Strength Characteristics Of Rocks Research Articles

Modified Mohr–Coulomb criterion for nonlinear strength characteristics of rocks

AbstractThe classical Mohr–Coulomb criterion has an extremely wide range of applications in the field of engineering geology, while it cannot accurately characterize rock failure under high confining stresses. Therefore, a nonlinear modification is implemented based on the Mohr–Coulomb criterion for achieving wider usage in all stress environments. The cohesion and internal friction angle are firstly calculated by regression based on the triaxial experiments of diorite and other typical rocks in different confining stress ranges, and the variation modes of cohesion and internal friction angle are then formalized and integrated into the classical Mohr–Coulomb criterion. Using the experimental results of 435 triaxial compression tests in existing publications, the predictions of the modified criterion are compared with those of the previous nonlinear criteria, which show that the predicted values of the modified criterion are in good agreement with the measured strength. Compared with the previous nonlinear criteria, the modified criterion has a wider application range and always maintains a higher accuracy.

Influence of water flow on the strength characteristics of rocks of the Lovosersk rare metal deposit

Data on the flow of water into the mine workings of the Karnasurt mine, which mines two concordant ore deposits of the Lovozero rare metal deposit, are considered. Statistical processing of the volumes of water collected by the mine over the past 4 years was carried out, with an assessment of the dynamics during the calendar year. Features associated with calendar climate changes have been identified. The main goal of the work was to assess the influence of water inflows on the strength characteristics of the rocks that make up the supporting pillars. Analysis and calculations of sedimentation within the mining allotment of the mine and the emerging water inflows into the mine workings were carried out, and they were compared with actual data on mine water. Samples of the most representative rocks of the deposit were selected and tested for compressive and tensile strength in dry and water-saturated states. The obtained data are presented in tabular form and in diagrams. Quantitative indicators of changes in the strength characteristics of rocks due to water saturation have been determined. A recommendation is given on the need to take into account the identified dependencies when calculating the stability of both supporting pillars and rock outcrops in the workings of the Karnasurt mine, which are subject to abundant water wetting.

Emphasizing the Creep Damage Constitutive Model of Hydro-Mechanical Properties of Rocks: A Case Study of Granite Gneiss

The constitutive model of rock materials can describe the mechanical behavior of rocks in creep tests. Also, it is one of the important means to study the deformation and strength characteristics of rocks in complex stress environments. This paper is based on the analysis of the porosity variation characteristics of the internal structure under the coupling effect of rock hydro-mechanical properties. The concept of the hydro-mechanical properties variable is proposed, and the relationship between the coupling variable, damage and plastic deformation is established. By introducing the coupling variable, instantaneous damage variable and time-dependent damage variable into the yield surface equation, as well as the plastic potential energy equation and the stiffness matrix of the elastic–plastic creep constitutive equation, a hydro-mechanical properties creep damage coupling model was established to simulate the creep mechanical properties of rock under coupling. Based on the triaxial creep test results of granite gneiss, the model parameters are determined. By comparing the test results with numerical results, it was revealed that the model can better describe the creep mechanical properties of rocks under the coupling effect of hydromechanical properties.

2D and 3D Modeling of Rock Mechanical Properties of Khasib Formation in East Baghdad Oil Field

