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1

Unsaturated soil properties of MICP treated granitic residual soil of Shantou region of China

Hao Li, Lin Peng, Garg Ankit

Acta Geophysica

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2023

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Vol. 71, no. 4

1885--1894

EN

Unsaturated soil properties such as soil–water characteristic curve (SWCC) and shear strength are required for seepage and stability flow analyses in various geo-engineering infrastructures. Microbial-induced calcite precipitation (MICP) has been recently adopted for enhancing strength of soils however, with rare focus on improvement in unsaturated soil properties of granitic residual soil. It is known that granite residual soil exhibits unique disintegration properties upon interaction with water. The objective of this study is to investigate the unsaturated properties under different vertical stresses (0, 100, 200 and 300 kPa) for MICP treated granitic residual soils. Further, microstructural characterization of MICP treated soil was conducted to analyse its water retention and shear strength, so as to provide theoretical basis for engineering application of MICP in strengthening granite residual soil. Pressure plate apparatus and FDJ-20 quadruple shear strength apparatus were utilized to obtain SWCCs and shear strength, respectively. Based on the result, it can be concluded that the treatment by MICP is found to enhance the air entry value of granitic residual soil. In addition, MICP treated soils possess higher water content than untreated soil at near-saturated condition. This is due to calcite precipitation on surface of grains and carbonate formation at contact points, which in turn reduces void ratio. However, the difference in water retention reduces with an increase in suction and also confining stress. It is possibly due to breakage of carbonate bonds at contact points at higher stresses. After five times grouting, the effective cohesion, internal friction angle and matric suction angle is found to increase very significantly.

2

Experimental and numerical investigation on runoff reduction and water stress of green roofs with varying soil depth and saturated water content under dry–wet cycles

Ma Ming, Wang Jun, Garg Ankit, Mei Guoxiong

Acta Geophysica

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2023

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Vol. 71, no. 2

893--903

EN

The soil layer is the most important structure for green roof runoff reduction and vegetation growth. The mechanisms of runoff reduction and water content of green roofs with varying soil depth and saturated water content (θs) under dry–wet cycles are not well understood. Field and numerical methodologies were adopted for investigation in this study. The green roof drainage and water content were observed for a given period (i.e., August 2020 to July 2021). A numerical model was calibrated and validated for the analysis of annual runoff reduction and water stress with different θs and soil depths. Based on climate in southern China, the green roof's annual runoff reduction rate (ARR) (100 mm soil) was 33%, and the annual water stress was 168 days. With an increase in θs by 0.1 mm3 /mm3 , the ARR of green roofs increased by an average of 5% while the water stress was reduced by an average of 32 days. With an increase in soil depth by 100 mm, the average ARR increased by 4%, whereas the average water stress was reduced by 6 days. It was shown that the runoff reduction is enhanced with an increasing θs and soil depth during a longer antecedent dry weather period, but it had no significant effect on runoff reduction during back-to-back rainfall events. Increasing soil depth had no significant improvement in runoff reduction and water stress beyond a certain point. Consequently, the optimal structural configuration of green roofs was considered as a soil depth of 200 mm (θs of 0.5 mm3 /mm3 ).

3

Biopolymer based stabilization of Indian desert soil against wind induced erosion

Dagliya Monika, Satyam Neelima, Garg Ankit

Acta Geophysica

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2023

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Vol. 71, no. 1

503--516

EN

Wind-induced soil erosion is a major global misfortune, which obliterates nearly one-third of worldwide soil. The windswept sand particles cover large areas including highways, and make the visibility vague. This results in accidents, damaged infrastructure, delayed fights, and various health issues. The erosive impact of the wind can be minimized by enhancing the intactness of the soil surface. There is a prerequisite to adopt viable measures to strengthen soil against wind erosion. There are certain nature-based solutions that can fortify soil against wind erosion and the application of biopolymers is one of them. The objective of this study is to examine the viability of non-toxic biopolymers for stabilizing desert sand by improving its erosion resistance property and strength. In the present experiment, three biopolymers, sodium alginate (SA), pectin (P), and acacia gum (AG), were used with 1, 2, and 3% concentrations for 1 and 0.75 PV as stabilizing agents. The treatment with biopolymers was performed either by surficial treatment (spraying or pouring of solution) or by mixing and compact method based on the viscosity of prepared biopolymer solutions. The biotreated sand samples were tested in a wind tunnel at varying wind speeds of 10, 20, and 30 m/s to assess sand erosion. Surface strengths were assessed by measuring compressive strength using a pocket penetrometer. Crust thickness measurement was performed to check the penetration depth of biopolymer solution and binding of sand particles. All three biopolymers with 1% concentration gave a feasible solution for erosion against wind and binding of particles through SEM analysis. SA and P could not be sprayed for 2 and 3% concentrations due to high viscosity. This solution is also not feasible for the field application. Simultaneously, AG with 2 and 3% concentration was highly soluble, less viscous, and gave more surface strength due to higher percentage of biopolymer concentration.

