Rock Stiffness Research Articles

Optimized gradient boosting models and reliability analysis for rock stiffness [formula omitted]

The Extreme gradient boosting algorithm XGBoost has been confirmed to be an accurate method for predicting rock stiffnesses and anisotropic parameters from basic input features such as rock porosity, density, vertical compression stress, pore pressure and burial depth (Nguyen-Sy, T., To, Q.D., Vu, M.N., Nguyen, T.D. and Nguyen, T.T., 2020. Study the elastic properties and the anisotropy of rocks using different machine learning methods. Geophysical Prospecting, 68(8), 2557–2578). This study has the following contributions: reducing the R2-error score (that is, 1-R2) by 35 %, RMSE by 21 % and MAE by 16 % comparing to the previous study by considering an advanced CatXG hybrid boosting model in combination with the optimizer Optuna for predicting C13 (the most difficult stiffness to accurately predict); 2-conduct a reliability analysis for the predicted stiffness C13 with respect to the randomness of the input features. We also discuss the use of C11 or C33 as additional input features for accurately predicting C13 as well as the prediction of the related anisotropic parameter δ. This significant improvement of predicted stiffness C13 is extremely important because it encourages petrophysical engineers to use machine learning for predicting the elastic stiffnesses of rocks.

A data-driven dynamic method of downhole rock characterisation for the vibro-impact drilling system

For the real-time characterisation of an inhomogeneous impact inhibiting constraint such as downhole rock layers, an unconventional method using machine learning (ML) and drill-bit vibrations is investigated. An impact oscillator with one-sided elastic constraint is employed in modelling the bit-rock impact actions. Measurable drill-bit dynamics, such as acceleration, were acquired and processed into features and 2D-images that were later used in developing ML models capable of predicting the stiffness of impacted rock constraint. Explored ML networks include Multilayer Perceptron (MLP), Convolutional Neural Network and Long Short-Term Memory Network. Both simulation and experimental studies have been presented to validate the proposed method while using coefficient of determination (R2) and normalised mean absolute error (NMAE) as the performance metrics of the ML models. Results showed that the feature-based models had better performances for both simulation and experiment compared to the raw signal and 2D-image based models. Aside being simple and computationally less expensive, the feature-based MLP models outperformed other models having R2 values > 0.7 and NMAE values < 0.2 for both simulation and experiment, thus presenting them as the preferred ML model for dynamic downhole rock characterisation. In general, this study presents a new modality to achieving logging-while-drilling during deep-hole drilling operations such as carried out in hydrocarbon, mineral and geothermal exploration.

Fault characteristics in exhumed basement rocks; implications for understanding subsurface basement faults

We studied fault core geometry and mechanical properties of exhumed basement rocks at two localities (Storskora and Lislaskora) in Sotra Island, western Norway. We combine outcrop studies with in-situ measurements of the rock stiffness (Young's modulus) to characterize the faults. Faults were investigated both along and across strike using multiple 1D scanlines on the outcrop. Our results show that both fault core thickness and stiffness values vary along the faults. Thicker fault cores (up to 0.8 m and 1.9 m in Storskora and Lislaskora loaclities, respectively) show higher values of stiffness (Young's modulus) up to 70 GPa. The stiffness values of the fault core are generally higher than those measured on the damage zone of the faults in this area. The presence of epidote and compacted fault gouge in the fault core can cause the increase in estimated fault core stiffness. In contrast, fractures are dominant in the damage zones causing local reductions in the stiffness. A map of recent seismic events in this area shows potential seismic activities along some of the major exposed faults in the Sotra Island (e.g. Rustefjorden Fault). Based on the evidence from outcrop, inferred displacements, and interpretation of an available reflection seismic section, we found that the exposed faults could be secondary and part of the damage zone of the Øygarden Fault Complex in the east margin of the rift system in the North Sea. The results of this study could be utilized to predict the architecture and changes in rock stiffness of basement-involved faults in the subsurface.