Knowing the distribution of the mechanical rock properties and the far field stresses for the field of interest is an important task for many applications concerning reservoir geomechanics, including wellbore instability analysis, hydraulic fracturing, sand production, reservoir compaction, and subsidence. A major challenge with determining the rock's mechanical properties is that they cannot be directly measured at the borehole. Furthermore, the recovered carbonate core samples for performing measurements are limited and they provide discrete data for specific depths. The purpose of this study is to build 2D and 3D geomechanical models of the Khasib reservoir in the East Baghdad oil field/ Central area. TECHLOG.2015.3 software was used to build the 1D-MEM while Petrel E&P 2018.2 software was used to build the 3D distributions of rock mechanical properties. The Khasib formation has nine units (from K1 to K9). The current results support the evidence that the horizontal stresses are somewhat similar for all layers in the vertical case, but their distribution varies horizontally due to the changes in pore pressures. The pore pressure increases vertically, but its distribution within one layer is different due to the production from different wells. Elastic and strength characteristics of rock, including Young modulus, Poisson ratio, and unconfined compressive strength (UCS), have the same behavior, the highest value of the parameters appeared in the surface layer (K1). This layer is more stiff than other layers that have high porosities and high permeability. The internal friction angle for all formations ranges between 38o-40o, which gives a good harmonization with the limestone friction angle. The 3D distribution of the rock's mechanical properties revealed the carbonate heterogeneity because of its marine depositional environment and complex diagenetic processes. The findings of this study can be used for future geomechanical applications in the East Baghdad oil field including wellbore stability analysis, fault reactivation, and CO2 sequestration.

Geostatistical assessment of unconfined compressive strength of rocks in Northeast Jeddah, Saudi Arabia

The determination of rock strength holds paramount importance in the field of engineering geology. In this study, we conduct a comprehensive geostatistical evaluation of the unconfined compressive strength (UCS) within a 100 km2 area situated in northeast Jeddah, Saudi Arabia. The UCS values were indirectly estimated using an empirical equation based on the Schmidt hammer rebound method, resulting in a range of strengths from 9.2 to 198.4 MPa. The corresponding mean UCS values vary between 60.3 to 81.7 MPa, with standard deviations ranging from 18.6 to 45.3 MPa. The analysis revealed that, among the sites examined, a specific location exhibited the highest median UCS value of 72.2 MPa, while another site recorded the lowest value of 56.2 MPa. Based on the distribution of UCS values, the study area was classified into five distinct strength categories: very low, low, medium, high, and very high. Notably, the majority of variability in UCS values was confined within the middle 50% range, as evident from the interquartile range (IQR) below 30 MPa. Additionally, certain sites displayed a tighter cluster of UCS values, while an IQR of DEFJ≥60 indicated a more widespread distribution of strength values. Furthermore, two locations were identified as representing the minimum and maximum UCS values within a 95% confidence interval. The UCS in location A was estimated at 60.25±9.14 MPa, whereas in location B, it was 81.72±8.50 MPa. These findings offer valuable insights into the rock strength characteristics of the designated area, providing essential data for engineering and geotechnical applications.

Mechanical Properties and Strength Characteristics of Rock–Coal–Rock Assemblages under Different Peripheral Pressures

To investigate the deformation and damage characteristics of internal coal bodies of small pillars under different pressures, rock–coal–rock assemblage samples were subjected to the conventional triaxial compression test to analyze the mechanical behavior characteristics under different pressures. The results showed that, with the increase in peripheral pressure, the peak strength and modulus of elasticity of the assemblage specimens increased, the range of fracture compaction stage gradually decreased, and the specimen was gradually transformed from brittle to ductile. With an increase in peripheral pressure, the residual strength gradually increased, and the strength decay coefficient gradually decreased. The strength decay coefficient decreased the most at 0–10 MPa, and this decrease slowed down after exceeding 15 MPa. When the peripheral pressure was 0 MPa, the damage degree of the coal pillar was larger. With the increase in peripheral pressure, the number of cracks in the coal column increased, the damage degree increased more, and mixed damage characteristics of tension–shear were found. Based on the Hoek–Brown criterion, the strength criterion applicable to the specimen of rock–coal–rock combination was obtained through numerical fitting iteration, which provides an experimental and theoretical basis for realizing the stability control of small coal columns.

