The evaluation and design of stone column improvement ground for liquefaction mitigation is a challenging issue for the state of practice. In this paper, a shear wave velocity-based approach is proposed based on the w...The evaluation and design of stone column improvement ground for liquefaction mitigation is a challenging issue for the state of practice. In this paper, a shear wave velocity-based approach is proposed based on the well-defined correlations of liquefaction resistance （CRR）-shear wave velocity （V）-void ratio （e） of sandy soils, and the values of parameters in this approach are recommended for preliminary design purpose when site specific values are not available. The detailed procedures of pre- and post-improvement liquefaction evaluations and stone column design are given. According to this approach, the required level of ground improvement will be met once the target V of soil is raised high enough （i.e., no less than the critical velocity） to resist the given earthquake loading according to the CRR-V relationship, and then this requirement is transferred to the control of target void ratio （i.e., the critical e） according to the V-e relationship. As this approach relies on the densification of the surrounding soil instead of the whole improved ground and is conservative by nature, specific considerations of the densification mechanism and effect are given, and the effects of drainage and reinforcement of stone columns are also discussed. A case study of a thermal power plant in Indonesia is introduced, where the effectiveness of stone column improved ground was evaluated by the proposed V-based method and compared with the SPT-based evaluation. This improved ground performed well and experienced no liquefaction during subsequent strong earthquakes.展开更多
This article presents a case study concerning a seismic characterization project.Full-wave sonic logging was used to characterize the shallow compressional wave and shear wave velocity profiles in the site.Anomalous v...This article presents a case study concerning a seismic characterization project.Full-wave sonic logging was used to characterize the shallow compressional wave and shear wave velocity profiles in the site.Anomalous values of the Poisson’s ratio derived from the velocity profiles suggested that the boreholes might have traversed slow formations(i.e.with shear wave velocity smaller than the borehole fluid compressional wave velocity or“mud-wave speed”)and that conventional processing of the sonic logs might have misinterpreted the direct arrivals of fluid acoustic waves as arrivals caused by shear wave propagation in the rock.Consequently,the shear wave velocity profiles provided by the contractor were considered to be unreliable by the project team.To address these problems,a non-conventional determination of the shear wave velocity was implemented,based on the relationship between the Poisson’s ratio of the rock formation and the shape of the first train of sonic waves which arrived to the receivers in the sonic probe.The relationship was determined based on several hundreds of finite element simulations of the acoustic wave propagation in boreholes with the same diameter as used in the perforations.The present article describes how this non-conventional approach was developed and implemented to obtain the shear wave velocity profiles from the raw sonic logs.The approach allows an extension of the range of applicability of full-wave sonic logging to determination of shear wave velocity profiles in formations with low compressional wave velocities.The method could be used to obtain shear wave velocity profiles where compressional wave velocity is as low as slightly larger than the mud-wave speed.A sample sonic log in Log ASCII Standard(LAS)format is provided as supplementary material to this paper via Mendeley Data,together with the FORTRAN source code used to process the log following the approach described in this study.展开更多
A layer-stripping method is presented for simultaneous inversion of compressional velocity and shear velocity in layered medium from single precritical-incident-angle data of P-P and P-SV plane wave seismogram. A fini...A layer-stripping method is presented for simultaneous inversion of compressional velocity and shear velocity in layered medium from single precritical-incident-angle data of P-P and P-SV plane wave seismogram. A finite bandwidth algorithm is provided and results obviously better than previous research work are obtained by the numerical experiments for band-limited seismogram and synthetic data including noise.展开更多
