Gongcheng Kexue Yu Jishu/Advanced Engineering Science

Creep deformation and stress relaxation are two properties of rock mass in underground engineering, but in many construction practices, rock mass is neither pure creep deformation nor pure stress relaxation, with stress and strain of rock masses simultaneously changed with time, which is time-dependent, and may ultimately cause failure. It’s hard to explain the phenomenon simply by creep deformation and stress relaxation, so it is a challenge for rock mechanics researchers. To ensure the long-term stability of underground engineering and its structures, it is necessary to further study the properties of rock mass in the generalized theory of rheological mechanics. In the linear viscoelastic theory, the creep compliance was obtained by creep deformation test while the relaxation modulus by stress relaxation test, and the two values were showing linear rheological features, in a reciprocal relationship with each other, and could be converted in each other under certain conditions, so they were no essential difference. But in non-linear viscoelastic theory, their relationship was not clear, and the generalized rheological theory by the stress-feedback controlling method provided the possibility to study mutual relationship. The generalized rheological tests of Tage tuff at 50%, 85% of the peak stress level, Sanjome andesite at 50%, 65% and 80% of the peak stress level were carried out by using the stress-feedback testing method, the generalized rheological direction coefficient for two rocks were 3.0, ±∞, –3.0, –1.0, –0.3, 0, 0.3, respectively. The experimental results showed that the generalized rheological law for two rocks was similar, and the variation of stress and strain obeyed the logarithms law. Based on the definitions of creep compliance and relaxation modulus in the linear viscoelastic theory, the generalized related strain and stress were defined, the calculating method for generalized rheological-compliance (GRC) and generalized rheological-modulus (GRM) was proposed. According to the testing results analyses, the proposed method was general, and creep compliance and relaxation modulus were two special forms of generalized rheological properties. It was found that GRC and GRM were relevant to viscoelastic deformation, had obvious characteristics of time-dependence, direction coefficient-dependence and non-linear rheology, and the ratio between GRC and GRM slightly decreased with time, which showed that the rock rigidity gradually reduced, and deformation quickly increased in pre-failure region. Consequently, the proposed method in this paper can further analyze the quantitative relationship between rock rigidity and plastic deformation, it is very valuable for further investigation of time effect and assessing the long-term stability of underground structures.

33 material specimens were tested to explore the mechanical properties of Q460 high-strength steel plate with holes under monotonic tension and low-cycle fatigue loadings. The stress-strain curve, skeleton curve and energy dissipation capacity comparison of the specimens were analyzed. The influence law of the design size of the specimen, the number of openings and the loading mode on the strength, stiffness, ductility and energy dissipation capacity of the specimens with holes were discussed. On this basis, a finite element model of specimen under fatigue loading was established by the ANSYS software to verify the correctness and reliability of the model. The test results showed that round holes have an adverse effect on the mechanical properties of specimens. The holes lead to stress concentration of specimens. Under the fatigue loads, increasing the number of axial holes of the specimens is beneficial to improve the ductility of specimen, but has an adverse effect on the energy dissipation capacity of the steel. Under low-cycle repeated loadings, the specimens usually cracked and destroyed near holes, and the failure shapes are saddle-shaped. The thickness of the specimens has a significant impact on the failure mode and mechanical properties of the high-strength steel. Under the fatigue loads, the damage forms of the opening specimens and the non-open tester are different, and two different fracture forms are exhibited as thickness. With the increase of the design thickness of the specimen, the fracture section shows two forms. With the increase of the thickness of the steel, the mechanical properties of the specimens have improved significantly. As the number of load cycles increases, the ductility of Q460 high-strength steel decreases and the energy consumption capacity increases.

To study the seismic performance of corrugated steel plate concrete-composite shear wall with replaceable component of wall toe, two shear wall specimens were designed and fabricated. The influences of different arrangement forms of corrugated webs on seismic performance of shear wall specimens were analyzed by quasi-static tests and ABAQUS finite element software. The test result indicated that the wall toes of the specimen were destroyed before the main member, and the damage was mainly concentrated on the replaceable components before the ultimate drift ratio was reached. Compared with the horizontal corrugated steel plate concrete-composite shear wall, the lateral bearing capacity of the vertical corrugated steel plate concrete-composite shear wall had increased by 18.3%, the ductility coefficient increased by 28.69%, and the energy dissipation capacity increased by 3.3 times; The rate of bearing capacity degradation and stiffness degradation, the equivalent viscous damping coefficient and the stiffness degradation ratio were all lower, and the initial stiffness of the latter was slightly improved, which demonstrated that the vertical corrugated steel plate concrete-composite shear wall had better mechanical and seismic performance. By comparing the ABAQUS finite element model analyses with the test processes, the failure mode was basically consistent with the test phenomenon, which indicated that the finite element model established in this article had a certain reliability.

