风化砂岩的力学特性及本构关系研究

以不同风化程度的砂岩试件为研究对象,对其单轴、三轴力学强度进行了试验研究。结果表明,随着风化程度的增加,砂岩的力学强度逐渐降低;三轴曲线的主应力差 对砂岩强度的影响基本呈线性;不同风化程度的砂岩试件的内摩擦角随着风化程度的增加,摩擦角逐渐增大;而凝聚力则随着风化程度的增加而减小。建立了岩石三轴受力的抛物曲线-线弹性-Duncan双曲线-塑性软化-残余理想塑性5段式模型,模型能够正确反映砂岩三轴受力变形特点。     

A geochemical aid to igneous rock type identification in deeply weathered terrain

A technique employing Ti, Zr and Cr to aid in the identification of primary igneous rock type in deeply weathered situations is described. The method is based on Ti/Zr ratio which is little affected either by primary alteration or weathering and adequately defines compositional fields for major igneous rock types. For volcanic rocks Ti/Zr ratios are rhyolite <4< dacite <12< andesite <60< basalt. Ultramafic rocks cannot be discriminated from mafic rocks by Ti/Zr ratio but are generally distinguished by high Cr.     

Trace-element patterns in lateritic soils applied to geochemical exploration

Geochemical soil surveys in areas underlain by Precambrian volcano-metasedimentary sequences and around rare-metal-bearing pegmatites of southwestern Nigeria demonstrate that residual geochemical soil patterns reflect a wide range of potential source rocks adequately. The secondary geochemical dispersion processes in these typically tropical weathering environments adjust the trace-element distribution during lateritic soil development to narrow fluctuation ranges in comparison to the differing Clarke values of various source rock units.The sample density in these soil surveys, averaging at one sample per square kilometer, favours geochemical inventories even at regional scale and shows great potentials to predict bedrock composition of tropical terrain where rock outcrops are rather scarce.     

Isolation and characterization of some polycyclic aromatic hydrocarbon degrading bacteria from Nsukka soils in Nigeria

Twenty-four bacteria capable of utilizing naphthalene, as their sole source of carbon and energy for growth were isolated from three different sites in Nsukka, Nigeria. By standard bacteriological methods, these bacteria were characterized taxonomically as belonging to the genus Pseudomonas, Burkholderia or Actinomycetes. Two of the isolates, which showed the highest growth during screening as demonstrated by an increase in their optical densities (OD₆₀₀) and identified as Pseudomonas aeruginosa and Burkholderia cepacia respectively, were also able to grow in anthracene and carbazole, but not very much so in 2,4-dichlorophenol and D-camphor. The isolates showed a concentration-dependent growth in all the compounds they grew in. There were visible changes in the colour of the growth medium of the isolates during their incubation, suggesting the production of different metabolites. There were also changes in their medium pH during growth. These studies demonstrate the possession by the bacterial species of novel degradative systems.     

贵州高原地区典型风化剖面地球化学特征及其对比研究

选取了贵州高原喀斯特地区的典型硅酸盐风化剖面(毕节邓家湾剖面)和碳酸盐岩风化剖面(安顺平坝剖面)作为研究对象,以贵州地区的铝土矿剖面和中国黄土作为对比,对其元素分布特征及化学风化作用和强度与进行了研究。结果表明:SiO2、Fe2O3、Al2O3均为两个剖面含量最高的组分,但由于成土母质的化学组分不同,元素分布差异比较明显;同时由于经历的化学风化阶段并不相同,两个剖面的化学蚀变指数(CIA)值相差较大,邓家湾剖面经历了中等强度的风化作用,而平坝剖面的风化强度则十分强烈,CIA反映了土壤剖面的化学组成的差别,以及成土母质、风化成土过程和程度上的差异;虽然两个剖面稀土元素总量都较高,但配分模式存在着明显的差异,剖面的形成基本上是由于各自基岩的风化作用形成的,受中国黄土的影响并不明显。      

