Use of Surface Waves in Statistical Correlations of Shear Wave Velocity and Penetration Resistance of Chennai Soils

Shear wave velocity (V _s) is one of the most important input parameter to represent the stiffness of the soil layers. It is preferable to measure V _s by in situ wave propagation tests, however it is often not economically feasible to perform the tests at all locations. Hence, a reliable correlation between V _s and standard penetration test blow counts (SPT-N) would be a considerable advantage. This paper presents the development of empirical correlations between V _s and SPT-N value for different categories of soil in Chennai city characterized by complex variation of soil conditions. The extensive shear wave velocity measurement was carried out using Multichannel Analysis of Surface Waves (MASW) technique at the sites where the SPT-N values are available. The bender element test is performed to compare the field MASW test results for clayey soils. The correlations between shear wave velocity and SPT-N with and without energy corrections were developed for three categories of soil: all soils, sand and clay. The proposed correlations between uncorrected and energy corrected SPT-N were compared with regression equations proposed by various other investigators and found that the developed correlations exhibit good prediction performance. The proposed uncorrected and energy corrected SPT-N relationships show a slight variation in the statistical analysis indicating that both the uncorrected and energy corrected correlations can predict shear wave velocity with equal accuracy. It is also found that the soil type has a little effect on these correlations below SPT-N value of about 10.     

Spatial Distribution of Shear Wave Velocity for Late Quaternary Alluvial Soil of Kanpur City,Northern India

Empirical correlation between standard penetration resistance (SPT-N) and shear wave velocity measured by seismic downhole techniques are prepared of the alluvial soil of quaternary age for the Kanpur city. The Kanpur city is having seismic threat from Himalaya and it falls in seismic zone III according to seismic zones of India. Standard penetration test as well seismic downhole test has been carried out up to 30 m at twelve different locations of Kanpur city. The measured SPT-N values and shear wave velocity values are used to develop empirical correlation between SPT-N and shear wave velocity. The proposed correlations have been compared with the existing regression equations by various other investigators. It is found that the proposed correlation exhibit good performance (10 % error bar). Also the measured shear wave velocity has been used to prepare spatially distributed contour map of 50, 75 and 100 m/s using ArcGIS-9 software. It is observed that the shear wave velocity values for the northern part of Kanpur city vary from 125 to 825 m/s. In southern part, it is varying from 125 to 500 m/s where as in the central part of the city the shear wave velocity varies from 125 to 375 m/s. The eastern part of the city also shows some variation in shear wave velocity which ranges from 250 to 625 m/s. The western part of the city shows the variation of shear wave velocity from ≤125 to 500 m/s. The soil type of the study area are classified as per NEHRP and new Italian O.P.M.C classification system as B, C and D type soil with having site period of 0.1–0.9 s and Poisson’s ratio varying from 0.1 to 0.4.     

Influence of magnetic fabric anisotropy on seismic wave velocity in paramagnetic granites from NW Himalaya: Results from preliminary investigations

Anisotropy of Magnetic Susceptibility (AMS) and seismic wave velocity studies of some paramagnetic Himalayan granitoids show good correlation between magnetic fabric anisotropy and P wave velocity (Vp). Vp shows strong positive correlation with magnetic lineation (L) and degree of magnetic anisotropy (P′) having correlation coefficient (r) values of 0.93 and 0.89 respectively. Both Vp and Vs show positive correlation with the SiO₂ content of Proterozoic and Paleozoic granitoids. Velocity of S wave (Vs) shows negative correlation with mean magnetic susceptibility (K_m) having ‘r’ value of 0.86. The correlation between Vs-K_m, V_p-P′, V_p-L also shows >95% probability in Spearman’s rank correlation. Based on the results from the present sample size it is suggested that, in paramagnetic granites, V_p is proportional to intensity of deformation and preferred orientation of minerals as well as the mineralogy. On the other hand, Vs is more dependent on the mineralogy alone.     