4

A new and simple model for predicting soil erosion based on hole erosion tests

Cai Weiling, Bora Manash Jyoti, Pekkat Sreeja, Bordoloi Sanandam, Garg Ankit, Sekharan Sreedeep

Acta Geophysica

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2023

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Vol. 71, no. 2

823--836

EN

Determination of erosion characteristics is of great significance to assess the erodibility of geomaterials that are subjected to seepage force. The erosion characteristics indicate soil particle removal in term of internal erosion that might occur in earthen structures. Hole erosion test (HET) is a simple and effective approach to determine erosion characteristics. It is noted that there are not many studies that focus on the development of a theoretical model describing the erosion characteristics and the associated process of soil particle detachment in HETs. The aim of this study is to propose a simple model based on Bernoulli’s principle to interpret erosion characteristics of geomaterials in HETs. An analytical equation was deduced from a physically based model incorporating Bernoulli’s principle and erosion constitutive law for internal erosion within a soil pipe driven by pressure gradient. The analytical equation could be applied to determine soil particle removal, radial erosion propagation, erosion coefficient, and critical shear stress. A series of HETs were performed under different flow rate to verify the proposed model. The obtained results demonstrated that the proposed model allowed for reasonably predicting the amount of soil particle removal and understanding erosion characteristics of soils through the HET.

5

Moisture management in biochar amended green roofs planted with Ophiopogon japonicus under different irrigation schemes: an integrated experimental and modeling approach

Liu Jiaqin, Garg Ankit, Wang Hao, Huang Shan, Mei Guoxiong

Acta Geophysica

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2022

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Vol. 70, no 1

373--384

EN

Green roof constantly suffers from the water stress that is developed during prolonged drought seasons. In general, periodical irrigation is required to ensure plant growth and hence serviceability of green roofs. Biochar, a carbon sink material, has been proposed as a substrate amendment in green roofs for enhancing water retention ability of soils. This study aims to conduct an assessment of the irrigation efficiency of green roofs with different biochar additions (0%, 5%, 10%, 15% and 20%; v/v) under sub-tropical climatic conditions. In order to achieve this objective, outdoor monitoring as well as numerical modeling using HYDRUS-1D was conducted. Soil columns mixed with different proportion of biochar were prepared. These columns were subjected to different irrigation schemes (three irrigation frequencies were assessed (i.e., per 3, 7 and 10 days after irrigation or rainfall); moreover, three irrigation amounts for the three irrigation frequencies were considered (i.e., to a fixed amount (FA10mm), to Field water holding capacity (FC) and to Saturated moisture content (SR))). As suggested from the results: (1) Biochar significantly improved water holding capacity and plant available water. 20% biochar delayed the onset of the significant plant wilting phenomenon by approximately 3 days and maintained the maximal transpiration rate of vegetation in the dry period. (2) As compared to irrigation scheme A (irrigation to FC per 7 days), the efficiency of scheme B (irrigation to SR per 10 days) was more vulnerable to the biochar amendment. Moreover, the total irrigation water and days of water stress decreased with an increase in the biochar addition. Furthermore, the combination of 20% biochar and irrigation scheme B could be the optimal choice for maintaining the health of the green roofs and water conservation. The present study helps to obtain desired outcomes in green roofs, e.g., stormwater management, cost reduction as well as providing greening.

6

Assessment of soil erosion models for predicting soil loss in cracked vegetated compacted surface layer

Bora Manash Jyoti, Bordoloi Sanandam, Pekkat Sreeja, Garg Ankit, Sekharan Sreedeep, Rakesh Ravi Ranjan

