Evaluation of soil liquefaction in the Chi-Chi, Taiwan earthquake using CPT

During the 1999 Chi-Chi, Taiwan earthquake, many sand boiling phenomena were observed in central Taiwan, which caused severe ground settlement and structure damages. According to the installed accelerograms, the peak ground surface horizontal accelerations in the liquefaction-affected areas range from 774.42 to 121.3 gal. The writers carried out an extensive investigation of soil liquefaction in this earthquake. In this paper, we present results of the CPT exploration and post-earthquake liquefaction analysis. Two hundred and seventy five (275) cone penetration test data were collected from the liquefaction-affected areas, and 46 liquefaction case histories and 88 non-liquefaction case histories were derived that can be used to evaluate the accuracy of existing liquefaction evaluation models. In addition, the strength of the liquefied soils after earthquake and the implication of its liquefaction potential in the future event are discussed.     

The penetration experiment to predict liquefaction resistance of reclaimed soils

The liquefaction resistance of the soils used to be estimated through the in situ tests, such as standard penetration test and cone penetration test; or by means of cyclic triaxial test in laboratory. However, both in situ tests and cyclic triaxial test are time-consuming and costly; this study introduces a quick and cost-effective method to evaluate the liquefaction resistance of soils under certain confining pressure in laboratory. A particular device modified from the conventional triaxial compression test apparatus, namely “Triaxial Cone Penetration Test”, was developed to obtain the peak values of cone resistance in soils so as to correlate the liquefaction resistance of the reclaimed soils evaluated by cyclic triaxial tests. The test result indicates a good correlation between the peak value of cone resistance and the corresponding cyclic stress ratio (CSR) at the state of initial liquefaction, in which the correlation for loose samples is better than that for dense samples. Besides, both peak values of cone resistance and corresponding CSR increase with fine content of soils reaches 10% and decreased with fine content varying between 10% and 50%. By examining the compositions of the soils with scanning electron microscopy and X-ray diffraction, it is found that the proportion and characteristics of the fines plays an important role on the liquefaction resistance of the reclaimed soils.     

Evaluation of liquefaction potential using neural-networks and CPT results

In this research, a reliable Cone Penetration Test data set was gathered with a wide range of parameters. This data was incorporated in a Neural-Networks computer software called STATISTICA Neural-Networks. The back propagation algorithm with a multilayer perceptron network is utilized to analyze the liquefaction occurrence in different sites. In this study, different sets of effective parameters for the neural-network analyses are selected such that to reduce the noise and to obtain more accurate results.Considering the relative importance of effective parameters in liquefaction assessment, it is indicated that σ₀, σ′₀ together play a more important role than what previously was assumed and hence the relative importance of the q_c and seismic parameters are decreased compared with the previous works. The results presented here have more accuracy than previous works while at the same time, the range of the parameters used in this study is much wider than what was previously used. This range of parameters makes the proposed method applicable for practical purposes.     

The evolution of pore pressure fields around standard and ball penetrometers: influence of penetration rate

Rate effects are examined in the steady pore pressure distribution induced as a result of penetration of standard and ball penetrometers. The incompressible flow field, which develops around the penetrometer is used to define the approximate soil velocity field local to the penetrometer tip. This prescribes the Lagrangian framework for the migration of the fluid saturated porous medium, defining the advection of induced pore pressures relative to the pressure‐monitoring locations present on the probe face. In two separate approaches, different source functions are used to define the undrained pore fluid pressures developed either (i) on the face of the penetrometer or (ii) in the material comprising the failure zone surrounding the penetrometer tip. In the first, the sources applied at the tip face balance the volume of fluid mobilized by the piston displacement of the advancing penetrometer. Alternately, a fluid source distribution is evaluated from plasticity solutions and distributed throughout the tip process zone: for a standard penetrometer, the solution is for the expansion of a spherical cavity, and for the ball penetrometer, the solution is an elastic distribution of stresses conditioned by the limit load embedded within an infinite medium. For the standard penetrometer, the transition from drained to undrained behavior occurs over about two orders of magnitude in penetration rate for pore pressures recorded at the tip (U1) and about two‐and‐a‐half orders of magnitude for the shoulder (U2). This response is strongly influenced by the rigidity of the soil and slightly influenced by the model linking induced total stresses to pore pressures. For the ball penetrometer, the transition from drained to undrained behavior also transits two‐and‐a‐half orders of magnitude in penetration rate, although it is offset to higher dimensionless penetration rates than for standard penetration. Copyright © 2012 John Wiley & Sons, Ltd.     

