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Minerals, rocks and sediments
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
Non-carbonate clastic sediments are subjected to a sequence of possible changes as they are progressively more deeply buried over longer periods of time. These changes involve four major steps: (1) Compaction, crushing and the decrease of porosity.(2) Syneresis, or dewatering under pressure.(3) Cementation, a complex set of cavity and pore-space filling mainly by carbonate, silica, or iron-oxide cements, plus the growth of individual grains by precipitation. In some heavily cemented sandstones cementation may comprise one-quarter to one-third of the total rock volume. In some chemical and pressure environments, however, solution, rather than cementation, may occur.(4) Incipient metamorphism. This occurs under higher temperatures and confining pressures and is responsible for the alteration of kaolin and montmorillonite to illite and, especially, chlorite. Under extreme diagenesis clays may be partially recrystallized to produce micas and schistose textures.
Review of Basic Chemistry and Geology
Published in Arthur W. Hounslow, Water Quality Data, 2018
One of the most important textures discussed above is that involving the mutual arrangement of mineral grains in the rock. The two textures that arise are crystalline—minerals that form an interlocking meshwork of grains, and clastic—rocks formed from broken pieces of minerals or rocks. A crystalline texture is characteristic of minerals crystallizing from a melt or from solution, or solid-state recrystallization. This texture, common in most igneous and metamorphic rocks as well as some sedimentary rocks, usually results in minimum primary porosity. Many of these rocks, however, because of stresses built up in them, may have significant secondary porosity because of fractures. Clastic textures, on the other hand, which are characteristic of pyroclastic rocks and many sedimentary rocks, lead to maximum primary porosity. Cementation of sedimentary rocks will usually result in lower porosity.
Design for seismic events
Published in Harry G. Poulos, Tall Building Foundation Design, 2017
Microbially induced calcite precipitation (MICP) occurs through a variety of microbiological processes, such as urea hydrolysis and denitrification. The process of calcite precipitation appears to have been discussed initially by van Meurs et al. (2006). Specific bacteria create a reaction which results in the precipitation of calcium carbonate in the form of crystalline calcite on the surface of sandy particles. When this reaction occurs under the right conditions, crystals are formed between two adjacent particles, producing a connection between them. This connection increases the strength and stiffness of the soil. The longer the nutrients, bacteria and reactants are present, the thicker the layer of mineralisation. An important characteristic of this process of cementation is that the permeability of the porous material only reduces slightly. The biomineralisation process progresses slowly in natural circumstances, but the rate of mineralisation can be enhanced by stimulating the conditions.
Enhancing mechanical characteristics of a collapsible sandy Sabkha soil using an eco-friendly admixture: An experimental and numerical study
Published in International Journal of Geotechnical Engineering, 2023
Mohamed B.D. Elsawy, Abderrahim Lakhouit
During inundation under a 200 kPa load, the untreated soil settled 2.0 mm, inducing collapsible behaviour with a collapsible potential of 8%. The dissolution of the cementation materials under the saturated condition was responsible for the collapse. The stabilized soils were tested after 7 days of curing. It was found that using 5% lime in sandy soil reduces the collapsible potential from 8% to 3.2%, thus changing the collapsing state from troubled to moderate, as illustrated in Figures 4 and 5. More decrements in the collapsible potential occurred by increasing lime percentage in the soil. For instance, stabilizing collapsible soil with 20% lime decreased the collapsible potential to less than 1%, which effectively converted the soil to a safe state from a collapsible one. In other words, 20% lime-stabilized soil is sufficient to prevent severe volume change and collapse. Furthermore, it was found that the important enhancements in the collapse behaviour of the stabilized Sabkha soil are due to the hydrated lime generating a firmer cementation. The effectivity of the cementation mainly depends on curing time, lime quantity and lime chemical reaction, all of which are controllable factors.
Consolidated drained behaviour of PVA fibre reinforced cemented Toyoura Sand
Published in International Journal of Geotechnical Engineering, 2022
Muhammad Safdar, Tim Newson, Colin Schmidt, Kenichi Sato, Takuro Fujikawa
Despite numerous applications, there are no field dosage methodologies based on rational criteria for fibre-reinforced cemented soils. Usually, the fibre-reinforced cemented soil strength is assessed by numerous laboratory tests that aim to find the minimum amount of cement or fibre that meet the target property. This approach probably results from the fact that soil-cement-fibre shows a complex behaviour that is affected by many factorsfor example, the physical-chemical properties of the soil, fibre characteristics, the amount of cement, and the porosity and moisture content at the time of compaction (Clough et al. 1981; Porbaha, Shibuya, and Kishida 2000; Consoli, Casagrande, and Coop 2007a; Consoli, Heineck, and Casagrande 2007b; Consoli et al. 2009, 2010). Cementation increases the strength and initial stiffness and reduces the compressibility of naturally occurring weak soils. As brittleness of soil increases with increasing cement content, sudden brittle failure might occur without plastic deformation.
An experimental investigation of fracturing fluids on physico-mechanical damage properties of carbonates in block Shunbei
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2019
Peng Deng, Yintong Guo, Jun Zhou, Lei Wang, Xiaogui Zhou, Feng Xu
The microstructure of carbonates immersed in different fracturing fluids after immersion for different times is shown in Figure 11. It can be observed that the gelation acid and the cross-linked acid have significant effects on the acid damage with the soaking time. The fracturing fluid acts between the calcareous particles, dissolving the cement between the calcareous particles. The changes in particle strength and cementation strength affect the mechanical properties of the rock. Under stress, it can cause stress concentration between the calcareous particles. The large calcite particles with the lamination morphology have the largest change. The mineral crystal spacing obviously increases. The mineral arrangement becomes looser. Deeper dissolution micro-pores and crack marks are formed, resulting in more new micro-porosity cracks, the microstructure characteristics show that the difference in structural characteristics from the initial samples is the largest for the samples immersed for 30 min.