Prediction of triaxial mechanical properties of rocks based on mesoscopic finite element numerical simulation and multi-objective machine learning

The deformation and strength characteristics of rocks are crucial for the effective development of underground resources and the construction of underground engineering projects. In this study, a novel approach is proposed to predict the triaxial mechanical properties of rocks by utilizing mesoscopic finite element numerical simulation and multi-objective machine learning. First, the mesoscopic mechanical properties of rocks are obtained through microscale finite element simulations to generate a training dataset. Then, three machine learning algorithms, namely support vector regression (SVR), artificial neural network (ANN), and random forest (RF), are employed to perform multi-objective machine learning on the triaxial elastic modulus, Poisson's ratio, and compressive strength of rocks, using uniaxial elastic modulus, Poisson's ratio, tensile strength, compressive strength, and confining pressure as feature variables. The performance evaluation, based on 10-fold cross-validation, demonstrates that all three models exhibit excellent predictive capabilities, especially the SVR and RF models, which show high accuracy and correlation, respectively. Among the five feature variables, confining pressure is the most important feature, while uniaxial tensile strength is the least important feature. The absence of uniaxial tensile strength does not significantly impact the predictive performance of the models. These findings offer novel insights into the investigation of the triaxial mechanical properties of rocks.

Geomechanics Successfully Implemented in a Deepwater Setting

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202146, “Successful Implementation of Geomechanics in a Deepwater Setting: A Case Study From KG Offshore India,” by Sarah Bhimpalli, ONGC; Ashok Shinde, Baker Hughes; and Bayye L. Rao, ONGC; et al. The paper has not been peer reviewed. _ Geomechanics plays an important role in assessing formation integrity during well construction and completion. In the complete paper, study field K belongs to a Plio-Pleistocene sequence in a deepwater environment with hydrocarbon prospects. As a part of exploration activity, four existing offset oil wells were considered for geomechanical model construction. The geomechanical model for the field was built by integrating available drilling, geology, petrophysics, and reservoir data. The methodology adopted in this paper highlights how a reliable geomechanical model can be built for a field with data constraints. Introduction The present study block is in deep water off the eastern Indian coast in the KG basin, with several hydrocarbon discoveries in a clay formation. These reservoirs have been deposited under marine conditions, and source rock is thought to be Eocene to Oligocene marine shale. During drilling, as the rock on the wellbore track was drilled and brought out of the hole, the drilling fluid would exert a corresponding pressure on the wellbore wall and the stress of the rock surrounding the wellbore would be redistributed, generating induced stress. To maintain wellbore stability, use of a drilling fluid of appropriate density (mud weight) to control induced wellbore stress is essential. Shear and tensile failures are the major causes of mechanical instability in boreholes. If it rises past the appropriate upper limit, drilling-fluid pressure can cause tensile failure in the wellbore wall; if lower than the appropriate lower limit, drilling-fluid pressure can cause shear failure in the wellbore wall. Because of several drilling complications and nonproductive time experienced during the exploratory phase, building of a geomechanical model for safe and cost-effective drilling during the development phase is necessary. The existing four wells (W, X, Y, and Z) targeted the hydrocarbon play. Using the data from the four offset wells, a comprehensive geomechanical study was completed. The main objectives of the study included pore-pressure prediction, wellbore-stability analysis, well-trajectory optimization, and sanding prediction. 1D Geomechanical Modeling To analyze wellbore stability, well logs, laboratory test results, and drilling reports of the wellbore were used to determine geomechanical characteristics of the drilled formations. The elastic properties, rock strength characteristics, in-situ stresses, and pore pressures are the most important geomechanical characteristics to be measured or calculated. The geomechanical model was built by integrating drilling, geology, petrophysics, and reservoir engineering data. The work flow to build the geomechanical model is presented in Fig. 2 of the complete paper. Vertical stress (Sv) was estimated by integration of density logs from seabed to reservoir. Pore pressure was predicted using normal compaction trend (NCT) on log data. Minimum horizontal stress (Shmin) was constrained using leakoff tests (LOTs) and mini- and microfracturing data. No rock-mechanical testing data were available, and rock properties were estimated from petrophysical logs using regional experience. Magnitude and orientation of maximum horizontal stress (Shmax) was constrained using the presence of stress-induced wellbore failures on image and caliper logs.

