Stress-strength Ratio Research Articles

Integrated approach of predicting rock stability in high mountain valley underground caverns

High mountain valleys are characterized by the development of intricate ground stress fields due to geological processes such as tectonic stress, river erosion, and rock weathering. These processes introduce considerable stability concerns in the surrounding rock formations for underground engineering projects in these regions, highlighting the imperative need for rigorous stability assessments during the design phase to ensure construction safety. This paper introduces an innovative approach for the pre-evaluation of the stability of surrounding rocks in underground caverns situated within high mountain valleys. The methodology comprises several pivotal steps. Initially, we conduct inverse calculations of the ground stress field in complex geological terrains, combining field monitoring and numerical simulations. Subsequently, we ascertain stress-strength ratios of the surrounding rocks using various rock strength criteria. To assess the stability characteristics of the surrounding rocks in the 1# spillway cave within our project area, we employ numerical simulations to compute stress-strength ratios based on different rock strength criteria. Furthermore, we undertake a comparative analysis, utilizing data from the 5# Underground Laboratory (Lab 5) of Jinping II Hydropower Station, aligning the chosen rock strength criterion with the damage characteristics of Lab 5′s surrounding rocks. This analysis serves as the cornerstone for evaluating other mechanical responses of the surrounding rocks, thereby validating the pre-evaluation methodology. Our pre-evaluation method takes into account the intricate geological evolution processes specific to high mountain valleys. It also considers the influence of the initial geostress field within the geological range of underground caverns. This comprehensive approach provides a robust foundation for the analysis and assessment of the stability of surrounding rocks, especially in high mountain valley areas, during the design phase of underground engineering projects. The insights derived from this analysis hold substantial practical significance for the effective guidance of such projects.

Study on fatigue parameters of high modulus asphalt pavement

High Modulus Asphalt Mixtures (HMAM) have gained widespread utilization in asphalt pavement construction. It is great critical to study the fatigue characteristics of HMAM. At present, various fatigue test methods are employed in indoor testing to assess HMAM under different mechanical states. Therefore, there is a critical problem that the value of fatigue parameters is not unique in the structural design of HMAM. In this study, three fatigue testing methods were initially used to address the above issues: direct tensile testing, indirect tensile testing, and uniaxial compression testing. These tests help to determine the strength yield surface states at different loading rates. And to reveal the effect of loading rate on the mechanical behavior of HMAM. The results show a power function fit and a good correlation between strength and loading rate. The relationship models of strength with speed for indirect tensile, direct tensile and uniaxial compression tests are SI=3.22(v)0.14, SD=3.22(v)0.15 and SU=3.22(v)0.12, respectively.The higher the loading rate for the three fatigue test results, the greater the expansion of the strength yield surface.The fatigue life (Nf) of HMAM underwent testing, yielding its fatigue effective stress ratio. The relationship between the two was and then established. It is found that the point (1, 1) appears on the backextension line, thus effectively complementing the conventional S-N equation. In addition, the fatigue equations for various fatigue test methods were unified based on effective stress strength ratio and the fatigue life. This paper introduces a novel method for the antifatigue design of HMAM.

Multifunctional Design for Arbitrary Multiband Radome Wall Accelerated by Artificial Intelligence

A hypersonic airborne radome must possess multiband electromagnetic transparency, high specific strength, and thermomechanical resistance to ensure proper antenna operation. However, achieving these multifunctional properties in radome wall design is challenging due to conflicting material requirements. Moreover, existing design methods for arbitrary multiband and broadband hypersonic radomes are insufficient. This paper presents an efficient method that integrates artificial intelligence and an evolutionary algorithm to enable the multidisciplinary synchronous design of the radome wall. The designed radome walls using multilayered porous silicon-nitride ceramics achieve power transmission efficiency exceeding 90% in a broadband of 30 GHz or arbitrary multiple bands with bandwidths of 5 GHz, covering the centimeter-to-millimeter wave range. Moreover, the designed laminate also meets requirements of flexural strength surpassing 60 MPa and a maximum thermal stress–strength ratio below 1. Notably, the utilization of artificial intelligence accelerates the design process by at least 1093 times compared to conventional methods.

