Study on Mechanical Characteristics and Failure Modes of Coal–Mudstone Combined Body with Prefabricated Crack

There are normally pre-existing cracks that can be observed in the coal seam and immediate roof that influences the stability of the rib spalling and the movement law of overlying strata. In this study, comprehensive research methods (e.g., theory analysis, experimental tests and numerical simulations) were adopted to reveal the mechanical characteristics, acoustic emission behaviors and failure modes of a coal–mudstone combined body with a single prefabricated non-penetrating crack. The results show that the influence of the crack angle on the elastic modulus of the coal–mudstone combined body samples was limited. With the increase in the crack angle, the unconfined compressive strength of samples decreased first and then increased in a V-shaped trend. In addition, the minimum unconfined compressive strength could be observed at a crack angle of 45°. Moreover, the number of acoustic emissions significantly increased with the process of continuous loading. In addition, the stress reduction zone could be observed in both ends of the prefabricated cracks at the initial stage of loading. The high- and low-stress zones were transformed with the process of continuous loading. Under an unconfined compression test, the failure models of the coal body part in the samples were mainly caused by shear failure, and only a few cracks occurred in the upper tip of the prefabricated cracks of the mudstone part. Therefore, airfoil cracks could be observed in the samples due to the strength difference of the coal mass and mudstone.

Assessment of Hydration Process And Mechanical Properties of Cemented Paste Backfill By Rebound Method

Backfilling mining method is a green mining method which is being used widely, nevertheless, the uniaxial compressive strength (UCS) of the cement backfill paste (CPB) on site is difficult to measure, and it is impossible to know the internal cementation, for this reason, the rebound method is improved and introduced in this paper. Standard specimens of CPB were made and cured for different curing age under standard curing conditions. The hardness test of each part of the CPB is completed, the unconfined compression test is carried out, and the functional model of the hardness of each part of the CPB is established, which was a function of radius and age. Based on the nonuniformity of the filling material, the failure mode of CPB is analyzed and verified in the test. The results show that the exponential function model is more suitable for the relationship between the external hardness and the overall strength, and this conclusion is of great significance in construction site. In addition, the corresponding relationship between hardness and local strength was calculated and verified, the results show that the simple model can predict the variation of local strength with hardness better, and the quadratic function model is the best choice.

Stabilization of Kaolin Clay Soil Reinforced with Single Encapsulated 20mm Diameter Bottom Ash Column

Ground improvement methods are used to reduce the weakness of soft clay, which is low strength and high compressibility. The stone column technique involves replacing any of the soil with crushed stone such as broken rocks or sand which is an efficient method of improving the strength parameters of soil. Bottom ash usage in materials of building will effectively decrease the buildup of the waste and hence protect the environment. This study is to determine the shear strength of kaolin soft clay reinforced with a 20 mm diameter single encapsulated bottom ash column with various lengths. The research will look into the physicomechanical qualities of the materials used, including subsoil and bottom ash. Three (3) batches of samples with each batch consists of five (5) samples were prepared by using compaction method. All kaolin samples with a diameter of 50mm and height of 100mm with single encapsulated bottom ash columns with various lengths which are 60mm, 80mm, and 100mm were tested under Unconfined Compression Test (UCT). The result illustrated that the strength of samples increases as the height and volume of encapsulated bottom ash column increases.

