Water Content Of Rocks Research Articles

Large-scale field model testing of the effects of soft rock water content on the bearing performance of tunnel-type anchorages

Large-scale field model testing of the effects of soft rock water content on the bearing performance of tunnel-type anchorages

Study on the Influence of Temperature and Water Content on the Static Mechanical Properties of Sandstone.

The area of permafrost worldwide accounts for approximately 20% to 25% of land area. In cold-climate regions of China, which are garnering international attention, the study of low-temperature and moisture effects on rock mass mechanical properties is of significant importance. China has a wide area of cold regions. This research can provide a foundation for China's exploration activities in such extreme environments. This paper examines the mechanical behavior of rock specimens subjected to various low temperatures and water contents through uniaxial compression tests. The analysis encompasses failure modes, stress-strain relationships, uniaxial compressive strength (UCS), and elastic modulus (EM) of these specimens. Findings reveal that at lower temperatures, the rock specimens' fracture patterns transition from compressive shear failure to cleavage failure, reflecting a shift from a plastic-elastic-plastic to a plastic-elastic response. Specifically, saturated rocks exhibit a 40.8% decrease in UCS and an 11.4% reduction in EM compared to their dry counterparts. Additionally, in cold conditions, an increased water content in rocks primarily leads to vertical cracking. Under such conditions, saturated rocks show a 52.3% decline in UCS and a 15.2% reduction in EM, relative to their dry state.

Rock moisture reinforces belowground water storage under different precipitation scenarios and vegetation coverage

Rock moisture is rarely deliberated but crucial for hydrologic regulation in semiarid loess hilly regions. In this study, using in-situ monitoring observation and simulation, soil and rock moisture spatiotemporal variations under planting alfalfa and caragana were analyzed and sketched, and the water storage contributions by weathered bedrock layers (WBLs) under different rainwater scenarios were then simulated and estimated. The results showed that WBLs had apparent spatiotemporal changes in water distribution and storage with rainfall events. Under water scarcity scenarios, WBLs increased the variabilities of water storage, with an average increase of 89.9 % in alfalfa and 14.2 % in caragana, providing wider water supply boundaries for vegetation. However, higher volumetric water content was presented under relatively abundant water scenarios. The average soil water content was 0.08 cm3 cm−3 in alfalfa and 0.09 cm3 cm−3 in caragana, while the average rock water content was 0.12 cm3 cm−3 in alfalfa and 0.13 cm3 cm−3 in caragana. Profile water consumption goes to surface soil evaporation and plant transpiration over an entire growing season, while extrawater would be stored in WBLs to maintain vegetation growth during the water-scarce seasons. Moreover, water storage had a positive linear relationship with the thickness of WBLs. Rock water storage increased by 6.9 % in alfalfa and 3.7 % in caragana after adding 20 cm WBLs, while it increased by 23.6 % in alfalfa and 9.9 % in caragana after adding 50 cm WBLs. Furthermore, various exogenous rainwater simulations showed that differences in water storage were significantly increased with WBLs thickness. This study would provide new insights into the deep-rooted plant distribution planning in semiarid loess hilly regions, and could also be helpful for the rational water resources utilization and management in shallow soil areas.

Effect of water saturation on Cerchar abrasivity index (CAI) of clay-rich rocks at different scratch lengths

Predicting the cutter consumption rate of mechanical excavators using the Cerchar abrasivity index (CAI) results is possible. However, changing operational parameters in the field may cause differences between the estimated cutter consumption rate based on CAI test results and the real cutter consumption rate observed in the field. One of the essential parameters in the field that affects the cutter consumption rate is the increase in the water content of the excavated rocks. In theory, an increase in the water content of rocks is expected to reduce their abrasivity. In addition, the prediction of cutter consumption rate is based solely on CAI test results conducted on dry surfaces. However, especially during the excavation of low-strength clay-rich rocks, the excavated rock material can adhere to the cutters and block them, leading to a higher cutter consumption rate than initially predicted. This study aims to analyze the rock-pin interaction in CAI tests conducted on wet surfaces of clay-rich rocks and investigate the effect of water saturation on CAI at different scratch lengths. CAI tests were conducted on dry and wet surfaces of 20 clay-rich rocks with low strength at 10, 30, 50, and 70 mm scratch lengths, respectively. The relationships between the CAI test results obtained on dry and saturated rock surfaces were statistically analyzed for each scratch length. A positive linear correlation was found between CAI values obtained on dry (CAIDry) and saturated surfaces (CAISat) at each scratch length. The percentage variations in CAI values at each scratch length were analyzed in detail. It was found that 90 % of samples have higher CAIDry than CAISat at 10 mm scratch length. However, it was observed that as the scratch length increased, the relationship between the CAI values obtained in dry and saturated conditions changed, and the proportion of samples with CAIDry higher than CAISat decreased to 65 %, 55 %, and 25 % at scratch lengths of 30 mm, 50 mm, and 70 mm, respectively. In CAI tests conducted on saturated surfaces, it was observed that the excavated rock material adhered to the test pins, and as the scratch length increased, the increase in CAISat values was considered to be due to this situation. This study revealed the importance of considering the adhesion potential of rocks to cutters at water-saturated conditions for the accurate prediction of cutter consumption in the excavation of clay-rich rocks.

