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Geotechnique
Institution of Civil Engineers
Geotechnique

Institution of Civil Engineers

0016-8505

Geotechnique/Journal GeotechniqueSCIEI
正式出版
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    Effects of urease and cementing solution concentrations on micro-scale enzymatic mineralization characteristics

    Zhao, ChangXiao, YangLiu, HanlongChu, Jian...
    732-746页
    查看更多>>摘要：Enzymatically induced carbonate precipitation (EICP) holds significant promise in geotechnical engineering. The concentrations of urease enzyme and cementing solution play vital roles in precipitation behaviors under distinct injection strategies. In-situ microscale experiments, conducted in S-shaped microchips, aimed to explore precipitation distribution characteristics and the micro-clogging effects due to biological precipitation. In the one-phase continuous injection methods, elevated urease concentrations correlated with increased Amorphous Calcium Carbonate (ACC) formation and more heterogeneous distributions. Conversely, lower cementing solution concentrations produced larger, fewer crystals and more uniform distributions. Higher urease improved efficiency but increased cost, while lower CS concentrations displayed efficient performance. Permeability reduction exhibited a power-law relationship with the precipitation area fraction. In the two-phase staged injection method, elevated urease concentrations fostered more regularly shaped crystals. Higher calcium ion concentrations could inhibit ureolysis rate, reducing precipitates. Higher urease concentrations proved beneficial in improving efficiencies. Permeability exhibited a marginal decrease initially, followed by a significant decline as the precipitation area fraction increased. The results offer microscale insights into concentration effects, aiding the understanding of upscaling mechanisms and numerical simulations.
      原文链接:
    • NETL
    • NSTL
    • Emerald Group Publishing

    Strength behaviour of stacked phosphogypsum incorporating dissolution-recrystallisation equilibrium

    Cai, Zhang ZhengKe, HanZhang, Peng ZeLan, Ji Wu...
    747-759页
    查看更多>>摘要：Large phosphogypsum (PG) stacks risk dam failure, with an insufficient consensus on the shear strength parameters for stability analysis. To this end, a combination of scanning electron microscopy (SEM) and triaxial tests was undertaken to investigate the underlying mechanism between crystal structure and shear strength of in situ and remoulded PG samples. The shear strength and deformation of PG were significantly affected by dissolution and recrystallisation. Dissolution weakened the cementation between particles, leading to a stabilisation of approximate 11 kPa under different confining pressures in the initial shear stage. The hardening phenomenon was related to the formation of cluster crystals under saturated conditions. An increase from 1.57 to 1.73 in the critical state stress ratio on remoulded samples occurred as the K0 consolidation time increased from 4 to 28 days. The compressive deformation of PG is accompanied by chemical consolidation, which is mainly impacted by the consolidation conditions (saturation) rather than the consolidation time. In the engineering design of the PG stacks, phi' could be taken to a higher value at saturation and c' could be higher when the dry density is higher than 1.2.
      原文链接:
    • NETL
    • NSTL
    • Emerald Group Publishing

    Particle tracking-aided digital volume correlation for clay-sand soil mixtures

    Wu, MengmengWang, JianfengPan, BingYin, Zhen-Yu...
    760-772页
    查看更多>>摘要：This study introduces a novel, interdisciplinary method that merges fundamental geomechanics with computer vision to develop an advanced hybrid feature-aided Digital Volume Correlation (DVC) technique. This technique is specifically engineered to measure and compute the full-field strain distribution in fine-grained soil mixtures. A clay-sand mixture specimen composed of quartz sand particles and kaolinite was created. Its mechanical properties and deformation behaviour were then tested using a mini-triaxial apparatus, combined with micro-focus X-ray Computed Tomography (mu CT). The CT slices underwent image processing for denoising, segmentation of distinct phases, reconstruction of sand particles, and feature extraction within the soil specimen. The proposed approach incorporated a two-step particle tracking method, which initially uses particle volume and surface area features to establish a preliminary matching list for a reference particle and then use the Iterative Closest Point (ICP) method for precise target particle matching. The soil specimen's initial displacement field was then mapped onto the DVC method's grid, and further refined through subvoxel registration via a three-dimensional inverse compositional Gauss-Newton algorithm. The proposed method's effectiveness and efficiency were validated by accurately calculating the displacement and strain fields of the soil mixture sample, and comparing the results with those from a traditional DVC method. Given the soil's compositional and microstructural characteristics, these image-matching techniques can be integrated to create a versatile, efficient, and robust DVC system, suitable for a variety of soil mixture types.
      原文链接:
    • NETL
    • NSTL
    • Emerald Group Publishing

