Abstract:In order to guarantee the long-term stability of silty mudstone in slope and tunneling projects, the DZSZ-150 multi-field coupling rock triaxial pressure testing machine was used to conduct creep tests on silty mudstone specimens of similar materials under different surrounding pressures. Based on the testing results, a nonlinear viscoelastic-plastic constitutive model describing the whole creep process of silty mudstone was established, and the proposed creep model was verified for its rationality and feasibility by taking the results at a confining pressure of 7 MPa as an example. It show that the steady-state creep rate of the specimen is related to the magnitude of the deviatoric stress, and with increase of the deviatoric stress, the steady-state creep rate and the deviatoric stress conform to an exponential function relationship; the creep rate in the accelerated creep stage is significantly greater than that in the decelerated creep and steady-state creep at low stress levels, and the creep damage occurs in a very short time; a nonlinear viscoelastic-plastic constitutive model is proposed to describe the whole creep process of the silty mudstone, which can describe the creep-deformation law of the whole process of creep-damage of silty mudstone, reflecting the creep characteristics of silty mudstone under different levels of deviatoric stress, and avoiding the problem that the classical model cannot accurately describe the accelerated creep process.

Abstract:Based on the ground treatment of the north extension of No. 31 provincial road in the urban section of Shaoxing in Zhejiang Province, the feasibility and treatment effect of two methods, i.e., ALLu strong stirring head stirring method with homemade equipment and ALLu strong stirring head combined application, by in-situ curing foundation treatment were studied. Plate loading test, unconfined compressive strength (UCS) test, standard penetration test and static cone penetration test were carried out, respectively. Meanwhile, in order to obtain the stress and deformation of the in-situ curing foundation, field monitoring was carried out by arranging the earth pressure box and settlement plate. The test results showed that the bearing capacity of foundation by in-situ curing were increased by at least 30% compared with the traditional replacement method. At 28 days of curing time, the ratio of UCS of curing soil in-situ to that of indoor value was 0.35-0.65. The bearing capacity of foundation was improved by standard penetration test and static cone penetration test，and the calculating bearing capacity were consistent with the measured results of plate loading test. The stress and additional stress coefficient of the two groups of road sections were analyzed, and the artificial crust layer had better effect on the diffusion stress, which can be used for detection of in-situ shallow stabilization in engineering practice.

Abstract:In the working process of energy pile, the pile body will produce thermal deformation influenced by temperature change and induce cyclic shear action on the soil around the pile, which would weaken the bearing capacity of the foundation and bring risks to the normal use of the pile foundation. Because the traditional direct shear apparatus could not simulate the temperature variation of the pile and soil in the working process of energy piles, there was limited research on the mechanical properties of the pile-soil interface affected by the temperature. In this paper, the traditional direct shear apparatus was modified to adjust the temperature of soil samples. The soil used in this test was sampled from a construction site in Chongqing, and the geotechnical direct shear tests of pile-soil interface under different temperatures were carried out. The effects of single and cyclic temperature variation on the mechanical properties of the pile-soil interface were analyzed. Meanwhile, the difference between the mechanical properties of pile-soil interface and soil was compared. The results showed that the shear strength of pile-soil interface was influenced significantly by the temperature. With the increase of temperature, the friction angle and cohesion of the pile-soil interface would firstly decrease and then increase. Temperature cycles had a great influence on the mechanical properties of pile-soil interface under low normal stress, while it had no significant influence under high normal stress. The variations of shear strength, friction angle and cohesion of the soil influenced by temperature was similar to those of pile-soil interface.

Abstract:When the vacuum preloading (VP) is used to consolidate the engineering waste slurry, there are several problems, such as the clogging of prefabricated vertical drain (PVD), formation of the soil columns and the attenuation of vacuum degree with depth, resulting in non-uniform consolidation. Considering the characteristics of prefabricated horizontal drain (PHD) in the treatment of soft soil foundation by VP method, a vacuum preloading method combined PHD with PVD (PHD-PVD-VP) is proposed to treat the slurry. Through four groups of large-scale indoor model tests, the drainage, settlement and pore water pressure during consolidation of engineering waste slurry were monitored, combined with the micro pictures of drainage board filter membrane obtained by scanning electron microscope, the consolidation effect of PHD-PVD-VP on engineering waste slurry under different initial PHD vacuum pressures was analyzed. The test results show that the PHD-PVD-VP reduces the radial movement rate of soil particles, delays the formation of "soil column", alleviates the silting effect of soil particles embedded in the filter membrane of drainage plate, and improves the overall consolidation effect of soil; initial PHD vacuum pressure of 40 kPa makes the drainage and consolidation effect of PHD-PVD-VP on engineering waste slurry the best, the average water content and vane shear strength of the treated soil were 40.9% and 25.5 kPa respectively. It not only effectively avoids the clogging of PHD and PVD, but also improves the uniformity of soil. Combined with the microstructure analysis, it is found that the initial PHD vacuum pressure affects the clogging of PHD and PVD filter membranes simultaneously, so as to affect their drainage performance. The initial PHD vacuum pressure of 40 kPa gives full play to the drainage performance of the two drainage boards.