The formation bulk density is one of the most important rock properties required for reservoir evaluation and geomechanical analysis.In intervals where the formation bulk density logs are not acquired,the industry pra...The formation bulk density is one of the most important rock properties required for reservoir evaluation and geomechanical analysis.In intervals where the formation bulk density logs are not acquired,the industry practice is to estimate the formation bulk density from the compressional-wave velocity using empirical relationships.The major problems with the existing empirical relationships are:(1)they were developed primarily for specific lithologies(in most cases clean formations)and have failed to produce reasonable estimates when applied over a lithological column that consists of several stratigraphic units;(2)they are not applicable to rocks that contain microcracks/fractures.In this paper,a new formation bulk density prediction method that can be applied to a wide range of intact and fractured siliciclastic rocks is being proposed based on experimental data.The model is then validated using wireline log data acquired from an onshore well in the tertiary deltaic system of the Niger Delta basin.In the new model,the formation bulk density is expressed as a function of sonic velocity difference and shale volume factor.In general,an excellent agreement exists between the predicted and measured formation bulk density using the new technique.The statistical analysis shows that the new formation bulk density prediction model outperforms the most widely used empirical relationships with the least-root-mean square errors and least residual values.展开更多
On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just at the south center of China’s Capital Circle area digital seismograph network. It is the strongest event recorded ever since the ne...On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just at the south center of China’s Capital Circle area digital seismograph network. It is the strongest event recorded ever since the network went into operation in 2002. We processed the vast amounts of phase data yielded by the 107 digital seismic stations between 2002~2007 using Wadati method. In order to improve the precision and stability of shear and compressional wave velocities (vP/vS) calculation, we impose a number of restrictions on the computation environment and condition, e.g., the earthquakes are densely concentrated, selected stations are limited in range, the number of stations in- volved in the computation is larger than 5 and linear fitting features high precision and small error. Under these restrictions, the study shows that vP/vS in and around Wen’an and Tangshan underwent a normal-low-normal proc- ess one year before Wen’an earthquake, vP/vS became obviously low and the low ratio lasted for about one year, meanwhile, little variation of vP/vS was seen in Xingtai, northwest of Beijing, southwest of Beijing, Beijing-Tianjin and Beijing; after the quake, the vP/vS returned normal in Wen’an and Tangshan. Error and stability analysis of the calculated result for vP/vS shows it is convincible that anomaly appeared in and around Wen’an and Tangshan be- fore Wen’an earthquake.展开更多
基金National Natural Science Foundation of China under Grant No.51578501 and No.51127005the Foundation for the Author of National Excellent Doctoral Dissertation of P R China under Grant No.201160+3 种基金the Zhejiang Provincial Natural Science Foundation of China under Grant No.LR15E080001the National Basic Research Program of China(973 Project)under Grant No.2014CB047005the Fundamental Research Funds for the Central Universities under Grant No.2014FZA4016Zhejiang University K.P.Chao’s High Technology Development Foundation(2014)
文摘The evaluation and design of stone column improvement ground for liquefaction mitigation is a challenging issue for the state of practice. In this paper, a shear wave velocity-based approach is proposed based on the well-defined correlations of liquefaction resistance （CRR）-shear wave velocity （V）-void ratio （e） of sandy soils, and the values of parameters in this approach are recommended for preliminary design purpose when site specific values are not available. The detailed procedures of pre- and post-improvement liquefaction evaluations and stone column design are given. According to this approach, the required level of ground improvement will be met once the target V of soil is raised high enough （i.e., no less than the critical velocity） to resist the given earthquake loading according to the CRR-V relationship, and then this requirement is transferred to the control of target void ratio （i.e., the critical e） according to the V-e relationship. As this approach relies on the densification of the surrounding soil instead of the whole improved ground and is conservative by nature, specific considerations of the densification mechanism and effect are given, and the effects of drainage and reinforcement of stone columns are also discussed. A case study of a thermal power plant in Indonesia is introduced, where the effectiveness of stone column improved ground was evaluated by the proposed V-based method and compared with the SPT-based evaluation. This improved ground performed well and experienced no liquefaction during subsequent strong earthquakes.
