研究剩余电磁效应的理想参数

在频谱激电法中利用剩余电磁效应(REM)研究地下电性分布已引起人们的重视。本文基于对数值计算结果的分析指出,选择适当高频f_G,以偶极装置观测视复电阻率的相位φ_s⁰(f_G),用相应条件下均匀大地的视复电阻率相位理论值(f_G)对其作归一,所得比值参数φ_s⁰(f_G)/(f_G)是表示剩余电磁效应的理想参数。文中还结合数值计算结果和野外实测资料,分析了这一参数的异常特征和在油气探测中的应用效果。     

非水平均匀极化条件下激电中梯ηs曲线及其接头畸变的分析讨论

在实际工作中,由于盲矿体与距离有限的中梯装置两个供电电极之间相互位置的原因,往往使得地下盲矿体实际处于某种非水平均匀极化条件之下,这就使所获得的η_s曲线以及由于移动供电电极获得的η_s曲线接头发生了不同程度的畸变。本文通过模拟激电中梯通常采用的装置形式,以体极化球体为例,运用点电源场公式计算其主剖面上的中梯η_s曲线及其接头来对上述畸变进行分析和讨论。本文还提出了在处理中梯η_s观测资料时应该注意的问题以及对推广激电η_s全域测量法的认识意见。     

轴向偶极装置在局部良导体上的感应耦合模型实验

交流激发极化法的使用在不同程度上受到感应耦合的干扰,这是目前应用和发展该法的一大障碍。经过野外实践及室内实验,大家一致认为中梯装置的感应耦合使频散率是负的,P_s剖面呈现大负异常。但对于偶极装置的感应耦合P_s是正是负看法不一,同时也需了解在局部良导体上偶极装置的感应耦合规律。为此我们在大水槽中做了轴向偶极装置感应耦合方面的实验。本文是报告通过实验所得到的一点认识。     

频谱激电法在几个金属矿区的应用效果

通过野外实例说明激电谱的视时间常数(τ_s)的稀释作用小,岩矿的时间常数差异大有可能发现为激电强度参数(η_sρ_sm_s或ψ_s)所不能发现的深部矿(或矿化)体的异常.以τ_s参数为主,综合激电谱的其它参数,有可能对浅源激电异常性质进行区分.     

山区找水的“相对衰减时法”探讨

实测资料表明,二次电场衰减时与视电阻率关系点分布区的下限存在正向密切区间、反向密切区间和不密切区间,即衰减时与视电阻率关系十分密切.忽视视电阻率的变化,有可能造成激电找水效果上的失误.针对衰减时与视电阻率关系的区间特性,我们采用“相对衰减时”的概念作为激电找水的含水因素(相对衰减时S_R＝ρS/_s).采用该参数的实际意义在于反向密切区间突出了含水异常,正向密切区间消除因极距增大引起的非水异常.因此,相对衰减时在研究山区地下水的富集情况时灵敏度较高.应用相对衰减时法在不同水文地质条件的山区找水中,取得了较好的效果,特别是在我国著名的玫瑰泉地下水工程中,在电阻率法和常用的衰减时法解释推断有困难时,能比较准确地确定了富水区,成井后获得水量6万t/d,建成大型农业地下水源地.     

某些复杂条件下电测深资料的解释方法

本文主要论述复杂条件下垂向电测探工作中的一些问题,尤其是在“非无限水平展状均匀介质”,例如在金属矿、岩溶地区等“有限电性体”上开展垂向电测深时的一些解释方法。还介绍了一些“有限电性体”在ρ₀断面等值线图上的异常特征和野外实验。对ρ₀断面等值线图的编绘方法也进行了讨论。     

水平层上“双极-偶极”电测深装置视电阻率理论曲线的计算与特点

本文给出了水平层上径向、轴向、方位、赤道、垂直、平行双极-偶极电测深装置的ρ_1理论公式。并根据大量计算结果阐述了该装置ρ_1曲线的特点与观测信号的大小。对U.C.Das等人的某些公式与观点作了修正与补充。     