Analysis of the dynamics of technogenic deformation processes during the development of oil and gas fields on the Earth’s surface

The need to take into account technogenic deformation processes during the development of oil and gas fields is due to their various negative consequences. The influence of the stiffness (load-bearing capacity) of rocks, including permafrost, over the developed deposit, its size and shape on the dynamics of technogenic deformation processes of drained formations and the manifestation of these processes on the daylight surface is shown. The dynamics of technogenic processes of rocks in the interwell space is described. In order to reduce the negative consequences of technogenic processes, uniform drainage of the entire area of the developed field is proposed.

Optimizing in-situ CO2 mineralisation: geomechanics and scalability in dunite and serpentinite rocks – Examples from Australia and New Zealand

The collective drive towards achieving net-zero greenhouse gas emissions by 2050 has spurred interest in engineering solutions for carbon capture and storage worldwide. One such approach involves the permanent storage of CO2 in earth-abundant Ca-, Fe-, and Mg-bearing silicate rocks and minerals as carbonates via the process of CO2 mineralisation. This necessitates a thorough understanding of carbonate conversion under geologically relevant conditions. Nevertheless, research on CO2 injection for mineralisation via naturally fractured host rocks or induced fractures, with a research emphasis on rock mechanics and stimulated reservoir volumes (SRV) within geoengineering CO2 storage, is continuously expanding. This research addresses critical challenges related to identifying favourable geographic locations for CO2 mineralisation. It specifically focuses on the abundant availability of Mg, Ca, and Fe cations for exothermic CO2 reactions and their impact on fracture conductivity during in-situ mineralisation. A comprehensive analysis of 26 dunite and serpentinite samples from diverse locations in Australia and New Zealand, including 10 from a cored drilled hole, was conducted. Quantification of divalent cation (Mg, Ca, Fe) content and cation release capacity using XRF and XRD revealed higher cation percentages in dunite samples (approximately 30 %) compared to serpentinite samples (approximately 26 %). Additionally, the study estimated the stimulated rock mass-to-CO2 sequestered ratio, RCO2, with dunite samples averaging approximately 2.20 RCO2 values and serpentinite samples averaging approximately 2.53. Geomechanical testing enabled the prediction of fracture propagation pressures during aqueous CO2 injection for in-situ mineralisation and the estimation of fracture geometries, emphasizing the role of rock stiffness in determining fracture width (averaging 6.0 mm). Furthermore, the research estimated the rock volume exposed to CO2-laden fluid during injection, particularly focusing on the GHQ-3 sample, which theoretically amounted to approximately 600 kg of rock capable of sequestering around 300 kg of CO2 for a 10 m3 fluid volume with a CO2 concentration of 1molkg−1. The study established a relationship between injected volume and CO2 uptake, suggesting the potential for significant CO2 sequestration scalability by employing horizontal wells and fracturing additional zones, thereby creating and intersecting multiple transverse fractures along a single target zone.

Time‐Dependent Deformation in the Damage Zone of the Chelungpu Fault System and Potential Stress Relaxation

AbstractHigh fracture density in fault damage zones not only reduces the elastic stiffness of rocks but may also promote time‐dependent bulk deformation through the sliding of fracture and thus alter the stress in fault zones. On comparing the damage zones of the three faults in the Chelungpu fault system encountered in the Taiwan Chelungpu fault Drilling Project (TCDP), the youngest damage zone showed pronounced sonic velocity reduction even though fracture density is the same for all three fault zones, consistent with the shorter time for velocity recovery in the youngest fault. Caliper log data showed a time‐dependent enlargement of the borehole wall at the damage zone. These damage zones record lower differential stress than the surrounding host rock, which cannot be explained by the reduced elastic stiffness in the damage zone. Stress relaxation caused by time‐dependent bulk deformation in the damage zone may be responsible for the observed low differential stress.