文摘This article presents a case study concerning a seismic characterization project.Full-wave sonic logging was used to characterize the shallow compressional wave and shear wave velocity profiles in the site.Anomalous values of the Poisson’s ratio derived from the velocity profiles suggested that the boreholes might have traversed slow formations(i.e.with shear wave velocity smaller than the borehole fluid compressional wave velocity or“mud-wave speed”)and that conventional processing of the sonic logs might have misinterpreted the direct arrivals of fluid acoustic waves as arrivals caused by shear wave propagation in the rock.Consequently,the shear wave velocity profiles provided by the contractor were considered to be unreliable by the project team.To address these problems,a non-conventional determination of the shear wave velocity was implemented,based on the relationship between the Poisson’s ratio of the rock formation and the shape of the first train of sonic waves which arrived to the receivers in the sonic probe.The relationship was determined based on several hundreds of finite element simulations of the acoustic wave propagation in boreholes with the same diameter as used in the perforations.The present article describes how this non-conventional approach was developed and implemented to obtain the shear wave velocity profiles from the raw sonic logs.The approach allows an extension of the range of applicability of full-wave sonic logging to determination of shear wave velocity profiles in formations with low compressional wave velocities.The method could be used to obtain shear wave velocity profiles where compressional wave velocity is as low as slightly larger than the mud-wave speed.A sample sonic log in Log ASCII Standard(LAS)format is provided as supplementary material to this paper via Mendeley Data,together with the FORTRAN source code used to process the log following the approach described in this study.
基金Project supported by the National Natural Science Foundation of China and General Corp. for Oil and Gas and Daqing Oilfield.
文摘A layer-stripping method is presented for simultaneous inversion of compressional velocity and shear velocity in layered medium from single precritical-incident-angle data of P-P and P-SV plane wave seismogram. A finite bandwidth algorithm is provided and results obviously better than previous research work are obtained by the numerical experiments for band-limited seismogram and synthetic data including noise.
基金support provided by the Advanced Drilling Technology Laboratory Group, Memorial University of Newfoundland, Canada
文摘The formation bulk density is one of the most important rock properties required for reservoir evaluation and geomechanical analysis.In intervals where the formation bulk density logs are not acquired,the industry practice is to estimate the formation bulk density from the compressional-wave velocity using empirical relationships.The major problems with the existing empirical relationships are:(1)they were developed primarily for specific lithologies(in most cases clean formations)and have failed to produce reasonable estimates when applied over a lithological column that consists of several stratigraphic units;(2)they are not applicable to rocks that contain microcracks/fractures.In this paper,a new formation bulk density prediction method that can be applied to a wide range of intact and fractured siliciclastic rocks is being proposed based on experimental data.The model is then validated using wireline log data acquired from an onshore well in the tertiary deltaic system of the Niger Delta basin.In the new model,the formation bulk density is expressed as a function of sonic velocity difference and shale volume factor.In general,an excellent agreement exists between the predicted and measured formation bulk density using the new technique.The statistical analysis shows that the new formation bulk density prediction model outperforms the most widely used empirical relationships with the least-root-mean square errors and least residual values.
基金Special Fund for Basic Scientific Research, IGPCEA (DQJB06B03)National Program for Key Science and Technology Projects during the 11th Five-year Plan Period (2006BAC01B03-04-04)Contribution No.08FE3004, Institute of Geophysics, China Earthquake Administration.
文摘On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just at the south center of China’s Capital Circle area digital seismograph network. It is the strongest event recorded ever since the network went into operation in 2002. We processed the vast amounts of phase data yielded by the 107 digital seismic stations between 2002~2007 using Wadati method. In order to improve the precision and stability of shear and compressional wave velocities (vP/vS) calculation, we impose a number of restrictions on the computation environment and condition, e.g., the earthquakes are densely concentrated, selected stations are limited in range, the number of stations in- volved in the computation is larger than 5 and linear fitting features high precision and small error. Under these restrictions, the study shows that vP/vS in and around Wen’an and Tangshan underwent a normal-low-normal proc- ess one year before Wen’an earthquake, vP/vS became obviously low and the low ratio lasted for about one year, meanwhile, little variation of vP/vS was seen in Xingtai, northwest of Beijing, southwest of Beijing, Beijing-Tianjin and Beijing; after the quake, the vP/vS returned normal in Wen’an and Tangshan. Error and stability analysis of the calculated result for vP/vS shows it is convincible that anomaly appeared in and around Wen’an and Tangshan be- fore Wen’an earthquake.