Investigation on the fracture mechanics characteristics and crack initiation of deep dense shale

The mechanical behavior of shale fractures significantly affects the structure and stability of hydraulic fracturing networks in shale gas reservoirs. Currently, there is insufficient research on the mechanical characteristics of fractures, crack initiation, and the prediction of fracture trajectories in deep dense shale. This study involved conducting direct tension, shear, and three-point bending fracture mechanical experiments on shale samples, complemented by numerical calculations and mechanistic analyses. The results show a significant influence of the bedding plane angle (γ) on the initiation properties and locations of shale fractures. With γ ranging from 0° to 90°, shale fractures transition from alignment with the bedding plane to penetration through it. Fracture initiation locations show a significant degree of randomness when fractures propagate along the bedding plane. The horizontal tensile stress changes with increasing γ, initially increasing and then decreasing as it moves away from the center. The evolution of the horizontal tensile stress field primarily causes alterations in shale fracture paths, reaching its peak value at γ = 45°. Shale initiation fractures can be classified into four types: tensile fractures through the bedding plane, tensile fractures along the bedding plane, shear fractures across the bedding plane, and shear fractures along the bedding plane. Established a criterion called the “maximum stress strength ratio” to determine fracture initiation, which can predict the initiation properties, locations, and paths of shale fractures. When γ is small, fractures mainly propagate along the bedding plane, with a higher likelihood of initiation occurring at the center of the specimen. Conversely, when γ is large, fractures mainly propagate through the bedding plane. The spacing of the bedding planes minimally affects the predicted fracture paths of shale. This study is of significant theoretical importance for reservoir stimulation and stability assessment in deep dense shale gas reservoirs.

Effects of Prestressing Magnitude and Position on Seismic Performance of Unbonded Prestressed Concrete Beams

To study the effects of the jacking stress level, height and strength ratio of the prestress tendons (λ) on the seismic performance of unbonded prestressed concrete (UPC) beams, six UPC beams and one reinforced concrete (RC) beam were tested under cyclic loads. The hysteretic characteristics, skeleton curves, ductility properties, energy dissipation capacity, strain distribution of reinforcement and self-centering capability of the specimens were studied and discussed. Numerical parameter analysis was also carried out by using OpenSees. The results indicate that three failure modes of UPC beams under cyclic loading were observed, namely the tension-failure mode involving a broken rebar, the compression-failure mode involving concrete crushing and the balanced failure. By considering the influence of the prestress position and magnitude, the modified reinforcing index ω was proposed to determine the failure mode. The ω is suggested to be less than 0.3 to ensure sufficient ductility. The effective stress level is linearly and positively related to the stiffness from cracking to yield Kcr and the ultimate bearing capacity of the UPC beam under cyclic loading. The stiffness of the UPC beam is slightly larger than that of the RC beam before yielding, and significantly greater than that of the RC beam after yielding. Due to the large strength reserve after yielding, the integrated seismic performance of the UPC beam is similar to that of the RC beam. When the λ was unchanged, the increase in the relative height of the prestressed tendons αh is beneficial for the overall performance factor F, ductility and crack control. The stiffness degradation performance depends on the λ but is independent of the αh. The total energy dissipation of the non-tensioned UPC specimen was 59% higher than that of the RC beam. The cumulative total energy dissipation of the tensioned UPC specimen was only 13% lower than that of the RC beam with the same number of cycles, indicating that the UPC specimen had a considerable energy dissipation capacity.