Influence of magnetic fabric anisotropy on seismic wave velocity in paramagnetic granites from NW Himalaya: Results from preliminary investigations

Anisotropy of Magnetic Susceptibility (AMS) and seismic wave velocity studies of some paramagnetic Himalayan granitoids show good correlation between magnetic fabric anisotropy and P wave velocity (Vp). Vp shows strong positive correlation with magnetic lineation (L) and degree of magnetic anisotropy (P′) having correlation coefficient (r) values of 0.93 and 0.89 respectively. Both Vp and Vs show positive correlation with the SiO₂ content of Proterozoic and Paleozoic granitoids. Velocity of S wave (Vs) shows negative correlation with mean magnetic susceptibility (K_m) having ‘r’ value of 0.86. The correlation between Vs-K_m, V_p-P′, V_p-L also shows >95% probability in Spearman’s rank correlation. Based on the results from the present sample size it is suggested that, in paramagnetic granites, V_p is proportional to intensity of deformation and preferred orientation of minerals as well as the mineralogy. On the other hand, Vs is more dependent on the mineralogy alone.     

Variations in shear wave velocity and soil site class in Kolkata city using regression and sensitivity analysis

The detrimental effects of an earthquake are strongly influenced by the response of soils subjected to dynamic loading. The behavior of soils under dynamic loading is governed by the dynamic soil properties such as shear wave velocity, damping characteristics and shear modulus. Worldwide, it is a common practice to obtain shear wave velocity (V _s in m/s) using the correlation with field standard penetration test (SPT) N values in the absence of sophisticated dynamic field test data. In this paper, a similar but modified advanced approach has been proposed for a major metro city of eastern India, i.e., Kolkata city (latitudes 22°20′N–23°00′N and longitudes 88°04′E–88°33′E), to obtain shear wave velocity profile and soil site classification using regression and sensitivity analyses. Extensive geotechnical borehole data from 434 boreholes located across 75 sites in the city area of 185 km² and laboratory test data providing information on the thickness of subsoil strata, SPT N values, consistency indices and percentage of fines are collected and analyzed thoroughly. A correlation between shear wave velocity (V _s) and SPT N value for various soil profiles of Kolkata city has been established by using power model of nonlinear regression analysis and compared with existing correlations for other Indian cities. The present correlations, having regression coefficients (R ²) in excess of 0.96, indicated good prediction capability. Sensitivity analysis predicts that significant influence of soil type exists in determining V _s values, for example, typical silty sand shows 30.4 % increase in magnitude of V _s as compared to silt of Kolkata city. Moreover, the soil site classification shows Class D and Class E category of soil that exists typically in Kolkata city as per NEHRP (Recommended provisions for seismic regulations for new buildings and other structures—Part 1: Provisions. Prepared by the Building Seismic Safety Council for the Federal Emergency Management Agency (Report FEMA 450), Washington, DC, 2003) guidelines and thereby highlighting the seismic vulnerability of the city. The results presented in this study can be utilized for seismic microzonation, ground response analysis and hazard assessment for Kolkata city.

     

土层剪切波速不确定性对场地刚性判断的影响

岩土工程中的不确定性是工程风险的重要来源。在我国7个主要地区的20个工程场地上开展了国内外首次大范围现场剪切波速不确定性专项试验,共由47家单位用11种工程常用仪器采用单孔法完成,获取了600组土层剪切波速Vs实测数据。依据实测结果拟合了场地时间平均剪切波速Vs, z的变异系数COV与计算深度Z的对应公式,揭示了土层剪切波速不确定性对场地刚性判断的影响,进而分析了我国场地分类的可能潜在误判区域。结论如下：在目前我国现场剪切波速测试水平下,Vs, z的变异系数与深度负相关——在近地表处达到极大值15%,并随着深度增加明显减小;地表至10 m深度区间内,Vs, z的变异系数迅速减小;10～20 m深度区间内,Vs, z的变异系数减小趋势变缓;超过20 m深度后,Vs, z的变异系数小于5%且基本不变;我国III、IV类场地分类采用的等效剪切波速Vse和欧美场地分类指标Vs, 30的变异系数基本相等;依据我国建筑抗震设计规范GB50011－2010,对I类场地以及覆盖层厚度小于5 m或等效剪切波速接近500 m/s的II类场地分类时需考虑剪切波速不确定性的潜在影响,其他类型的II类场地、III类和IV类场地在分类时基本可忽略其影响。     

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.     

