Decomposed Granite Research Articles

Improvement in Mechanical Properties of Completely Decomposed Granite Soil Concrete Fabricated with Pre-Setting Pressurization.

This paper investigates the effectiveness of applying continuous high-compression pressure on the initial setting of fresh concrete to produce hardened concrete materials with excellent mechanical properties. A novel experimental apparatus was self-designed and used for the pre-setting pressure application. The utilization of the completely decomposed granite (CDG) soil as an alternative aggregate in concrete production was also explored. A total of twenty-eight specimens were fabricated using two types of fine aggregates, six mix ratios, two initial pressure values, and two distinct durations of the initial pressure application. The density and uniaxial compressive strength (UCS) of the specimens were examined to evaluate their mechanical qualities, while micro-CT tests with image analysis were used to quantify their porosity. The results indicated that the 10 MPa initial pre-setting pressurization can effectively eliminate the excess air and voids within the fresh concrete, therefore enhancing the mechanical properties of the hardened concrete specimens of various types. Compared with non-pressurized specimens, the porosity values of pressurized specimens were reduced by 73.11% to 86.53%, the density values were increased by 1.43% to 8.31%, and the UCS values were increased by 8.42% to 187.43%. These findings provide a reference for using a continuous high pre-setting compression pressure and using CDG soil as an aggregate in the fabrication of concrete materials with improved mechanical performance.

Matching of crushed highly decomposed granite particles using 3D SHOT descriptors

Owing to the complex morphology and the fragility of highly decomposed granite (HDG), it is still a challenge to track the breakage process of HDG particles within a deformed sample in geomechanics research. An HDG particle matching method is proposed in this paper for the first time to track and match HDG fragments with their mother particles from which they break off. First, the X-ray micro-computed tomography (μCT) images of HDG particles were acquired from a one-dimensional compression test and a certain number of HDG particles and fragments were selected and reconstructed. Second, the original and fracture surfaces of the fragments were identified and segmented. Then, the essential morphological features of the particles and fragments were represented with the key points. The neighbourhood information around the key points was encoded by the three-dimensional (3D) feature descriptor. Next, the mismatches were filtered out by the random sample consensus (RANSAC) algorithm based on the similarity of the local neighbourhood information. Finally, the influences of several parameters on the matching results were investigated. The capability and efficiency of the HDG particle matching method were demonstrated using the μCT data of ten HDG particles and 32 fragments that resulted from the crushing of these particles.

Effect of Composite Microbial Biopolymer Treatment on Hydraulic Conductivity of Completely Decomposed Granite Soil

In southeast China, slope with completely decomposed granite (CDG) soil is susceptible to landslide under heavy rainfall, due to the fissure-rich and slaking characteristics of this kind of soil. In this context, this study attempted to hydraulically improve the CDG soil in a low-carbon manner by using the composite of xanthan gum and guar gum (i.e., two different microbial biopolymers), as an alternative to cement. Hydraulic conductivity of the treated soil was measured using a tailer-made apparatus. Test result shows that the biopolymer content of 2% could lower the conductivity by over 1000 times, and the ratio of 1:1 between Xanthan and guar gums yielded the best performance in general. Application of composite biopolymer to the slope with weathered granitic soil was investigated using the finite element method simulation. Numerical result indicates that the treatment can eliminate the slope failure effectively under rainfall with a hundred-year return period.

Experimental Investigation on the Influencing Factors of Compressive Strength of Foamed Lightweight Material Utilizing Completely Decomposed Granite.

The utilization of construction waste soil to produce foamed concrete together with cement and a foaming agent is a promising method for waste recycling. Completely decomposed granite (CDG), which is widely available in southern China, was selected as a typical construction waste soil in foamed material production. The Taguchi method was applied to study the influence of various parameters on compressive strength, including cement dosage, CDG dosage, water to solid materials ratio (W/M), fine particles content, and gravel particles content. Analysis of variance (ANOVA) on a CDG-based sample showed that all factors have significant effects on compressive strength and the most effective parameter was cement dosage, followed in sequence by CDG dosage, W/M, gravel particles content, and fine particles content. However, only cement dosage and W/M influence the internal structure significantly during water/vacuum-immersion tests. The relationship between micro-pore structure and compressive strength suggested that with the decrease of open porosity, the compressive strength showed an increasing trend. This study reveals the possibility of CDG as a raw material for foamed lightweight soil and provides a technical reference of production procedure.

