Granite Soil Research Articles

Effectiveness and characteristics of atmospheric CO2 removal in croplands via enhanced weathering of industrial Ca-rich silicate byproducts

Enhanced weathering of industrial Ca-rich silicate byproducts in croplands is potentially profitable for large-scale atmospheric CO2 removal; during the weathering process, CO2 dissolves to form HCO3− and CO32− in alkaline soil pore water, which eventually flows into the ocean. However, the effectiveness of such systems is still in doubt, owing to the unrealistic models used for prediction and the insufficient consideration of the dynamic influences of soils on fluid chemistry. We determined the effectiveness of such systems for atmospheric CO2 removal, along with their characteristics, through a set of batch- and flow-through-type laboratory experiments, using andosol and decomposed granite soil as agricultural and non-agricultural soils, respectively, and Portland cement, steelmaking slag, and coal fly ash as industrial byproducts. The results of the batch-type experiments demonstrated that agricultural soils were suitable for CO2 removal, owing to their moderately high pH and Ca concentrations in pore water that prevented intensive calcium carbonate precipitation. The flow-through experiments demonstrated that a higher Ca-content byproduct can have a large atmospheric CO2 removal capacity. However, the magnitude of CO2 removal and its time-dependent behavior were difficult to predict because they were not in conjunction with the changes in the average pH value. This indicated that the diffusive transport of CO2 from the atmosphere-soil interface to deeper soils was more complex than expected. Maximizing CO2 removal requires a better understanding of the diffusive transport of CO2 through gas-filled pore spaces, created by unsteady-state air–water two-phase flow, due to intermittent rainfall.

Relationships between soils and productivity of NSW blackbutt (Eucalyptus pilularis Sm.) forests

Relationships between site factors, soil and foliage nutrients and growth using growth plots established in pure regrowth blackbutt (Eucalyptus pilularis) on the North Coast of NSW were analysed. The plots were located on five different soil parent materials and were part of research into Eucalyptus stand growth dynamics. When all the plots were combined growth (basal area and volume) were related to rainfall, and elevation. Growth was related to soil texture with lower growth on soils high in sand. Growth rate (periodic annual increment) was related to soil nutrients with the highest correlations with soil total phosphorus. The relationships between growth and growth rates and soil parameters differed with soil parent material with texture, soil rooting depth, total phosphorus concentration and exchangeable calcium important factors. The relationships between soil nutrient quantities (kg ha−1) to 40 cm soil depth and volume mean annual increment were analysed, this providing a method to quantitatively related nutrients in biomass or harvesting removals. There was a positive correlation between volume increment and soil nitrogen on soils derived from sands but not on other parent materials where phosphorus and calcium were positively correlated. It was estimated that if the quantity of P and Ca accumulated in stem biomass at age 50 years were removed it would only potentially affect growth by 0.48% on soils derived from sedimentary rocks but by 12% on granitic soils. The information may used to develop an estimate of sensitively to change in site as a result of management practices. Growth was analysed in relation to foliage nutrients and foliage phosphorus was the nutrient most significantly (positively) related to growth with nitrogen and cations positively related but to a lower level of significance. Manganese concentrations were negatively correlated with growth. There is no clear answer to what limits the spatial extent of blackbutt especially at the fertile end of the spectrum, that is, why is it not found on very fertile soils? The question also arises as to whether populations on different soil types, although in close proximity, are different provenances.

A Machine Learning Architecture Replacing Heavy Instrumented Laboratory Tests: In Application to the Pullout Capacity of Geosynthetic Reinforced Soils.