Shear Wave Velocities in the Estimation of Earthquake Hazard Over Alluvium in Seismically Active Region

It is well known that the potential hazard during an earthquake is mainly in alluvium or alluvium filled basins; shear wave velocity plays a significant role in estimating the possible hazard during an earth quake in such an area. This paper presents shear wave velocity profile from Jabalpur, Central India mainly dominated by alluvial soil that was moderately affected by an earthquake of magnitude 6.5 in May, 1997. The acquired shear wave velocity by Multichannel Analysis of Surface Wave (MASW) in as many as 36 sites over alluvial soil ranges from 200 m/sec to 400 m/sec and in a few sites marginally less than 200 m/sec corresponding to a sub-surface depth of 30–35 m. Further, the computed N values vary as low as near zero to less than 25. The study is substantiated by the estimation of P-wave velocity by refraction seismic method at the same locations of MASW which ranges from 350 m/sec to 2200 m/sec. The results suggest that the damage during an earth quake appears to be highly unlikely in view of the marginally high Vs up to depth of 30 m. This study on seismic hazard is substantiated by the estimation of frequency of the ground as well as amplification which is found to be a maximum of about 2.5 in the frequency band of 2–6 Hz in west and north western portion of the study area.     

表面波法确定卵石土地基承载力模型研究

利用统计学的原理,对卵石土地基动力触探击数和剪切波速的关系进行了研究,推导了它们之间的二次多项式、幂函数和指数函数回归方程。通过对比研究发现,二者之间具有良好的指数函数相关关系。为了验证该指数函数回归模型的可行性,选择了相似场地进行面波检测试验,试验结果与勘探结果完全吻合。研究结果表明,应用表面波法不但可以进行卵石土地基分层,而且还可以定量地评价其地基承载力。     

Dynamic soil properties for microzonation of Delhi,India

Delhi, the capital of India, has experienced mild seismic shaking during several earthquakes in the past. The large variations of depth to bedrock and ground water table coupled with different soil types at different locations of Delhi necessitate a seismic microzonation study. Dynamic soil properties such as shear wave velocity, modulus reduction and damping characteristics of local soils are the basic and essential input parameters for conducting even a preliminary ground response analysis which is an essential input in microzonation studies. Shear wave velocity is not measured routinely due to its high cost and lack of the required expertise. Several researchers in the past developed correlations between shear wave velocity (V _s ) and routinely measured N values. In the present study, shear wave velocity profiles measured in the field at more than 80 borehole locations to a depth of about 20 to 32m using Spectral Analysis of Surface Waves (SASW) are presented and correlations between shear wave velocity and N values are also presented for use by engineers and designers. Results of strain and stress controlled cyclic triaxial tests on remoulded samples of sand-silt mixtures in the high strain range are used for generating the modulus reduction and damping curves and are compared with the well-known curves in the literature. The results presented in this article can be used for microzonation studies as well as site specific ground response analyses at Delhi.     

Geospatial contour mapping of shear wave velocity for Mumbai city

Shear wave velocity is one of the most important input parameter in the analysis of geotechnical earthquake engineering problems, particularly to estimate site-specific amplification factor and ground response study. Dynamic in situ tests such as spectral analysis of surface waves (SASW) or multichannel analysis of surface waves (MASW) are very expensive. Also due to lack of specialized personnel, these tests are generally avoided in many soil investigation programs. Worldwide, several researchers have developed correlations between the SPT ‘N’ value and shear wave velocity ‘V _s’, which are useful for determining the dynamic soil properties. In the present study, more than 400 numbers of soil borehole data were collected from various geotechnical investigation agencies, government engineering institutes and geotechnical laboratories from different parts of Mumbai city, which is financial capital of India with highest population density. In this paper, an attempt has been made to develop the correlation between the SPT ‘N’ value and shear wave velocity ‘V _s’ for various soil profile of Mumbai city and compared with other existing correlations for different cities in India. Using Geographical Information System (GIS), a geospatial contour map of shear wave velocity profile for Mumbai city is prepared with contour intervals of 25 and 50 m/s. The scarcity of database or maps of shear wave velocity profile for Mumbai city will make the present geospatial contour maps extremely useful and beneficial to the designer, practitioners for seismic hazard study involved in geotechnical earthquake engineering.     

强夯处理碎石回填土地基相关性试验研究

在高填方地基强夯处理过程中检测与评价强夯质量是整个工程中非常重要的一部分。对某1 000 kV特高压变电站工程高填方碎石土回填强夯地基,从理论和实践的角度出发,研究瑞利波（RWT）、动力触探（DPT）和静载荷（PLT）各试验结果的相关性,表明瑞利波和动力触探试验结果可以验证静载荷试验结果。前两者可作为强夯地基检测的间接手段,适当减少费用昂贵、历时较长的静载荷试验,节省工程造价和加快工程进度。由试验结果拟合出各试验结果之间的数学表达式表明,剪切波速和地基承载力特征值近似服从幂函数相关,与变形模量和超重型动力触探击数近似服从指数函数相关,可推测出强夯地基有效加固深度和其他地基土力学参数。根据强夯有效加固深度实测结果,提出基于梅拉公式计算结果的修正系数在0.24~0.27之间,其结果可供类似工程的设计及施工参考。     