江苏土壤地球化学分区

土壤地球化学分区的实质就是依据不同地区土壤中元素含量等差异及其分布规律,划分地球化学特征一致或相似的土壤分布范围。以江苏1:25万区域生态地球化学调查新获得的大量土壤样品元素含量等测试数据为基础,从全省土壤元素含量等分布不均匀的现状出发,根据土壤中的元素组合、特殊元素含量差异、酸碱度差异等,并结合各地第四纪地质作用特点等要素,将江苏土壤划分为3个地球化学区、24个地球化学亚区,指出了部分土壤地球化学亚区的特殊用途,为江苏土地资源保护与利用提供了新的线索。     

Fe and Al oxides distribution in some ultisols and inceptisols of southeastern Nigeria in relation to soil total phosphorus

Ten highly weathered soils in southeastern Nigeria were sampled from their typical A and B horizons for analyses. The objectives were to determine the different forms of Fe and Al oxides in the soils and relating their occurrence to phosphate availability and retention in the soils. The soils are deep and often physically degraded but are well drained and coarse in the particle size distribution. They are mostly dominated by kaolinite in their mineralogy with very high values of SiO₂. The soils are acidic with low soil organic carbon (SOC) contents. The elements in the exchange complex are also low thus reflecting in the low CEC of the soil. Available phosphorus (P) in the soils are generally low while total P ranged from 157 to 982 mg kg⁻¹ with an overall average of 422 mg kg⁻¹. Total Fe in the soil is highest and their order represented as follows: Fe_t > Fe_d > Fe_ox ≥ Fe_p. The pyrophosphate extractable Fe was always higher in the top soil than in the subsoil and was attributed to the fact that these forms of Fe are associated with organic matter which is more abundant in topsoil than in subsoil. Like in Fe forms, the order of Al occurrence could generally be presented as; Al_t > Al_d > Al_ox > Al_p. More Fe and Al oxides in the soils are strongly crystalline while a small quantity is poorly crystalline Fe forms. The amorphous forms of both Fe and Al are very low in the soils when compared with the crystalline forms. The oxides that show very strong affinity to total P are Fe_d–Fe_ox, Fe_d, Al_d, Fe_t, Fe_ox and Al_ox/Al_d. To overcome this problem of P retention in the soil, we recommend constant liming of these soils to neutralize them, application of organic matter and of high dosage of phosphate fertilizer to the soils.     

Mineralogical and chemical composition of some Bauchi soils and their relationship to passive Earth movement

Field and chemical data show that soils in some parts of Bauchi State, Nigeria, are rich in illite (20–35%), montmorillonite (60–75%), and kaolinite (45–73%). These expansive clays cause the soils to shrink and swell alternatively in response to the seasonal supply of moisture; resulting in observed damaging cracks. Plasticity index (PI) determinations on these soils are high (7–13.4%) suggesting that they are potentially hazardous. The attendant hazards and huge losses to the State are blamed on the expansive nature of these soils. The hazardous conditions can be mitigated by adopting proper construction precautions as well as by using chemical additives such as lime and phosphates, to lower the PI and help to increase the strength of the soils.     

Influence of rainfall-induced wetting on the stability of slopes in weathered soils

Shallow failures of slopes in weathered soil are caused by infiltration due to prolonged rainfall. These failures are mainly triggered by the deepening of the wetting band accompanied by a decrease in matric suction induced by the water infiltration. This paper reports trends of rainfall-induced wetting band depth in two types of weathered soils that are commonly found in Korea. Both theoretical and numerical analyses for wetting band depth are presented based on the soil–water characteristic curve obtained using filter paper as well as tensiometer tests. It is found that the magnitude of wetting front suction plays a key role in the stability of slopes in weathered soils. Theoretical analysis based on modified Green and Ampt model tends to underestimate the wetting band depth for typical Korean weathered soils. It was also deduced that for Korean weathered soils, the factor of safety drops rapidly once the wetting band depth of 1.2 m reached.     