Effect of Water Content on the Impact Propensity of White Sandstone

Impact ground pressure is one of the most common dynamic disasters induced by mining activities, and water content is an important factor affecting such dynamic disasters. In this paper, uniaxial compression test, cyclic loading and unloading test, and acoustic emission test were conducted on white sandstone using RMT-150B rock mechanics test system and DS5 acoustic emission test system. The influence law of water content was analyzed on the strength characteristics, energy change characteristics, and impact propensity of white sandstone. The results showed that (1) the internal structure of the sandstone gets softened with the increase of the water content. The cohesive effect within the rock also begins to weaken, which in turn reduces the stiffness of the material and enhances its plasticity. The ability of the rock to resist elastic deformation becomes weaker, resulting in lower compressive strength and elastic modulus when the rock is subjected to external forces, making it more prone to deform and fail. The decrease in compressive strength of the water-saturated rock is 33.3%, and the decrease in its elastic modulus is 28.1% compared to the dry rock. (2) As the water content increases, the cohesion of the rock decreases and the internal structure of the rock fails more easily, which ultimately makes the energy needed for rock destruction lower. As a result, the total energy, elastic energy, and dissipative energy of the rock are reduced. The accumulated AE energy also decreases with the increase of the water content, indicating that rocks with higher water content gather less elastic energy before damage and accumulate less energy when deformation damage occurs. (3) The impact energy index and elastic energy index are negatively correlated with the water content. The impact energy index is reduced by 28.6%, and the elastic energy index is reduced by 20.9% for the saturated rock compared to the dry rock. The elastic energy index and impact energy index both decrease with the increase of rock water content, indicating that the less elastic energy is stored before the destruction of the rock and no excess energy is transformed into energy in rock crushing when the rock breaks, and therefore, the impact propensity of the rock is smaller. The results of the study can provide a theoretical basis for underground construction as well as rock fracture destabilization.

Physics-informed machine learning for understanding rock moisture dynamics in a sandstone cave

Abstract. Rock moisture, which is a hidden component of the terrestrial hydrological cycle, has received little attention. In this study, frequency domain reflectometry is used to monitor fluctuating rock water content (RWC) in a sandstone cave of the Yungang Grottoes, China. We identified two major cycles of rock moisture addition and depletion, one in summer affected by air vapour concentration and the other in winter caused by freezing–thawing. For the summer-time RWC, by using the long short-term memory (LSTM) network and the SHapley Additive exPlanations (SHAP) method, we find relative humidity, air temperature and wall temperature have contributions to rock moisture, and there is a good match between predicted and measured RWC using the three variables as model inputs. Moreover, by using summer-time vapour concentration and the difference between dew point temperature and wall temperature as input variables of the LSTM network, which belongs to physics-informed machine learning, the predicted RWC has a better agreement with the measured RWC, with increased Nash–Sutcliffe efficiency (NSE) and decreased mean absolute error (MAE) and root mean square error (RMSE). After identifying the causal factors of RWC fluctuations, we also identified the mechanism controlling the inter-day fluctuations of vapour condensation. The increased vapour concentration accompanying a precipitation event leads to transport of water vapour into rock pores, which is subsequently adsorbed onto the surface of rock pores and then condensed into liquid water. With the aid of the physics-informed deep learning model, this study increases understanding of sources of water in caves, which would contribute to future strategies of alleviating weathering in caves.