Геомеханическое обоснование формирования зон хрупкого разрушения пород в окрестности сопряжений горных выработок рудников АО «Апатит»

Introduction. Prediction of excavations stability is an important step towards ensuring geo-mechanical safety during their construction. A reliable prediction of the stability of excavations includes such factors as the initial stress state, physical and mechanical characteristics of rocks, rock mass fracturing, and a number of others. These factors should be considered when performing calculations. The geo-mechanical conditions of the Apatite deposits are different, rock pressure can manifest itself in the form of brittle fracture of rocks, limited displacement of the rock contour, the formation of local rock failures or arching. In this paper, we consider only areas of the rock mass, where the loss of stability of the excavation contour is associated with the formation of brittle fracture zones. An analysis of methods for predicting brittle fracture zones suggests that they are devoted to their formation in the vicinity of single excavation and do not consider the formation of brittle fracture zones in the areas of excavation junctions. Despite the fact that a significant number of research papers are devoted to the formation of plastic deformation zones and the assessment of the excavation contour stability, they mainly consider two forms of geo-mechanical processes - rock failure along fractures and rock contour deformations. At the same time, little attention is paid to the formation of brittle fracture zones in the areas of excavation junctions in rocks predisposed to the development of such geo-mechanical processes. Considering the conditions of the Apatite deposits, it can be noted that the values of deformational and strength characteristics of rocks are very high. The rock mass is different in fracturing characteristics, however, the volume of rocks with excavations, which can be classified as weakly fractured, is very significant. The initial stress state of rock mass is characterized by the tectonic nature, where the magnitudes of the largest horizontal stresses are several times greater than the vertical stress component. All this makes it possible to classify the conditions of Apatite deposits as very difficult and rock burst hazardous. Methods and materials. To assess the correctness of the numerical modeling using model of brittle fracture of rocks, the following typical problems are considered: forecasting the development of brittle fracture zones in the vicinity of excavations of research laboratory in Canada; forecast of zones of brittle fracture of rocks for mining-geological and geo-mechanical conditions of the Apatite enterprises. Numerical modeling and the stress-strain state prediction in the vicinity of excavations was carried out in a generalized plane-strain formulation (three-dimensional formulation with the assignment of appropriate boundary conditions). An analysis of numerical simulation results suggests that the increase in the size of the brittle fracture zone is that greater, the larger the junction span. This effect was obtained for all four variants of excavation junction. The following results of the stress-strain state formation in rock mass in the vicinity of excavation junctions were obtained: the size of the brittle fracture zone as a whole tends to increase in the areas of excavation junctions, while the type of junction plays a significant role in its size; the higher the value of the σmax index, the more clearly the influence of the junction type on the size of the brittle fracture zone is manifested, while at the ratio σmax/σc < 0.8, the difference in the sizes of the zones in the junction and the extended section of the excavation is not significant. It was noted that the excavation junction has an impact not only on the size of the brittle fracture zone, but also on the nature of this zone formation. There is a “flow” of the brittle fracture zone from the junction area directly to the single excavation, the direction of which coincides with the direction of the maximum principal stresses. Thus, it is possible to form rock failure in the excavation located in a moderately stressed rock mass; The proposed model for predicting brittle fracture zones based on setting the functions of hardening/softening of the medium, makes it possible to effectively predict brittle fracture zones in the vicinity of excavation junctions. In general, the research results confirm the patterns of brittle fracture zones development in the vicinity of excavation junctions obtained by the authors, however, an improved model for describing the development of geo-mechanical processes in rocks prone to brittle fracture made it possible to significantly increase the reliability of predicting the shape of the brittle fracture zone near the excavation.

Strength characteristics of rock anchored by NPR bolt with different preloads

Strength characteristics of rock anchored by NPR bolt with different preloads

Determination of Strength Characteristics of Rocks in Air-Dry and Water-Saturated State

Determination of Strength Characteristics of Rocks in Air-Dry and Water-Saturated State