Acta Geophysica

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2022

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Vol. 70, no 1

333--347

EN

Rainfall-induced progressive soil erosion of compacted surface layer (SL) impedes the functioning of cover system (CS) of landfills with high expected design life (≈ 100 years). The existing soil erosion models are not tested extensively for compacted soil with cracks and vegetation. This study evaluated the efficacy of three popular soil erosion models for estimating the soil loss of compacted SL of CS, which is useful for annual maintenance. The interactive effect of rainfall, vegetation and desiccation cracks on erosion of compacted surface layer was investigated under the influence of both natural and simulated rainfall events for one year. Among all, the Morgan, Morgan and Finney (MMF) model was found to be effective in predicting soil erosion of compacted SL. However, the MMF model overestimated soil erosion when the vegetation cover exceeded 60%. The soil loss estimated from Revised Universal Soil Loss Equation (RUSLE) and Water Erosion Prediction Project (WEPP) models was poor for high rainfall intensity (100 mm/h). The RUSLE and WEPP model overestimated the soil erosion for low vegetation cover (≤3%) and underestimated for vegetation area>3%. The mechanism of root reinforcement, strength due to root water uptake-induced soil suction and its effect on soil loss mitigation could not be adequately captured by the existing models for compacted SL. Further studies are needed to improve the existing erosion models for incorporating the effects of desiccation and vegetation on soil loss from the compacted SL.

7

Infuence of biochar amendment on stormwater management in green roofs: experiment with numerical investigation

Gan Lin, Garg Ankit, Wang Hao, Mei Guoxiong, Liu Jiaqin

Acta Geophysica

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2021

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Vol. 69, no. 6

2417--2426

EN

Green roof is known to minimize urban waterlogging owing to its water retention capacity due to the presence of substrate soil layer. Biochar, which is a carbon-negative material, appears to be an essential soil amendment in green roof due to its water-holding capacity and stability. Recently, incentives are provided in developed countries to enhance commercial pro duction of biochar for usage in green infrastructure, with an aim to meet carbon reduction goals of 2030. Further, biochar has a longer half-life (over 100 years), compared to other materials that are easier to degrade. In this study, the influence of different biochar contents on hydrological performance of green roof is evaluated using a combination of experiment and numerical simulation. Four soil columns with different biochar contents (0, 5, 10 and 15%) were subjected to artificial rainfall. Hydraulic parameters were obtained using inverse solution from the collected rainfall data. Numerical simulations were used to explore the impact of different biochar contents on green roof rainwater management performance during real rainfall process. Biochar is found to enhance saturated water content and, however, tends to reduce saturated hydraulic conductivity. The green roof with 10% BAS (10% biochar content) has better ability of comprehensive rainwater management, with the highest peak outflow reduction and the longest rainwater outflow delay. Green roof with 5% BAS has highest runoff reduction and longest peak outflow delay. These results provide a suitable selection of biochar content for urban areas with different rainwater management requirements.

8

Utilization of coconut shell residual in green roof: hydraulic and thermal properties of expansive soil amended with biochar and fbre including theoretical model

Wang Hao, Garg Ankit, Zhang Xiaoyong, Xiao Yangyang, Mei Guoxiong

Acta Geophysica

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2020

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Vol. 68, no. 6

1803--1819

EN

The study intends to explore hydraulic and thermal properties of expansive soils treated with fbre, biochar and biochar–fbre mix. Both fbre and biochar are derived from coconut shell, which is highly common in coastal regions around the world. Besides, benefts, limitations and engineering feasibility of these geomaterials in green roofs are explored. Theoretical framework for thermal–hydraulic analysis is proposed based on mass conservation and the frst law of thermodynamics. Heat capacity, thermal conductivity, water retention curve, crack intensity factor (CIF) and saturated and unsaturated hydraulic conductivities of four kinds of soils are evaluated and compared. Characterizations of geomaterials are also investigated via thermal mass loss, micro-structure, surface area and functional groups identifcation. Both biochar and fbre admixtures contribute to improvement in soil heat capacity and saturated and unsaturated hydraulic conductivities. Biochar enhances saturated and residual water contents of expansive soil by 10% and 8%, respectively. Also, biochar decreases soil thermal conductivity and CIF by 31% and 5%, respectively, while fbre decreases soil-saturated and residual water contents by 15% and 29%, respectively, and reduces soil thermal conductivity and CIF by 21% and 50%, respectively. Soil–biochar–fbre composite is also recommended due to low air-entry value, acceptable water-holding capacity and limited crack propagation. The study flls the knowledge gap of how soil thermal–hydraulic properties are afected due to biochar and/or fbre admixture. It is recommended to pay more attention on production and utilization of biochar derived from coconut shell currently utilized for fbre extraction.