Study on the Damage Mechanism of Sandstone under Different Water Content States

Understanding the failure mechanisms of rocks that are exposed to different water contents is important for rock stability in rock engineering applications, and the quantitative analysis of rock behavior is necessary for predicting and preventing the occurrence of rock failure due to water effects. Mechanical tests using real-time acoustic emission (AE) technology were carried out to reveal the damage evolution in sandstone rocks in a dried state, natural state, and saturated state, which includes a quantitative analysis of AE characteristics and cracking properties. The testing results indicate that with the growth of water content, sandstone rocks show a decreasing trend in strength and tend to experience gentle damage with relatively fewer fractures. The crack morphology of the main fracture surfaces is quantitatively described, including a fractal dimension calculation and cracking length measurements. As the water content rises, when rock failure occurs, a higher AE b-value can be obtained, revealing an increasing proportion of large-scale cracks. The fractal dimension of the acoustic emission hit rate shows that the evolution of rock damage and deformation has self-similarity, that is, the transformation from order to disorder to order, and it is affected by different water contents. The AE waveforms of the sandstone have two dominant frequency bands (0~75 kHz and 75~150 kHz) no matter which water-bearing state they are in. The increase in rock water content has resulted in the decline of AE waveforms located in the range of 200–300 kHz, whereas the rise of AE waveforms is located in the range of 0–50 kHz. The findings of this study deepen our understanding of the mechanism behind rock failure and provide a meaningful reference for disaster assessment and control.

Experimental Investigation of the Influence of Freeze–Thaw Mode on Damage Characteristics of Sandstone

The influence of rock weathering caused by freezing–thawing on stone cultural relics cannot be ignored. For immovable stone cultural relics, different parts under different environmental conditions will be under different freeze–thaw actions and suffer different degrees of damage. In this paper, three typical freeze–thaw cycle tests of sandstone are designed, namely immersion test, capillary action test, and periodic saturation test. The macroscopic and microscopic morphologies of rock samples under different freeze–thaw cycles were analyzed. Weathering indicators such as porosity, water content, wave velocity, and surface hardness were tested, as well as uniaxial compressive strength. The variation law of weathering index and uniaxial compressive strength under different freezing–thawing cycles was obtained, and the quantitative relationship between each index parameter was further analyzed. The results show that under different freezing–thawing conditions, the apparent morphology of rock samples is different, and the trend of weathering indexes is similar, but the rate of change is different. The water content of rock has a great influence on the test results of wave velocity but has little influence on the surface hardness. The function relationship between weathering index and compressive strength under different freezing–thawing modes is similar, but the fitting parameters are different. Finally, the strength and wave velocity damage factors were used to quantitatively evaluate the degree of rock weathering. The results show that the immersion freeze–thaw damage is the highest, the periodic saturated freeze–thaw damage is the second highest, and the capillary freeze–thaw damage is the least highest. This is consistent with the field observation results. The conclusion of this paper can provide reference for the detection of stone cultural relics and provides a scientific basis for the anti-weathering protection of stone cultural relics.

A model of unfrozen water content in rock during freezing and thawing with experimental validation by nuclear magnetic resonance

The unfrozen water content of rock during freezing and thawing has an important influence on its physical and mechanical properties. This study presented a model for calculating the unfrozen water content of rock during freezing and thawing process, considering the influence of unfrozen water film and rock pore structure, which can reflect the hysteresis and super-cooling effects. The pore size distribution curves of red sandstone and its unfrozen water content under different temperatures during the freezing and thawing process were measured using nuclear magnetic resonance (NMR) to validate the proposed model. Comparison between the experimental and calculated results indicated that the theoretical model accurately reflected the water content change law of red sandstone during the freezing and thawing process. Furthermore, the influences of Hamaker constant and surface relaxation parameter on the model results were examined. The results showed that the appropriate magnitude order of Hamaker constant for the red sandstone was 10 −19 J to 10 −18 J; and when the relaxation parameter of the rock surface was within 25–30 μm/ms, the calculated unfrozen water content using the proposed model was consistent with the experimental value. • Theoretically derived formula for unfrozen water film calculation. • Considering the super-cooling effect and hysteresis effect during freezing-thawing. • The calculation model of unfrozen water content was proposed and verified by experiments.