3种特殊土物理力学性质指标统计分析

常规物理力学指标可以良好反映土的工程性质。收集全国范围内软土、黄土和红土的相关专著、科技论文和地震安全性评价报告,统计得出3种特殊土各项物理力学指标的范围、平均值和变异系数,通过对各项物理力学指标间的相关性分析,对3种特殊土的工程特性进行了研究。对比结果发现：3种特殊土物理性质的变异系数总体较小、较为稳定,而力学性质的变异系数变化较大、离散程度较高;3种特殊土各项物理力学性质指标间存在相关性,或呈线性关系,或呈带状变化,同类指标软土和红土的相关系数高于黄土。通过回归拟合方法给出了|r|∈[0.5,1.0]的拟合公式,利用线性关系检验方法对公式的精度和准确性进行检验,结果表明：本文给出的拟合公式F>F_0.05,回归效果较为显著,便于工程应用。     

Natural background and pollution levels of some heavy metals in soils from the area of Dayton,Ohio

In a reconnaissance study, trace amounts of Cd, Cu, Pb, and Zn were determined in “A-zone” soil from 22 locations in the Dayton, Ohio, area. Soil samples were collected at high-volume air monitoring sites in urban, suburban, and rural areas. Measurable amounts of the elements were found in all of the samples. Positive correlations occur between each metal and particulate matter, with correlation coefficients of aboutr=0.70, at the 99% confidence level. Natural background values for the elements were measured in soil from rural areas. Theoretical background values, which are very close to those measured, were calculated from the individual regression equations. Natural background levels do not exceed 1.00 ppm Cd, 15 ppm Cu, 25 ppm Pb, and 55 ppm Zn. The heavy metal contents of most soils in the area exceed background by factors of up to 3.0 for Cd, up to 4.5 for Cu, up to 11 for Pb, and up to 4.5 for Zn. Significant positive correlations among the metals suggest a common source (or sources) for at least some, if not most, of the heavy metals. For the most part, the highest metal values are found in soils near coal-burning plants. Fly ash from a local plant contains substantial amounts of the elements. The high lead values are largely due to vehicular exhaust. However, there is evidence that the metals can also come from the normal deterioration of vehicles. It appears that airborne pollution is an important source of heavy metals in Dayton area soils.     

Indirect estimation of the swelling percent and a new classification of soils depending on liquid limit and cation exchange capacity

This paper describes the dependence of the swell percent (%S) on the soil properties, namely, liquid limit (LL) and cation exchange capacity (CEC). This study provides the statistical model that can be used to obtain an indirect estimation of %S due to CEC and LL. According to the coefficient of correlation (R² = 0.91), VAF (91.5%) and RMSE (0.727) indices, multiple regression model has a high prediction performance. Although CEC values play an important role in the swelling behaviour of clayey soils, there is no universally accepted simple quantitative swelling potential classification at present. In this paper, a new swelling potential classification and graph, having four respective zones indicating the low, moderate, high, very high swelling potential, was also developed and proposed. This classification will serve to the engineers in order to evaluate the expansivity of the soils, in practice.     

基于可见—近红外反射光谱的典型农田重金属污染风险分类研究

对于人为因素或自然因素造成的农田土壤重金属元素污染,需要进行大面积的土壤环境质量调查和分类管控,然而传统的采样测试方法存在工作量大、代价高等问题。可见—近红外（Vis-NIR）反射光谱是一种快速低成本获取土壤理化信息的手段。为研究Vis-NIR反射光谱预测模型划分土壤重金属污染风险类别的能力,文章以典型人为污染地区（浙江温岭）和典型地质高背景地区（广西横县）的390份农田土壤为样本,测定8种重金属元素（As、Cd、Cr、Cu、Hg、Ni、Pb和Zn）的含量和pH值,并测定土壤Vis-NIR光谱。使用偏最小二乘（PLS）和支持向量机（SVM）算法建立回归模型,对土壤重金属含量和pH值进行预测,并基于预测值进行土壤重金属污染风险分类。结果显示,温岭土壤主要污染元素Cd和Cu的光谱模型回归预测偏差（RPD）分别为1.23和1.19,预测机制与有机质有关。横县土壤主要污染元素As和Cd的RPD分别为1.98和1.93,预测机制与铁氧化物和粘土矿物有关。地质高背景土壤重金属与铁氧化物的正相关性普遍较强,使得光谱模型对重金属含量预测准确度较高。温岭和横县土壤pH值的光谱模型RPD分别为1.76和1.68。土壤重金属污染风险光谱分类的总体 准确度分别为75.0%~100%（温岭）和80.0%~100％（横县）。将Vis-NIR光谱与遥感技术相结合,对农田土壤重金属污染风险进行快速分类总体是可行的。     