Study Of The Effectiveness Of The Use Of Gypsum And Volcanic Ash On Stability Of The Clay Soil Based On The CBR Value And The Unconfined Compression Test

Stabilization is one of the efforts to improve the condition of the soil which has a poor index of properties. One of the soil stabilization that is usually done is by adding chemicals to the soil. Chemicals commonly used in the form of cement, lime, bitumen. In this study, the stabilization of clay was carried out by adding gypsum and volcanic ash. The purpose of this study was to determine the value of the index properties due to the addition of 2% gypsum and volcanic ash on the clay soil, then to determine the maximum compressive strength value due to the addition of variations in stabilizing materials by testing the Unconfined Compression Test (UCT) and testing the California Bearing Ratio (CBR). ) laboratory. From the research, it was found that the original soil sample had a moisture content of 12.42%; specific weight 2.65; liquid limit 46.82% and plasticity index 29.40%. The original soil classification according to USCS is classified as Clay – Low Plasticity (CL) and according to AASHTO it is classified as A-7-6 (10). Unconfined Compression Test (UCT) values ​​for native soil and native soil plus 2% gypsum were 1.40 kg/cm2 and 1.66 kg/cm2. The laboratory CBR values ​​for soaked and unsoaked for the original soil were 4.44% and 6.28%, respectively. While the laboratory CBR values ​​soaked and unsoaked for the original soil plus 2% gypsum were 6.74% and 8.02%, respectively.The most effective results were obtained from a mixture of 2% gypsum and 10% volcanic ash with a UCT value of 2.79 kg/cm2 (an increase of 99.28%). For laboratory CBR testing, the most effective mixture was on a mixed variation of 2% gypsum and 9% volcanic ash with laboratory CBR values ​​soaked and unsoaked of 9.07% (an increase of 104.27% from the original soil) and 10 ,29% (an increase of 63.85% from the original land). The soil that has been mixed with the most effective stabilizer material, namely 2% gypsum and 9% volcanic ash is classified as Clay - Low Plasticity (CL) based on the USCS classification and is classified as A-6 (4) based on the AASHTO classification.

Rock Strain Prediction Using Deep Neural Network and Hybrid Models of ANFIS and Meta-Heuristic Optimization Algorithms

The majority of natural ground vibrations are caused by the release of strain energy accumulated in the rock strata. The strain reacts to the formation of crack patterns and rock stratum failure. Rock strain prediction is one of the significant works for the assessment of the failure of rock material. The purpose of this paper is to investigate the development of a new strain prediction approach in rock samples utilizing deep neural network (DNN) and hybrid ANFIS (adaptive neuro-fuzzy inference system) models. Four optimization algorithms, namely particle swarm optimization (PSO), Fireflies algorithm (FF), genetic algorithm (GA), and grey wolf optimizer (GWO), were used to optimize the learning parameters of ANFIS and ANFIS-PSO, ANFIS-FF, ANFIS-GA, and ANFIS-GWO were constructed. For this purpose, the necessary datasets were obtained from an experimental setup of an unconfined compression test of rocks in lateral and longitudinal directions. Various statistical parameters were used to investigate the accuracy of the proposed prediction models. In addition, rank analysis was performed to select the most robust model for accurate rock sample prediction. Based on the experimental results, the constructed DNN is very potential to be a new alternative to assist engineers to estimate the rock strain in the design phase of many engineering projects.

Improving the Characteristics of a Soft Clay Soil Using Cement Activated Low-Calcium Fly Ash

In this research, the potential improvement of some geotechnical characteristics of soft clay soil using the low Calcium fly ash was evaluated. (These characteristics include unit weight, shear strength, compaction characteristics and soil plasticity characteristics). In addition, the X-ray diffraction test was performed to measure the mineralogical changes in the soft clay soil when the low Calcium fly ash is added. The ordinary Portland cement was used to activate the fly ash. The total percent of flash and cement was10% to investigate the variation in the effectiveness of activation. The optimum moisture content that which computed by the compaction test was adopted in the rest of the experimental program. The test results revealed that the cement could be used to improve the activating of the fly ash efficiently. The maximum value of dry density was marginally affected due to activation from 1.747 to 1.738 g/cm3 along with a corresponding change in optimum water content from 17.45 to 15.5 %. The soil cohesion parameter increased from 188 to 206 kN/m2 whereas the angle of internal friction rose from about 56.7o to 59.1o. Finally, the results of the unconfined compression test reveal that the cement-activated fly ash could present better results than those obtained from a 28-days curing cement.