Mechanical Behaviour of Completely Decomposed Granite Soil with Tire Rubber Granules and Fibres.

Mixing soil with waste tire rubber granules or fibres is a practical and promising solution to the problem of global scrap tire pollution. Before successful applications, the mechanical behaviour of the soil–rubber mixture must be thoroughly investigated. Comprehensive laboratory studies (compaction, permeability, oedometer and triaxial tests) were conducted on the completely decomposed granite (CDG)–rubber mixtures, considering the effects of rubber type (rubber granules GR1 and rubber fibre FR2) and rubber content (0–30%). Results show that, for the CDG–rubber mixture, as the rubber content increases, the compaction curves become more rubber-like with less obvious optimum moisture content. The effect on permeability becomes clearer only when the rubber content is greater than 30%. The shape effect of rubber particles in compression is minimal. In triaxial shearing, the inclusion of rubber particles tends to reduce the stiffness of the mixtures. After adding GR1, the peak stress decreases with the increasing rubber content due to the participation of soft rubber particles in the force transmission, while the FR2 results in higher peak stress especially at higher rubber contents because of the reinforcement effect. For the CDG–GR1 mixture, the friction angle at the critical state (φ’cs) decreases with the increasing rubber content, mainly due to the lower inter-particle friction of the CDG–rubber interface compared to the pure CDG interface, while for the CDG–FR2 mixture, the φ’cs increases with the increasing rubber content, again mainly due to the reinforcement effect.

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

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.

Mechanics of Completely Decomposed Granite: Example of Transitional Behavior

Abstract A completely decomposed granite (CDG) soil containing a significant amount of sand and silt was tested on a triaxial apparatus to determine whether it complies with the critical state fram...

Energy balance and temperature regime of different materials used in urban landscaping

In an effort to conserve water, conversion of irrigated lawns to “water-saving” landscape designs are being promoted in urban areas. Different materials, with different radiative and thermal properties, are used to accomplish this. We conducted a field study where we measured reflected spectral irradiance, albedo, energy balance, and soil and surface temperatures of grass (GR), artificial turf (AT), decomposed granite (DG), and hardwood mulch (MU) to better understand how surface temperature is controlled in landscapes composed of these materials. DG had the highest albedo and a large fraction of the reflected solar energy was in the visible band. AT had the lowest albedo and highest net radiation of the materials we tested. DG was the most efficient material in conducting energy into the subsurface, whereas MU was the least. Both AT and MU concentrated most of their thermal energy in the surface, indicating poor ability to diffuse thermal energy into the subsurface. Latent heat flux was the major component of the energy balance of GR, as expected. After GR, DG maintained the lowest surface temperature due to a combination of high albedo and high heat flux into the subsurface.

Effect of Moisture Content on the Shear Behaviour of a Completely Decomposed Granite: An Experimental Study

To figure out the effect of moisture content on the shear behaviour of undisturbed completely decomposed granite (CDG) soil, a series of in situ and laboratory direct shear tests were carried out, under different normal stress and moisture contents. The test results showed that the increasing moisture content could obviously weaken the shear strength, cohesion, and frictional angle. Two linear equations were proposed for estimating the cohesion and the frictional angle at any moisture content in the field. The estimated strength parameters could be used for safety evaluation and/or engineering design of CDG cutting slope. The rate of reduction of the cohesion was much higher than that of the tangent value of frictional angle. Due to the disturbance of laboratory sample and size effect, the strength parameters obtained from the in situ test were a little bit higher than those from the laboratory test.

Modelling the hydraulic/mechanical behaviour of an unsaturated completely decomposed granite under various conditions

Because the hydraulic/mechanical behaviour of unsaturated soil is more complicated than that of saturated soil, one of the most important issues in modelling unsaturated soil is to properly couple its stress-strain relationship with its water retention characteristics. Based on the results of a series of tests, the stress-strain relationship and the changes in suction and saturation of unsaturated completely decomposed granite (CDG, also called Masado) vary substantially under different loading/hydraulic conditions. To precisely model the hydraulic/mechanical behaviour of unsaturated Masado, in this study, the superloading concept was firstly introduced into an existing saturated/unsaturated constitutive model to consider the structural influences. Then a water retention curve (WRC) model considering the volumetric change in the soil, in which the skeleton and scanning curves of the water retention characteristics were assumed to shift in parallel in accordance with the change in the void ratio, was proposed. The proposed WRC model was incorporated into the constitutive model, and the validity of the newly proposed model was verified using the results of tests conducted on unsaturated Masado, including water retention, oedometer and triaxial tests. The accuracy of the proposed model in describing the stress-strain relationship and the variations in suction and saturation of unsaturated Masado is satisfactory.