电法测定水文地质参数的尝试

1. 含水层导水系数(T)的确定在相同条件下,含水层厚度大,视横向电阻(R_t)大,颗粒粗Rt也大,公式R_t＝P₂·H₂;含水层导水系数(T)也取决于含水层厚度和结构,即T=K·h.可见T与R_t存在着正相关关系.这样求取了T-R_t相关曲线,其导水系数便可求出.解释野外所做的电测深曲线确定出R_t;利用7个已知抽水孔的资料确定含水层导水系数;将计算出的T值与R_t值对比,分别建立Q₃砂卵石层和Q₂泥质卵石层中T-R_t相关曲线(直线).经计算,Q₃层中T－Rt相关系数γ=0.964(Q₂层略),证明相关曲线可靠.依据T=R_t相关关系绘制了“导水系数分布图”,计算出Q₃层的渗透系数(K)值80-120m/d,R_t/T值2.13-2.68,Q₂层的K值40-50m/d,R_t/T 值5-8.2.含水层有效孔隙度(ψ)的求取利用阿尔奇公式ρ=ψ^-mS^-nρ_w求取.野外采用电测深法.先求出11个已知孔含水层电阻率(ρ_s);野外采水样,室内分析,依据16℃时地层水(ρ_w)与矿化度(C)关系图确定各孔ρ_w;取m=1.5,利用上述公式求出各孔ψ值.Q₃层 值0.1769-0.3444,多数0.2-0.25.此值与室内试验得出的值0.25一致,与重力给水度经验值0.23-0.26相近.     

金属因素在激电异常评价中的应用

当激电异常较为复杂时,利用η_s(或F_s)这些激电法的基本参数难以对异常源的性质进行合理的解释.通过具体实例,说明应用激电法的二次信息--金属因素解释复杂激电异常的有效性.金属因素能将矿致异常与非矿致异常分离,对异常的定性及定量解释有很好的作用.     

用激发极化法开展大面积地下水普查的初步尝试

1981年以来,作者们用地质与物探紧密结合的激发极化井字型剖面法,先后在河南省灵宝县黄土塬区,新安县浅山丘陵区和修武县平原区等不同地貌单元、不同时代地层岩性分布区,开展了大面积(1933·8km²)的激发极化法普查地下水工做.本文概略地介绍了大面积普查的基本工作方法,用大量的实测资料勾绘ρ_s、D、 η_s、J等值图,并据此作出相应的地质推断图,其中包括灵宝县黄土塬区(灵—陕断陷盆地)深埋下更新统(Q_t)河湖相砂卵石承压含水层组、新安县浅山丘陵区中的“南岗地下水库”和修武县平原区中的沁河古河道.经打井验证,均取得了好的地质效果与经济效益,含水层吻合率在95%以上.     

Effect of Fines Type and Content of Sand on Correlation Between Shear Wave Velocity and Liquefaction Resistance

The use of shear wave velocity (V _s) measurements as an in situ test for evaluation of liquefaction potential has increased substantially due to its advantages. Relatively large numbers of studies have been performed to establish the correlation between V _s and liquefaction resistance (CRR) of clean sands. Usually, natural sands contain silt and/or clay, and previous studies have shown that both the amount of fines and their nature influence the values of CRR as well as V _s. Therefore, the CRR–V _s correlations may also be affected by fines content and type of sandy soils. However, effect of fines content and especially fines type of sandy soils on the correlation between V _s and CRR is inadequately addressed in the literature. In this study, cyclic triaxial and bender element tests were conducted on samples of sand containing various amounts of different types of fines, and the effects of fines on the values of CRR and V _s are investigated. The results show that G ₀ and CRR reduce even when small amounts of fines are added to sand. Therefore, use of plasticity index (PI) of the fines fraction is better than the PI of the overall soil when trying to assess the effects of fines. Using obtained experimental data as well as the established semiempirical CRR–V _s relationship, the CRR–V _s correlation was developed for all the tested soils, and the effect of fines type on the correlation is also examined. Based on the results obtained in this study, CRR–V _s correlation is affected by both the amount and the plasticity of the fines present in the sand, and this correlation is soil specific.     

Impact of pore water conductivity and porosity on the electrical conductivity of kaolinite

The purpose of this study is to quantify the magnitudes of surface conduction and pore water conduction from the measured electrical conductivity of kaolinite, with the ultimate goal of estimating the electrical conductivity of kaolinite with a wide range of pore water conductivities (σ _w = 0.013–3.356 S/m) and porosities (n = 0.368–1.0). Therefore, the theoretical background of the electrical conductivity in soils was reviewed, and electrical conductivity measurements on kaolinite were performed using both slurry and consolidation tests in this study. The results of this study demonstrate that the variations of measured electrical conductivity (σ _mix) with n are debatable according to the values of σ _w, because a decrease in n results in both an increase in surface conduction (K _s) and a decrease in pore water conduction (K _w); this causes the relative magnitude of K _s compared to that of K _w to vary with σ _w and n. Consequently, this study develops the relation between the porosity-normalized K _s/K _w and 1/σ _w. Additionally, the surface conductivity of the tested kaolinite is back-calculated and compared with the previous relationship between K _s and zeta potential of kaolinite. The measured and estimated σ _mix values are compared with the varying pore water conductivity and porosity values.     

