• Geomechanics and Engineering
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• 제33권4호
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• pp.327-339
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• 2023

The expansion capacity and strength of expansive grout have a significant influence on the stress state of a supported rock mass and the strength of a grout-rock mass structure. The expansion and strength characteristics are vital in grouting preparation and application. To analyze the expansion performance and mechanical properties of expansive grout, uniaxial compressive strength (UCS) tests, expansion ratio tests, XRD, SEM, and microscopic scanning tests (MSTs) of expansive grout under different curing pressure conditions were conducted. The microevolution was analyzed by combining the failure characteristics, XRD patterns, SEM images, and surface morphologies of the specimens. The experimental results show that: (1) The final expansion ratio of the expansive grout was linear with increasing expansion agent content and nonlinear with increasing curing pressure. (2) The strength of the expansive grout was positively correlated with curing pressure and negatively correlated with expansion agent content. (3) The expansion of expansive grout was related mainly to the development of calcium hydroxide (Ca(OH)2) crystals. With an increase in expansion agent content, the final expansion ratio increased, but the expansion rate decreased. With an increase in the curing pressure, the grout expansion effect decreased significantly. (4) The proportion of the concave surfaces at the centre of the specimen cross-section reflected the specimen's porosity to a certain extent, which was linear with increasing expansion agent content and curing pressure.

• Steel and Composite Structures
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• 제45권2호
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• pp.281-291
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• 2022

Surmounting complexities in analyzing the mechanical parameters of concrete entails selecting an appropriate methodology. This study integrates a novel metaheuristic technique, namely satin bowerbird optimizer (SBO) with artificial neural network (ANN) for predicting uniaxial compressive strength (UCS) of concrete. For this purpose, the created hybrid is trained and tested using a relatively large dataset collected from the published literature. Three other new algorithms, namely Henry gas solubility optimization (HGSO), sunflower optimization (SFO), and vortex search algorithm (VSA) are also used as benchmarks. After attaining a proper population size for all algorithms, the Utilizing various accuracy indicators, it was shown that the proposed ANN-SBO not only can excellently analyze the UCS behavior, but also outperforms all three benchmark hybrids (i.e., ANN-HGSO, ANN-SFO, and ANN-VSA). In the prediction phase, the correlation indices of 0.87394, 0.87936, 0.95329, and 0.95663, as well as mean absolute percentage errors of 15.9719, 15.3845, 9.4970, and 8.0629%, calculated for the ANN-HGSO, ANN-SFO, ANN-VSA, and ANN-SBO, respectively, manifested the best prediction performance for the proposed model. Also, the ANN-VSA achieved reliable results as well. In short, the ANN-SBO can be used by engineers as an efficient non-destructive method for predicting the UCS of concrete.

• Geomechanics and Engineering
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• 제35권4호
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• pp.333-366
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• 2023

Rock as a mass generally exhibits discontinuities, commonly witnessed in rock slopes and underground structures like tunnels, rock pillars etc. When these discontinuities experiences loading, a new crack emerges from them which later propagates to a macro scale level of failure. The failure pattern is often influenced by the nature of discontinuity, geometry and loading conditions. The study of crack growth in rocks, namely its initiation and propagation, plays an important role in defining the true strength of rock and corresponding failure patterns. Many researchers have considered the length of the discontinuity to be fully persistent on rock or rock-like specimens by both experimental and numerical methods. However, only during recent decades, there has been a substantial growth in research interest with non-persistent discontinuities where the crack growth and its propagation phenomenon were found to be much more complex than persistent ones. The non-persistence fractures surface is generally considered to be open and closed. Compared to open flaws, there is a difference in crack growth behaviour in closed or narrow flaws due to the effect of surface closure between them. The present paper reviews the literature that has contributed towards studying the crack growth behaviour and its failure characteristics on both open and narrow flaws subjected to uniaxial and biaxial compression loading conditions.