For economical and sustainable benefits, conventional retaining walls are being replaced by geosynthetic reinforced soil (GRS). However, for safety and quality assurance purposes, prior tests of pullout capacities of these materials need to be performed. Conventionally, these tests are conducted in a laboratory with heavy instruments. These tests are time-consuming, require hard labor, are prone to error, and are expensive as a special pullout machine is required to perform the tests and acquire the data by using a lot of sensors and data loggers. This paper proposes a data-driven machine learning architecture (MLA) to predict the pullout capacity of GRS in a diverse environment. The results from MLA are compared with actual laboratory pullout capacity tests. Various input variables are considered for training and testing the neural network. These input parameters include the soil physical conditions based on water content and external loading applied. The soil used is a locally available weathered granite soil. The input data included normal stress, soil saturation, displacement, and soil unit weight whereas the output data contains information about the pullout strength. The data used was obtained from an actual pullout capacity test performed in the laboratory. The laboratory test is performed according to American Society for Testing and Materials (ASTM) standard D 6706-01 with little modification. This research shows that by using machine learning, the same pullout resistance of a geosynthetic reinforced soil can be achieved as in laboratory testing, thus saving a lot of time, effort, and money. Feedforward backpropagation neural networks with a different number of neurons, algorithms, and hidden layers have been examined. The comparison of the Bayesian regularization learning algorithm with two hidden layers and 12 neurons each showed the minimum mean square error (MSE) of 3.02 × 10-5 for both training and testing. The maximum coefficient of regression (R) for the testing set is 0.999 and the training set is 0.999 for the prediction interval of 99%.

The Shrink–Swell Process of the Granite Residual Soil with Different Weathering Degree in a Gully System in Southern China

The soil shrink–swell phenomenon produces crack networks and slope instability. However, few studies have involved the continuous shrink–swell process of granite residual soils. The objective of the study is to explore the shrink–swell process of weathered granite soils and its effects on gully development in southern China. The bulk density, soil water content (SWC), shrink–swell ratio (SSR), clay mineral content, and mechanical composition, etc., of soil samples from five soil layers (at depths of 0.3 m, 3.0 m, 7.0 m, 12.0 m, and 16.0 m) along a profile in Yudu County was analyzed. After quantifying the soil properties at different soil depths, we analyzed these data statistically in an effort to identify strong parametric relationships. The results indicated that some properties such as bulk density and shear stress increased with soil depth, while other soil properties, such as plasticity index and liquid limit, were inversely related to depth. Soil cohesion, the angle of internal friction, and shear stress were closely related to the SWC. Every 1% decrease in the SWC resulted in a shear stress reduction of 6.62 kPa. The SSR values exhibited significant variation between the three dry–wet cycles and were closely related to the bulk density values of our kaolin and montmorillonite samples. As an environmental factor, the SWC can trigger changes in internal soil properties such as shear stress and the SSR. Using these data and observations made during our field survey, it can be proposed that continuous shrink–swell variation in deep granite-weathering crust can result in crack formation and gully erosion. It can be inferred that crack development velocity and gully retreat rate may be affected by the soil’s shrink–swell process. Consequently, this information provides insight to understanding the mechanism of gully development in southern China.

STUDY ON EVALUATION OF BOND CHARACTERISTIC FOR SPRAYING MATERIAL WITH BAMBOO

In this study, bamboo and solidification material are used as spraying materials and their bond characteristic with the mortar as the base material is evaluated. Four different proportions of specimens are prepared as the spraying material. The types of fine aggregate, the mixing ratio, and the bamboo content are applied as the different parameters. The box shear test is used in this study to investigate these characteristics. As a result, under the same mixing ratio, the bond strength of the spraying material mixed with flying sand is greater than that of the splayed material mixed with decomposed granite soil. Also, the strength of the spraying material using flying sand decreases with increasing the bamboo fiber amount, while the strength of the spraying material using decomposed granite soil increases. Therefore, it is clarified that although using flying sand is effective as the spraying material, in the case of using decomposed granite soil, increasing the bamboo fiber amount is required.

Soil moisture dynamics near a gully head in relation to the trigger of collapse in granite red soil slope in southern China