Research on the Modulus Decay Model under a Three-Dimensional Stress State of Asphalt Mixture during Fatigue Damage

Fatigue damage can develop within asphalt pavement due to the continuous impact of driving loads and natural elements. Understanding the process of asphalt mixtures’ fatigue damage is crucial for guiding the design, maintenance, and repair of asphalt pavement. This research aims to establish a model that characterizes the mixtures’ modulus decay under a three-dimensional (3-D) stress state. Firstly, asphalt mixes were subjected to direct tensile (DT), indirect tensile (IDT), unconfined compressive (UC) strength and fatigue tests, and the resulting data were analyzed. Then, modulus decay models under DT, IDT, and UC conditions were established, and the modulus decay patterns under the three loading modes were compared and analyzed. Finally, using the fatigue stress strength ratio Δ (a fatigue resistance index for asphalt mixtures that takes into account the impacts of stress state and loading rate), a unified characterization model for asphalt mixes’ modulus decay under a 3-D stress state was created. According to the study’s findings, asphalt mixes’ modulus decay during fatigue damage exhibits obvious nonlinear characteristics. While the asphalt mixes’ modulus decay law with various loading modalities is similar under the same conditions, the decay rate may differ. Essentially, the speed of the modulus decay of a certain asphalt mixture primarily depends on the value of Δ during service. A larger Δ indicates a faster modulus decay. This study offers a theoretical foundation for the conversion from material fatigue damage to structural fatigue damage, which is vital for enhancing the asphalt pavements’ construction quality and longevity.

Creep and strength characteristics of cemented gangue backfill under coupling effect of load and acid corrosion.

Cemented gangue backfill technology is beneficial to the reuse of solid waste and sustainable economic development. However, mine water has a great impact on the strength and deformation of cemented gangue backfill (CGB). In this study, the CGB specimens under load were placed in simulated acid mine water (H2SO4 solution). The changes in deformation, resistivity, and ultrasonic pulse velocity (UPV) of CGB were monitored. On the 360th day, the stress-strain curve and acoustic emission (AE) energy of the specimen during loading were recorded. The degradation mechanism of CGB was discussed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that the deformation of CGB increased with time. The effect of H2SO4 solution concentration on the deformation was different in the early and late stages. Applying an 80% stress-strength ratio (SSR) reduced the strength and increased the deformation. The UPV and resistivity had different characteristics at different corrosion ages, which could be used for long-term stability monitoring of CGB. The CGB showed the strongest AE energy characteristics near the peak stress. The AE energy decreased with the increase of pH value in the pore compaction stage, and the AE activity of the CGB under 80% SSR was much greater than that of the CGB under 40% SSR. The erosion of the H2SO4 solution on the CGB was inhibited by applying a small load. Excessive load aggravated the erosion deterioration of CGB due to initial plastic damage. The research results can provide a reference for the durability design of CGB.

Investigation on permanent deformation of unbound granular material base for permeable pavement: Laboratory and field study

• Deformation of Unbound Granular Materials was investigated in laboratory and field synchronously. • The confining pressures and Shear Stress-strength Ratios affect the deformation greatly. • The deformation prediction model was consistent with the trends of laboratory test results. • A deformation model based on laboratory triaxial load tests, dynamic triaxial repeated load tests and filed LWD tests was developed. Unbound Granular Materials (UGM) base is widely used in permeable pavement structure for infiltration, water storage, and load bearing. However, because of large void content, UGM base easily deforms under repeated loads, resulting in surface rutting and even reducing durability of permeable pavement. Thus, research on practical deformation prediction model of UGM base is necessary to improve the pavement structure design and evaluate the base layer construction quality. This study conducted laboratory and field tests to develop a deformation prediction model of UGM base under varied stress states. The deformation of UGM specimen was tested and analyzed through triaxial shear test and dynamic triaxial repeated load test, with varied confining pressures and Shear Stress-strength Ratios (SSR). A laboratory deformation model based on SSR was developed, and the linear relationship between total deformation and permanent deformation was obtained. The deformation of UGM base in situ was tested with Light Weight Deflectometer (LWD). The trends of laboratory deformation model and field test results were similar, and deformation prediction model for field was fitted. The values of parameters in permanent deformation model were recommended in varied stress ranges, based on mathematical analysis. Accordingly, the deformation of UGM base can be estimated. This study developed a model to estimate the permanent deformation of UGM based on deformation data from field and laboratory tests.