Abstract:To realize the utilization of silt waste from foundation pit excavation, the characteristics of engineering mechanics and stability of the Yangtze river floodplain silt subgrade solidified by cement and lime were investigated. A series of laboratory tests including compaction test, unconfined compressive strength test, water stability test and microscopic test were conducted to analyze the variation of strength and durability of lime-cement solidified silt. Feasibility of using soft soil of Yangtze River floodplain as subgrade filling is demonstrated. The results show that the mechanical properties of silt are greatly improved after addition of cement and lime; after soaking in water for 5 days with different content, the water stability coefficient of the solidified soil is greater than 0.6. The water stability coefficient increases with the increase of cement content, and increases first and then decreases with the lime content. Microscopic tests show that the cementitious substances generated by cement and lime in the soil can encapsulate and bond the soil particle. Considering the strength and water stability of the solidified soil, the Yangtze River floodplain silt can be used as subgrade filling after solidification and the optimum percentage of cement and lime was both 6%. Under this content, the unconfined compressive strength of the improved soil for 28d is 2.05 MPa, and the water stability coefficient after soaking in water for 5 days is 0.76, which shows that the improved soil has good mechanical performance.

Abstract:In order to investigate general stability during shield tunneling in soft soil stratum, a TJ-TBM2015 multi-functional micro-tunneling test platform is developed independently. The shield shell diameter is changed to simulate the ground loss. By using the dynamic control system, the micro-tunneling boring machine can realize the continuous dynamic mechanical excavation. Based on the test platform, three tests of shield tunneling under different tunnelling conditions are carried out, including no overloading, local overloading and tunneling near the pile group foundation. The surface subsidence and stress variety around tunnel are monitored by transducer to investigate the general stability of different tests, which further give the comparison and discussion on the different test results. The results show that the soil within the one diameter of the tunnel center is greatly affected by tunneling; the influence of local overloading on soil stability is limited, but local overloading may increase the surface settlement; pile group foundation plays a certain role in strengthening and isolating the stratum.

Abstract:In deep foundation excavation projects, using reasonable soil mechanical parameters to calculate the lateral deformation of diaphragm wall is essential to optimize the support design and reduce engineering risks. However, the soil parameters are generally affected by the uneven distribution and geotechnical testing errors, which often show obvious uncertainties and reduce the credibility of the lateral deformation calculated of diaphragm walls. In view of the considerations above, this paper proposes a back analysis method of soil parameters based on Bayesian parameter updating framework and site monitoring data. This method uses GA-BP neural network to establish the implicit function relationship between the soil parameters and the diaphragm wall lateral displacement in the numerical model, and combines the site monitoring data to establish the Bayesian back analysis model of the soil parameters. This method was used to analyze a deep excavation project, and the feasibility of the method was verified. The maximum lateral displacement and multi-point displacement value of the diaphragm wall were used as indicators to invert the soil mechanical parameters, and the updated soil parameters were used to predict the final lateral displacement. The results show that compared with the non-updating soil parameters, the variation coefficient of soil parameters decreases after updating, and the obtained results fit with the monitoring results better in the subsequent construction steps; the prediction effect of using multi-point observations for soil parameter updating is significantly better than that when only the maximum displacement value is used.

