剪切波速判别地震液化势的适用性研究

本文阐述了剪切波速判别地震液化势的可行性, 对目前国内外各种剪切波速判别地震液化势的方法进行了分析对比, 指出公式(6)是一实用、可靠的判别方法。     

Multilinear Regression Analysis for Seismic Response and Engineering Properties of Liquefiable Coromandel Coastal Soil Deposits

This paper investigates the seismic characteristics and geotechnical properties with respect to the liquefaction potential of the deposits in the Coromandel coastal line of Nagapattinam town, Tamilnadu, India. A series of field tests were conducted using standard penetration test, cone penetration test and plate load test. Laboratory tests were conducted on the collected samples. From the results, a microzonation map was developed for the liquefaction potential and settlements. Some multilinear regression models between permeability, fines content, relative density, coefficient of curvature, coefficient of uniformity, mean particle size, factor of safety, settlement, standard penetration test values and cone penetration test values were developed. The shear wave velocity and shear modulus were calculated from the field penetration tests and correlations between the normalized values of peak ground accelerations, velocities and displacements, which were obtained from the equivalent linear ground motion analysis using SHAKE software, with other parameters of soil. From the results, it was found that at some of the areas are vulnerable to high amplification of waves even for small earthquake.     

基于土层常规参数的剪切波速液化概率计算公式

分析国际上现有液化场地剪切波速473组数据进行参数特征后,以此为基础,采用分区方法,利用成熟的Logistic模型,提出了以地表峰值加速度、剪切波速、地下水位、可液化层埋深等4个参数表达的土体液化概率计算公式和不同概率下液化临界值计算公式,研究了不同概率水平下公式的适用性,并与现有主要方法进行比较。研究表明:地震动强度为液化判别首要影响参数,液化层与非液化层剪切波速区分度不显著,采用以往一个公式构造液化判别公式的方式难以要达到基本要求;现有Andrus公式和石兆吉公式会将很多明显为非液化的场地误判为液化场地,违背了现有认识,达到了不可接受的程度,需要改进。文中公式取50%概率时液化点和非液化点回判成功率符合对等原则,不同烈度下成功率均在70%左右;总体看,公式表现良好,可为中国工程建设提供一个合理、可操作性强的剪切波速液化概率判别方法。     

剪切波速测试技术及场地土液化势判别

文章简要地介绍了剪切波测试技术的基本原理、野外测试方法及其在工程中的主要用途.结合工程实例,对于在资料处理中碰到的场地液化势判别的问题,采用石兆吉判别式,丁伯阳判别式,谢生荪判别式及标准贯入试验法等目前运用较多的多种液化判别方法进行对比分析,最后得出在本次工程中石兆吉判别式结果最切合本次工程,其结果予以采用,并且就液化判别问题提出了一些建议.     

Soil liquefaction evaluation using shear wave velocity

A reasonably good relationship between shear wave velocity (SWV) and standard penetration resistance (SPT) of granular soils in agreement with previous studies was obtained from field tests. A similar correlation between SWV and cone penetration resistance of granular soils was also obtained. Using Seed's Standard Penetration Test (SPT)-based soil liquefaction charts, new charts of soil liquefaction evaluation based on SWV data were developed for various magnitude earthquakes.     

Essential Findings in Pressuremeter Theories

The pressuremeter, used for in situ soil testing, has undergone significant development both in its technical applications and in the interpretation methods employed for a range of parameters. Several methods have been developed to evaluate the undrained strength of a soil using a pressuremeter. Test results based on these methods show distinctive discrepancies. Different methods for evaluating the limit pressure are also presented. The values of these limit pressure evaluations vary based on the evaluation method used. In any given test, the limit pressure results also affect the values deduced for undrained shear strength. The discrepancies in the undrained shear strength values exceeded 80 % for the same test when evaluations were made with different interpretation methods. Because of the large discrepancies in the results of the undrained shear strength when using different analysis methods, the Gibson and Anderson method is recommended as being most reliable in deducing undrained shear strength values from pressuremeter tests, particularly for use in the design of foundations.     