Gully head collapse is caused by the combined action of water and gravity, resulting in the loss of soil and water in granite soil slope of southern China. However, the soil moisture dynamics near a gully head and the mechanism triggering collapse are still unclear. A five-year high-time-resolution soil water content (SWC) dataset was obtained from soil moisture sensors that were buried at four to seven depths at three positions near a typical gully head on a hillslope in Hubei Province. From 2016 to 2020, two large collapse events were recorded in June in 2016 and 2017. The results showed that the soil moisture regimes were relatively heterogeneous in terms of spatial variation near the gully head: the closer to the gully head, the lower the SWC; the closer to the surface, the greater the SWC variation. This was attributed to the different texture and hydraulic properties of the soil layers. Moreover, the SWC showed obvious periodic dynamics on a seasonal and annual basis, which was consistent with the seasonal precipitation pattern. Although single heavy rainfall events increased the SWC at the surface, high SWC at deep sandy soil layers (≥130 cm) occurred only late in the rainy season after a long period of infiltration during the wet years of 2016 and 2017. Only when the antecedent SWC reached a certain threshold at the deep soil (0.37 m3 m−3, 0.22 m3 m−3, and 0.30 m3 m−3 at 130 cm, 210 cm and 270 cm depth, respectively), the additional heavy rain (53.6 mm in 9 h) triggered the gully head collapse. The exact time of collapse was indicated by a specific instantaneous variation in SWC near the gully head, when the mean SWC in the soil profile increased to high level, whereas the standard deviation of SWC was low during the heavy rainfall. The results confirm that gully head collapse is driven by rainfall and a high SWC in the deep sandy soil layer, as well as provides a useful reference for soil and water conservation control.

Sandaracinobacteroides saxicola sp. nov., a Zeaxanthin-Producing and Halo-Sensitive Bacterium Isolated from Fully Weathered Granitic Soil, and the Diversity of Its ARHDs

A yellow, Gram-stain-negative, aerobic, non-spore-forming, motile, and rod-shaped bacterial strain designated M6T was isolated from fully weathered granitic soil. The strain showing the highest 16S rRNA gene sequence similarity to M6T was Sandaracinobacteroides hominis SZY PN-1T (96.3%), the only species in the genus Sandaracinobacteroides. The average nucleotide identity and digital DNA-DNA hybridization value between these two strains were 72.6% and 18.0% respectively. Growth was inhibited by NaCl (≥0.1% (w/v)). Strain M6T contained C18:1ω7c (33.8%), C14:0 2-OH (16.6%), summed feature 3 (15.8%), and C16:0 (12.6%) as the major fatty acids. The polar lipids profile consisted of phosphatidylglycerol, phosphatidylethanolamine, an unidentified glycolipid, four unidentified phospholipids, and four unidentified lipids. The genome of strain M6T was 3.4 Mb with 67.7% GC content. Further genomic analysis revealed a biosynthetic gene cluster for zeaxanthin, the production of which was verified by a high-resolution mass spectrum. The existence of multiple genes for aromatic ring-hydroxylating dioxygenases implies the potential ability for organic pollution controlling. The morphological, physiological, chemotaxonomic, and phylogenetic analysis clearly distinguished this strain from its phylogenetic neighbors, thus strain M6T represents a novel species of the genus Sandaracinobacteroides, for which the name Sandaracinobacteroides saxicola sp. nov. is proposed. The type of strain is M6T (=CGMCC 1.19164T=NBRC 115420T).

Structure Degradation Induced by Wetting and Drying Cycles for the Hilly Granitic Soils in Collapsing Gully Erosion Areas

The hydrological and mechanical properties of granitic residual soils can be significantly altered by periodical wetting and drying (W-D) cycles. The soil structure degradation induced by W-D cycles can lead to soil mass failure and collapsing gully erosion in granitic hilly slopes in south China. However, limited attempts have been made at a comprehensive investigation of the effects of W-D cycles on the structure degradation of granitic residual soils, especially at the pedon scale. The purpose of this paper is to investigate the structural degradation of granite soils induced by W-D cycles and explore its potential influence on the development of collapsing gully erosion. The granitic soil properties, including hydraulic properties, shear strength, and disintegration characteristics, were performed after W-D cycles. The results indicated that the W-D cycles altered the soil pore structure, leading to variations in soil hydraulic properties. Specifically, with increasing alternate W-D cycles, the initial saturated water content and residual water content decreased, while the saturated hydraulic conductivity increased. Meanwhile, increasing W-D cycles contributed significantly to variations in cohesion and internal friction strength by decreasing the shear strength variables, especially the soil cohesion strength. Correspondingly, soil disintegration was increased during W-D cycles. Furthermore, most degradation of soil structure was recorded within the first two cycles of W-D. The obtained results indicate that the W-D cycles weaken soil structure, increase rainwater infiltration, decrease soil shear strength and disintegration resistance, and accelerate soil erosion. A vicious cycle of granitic slope failure induced by W-D cycles is eventually formed. This study provides useful information about the mechanism of soil mass failure and collapsing gully erosion in granitic hilly slopes.