Study on mechanical characteristics of pipe umbrella support in shallow buried tunnels

Considering the micro-arching effect between pipe umbrella, the paper investigates the mechanical response of pipe umbrellas during tunnel excavation by simulating pipe umbrellas as Timoshenko beams on a Pasternak foundation. The finite difference method is employed to solve the deflection, bending moment, and shear force of pipe umbrellas. By analyzing and contrasting with real-world engineering monitoring data, finite element computation results, and existing theories of other researchers, the reliability of the proposed method is verified, and good agreements are observed. A new parameter δp is introduced in our method to represent the proportion of overlying load transmitted through the pipe umbrella, and influences of stiffness of the surrounding rock in front of the tunnel face, initial support stiffness, pipe umbrella design schemes, and excavation depth on the load transfer capacity of the pipe umbrella are subsequently investigated. The conclusions reveal that increases of surrounding rock stiffness, initial support stiffness, and diameter of pipe umbrellas would all enhance the stability of both the tunnel and pipe umbrellas. However, such enhancements have certain limitations. Particularly, when the excavation footage c <1 m, the pipe umbrella diameter should be specifically selected based on cases.

Influence of Radial Stiffness of Surrounding Rock on Dynamic Behaviour of End-anchored Rockbolt under Impact Loading

Influence of Radial Stiffness of Surrounding Rock on Dynamic Behaviour of End-anchored Rockbolt under Impact Loading

Microwave assistance effect for rock breaking of TBM disc cutter using the coupled method of continuum and grain-based model

Microwave-assisted rock breaking technique can significantly weaken the strength and the stiffness of hard rock, and can consequently enhance TBM efficiency as well as relieve wear of disc cutters. Understanding the mechanism of microwave-assisted rock breaking requires knowledge of the intersection and connectivity properties of freshly formed fractures below the cutter and the fracture network resulting from microwave-induced damage. In this study, a numerical approach, coupled with the grain-based model (GBM) and continuum based microwave electromagnetic analysis, for simulating the microwave-treated granite is proposed firstly. Subsequently, the numerical experiment of TBM cutter penetration is conducted with the consideration of five levels of microwave power irradiation as well as two waveguide arrangements. The temperature field and fracture behavior are analyzed to investigate the thermal damage of the granite after the treatment of the microwave. Furthermore, the reduction of peak normal force and variation of average coordination number are examined to evaluate the impact of waveguide position on the effectiveness of microwave-assisted rock breaking. The simulation results indicate that the suitable power of microwave irradiation (≥ 30 kW) can promote the rise of granite temperature directly below the waveguide, further resulting in an increase in the quantity of microcracks and noticeable damage to the rock block. When the microwave power exceeds 30 kW, the peak normal force and average coordination number progressively start to decline for the case of a waveguide port facing the centerline of a single cutter. In the case of waveguide facing the gap between double cutters, the decreasing trend of the peak normal force is similar to that under the condition of single cutter, but the starting threshold has been raised to 45 kW. When the microwave power is below 60 kW, the average coordination does not change significantly. After comparing the improvement effects of microwave-assisted rock breaking under the two waveguide arrangements, a preferred condition of the microwave for breaking is determined. The waveguide port facing the centerline of a single cutter, and the microwave power of 30 ∼ 60 kW can lead a success in a satisfactory effect in term of the reduction rate of peak normal force and average coordination number.

Hydromechanical behavior analysis of fractured vuggy carbonate rocks based on homogenization theory

Fractured vuggy carbonate rocks are important for underground water and geo-energy reservoirs due to their significant contribution on water and hydrocarbon reserves and production. A vug is a small cavity in a carbonate rock, which is relatively larger than the intergranular pore space. The presence of multiscale fractures and vugs makes the hydromechanical behavior of rocks different from that of most geological materials. The objective of this work is to develop an upscaling method to analyze the hydromechanical behavior of fractured vuggy carbonate rocks based on homogenization theory. To this end, at first a novel conceptual model named discrete fracture-vug network (DFVN) model was proposed to describe the hydromechanical behavior on the fine scale. The matrix and fractures are poroelastic domains in which Biot equations are applied. The vugs are free fluid domains governed by Stokes equations. Two domains are coupled with extended Beavers–Joseph–Saffman interface conditions. Then, an upscaled hydromechanical model was developed via two-scale asymptotic homogenization. The model consistent with classical Biot equations, but the model coefficients possess explicit formulations which can be determined by three periodicity cell problems. Subsequently, efficient numerical solutions of cell problems are provided using finite element methods. Herein, the discrete fractures are modeled as lower-dimensional interfaces between matrix elements. The proposed model and method are verified through several numerical examples and experimental data. The results show that the storage coefficient and Biot coefficient increase with the presence of fractures and vugs. The equivalent elastic stiffness of a fractured vuggy rock is majorly affected by the vugs' volume ratio. The connectivity of DFVN has an important impact on the equivalent permeability.