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

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.

Influence of Degree of Compaction on Unsaturated Hydraulic Properties of a Compacted Completely Decomposed Granite

It is crucial to understand hydraulic properties, i.e., soil-water characteristic curve (SWCC) and unsaturated permeability function (UPF), of completely decomposed granite (CDG) for relevant engineering projects in southeastern China. Previous studies mainly focused on SWCCs of CDG, whereas UPFs of CDG have not yet been well understood. In this study, the effects of the degree of compaction (DOC) on SWCCs and UPFs of CDG were investigated based on experiments where suction range was from 0 to 500 kPa. The microstructure of soil specimens was then analyzed by mercury intrusion porosimetry (MIP). Furthermore, the UPFs of CDG under different values of DOC were calculated using four prediction models and compared with experimental data. Results showed that the pore volume of specimens at higher DOC was smaller than that at lower DOC, and there were more macropores observed in specimens at lower DOC. Meanwhile, it was found that increasing compaction effort produced negligible influence on the volume of micropores. When the suction was less than 100 kPa, the permeability was reduced with the increase in DOC, due to the decrease of macropore volume. However, the influence of DOC on SWCCs and UPFs became marginal when the suction exceeded 100 kPa. The Fredlund and Xing model provided the best prediction of UPF among the four models when suction was smaller than air entry value (AEV). It is suggested that these models could be improved to capture UPFs at higher suctions than AEV by considering suction-induced volume contraction.

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

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°.

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

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.

Performance of Fiber Reinforcement in Completely Decomposed Granite

Adding discrete fibers to soils can improve their strength; however, fiber reinforcement remains scarce in practice. Previous studies on the performance of soils reinforced with discrete fibers consist mainly of laboratory studies with either clay or, most often, uniform sand as the host soil, so there is a lack of data on other types of soils such as weathered soils, which tend to be well graded. Unlike uniform soils, which are generally dilative, well-graded soils usually show a contractive behavior. This study examines the effect of adding fibers to a completely decomposed granite (CDG) typical of many residual soils, which has the characteristics to be sensitive to material and sample preparation and also to be compressive during shearing. It is found that adding discrete fibers to the CDG homogenizes it because the reinforced soil is not sensitive to the method of material or sample preparation. It is also found that, despite its compressive nature, fibers mobilize extra strength compared with the unreinforced soil, and this effect does not reduce at large confining stresses. Adding discrete fibers to soils can improve their strength; however, fiber reinforcement remains scarce in practice. Previous studies on the performance of soils reinforced with discrete fibers consist mainly of laboratory studies with either clay or, most often, uniform sand as the host soil, so there is a lack of data on other types of soils such as weathered soils, which tend to be well graded. Unlike uniform soils, which are generally dilative, well-graded soils usually show a contractive behavior. This study examines the effect of adding fibers to a completely decomposed granite (CDG) typical of many residual soils, which has the characteristics to be sensitive to material and sample preparation and also to be compressive during shearing. It is found that adding discrete fibers to the CDG homogenizes it because the reinforced soil is not sensitive to the method of material or sample preparation. It is also found that, despite its compressive nature, fibers mobilize extra strength compared with the unreinforced soil, and this effect does not reduce at large confining stresses.

Estimating Spatial Variations in Bedrock Depth and Weathering Degree in Decomposed Granite from Surface Waves

AbstractIn Singapore, sudden changes of bedrock depth and highly variable weathering degrees in residual soils are commonly observed. This study employed the dispersive characteristics of Rayleigh-...

