scholarly journals Mineralogy, Micro-fabric and the Behavior of the Completely Decomposed Granite Soils

2019 ◽  
Vol 5 (12) ◽  
pp. 2762-2772 ◽  
Author(s):  
Elsayed Elkamhawy ◽  
Bo Zhou ◽  
Huabin Wang
Keyword(s):  
Mineral Composition ◽  
Critical State ◽  
Compressive Behavior ◽  
Volumetric Change ◽  
Isotropic Compression ◽  
Stress Levels ◽  
Decomposed Granite ◽  
Granite Soil ◽  
The Impact ◽  
Completely Decomposed Granite

The main objective of this study is to investigate the impact of the micro-fabric and soil mineralogy on the overall macro-behavior of the completely decomposed granite soil through a set of drained and undrained triaxial shearing and isotropic compression tests on a medium-coarse grading completely decomposed granite soil. The mineral composition of the soil was a substantial factor governing the compressive behavior. The soil compressibility increased significantly in the case of existence crushable and weak minerals within the soil minerals like fragile feldspar, as well as the high content of fines, especially the plastic fines. The scanning electron microscopic photos indicated that the micro-fabric of the soil had a paramount impact on the compressive behavior. The mechanism of the volumetric change depended on the stress levels, the soil mineral composition and the grain morphology. In the low consolidated stress levels, the soils’ grains rearrangement was the prevailing mechanism of the volumetric change, particularly with the absence of weak and crushable minerals. On the other hand, at the high consolidated stress levels, particles’ crushing was the prevailing mechanism in the volumetric change. Both the mechanisms of volume change could occur simultaneously at the low stress levels in the case of presence crushable minerals in addition to micro-cracks in the soil grains. The soil showed an isotropic response after 250 kPa, as this stress level erased the induced anisotropy from the moist tamping preparation method. Under the drained shearing conditions, the soil showed a contractive response, while during the undrained shearing conditions, the soil exhibited both the contractive and dilative responses with phase transformation points. The studied soil showed a unique critical state line, irrespective of the drainage conditions and initial states, the critical state line was parallel to the isotropic compression line in the void ratio effective stress space. In the deviator effective mean stresses space, the studied soil approached a unique CSL with a critical stress ratio equal 1.5, corresponding to critical friction angle of 36.8°.

scholarly journals Effect of Loading Path on the Mechanical Properties of Completely Decomposed Granite Soil Based on the Multiscale Method

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Yanru Zhao ◽  
Tiande Wen ◽  
Xiaohui Sun ◽  
Liping Huang ◽  
Rui Chen
Keyword(s):  
Mechanical Properties ◽  
Confining Pressure ◽  
Loading Path ◽  
Construction Site ◽  
Brittle Behavior ◽  
Second Stage ◽  
Strain Relationship ◽  
Decomposed Granite ◽  
Granite Soil ◽  
Completely Decomposed Granite

Mechanical properties of intact completely decomposed granite (CDG) soil, widely distributed in South China, decrease drastically as encountering external load-related disturbance or soaked by water. In this study, staged triaxial consolidated drained (CD) test and microscopic scanning were conducted using intact CDG specimens extracted from a construction site to investigate the mechanical behavior and microscopic pore distribution. The results show that the stress-strain relationship reveals a shrinking behavior in the first-stage loading and a brittle behavior in the second-stage loading. The development of cracks is affected by the principal stress, which causes the pores and cracks to shrink or partially close. In addition, Esec-1 increases linearly with the increase of confining pressure, but Esec-2 decreases exponentially.

scholarly journals Soil Fabric and Transitional Behavior in Completely Decomposed Granite: An Example of Well-Graded Soil

2021 ◽  
Vol 9 (10) ◽  
pp. 1046
Author(s):  
Elsayed Elkamhawy ◽  
Huabin Wang ◽  
Tarek N. Salem ◽  
František Vranay ◽  
Martina Zelenakova
Keyword(s):  
Dominant Factor ◽  
Soil Behavior ◽  
Isotropic Compression ◽  
Disturbed Soil ◽  
Soil Fabric ◽  
Transitional Behavior ◽  
Decomposed Granite ◽  
Disturbed Soils ◽  
Intact Soil ◽  
Completely Decomposed Granite

Unlike sedimentary soils, limited studies have dealt with completely decomposed granite (CDG) soils, even though they are plentiful and used extensively in several engineering applications. In this paper, a set of triaxial compression tests have been conducted on well-graded intact and disturbed CDG soils to study the impact of the fabric on soil behavior. The soil behavior was robustly affected by the soil fabric and its mineral composition. The intact soil showed multiple parallel compression lines, while a unique isotropic compression line was present in the case of disturbed soil. Both the intact and disturbed soils showed unique critical state lines (CSL) in both the e-log p′ and q-p′ spaces. The intact soil showed behavior unlike other transitional soils that have both distinct isotropic compression lines ICLs and CSLs. The gradient of the unique ICL of the disturbed soil was much more than that of the parallel compression lines of the intact soil. In the intact soil, the slope of the unique CSL (M) in the q-p′ space was higher than that of the disturbed soil. The isotropic response was present for both the intact and disturbed soils after erasing the inherited anisotropy as the stress increased with irrecoverable volumetric change. Soil fabric is considered the dominant factor in the transitional behavior and such a mode of soil behavior is no longer restricted to gap-graded soil as previously thought.