Detection and picking of shear wave arrival for stiffness evaluation of highly porous chalk

AbstractElastic wave velocities of compressional and shear waves propagating through sedimentary rocks are often coupled with information of bulk density to derive the rock stiffness. Acquiring the transit time of compressional and shear waves often involves manual picking of wave arrival times from wave trains recorded in the laboratory or by well‐logging tools. Picking the compressional wave arrival time is commonly accepted as straightforward. Oppositely, detecting the shear wave arrival and picking its arrival time is often troublesome because the transmitted shear wave partly converts to compressional waves and back to a secondary shear wave, concealing the transmitted shear wave arrival in the wave train. In laboratory settings, we illustrate the difficulty of shear wave detection in wave trains recorded on highly porous chalk plug samples from the Danish North Sea Basin. Wave trains were recorded on plugs dry, Tap‐water or Isopar‐L saturated during uniaxial strain compaction. The recorded shear wave trains showed two distinct features, which could be interpreted as the transmitted shear wave first arrival; we denoted them as early and late arrivals. However, as only one feature can mark the arrival of the transmitted shear wave, we propose a semi‐empirical disclosure strategy combining a graphical representation of stacked wave trains with rock physical modelling. By stacking recorded wave trains in a graphical strain–time–amplitude domain, we demonstrate that an early shear wave feature marks a converted shear to compressional to shear wave and not the transmitted shear wave. We used physical modelling to identify early shear wave features and illustrate the consequences of adopting a falsely interpreted shear wave on stiffness properties.

Effects of Quartz Precipitation on the Abundance and Preservation of Organic Matter Pores in Cambrian Marine Shale in South China

To evaluate the effects of quartz precipitation on the abundance and preservation of organic matter pores in marine shale reservoirs, the type of authigenic quartz and the source of silica, as well as the corresponding relation of the Lower Cambrian Shuijingtuo Formation shale in South China were investigated. Quartz in the Shuijingtuo shale occurs as four different types: detrital quartz, replacement of biosiliceous debris, euhedral quartz filled in interparticle pores, and microquartz dispersed in a clay matrix. Euhedral quartz (1–5 μm) and matrix-dispersed microquartz (100–400 nm) are found to be the dominant forms of authigenic quartz. The euhedral quartz accumulates along the interparticle pores, and the porous organic matter fills the interior of the space. Microquartz is mainly wrapped in porous organic matter. Two silica sources were revealed: biogenic silica and clay-derived silica. Biogenic Si is most likely the major source for authigenic quartz in the organic-rich (total organic carbon (TOC) &gt; 2.55 wt.%) samples, which accounts for 23–57 wt.% (average 35 wt.%) of the total Si. Based on petrographic observations, we posit that the precipitation of large-sized euhedral quartz in the interparticle pores most likely originated from biogenic silica in the early stage of diagenesis and that the silica for the clay matrix-dispersed microquartz is provided by biogenic silica and clay-derived silica. The observation of SEM images indicates that the precipitation of early diagenetic euhedral quartz in the interparticle pores enhances rock stiffness, and the buttressing effect can protect the organic matter pores from compaction during the late-stage burial diagenesis. In contrast, the precipitation of late diagenetic microquartz in the clay matrix can lead to a reduction in the capacity of the accommodation space to host retained petroleum, consequently leading to a reduction in the development of organic matter pores and the generation of shale gas.

