The effect of moisture on some mechanical properties of rock

doi:10.1016/0167-9031(90)90158-O

Mining Science and Technology

Volume 10, Issue 2, March 1990, Pages 145-156

Mining Science and T...

https://doi.org/10.1016/0167-9031(90)90158-O Get rights and content

Abstract

For the effective working of mine rocks, breakage of fragments from the solid rock of the working face is generally necessary. The reduction in strength of rock due to increase in moisture content can be used to advantage if drilling and blasting operations are well planned. The results of the reported investigations show that the effect of moisture on the mechanical properties, within certain values of relative saturation, is one of the rock attaining a stable minimum or maximum strength. It is also established that rocks have lower strength during a rainy season than during a snowy season.

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X-ray diffraction and SEM scanning are conducted to examine the alterations in sandstone under different saturation conditions to reveal the water-rock softening effect on sandstone from the Qilicun tunnels in China under varying saturation pressures. The mechanisms underpinning the strength softening of sandstone are analyzed using uniaxial compression tests. The experimental results demonstrated that after immersion in water, the internal cementing material within the sandstone dissolves, and the mineral particles fragment or disintegrate, increasing porosity. In the presence of water, the macroscopic compressive strength of sandstone exhibits a declining trend. Concurrently, as the saturation pressure escalates, the compressive strength diminishes by approximately 10%, the elastic modulus decreases by about 30%, and Poisson's ratio incrementally falls by about 25%. The sandstone's failure is characterized by both axial multiple splitting surface failure and shear failure surface. Finally, a strain-softening numerical model is employed to simulate the failure behaviors of sandstone under various saturation pressures. The findings indicated that the sandstone sample exhibits plastic failure characteristics under high saturation pressure.
Experimental investigation on multiscale damage characteristics of plagioclase amphibolite under water immersion
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Water immersion significantly influences the mechanical characteristics of rock materials, with the degradation of these properties often leading to engineering hazards. Understanding the micro mechanism of rock-water interaction is crucial when evaluating the mechanical behavior of a rock mass. A series of multiscale tests were conducted to investigate the micro and macro behaviors of Plagioclase amphibolite, sourced from Gansu, China, under water immersion conditions. The results indicated that the micro particles transitioned from a flake-dispersed structure in a dry state to floc clusters after 20 days of immersion. The surface micro morphology was analyzed using a laser scanning machine, revealing a transformation from a smooth state to roughness, attributed to the emergence and swelling of numerous micro humps. The evolution of parameters such as the standard deviation of the height distribution (S_q), profile area ratio(S_dr), and the root mean square of the first derivative of surface (S_dq) demonstrated that the rock expanded uniformly, with the micro grains swelling to varying degrees. NMR-based porosity testing suggested an exponential increase in damage, leading to the interconnectedness of newly formed micro-pores with neighboring ones due to water immersion. Ultimately, the water-induced porosity doubled compared to the original porosity. Additionally, the axial swelling rate exhibited a corresponding increase in tandem with the growth in porosity, with an average value of 0.141 %. Finally, linear functions were established between uniaxial compressive strength, elastic modulus, and axial swelling rate. These findings offer a comprehensive understanding of the multiscale evolution characteristics of Plagioclase amphibolite under water intrusion.
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This study investigates the alteration of felsic sandstone-type rock, which is used as a coarse aggregate in concrete, subject to the effects of gamma-ray and neutron irradiation. The effects of three gamma-ray doses (27, 55, and 108 MGy) and four neutron fluence levels (1.22, 2.19, 6.99, and 14.30 × 10¹⁹ n/cm², E ≥ 0.01 MeV) were investigated. Quartz and albite were found to be the major rock-forming minerals, with microcline intermediates, chlorite, and muscovite as the minors. Gamma rays caused no significant changes to the physical properties of the sandstone aggregates, even at high doses (108 MGy). In contrast, neutron irradiation caused alterations that became more pronounced at higher