• Steel and Composite Structures
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• 제49권6호
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• pp.645-666
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• 2023

Due to the steadily declining supply of natural coarse aggregates, the concrete industry has shifted to substituting coarse aggregates generated from byproducts and industrial waste. Oil palm shell is a substantial waste product created during the production of palm oil (OPS). When considering the usage of OPSC, building engineers must consider its uniaxial compressive strength (UCS). Obtaining UCS is expensive and time-consuming, machine learning may help. This research established five innovative hybrid AI algorithms to predict UCS. Aquila optimizer (AO) is used with methods to discover optimum model parameters. Considered models are artificial neural network (AO - ANN), adaptive neuro-fuzzy inference system (AO - ANFIS), support vector regression (AO - SVR), random forest (AO - RF), and extreme gradient boosting (AO - XGB). To achieve this goal, a dataset of OPS-produced concrete specimens was compiled. The outputs depict that all five developed models have justifiable accuracy in UCS estimation process, showing the remarkable correlation between measured and estimated UCS and models' usefulness. All in all, findings depict that the proposed AO - XGB model performed more suitable than others in predicting UCS of OPSC (with R², RMSE, MAE, VAF and A_15-index at 0.9678, 1.4595, 1.1527, 97.6469, and 0.9077). The proposed model could be utilized in construction engineering to ensure enough mechanical workability of lightweight concrete and permit its safe usage for construction aims.

• Structural Engineering and Mechanics
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• 제89권6호
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• pp.601-615
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• 2024

Effect of ring and straight stiffeners in the buckling as well as vibration characteristics of metal-ceramic functionally graded plates with cutout subjected to various uniaxial and localized in-plane compressive edge loadings was explored in the present work. In the current work, the distinguishing characteristics of metal and ceramic are merged in a single volume, and power law was used for estimating the material composition throughout thickness. Buckling and free vibration characteristics were studied initially for unstiffened Al/SiC functionally graded plates with cutout. Subsequently, the influence of cutout ratio on buckling load as well as natural frequency for different power law indices was discussed. The functionally graded plate was stiffened by three different stiffener patterns, namely; ring stiffener, straight stiffener, as well as a combination of the ring and the straight stiffener, to enhance the buckling as well as vibration characteristics. The effect of stiffener depth ratio for different stiffener patterns was also presented for functionally graded plates having different cutout sizes under various loading conditions. Such studies on functionally graded material have potential applications in a variety of technological fields including the aerospace and defense sectors.

• Computers and Concrete
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• 제33권6호
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• pp.659-670
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• 2024

The mechanical behaviour of layered concrete samples containing an internal crack was numerically studied by modelling the geo-mechanical specimens in the particle flow code in two dimensions (PFC2D). The numerical modelling software was calibrated with the experimental results of the Brazilian tensile strengths gained from the laboratory disc-type specimens. Then, the samples with the bedding layers and internal notch were numerically simulated with PFC2D under uniaxial compressive loading. In each specimen, the layers' thickness was 10 mm but the layer's inclination angle was changed to 0°, 30°, 60°, 90°, 120° and 150°. Of course, the layers'interfaces are considered to have very low strengths. The internal notch was kept at 3 cm in length however, its inclination angle was changed to 0°, 40°, 60° and 90°. Therefore, a total, of 24 numerical models were made to study the failure mechanism of the layered concrete samples. Considering these results, it has been concluded that the inclination angles of both internal crack and bedding layers affect the failure mechanism and uniaxial compressive strength of the concrete.

• Geomechanics and Engineering
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• 제15권5호
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• pp.1081-1089
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• 2018

The deformation and strength of brittle rocks are significantly influenced by the crack closure behavior. The relationship between the strength and deformation of rocks under uniaxial loading is the foundation for design and assessment of such scenarios. The concept of relative crack closure strain was proposed to describe the influence of the crack closure behavior on the deformation and strength of rocks. Considering the crack compaction effect, a new damage constitutive model was developed based on accumulated AE counts. First, a damage variable based on the accumulated AE counts was introduced, and the damage evolution equations for the four types of brittle rocks were then derived. Second, a compaction coefficient was proposed to describe the compaction degree and a correction factor was proposed to correct the error in the effective elastic modulus instead of the elastic modulus of the rock without new damage. Finally, the compaction coefficient and correction factor were used to modify the damage constitutive model obtained using the Lemaitre strain equivalence hypothesis. The fitted results of the models were then compared with the experimental data. The results showed that the uniaxial compressive strength and effective elastic modulus decrease with an increase in the relative crack closure strain. The values of the damage variables increase exponentially with strains. The modified damage constitutive equation can be used to more accurately describe the compressive deformation (particularly the compaction stage) of the four types of brittle rocks, with a coefficient of determination greater than 0.9.