饱和砂土液化研究现状及展望

通过多年的研究,人们对饱和砂土液化有了很深的认识。在Seed简化法,剪切波速法和标准贯入试验等判别的方法的研究方面也取得了很多的成果。本文主要介绍了我国广泛应用的标准贯入试验的方法,以及应用数值方法如何更好的判断场地的抗液化性。提出应用室内的微型贯入试验来判断饱和砂土液化的展望。     

Seismic piezocone interpretation for shear wave velocity (<Emphasis Type="Italic">V</Emphasis><Subscript>S</Subscript>) determination in the Persian Gulf

Shear wave velocity is one of the important factors representing the dynamic characteristics of soil layers. Hence, many researchers have focused their studies on determining shear wave velocity by direct field measurements or expressions developed by other soil parameters. The shear module and damping ratio of the soil layers also play a similar role in the majority of dynamic soil response analyses. Nevertheless, since they have to be measured in the laboratory by resonant column or cyclic triaxial tests on undisturbed samples, the possibility of preparing such samples and the reliability of the obtained results are of great concerns. In the present study, great effort has been made to determine the above dynamic factors by means of field data obtained from a versatile instrument, namely the seismic piezocone (SPCT_U), and to derive expressions correlating them with some parameters obtainable by much simpler instruments. The reliability of laboratory measurements on undisturbed samples is also evaluated. The seismic piezocone test apparatus has been employed to evaluate the soil properties at 1-m depth intervals by means of measuring tip resistance, sleeve resistance, pore pressure and shear wave velocity. The shear module and the damping ratio are calculated using field data. Meanwhile, in order to assess the laboratory measurements of these parameters, some resonant column tests and cyclic triaxial tests on undisturbed samples of the same soil layers have been carried out. In order to compare the field results of shear modulus and damping ratios with those obtained from laboratory tests, the influences of the soil nature and sample disturbance on the conventional laboratory methods are evaluated and discussed. The shear wave velocity is correlated to overburden pressure and the corrected tip resistance for two groups of fine soils, namely silty clays and carbonate clayey silts, which mainly cover the areas under study in this project, are located in southern parts of Iran near the Persian Gulf. According to the results of the present study, there are narrow limits of shear modulus regarding soils for which the laboratory tests and the field measurements yield approximately the same shear modulus. This limit of shear modulus is about 30–50(MPa) for clay deposits and 70–100 (MPa) for sandy deposits. Also the shear wave velocity can be calculated by a simple expression from total overburden pressure and the tip resistance of simple cone penetration test results conventionally available in many soil explorations prior to engineering practices. However, if the pore pressure inside the saturated soil deposits can be measured by a piezocone apparatus, the shear wave velocity may be calculated using another suggested equation in terms of effective overburden pressure in the present study. Regarding the shear module and the damping ratio, due to the disturbances of the stiff deposits in the sampling process and great deviations of laboratory results from field results, the laboratory measurements of these parameters out of the above limits are not recommended.     

Assessment and Prediction of Liquefaction Potential Using Different Artificial Neural Network Models: A Case Study

Soil liquefaction as a transformation of granular material from solid to liquid state is a type of ground failure commonly associated with moderate to large earthquakes and refers to the loss of strength in saturated, cohesionless soils due to the build-up of pore water pressures and reduction of the effective stress during dynamic loading. In this paper, assessment and prediction of liquefaction potential of soils subjected to earthquake using two different artificial neural network models based on mechanical and geotechnical related parameters (model A) and earthquake related parameters (model B) have been proposed. In model A the depth, unit weight, SPT-N value, shear wave velocity, soil type and fine contents and in model B the depth, stress reduction factor, cyclic stress ratio, cyclic resistance ratio, pore pressure, total and effective vertical stress were considered as network inputs. Among the numerous tested models, the 6-4-4-2-1 structure correspond to model A and 7-5-4-6-1 for model B due to minimum network root mean square errors were selected as optimized network architecture models in this study. The performance of the network models were controlled approved and evaluated using several statistical criteria, regression analysis as well as detailed comparison with known accepted procedures. The results represented that the model A satisfied almost all the employed criteria and showed better performance than model B. The sensitivity analysis in this study showed that depth, shear wave velocity and SPT-N value for model A and cyclic resistance ratio, cyclic stress ratio and effective vertical stress for model B are the three most effective parameters on liquefaction potential analysis. Moreover, the calculated absolute error for model A represented better performance than model B. The reasonable agreement of network output in comparison with the results from previously accepted methods indicate satisfactory network performance for prediction of liquefaction potential analysis.     