    Anisotropic hydraulic conductivity of as-compacted, bare and vegetated soils

    Gholami, MostafaSadeghi, HamedAlipanahi, Pouya
    773-786页
    查看更多>>摘要：Soils are generally considered anisotropic with respect to hydraulic conductivity, while the evolution of anisotropy condition is unknown for bare and vegetated soils. Therefore, the main goal of this study is to compare the anisotropic hydraulic conductivity of as-compacted, bare, and vegetated specimens. Accordingly, a series of 54 hydraulic conductivity tests were conducted in a custom-made cube triaxial permeameter. The as-compacted specimens were revealed isotropic because the loosely packed preparation procedure resulted in a dominant flocculent structure. However, a fivefold increase in the anisotropy ratio of bare specimens was measured along the isotropic loading path because of the induced surficial degradation zone formed by irrigation and desiccation processes as evident in preliminary observations and crack network analysis. The variations in anisotropy ratio vs. void ratio function of vegetated soil generally fall below the corresponding function of the bare soil. The function was revealed to have a crossed nature, varying from sub-isotropic to super-isotropic states, corresponding to the lower and upper bounds of 0.3 and 3, respectively. It was postulated that vegetation impacts the flow differently by reducing the potential of desiccation cracks, creating preferential flow through the propagation of primary roots and clogging flow channels by secondary roots.
      原文链接:
    • NETL
    • NSTL
    • Emerald Group Publishing

    Role of bacteria on bio-induced calcium carbonate formation: insights from droplet microfluidic experiments

    Zhang, JinxuanXiao, YangLiu, HanlongChu, Jian...
    787-799页
    查看更多>>摘要：Microbially induced calcium carbonate precipitation (MICP) has emerged as a promising solution for geotechnical issues. However, the role of bacteria in the formation of calcium carbonate (CaCO3) remains incompletely comprehended. In this study, a droplet microfluidic chip was developed to observe the growth process of CaCO3 and bacterial behavior during the MICP process under various bacterial density conditions at the monocrystal-scale. Scanning electron microscope (SEM) was then utilized to analyze the CaCO3 morphology, and Raman spectroscopy was employed to identify CaCO3 polymorphs. Nucleation within microspaces showed a stochastic nature. Within the droplets where crystals formed, all crystals manifested as cubic calcite. Higher bacterial density led to the formation of larger and more irregularly shaped crystals, with crystal size showing a significant correlation with urease activity. In droplets where no crystals formed, higher bacterial density and urease activity resulted in the precipitation of amorphous calcium carbonate (ACC) on the bacterial surface. However, this precipitation pattern differed from the formation of monocrystalline CaCO3. Our results demonstrate that bacteria act primarily as urease secretors to regulate crystal growth during the MICP process, while their role as nucleation sites for crystals remains controversial. This study provides a novel insight into understanding the bio-induced CaCO3 formation mechanism.
      原文链接:
    • NETL
    • NSTL
    • Emerald Group Publishing

    Axial behaviour of steel pipelines buried in sand: effects of surface roughness and hardness