Probabilistic evaluation of primary consolidation settlement of Songdo New City by using kriged estimates of geologic profiles

The uncertainty in the spatial distributions of consolidation settlement (s _c) and time (t _p) for Songdo New City is evaluated by using a probabilistic procedure. Ordinary kriging and three theoretical semivariogram models are used to estimate the spatial distributions of geo-layers which affect s _c and t _p in this study. The spatial map of mean (μ) and standard deviation (σ) for s _c and t _p are determined by using a first-order second moment method based on the evaluated statistics and probability density functions (PDFs) of soil properties. It is shown that the coefficients of variation (COVs) of the compression ratio [C _c/(1 + e ₀)] and the coefficient of consolidation (c _v) are the most influential factors on the uncertainties of s _c and t _p, respectively. The μ and σ of the s _c and t _p, as well as the probability that s _c exceeds 100 cm [P(s _c > 100 cm)] and the probability that t _p exceeds 36 months [P(t _p > 36 months)] in Sect. 1, are observed to be larger than those of other sections because the thickness of the consolidating layer in Sect. 1 is the largest in the entire study area. The area requiring additional fill after the consolidation appears to increase as the COV of C _c/(1 + e ₀) increases and as the probabilistic design criterion (α) decreases. It is also shown that the area requiring the prefabricated vertical drains installation increases as the COV of c _v increases and as the α decreases. The design procedure presented in this paper could be used in the decision making process for the design of geotechnical structures at coastal reclamation area.     

Estimation of undrained shear strength in moderately OC clays based on field vane test data

The undrained shear strength (s _u) of cohesive soils is a crucial parameter for many geotechnical engineering applications. Due to the complexities and uncertainties associated with laboratory and in situ tests, it is a challenging task to obtain the undrained shear strength in a reliable and economical manner. In this study, a probabilistic model for the s _u of moderately overconsolidated clays is developed using the Bayesian model class selection approach. The model is based on a comprehensive geotechnical database compiled for this study with field measurements of field vane strength (s _u), plastic limit (PL), natural water content (W _n), liquid limit (LL), vertical effective overburden stress (\(\sigma_{\nu }^{\prime }\)), preconsolidation pressure (\(\sigma_{\text{p}}^{\prime }\)) and overconsolidated ratio (OCR). Comparison study shows that the proposed model is superior to some well-known empirical relationships for OC clays. The proposed probabilistic model not only provides reliable and economical estimation of s _u but also facilitates reliability-based analysis and design for performance-based engineering applications.     

Shear wave velocity as function of cone penetration resistance and grain size for Holocene-age uncemented soils: a new perspective

For feasibility studies and preliminary design estimates, field measurements of shear wave velocity, V _s, may not be economically adequate and empirical correlations between V _s and more available penetration measurements such as cone penetration test, CPT, data turn out to be potentially valuable at least for initial evaluation of the small-strain stiffness of soils. These types of correlations between geophysical (Vs) and geotechnical (N-SPT, q _c-CPT) measurements are also of utmost importance where a great precision in the calculation of the deposit response is required such as in liquefaction evaluation or earthquake ground response analyses. In this study, the stress-normalized shear wave velocity V _s1 (in m/s) is defined as statistical functions of the normalized dimensionless resistance, Q _tn-CPT, and the mean effective diameter, D ₅₀ (in mm), using a data set of different uncemented soils of Holocene age accumulated at various sites in North America, Europe, and Asia. The V _s1–Q _tn data exhibit different trends with respect to grain sizes. For soils with mean grain size (D ₅₀) < 0.2 mm, the V _s1/Q _tn ^0.25 ratio undergoes a significant reduction with the increase in D ₅₀ of the soil. This trend is completely reversed with further increase in D ₅₀ (D ₅₀ > 0.2 mm). These results corroborate earlier results that stressed the use of different CPT-based correlations with different soil types, and those emphasized the need to impose particle-size limits on the validity of the majority of available correlations.     

A molecular orbital study of bond length and angle variations in framework structures

Molecular orbital calculations on a variety of silicate and aluminosilicate molecules have been used to explore the bonding forces that govern tetrahedral bond length variations, r(TO), in framework silicates and aluminosilicates. Not only do the calculations provide insight into the variety of structural types and the substitution limits of one tetrahedral atom for another, but they also provide an understanding of the interrelationships among r(TO) and linkage factors, bond strength sum, coordination number, and angles within and between tetrahedra. A study of these interrelationships for a theoretical data set shows that r(SiO) and r(AlO) are linearly correlated with (1) p _o, the bond strength sum to a bridging oxygen, (2) f _s(O), the fractional s-character of a bridging oxygen, and (3) f _s (T), the fractional s-character of the T atom. In a multiple linear regression analysis of the data, 92% of the variation of r(SiO) and 99% of the variation of r(AlO) can be explained in terms of a linear dependence on p _o, f _s (O), and f _s (T). Analogous regression analyses completed for observed r(Al, SiO) bond length data from a number of silica polymorphs and ordered aluminosilicates account for more than 75% of the bond length variation. The lower percentage of bond length variation explained is ascribed in part to the random and systematic errors in the experimental data which have a negligible effect on the theoretical data. The modeling of more than 75% of the variation of r(Al, SiO) in the framework silicates using the same model used for silicate and aluminosilicate molecules strengthens the viewpoint that the bonding forces that govern the shapes of such molecules are quite similar to the forces that govern the shapes of chemically similar groups in solids. The different regression coefficients calculated for f _s (T) indicate that SiO and AlO bond length variations in framework structures should not be treated as a single population in estimating the average Al, Si content of a tetrahedral site.     