Structural Design and Analysis of a Super-High Building in Nanjing, China

This study analyzes a high-rise building with B-level height (i.e., a total height of 146.5 m) and a shear wall structure. Since the project contains many plane irregularities (including 1a torsional irregularity, 1b eccentric arrangement, and 2a plane convex irregularity), it should be treated as a super high-rise building. This study introduces the main characteristics and overrun conditions of the project and describes the structural design of the foundation and the basement, upper structural layout, force conditions under frequent, fortified, and rare earthquake actions, and structural performance-based objectives in detail. The following measures can be adopted to address the overrun problem. First, the floor at the thin waist of the structure was thickened to 150 mm and reinforced in the bilayer and bidirectional patterns, with a reinforcement ratio of no less than 0.25%. The damage condition on the floors under a great earthquake was analyzed. The vertical components at the waist were reinforced to constrain the extension of the edge components toward the top. Second, the structure’s peripheral stiffness was strengthened to enhance the anti-torsional performance and minimize the adverse effects on torsional irregularities. Third, using two software programs, the performance-based envelope design under medium earthquake action and dynamic elastoplastic analysis under great earthquake action were analyzed to ensure structural safety. Fourth, the edge components were constrained for the shear wall columns with axial-to-compressive stress strength ratios exceeding 0.3. For the overall structure and critical parts, force conditions under frequent, fortified, and rare earthquake conditions were calculated and examined with the SATWE, MIDAS GEN, and SAUSAGE software packages. The calculation results revealed that the structure shows favorable anti-seismic performance, with an overall anti-seismic C-level and a safe and reliable structure. The structural design method introduced in this article can promote the sustainable development of structural design.

Autogenous deformation induced- stress evolution in high-volume GGBFS concrete: Macro-scale behavior and micro-scale origin

This study aims to experimentally investigate the autogenous deformation and the stress evolution in restrained high-volume ground granulated blast furnace slag (GGBFS) concrete. The Temperature Stress Testing Machine (TSTM) and Autogenous Deformation Testing Machine (ADTM) were used to study the macro-scale autogenous deformation and stress evolution of high-volume GGBFS concrete with w/b ratios of 0.35, 0.42, and 0.50. The early-age cracking (EAC) risk (quantified by stress-strength ratio) and stress relaxation were analyzed extensively based on ADTM and TSTM results. Furthermore, Environmental Scanning Electron Microscopy (ESEM), X-ray Diffraction (XRD), and Mercury Intrusion Porosimetry (MIP) were conducted to explore the micro-scale origin of the autogenous deformation of high-volume GGBFS concrete, which supports the observations on the macroscale measurement of TSTM/ ADTM tests. This study finds that the ettringite formation in the first two days results in autogenous expansion, which can delay the appearance of tensile stress. The magnitude of autogenous expansion depends on the compatibility of ettringite content and pore size. The w/b ratio of 0.42 turns out to be optimal because it produces the highest amount of ettringite and results in the highest autogenous expansion. In comparison, the w/b ratio of 0.35 introduces significant autogenous shrinkage after the expansion peak and therefore corresponds to a high early-age cracking risk.