Macro-Microscopic Deterioration Behavior of Gypsum Rock after Wetting and Its Constitutive Model Based on Acoustic Emission

Gypsum rock is highly sensitive to a water environment due to its unique physical and chemical properties, such as high solubility. After wetting, the internal microstructure of gypsum rock is damaged, and the mechanical properties deteriorate accordingly, leading to serious engineering problems for gypsum-bearing geotechnical structures. Therefore, it is particularly necessary to investigate the mechanical deterioration behavior of gypsum rock after wetting. In this paper, the mechanical behavior of gypsum rocks with different water contents were studied. The relationship between the rock water content and the water immersion time was established through the water content test. The scanning electron microscope (SEM) images of the gypsum rock after the water immersion showed that the internal microstructure of the gypsum rock became looser and more complex as the immersion time increased. The fractal dimensions of the SEM images were calculated to quantify the degree of damage to the gypsum rocks after wetting. These images showed that the degree of damage increased with the increasing immersion time, but the increase rate tended to be slow. The relationship between the rock water content and the mechanical responses of gypsum rock were established by triaxial compression tests, and the concomitant acoustic emission (AE) characteristics in the loading processes showed that the immersion time had a positive correlation with the AE frequency and a negative correlation with the AE cumulative count. Based on the AE characteristics, a damage constitutive model of gypsum rock as a function of immersion time was developed and this can reproduce the mechanical responses of gypsum rock after wetting.

The challenge of measuring rock moisture–a laboratory experiment using eight types of sensors

Surface geomorphological processes and the decay of heritage buildings are amplified by rock weathering, which mostly either requires water or is augmented by its presence. Measuring of water content in rock is, however, challenging and different scientific aims require different approaches. To find the most suitable rock moisture investigation methods, we conducted an experiment using eight types of moisture measurement (1D resistivity, 2D resistivity, TDR, borehole humidity, microwave reflectance, capacitance, IR thermography, and uranine-probes) under controlled conditions in a sandstone block that was subject to a slow wetting and drying cycle and to a series of freeze-thaw cycles. Critical evaluation of methods shows that measurement of dielectric properties as a proxy of rock water content can be recommended for most research aims whether for long-term monitoring, non-destructive measurement of surface moisture patterns, or for applications in deeper areas of rock. Moreover, observation of moisture dynamics in deeper subsurface requires either drilling inside the rock or the use of ERT. To determine the location of the subsurface evaporation front, uranine-probes and borehole humidity sensors are recommended. Lastly, the specific nature of freeze-thaw environments shows that the use of 1D resistivity and TDR can outperform other methods tested, with TDR being more reliable than resistivity but lacking in defined depth moisture fluctuations. To challenge the disadvantages of tested methods, a combination of techniques should always be considered.

Stress evolution around a TBM tunnel in swelling clay shale over four years after excavation

The old Belchen tunnel tubes in the Swiss Jura Mountains were excavated with drill-and-blast in swellable sedimentary rocks, i.e., anhydrite-rich marls (Gipskeuper) and Opalinus Clay shale (OPA). Already during construction in the 1960s both rock formations caused substantial damage to the tunnel support through high swelling pressures and heave, and in later years the tubes had to be refurbished again. Important maintenance and repair prompted the construction of a new, third Belchen tunnel tube (2016–2021) with a tunnel-boring machine (TBM).In this study we present in-situ datasets acquired to investigate the stress evolution and controlling mechanisms over more than four years at a monitoring section located in a strongly faulted OPA section of the new Belchen tunnel tube. The main datasets include time series of total radial pressure, radial strain, rock water content, rock and concrete temperatures, as well as details of the geological structures obtained from analyses of borehole logs and three-dimensional photogrammetric excavation face models. Finally, a series of idealised numerical simulations explore the impact of measured temperature variations on the measured total pressures, which confirm a strong temperature effect on radial pressures related to the setting of concrete and seasonal climatic variations.We find that in our monitoring section radial pressures on the tunnel support are very heterogeneous, i.e., they range between 0.5 MPa and 1.5 MPa, and still gently increasing 4 years after excavation. The measured pressures are 2–5 times greater than measured in the old Belchen tunnel tubes and similar in magnitude to swelling pressures obtained in laboratory tests. EDZ permeability measurements, water content evolution, and radial strain data from the tunnel invert suggest that swelling processes contribute to the long term radial pressure build-up. Thermo-elastic deformation and swelling might be superimposed by local reactivation of tectonic faults and gap grout cracking at crack-initiation stress levels.

Effect of water content on the failure pattern and acoustic emission characteristics of red sandstone

Increased water content in rocks can result in a decline in their strength and an increase in deformation, which can lead to geological disasters such as landslides and tunnel collapses. Hence, rock characteristics with respect to water content need to be investigated for the purposes of conducting risk assessments and implementing preventive measures. In this study, the influence of the water content on rock failure patterns and acoustic emission (AE) characteristics was investigated. Uniaxial compression tests and numerical simulations with the PFC2D software were used to study the evolution process of microcracks and failure patterns in red sandstones with different water contents. The increases in the water content reduced the rock strength, Young's modulus, ratio of strain to peak strain in the elastic deformation stage, maximum energy of a single AE event, and average AE energy. The red sandstone specimens in the saturated state formed a shear macroscopic fracture surface, whereas those in the natural state formed a failure pattern in which shear failures and splitting failures coexisted. The red sandstone failure pattern in the dry state remained between these two conditions. The average frequency centroid of AEs revealed the precursory characteristics for critical failures of red sandstone with different water contents. The findings of this study are useful for future risk assessment and disaster prevention studies.