The Improvement of Engineering Properties of Expansive Soil using Waste Glass Powder (WGP) and Quick Lime

This study was carried out with an intention to observe any sign of improvement of expansive clayey soil due to the addition of Waste Glass Powder (WGP) with it. In this laboratory work clayey (BC) type soil has been chosen. The reason behind choosing clay is that it has many problems. The main problem is that it undergoes consolidation settlement due to the application of long-term loading. Another problem is it shrinks significantly if it is dried and expands significantly, if it absorbs moisture than exerts much pressure on the substructure. Quick Lime and Waste Glass powder is chosen to check the improvement because waste glass powder is cohesionless material and also contains silica, lime etc. Addition of cohesionless material to the cohesive soil means it will lesser the consolidation settlement and expansive nature of soil and Lime provides binding property. To investigate the traditional methods of analysing, the effect of additives on soil has been adopted i.e., conducting several tests of untreated soil and soil treated with waste glass and lime with varying percentage and then comparing the results obtained. The tests that were carried out in this study are Compaction test (Proctor test), Consolidation test (unconfined compression test). MDD and Unconfined compressive strength increases with the addition of glass powder and lime with oven dried expansive soil.

Anisotropic and age-dependent elastic material behavior of the human costal cartilage

Compared to articular cartilage, the biomechanical properties of costal cartilage have not yet been extensively explored. The research presented addresses this problem by studying for the first time the anisotropic elastic behavior of human costal cartilage. Samples were taken from 12 male and female cadavers and unconfined compression and indentation tests were performed in mediolateral and dorsoventral direction to determine Young’s Moduli EC for compression and Ei5%, Ei10% and Eimax at 5%, 10% and maximum strain for indentation. Furthermore, the crack direction of the unconfined compression samples was determined and histological samples of the cartilage tissue were examined with the picrosirius-polarization staining method. The tests revealed mean Young’s Moduli of EC = 32.9 ± 17.9 MPa (N = 10), Ei5% = 11.1 ± 5.6 MPa (N = 12), Ei10% = 13.3 ± 6.3 MPa (N = 12) and Eimax = 14.6 ± 6.6 MPa (N = 12). We found that the Young’s Moduli in the indentation test are clearly anisotropic with significant higher results in the mediolateral direction (all P = 0.002). In addition, a dependence of the crack direction of the compressed specimens on the load orientation was observed. Those findings were supported by the orientation of the structure of the collagen fibers determined in the histological examination. Also, a significant age-related elastic behavior of human costal cartilage could be shown with the unconfined compression test (P = 0.009) and the indentation test (P = 0.004), but no sex effect could be detected. Those results are helpful in the field of autologous grafts for rhinoplastic surgery and for the refinement of material parameters in Finite Element models e.g., for accident analyses with traumatic impact on the thorax.

Convergence Study for Rock Unconfined Compression Test Using Discrete Element Method

Mesh convergence is a vital issue that needs to be addressed in a numerical model. This study investigated the effects of mesh element number on the Discrete Element Method (DEM) to granite rock response under compression loading. This study used the 3D finite-element code LS-DYNA to model the Unconfined Compression Test (UCT) numerical simulation. Models with five different mesh types were conducted for convergence mesh, namely normal mesh, fine mesh, super fine mesh, coarse mesh, and super coarse mesh. The mesh convergence of rock media has been conducted using DEM and steel plates simulated using the Finite Element Method (FEM). The DEM-FEM numerical analysis is compared with the results obtained from the experimental test. The best mesh was obtained as the simulation could reproduce the stress-strain curve trends, the failure behaviour and compression strength observed in the experimental test. The normal mesh was selected as the best mesh type in this study based on the comparisons that have been made. This study shows that the DEM-FEM numerical simulation can represent granite rock and can be used for further study based on mesh convergence.