eMedicine创建于1996年，由近万名临床医师作为作者或编辑参与此临床医学知识库的建设，其中编辑均是来自美国哈佛、耶鲁、斯坦福、芝加哥、德克萨斯、加州大学等各分校医学院的教授或副教授。

eMedicine

Role and impact of CO2–rock interactions during CO2 storage in sedimentary rocks

This report presents information on the characterization of cementitiously stabilized layers and the properties that influence pavement performance. It also contains recommended performance-related procedures for characterizing these layers and performance-prediction models for incorporation into the mechanistic–empirical pavement analysis methods. Individual chapters highlight pavement distresses of hot-mix asphalt pavements and concrete pavements, laboratory tests and model development, and model calibration. The material contained in the report will be of immediate interest to state materials, pavement, and construction engineers and others involved in the different aspects of pavement design and construction.

Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis

Experimental characterization of shrinkage and desiccation cracking in thin clay layer

CO(2) capture and geologic sequestration is one of the most promising options for reducing atmospheric emissions of CO(2). Its viability and long-term safety, which depends on the caprock's sealing capacity and integrity, is crucial for implementing CO(2) geologic storage on a commercial scale. In terms of risk, CO(2) leakage mechanisms are classified as follows: diffusive loss of dissolved gas through the caprock, leakage through the pore spaces after breakthrough pressure has been exceeded, leakage through faults or fractures, and well leakage. An overview is presented in which the problems relating to CO(2) leakage are defined, dominant factors are considered, and the main results are given for these mechanisms, with the exception of well leakage. The overview includes the properties of the CO(2)-water/brine system, and the hydromechanics, geophysics, and geochemistry of the caprock-fluid system. In regard to leakage processes, leakage through faults or fracture networks can be rapid and catastrophic, whereas diffusive loss is usually low. The review identifies major research gaps and areas in need of additional study in regard to the mechanisms for geologic carbon sequestration and the effects of complicated processes on sealing capacity of caprock under reservoir conditions.

Comprehensive review of caprock-sealing mechanisms for geologic carbon sequestration.

Laboratory tests were conducted on three lateritic soil samples to illustrate some pertinent considerations in the design of compacted lateritic soil liners and covers. The three design parameters investigated are hydraulic conductivity, desiccation-induced volumetric shrinkage, and unconfined compressive strength. Test specimens were compacted at various molding water contents using four compactive efforts. The compaction conditions were shown to have some relationship with soil compaction using either the plasticity modulus or the plasticity product (i.e., clay index). For construction quality assurance purposes, the traditional approach was compared with the modern criterion. Deficiencies associated with the traditional approach for soil liners found in literature also apply to lateritic soils. Overall acceptable zones were constructed on the compaction plane to meet design objectives for hydraulic conductivity, volumetric shrinkage strains, and unconfined compressive strength. The line of optimums was identified as a suitable lower bound for overall acceptable zones of lateritic soils. The volumetric shrinkage strain was also identified as the second most important design parameter for lateritic soils. The shapes of the acceptable zones were affected by the fines contents of the soils.

Design of Compacted Lateritic Soil Liners and Covers

The results of a laboratory study on the influence of standard Proctor and West African standard compactive efforts as well as compaction delays up to 3 h on the compaction and strength characteristics of lateritic soil treated with a maximum of 8% lime (by dry weight of soil) is presented. The results obtained show that the compaction and strength properties of the lime-treated soil decreased with increases in compaction delays. The decreases that were generally greater at higher lime contents were more prominent in specimens compacted at the energy of the West African standard. The determination of properties of lime-treated soil at no compaction delay defines optimum properties of the soil-lime mixtures, while compaction and strength properties determined following compaction delays define the minimum that can be achieved in the field for the specified elapsed times between mixing and compaction.

Influence of Compactive Efforts and Compaction Delays on Lime-Treated Soil

Laboratory investigations were carried out on a residual lateritic soil treated with quicklime (up to 8% by weight of dry soil) in order to evaluate the effect of lime content, curing period, and compactive effort on the permeability of lateritic soil-lime mixtures prepared at various maximum dry densities and corresponding optimum moisture contents. The permeability of uncured specimens (standard Proctor) increased to a maximum at 4% lime content and decreased with increasing lime content. Specimens compacted at the energy of the West African Standard had coefficients of permeability that decreased with increasing lime content. For the cured condition, the permeability of all the lime-treated specimens compacted at the two energy levels increased with curing age up to 14 days and decreased with curing age beyond 14 days.

Permeability of lime-treated lateritic soil

The effect of iron ore tailings (IOT) on cement modified tropical black clay was studied. The natural soil was treated with up to 4% cement and 10% IOT by dry weight of soil. Specimens of treated soil compacted with British Standard light, BSL or standard Proctor (relative compaction = 100%) were subjected to index, sieve analysis, compaction, and shear strength parameters tests. The results of laboratory tests show that properties of the modified soil improved when treated with cement–IOT blends. Test results show a decrease of the fine fraction, decrease in liquid and plastic limits, and an increase in maximum dry density (MDD), with a decrease in optimum moisture content (OMC) as well as a decrease in shear strength value of the natural soil up to 6% IOT content. Microanalysis of the natural and optimally (4% cement/6% IOT) modified soil using scanning electron microscope (SEM) showed a change in the fabric orientation of the soil particles. Although the engineering properties of the soil was improved, the modified soil did not meet the requirements of the Nigerian General Specifications of not more than 35% passing sieve No. 200, maximum plasticity (PI) index of 30% and liquid limit (LL) of a maximum of 50% when used as a sub grade material in road construction. However, an optimal blend of 4% cement/6% IOT improved its workability with increase in curing period.

Cement modification of tropical black clay using iron ore tailings as admixture

An expansive soil (black cotton soil) treated with up to 10 % cement kiln dust (CKD), a waste obtained from the manufacture of cement, was evaluated for use as a flexible pavement construction material. Laboratory tests were carried out on specimens compacted with British Standard light, British Standard light or standard Proctor (relative compaction = 100 %) energy. Results obtained show that the index properties of the soil improved with CKD treatment. Peak unconfined compressive strength of 357.07 kN/m2 and California bearing ratio (CBR) of 7 % as well as resistance to loss in strength of 44 % were recorded at 10 % CKD treatment. Reduction in the particle sizes with curing period was observed when samples were viewed through the scanning electron microscope. The study showed that CKD can be beneficially used to improve the subgrade of lightly trafficked roads and as admixture in lime stabilization during construction of flexible pavements over expansive soil.

Kolawole J. Osinubi

Papers

Design of Compacted Lateritic Soil Liners and Covers

Influence of Compactive Efforts and Compaction Delays on Lime-Treated Soil

Permeability of lime-treated lateritic soil

Cement modification of tropical black clay using iron ore tailings as admixture

Assessment of Cement Kiln Dust-Treated Expansive Soil for the Construction of Flexible Pavements