Effects of meteorological factors and groundwater depths on plant sap flow velocities in karst critical zone

Determining water supply intensity of fracture/conduits is one of the difficulties involved in the research of plant transpiration water consumption in the Karst Critical Zone (KCZ). Our aims were to evaluate the effect of groundwater depth on plant sap flow velocities in KCZ. Thus, four sampled plots with different groundwater depth (GD) in boreholes KCZ7 (4 to 10 m GD), KCZ5 (2 to 9 m GD), KCZ1 (0 to 8 m GD) and KCZ3 (2 to 5 m GD), were selected, and the plant stem sap flow velocity in each plot were also monitored continuously and automatically using heat ratio techniques. The daily sap flow flux of Toona sinensis varied between 0.35 kg d−1 in KCZ3 and 1.50 kg d−1 in KCZ1. Photosynthetically active radiation (PAR), vapor pressure deficit (VPD), and gust velocity (ZWS) were the primary meteorological factors that determined the sap flow velocity of T. sinensis, which contributed to a regression equation, while the influence of GD on sap flow was complex. Most of the sap flow velocity had no obvious significant correlation with the GD; however, the sap flow velocity in four different GD showed significant differences (P < 0.05). Unit sap flow velocity changes induced by unit GD changes (Kv) in KCZ7 and KCZ1 samples was faster than that of other samples. In brief, the sap flow velocity was mainly affected by the PAR and VPD in KCZ7, KCZ5 and KCZ1 because of the sufficient epikarst water, while the sap flow velocity in KCZ3 was mainly affected by the rock water content. The karst aquifer medium and GD was the main factors causing the difference sap flow velocity in the four sample plots. This finding indicated that KCZ aquifer medium structure may have an important influence on plant water utilization.

Effect of Porosity on Uniaxial Compressive Strength in Sedimentary Rocks

The rock strength parameter is an important factor used in determining the geotechnical design in determining the stability of the underground slope or mine. One of the rock strength tests in the laboratory (intact rock) is the uniaxial compressive strength test. One of the factors that influence rock strength is the porosity of the rock itself, especially in sedimentary rocks. The rock porosity test is carried out by testing the physical properties of the rock, then a regression analysis is carried out to obtain the correlation of the effect of porosity on rock strength and the correlation between porosity and absorption considered in the analysis. The linear regression results obtained between porosity and saturated water content of rocks showed a positive correlation where the increase in porosity, the saturated water content also increased. The correlation between porosity and uniaxial compressive strength obtained a strong correlation with the power regression model as the best model compared to other regression models because it has the lowest error based on the Root Mean Square Error (RMSE). The final result is obtained by comparing the effect of porosity on rock strength, that is the higher the porosity value have the smaller porosity, so that an increase in rock porosity will reduce the strength of the rock.

Influence of water content on seismic activity of rocks mass in apatite mining in Khibiny

The authors analyze connection between the rock mass water content due to surface water (precipitation, snow melting and water bodies) and rock bursts in mines. The seismological monitoring performed from 2001 at the surroundings of the Apatite Circus and Rasvumchorr Plateau apatite deposits identified fluctuation of the general seismic background from year to year and seasonably. For these deposits, increased water content of rocks is seen as a natural trigger for rock mass seismicity during intensive rains and snow melting. The 15 year-long seismic monitoring of the apatite deposits under study has revealed regularity in a seasonal growth of seismicity during snow melting and precipitations, mainly in spring months. Particularities of geodynamical event occurrence allow a conclusion on the ultimately stress state of the upper earth’s crust in whole in the deposits’ vicinities. Reactivation of tectonic disturbances and weakened rock mass zones occurring due to relief of normal compression during infiltration can be a potential principal mechanism of seismic activation of the rock mass during the increased water content periods. The origin of the events observed is linked with the dynamic release of ultimate rock mass stresses when geomechanical conditions change under the action of hydrostatic pressure on tectonically disturbed zones. The authors make a conclusion on necessity to apply the revealed regularities of impact of natural factors on rockburst hazard when planning mining operations and performing geomechanical monitoring.