Shallow subsurface investigations for soil properties at Pedas, Negri Sembilan, Peninsula Malaysia using MASW, ERT,IP, and TEM methods

ABSTRACT The development of hot spring tourism projects receives more interest in Malaysia. The country has several hot springs utilized mostly as recreational complexes. Three geophysical methods were applied (MASW), (ERT), and (TEM). Both ERT and TEM are related to the electric properties of the subsurface geological structures, whereas MASW is more sensitive to rock stiffness. The integration of results obtained is used to guide the development plans of the complex. The results indicated that the hot spring is associated with a structure characterized by low resistivity and low shear wave velocity. The study assumes that a fault is controlling the hot water path to the surface. Besides, an IP survey was conducted to differentiate between water and clay since both are characterized by low resistivity. Based on this finding, the study suggests that the site suggested for new facilities is located near the north fence as characterized by high shear wave velocity and is considerably away from the structures controlling the water flow through the hot spring. From MASW depth slices, it appears that two conjugate faults control the geothermal system at the site. The faults are intersecting at the surface location of the hot spring.

Evolving geometries, topologies, and apertures in fracture networks: Quantitative insights from lattice modeling

Fracture networks are crucial in controlling rock mass permeability. Some of the important features of the fracture networks like the density, interconnectivity, spatial distribution, and fracture apertures determine the success of the subsurface operations. Fracture networks can be studied with analogue studies, physical experiments, and numerical modeling. In this study, we analyse the evolution of a two-dimensional fracture network under gravitational and shear loads using the lattice modeling capabilities of the microstructural modeling environment “Elle”. The simulation cases include varying gravitational loads and Young’s moduli of the formations. The topological progression of the modeled fracture network from isolated to interconnected nodes depicts a realistic network evolution process. The study shows that the rock stiffness exhibits a direct correlation with the number of fractures influencing the average aperture size of the network. A higher gravity load resulted in the development of a sparse fracture network. Stiffer rock models also showed an early onset of fracturing.

Quantifying the Rock Damage Intensity Controlled by Mineral Compositions: Insights from Fractal Analyses

Since each rock type represents different deformation characteristics, prediction of the damage beforehand is one of the most fundamental problems of industrial activities and rock engineering studies. Previous studies have predicted the stress–strain behaviors preceding rock failure; however, quantitative analyses of the progressive damage in different rocks under stress have not been accurately presented. This study aims to quantify pre-failure rock damage by investigating the stress-induced microscale cracking process in three different rock types, including diabase, ignimbrite, and marble, representing strong, medium-hard, and weak rock types, respectively. We demonstrate crack intensity at critical stress levels where cracking initiates (σci), propagates (σcd), and where failure occurs (σpeak) based on scanning electron microscope (SEM) images. Furthermore, the progression of rock damage was quantified for each rock type through the fractal analyses of crack patterns on these images. Our results show that the patterns in diabase have the highest fractal dimensions (DB) for all three stress levels. While marble produces the lowest DB value up to σci stress level, it presents greater DB values than those of ignimbrite, starting from the σcd level. This is because rock damage in ignimbrite is controlled by the groundmass, proceeding from such stress level. Rock texture controls the rock stiffness and, hence, the DB values of cracking. The mineral composition is effective on the rock strength, but the textural pattern of the minerals has a first-order control on the rock deformation behavior. Overall, our results provide a better understanding of progressive damage in different rock types, which is crucial in the design of engineering structures.

