مقاومت در برابر روان شدگی ماسه ها
Abstract
1. Introduction
2. Tested materials
3. Undrained cyclic triaxial tests
4. CPT soundings in the calibration chamber
5. Correlation between CPT tip resistance and liquefaction resistance
6. Measurements of shear wave velocity with bender elements
7. Correlation between shear wave velocity and liquefaction resistance
8. Summary, conclusions and outlook
References
Abstract
Correlations between the liquefaction resistance of sands in spreader dumps of lignite opencast mines on one side and the CPT tip resistance or the shear wave velocity on the other side have been developed based on an extensive experimental study on 10 different sands. The cyclic resistance ratio CRR N( 10) f = for a failure in 10 cycles, defined as the liquefaction resistance herein, was determined from undrained cyclic triaxial tests for all materials. The CPT tip resistance qc was measured in soundings performed in a calibration chamber. The shear wave velocity vS was obtained from measurements in a triaxial cell by means of bender elements. All three quantities CRR N( 10) f = , qc and vS were determined for different relative densities Dr. In case of qc and vS also the pressure-dependence was examined in order to derive suitable equations for a pressure-normalization being necessary for the interpretation of field test data, giving values qc1 and vS1 for a mean effective stress of p = 100 kPa. The procedure for the development of the CRR N( 10) f = -qc1 and CRR N( 10) f = -vS1 correlations based on the experimental data is explained. The correlations derived for the various sands in the present study are analyzed with respect to the influence of the grain size distribution curve and compared to respective relationships for natural soils or uncompacted recent artificial fills from the literature.
Introduction
The liquefaction resistance of a ground is often evaluated based on correlations with the CPT or SPT penetration resistance [5,6,10,19,23,24,27,28,30–۳۳] or with the shear wave velocity [4,10,11,20,29,35]. Examples for respective correlation diagrams are shown in Figs. 1–۳٫ They are showing a cyclic resistance ratio, defined as the shear stress amplitude ampl causing a liquefaction in a certain number of cycles divided by the vertical effective stress v on the ordinate and the penetration resistance or shear wave velocity on the abscissa. Such diagrams have been developed by collecting field data from CPT or SPT (tip resistance qc in case of CPT, blow count NSPT in case of SPT) or shear wave velocity measurements (vS). Furthermore, one needs information regarding the cyclic stress ratio CSR induced in the ground by an earthquake and whether this action has lead to a liquefaction or not. Combinations of CSR with qc, NSPT or vS having lead to liquefaction are usually marked by filled symbols (see Figs. 1–۳), while the symbols for combinations without any visible signs of liquefaction remain empty. Finally, a bounding curve is drawn, separating the “liquefaction” from the “no liquefaction” cases. These bounding curves sometimes consider further parameters like fines content or mean grain size. They are usually established for a certain earthquake magnitude MW . Curves for other magnitudes can be obtained by multiplication with a correction factor MSF . However, almost all such correlations proposed in the literature are valid for natural soils only (see Figs. 1 and 2). A first CSR-vS correlation diagram for uncompacted recent artificial fills has been recently proposed by Dobry et al. [11] (Fig. 3). No correlations for an estimation of the liquefaction resistance of such fills based on CPT or SPT field data exist so far.