neutron fluences. The solid was confirmed to expand through metamictization of the rock-forming minerals. Quartz and muscovite were the most affected phases, whereas albite and microcline intermediates were only slightly affected, and chlorite was almost unaffected. The decrease in density was measured by He and water pycnometry, and this value was almost reproduced by calculations using the rock-forming mineral composition of the pristine sample measured using X-ray powder diffraction/Rietveld analysis and the cell volume change of the major forming minerals. In addition, light optical microscopy and scanning electron microscopy images confirmed the presence of intergranular and intragranular cracks. Intergranular cracks appeared to have initiated from the quartz grains, which expanded significantly. The intragranular cracks were frequently observed in the albite and microcline intermediates. These cracks can be described as radial cracks starting from the expanding quartz, caused by enforced displacement for deformation consistency with quartz expansion. The crack area ratio quantified by SEM image analysis corresponds to the discrepancy of the volume expansion difference calculated by He or water pycnometry and dimensional change measurements. An evaluation of solid expansion and crack openings in aggregates is important to estimate concrete degradation.
Assessing water-induced changes in tensile behaviour of porous limestones by means of uniaxial direct pull test and indirect methods
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Citation Excerpt :
Finally, global softening coefficients higher than 1 (i.e. those indicating an increase on mechanical properties caused by the saturation of the rock) have not been reported in the scientific literature. The through-the-origin linear fit performed for the dry and water-saturated UTS values (Fig. 13a) provides a KUTS number (slope of the line) equal to 0.58, which is lower than the values reported in Inada granite (i.e. KUTS = 0.92) (Hashiba and Fukui, 2015) and Indiana limestone (i.e. KUTS = 0.71) (Hawkes et al., 1973), higher than the numbers obtained in Woodkirk sandstone (i.e. KUTS = 0.49) (Ojo and Brook, 1990) and fine-grained limestone (i.e. KUTS = 0.40) (Parate, 1973), and that falls within the range of values found in andesites (i.e. KUTS = 0.42–0.66) (Hashiba and Fukui, 2015). Similarly, the line of fit that correlates the water-saturated and dry Et values (Fig. 13b) returns a global KEt number equal to 0.59, which is smaller than the values measured in Berea sandstone (i.e. KEt = 0.85) and Barre granite (i.e. KEt = 0.73), greater than the number measured in Indiana limestone (i.e. KEt = 0.51) (Hawkes et al., 1973) and quite similar to the value found in Sanjome andesite (i.e. KEt = 0.54) (Hashiba and Fukui, 2015).
Understanding the uniaxial tensile behaviour of rocks and its water-induced variation are key issues for designing effective mining and civil engineering structures and for assessing numerous geotechnical hazards. However, these aspects remain poorly analysed because conducting uniaxial direct pull tests is a difficult and time-consuming laboratory task that requires the use of sophisticated equipment and complex rock sample preparation and processing. This work attempts to expand knowledge by determining several tensile properties of three porous limestone lithotypes under dry and water-saturated conditions through two different approaches: by conducting direct tensile tests and by means of indirect methods (i.e. Brazilian and point load tests). The results revealed that water saturation generated important reductions in their uniaxial tensile strength (UTS), tensile elastic modulus (E_t), Brazilian tensile strength (BTS) and point load strength index (I_s(50)). In addition, their petrological characteristics and mineralogical composition are used to discuss the main causes of the observed tensile softening. Furthermore, highly accurate correlation functions were established between the direct tensile strength parameters (UTS and E_t) and the indirect ones (BTS and I_s(50)) for the whole set of tested rocks. The proposed relationships are a novel and useful contribution to geomechanics because they enable the estimation of pure tensile parameters using alternative, cheap, rapid and versatile tests.
Effects of water saturation and loading rate on direct shear tests of andesite
2022, Journal of Rock Mechanics and Geotechnical Engineering
Citation Excerpt :