Closure to “Shear Strength Anisotropy of Natural Granite Residual Soil” by Xinyu Liu, Xianwei Zhang, Lingwei Kong, Song Yin, and Yiqing Xu

Closure to “Shear Strength Anisotropy of Natural Granite Residual Soil” by Xinyu Liu, Xianwei Zhang, Lingwei Kong, Song Yin, and Yiqing Xu

Discussion of “Shear Strength Anisotropy of Natural Granite Residual Soil” by Xinyu Liu, Xianwei Zhang, Lingwei Kong, Song Yin, and Yiqing Xu

Discussion of “Shear Strength Anisotropy of Natural Granite Residual Soil” by Xinyu Liu, Xianwei Zhang, Lingwei Kong, Song Yin, and Yiqing Xu

Numerical Application of a Proposed Material Constant Estimation Method Based on Ideal Mixing Theory

In large projects such as dams, embankments, and seawalls, it is sometimes important to determine the compressive properties of a mixture containing soil and gravel with particle sizes exceeding 75 mm. The Saemangeum Renewable Energy Vision Proclamation Ceremony, held in October 2018 in Korea, confirmed and promulgated the plan to build a total of 4.0 GW of renewable energy power generation complex in the Saemangeum area. The project will be carried out on an area of 31.95 km2, and a 1.0 GW offshore wind power development plan is in progress. Since most of the Saemangeum area has a soft ground layer that has been reclaimed, a key research institute is absolutely necessary to lead in the stabilization of the supporting structures for power generation facilities and to achieve the renewable energy 3020 policy in extreme environments. Hence, it is meaningful to investigate the effect of gravel content (P) on the ground strength characteristics. However, such investigation cannot be routinely performed due to the limited size of the equipment available. Several equations have been proposed in the literature to modify the compaction properties of gravel-mixed soils containing coarse aggregates. Among these is the proposed equation by Walker and Holtz, which has widely been used. However, the use of this equation in the case of high gravel content is not appropriate because the physical meaning of this equation is not clear and does not apply to materials with gravel content exceeding 40%. Therefore, a better quantitative evaluation method in determining material characteristics according to gravel content must be established through laboratory tests on samples of acceptable particle size for the experimental equipment. To obtain the compressive properties of decomposed granite soil (D-G-S), in this study, the results from large-scale one-dimensional compression tests on samples compacted at various gravel concentrations, constant compaction energy, and constant water content were analyzed. To quantitatively evaluate the properties of D-G-S according to the gravel content, a modified formula based on the two-phase mixing theory was utilized. It was shown that the degree of mixing between the gravel and sand for the conditions of D-G-S used in the experiments was high, at 0.85. To estimate the compression curves of D-G-S at various gravel content, the compression curves of purely sand (P = 0%) and purely gravel (P = 100%) materials, and the value of Rm = 0.85 were utilized, and it was shown that the compression index and swelling index curves estimated using the method presented in this study were in good agreement with the experimental results. To confirm the engineering applicability of the presented method, finite element analysis was performed, and as a result, it was revealed that it can be sufficiently applied in the simulation of embankment settlement. In order to obtain more reliable results in the future, verification using various samples is required.

Soil development and management effects on hydraulic properties along a granitic soil toposequence in southern China

A profound understanding of the effects of natural soil development and anthropogenic land management on soil hydraulic properties is essential for soil productivity and water conservation. The objective of our research was to explore the effects of soil development on soil bulk density (BD), pore size distribution, saturated hydraulic conductivity (Ksat), and soil water retention characteristics under horseweed grass (Erigeron canadensis) and corn (Zea mays)-rapeseed (Brassica napus) rotation systems in weathered granitic soils in southern China. Pore size classes determined were macropores (effective diameter > 1000 μm), coarse mesopores (effective diameter 60–1000 μm), fine mesopores (effective diameter 10–60 μm), and micropores (effective diameter < 10 μm). Soil samples from each treatment were collected to a depth of 40 cm in 10 cm increments. The results showed that Ksat was highest in Entisols (6.08 cm h−1) and lowest in Alfisols (2.58 cm h−1), and these values were averaged across management systems and depths. The saturated water content was 12.8% higher in Alfisols than that in Entisols. With soil development, soil water retention increased for all measured soil water pressures. The highest macroporosity as well as coarse and fine mesoporosity were recorded in Entisols, while the highest microporosity was found in Alfisols. Improvement in soil physical and hydraulic properties was seen in the horseweed grass system (HG) compared with that in the corn-rapeseed rotation system (CR). The bulk density was 6% lower for the HG than that for the CR. The HG had 30% higher Ksat and 10.3% greater saturated water content than the CR. The HG also had 15.2% increased macroporosity compared with the CR, which may enhance water infiltration and reduce runoff loss.