面极化和体极化球体上复视极化率的频谱特征及其理论计算的某些结果

用面极化的等效电阻率ρ₀^*=ρ₀+(λω)/aρ₁经验公式λ(ω)=λ₀β/β+iω和组合电阻率ρ₂=ρ¹1-V/1+2V(当ρ₂→0时)公式,代入已有的基本理论公式,分别导出了有关面极化和体极化球体的η_s(ω)公式,使两者通过λ(ω)建立了基本联系。根据推出的公式进行了理论计算,获得了某些有意义的结果。     

Zum Gebirgsbau der nördlichen Appalachen

Zusammenfassung Die Appalachen, als geologische Einheit, erstrecken sich vom nördlichen Alabama bis Neufundland. Der Hauptakt des gesamten Orogens wird heute als akadisch (bretonisch) angesehen. Hier betrachtet ist vor allem der Sektor, welcher sich im Staate Vermont befindet.Das Bewegungsbild in Vermont ist aus kleintektonischen Beobachtungen entstanden. In den Green Mountains deutet schichtparallele Schieferung (s ₁), mit Fältelungsachsen im Fallen dieser Schieferung, auf Streckung. Dies läßt auf Aufwölbung als Faltungsmechanismus des Antiklinoriums schließen. Weiter westlich geht die gleiche Schieferung in Achsenflächenschieferung mit Westvergenz über.Eine spätere rotationale Schieferungsphase (s ₃) in den Green Mountains steht steil und ist Ursache einer Scherfaltung. Östlich der Green Mountains erstreckt sich eine Reihe von Gneisdomen und Wölbungen; eine umschmiegende Schieferung (s ₂) und die Vergenz der zugehörigen Kleinfaltung deuten hier auf ein relatives, passives Abgleiten des Sedimentmantels zur Zeit der Aufwölbung.Das Gesamtbild in Vermont betont daher Vertikalbewegung als Verformungsursache.

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The Appalachians, as a geological unit, extend from northern Alabama to Newfoundland. The main phase of orogeny in the whole belt, notwithstanding its name, is now understood to be Acadian (Bretonic). Only the Vermont sector of this deformed belt is considered here.The movement pattern in Vermont as revealed by minor structures is displayed to tell its own story: In the Green Mountains, bedding schistosity (s ₁) associated with down-dip minor folds indicates stretching, implying that updoming was the deforming mechanism of the anticlinorium. Farther west, the same schistosity becomes axial plane cleavage to folds which face west.A later rotational cleavage (s ₃) in the Green Mountains is steep and is associated with shear folding. Farther east a zone of gneiss domes and arches extends parallel to the Connecticut and Passumpsic rivers; enveloping cleavage (s ₂) and down-dip facing minor folds here indicate passive flowage of the sedimentary mantle away from the crest of the arch. Hence the overall tectonic pattern in Vermont seems to emphasize vertical movement as the primary cause of orogenic deformation.

     

Pressure and temperature dependence of the elastic properties of synthetic MnO

The adiabatic elastic stiffness constants of synthetic single-crystal MnO were measured in this study using pulse superposition interferometry. Data were obtained up to 1.0 GPa in pressure and over the temperature range 273 to 473 K. As a result, we were able to determine the complete set of second-order stiffness moduli (C _ij ^s ) and their pressure and temperature derivatives, as well as higher-order properties for selected modes. Relevant results for the adiabatic bulk modulus are: K ^s=155.1±0.8 GPa; (K^s/P)_T=4.70±0.13; and, (K ^s/T)_P= -0.0203±0.0009 GPa/K. Our results for the second-order moduli are generally consistent with the data from previous studies. However, relative to the estimated uncertainties, small and systematic discrepancies appear to characterize the data set. The available evidence indicates that the differences result from microstructural variations (in particular, microcracks and Mn₃O₄ inclusions) between the synthetic MnO specimens used in different investigations. The pure shear mode C ₄₄ exhibits anomalous soft-mode behavior with both temperature (the ambient derivative is positive) and pressure (the ambient derivative is negative). In both cases the C ₄₄ data trends appear to primarily reflect the influence of Mn-Mn magnetoelastic interactions associated with the onset of a paramagnetic-antiferromagnetic (PM AFM) phase transition.