土壤与植物根系特征及碳积累探究

为研究土壤与植物根系生长及有机碳输入之间的关系,2011年分别将构树（Broussonetia papyrifera）、铁仔（Myrsine africana）、紫花苜蓿（Medicago sativa）、皇竹草（Pennisetum sinese）移栽入贵州大学林学院苗圃基地,采用石灰土（岩溶地区土壤）与硅质黄壤（非岩溶地区土壤）进行培育,然后对根系生长特征和根系对土壤有机碳积累进行了研究。研究结果表明,构树根系在岩溶地区土壤比非岩溶地区土壤发达,即岩溶地区土壤根系碳沉积比非岩溶高。岩溶地区土壤上,紫花苜蓿死亡根系体积最大,其根系对土壤有机碳积累贡献最大。构树根系生长无论在哪种土壤均随土层深度增加而增加,使得森林土壤深层有机碳含量比草地高。因此,可确定土壤有机碳积累与植被生长环境和植被种类密切相关。      

基于大型直剪试验的强风化粗粒料剪胀特性试验研究

剪胀性是岩土材料的重要特性之一,为研究不同工况条件下粗粒料室内大型直剪试验中的剪胀特性,采用新型室内大型直剪仪对3组不同含水率、4组不同剪切速率、5组不同含砾率等3种不同影响因素的试样进行了室内大型直剪试验,分析了剪切时试样的垂直位移与水平剪切位移及垂直应力的关系。试验结果表明：在保持其他影响因素相同条件下,垂直应力的增加导致相同水平剪切位移对应的剪缩量增加;试样的最大剪缩量随着含水率的增加有一定程度的增大,而随着剪切速率的增加而减小;含砾率低于30%试样的最大剪缩量较含砾超过于30%试样的剪缩量大很多,最大剪缩量差别为3倍。当试样含砾率小于50%时,由于试样中富含细颗粒的影响,使得应力-应变曲线具有应变软化属性以及剪胀性趋于一固定值。峰值强度前的应力比-位移增量关系采用非线性的二次项拟合比线性关系的拟合度更好,认为Matsuoka提出的二维剪胀公式不适用于粗粒料,将其修正成二次多项式并给出试验中的经验参数μ的取值区间。     

An investigation into the geotechnical and engineering properties of some laterites of Eastern Nigeria

The economic importance of laterites as a road-building material and their other structural uses, together with their varied properties which depend on very many factors, have made the study of laterites a subject of continuing interest. This paper traces the geological origins of some Eastern-Nigeria laterites, gives their genetic classification based on their silica/sesquioxide ratio, outlines their physiochemical and chemical properties and seeks some relations between the iron-oxide content, the specific gravity, the sesquioxide content and the other physical and engineering properties of the samples. An attempt is made to rank the laterites with D'Hoore's specifications.Since the properties of laterites are dependent on the type of pretreatment given to the samples, fresh and four-year-old samples were tested after being subjected to varying degrees of drying. The engineering and physical properties tested included the specific gravity of samples divided into particle size-groups, the Atterberg limits, the linear shrinkage, the dry density-moisture content relations, the CBR-moisture content relations and, for coarse particles of the samples, the aggregate tests of moisture absorption, the aggregate crushing value, ‘10%’ fines, flakiness test and elongation-index tests.The conclusion reached is that, while the results agree broadly with those obtained previously, no correlation was found between iron-oxide content and any other physical or engineering properties as has been suggested by others. However, the results suggest that there is some relation between the sesquioxide content and other physical and engineering properties. The strength properties as determined by the CBR tests give high results for most of the samples.     