Abstract:The geotechnical parameter of soil mass in colluvial landslide is uncertain. Saturated hydraulic conductivity and soil-water characteristic curve (SWCC) are important parameters for the unsaturated seepage analysis. It is of great significance to carry out the reliability analysis of reservoir bank landslide considering the spatial variability. In this study, the Jvzhoudao slope in the Ganjiang Reservoir Area is investigated as a case. Firstly, according to the limited laboratory test data of saturation-matrix suction, the statistical characteristics of the SWCC properties, such as VGM, VGB, VG, and FX model parameters are calibrated by the Bayesian method, and the applied probabilities of SWCC model combination are determined by the laboratory measurements. Secondly, combining the random field characteristics of the saturated hydraulic conductivity with the random characteristics of the SWCC models, spatial distributions of the unsaturated hydraulic conductivity are generated in the slide body. Finally, for the extreme conditions in the Ganjiang Reservoir Area in May 2021, the proposed method was applied to the case stability analysis. Results indicate that the combined effect of rainstorm and water level change has a significant impact on the safety factor, and that the safety factor of the deterministic analysis is low. Reliability index calculated after considering the spatial variability of the unsaturated permeability coefficient cannot meet the specification requirements, while additional slope engineering reinforcement measures should be taken to guarantee the long-term stability of the slope.

Abstract:Biocementation is a green and low-carbon building technique that has emerged in recent decades. It shows promising prospects in foundation treatment, slope treatment, and concrete crack repair. Biocementation involves complex bio-physical-chemical dynamic processes, requiring developing a real-time visualization system to figure out the regimes of reaction and reinforcement. The necessity of developing the visualization system for biocementation is analyzed. A framework of the visualization test system is established for biocementation, composing of a solution transport system, microreactor, observation system, as well as environmental control and monitoring system. The solution transport system is used for solution delivery and fixing of boundary conditions. The microreactor is used as a mold for reaction. The observation system is used to visualize the reaction process. The environmental control and monitoring system is used to control the environmental conditions such as temperature and light and also collect the feedback data including fluid pressure. The methods for test data acquisition are based on image processing associated with the data logged by the environmental monitors. Analytical approaches are also proposed to deal with the test data. Results show that the biocementation visualization system can not only directly obtain the image of the reinforcement process and the data of the osmotic pressure change, but also be combined with microscopic test methods such as scanning electron microscopy for material characterization and micro-mechanical characteristics analysis. It can be used for microscopic real-time research of biocementation, providing a new method for study of the microscopic mechanism of biocementation, which is conducive to revealing the mechanism of biocementation.

Abstract:The foundation of onshore wind turbine (OWT) structure is usually constructed by cast-in-situ concrete, which is inefficient, polluting, and difficult to guarantee quality, either not conducive to the high-quality development of the wind power industry. The prefabricated wind turbine foundation adopts the construction method of standardized design and factory production, which can significantly shorten the construction period of wind farms, effectively guarantee the quality of the foundation, and reduce the pollution to the environment. It is one of the important measures for the transformation and upgrading of wind power and reducing costs and increasing efficiency. This paper collects, sorts out and summarizes the research of prefabricated OWT foundation and its state-of-the-art research. According to the characteristics of the wind power prefabricated infrastructure, it lists six main types of wind power prefabricated infrastructure, such as raft foundation and multi-footing foundation, and makes a detailed analysis of the characteristics and research status of each type, and lists some onshore wind farm projects that apply prefabricated wind turbine foundation worldwide. The results show that the design basis of OWT prefabricated foundation structures needs to be further improved, the existing structure forms should be optimized, and further research on design methods and performance control should be promoted.

Abstract:The soil nail head is the weak point in the overall structure of the soil nail wall. In order to study the anchorage performance of soil nail head, this paper takes an assembled flexible surface GFRP reinforced soil nail wall as an example. Through indoor nail head anchorage performance test and 3D numerical simulation the ultimate tensile strength, nail head deformation and damage pattern of hollow GFRP bar nail head with 32 mm outer diameter were investigated. It was found that the ultimate load bearing capacity of such GFRP bar nail head is between 240 kN and 290 kN. When the nut is tightened, the stress of the thread is mainly distributed in the first three rings of threaded teeth, with significant stress concentration exists at the first ring of threaded teeth in the head of the nail. In addition, a mechanical model of the threaded tooth of the nail head was developed using the thread expansion method, and the relationship between the ultimate shear strength of the first ring thread and the ultimate load on the nail head was derived. The ultimate load-carrying capacity of this GFRP bar nail head was calculated to be 244.54 kN, which is consistent with the test results.The brittle damage characteristics of the indoor nail head anchorage performance test determined that the safety factor of GFRP tendon nail head is between 1.8 and 2.0. It is also determined that the safe load of such GFRP tendons is between 125 kN and 135 kN, providing a reference for the research and application of similar projects.