Geotechnical reconnaissance and liquefaction analyses of a liquefaction site with silty fine sand in Southern Taiwan

Geotechnical reconnaissance of a recurrent liquefaction site at a Quaternary alluvial deposit in southern Taiwan was conducted to establish a comprehensive case history for liquefaction on silty fine sand with high fines content. The liquefaction occurred at a silty fine sand layer with D₅₀ = 0.09 mm and fines content greater than 35% and was triggered by a M_w = 6.4 earthquake on March 4, 2010, which induced maximum horizontal acceleration up to 0.189 g at the site. In situ subsurface characterizations, including standard penetration test, cone penetration test, and shear wave velocity measurement, were performed as well as cyclic simple shear tests on undisturbed specimens retrieved by a modified hydraulic piston sampler. Comparisons of cyclic resistance ratios (CRRs) indicate that CPT sounding with standard penetration rate could overestimate the resistance ratio and drainage conditions during penetration should be considered for high fines content soil in the liquefaction analysis. Additionally, variations of CRRs from different in situ tests indicate that correlations among in situ tests and CRR could be soil specific and precautions should be taken when using these curves on silty fine sands.     

东帝汶帝力市珊瑚砂地基的工程性质

珊瑚砂属珊瑚礁碎屑土,是一种特殊的地质体,具有典型的疏松多孔、硬度低、易碎的特点,由于珊瑚礁仅分布在热带海域,往往位于远离大陆的礁岛,当前对珊瑚礁岩土的勘察研究较少,相关规范也尚未涉及。以实际工程为对象,对东帝汶某珊瑚砂场地的工程性质进行了一些探讨,从标准贯人试验和钻孔剪切波速试验等原位试验结果进行分析,借鉴了目前石英砂工程性质的评价方法作为对珊瑚砂工程性质判断的参考,对珊瑚砂的强度特性和地震液化特性进行了讨论。相对石英砂的一般性质而言,珊瑚砂的标贯击数较低而相应的剪切波速相对较大,珊瑚砂在地震作用下液化的可能性较大。     

常德-张家界高速公路某大桥桥基砂土液化评价

结合常德张家界高速公路某大桥桥基工程,在DSD160型电磁式振动三轴试验仪上,通过往返加荷三轴试验,对饱和砂土进行了液化试验研究,探讨了基于动三轴液化试验结果判断饱和砂土液化的方法。并尝试了这种室内研究反应分析的液化可能性估计方法与地震剪应力时程相结合的综合判断方法。在该高速公路大桥桥基的饱和砂土液化评价中,采用这种综合判断方法,对大桥桥基砂土液化进行了判断。在判断场地是否液化后,对其液化危害程度进行了等级划分,给出了该工程场地在未来遭受到不同超越概率下的地震作用时发生液化的危害程度,得到了一些有工程实用意义的结果。     

波速扁铲侧胀试验（SDMT）在液化判别中的应用

波速扁铲侧胀仪（SDMT）是由标准的扁铲侧胀仪（DMT）和测量剪切波速砜的地震测试模块组成。综合描述了SDMT试验方法,对SDMT和钻孔波速试验测出的剪切波速砜比较,以及SDMT的液化判别初步分析。SDMT在南京的测试应用证明了SDMT的可靠性。     

Seismic liquefaction potential assessed by fuzzy comprehensive evaluation method

Liquefaction of loose, saturated granular soils during earthquakes poses a major hazard in many regions of the world. The determination of liquefaction potential of soils induced by earthquake is a major concern and an essential criterion in the design process of the civil engineering structures. A large number of factors that affect the occurrence of liquefaction during earthquake exist a form of uncertainty of non-statistical nature. Fuzzy systems are used to handle uncertainty from the data that cannot be handled by classical methods. It uses the fuzzy set to represent a suitable mathematical tool for modeling of imprecision and vagueness. The pattern classification of fuzzy classifiers provides a means to extract fuzzy rules for information mining that leads to comprehensible method for knowledge extraction from various information sources. Therefore, it is necessary to handle the soil liquefaction problem in a rational framework of fuzzy set theory. This study investigates the feasibility of using fuzzy comprehensive evaluation model for predicting soil liquefaction during earthquake. In the fuzzy comprehensive evaluation model of soil liquefaction, the following factors, such as earthquake intensity, standard penetration number, mean diameter and groundwater table, are selected as the evaluating indices. The results show that the method is a useful tool to assess the potential of soil liquefaction.     

