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Hydraulics of Wells
Published in David H.F. Liu, Béla G. Lipták, Paul A. Bouts, Groundwater and Surface Water Pollution, 2019
David H.F. Liu, Béla G. Lipták, Paul A. Bouts
Nonsteady or transient flow in aquifers occurs when the pressure and head in the aquifer change gradually until steady-state conditions are reached. During the course of transient flow, water can be either stored in or released from the soil. Storage has two possibilities. First, water can simply fill the pore space in soil without changing the soil volume. This storage is called phreatic storage, and usually occurs in unconfined aquifers as the groundwater table moves up or down. In the other storage, water is stored in the pore space increased by deformation of the soil and involves a volume change. This storage is called elastic storage and occurs in all types of aquifers. However, in confined aquifers, it is the only form of storage.
Resilient modulus and microstructure of unsaturated expansive subgrade stabilized with activated fly ash
Published in International Journal of Geotechnical Engineering, 2021
Aneke Frank Ikechukwu, M. Mostafa Hassan, A. Moubarak
Comparative study was conducted on stabilized and unstabilized NAT-S specimens. A laboratory test was employed using SEM apparatus VEGA3 TESCAN-6480 SEM operated at 20 kV. The morphology of stabilized and unstabilized NAT-S with different percentages cured for 14 days period is presented in Figures 35–37. The morphologies of the stabilized soils portrayed fragment of floccules with a tight matrix and pozzolanic compounds (calcium silicate hydrates and calcium aluminium) sealed within surface of the soil particles. The morphology showed traces of quartz and they bear a scruffy-form. The reaction of AFA with the clay minerals led to the formation of new cementitious compound after 14 days curing period and this was responsible for increase in resilient modulus of the stabilized soils. Significant, change was observed on stabilized NAT-S system as a result of pozzolanic reaction that coated the soil particles and as well filled pore spaces with the soils. The spiny crystals led to development of network of stabilization as it is noted in 8% AFA stabilized soil. The cementitious compounds developed within the pores spaces of soil stabilized with 10% AFA resulted in reduction of radius of pore space of soil and this observation is noticed in 6%, and 8% AFA except for 4% AFA. Basically, the pore spaces of the stabilized soils were reduced drastically causing it to be relatively smaller compared to the pore space observed with the unstabilized soils.
Physico-chemical characterization of alkali-contaminated tropical kaolinitic clays
Published in International Journal of Geotechnical Engineering, 2020
Sruthi P L, Reddy P H P, R V P Chavali
Several interesting case studies came into the frame with noticeable deformations in the structures because of the accidental spillage of alkalis onto the ground (Vronskii, Boldyrev, and Terent’ev 1978; Sibley and Vadgama 1986; Sinha et al. 2003). Maltsev (1998) mentioned that due to the action of alkalis, clays may swell and it mainly depends on pH of medium, soil exchange capacity, concentration of infiltrating solution, chemicomineralogical composition. Mitchell (1993) reported that even a small concentration of alkali is capable of causing a change in soil structure. At higher concentrations, new mineralogical formations take place and also affect the clay structure. In addition to this, new gel like formations formed in pore space of soil due to the reaction between its minerals and alkali solution, which enhanced the appreciable increase in the volume of soil (Sokolovich and Troitskii 1976). Increase in soil volume was also due to the considerable increase in soil moisture content; interparticle and intracrystalline swelling. It was clear from the literature review that alkali contamination has a notable influence on the volume change behaviour of soils (Assa’ad, 1998; Maltsev 1998; Sunil, Nayak, and Shrihari 2006; Yukselen and Kaya 2008).
A three-dimensional DEM modelling of triaxial test on gas hydrate-bearing sediments considering flexible boundary condition
Published in Marine Georesources & Geotechnology, 2022
Shichen Zhou, Bo Zhou, Shifeng Xue
To study the interaction between different contact subsets, Minh and Cheng (2013) defined the contact-type-related coordination number which can be calculated in a similar way to the average coordination number. Following this approach, the coordination numbers for soil-soil contact subset Zss, soil-hydrate contact subset Zsh, and hydrate-hydrate contact subset Zhh are defined as where Ns, Nh are the number of soil and hydrate particles respectively. Figures 9(b) (c), and (d) show the evolutions of the contact-type-related coordination numbers for the samples with different hydrate saturations, respectively. As can be seen, the soil-soil contact coordination number Zss is approximately 5.5 at the initial state for all cases, which is greater than the minimum stability requirement (i.e., coordination number equals 4). Therefore, it would not cause a major disturbance to the soil-soil contact network if the hydrates were removed. The value of Zss gradually declines during shear. The soil-hydrate contact coordination number Zsh for all cases remains almost unchanged, and its value is in the range of 3.5 ∼ 4.0, indicating that the soil-hydrate contact network is relatively stable. As for the hydrate-hydrate contact coordination number Zhh, an initially small value is observed for the samples with a hydrate saturation of less than 40% because a small number of hydrate particles fill the pore space among soil particles, and the hydrate-hydrate contacts are poorly connected. For the sample with hydrate saturation of 55%, by comparison, the hydrate-hydrate contact coordination number Zhh is up to 4.1, greater than the minimum stability requirement at the initial state and decreases gradually due to the dilatancy effect during shear.