Wyniki wyszukiwania - BazTech

1

Numerical modelling of uniaxial compressive strength laboratory tests

Nguyen Phu Minh Vuong, Walentek Andrzej, Waclawik Petr, Souček Kamil, Antoniuk Michał

Journal of Sustainable Mining

|

2023

|

Vol. 22. iss. 4

280--294

EN

In the last decades, numerical modelling has been widely used to simulate rock mass behaviour in geo-engineering issues. The only disadvantage of numerical modelling is the reliability of required input data (e.g. mechanical parameters), which is not always fully provided due to the complexity of rock mass, project budget, available test methods or human errors. On the other hand, it was proven in many cases that numerical modelling is a helpful tool for solving such complex problems, especially when coupled with the results of laboratory and in-situ tests. This paper presents an attempt to determine the proper numerical constitutive model of rock and its mechanical parameters for further simulating rock mass response based on the outcomes of laboratory testing. For this purpose, the available constitutive models, including mechanical parameters, were taken into account. The simulation performance with the selected constitutive models is demonstrated by matching the numerical modelling results with the uniaxial compressive strength laboratory tests of rock samples from the Bogdanka coal mine. All numerical simulations were carried out using the finite difference method software FLAC3D.

2

Behaviour of moraine soils stabilised with OPC, GGBFS and hydrated lime

Lindh Per, Lemenkova Polina

Archives of Mining Sciences

|

2023

|

Vol. 68, no. 2

319--334

EN

This paper aims to evaluate the effects of blended binders on the development of strength in moraine soils by optimising the proportion of several binders. We tested three types of soil as a mixture of moraine soils: A (sandy clay), B (clayey silt) and C (silty clay), collected in southern Sweden. The soil was compacted using a modified Proctor test using the standard SS-EN 13286-2:2010 to determine optimum moisture content. The particle size distribution was analysed to determine suitable binders. The specimens of types A, B and C, were treated by six different binders: ordinary Portland cement (OPC); hydrated lime (Ca(OH)2); ground granulated blast furnace slag (GGBFS) and their blends in various proportions. The strength gain in soil treated by binders was evaluated by the test for Unconfined Compressive Strength (UCS) against curing time. For soil type A, the strength increase is comparable for most of the binders, with the difference in behaviour in the UCS gain. The OPC/lime, GGBFS and hydrated lime showed a direct correlation, while OPC, OPC/GGBFS and GGBFS/hydrated lime – a quick gain in the UCS by day 28th. After that, the rate of growth decreased. Compared to soil type A, Ca(OH)2 performs better on the stabilisation of soil type B. Besides, the hydrated lime works better on the gain of the UCS compared to other binders. The GGBFS/Ca(OH)2 blend shows a notable effect on soil type A: the UCS of soil treated by Ca(OH)2 performs similarly to those treated by OPC with visible effects on day 90th. Cement and a blend of slag/hydrated lime demonstrated the best results for soil type B. An effective interaction was noted for the blends GGBFS and hydrated lime, which is reflected in the UCS development in soils type A and B. Blended binder GGBFS/hydrated lime performs better compared to single binders.

3

Artificial intelligence-based modeling for the estimation of Q-Factor and elastic young’s modulus of sandstones deteriorated by a wetting-drying cyclic process

Rashid Hafiz Muhammad Awais, Ghazzali Muhammad, Waqas Umer, Malik Adnan Anwar, Abubakar Muhammad Zubair

Archives of Mining Sciences

|

2021

|

Vol. 66, no. 4

635--658

EN

In this study, a series of destructive and non-destructive tests were performed on sandstone samples subjected to wetting-drying cycles. A total of 25 Wet-Dry cycles were provided to investigate any significant change in the engineering properties of sandstones in terms of their porosity, permeability, water absorption, density, Q-factor, elastic modulus (E), and unconfined compressive strength (UCS). The overall reduction in the values of density, E, Q-factor, and UCS was noted as 3-4%, 42-71%, 34-62%, and 26-70% respectively. Whereas, the overall appreciation in the values of porosity, permeability, and water absorption was recorded as 24-50%, 31-64%, and 25-50% respectively. The bivariate analysis showed that the physical parameters had a strong relationship with one another and their Pearson’s correlation value (R) ranged from 0.87-0.99. In prediction modeling, Q-factor and E were regressed with the contemplated physical properties. The linear regression models did not provide satisfactory results due to their multicollinearity problem. Their VIF (variance inflation factor) value was found much greater than the threshold limit of 10. To overcome this problem, the cascade-forward neural network technique was used to develop significant prediction models. In the case of a neural network modeling, the goodness of fit between estimated and predicted values of the Q-factor (R2 = 0.86) and E (R2 = 0.91) was found much better than those calculated for the Q-factor (R2 = 0.30) and E (R2 = 0.36) in the regression analysis.

4

Discrepancy between measured dynamic poroelastic parameters and predicted values from Wyllie’s equation for water saturated Istebna sandstone

Knez Dariusz, Rajaoalison Herimitsinjo

Acta Geophysica

|

2021

|

Vol. 69, no. 2

673--680

EN

The drilling-related geomechanics requires a better understanding of the encountered formation properties such as poroelastic parameters. This paper shows set of laboratory results of the dynamic Young’s modulus, Poisson’s ratio, and Biot’s coef fcient for dry and water-saturated Istebna sandstone samples under a series of confning pressure conditions at two diferent temperatures. The predicted results from Wyllie’s equation were compared to the measured ones in order to show the efect of saturation on the rock weakening. A negative correlation has been identifed between Poisson’s ratio, Biot’s coefcient and confning pressure, while a positive correlation between confning pressure and Young’s modulus. The predicted dynamic poroelastic rock properties using the P-wave value from Wyllie’s equation are diferent from measured ones. It shows the important infuence of water saturation on rock strength, which is confrmed by unconfned compressive strength measurement. Linear equations have been ftted for the laboratory data and are useful for the analysis of coupled stress and pore pressure efects in geomechanical problems. Such results are useful for many drilling applications especially in evaluation of such cases as wellbore instability and many other drilling problems.

5

Stabilization of fly ash and lime sludge composites: Assessment of its performance as base course material

Sahu V., Srivastava A., Misra A. K., Sharma A. K.

Archives of Civil and Mechanical Engineering

|

2017

|

Vol. 17, no. 3

475--485

EN

In the present study, two potential industrial waste materials, such as, fly ash (FA) and lime sludge (LS) that are generated in bulk quantities and poses environmental hazards were mixed and stabilized using lime (CL) and gypsum (G) in order to make them suitable for use in Civil Engineering construction applications. Different mix proportion of FA and LS stabilized with different % of CL and G were studied and tested for unconfined compressive strength (UCS), split tensile strength test (STS) and California bearing ratio (CBR) to check the suitability of prepared composite for construction industries. It is noted that the optimal composition consisted of FA and LS in 1:1 ratio, 12% CL and 1% G content. The composite was also found to be durable with no leaching of heavy metals. Further, the selected composite was further studied for the microstructural development through scanning electron microscopy (SEM) and X-ray diffraction (XRD) to understand the phenomenon of chemical process or reaction and reason for strength gain. The developed composite (50FA + 50LS + 12CL + 1G) is suggested for application as base course layer material in flexible pavements due to its good requisite strength and durability. It is further highlighted that issues of uncertainty in strength and stiffness characteristics of pavement layer materials and its implications on analysis and design of flexible pavements can be studied through reliability based approach in combination with numerical analysis and Monte Carlo simulations.