Analysis of the Influence of Geomechanical Parameters and Geometry on Slope Stability in Granitic Residual Soils

Granitic residual soils are soils formed by the in situ weathering of intrusive granitic rocks and are present in different parts of the world. Due to their large presence, many civil engineering projects are carried out on and within these soils. Therefore, a correct characterization of the slopes is necessary for slope stability studies. This investigation aims to study the influence of the values of geomechanical parameters (specific weight, cohesion, and friction angle) and the geometry of a slope (height and inclination) on slope stability of residual granitic soils in dry and static conditions. To this end, an automatic system was developed for the numerical study of cases using the finite element method with limit analysis. The system allows modeling, through Monte Carlo simulation and different slope configurations. With this system, the safety factors of 5000 cases were obtained. The results of the models were processed through the SAFE toolbox, performing a Regional Sensitivity Analysis (RSA). The results of this research concluded that the order of influence of the factors were: slope angle &gt; slope height &gt; cohesion &gt; friction angle &gt; unit weight (β &gt; H &gt; c &gt; ϕ &gt; γ).

Influence of Rainfall Infiltration on Stability of Granite Residual Soil High Slope

The seepage evolution characteristics and stability change rule of granite residual soil inside the high cutting slope under the action of rainfall infiltration were studied. Based on the saturated-unsaturated seepage theory, the numerical simulation of the rainwater infiltration path inside the granite residual soil slope was carried out under the condition of rainwater infiltration. The evolution characteristics of the seepage field of the granite residual soil cutting high slope under the condition of rainfall infiltration were revealed, and the influence of the rainwater infiltration on the stability of the granite residual soil slope was mainly studied. The research results show that with the accumulation of rainfall infiltration, the pore water pressure of the granite residual soil slope increases continuously, and the pore water pressure of the soil below the platform increases the fastest. With the increase in elevation, the water content of the slope presents a wave crest distribution. In the early stage of rainfall, the seepage velocity vector distribution on the slope surface is relatively uniform. In the middle stage of rainfall, the seepage velocity vector is the most dense at the platform, and the rainwater migration rate is accelerated. In the later stage of rainfall, the infiltrated rainwater at the slope angle of the first-level slope spreads to the surrounding area. With the continuous rainfall, the slope stability safety factor gradually decreased unevenly, and after the rainfall stopped, it gradually increased with the rainwater infiltration.

Expanding the Paradigm: The influence of climate and lithology on soil phosphorus