Nature and profile distribution of iron and aluminum in relation to pedogenic processes in some soils developed under tropical environment in India

Different extractants were used to determine various forms of Fe and Al in three soil profiles developed under a tropical environment in India. The average contents of Fe and Al, extracted by different extracting reagents were found to be in descending order, as follows:

The loess of north-central China: Geotechnical properties and their relation to slope stability

Loess is an aeolian deposit consisting of predominantly silt-sized quartz particles, and containing variable amounts of clay-sized minerals. Loess is generally classified as a water-softening material, because upon wetting the loess fabric rapidly weakens or collapses. The strain hardening of Malan loess and the brittle failure of Lishi and Wucheng loess are in strong contrast to the failure behaviour of these loess deposits in a remoulded state. From tests carried out on samples with varying moisture contents, using a modified Bromhead ring shear apparatus, it was found that the effective apparent cohesion gradually increases and the effective internal friction angle decreases with an increase in moisture content. When the moisture content reaches a material-specific threshold, the effective cohesion decreases rapidly and the effective internal friction angle stabilises at a residual value.

The frequent failure of loess slopes in the western part of the Chinese Loess Plateau is closely related to progressive weathering along zones in these slopes, which causes a dramatic decrease in strength from the peak strength condition. Progressive weathering is common in the loess slopes in the western part of the Chinese Loess Plateau. During the process shear strength reduction along potential slip surfaces may be achieved by leaching of readily soluble salts, destruction of cementation bonds, and redistribution of particles. Localized collapse of the loess fabric causes internal deformation and consequently peak strength conditions are concentrated on a progressively smaller area of the failure plane. Therefore, the mode of failure of loess slopes is generally determined by brittle failure of the undisturbed, and unweathered, central parts of the slopes. It is important that both the weathered and unweathered strength of the loessmaterials in this area be established in order to analyze the stability of existing loessslopes, many of which are steepand lie directly above domestic and industrial urban areas.     

Studying surface properties of desert pavements and their relation to soil properties and plant growth in Hajaligholi playa,Iran

As we know, desert pavement is a superficial feature from wind erosion widespread throughout arid lands and plays a dynamic role in geomorphic, hydrologic, and ecologic processes. In these regions, the plant cover is low or inexistent. Desert pavement is usually covered with large, small, and angular stones. Spatial distribution of stones at the surface is reflecting rainfall distribution at the land surface. Our objective in this study was to determine the relationship between the surface physical characteristics of desert pavement (meter scale), water movement, subsoil, and plant cover. The density and type of cover in land surface are also investigated. For this purpose, two different areas (Hajaligholi playa, Damghan) with different geology were selected. In each region, profiles were dogged. In site one, six different profiles were dogged, and each profile samples in different horizons (0–10, 10–20, 20–30, 30–40, and 40–50 cm) were being taken. In site two, three profiles were dogged, and the same horizon samples were being taken. The type and density of vegetation were determined. Finally, two sites were being compared. The results showed that strong relationship is between the stone cover, soil genesis, and plant distribution. Physicochemical properties (particle sorting, stones rates, electrical conductivity, pH, and gypsum) highly depend on the upland geological characteristics of the region. Also, soil structure and salt concentration have strong relationship with stone component. The distribution and density of vegetation show strong linkage with these properties. Also, in sites with desert pavements and dense plant cover, soils are protected and, thus, reduce desertification (loss fertile soils).     

Evolution of regoliths and landscapes in deeply weathered terrain — implications for geochemical exploration