Influence of rainfall on transient seepage field of deep landslides: A case study of area II of Jinpingzi landslide

Rainfall is one of the primary factors that induce landslides. Rainfall infiltration forms a transient seepage field in slopes, thereby leading to an increase in water content, a decrease in matric suction, and an increase in the volume weight of slopes. The increase in water content in rock and soil leads to the degradation of the mechanical properties of the slope medium and reduces the shear strength, thus causing slope instability. In this study, a large-scale accumulation landslide is taken as the research object. The front edge of the landslide is high and is not eroded by river water. Hence, rainfall is regarded as the main external factor that changes the groundwater and seepage field of the landslide. According to the landslide’s topography, geological data, local rainfall, and hydrological monitoring results, the saturated–unsaturated seepage theory of rock and soil and the finite difference method are used to analyze the impact of rainfall on the landslide’s seepage field and groundwater. The evolution law of the transient seepage field of the landslide under the condition of rainfall duration is studied. The results provide a basis for the analysis of landslide deformation and stability.

Electromagnetic-heating enhancement of source rock permeability for high recovery

Source rock shales have permeability in the nano-Darcy range and require drilling long horizontal wells and extensive hydraulic fracturing to commercially produce hydrocarbons. Recently, an electromagnetic (EM) thermal method was proposed as a primary, or secondary, stimulation method to produce light hydrocarbons from extremely tight reservoirs. This method was based on the fact that EM heating rapidly elevates the pore-water pressure in tight rocks to fracture the reservoir. Since only the in-situ pore-water is needed, this is considered to be a water-free stimulation method, which is especially desirable for regions with limited water resources. Herein this further study provides an in-depth and quantitative investigation of the effects of laboratory EM stimulation on the permeability of the source rock shales under hydrostatic confinement and its dependence on the rock water content. In order to maintain hydrostatic pressure, a special pressure cell was built using nearly microwave transparent materials. Permeability of the samples before and after EM stimulation was acquired using a novel method capable of simultaneously measuring both matrix and fracture permeability. Microwave heating was found to generate extensive fractures in the source rock samples with a moderate amount of pore-water, which resulted in an increase of more than three orders of magnitude in permeability. This study provides further comprehensive evidence suggesting that EM thermal stimulation can be an efficient production method for source rock reservoirs and can result in both a high recovery rate and large estimated ultimate recovery of hydrocarbons.

Prediction of unconfined compressive strength and deformation modulus of weak argillaceous rocks based on the standard penetration test

Standard penetration test is often used as an index for prediction of geomaterial elastic and strength properties. It consists of releasing a 63.5 kg hammer from a specified distance of 762 mm on a series of connected drill rods. The N-value is defined after a total 457 mm of penetration is achieved by counting the below counts for the last 300 mm of penetration. This required penetration is not often achieved in weak rocks due to their relatively large compressive strength. To eliminate the need for achieving a total required 457 mm of penetration, a novel approach is introduced where the rate of penetration of the split spoon sampler is used for the characterization of the engineering properties of the weak argillaceous rocks. The rate of penetration is defined as the slope of the final segment of the blow count versus penetration plot. The test results show that the average penetration rate at each test depth approaches a relatively constant value as the penetration increases. It is found that penetration rate is affected by the unconfined compressive strength, deformation modulus, and water content of the rock mass as well as the mean effective stress at the elevation of each test. Using in situ tests from 21 weak rock sites in Illinois, United States, models are proposed for the prediction of deformation modulus and unconfined compressive strength based on the penetration rate. The models account for the influence of mean effective stresses and the in situ water content of rock.

Weakening effects of the presence of water on the brittleness of hard sandstone

The weakening effects of increasing the water content in rocks have been studied extensively in a wide variety of rock types over the past few decades. High energy release is typically characteristic of rock burst hazards. However, few studies have investigated the mechanism of water involved in rock bursts from the perspective of energy distribution based on the water content. Therefore, in this study we investigated the evolution of microcracks in hard sandstone determined from triaxial tests combined with an acoustic emission analysis for different water contents and confining pressures. Then, the weakening effects of water on the brittleness of the rock were studied from an energy viewpoint. The study shows that the capacity of the storage energy of hard rock decreases due to the dissipation of internal elastic energy in the compression stage in the presence of water. These results revealed the mechanical and energetic mechanisms that caused the weakening effects induced by water on rock burst and can contribute to design and construction improvements in tunnel engineering.