Biomechanics and early sac regression after endovascular aneurysm repair of abdominal aortic aneurysm

BackgroundSac regression after endovascular aneurysm repair (EVAR) of abdominal aortic aneurysms (AAA) is regarded as a marker of successful response to treatment. Several factors influence sac behavior after EVAR, yet little is known about the value of preoperative biomechanics. The aim of this study was to investigate the difference in aortic biomechanics between patients with and without sac regression. MethodsPatients treated with standard EVAR for infrarenal AAA at the Karolinska University Hospital between 2009 and 2012 with one preoperative and a minimum of two postoperative computed tomography angiography (CTA) scans were considered for inclusion in this single-center retrospective cohort study. Biomechanical indices such as AAA wall stress and wall stress-strength ratio as well as intraluminal thrombus (ILT) thickness and stress were measured preoperatively in A4ClinicRE (VASCOPS GmbH). AAA diameter and volume were analyzed on preoperative, 30-day, and 1-year CTAs. Patients were dichotomized based on sac regression, defined as a ≥5 mm decrease in maximal AAA diameter between the first two postoperative CTA scans. Multivariable logistic regression was used for analysis of factors associated with early sac regression. ResultsOf the 101 patients treated during the inclusion period, 64 were included. Thirty-nine (61%) demonstrated sac regression and 25 (39%) had a stable sac or sac increase. The mean patients age (73 years vs 76 years), male sex (85% vs 96%), and median AAA diameter (58 mm vs 58.5 mm) did not differ between patients with and without sac regression. Although no difference in preoperative biomechanics was seen between the groups, multivariable logistic regression revealed that a larger AAA diameter (odds ratio [OR], 1.27; 95% confidence interval [CI], 1.06-1.51; P = .009) and smoking (OR, 22.1; 95% CI, 2.78-174; P = .003) were positively associated with sac regression. In contrast, the lumen diameter (OR, 0.87; 95% CI, 0.77-0.98; P = .023), ILT thickness (OR, 0.85; 95% CI, 0.75-0.97; P = .013), aspirin or direct-acting oral anticoagulant use (OR, 0.11; 95% CI, 0.02-0.61; P = .012), and mean ILT stress (OR, 0.35; 95% CI, 0.14-0.87; P = .024) showed a negative association. Patients with sac regression had fewer reinterventions (log-rank P = .010) and lower mortality (log-rank P = .012) at the 5-year follow-up. ConclusionsThis study, characterizing preoperative biomechanics in patients with and without sac regression, demonstrated a negative association between mean ILT stress and ILT thickness with a change in sac diameter after EVAR. Given that the ILT is a highly dynamic entity, further studies focusing on the role of the thrombus are needed. Furthermore, patients presenting with early sac regression had improved outcomes after EVAR.

A new rockburst criterion of stress–strength ratio considering stress distribution of surrounding rock

A new rockburst criterion of stress–strength ratio considering stress distribution of surrounding rock

Research on strength and fatigue properties of asphalt mixture with different gradation curves

The gradation design has an essential influence on the mechanical properties of asphalt mixture. Strength and fatigue are two critical mechanical properties of asphalt pavement structure. The purpose of this paper is to reveal the strength and fatigue properties of asphalt mixture with four gradation curves within the range of AC-16, namely Types A, B, C, and D. Strength and fatigue tests were conducted under indirect tensile, direct tensile, and unconfined compressive loading modes. The strength of asphalt mixture with various gradation curves shows a power function relationship with the loading rate. The fatigue performance of asphalt mixture with different gradation curves was first analyzed based on the conventional S-N fatigue model. Then, the unified fatigue models under three different loading modes were established based on the fatigue stress strength ratio, which reduced the difference of S-N fatigue equation parameters. Furthermore, the unified fatigue equations achieved the unity of strength failure and primary fatigue failure. The analysis results indicate that the mixture with Type D gradation curve realizes the highest strength and most extended fatigue life. This research contributes to the gradation design of asphalt mixture. And the unified fatigue equation provides a reference for the durability design of pavement.