scholarly journals Performance of Geosynthetic-Reinforced and Cement-Fly Ash-Gravel Pile-Supported Embankments over Completely Decomposed Granite Soil: A Case Study

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Lijun Wu
Keyword(s):  
Fly Ash ◽  
High Speed ◽  
Soil Consolidation ◽  
Soil Arching ◽  
Model Method ◽  
Ca Model ◽  
Decomposed Granite ◽  
Granite Soil ◽  
Completely Decomposed Granite ◽  
Cfg Pile

This paper presents a full-scale test of the high-speed railway embankment to investigate the performance of cement-fly ash-gravel (CFG) pile-supported embankments over completely decomposed granite (CDG) soils. The authors compared the embankments built on CDG soils reinforced by geogrid only and geogrid and CFG piles in terms of ground settlement, layer settlement, and pile efficacy. Experimental results show that the CFG pile-supported embankment built on CDG soils performs well. The soil arching of CFG piled reinforcement is effective and significantly increases with surrounding soil consolidation. Furthermore, the increase in the soil arching effect is heavily dependent on differential settlements between surrounding soils and piles. Five methods widely adopted in current designing were used to calculate the pile efficacy. The prediction for pile efficacy by the Nordic method, BS8006, and its modified version is significantly higher than measured values. By contrast, the calculation by the EBGEO and CA model method is more approximate to the measured results in both the pattern and the value at the end of construction. Therefore, the adaptability of the EBGEO and CA model method outperformed that of the Nordic method, BS8006, and its modified version. Finally, in this case, the CA model method was recommended to estimate the pile efficacy of CFG pile-supported embankments built on CDG soils.

Study on Settlement of Railway Embankment on Deep Completely Decomposed Granite Ground by Centrifugal Model Tests

2011 ◽  
Vol 243-249 ◽  
pp. 4213-4219 ◽  
Author(s):  
Hong Bing Xiao ◽  
Guo Sheng Lu
Keyword(s):  
High Speed ◽  
Weibull Model ◽  
Model Tests ◽  
Dynamic Compaction ◽  
Treatment Measures ◽  
Decomposed Granite ◽  
Centrifugal Model ◽  
Granite Soil ◽  
The Relationship ◽  
Completely Decomposed Granite

The settlement cntrol of high-speed railway is a key technology in embankment engineering. In order to reveal the engineering characteristics of the deep completely decomposed granite soil in Hainan east loop line, a passenger dedicated line, four groups of centrifuge model tests were conducted to study the settlement properties of the subsoils untreated, treated by dynamic compaction, and reinforced with cement-mixed piles, under the action of the embankment, especially the relationship between settlement and time, including the settlement during and post-construction. The results show that the Weibull model can describe the relationship between embankment settlement and time well, and that the post-construction settlements of the subsoil meet the requirements of the relevant code. Among the two foundation treatment measures, dynamic compaction is more effective than reinforcement with cement-mixed piles, and the pressure on the contact surface between embankment and subsoil was obviously different from the commonly used calculated values.

scholarly journals The Impact of Salt Stress on Plant Growth, Mineral Composition, and Antioxidant Activity in Tetragonia decumbens Mill.: An Underutilized Edible Halophyte in South Africa

Horticulturae ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 140
Author(s):  
Avela Sogoni ◽  
Muhali Jimoh ◽  
Learnmore Kambizi ◽  
Charles Laubscher
Keyword(s):  
Antioxidant Activity ◽  
Plant Growth ◽  
Mineral Composition ◽  
Nutrient Solution ◽  
Crop Production ◽  
Saline Water ◽  
Total Yield ◽  
Control Treatment ◽  
Antioxidant Power ◽  
The Impact

Climate change, expanding soil salinization, and the developing shortages of freshwater have negatively affected crop production around the world. Seawater and salinized lands represent potentially cultivable areas for edible salt-tolerant plants. In the present study, the effect of salinity stress on plant growth, mineral composition (macro-and micro-nutrients), and antioxidant activity in dune spinach (Tetragonia decumbens) were evaluated. The treatments consisted of three salt concentrations, 50, 100, and 200 mM, produced by adding NaCl to the nutrient solution. The control treatment had no NaCl but was sustained and irrigated by the nutrient solution. Results revealed a significant increase in total yield, branch production, and ferric reducing antioxidant power in plants irrigated with nutrient solution incorporated with 50 mM NaCl. Conversely, an increased level of salinity (200 mM) caused a decrease in chlorophyll content (SPAD), while the phenolic content, as well as nitrogen, phosphorus, and sodium, increased. The results of this study indicate that there is potential for brackish water cultivation of dune spinach for consumption, especially in provinces experiencing the adverse effect of drought and salinity, where seawater or underground saline water could be diluted and used as irrigation water in the production of this vegetable.

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