9

Mechanism of compacted biochar amended expansive clay subjected to drying–wetting cycles: simultaneous investigation of hydraulic and mechanical properties

Wang Hao, Garg Ankit, Huang Shan, Mei Guoxiong

Acta Geophysica

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2020

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Vol. 68, no. 3

737--749

EN

Biochar has been extensively studied in the aspect of amendment of compacted sandy/clayed soils, whereas its application as amendment in expansive soil is rare. Hydraulic and mechanical properties of biochar-amended expansive soil especially impacts of drying–wetting cycles have been rarely investigated. Aiming at construction of sponge city, straw biochar-amended expansive soil and the control soil (i.e., without biochar) are subjected to drying–wetting cycles in this study. During drying–wetting cycles, energy-dispersive spectrometer and Fourier transform infrared (FTIR) spectroscopy analyses were conducted to investigate microchemical composition including. Pore size distribution and microstructure were measured using nitrogen gas-adsorption technique and scanning electron microscope, respectively. Further, changes in soil water retention curve, void ratio, crack intensity factor (CIF, i.e., ratio of cracked section area to the total soil area) and shear strength were also determined. It is found that there is no diference in water retention capacity between various soils for near-saturated samples. Under high suction, however, more water could be retained within mesopores of biochar-amended soil. FTIR analysis indicates that biochar-amended expansive soil shows stronger chemical bonding, irrespective of them being subjected to drying–wetting cycles. The weak alkalinity of straw biochar results from its main chemical composition (i.e., calcium carbonate). It is noteworthy that straw biochar improves soil water retention capacity, which further restrains desiccation cracks. Cohesion of biochar–soil composite is also improved due to chemical bonding. Aiming at green roofs, straw biochar could be promising option for expansive soil amendment technically and economically.

10

Mechanism of biochar soil pore-gas-water interaction: gas properties of biochar-amended sandy soil at diferent degrees of compaction using KNN modeling

Garg Ankit, Huang He, Kushvaha Vinod, Madhushri Priyanka, Kamchoom Viroon, Wani Insha, Koshy Nevin, Zhu Hong-Hu

Acta Geophysica

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2020

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Vol. 68, no. 1

207--217

EN

Soil compaction has contrasting efect on soil strength (i.e., positive) and vegetation growth (i.e., negative), respectively. Biochar has been utilized mostly in combination with soils in both agricultural felds (i.e., loose soils) and geo-structures (i.e., dense soil slopes, landfll cover) for improving water retention due to its microporous structure. Biochar is also found to be useful to reduce gas permeability in compacted soil recently. However, the efciency of biochar in reducing gas permeability in loose and dense soils is rarely understood. The objective of this study is to analyze efects of compaction on gas permeability in soil at diferent degrees of compaction (i.e., 65%, 80% and 95%) and also diferent biochar amendment contents (0%, 5% and 10%). Another aim is to identify relative signifcance of parameters (soil suction, water content, biochar content and compaction) in afecting gas permeability. Experiments were conducted before applying k-nearest neighbor (KNN) modeling technique for identifying relative signifcance of parameters. Biochar was synthesized from a coastal invasive species (water hyacinth), which has relatively no infuence on food chain (as unlike in biochar produced from biomass such as rice husk, straw, peanut shell). Based on measurements and KNN modeling, it was found that gas permeability of biochar-amended soil is relatively lower than that of soil without amendment. It was found from KNN model that for denser soils, higher amount of soil suction is mobilized for a signifcant increase in gas permeability as compared to loose soils. Among all parameters, soil suction is found to be most infuential in afecting gas permeability followed by water content and compaction.

11

Investigation of infiltration rate for soil‑biochar composites of water hyacinth

Gopal Phani, Bordoloi Sanandam, Ratnam Raval, Lin Peng, Cai Weiling, Buragohain Poly, Garg Ankit, Sreedeep S.

Acta Geophysica

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2019

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Vol. 67, no. 1

231--246

EN

The objective of this short communication is to investigate the interactive effects of CIF, suction and volumetric water content (VWC) on infiltration rate for compacted soil–biochar (BC) composites (0%, 5% and 10%). The biochar was produced from an invasive weed Eichhornia crassipes. Soil parameters such as suction (ψ), VWC, CIF and infiltration rate were monitored simultaneously for 63 days (9 drying–wetting cycles) in those composites. This was followed by statistical modeling using artificial neural networks. Results showed that increase in WH BC content reduced the infiltration rates. The role of CIF in determining the infiltration rate reduced (50–38%) with the addition of BC to soil. Suction played an equal role (36–35%), both for bare soil and for WH BC composites, in determining the infiltration rate. Significance of VWC in determining rate of infiltration increases (14–27%) as the BC content increases. This is more likely, as the addition of BC enhanced the water retention capacity.