Experimental investigation on the deformation and strength properties of cemented gangue backfill column under long-term axial compression

To reveal the time-dependent deformation and the effect of loading history from early curing age on mechanical properties of cemented gangue backfill column (CGBC) under long-term axial compression in constructional backfill mining, the step-by-step load was adopted to simulate the loading history of the roof before 28d and then enter the long-term creeping stage, and the uniaxial compressive strength and elastic modulus of samples after 360d loading were tested. Four initial loading ages (ILA) and four stress-strength ratios (SSR) were set to simulate the actual loading conditions. The time-dependent damage process of CGBC was monitored by ultrasonic and electrical resistivity equipment. The results show that: the strain of CGBC increases with the increase of loading time and SSR; the earlier the ILA is, the higher the total strain shows, but the smaller the creep strain after 28d will be. The loading history at early curing age increases the compactness of CGBC and promotes the cement hydration process, and decreases the deformation after 28d. The final strength and elastic modulus of the long-term loading samples are larger than those of the control ones, and increase first and then decrease with SSR 60% and ILA 7d as the turning point, and the most increase reaches 33% and 82%, respectively. The CGBC can keep long-term stability at 80% SSR. The competition of compaction, healing and damage of CGBC under different SSRs at early curing age determines the final mechanical properties. Ultrasonic pulse velocity and resistivity of CGBC increase with the increase of time and are also affected by the SSR. A rheology-based model that considered the time-hardening of CGBC at early curing age was proposed to predict the time-dependent deformation of CGBC starting from early age. The results could be used to guide the design of CGBC and deformation prediction of the roof.

Study on strength and deformation characteristics of cemented gangue backfill body under the coupling action of load and salt erosion

The durability of backfill body is very important to maintain the stability of goaf. To explore the long-term strength and deformation characteristics of backfill body under the coupling action of load and salt erosion, the cemented gangue backfill body (CGBB) under different compressive stress levels was eroded in MgSO4 solution for 210 days. The ultrasonic and resistivity changes of CGBB at different ages were monitored and the microstructure of CGBB was analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The results showed that the compressive strength of CGBB increased with the rise of compressive stress level, and the compressive strength of the eroded specimens was less than that of the not eroded specimens. The deformation of CGBB increased with the increase of time and compressive stress level, and there was still a certain increase in the later deformation of the eroded CGBB. The ultrasonic pulse velocity (UPV) of eroded CGBB can be divided into three stages: rapid growth, slow growth and gradual decrease. The resistivity of the eroded CGBB decreased rapidly in the early stage, and then increases slowly. The greater the compressive stress is, the smaller the growth rate is. By analyzing microstructure, the formation of expansion products changed the compactness of CGBB in different erosion stages, and the compressive stress within 50 % stress-strength ratio inhibited the erosion of CGBB. The research results can provide reference for the design of backfill body.

Assessment of Modulus Attenuation of Cement and Lime-Fly Ash Semi-Rigid Road Base Materials

For asphalt pavement structures, semi-rigid road base course has to sustain repeated high-axle load during its service life and the performance of semi-rigid road base materials directly influences the durability of pavement structures. The dynamic compressive resilience modulus of two commonly used semi-rigid road base materials, cement stabilized aggregates (CSG) and lime-fly ash stabilized aggregates (LFSG) were evaluated at different frequencies using a Universal Testing Machine (UTM). The results showed that LFSG had higher dynamic modulus than that of CSG and the load frequency had less influence on the dynamic modulus of these two semi-rigid road base materials. The four-point bending test was applied to measure the flexural-bending strength and the fatigue life of these two semi-rigid materials. A higher flexural-bending strength of LFSG indicated its better bearing capacity than that of CSG. The fatigue life of LFSG and CSG decreased with the increase of stress–strength ratio and the LFSG performed better in terms of fatigue resistance. The fatigue damage models of CSG and LFSG based on Stress-Life (S-N) curve are established. As per incremental-recursive mechanics, a general modulus degradation model was established and verified by the results of full-scale accelerate loading test. This model cannot only be used to predict the fatigue deterioration of semi-rigid road base materials under different stress levels, but is also able to calculate the current bending elastic modulus based on its initial modulus value.