    Guo, ChangZhou, Chao
    800-813页
    查看更多>>摘要：Surface roughness and coating hardness of underground pipelines are expected to play decisive roles in their axial pullout behaviour, which is an important aspect of pipeline design. Existing guidelines and previous studies underestimated or ignored these effects, resulting in potentially unsafe design. To address this problem, the current study conducted nine large-scale physical modelling tests on pipes in dry and dense sand. Five steel pipes with varying normalised roughness (0.04-1.01) and coating hardness (32.6-59.0 HRA) were used and instrumented with a novel type of film-like piezoresistive sensors for measuring soil-pipe contact pressure. The measured pullout resistance of rough pipes is 2.70-2.85 times of smooth pipes, significantly greater than the value specified in current design guidelines (i.e., 1.17 times). This substantial increase stems from an increase in interface friction coefficient (accounting for 72-79%) and a contact pressure increase induced by constrained dilation and soil arching (contributing the remaining 21-28%). Regarding coating hardness, a critical hardness was observed (around 35 HRA). Due to equivalent roughness from particle embedding, pipes with hardness below this value exhibited similar behaviour to rough pipes. Finally, a new and simple method was proposed for calculating the pullout resistance with consideration of the effects of roughness and dilatancy.
      原文链接:
    • NETL
    • NSTL
    • Emerald Group Publishing

    Quantification of spatial heterogeneity and its influence on particle migration

    Annapareddy, V. S. RamakrishnaSufian, AdnanBore, ThierryScheuermann, Alexander...
    814-828页
    查看更多>>摘要：Suffusion experiments were utilised to quantify the evolving degree of heterogeneity in gap-graded soils. Upward flow was imposed on test specimens comprising a mixture layer with varying finer fraction contents overlaid by a coarse layer. A coaxial permeameter cell enabled the local permeability to be obtained using spatial time domain reflectometry. Three methods (coefficient of variation, Dykstra-Parsons coefficient, and Lorenz coefficient) were employed to quantify heterogeneity based on spatial variability in local permeability. For the two-layered specimen in this study, all three methods demonstrated that suffusion had a homogenising effect with particle migration from the mixture layer to the coarse layer. Detailed insights were obtained from a multi-layered approach, where the Dykstra-Parsons coefficient was found to be more sensitive to spatial variations, while the Lorenz coefficient was less dependent on the amount of data. The key observation was that an increase in heterogeneity led to a reduction in particle migration. This is an important finding as prior studies focused on homogeneous specimens, while this study demonstrates that small amounts of heterogeneity can significantly impact particle migration characteristics. This reinforces the need to quantify the evolving degree of heterogeneity.
      原文链接:
    • NETL
    • NSTL
    • Emerald Group Publishing

    Development of a new soil-structure contact stress sensor for underground construction applications

    Templeman, JackSheil, Brian
    829-842页
    查看更多>>摘要：This paper describes the design, development, calibration and validation of a novel soil-structure contact stress sensor. The new sensor design combines a novel operating principle, fibre Bragg grating (FBG) strain sensing and data-driven mapping techniques to create a multi-axis contact stress sensor that is both economical and suitably robust for deployment in underground construction applications. The instrumentation process is informed using a 'virtual twin' of the sensor in which synthetic data is generated by extracting and interpolating virtual FBG strains obtained from a large number of 3D finite element calculations. A physical prototype is subsequently developed to demonstrate proof of concept. Results from laboratory validation tests give confidence in the sensor's ability to provide accurate contact stress measurements in typical soil-structure interface shear applications. In particular, the novel sensor structure and operating principle was shown to achieve excellent measurement of effective normal stress. The new sensor design harnesses many of the inherent benefits of FBGs including immunity to electromagnetic noise and water ingress, and the use a single lightweight cable and connector, which significantly simplifies installation on site compared to electrical multi-axis sensors.
      原文链接:
    • NETL
    • NSTL
    • Emerald Group Publishing

    Discussion: Scale effects during cone penetration in spatially variable clays

    Zhang, WangchengPan, YutaoBransby, FraserMesri, Gholamreza...
    843-844页
      原文链接:
    • NETL
    • NSTL
    • Emerald Group Publishing