Effect of mineralogy on elastic properties of the Bakken formation: A lab scale rock physics modelling

The Bakken formation in the Williston Basin, is one of the largest tight oil reserves in the U.S.A. and is currently the second largest oil producer in the nation. The Bakken formation is divided into the upper and lower shale members which comprise the source rocks, while the middle Bakken, which is a fractured silicious-carbonate formation, is the main producer. The Bakken has a complex mineralogy, composed of mainly quartz and clay in the two shale members and quartz, calcite, dolomite, and anhydrite in the middle member, along with several other minerals with lower volume fractions. Past studies have reported the importance of mineral composition in development, completion, and production from shales.In this study, the effect of mineral composition of the three Bakken members on rock elastic and velocity properties are investigated. Rock physics models were developed at macro (core) scales from data in Dunn and Mountrail Counties. The minerals' volume fractions from core XRD data were used for estimation of rock stiffness and velocities. The calculations were performed for the upper and lower Bakken (UB, LB) shales as well as the clastic and carbonate intervals of the middle Bakken (MB). Hill averaging was used to mix the non-clay members. Clays were added using both Kuster-Toksoz (K-T) model and differential effective medium (DEM) theory. The effect of fluid phase (assuming both homogeneous and patchy fluids) was applied using K-T (Kuster and Toksöz, 1974) and Gassmann equations (Gassmann, 1951) for frequency-dependent velocity estimation. For shales, Backus averaging (Backus, 1962) captured the upper and lower bounds of the data, whereas the K-T model developed for parallel and perpendicular to the laminations, allowed accurate curve fits to the lab data by changing the pore's aspect ratios to capture the pores heterogeneity exhibited in Bakken. The results showed that, In overall, the UB and LB shales, due to the presence of clay minerals, show lower properties than the MB and composed mainly of microfracures (pores). The MB is shown to have more intraparticle pores with stiffer properties. The estimated stiffness and velocity properties are valuable input data for the development, completion and production planning from future wells.

Log scale rock physics modelling to study the effect of mineralogy on elastic properties of the Bakken Formation

The Bakken Formation is a geographically extensive, organic-rich, tight formation in the Williston Basin and currently serves as the second largest producer of oil in the USA. With respect to stratigraphy, the Devonian–Mississippian-age Bakken Formation typically comprises three members: the Upper (UB), Middle (MB), and Lower Bakken (LB). Lithologically, the upper and lower members of the Bakken are dominated by shales rich in organic-carbon, which act as the source rock for oil reservoirs in the Middle Bakken. The lithology of the Middle Bakken varies widely from siliciclastic to carbonates, with multiple distinct lithofacies typically being identified in the North Dakota portion of the Williston Basin. Good knowledge of the rock properties of the various Bakken members and lithofacies are a key component of their production potential.This study is a continuation of earlier rock physics modelling, which was done at core scale. Data from one well in Mountrail County was used for estimation of rock stiffness and velocities. Rock physics models were developed at log scale to obtain knowledge of formations' elastic properties across the Bakken members, as a function of porosity and pores' fluid type and geometry. Furthermore, the effect of frequency on fluid mixing type was investigated using both homogeneous and patchy models, then fluids were incorporated into the inclusion system using K-T, DEM, or Gassmann's equations. Kerogen was added to the system as a part of the inclusion in a way that fluid was embedded into the organic-matter. Critical porosity of 30% was also applied during DEM modeling to investigate the effects of kerogen being the load-bearing and rock matrix being suspended into it for case of high kerogen content in thermally immature source-rocks. The UB and LB shales, due to the presence of clay minerals, showed lower properties than MB and composed mainly of microfracture pores. Furthermore, the conversion of kerogen into hydrocarbons lowers the overall rock properties of the Bakken shales. The MB siliciclastic intervals showed to have more of intraparticle pores (primary porosity) with stiffer properties, whereas carbonate zones exhibited fracturing (secondary porosity). The rock physics models at macro and log scale complement each other and present a full picture of formations' elastic properties. The estimated stiffness and velocity properties are valuable input data for the development of and production from future wells.

