A Compound Damage Constitutive Model Considering Deformation of Nonpersistent Fractured Rock Masses

This paper describes a study on the interaction between joint fissures in a nonpersistent jointed rock mass by introducing a self-consistent methodology, amending the traditional method of self-consistency by increasing the number of joints one by one, and deducing a new compound mesoscale and macroscale constitutive damage model based on the Betti energy reciprocity theorem. By analyzing the Mohr–Coulomb failure criterion and generalized von Mises yield criterion and their impact on the calculation result of macroscopic damage, the generalized von Mises criterion is proven to be more appropriate, and it is, thus, chosen for this compound damage constitutive model. Comparing the theoretical calculation and laboratory results of the compound damage model with the existing theoretical calculation results indicates the following: 1. The compound damage model in this paper provides a better fit of the stress–strain curves from the laboratory tests. 2. The theoretical calculative results for the compound damage model in this paper are consistent with the experimental results; that is, the peak load decreases as the connectivity rate increases. 3. For different joint angles and connectivity rates, the overall absolute deviations and relative deviations of the peak stress from the theoretical calculations and the laboratory tests are less than those from the theoretical calculations provided in the original literature. The theoretical calculations of the compound damage model in this paper are more aligned with the experimental results, verifying its correctness and rationality

A Prediction Method Based on Monte Carlo Simulations for Finite Element Analysis of Soil Medium considering Spatial Variability in Soil Parameters

With the Stochastic Finite Element Method (SFEM), the spatial variability of soil properties can be incorporated into the analysis of geotechnical structures. Although this method is significantly superior in principle to the homogeneous analysis of soil parameters, generalizing the method in engineering practice is difficult due to its computational inefficiency. In this paper, we propose a new method for the fast calculation of convergence results. The proposed method introduces a distance space to the Monte Carlo Method (MCM) random field instances and, considering the importance of a safety margin in structures, uses selected spatial interpolation to predict the MCM instances to be solved. Two case study simulations are presented. The results show that compared to the full Monte Carlo Simulation, the fast calculation method proposed in this paper can achieve very accurate convergence results while substantially reducing the computational cost, and the simulation errors for the structure are on the safer side

A New Rock Joint Generation Method and Its Verification in PFC2D

The first part of this paper presents the major drawbacks of the traditional methods for generating joints in Particle Flow Code 2D (PFC2D). Violent oscillations in the postpeak shear stress and shear-induced dilation in the normal direction occur in specimens generated by directly removing bonds in joints and using the discrete fracture network (DFN) method. The specimens generated by the additional wall method can be used to simulate realistic shear mechanical properties in the direct shear test, but it is difficult to achieve a uniform initial stress distribution within the specimen due to the constraint of particle motion. The second part of this paper explores an improved method to generate realistic joints based on the particle grouping technique and the smooth joint model, and the validity of this method is verified by a set of numerical direct shear tests. The numerical results show that the proposed joint generation method can effectively eliminate the oscillation of the postpeak shear stress and shear-induced dilation in the normal direction. In addition, the mechanical behaviours of the rough jointed rock mass correspond well with the theoretical results obtained from Patton’s and Barton’s models. The proposed model can also simulate the asperity degradation of rough jointed rock masses

Study on Temperature Field Massive Concrete in Early Age Based on Temperature Influence Factor

In order to solve the problem of insufficient accuracy of early temperature field caused by the change of hydration rate under different temperatures, the theoretical formula of finite element calculation based on temperature influence factor is put forward and then the theory is tested. On this basis of this theory, the early temperature field of a RCC dam is numerically simulated and the variation law of concrete hydration rate under different temperatures is studied. The numerical simulation results are compared with the results without considering the temperature effect and the measured temperature data. The results show that the theoretical results are in agreement with the measured temperature data, and the accuracy and applicability of the theoretical formula are proved

A modelling resin material and its application in rock-failure study: Samples with two 3D internal fracture surfaces