Morphometric parameters of sulphide ores as a basis for selective ore dressing

To assess the possibility of selective disintegration and reduction of overgrinding of hard-to-reproduce ores, optical microscopic and X-ray microtomographic studies were carried out and quantitative characteristics of morphological parameters of disseminated and rich cuprous ore samples from Norilsk-type Oktyabrsky deposit were identified. Among quantitative morphological parameters the most informative are area, perimeter, edge roughness, sphericity, elongation and average grain spacing for disseminated copper-nickel ores; area, perimeter, edge roughness and elongation for rich cuprous ores. The studied parameters are characterized by increased values and dispersion in ore zones, which is especially important for fine-grained ores, which are difficult to diagnose by optical methods. Three-dimensional modelling of the internal structure of sulphide mineralisation samples was carried out using computed X-ray microtomography, which allows observation of quantitative parameters of grains, aggregates and their distribution in the total rock volume and interrelationship with each other. The evaluation of rock pore space by computer microtomography made it possible to compare the results obtained with the strength characteristics of rocks and ores, including those on different types of crushers. The obtained quantitative characteristics of structural-textural parameters and analysis of grain size distribution of ore minerals allow us to evaluate the possibility of applying selective crushing at various stages of ore preparation

Influence of the oval hole on rock mechanical mechanism under uniaxial and biaxial compression: insights from the combined finite-discrete element method

To investigate the effects of the oval hole on the strength and the failure mechanisms of rock materials, a series of uniaxial and biaxial compression numerical simulations were carried out using the combined finite-discrete element method (FDEM). Based on the numerical simulation results, the effects of dip angle (β), major–minor ratio (ω) and position of the oval hole on rock strength characteristics crack initiation and development process and final failure modes were analysed in detail. The numerical simulation results indicate that: (1) Under uniaxial compression, the ultimate failure modes of rock containing oval holes can be mainly classified into single inclined plane shear failure, X-shaped tensile-shear composite failure and Y-shaped tensile-shear composite failure. Under biaxial compression, the ultimate failure mode is single-inclined plane shear failure dominated by shear cracks. Whether it is uniaxial compression or biaxial compression, the crack initiation position of the main fracture surface is near the end of the major axis of the oval hole. (2) Under uniaxial compression, the axial stress–strain curve of rock containing the oval hole is smooth before and after the peak, but under biaxial compression, there is obvious fluctuation in the post-peak stage due to crack initiation and propagation. In both uniaxial and biaxial compression, the pre-peak elastic stage of the axial stress–strain curve of the rock containing the oval hole is significantly shortened and the peak stress is significantly reduced compared with the intact rock, which indicates that the bearing capacity of the rock is seriously reduced by the existence of oval hole. (3) When the position and major–minor axis ratio of the oval hole remain unchanged, the uniaxial compressive strength and biaxial compressive strength increase with the increase of the dip angle of the oval hole. When the position and dip angle of the oval hole remain unchanged, the uniaxial compressive strength and biaxial compressive strength decrease with the increase of the major–minor axis ratio of the oval hole. (4) At different dip angles, the brittleness index Bi of rock containing oval holes decreases with the increase of confining pressure, and the brittleness degree shows a gradual weakening trend. At the same time, when the dip angle increases, the decreasing amplitude of brittleness index Bi decreases with the increase of confining pressure.

Application of geomechanics in the construction of horizontal wells at the fields of Embamunaigas JSC

Horizontal drilling is currently being actively developed in the near and far abroad to increase oil production, and Embamunaigas JSC is a prime example of this type of drilling in Kazakhstan. At the same time, horizontal drilling is a fairly complex and costly process, just like the construction of deep exploration wells, which requires a comprehensive approach to planning and execution of work.
 Geomechanical modelling plays a crucial role in selecting process parameters for drilling, determining optimum well design and other characteristics required to ensure wellbore integrity and overall well construction success.
 The mechanical properties model takes into account rock strength characteristics, horizontal stress directions of the geological environment and many other aspects that help make drilling safer, reduce the risk of complications and maintain borehole integrity.
 This study describes the process of creating geomechanical models for the construction of complex horizontal wells in the fields of Embamunaigas JSC based on the geomechanical core studies carried out at the S. Nurzhanov field and an analysis of the hydraulic fracturing database for the fields of Embamunaigas JSC. As a result, a safe drilling mud density range (safe drilling window) was determined and recommendations were given for the optimisation of drilling parameters and well design.