In order to solve the engineering application problems such as low cohesion and poor water stability of silt in the alluvial plain of the Yellow River, the sintering red mud and matrix asphalt were utilized as the main materials to prepare red mud-asphalt powder curing agent (RAC) for comprehensively stabilizing the silt. Setting the optimum dosage of cement as 5% and adding 0, 2%, 4%, 6%, 8% RAC to form stable silt specimens, the compressive strength and uniaxial compressive elastic modulus tests were conducted at 3 d, 7 d, 28 d ages after standard curing, immersion softening, cyclic heating, low-temperature freeze-thaw and high-temperature self-healing methods. The change rules of comprehensive road performance of stabilized silt with different dosage of RAC were compared and analyzed. The scanning electron microscope (SEM) was used to observe the microstructure and pore characteristics of silt, cement stabilized silt and RAC stabilized silt, and then the mechanism of solidification and stabilization was discussed. Combined with the practical application of entity engineering, the road performance of RAC stabilized silt was tested and verified. The results showed that RAC stabilized silt had good mechanical properties and water stability compared to cement alone, the strength of 2%, 4%, 6%, and 8% RAC stabilized silt increased by 110%, 146%, 156%, and 161%, respectively after standard curing of 3 d, and the loss rate of immersion strength at 28 d age is reduced from more than 50% to less than 20%. The strength of cement stabilized silt increased slightly after 5 cycles of heating, but the strength of RAC stabilized silt increases by more than 140% when the dosage was higher than 4%. After the low-temperature freeze-thaw tests, the cement stabilized silt specimen cracked and damaged, the RAC stabilized silt specimen was intact, and the loss rate of strength was less than 15%. The specimen was loaded to 90% ultimate load and heated for 5 times, the strength change rates of 2%, 4%, 6%, and 8% RAC stabilized silt were –8.3%, –2.3%, 8.0%, and 12.9%, respectively. The SEM images showed that RAC stabilized silt had dense cemented aggregates and non-connected microporous structure with uniformly distributed pore diameter less than 1 μm, which were beneficial to improve the water stability and frost resistance of stabilized silt. The asphalt components wet-bonded and wrapped with silt particles and hydration products under high temperature conditions, which accelerated the diffusion to fill the internal pores and micro cracks and realized damage repair and structural reinforcement of stabilized soil. In the entity project, the road base was filled with “4% RAC+5% cement” stabilized silt. After opening to traffic, the overall bearing capacity and service condition of the road were in good condition through field coring and FWD deflection tests. There were no cracks, pits, loose and other damages.

As an effective means for the exploitation of Hot Dry Rock (HDR) resources, the Enhanced Geothermal System (EGS) has broad development prospects and a great utilization value. Therefore, it is particularly important to predict its capacity and longevity. In order to realize the productivity and longevity prediction of the double-well EGS, the productivity and longevity prediction methods of the EGS system under different working conditions were analyzed through theoretical derivation and numerical simulation. Firstly, based on the Dupuit formula and the endothermic formula, the EGS productivity and longevity control equation was established to provide theoretical support for EGS longevity prediction. Then, according to the groundwater flow equation and the heat transfer equation, combined with the Newton’s cooling law, five factors affecting the four unknown parameters in the EGS productivity and longevity control equation were analyzed. The four unknown parameters were the reduction of thermal reserves, the amount of geothermal compensation, the average conversion temperature of production wells, and the shape coefficient of thermal reserves. The five factors obtained were the initial temperature of thermal storage, the injection temperature of thermal medium, the volume of thermal storage, the specific surface area of thermal storage, and the EGS running time. Under the condition of considering the geothermal compensation, the three parameters of EGS with double-well were used to analyze, correct and quantify the influence factors of each unknown parameter when the thermal storage breakthrough occurred, and then obtained the prediction formula of the four unknown parameters changing with the five factors. Based on the above results, a method for predicting the productivity and longevity of the double-well EGS was obtained: using the EGS productivity and life control equation, the prediction formula of four unknown parameters, and the thermal reserve permeability to predict the productivity and longevity of the double-well EGS. Finally, the prediction method of production capacity and longevity of the double-well EGS was used to predict the working conditions of the existing literature and compare them. The two results were in good agreement, which proved the applicability of the control equation and the prediction formula and the accuracy of the prediction method.