Compressive strength performance of geopolymer paste derived from Completely Decomposed Granite (CDG) and partial fly ash replacement

The compressive strength after the addition of Completely Decomposed Granite (CDG) to fly ash to initiate the polymerization reaction and to form a new geopolymer material was studied. A series of experimental test were performed on 70.7×70.7mm cubic specimens with full and partial replacement of CDG. The proportion of 0, 10, 20, 30, 50, 70, 80 and 100% of dried CDG soil was mixed with sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solution to examine the compressive strength behavior. Experimental results showed that the geopolymer paste specimen with 100% CDG as source material had a compressive strength of up to 13.89MPa. It was found that the Completely Decomposed Granite (CDG) can be synthesized with an alkaline activator and some proportion can be added into fly ash to form a high strength geopolymer mixture. It was also found that the high compressive strength of the combination of CDG-fly ash can be obtained within 7days curing period but only the CDG compressive strength will keep on increasing over time.

Interface Behavior from Suction-Controlled Direct Shear Test on Completely Decomposed Granitic Soil and Steel Surfaces

AbstractA soil-structure interface is defined as the contact surface between a soil and a structure through which stresses are transferred from the soil to the structure or vice versa. The ultimate shear strength at the interface is one of the key parameters required for the design and safety assessment of a structure in the soil, such as pile foundations, retaining walls, buried pipelines, and soil nails. In this paper, the shearing behavior of completely decomposed granite soil and steel interfaces is examined using a modified suction-controlled direct shear apparatus. A series of direct shear tests was performed on two different types of soil-steel interfaces under different stress state variables. The experimental results were used to investigate the influence of counterface roughness on the failure envelopes of soil-steel interfaces. Test results show that matric suction has a significant influence on the shear behavior and shear strength of the interfaces. It has been observed that the critical inte...

An investigation of single sand particle fracture using X-ray micro-tomography

Particle breakage is of fundamental importance for understanding the mechanical behaviour of sands and is relevant to many geotechnical engineering problems. In order to gain new insights into the mechanism of breakage of individual sand particles under single-particle compression, this study combines mechanical tests with three-dimensional X-ray micro-computed tomography (μCT) performed ‘in situ’, that is, during loading. A novel mini-loading apparatus was developed to perform in-situ compression tests within a laboratory nanofocus X-ray CT. The tests were performed on eight particles, four Leighton Buzzard sand (LBS) particles and four highly decomposed granite (HDG) particles, to study their different fracture mechanisms. A series of image processing and analysing techniques was utilised to obtain both qualitative and quantitative results. The most important factors in determining the fracture patterns of the LBS and HDG particles were found to be particle morphology and initial microstructure, respectively. Versatile fracture patterns deviating from simple vertical splitting were observed, particularly in HDG particles. The change of morphology parameters during loading was found to depend on the fracture mechanisms and material properties, independently of their initial values. The fragments of both the LBS and HDG particles satisfy the fractal distribution, which indicates that the fragmentation is scale invariant. Different energy dissipation mechanisms were found. The energy dissipation by friction gradually prevails against the energy dissipated in generating new surfaces.

울릉연화바위솔 분화재배를 위한 적정 광도, 분용토 및 시비 수준

Proper light intensity, shading tolerance, potting media, and fertilization level were investigated to develop Orostachys iwarenge for. magnus (Korean name, Ullungyeonwhabawisol) as a potted ornamental plant. The plants were grown under different light intensity (52, 82, 90, and 97% shading). The best growth was shown at 52% shading, which indicated that the proper light intensity for O. iwarenge for. magnus is less than 52% of shading. Plant growth decreased severely at 82% shading and leaf color became lighter as the shading rate increased, which indicated that O. iwarenge for. magnus has no tolerance against low light intensity. To select a proper potting media, decomposed granite (DG), fertilizer-amended media (FAM), river sand (RS) were used as potting medium with different ratio of 60:20:20 (DG:FAM:RS, v/v/v), 80:20 (DG:FAM, v/v), 60:40 (DG:FAM, v/v), and 20:80 (FAM:RS, v/v). DG:FAM:RS (60:20:20) showed the highest values in shoot fresh weight, plant width, and number of runner in potted O. iwarenge for. magnus. Fresh weight of shoot part was 16 g in DG:FAM:RS (60:20:20), which was about 2 folds of those at the other medium. At the experiment for selection of proper fertilization level, plants showed a better growth as the concentration of hyponex solution and application frequency increased. Once drenching 1 week interval of hyponex solution diluted by 1,000 folds brought the highest results in fresh weight, plant width, and runner number. Particularly, fresh weight of shoot part was 35 g at once drenching per week of 1,000 folds solution, indicating 84% improvement comparing with non treatment (19 g).