The fate of phosphorus (P) during pedogenesis has been historically conceptualized (Walker-Syers model) with time as the primary controlling state factor. Herein, we demonstrate that both climate and lithology exert a strong and interacting influence on the fate of P by examining coupled bioclimatic and parent material effects on soil P fractions. Three transects were investigated spanning a 2150-m elevation gradient (MAT = 17 → 3 °C/MAP = 330 → 1400 mm) across three separate bedrock lithologies (lithosequence: granite, andesite and basalt) within the Sierra Nevada and southern Cascades of California. The elevation gradient entails four bioclimatic zones (bioclimosequence: blue oak, ponderosa pine, white fir and red fir). Soil P fractions were determined by sequential fractionation and interpreted in the context of associated soil characterization data. The bioclimatic sequences demonstrate a weathering gradient with maximum intensity at mid-elevation sites, and corresponding changes in Fe/Al-(hydr)oxide content and aluminosilicate crystallinity. Phosphorus content of parent material varied by an order of magnitude (mean; mg P kg−1): andesite (1500) > basalt (1000) > granite (131). Differences in P content of parent material influenced Pt in soils. However, amounts and proportions of P in fractions were influenced by subtle to significant interactions between climate and lithology, owing to differences in chemical weathering and the abundance and crystallinity of Fe/Al-(hydr)oxides and aluminosilicates. This interactive effect of pedogenesis on clay mineralogy led to differences in P fractions dependent upon lithology and bioclimatic zone. Labile inorganic P (Pi) was uniformly higher in soils derived from granite, despite granite having significantly lower P content, a result of lower Fe/Al-(hydr)oxide generation in granitic soils. With descending elevation and increased weathering intensity, HCl-Pi (primary mineral bound P-apatite) declined in basalt and andesite but remained unchanged in granite owing to its greater resistance to chemical weathering. As weathering intensity increased, occluded P increased in basalt, decreased in andesite and was unchanged in granite, contradicting the paradigm of progressive P occlusion with increased weathering. This incongruity for andesite results from a dominance of poorly crystalline materials (e.g., ferrihydrite, allophane/imogolite) at less weathered sites versus more crystalline minerals at more weathered sites. This study highlights several caveats to the paradigm that time (i.e., degree of weathering) is universally the dominant pedogenic control of P fractionation. We identify the importance of interactions between lithology and climate in regulating the amount and types of weathering products that in turn control P fractionation and ecosystem P availability.

Linkage between aggregate stability of granitic soils and the permanent gully erosion in subtropical China

As an integrated parameter for soil structure and function, aggregate stability is crucial to soil quality and erodibility, resulting in extensive studies on the formation and stability mechanisms of aggregates, especially for heavy-textured soils. Granitic soils with a wide range of particle composition are concentrated by large-scale permanent gullies in subtropical China, while limited information is available on the aggregate structure of granitic soils. To investigate the formation mechanism of these gullies, granitic soils were sampled systemically from different genetic horizons from temperate (no gully erosion) and subtropic (concentrated by gully erosion) areas, and the aggregate size distribution and stability of these soil were measured by Yoder method with sand correction. The results showed that macroaggregate (especially the 0.25 ~ 2 mm-sized fraction) occupied 56.92% of the aggregation. The disaggregation reduction (DR) ranging from 0.18 to 1.12 mm was shown to be more reasonable than the mean weight diameter in characterizing the aggregate stability of granitic soils. Additionally, macroaggregate and DR were unveiled to increase with the increase of weathering degree, implying that the humid climate with high rainfall conditions in the subtropic areas was responsible for the formation of the permanent gullies at a regional scale. The formation and stability of aggregates were generally determined by clay content (R2 = 30.6%), soil organic carbon (R2 = 20.1%), free aluminum oxides (R2 =11.1%), and free iron oxides (R2 =6.7%). Among these influential factors, clay fraction associated with aggregates in a size of > 2 mm was a promising variable for predicting DR (R2 =75%, p < 0.001). Collectively, the aggregate structure of granitic soils is directly determined by inorganic cementing matters controlled by the variation of phyllosilicate mineralogy under different rainfall conditions, while the coarse texture of granitic soils emphasizes the contribution of organic cementing agent (SOC). This study facilitates the understanding of aggregate structure and its stability mechanism of coarse-grained soils as well as erosion control in granitic soil areas.

Effects of in situ leaching on the origin and migration of rare earth elements in aqueous systems of South China: Insights based on REE patterns, and Ce and Eu anomalies

In situ leaching of ion-adsorption rare earth element (REE) deposits has released large amounts of REE-containing wastewater. However, the origin, speciation, distribution and migration of REEs in aqueous systems of the mining catchment are poorly understood. Groundwater, surface water, in situ leachates and weathered granite soil samples were collected from a catchment affected by mining activities in South China. The REE concentrations in groundwater (6.18 × 10–3–0.49 μmol L–1) and surface water (2.54–44.05 μmol L–1) decreased from upstream to downstream. REEs in groundwater were detected in organic matter associated (FA-REE) colloids, while the REE3+ and REE(SO4)+ were converted to REE(CO3)+ and FA-REE colloids from leachates and upstream surface water to downstream. The REE patterns of leachates and upstream groundwater (light and middle REE enrichment) resembled those of soil, but showed heavy REE enrichment due to FA-REE colloids in the downstream. REE in surface water were derived from middle REE enriched leachate. The Ce and Eu anomalies in the water samples indicated the REE origin (i.e., mining activities) and the hydrological variations (e.g., oxidation environment and water-rock interaction). Our results reveal the origin and fate of REE in aqueous systems of ion-adsorption REE mining catchments.