The mechanism of fracture propagation, interaction and coalescence inside rock masses is a highly concerned issue in geotechnical engineering. But as it is difficult to manufacture 3D internal pre-fractures and observe directly the failure evolution process inside real rocks or their opaque similar materials, most previous studies have been limited to 2D conditions. The experiment investigation on 3D rock failure is still in a preliminary stage. In this study, a resin material has been developed by extensive formula tries. It is absolutely transparent and the ratio of tension–compression strength (brittleness value) can be 1/6.6 at −10 to −15℃. It is much more brittle and rock-like than analogous materials used by former scholars. A set of preparation, casting mould, and post-processing technologies were established and specimen-making with multiple pre-fractures is enabled. In the designed scheme, specimens are made with two parallel internal fracture surfaces yet of four different stagger separations. Uniaxial tests were carried out and the stress–strain relationship is analysed. It is shown that the specimen has gone through four stages as the traditional rock test before failure. Many diverse forms of secondary fractures, such as wrapping wing crack, petaloid crack, and giant quasi-wrapping fracture surface, which were not found in 2D conditions have appeared and their evolutions were clearly seen in each stage

A Compound Damage Constitutive Model Considering Deformation of Nonpersistent Fractured Rock Masses

This paper describes a study on the interaction between joint fissures in a nonpersistent jointed rock mass by introducing a self-consistent methodology, amending the traditional method of self-consistency by increasing the number of joints one by one, and deducing a new compound mesoscale and macroscale constitutive damage model based on the Betti energy reciprocity theorem. By analyzing the Mohr–Coulomb failure criterion and generalized von Mises yield criterion and their impact on the calculation result of macroscopic damage, the generalized von Mises criterion is proven to be more appropriate, and it is, thus, chosen for this compound damage constitutive model. Comparing the theoretical calculation and laboratory results of the compound damage model with the existing theoretical calculation results indicates the following: 1. The compound damage model in this paper provides a better fit of the stress–strain curves from the laboratory tests. 2. The theoretical calculative results for the compound damage model in this paper are consistent with the experimental results; that is, the peak load decreases as the connectivity rate increases. 3. For different joint angles and connectivity rates, the overall absolute deviations and relative deviations of the peak stress from the theoretical calculations and the laboratory tests are less than those from the theoretical calculations provided in the original literature. The theoretical calculations of the compound damage model in this paper are more aligned with the experimental results, verifying its correctness and rationality

Experimental Study on the Effect of Compound Activator on the Mechanical Properties of Steel Slag Cement Mortar

In this study, activator, metakaolin, and silica fume were used as a compound activator to improve the activity of steel slag powder. The influence of activator, steel slag powder, metakaolin, and silica fume on the resulting strength of steel slag cement mortar was investigated by orthogonal experiments. For four weight fractions of steel slag powder (10%, 20%, 30%, 40%), the experimental results indicate that the compressive strength of mortar can reach up to more than 85% of the control group while the flexural strength can reach up to more than 90% of the flexural strength of the control group. Through orthogonal analysis, it is determined that the activator is the primary factor influencing the mortar strength. According to the result of orthogonal analysis, the optimal dosages of activator, steel slag powder, metakaolin, and silica fume are suggested. The GM (0, N) prediction model of compressive strength and flexural strength was established, and the compressive strength and flexural strength of mortar with the optimal dosage combinations were predicted. The prediction results show that by using the optimal dosage combination, the mortar strength can reach the level of P·O·42.5 cement. Considering the different strength and cost requirements of cementitious materials in practical engineering, the economic benefits of replacing cement with steel slag powder activated by compound activator in various proportions and equal amounts were presented. The results show that the method proposed in this study can reduce the cost of cementitious materials

Residual Mechanical Properties and Constitutive Model of High-Strength Seismic Steel Bars through Different Cooling Rates

In this study, the high-temperature test (i.e., temperature to 1000 °C) is conducted on 600 MPa seismic steel bars, and its residual mechanical properties and constitutive relations are investigated though three cooling rates, i.e., under air, furnace, and water-cooling conditions. Results show that three cooling methods have significant effects on the apparent characteristics of 600 MPa steel bars, when the heating temperature is greater than 600 °C. In addition, the ultimate and yield strength of steel bars have been significantly affected by different cooling methods, with increasing heating temperature. However, the elastic modulus is significantly not affected by temperature. Furthermore, the elongation rate after fracture and the total elongation rate at the maximum force do not change significantly, when the heating temperature is less than 650 °C. The elongation rate, after fracture, and the total elongation rate, at the maximum force, have different changes for three cooling methods. The degeneration of the stress–strain curves occurs when the heating temperature is high. The two-fold line, three-fold line, and Ramberg–Osgood models are developed based on the stress–strain curve characteristics of steel bars after cooling. The fire resistance of 600 MPa steel bars of reinforced concrete structure is analyzed, which provides a basis for post-disaster damage assessment, repair, and reinforcement of the building structure