Thick, commonly lateritic, regoliths are widespread in inter-tropical regions of the world and present particular challenges in exploration. These are best tackled through a sound understanding of the evolution of the landscapes in which they occur. The regoliths formed under humid, warm to tropical conditions and, although they may have been modified by later climatic changes, i.e., to more humid or more arid conditions, many chemical and mineralogical characteristics are retained. These include the geochemical expressions of concealed mineralization. Erosional and depositional processes control the preservation and occurrence of specific regolith units that may be used as sample media and, in turn, target size, element associations and contrast, thereby influencing sampling procedures, analysis and data interpretation. These parameters are best summarized in terms geochemical dispersion models based on the degree of preservation of the pre-existing lateritic regolith. Regolith–landform mapping permits an assessment of the terrain in terms of such models. In relict regolith–landform regimes, in which the lateritic regolith is largely preserved, broad multi-element anomalies in the upper ferruginous horizons (lateritic residuum) can be detected using sample intervals of 1 km or more. In contrast, in erosional regimes, where this material is absent, anomalies in upper saprolite, and the soil and lag derived from it, are more restricted in area and closer sampling intervals, (200×40 m or less) may be necessary. Lag and soil are, generally, ineffective in depositional areas, except where the sediments are very thin (e.g.,<2 m) or overburden provenance can be established. Stratigraphic drilling is necessary to establish whether the overburden overlies a buried lateritic horizon or an erosion surface cut in saprolite. Lateritic residuum remains an excellent sample medium if present, again with widespread haloes, but where it is absent, leaching and the restricted haloes in upper saprolite present formidable problems. Ferruginous saprolite or composites across the unconformity may be effective, but otherwise carefully targeted drilling and sampling through saprolite and saprock may be necessary. Partial extraction analyses have yet to demonstrate significant results except in very specific environments. In arid regions, pedogenic carbonate (calcrete, caliche) may be a valuable sample medium for Au exploration, principally in erosional regimes, and in depositional areas where the overburden is shallow. Sample intervals range from 1 km for regional surveys, through to 100×20 m in prospect evaluation. Saprolite is an essential sample medium in all landform environments, but the restricted halos and possibility of leaching requires that drilling and sampling should be at close intervals.     

Stability of biomass-derived black carbon in soils

Black carbon (BC) may play an important role in the global C budget, due to its potential to act as a significant sink of atmospheric CO₂. In order to fully evaluate the influence of BC on the global C cycle, an understanding of the stability of BC is required. The biochemical stability of BC was assessed in a chronosequence of high-BC-containing Anthrosols from the central Amazon, Brazil, using a range of spectroscopic and biological methods. Results revealed that the Anthrosols had 61-80% lower (P < 0.05) CO₂ evolution per unit C over 532 days compared to their respective adjacent soils with low BC contents. No significant (P > 0.05) difference in CO₂ respiration per unit C was observed between Anthrosols with contrasting ages of BC (600-8700 years BP) and soil textures (0.3-36% clay). Similarly, the molecular composition of the core regions of micrometer-sized BC particles quantified by synchrotron-based Near-Edge X-ray Fine Structure (NEXAFS) spectroscopy coupled to Scanning Transmission X-ray Microscopy (STXM) remained similar regardless of their ages and closely resembled the spectral characteristics of fresh BC. BC decomposed extremely slowly to an extent that it was not possible to detect chemical changes between youngest and oldest samples, as also confirmed by X-ray Photoelectron Spectroscopy (XPS). Deconvolution of NEXAFS spectra revealed greater oxidation on the surfaces of BC particles with little penetration into the core of the particles. The similar C mineralization between different BC-rich soils regardless of soil texture underpins the importance of chemical recalcitrance for the stability of BC, in contrast to adjacent soils which showed the highest mineralization in the sandiest soil. However, the BC-rich Anthrosols had higher proportions (72-90%) of C in the more stable organo-mineral fraction than BC-poor adjacent soils (2-70%), suggesting some degree of physical stabilization.     

Stability of mine workings in frozen soils

The laws of rheological processes (creep and long-term strength) occurring in frozen soils are considered and initial equations formulated. Methods for determining the strength and deformability characteristics are described; the values of these characteristics are given.

Methods are considered for calculating the optimum thickness of the walls of ice—soil retaining structures built by means of artificial freezing and proposed by the authors, as well as methods of design for creep and long-term strength of the frozen soil surrounding various mine workings. The corresponding calculation equations are given; graphs are attached to facilitate the use of these equations. The calculation techniques are illustrated with examples.