• Geomechanics and Engineering
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• 제12권3호
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• pp.541-560
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• 2017

In this research, experimental and numerical simulations were adopted to investigate the effects of ligament angle on compressive strength and failure mode of rock-like material specimens containing two non-coplanar filled fissures under uniaxial compression. The experimental results show that with the increase of ligament angle, the compressive strength decreases to a nadir at the ligament angle of $60^{\circ}$, before increasing to the maximum at the ligament angle of $120^{\circ}$, while the elastic modulus is not obviously related to the ligament angle. The shear coalescence type easily occurred when ${\alpha}$ < ${\beta}$, although having the same degree difference between the angle of ligament and fissure. Numerical simulations using $PFC^{2D}$ were performed for flawed specimens under uniaxial compression, and the results are in good consistency with the experimental results. By analyzing the crack evolution process and parallel bond force field of rock-like material specimen containing two non-coplanar filled fissures, we can conclude that the coalescence and propagation of crack are mainly derived from parallel bond force, and the crack initiation and propagation also affect the distribution of parallel bond force. Finally, the displacement vectors in ligament region were used to identify the type of coalescence, and the results coincided with that obtained by analyzing parallel bond force field. These experimental and numerical results are expected to improve the understanding of the mechanism of flawed rock engineering structures.

• Computers and Concrete
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• 제27권2호
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• pp.99-109
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• 2021

Experimental and discrete element methods were used to investigate the effects of echelon non-persistent joint on the failure behaviour of joint's bridge area under uniaxial compressive test. Concrete samples with dimension of 150 mm×100 mm×50 mm were prepared. Uniaxial compressive strength and tensile strength of concrete were 14 MPa and 1MPa, respectivly. Within the specimen, three echelon non-persistent notches were provided. These joints were distributed on the three diagonal plane. the angle of diagonal plane related to horizontal axis were 15°, 30° and 45°. The angle of joints related to diagonal plane were 30°, 45°, 60°. Totally, 9 different configuration systems were prepared for non-persistent joint. In these configurations, the length of joints were taken as 2 cm. Similar to those for joints configuration systems in the experimental tests, 9 models with different echelon non-persistent joint were prepared in numerical model. The axial load was applied to the model by rate of 0.05 mm/min. the results show that the failure process was mostly governed by both of the non-persistent joint angle and diagonal plane angle. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the joint angle. The strength of samples increase by increasing both of the joint angle and diagonal plane angle. The failure pattern and failure strength are similar in both methods i.e. the experimental testing and the numerical simulation methods.

• Computers and Concrete
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• 제31권3호
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• pp.207-221
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• 2023

In this investigation, the interaction between opening space and neighboring joint has been examined by experimental test and Particle flow code in two dimension (PFC2D) simulation. Since, firs of all PFC was calibrated using Brazilian experimental test and uniaxial compression test. Secondly, diverse configurations of opening and neighboring joint were provided and tested by uniaxial test. 12 rectangular sample with dimension of 10 cm*10 cm was prepared from gypsum mixture. One quarter of tunnel and one and or two joint were drilled into the sample. Tunnel diameter was 5.5 cm. The angularities of joint in physical test were 0°, 45° and 90°. The angularities of joint in numerical simulation were 0°, 30°, 60°, -30°, -45°, -60° and its length were 2cm and 4cm. Loading rate was 0.016 m/s. Tensile strength of material was 4.5 MPa. Results shows that dominant type of crack which took place in the model was tensile cracks and or several shear bands develop within the model. The Final stress is minimum in the cases where oriented angle is negative. The failure stress decrease by decreasing the joint angle from 30° to 60°. In addition, the failure stress decrease by incrementing the joint angle from -30° to -60°. The failure stress was incremented by decreasing the number of notches. The failure stress was incremented by decreasing the joint length. The failure stress was incremented by decreasing the number of notches. Comparing experimental results and numerical one, showed that the failure stress is approximately identical in both conditions.