Water is widely recognized as one of the major influencing factors on the deformation and failure of intact rock (Kirby, 1984). Several studies have revealed that uniaxial compressive strength (Dyke and Dobereiner, 1991; Vásárhelyi and Ván, 2006; Talesnick and Shehadeh, 2007), uniaxial tensile strength (Hawkes et al., 1973; Ojo and Brook, 1990; Hashiba and Fukui, 2015), and Brazilian tensile strength (Gunsallus and Kulhawy, 1984; Talesnick et al., 2001; Erguler and Ulusay, 2009) are lower in wet conditions than in dry conditions. Although these studies focused on only wet and dry conditions, Hashiba et al. (2019) and Bao et al. (2021) researched the uniaxial compressive and Brazilian tensile characteristics of rock in various situations of water saturation and clarified the relationship between the water saturation and the strength.
For estimating the long-term stability of underground framework, it is vital to learn the mechanical and rheological characteristics of rock in multiple water saturation conditions. However, the majority of previous studies explored the rheological properties of rock in air-dried and water saturated conditions, as well as the water effects on compressive and tensile strengths. In this study, andesite was subjected to direct shear tests under five water saturation conditions, which were controlled by varying the wetting and drying time. The tests were conducted at alternating displacement rates under three vertical stresses. The results reveal that the shear strength decreases exponentially as water saturation increases, and that the increase in shear strength with a tenfold increase in displacement rate is nearly constant for each of the vertical stresses. Based on the findings of the shear tests in this study and the compression and tension tests in previous studies, the influences of both water saturation and loading rate on the Hoek-Brown failure criterion for the andesite was examined. These results indicate that the brittleness index of the andesite, which is defined as the ratio of uniaxial compressive strength to tensile strength, is independent of both water saturation and loading rate and that the influences of the water saturation dependence and the loading rate dependence of the failure criterion can be converted between each other.
Failure analysis of water-bearing rock under direct tension using acoustic emission
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The potential mechanism responsible for water-weakening effects on the direct tensile failure of rocks remains poorly understood due to the difficulty of experimental control and the occurrence of multiple water-rock interactions. To obtain such knowledge, a series of direct tension tests of marble rock under dry, natural and saturated conditions, coupling with the acoustic emission (AE) signals monitoring, were conducted. Some indices, such as AE energy, the ratio of rise time to amplitude (RA) and the average frequency (AF), were unitized to investigate the micro failure process of marble rock. Test results show that the tensile strength of marble rock significantly decreases with the increase of water content, characterizing variable fracture surfaces. The cumulative AE energy released in each loading stage (i.e., entire loading stage, loading stage before peak stress, and loading stage after peak stress) significantly decreases with growing water content. The greater reduction rate of cumulative AE energy released before peak stress can be result from prominent frictional weakening effect induced by water. Also, investigation of crack classifications and failure patterns based on the polarity and AE parameter methods suggests that, the number of tensile cracks, which dominates the progressive failure process of rock under direct tension, is positively correlated to the water content. The crack classification criterion described as the optimal ratios of AF and RA values in AE parameter method is found to be affected by water content. Finally, the primary mechanism for the marble rock deterioration under direct tension is friction weakening, and the effect of pore water pressure is very limited due to the loading regime. The friction weakening effect is largely attributed to the water film but not likely to the mineral dissolution.

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The effect of moisture on some mechanical properties of rock

Abstract

Int. J. Rock Mech. Min. Sci.

Int. J. Rock Mech. Min. Sci.

Int. J. Rock Mech. Min. Sci.

Int. J. Rock Mech. Min. Sci.

Int. J. Rock Mech. Min. Sci.

Aspects of energy requirements for rock drilling

Fragmentation Principles

Hardness reducers in drilling

Trans. CSIRO

The Surface Energy of Solids

Standardised tests for determining the physical properties of mine rocks

U.S. Bur. Mines Rep. Invest. N.O. 3891

The compressive strength of coal measure rocks

Colliery Eng.

A study of the influence of petrology and physical properties on the compressive strength of coal measure rocks

U.K. Natl. Coal Board Rep.

Some engineering aspects of Brunswick Shale

The influence of moisture content on the compressive strength of rocks

Suggested methods for determination of compressive strength

Int. Soc. Rock Mech. Comm. Lab. Tests Doc.