens with given stress histories (overconsolidation ratio = 2, 4 and 6) were frozen one-dimensionally and then used in comparative tests. The horizontal stress in the sand specimen before freezing was directly measured for comparison. Good agreement of the horizontal stress measured with Test Method A and in the sand before freezing was measured. Good agreement of the horizontal stress measured in the Method B and in the sand before freezing was also observed. These results indicate that a freeze-thaw sequence used in this study did not change the state of stress in the sand before freezing. The results also indicated that both Test Method A and Test Method B proposed in this study are reliable for measuring the in-situ state of stress in the cohesionless soil.
This paper is concerned with an extension of a rotational limit equilibrium method for determining the permanent displacements of slopes under seismic excitation. In the proposed procedure, the sliding mass is treated as a rigid rotating body defined by a log spiral trace. Permanent displacements are obtained by double-integration of the equation of motion in a manner similar to Newmark's translational sliding block method. The seismic slope stability analysis is based on the rotational (variational) limit equilibrium approach. This stability analysis was verified with dynamic experimental results obtained from centrifuge model testing. A series of parametric studies was conducted on"unstable"slopes, investigating the effects of soil properties and characteristics of excitation on the magnitude of permanent displacements. The higher the frictional angle, the smaller the permanent displacement of the slope is. Low excitation frequency yields larger slope displacement if the excitation is extended for the same time period of time. The effect of frequency becomes less distinct when a larger value of yield seismic coefficient is used. The proposed procedures produce a rational criterion to evaluate the seismic performance of simple slopes. This criterion is based on permanent displacement limit rather than factor of safety alone.
In Japan, the unconfined compression test is used widely to determine undrained strength for natural clays. The scatter of test data caused by sample disturbance, however, prevents this test from being used effectively and economically in geotechnical engineering practice. This paper is aimed at proposing a simple rational approach to correct the unconfined compressive strength, qu, of natural clays for sample disturbance. The effect of sample disturbance on qu is analyzed both qualitatively and quantitatively based on the experimental data for five types of natural clay. The results indicate that qu normalized by the corrected yield stress, pyf, decreases linearly with the increase of the defined degree of sample disturbance. The straight line representing the relationship between the reduction value of qu/pyf and the disturbance degree is determined by regression analysis. The slope of the linear regression line is defined as a strength correction coefficient. Based on such correction coefficient, a simple method is proposed in this paper for correcting qu for sample disturbance. The problem of scattered test data on qu can be eliminated with the proposed method. Analyses and comparisons are also made of the experimental data on unconfined compression tests and triaxial consolidated undrained shear tests for some natural clays as well as the data published in the literature. The results indicate that the proposed method is valid for natural clays.
Empirical correlations for estimating the shear wave velocity (Vs) from cone penetration tip resistance (qc) are derived from measured field data taken in 31 different natural clays. Despite the face that Vs and qc are operational at the opposite extremes of a highly nonlinear stress-strain-strength relationship, the two parameters can be interrelated because they are both influenced by effective confining stress level, anisotropic K0-stress state, mineralogy, aging, bonding, and other factors. Regression analyses indicate that the estimate is significantly improved if measurements of void ratio (e0) with depth are also known, resulting in an expression that relates Vs to both qc and e0. Results are applied to an independent recent case study involving a sensitive marine clay where the relevant parameters are well documented.
The flat dilatometer (in-situ) testing device (DMT) has been used frequently North America and Europe during the short period of time since its introduction. The main advantages of the DMT are its simplicity, rapid and repetitive use for geotechnical engineering practice. This paper describes the use of the flat dilatometer (in-situ) testing device (DMT) in Japan. The discussion concentrates on the evaluation of undrained shear strength. Based on the limited available test data in Japan, an attempt has been made to determine the usefulness of Marchetti's equation related to undrained shear strength and to show the important modifications of the Marchetti's equations concerning the evaluation of undrained shear strength. In addition, a new equation has been developed to estimate the undrained shear strength cu obtained from an unconfined compression test to establish a Japanese design manual for clay foundations.
A substructure on-line testing (SOT) system was developed for the purpose of conducting a quantitative simulation of the behavior of horizontal subsurface layers subjected to earthquake motions (SH wave) under undrained conditions. In this method, a computer analysis of the seismic response and a pseudo-dynamic loading test which estimates the restoration force of the materials were combined with a computer on-line data processing system. With the SOT system, which was devised to analyze the overall seismic response behavior of subsoils, an on-line test was adopted only for layers demonstrating complicated hysteretic behavior with respect to restoration force, while a numerical model was applied to the remaining layers. The following tests were conducted in order to verify this system : 1) The reliability of a series of 6 hollow torsional shear apparatus installed in the SOT system was verified by comparing the test results with the results of cyclic undrained simple shear tests conducted by Tatsuoka et al. (1989); 2) A test on a quasi-elastic specimen was conducted based on the SOT system using a test algorithm developed for this study, and an elastic analysis was carried out using the modulus of elasticity obtained from this test. Based on a comparison between the respective results of the test and the analysis, the reliability of the test algorithm was verified; 3) Using the system thus verified, a seismic response liquefaction test on a saturated sandy subsoils was conducted, which showed that the SOT system developed in this study was capable of accurately simulating the seismic response of a level subsoils.
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