Dynamic Response of Machine Foundation on Layered Soil: Cone Model Versus Experiments

This paper presents the experimental validation of analytical solution based on cone model for machine foundation vibration analysis on layered soil. Impedance functions for a rigid massless circular foundation resting on a two layered soil system subjected to vertical harmonic excitation are found using cone model. Linear hysteretic material damping is introduced using correspondence principle. The frequency-amplitude response of a massive foundation is then computed using impedance functions. To verify the solution field experiments are conducted in two different layered soil systems such as gravel layer over in situ soil and gravel layer over concrete slab (rigid base). A total 72 numbers of vertical vibration tests on square model footing were conducted using Lazan type mechanical oscillator, varying the influencing parameters such as depth of top layer, static weight of foundation and dynamic force level. The frequency-amplitude response in general and in particular the resonant frequencies and resonant amplitudes predicted by cone model is compared with the results of experimental investigation, which shows a close agreement. Thus the cone model is reliable in its application to machine foundation vibration on layered soil.     

Application of a nondestructive method to evaluate the active layer in a cold region

To provide a safe transportation system in an extremely cold region,evaluation needs to be conducted of the thickness and the volumetric water content of the active layer,as they significantly affect frost heave.The objective of this study was to evaluate the dielectric constant(κ)of the active layer using ground-penetrating radar(GPR)and a dynamic cone penetrometer(DCP);this evaluation was then used to estimate the thickness and the volumetric water content of the active layer.A field located in midwest Alaska was selected as the study site.A GPR survey and two DCP tests were conducted on the surface of the ground,and the ground temperature was measured.From the GPR survey,travel times of the electromagnetic wave in the active layer were obtained.In addition,the thickness of the active layer was determined by using the dynamic cone penetration index(DCPI)and ground temperature.By using the travel time and travel distance of the electromagnetic wave in the active layer,dielectric constants were calculated as 26.3 and 26.4 for two DCP points.From the mean dielectric constant,the volumetric water content was estimated to be 40%~43%,and the thickness of the active layer was evaluated along the GPR survey line.The spatial-scaled GPR image showed that the thickness of the active layer varied from 520 mm to 700 mm due to the presence of a puddle,which accelerated the heat exchange.The results show that evaluation of the dielectric constant using the GPR survey and the DCP test can be effectively used to estimate the thickness and the volumetric water content of the active layer.     

Field measurements of shear strength of an underconsolidated marine clay

This paper presents the observations of cone penetration testing (CPT), in situ vane shear testing and undrained triaxial testing of underconsolidated marine clay in the Craney Island Dredged Material Management Area (CIDMMA), Norfolk, VA. Comparison of vane shear measurements, taken during 1981–1983, to CPT measurements, taken during 1993, indicates a change in undrained shear strength. Both the vane shear and cone penetration resistances are lowest at the mid-heights of the clay layers and the excess pore water pressures are highest at the mid-height of the clay layers, indicating that the clay layer is underconsolidated.     

Comparing liquefaction evaluation methods using penetration-VS relationships

Three methods that follow the general format of the Seed-Idriss simplified procedure for evaluating liquefaction resistance of soils are compared in this paper. They are compared by constructing relationships between penetration resistance and small-strain shear–wave velocity (V_S) implied from cyclic resistance ratio (CRR) curves for the three methods, and by plotting penetration-V_S data pairs. The penetration-V_S data pairs are from 43 Holocene-age sand layers in California, South Carolina, Canada, and Japan. It is shown that the V_S-based CRR curve is more conservative than CRR curves based on the Standard Penetration Test (SPT) and Cone Penetration Test (CPT), for the compiled Holocene data. This result agrees with the findings of a recent probability study where the SPT-, CPT-, and V_S-based CRR curves were characterized as curves with average probability of liquefaction of 31, 50, and 26%, respectively. New SPT- and CPT-based CRR equations are proposed that provide more consistent assessments of liquefaction potential for the Holocene sand layers considered.