Shear Failure Mechanism and Numerical Simulation Analysis of Rock-like Materials with an Embedded Flaw

In this study, the failure characteristics of self-made rock with internal flaws under shear were studied and a numerical simulation analysis was carried out. Firstly, based on basic physical and mechanical tests, the shear strength characteristics of rocks with built-in 3D defects were summarized. PFC3D simulation software was used to model the samples with flaws, and the microscopic parameters were calibrated according to the test results. From the simulation results, it was found that the generation mode of microcracks from the flaw tip was different. The microcracks of forward shear and reverse shear were mainly generated from the horizontal direction, while the microcracks of lateral shear gradually increased from the upper and lower ends of the flaw in the opposite direction. When the peak shear strength was reached, the total number of cracks was the largest in lateral shear and the smallest in forward shear. When studying the particle velocity vector field, it was found that when reaching the peak shear strength, the particles on both sides of the prefabricated flaw appeared to be in vortex motion. When α = 45° and σn = 2 MPa, the failure mode of forward shear and lateral shear was shear-tensile-shear (S-T-S), and that of reverse shear and the intact specimen was shear-shear-shear (S-S-S). The lateral shear tensile effect was the most obvious and was mainly concentrated in the middle part of the sample.

Activation of exogenous processes within the Kama region local structures of the red-colored terrigenic formation

Introduction. On the example of a number of exogenous processes that are essential in the formation of engineering-geological conditions, the dependence of their activation on the intensity of tectonic fracturing within local structures is shown. The reason for the activation of these processes was the previous stages of hypergenesis, which led to a decrease in the strength characteristics of rocks during the formation of local tectonic structures and the emergence of high stress zones in massifs. Research objective is to evaluate the role of local structures tectonic fracturing in the activation of exogenous geological processes and confirm the correctness of their relationship. Methods of research consist in analyzing the location of exogenous processes activation zones within local structures and comparing these zones with areas of intense fracturing. The correctness of unfavorable areas identification was controlled by changes in the state of rocks and by fracture maps built according to a previously developed technique. Results obtained made it possible to confirm the previous conclusions about the influence of tectonic fracturing on hypergenesis processes activation at the level of the state of the rocks that make up the massif, which eventually became the cause of exogenous processes activation in the same areas of intense fracturing. The research findings make it possible to use the method of identifying zones of high fracturing and hazardous geological processes activation as the basis for large-scale engineering-geological zoning in massifs under similar conditions.

Ultimate state criteria and strength characteristics of the rock massifs being undermined repeatedly

Methodological approaches to the selection of ultimate state criteria and strength characteristics of the repeatedly undermined rock massifs were developed. These approaches were designed to provide parametric support to the geomechanical modelling of the massif stress-strain state and the mining systems of the Starobin potash deposit mine fields planned for the additional mining of the mineral reserves left. It was established that a complex criterion must be used to study the massif ultimate state. Determination of such criterion can be carried out using the developed approaches. The first approach is to select several criteria that evaluate the massif ultimate state by certain types of the massif stress-strain state. These criteria are the following: the criterion of the maximum normal stresses, criterion of the maximum linear strains, the criterion of the maximum shear stresses and the Coulomb–Mohr failure criterion. The second approach is to construct an integrated failure state criterion for materials whose ultimate tensile and compressive stresses differ significantly. In this case, parameters characterizing the type of stress state and properties of the material are introduced. These parameters together determine the destruction character – tear or shear. To describe the rocks behavior in the extreme strength stage of deformation, it is proposed to apply deformation theory of strength using the developed strain failure criterion. When calculating the strength characteristics of the repeatedly undermined rock massif, it is recommended to use a structural attenuation coefficient as the product of several factors, taking into account various types of disturbances in the primary undermined massif and the time factor. The Coulomb–Mohr strength condition is recommended to be used taking into account the composite structural attenuation coefficient. Dependencies have been developed to describe the change in the strength characteristics of rocks in the undermined massif, considering the attenuation coefficient.