Determination of undrained strength of fine-grained soils by means of SPT and its application in Turkey

The Standard Penetration Test (SPT) is one of the oldest and the most common in situ test used in soil explorations. In the recent years with the advent of new technology and techniques in determining the drawbacks in SPT, several researchers have attempted to correlate corrected field measured values with several soil properties. In this context, corrections applied to field values have become critical. In this study a questionnaire including the performance of the standard penetration test and equipment used in practice in Turkey is circulated in order to determine the relevant correction factors. Thus the appropriate corrections are used in acquiring corrected SPT-N values. The relationships between SPT-N and the undrained shear strength (S_u) are examined from the statistical point of view by taking the test types and SPT corrections into consideration, and comparison is made with previous studies. It is observed that SPT corrections play an important role on the obtained correlation equations. In addition, the importance of the effects of test types on the correlations is also emphasized. The Standard Penetration Test is found to be sufficient for reliable assessment of S_u.     

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.     

Improving the performance of precipitation outputs from Global Climate Models to predict monthly and seasonal rainfall over the Indian subcontinent

Skilful prediction of the monthly and seasonal summer monsoon rainfall over India at a smaller spatial scale is a major challenge for the scientific community. The present study is aimed at achieving this objective by hybridising two mathematical techniques, namely synthetic superensemble (SSE) and supervised principal component regression (SPCR) on six state-of-the art Global Climate Models (GCMs). The performance of the mathematical model is evaluated using correlation analysis, the root mean square error, and the Nash–Sutcliffe efficiency index. Results feature reasonable improvement over central India, which is a zone of maximum rainfall activity in the summer monsoon season. The study also highlights improvement in the monthly prediction of rainfall over raw GCMs (15–20% improvement) with exceptional improvement in July. The developed model is also examined for anomalous years of monsoon and it is found that the model is able to capture the signs of anomalies over different gridpoints of the Indian domain.     

Spatial distribution and geochemical baselines of major/trace elements in soils of Medak district,Andhra Pradesh,India

Regional-scale variations in soil geochemistry were investigated with special reference to differences among soil groups and lithology in an area of 9,699 km² in Medak district, Andhra Pradesh, India. The concentrations of 29 elements (major: Si, Al, Fe, Mn, Mg, Ca, Na, K, Ti, P and trace: As, Ba, Cd, Co, Cr, Cu, F, Mo, Ni, Pb, Rb, Se, Sr, Th, U, V, Y, Zn, Zr) in 878 soil samples collected (557-topsoil, 321-subsoil) at a sampling density of 1 site/17 km² from 557 sites representative of all the soil types present in studied area were determined, and their elemental composition are discussed. The baseline levels of these elements in soils are determined over different lithological units for the identification of anomalous values relative to these. For the first time, geochemical maps for Medak district are prepared on 1:50,000 scale and the lithogeochemical database generated provides information on the lateral and vertical distribution of elements in soil. The spatial variations in the distribution of elements reflect underlying geologic characteristics. Box-plots reveal that the concentration of most of the elements in soils were not strongly dependent on the soil group but the soil-geochemistry abruptly changes with the change in the soil parent materials indicating that the distribution of elements is mostly influenced by the bedrock lithology and other natural processes acting on them. For instance, the concentrations of Co, Cu, Fe, Mn, Ti, V and Zn are high in soils developed on basaltic terrain while the soils developed on granitic and gneissic terrain exhibit high elemental concentrations of K, Pb, Rb, Si, Th and Y. Alfisols had relatively high contents of elements while entisols had lower concentrations of most of the elements. The database can be used in the chemical characterisation of different geological units as well as applications in various environmental and agricultural fields. The results indicate that regional geology is an important determinant of soil geochemical baselines for soil pollution assessment and further emphasizes the importance of determining background levels locally. The defined baselines can be used to establish background values for future soil surveys.