震动液化间接测试技术在吉林西部砂土地层中的应用

鉴于目前常用的剪切波速测试法、液性指数法和原位测试法等进行砂土震动液化的复判方法存在弊端,本文提出标准贯入击数--锥尖阻力复判法( qc--N 复判法) 及瑞利波法等间接测试击数的方法进行砂土震动液化判别。通过理论计算及实例验证表明,判别结果与相对密度法测得结果一致,同时具有工作效率高、生产成本低的优点,有较高的实际应用价值。     

A performance-based framework for assessing liquefaction potential based on CPT data

This article describes a new performance-based approach for evaluating the return period of seismic soil liquefaction based on standard penetration test (SPT) and cone penetration test (CPT) data. The conventional liquefaction evaluation methods consider a single acceleration level and magnitude and these approaches fail to take into account the uncertainty in earthquake loading. The seismic hazard analysis based on the probabilistic method clearly shows that a particular acceleration value is being contributed by different magnitudes with varying probability. In the new method presented in this article, the entire range of ground shaking and the entire range of earthquake magnitude are considered and the liquefaction return period is evaluated based on the SPT and CPT data. This article explains the performance-based methodology for the liquefaction analysis – starting from probabilistic seismic hazard analysis (PSHA) for the evaluation of seismic hazard and the performance-based method to evaluate the liquefaction return period. A case study has been done for Bangalore, India, based on SPT data and converted CPT values. The comparison of results obtained from both the methods have been presented. In an area of 220 km² in Bangalore city, the site class was assessed based on large number of borehole data and 58 Multi-channel analysis of surface wave survey. Using the site class and peak acceleration at rock depth from PSHA, the peak ground acceleration at the ground surface was estimated using probabilistic approach. The liquefaction analysis was done based on 450 borehole data obtained in the study area. The results of CPT match well with the results obtained from similar analysis with SPT data.     

Liquefaction Hazard Assessment of Earth Quake Prone Area: a Study Based on Shear Wave Velocity by Multichannel Analysis of Surface Waves (MASW)

The shear wave velocity (V_S) profile based on the dispersive characteristics of fundamental mode of Rayleigh type surface waves indicate underground stiffness change with depth as well as near surface stiffness. The most important utility of shear wave velocity (V_S) is to estimate the liquefaction hazard potential of an area particularly in seismically active region. Rayleigh type surface waves were utilized to estimate the velocity (V_S) of shallow subsurface covering a depth range of 30–50 m employing multichannel analysis of surface waves. The liquefaction hazard map predicts an approximate percentage of an area that will have surface manifestation of liquefaction during an earth quake. The surface wave data acquired in an earth quake prone region of Jabalpur (Seismic zone III), India, yields a velocity (V_S) range of 200–750 m/s corresponding to the subsurface depth of 30–35 m. The results were analyzed for possible liquefaction hazard in the study area and presented here besides the N values.     

用剪切波速判别砂土液化的新方法

本文目的是建立剪切波速评价场地砂土液化的定量方法,以西特简化法的思路为基础,提出了用剪切波速估算地震应力和抗液化应力的计算公式,并编制了相应的程序,计算了液化与非液化实例,计算结果与实际情况颇为一致。     

饱和砂土的剪切波速与其抗液化强度关系研究

根据饱和砂土剪切波速与其抗液化强度的相关性原理,利用剪切波速与振动三轴联合实验装置,进行了控制饱和砂土初始剪切波速的振动液化实验,依据实验结果建立了剪切波速与抗液化强度的定量关系。最后用现场勘查数据对此定量关系进行验证,结果表明：该关系式对实际 66 个未液化地点的判别准确率达到 81.2 %;对 108 个实际液化地点的判别准确率达到 62.8 %;平均判别准确率达到 69.5 %。     

基于静力触探试验的液化判别新方法

近来地震液化灾害频发,再次成为研究重点,发展具有良好应用前景的基于静力触探试验（CPT）的液化判别方法对预防液化灾害具有重要意义。以Boulanger数据库171组数据为回归样本,分析既有方法存在的问题,提出了基于CPT液化判别的双曲线模型和计算公式,并通过提取2011年新西兰地震147组液化新数据,对该方法进行对比检验。研究表明,我国岩土工程勘察规范的CPT液化判别方法对浅埋砂层偏于保守,对深层土又明显偏于危险,而国际上具有代表性的Robertson方法,其液化临界线存在低烈度区不合理回弯、高烈度区又偏于保守的问题。提出的新公式在不同地震动强度和砂层埋深下均可给出合理判别结果,克服了国内外既有方法的缺点,并纳入到具有样板规范性质的《建筑工程抗震性态设计通则》修订稿中,可为我国相关规范修订和工程应用提供支持。