Physical Investigation of Deformation Behaviour of Single and Twin Tunnel under Static Loading Condition

This paper presents a new testing method for the problems encountered in field testing. To this end, single-tunnel and twin-tunnel small-scale rock models are prepared in the laboratory. A new methodology is proposed to encounter problems that are faced during field testing. The test results show that rock strength characteristics, overburden pressure, and tunnel spacing have important effects on the stability of underground structures. For rocks with poor strength properties, the damage degree is greater. When the strength property of rock changes, the deformation value of unlined tunnels changes from 21.05% to 27.58%, while that of lined tunnels changes from 11% to 21.42%. Also, in the twin tunnel, the deformation value reduces from 20% to 15.78% when the spacing between the tunnels is increased. For the measurement of stress and deformation in tunnels, the results obtained from experiments are analyzed. The method adopted in this study helps determine the tunnel’s design parameters to make it safe under overlying static loads. Finally, the key factors affecting the stability of underground structures are determined by simulating the field conditions through experimental research.

Seepage Damage Statistical Model of Filled Fractured Rock considering Structural Surface and Failure Characteristic

Damage theory studies the whole process of initiation, propagation, and instability of microcracks in materials and provides an important basis for the estimation of the risk of materials. Therefore, it is assumed that the rock microunit strength is the damage variable of the medium and obeys the Weibull distribution. According to the tensile failure characteristics of filled fractured rock under the action of seepage stress, the maximum tensile strain criterion is used to define the rock microunit strength parameters, and the equivalent elastic modulus of the fractured rock is used to establish a new damage statistical model. This paper mainly studies the rationality and feasibility of using this new constitutive model to describe the seepage failure process and damage characteristics of filled fractured rock. The results indicate that (1) the accuracy of the equivalent elastic modulus is affected by the confining pressure and the characteristics of the structural surface. In the elastic phase, using the equivalent elastic modulus, E V R H has better fit. In the plastic phase, it is better to use the E V parameter. (2) The established Weibull distribution statistical model can better calculate the stress-strain curve of fractured rocks with weak and soluble fillings. (3) The rock strength characteristics affected by different stress conditions and different filling fracture states calculated by the model are the same as the experimental data. (4) The model using equivalent elastic modulus parameters reflects the threshold characteristics of rock failure and the damage evolution process. After comparison, it is found that the model can accurately calculate the final damage value of the fractured rock with weak and soluble filling. However, the final damage value used to calculate the fractured rock of the hydraulic material filling is much higher and inaccurate.

Investigation on strength characteristics of bio-asphalt mixtures based on the time–temperature equivalence principle

Bio-asphalt mixture is prone to strength damage due to its unfavorable high-temperature performance and anti-aging properties. In order to improve the strength of the bio-asphalt mixture, this paper selected rock asphalt to modify bio-asphalt and studied the strength characteristics of rock asphalt modified bio-asphalt mixture. First, the neat asphalt mixture, rock asphalt modified asphalt mixture, bio-asphalt mixture, and rock asphalt modified bio-asphalt mixture were prepared. After that, the indirect tensile strength (ITS) tests at different temperatures and various loading rates were conducted. Based on the test results, linear function and Sigmoidal function were used to establish prediction models of four asphalt mixtures strength. Finally, the strength behavior of four asphalt mixtures was compared and analyzed according to the master curve. The test results indicated that the strength of the four asphalt mixtures increases with the increase in the loading rate and decreases with the increase in the temperature. Compared with the bio-asphalt mixture, the strength of the rock asphalt modified bio-asphalt mixture was better, proving the feasibility of the rock asphalt modification technology. Compared with the linear function, the master curve determined by the Sigmoidal function is smoother. The fitting correlation coefficient by the Sigmoidal function is higher than that by the linear function. The strength prediction model proposed in this study can effectively predict the strength of the asphalt mixture outside the test range through limited test data, which provides a test basis for applying bio-asphalt mixture in pavement design under different climate and traffic load conditions.