Effect of Stress–Strength Ratio and Fiber Length on Creep Property of Polypropylene Fiber-Reinforced Alkali-Activated Slag Concrete

Alkali-activated slag (AAS) is an environmentally friendly green cementitious material that can replace ordinary Portland cement (OPC) and has attracted extensive research by scholars all over the world. However, research regarding its creep performance has been lacking, which in turn affects its further application. The creep of alkali-activated slag concrete is large, and fiber addition has been shown to improve this problem. Polypropylene (PP) fiber has good alkali resistance and is economical. This paper studies the effect of the stress–strength ratio and fiber length on the creep property of PP fiber-reinforced alkali-activated slag (FRAAS) concrete. At the stress–strength ratio of 0.15, PP fiber addition is able to greatly reduce the creep of concrete. When the stress–strength ratio increases, the shorter fiber loses the anchoring force and the holes caused by the longer fiber crack. This in turn leads to the deterioration of the inhibition effect on concrete creep. The CEB-FIP 2010 model is highly accurate, but the final value prediction is small. The early prediction value of the GL2000 model is rather large and conservative. The creep coefficient of the prediction model and the measured secant modulus of PP FRAAS concrete with different fiber lengths under different stress–strength ratios may solve the issue of creep prediction.

Effect of fiber content and stress–strength ratio on the creep of basalt fiber–reinforced alkali‐activated slag concrete

AbstractAlkali‐activated materials are increasingly being used in practical applications as potential alternatives to Portland cement. If alkali‐activated slag (AAS) is to be applied to prestressed engineering and large‐size structures, it is necessary to study the creep performance of AAS. Existing studies have found that the creep of AAS concrete is larger than that of ordinary Portland cement (OPC) concrete, and adding fiber is an effective way to overcome this defect. In this study, we investigated the creep of basalt fiber–reinforced AAS (FRAAS) concrete for fiber contents ranging from 0% to 0.9% (by volume) at a stress–strength ratio of 0–0.6. After analyzing the experimental results, it was found that the basalt FRAAS concrete had no obvious linear creep range. It was observed that with an increase in the fiber content, the inhibition effect of fiber on creep became stronger initially and then weaker. The inhibitory effect of fiber on creep was strengthened by the increase in the stress–strength ratio. The creep coefficient showed no obvious change when the fiber content was in the range of 0%–0.9%. Based on the existing OPC concrete creep models, a method for predicting the creep of basalt FRAAS concrete was proposed.

Experimental Study on the Effects of In Situ Stress on the Initiation and Propagation of Cracks during Hard Rock Blasting

In situ stress is one of the most important factors affecting rock dynamic fractures during blasting excavation of deep rock mass that generally is hard rock. In this research, crater blasting experiments on hard rock under different uniaxial static stresses were conducted to investigate the initiation and propagation process of crack networks that were induced by coupled dynamic and static loads. Furthermore, the effects of anisotropic static stress fields on the initiation and propagation of crack networks during hard rock blasting, and the crack network morphological characteristics were analyzed and elucidated. The experimental results showed that the static stress field changed the process of crack network initiation and propagation during hard rock blasting, and then control the crack network morphology. Under uniaxial static stress, the crack network was elliptical with the long axis parallel to the static stress. In addition, the larger the anisotropic static stress is, the more obvious the elliptical morphology of the crack network. Moreover, the static stress lead to the delay of crack formation which indicates that the delay time during millisecond blasting excavation of deep rock mass should be adjusted appropriately according to the in situ stress. A stress-strength ratio (SSR) of 0.15 is the threshold value where static stress may have a significant effect on the initiation and propagation of a crack network. Meanwhile, the strain field prior to crack initiation during rock blasting controlled the morphological characteristics of the crack network. Finally, the mechanism of static stress affecting propagation and morphology of crack network was revealed theoretically.

Effect of fibre dosage and stress-strength ratio on creep of polypropylene fibre-reinforced alkali-activated slag concrete

Effect of fibre dosage and stress-strength ratio on creep of polypropylene fibre-reinforced alkali-activated slag concrete