Experimental study on the monotonic mechanical behavior of completely decomposed granite soil reinforced by disposable face-mask chips

In response to the global outbreak of the coronavirus pandemic (COVID-19), a staggering amount of personal protective equipment, such as disposable face masks, has been used, leading to the urgent environmental issue. This study evaluates the feasibility of mask chips for the soil reinforcement, through triaxial tests on samples mixed with complete decomposed granite (CDG) and mask chips (0%, 0.3%, 0.5%, 1%, 5% by volume). The experimental results show that adding a moderate volumetric amount of mask chips (0.3%–1%) improves the soil strength, especially under high confining pressure. The optimum volumetric content of mask chips obtained by this study is 0.5%, raising the peak shear strength up to 22.3% under the confining stress of 120 kPa. When the volumetric content of mask chips exceeds the optimum value, the peak shear strength decreases accordingly. A limited amount of mask chips also increases the elastic modulus and makes the volumetric response more dilative. By contrast, excessive mask chips create additional voids and shift the strong soil-mask contacts to weak mask-mask contacts. The laser scanning microscope (LSM) and scanning electron microscope (SEM) images on the typical samples demonstrate the microstructure of mask fibers interlocking with soil particles, highly supporting the macro-scale mechanical behavior.

A Case Study of Deep Shaft and Open Face Tunnelling Induced Excessive Ground Settlement in Water Rich Strata in Guangzhou, China

During a shaft and associated sprayed concrete lining (SCL) tunnel construction in a new line of Guangzhou Metro, site monitoring recorded ground surface settlement was much larger than that predicted in the design. This raised the alarm to the safety of an adjacent high-pressure gas pipe. Close-form and analytical calculations and non-coupled and coupled numerical analyses were carried out to back analyze the settlement. It was found the primary contributing factor to the excessive ground settlement is water loss-induced ground consolidation, which is commonly encountered during underground construction in south China where complex strata, such as granite residual soil and fully weathered granite, are present. This paper details the back analysis process and discusses mitigation measures that should be adopted for construction in similar ground in the future.

Compressive Strength of Stabilised Granitic Residual Soil Using Mixture of Pineapple Fibre—Hydrated Lime

Granitic Residual Soil (GRS), referring to the weathered soil from rocks, widely exists all over the world, especially in tropical regions. This type of soil is considered weak for construction due to unsaturated soils and the fact that granitic soil properties can vary from one location to another during formation. As a result, soil stabilisation is necessary. In Malaysia, pineapple fibre (PA fibre) is one of the most widely available waste materials. Chemical stabilisation technology is an attractive stabilisation technique that has been successfully used as a soil stabilising agent for many years. Hydrated lime (HL) is an activation agent and is very commonly used to replace cement application in soil stabilisation. Utilising HL and PA fibre as a soil stabilising agent is an economical and sustainable option as HL contains high pozzolanic characteristics that make it more suitable and reliable to stabilise soil, and PA fibre has high specific stiffness and strength. This study uses the replacement portion of the GRS with stabilising agents—HL and PA fibre, aiming to achieve Malaysia’s green technology goals by balancing economic expansion and environmental privilege. However, the aim of this study is to determine the effect of HL–PA fibre mixture replacement on the performance of mechanical and physical properties enhancements of GRS. GRS is the control sample whereas HL and PA fibre are used as binders. The unconfined compressive strength with the curing period was tested. The result showed that for untreated GRS, the moisture content, Atterberg limit, and specific gravity were 9.44%, 37.3%, and 2.3%, respectively, while the maximum dry density was 1.55 g/cm3 and the optimum moisture was 13.5%, according to the compaction test. Due to weathering conditions, the soil was classified using the Unified Soil Classification System (USCS) as well-graded sand soil, based on the sieve analysis. Sieved soil of 2 mm was used to stabilise the GRS mix with HL and PA fibre. The resulting UCS showed that 0 curing days increased strength by 31%, while 7 curing days increased strength by 26% before decreasing the strength by 8.4% to 9%.