МОДЕЛЮВАННЯ ЗСУВНИХ ДЕФОРМАЦІЙ ПІД ДІЄЮ СИЛИ ТЯЖІННЯ

Nowadays, there are actual problems associated with destructive slope processes under the influence of gravity load. Indeed, gravitational slope processes, together with other erosion and tectonic processes, contribute a lot to the formation of the modern relief and at the same time very often complicate the rational using of the corresponding territory. Landslide processes can be distinguished among the most dangerous gravitational slope processes. These processes are characterized by widespread distribution and significant material losses and human casualties to which they lead. Due to its social importance and practical engineering significance, the problems of studying gravitational shear processes have a long history. Therefore, many works are devoted to these problems, but from another hand, the cases of strict mathematical and mechanical description and determination of certain quantitative mechanisms and criteria for the development of sliding gravitational processes have been considered in a rather limited way. In presented work on the base of variational finite-element method, we calculate the rotational deformation and failure criteria of a wide class of three-dimensional heterogeneous anticlinal geostructures under the gravity load conditions. The simulation results show that the shear deformation of anticlinal geostructures under the influence of gravity depends on the shape, size of the structure, and mechanical properties of the rocks that make up these geostructures. We have established that more compact geostructures are subjected to the smallest deformation. In the solid geostructures that retain elastic properties, the deformations are inversely proportional to the degree of rock stiffness, and a decreasing in the curvature radius of the geostructure leads to an inversely proportional increase in the deformation of the corresponding geostructure. We have shown that in order to maintain resistance to shear soil gravity failure, anticlinal geostructures cannot be completely composed of rocks softer than semi-solid dispersed soils. It was established that the resistance to shear gravity soil failure of heterogeneous anticlinal geostructures is mainly determined by the rigidity of the internal bearing rocks, while the influence of the stiffness of the external soft rocks is relatively insignificant and has a non-linear character.

Effect of soaking time on the geotechnical behavior for different types of sedimentary rocks in Egypt

ABSTRACT Weathering problems of weak sedimentary rocks, especially when subjected to water immersion, are considered one of the serious geotechnical engineering issues. Examples of rock water submersion include foundations subject to seepage, regular irrigation, residence daily activities, service water, frequent plant watering, an increase in groundwater level and heavy rain, in addition to numerous urban and rural water use consequences; hence, it is necessary to quantify the effect of water on the physical and mechanical characteristics of sedimentary rocks. The objective of this study is to assess, evaluate and estimate the strength and stiffness of deterioration of sedimentary rocks in Egypt subject to freshwater soaking in three states (natural/presoaking state, after 48 h and after 30 days of soaking). An extensive laboratory testing program including slake durability, uniaxial compression and point load tests was conducted in the three states on sandstone and limestone specimens collected from Galala, Attaka-Suez Governorate, Egypt. The influence of water immersion on the physical and mechanical characteristics such as rounding, stress–strain envelope, strength and stiffness was studied. The results showed a reduction of up to 87% and 93% in the uniaxial compressive strength and elastic modulus, respectively, post 30 days of freshwater soaking. The limestone showed more resistance to deterioration compared to the sandstone. The stiffness and strength of sedimentary rocks decrease with long contact with water. This paper results provide guidance when assessing, planning and preliminarily evaluating similar rock formation/s considered as a candidate for engineering projects.

A Review of the Force-Transferring Mechanism of Entirely Grouted Cable Tendons Performed with Experimental Pull Tests

Entirely grouted cable tendons are commonly used in mining engineering. They have superior working ability in reinforcing the excavated rocks and soils. During the working process of cable tendons, the force-transferring ability and the corresponding mechanism are significant in guaranteeing the safety of underground openings. To further understand the force-transferring mechanism of entirely grouted cable tendons, this paper provided a literature review on the force transfer of cable tendons. First, the force-transferring concept of entirely grouted cable tendons was summarised. The force-transferring process and failure modes of cable tendons were illustrated. Then, the experimental test program used in testing the entirely grouted cable tendons was summarised. The advantages and disadvantages of various test programs were illustrated. After that, the working ability of entirely grouted cable tendons was reviewed. The effect of various parameters on the working ability of cable tendons was summarised and compared. These parameters include the rock stiffness, embedment length, cement grout property, resin grout property, modified geometry, borehole size, rotation and pre-tensioning. Last, a discussion was provided to elaborate the working ability and force-transferring mechanism of entirely grouted cable bolts. This literature review is beneficial for researchers and engineers, furthering their understanding of the working ability of cable tendons.