Abstract:The crack propagation mode, fatigue deformation characteristics and energy evolution pattern of cracked rock under graded cyclic loading are of great significance to the safe construction and operation of underground engineering. Conventional splitting test, graded cyclic load test and non-contact deformation measurement test were carried out considering the crack angle, crack number and distribution. The failure characteristics and dynamic elastic modulus were analyzed, and the relationship between axial irreversible deformation and fatigue life was studied. From the perspective of energy, the total absorbed energy, released strain energy and dissipated energy in the failure process were calculated, and the relationship between energy evolution and the response of crack propagation mode was analyzed. The results show that :(1) The fatigue deformation of rock can be divided into the initial deformation stage, stable stage and the accelerated failure stage, and the hysteretic loop curve presents the characteristics of “thin-dense-thinness”. The dynamic elastic modulus of every 200 cycles is analyzed and that of the second loading stage is strengthened. In addition, the dynamic elastic modulus decreases after the third loading stage. (2) The total absorbed energy, dissipated energy and elastic energy all showed an upward trend. The total absorbed energy increased slowly, and the growth rate gradually slowed down with the increase of cycles. The dissipated energy increases rapidly after entering the failure stage, but the elastic strain energy does not change obviously, and the dissipated energy is more in the middle dip angle. (3) During failure process, wing cracks and inclined secondary cracks are generated, and the interaction and merger of the cracks result in continuous plastic strain accumulation and small particle debris, which is different from the brittle failure mechanism under static load.

Abstract:With the rapid construction of large-scale wind farms, the upstream wind turbine will deteriorate the wind velocity in the wind turbine wake region and increase the wake turbulence, thereby reducing the power efficiency of the downstream wind turbine and aggravating the fatigue damage of the wind turbine to shorten its service life. Therefore, it is urgent to carry out the study of wind turbine wake characteristics. The main purpose of this study is to reveal the wake characteristics of a standalone wind turbine under different upstream flow conditions and with various yaw angles. Firstly, the accuracy of Large Eddy Simulation (LES) combined with Actuator Line Model (ALM) was verified by the corresponding wind tunnel test. And then, based on the LES-ALM simulation method, the effects of inlet (including velocity and turbulence intensity) and yaw angle on the turbine wake characteristics were studied, and the symmetry of the horizontal profiles of the wind turbine wake at the hub height was clarified with positive and negative yaw angles. The results show that with the increase of the background turbulence intensity, the recovery of the wind turbine wake will be accelerated. Moreover, under the same upstream flow conditions and symmetrical yaw angle, the certain symmetry of wind turbine wake velocity was also identified. When the yaw angle of the wind turbine increases, both the expansion rate of the turbine wake width and the deficit degree of the wake wind velocity would decrease.

Abstract:In the pressure test, the presence of the piezometric tube will distort the pressure signal and affect the accuracy of the subsequent data analysis. Through the actual measurement of the frequency response function of the measuring system, the influence law of the piezometric tube on the signal is obtained, and the shortcomings of the “B-T theory” are revealed. Based on this, under the actual turbulent flow, the influence of the piezometric tube length on the pressure data of a single measuring point and the total force of the model is studied, and the correction effect of the “B-T theory” is verified. The results show that for single-point pressure data, the piezometric tube will not affect the data mean and variation coefficient, the standard deviation increases first and then decreases as the tube length increases, the signal time domain approaches the mean value as the tube length increases, the phase keeps lagging, and the signal frequency domain value gradually deviates from the true value with the increase of the tube length and frequency. For the overall force of the model, the overall resistance, the correlation and coherence of each force can be regarded as not affected by the piezometric tube, the change rule of the force spectrum is the same as that of the frequency domain value of single measuring point. “B-T theory” has a poor correction effect in the signal time domain, and performs well in the frequency domain correction.

Abstract:The shear test of self-tapping screw connection of cold-formed thin-walled steel-structure fireproof integrated board was carried out, and the monotonic tensile and low-cycle reciprocating loading tests of 35 typical specimens were completed, and the effects of structural fireproof integrated plate thickness, screw diameter, screw end distance and loading angle on their shear resistance were analyzed. The results show that the specimens with different loading angles and screw end distance showed different failure modes, mainly including tear failure at the end of the plate, pressure failure of the hole wall of the plate, and the failure of the plate to be pulled off, etc., and the self-tapping screws of the specimens had different degrees of inclination during the failure. For test pieces with screws with a diameter of 4.8 mm and 5.5 mm respectively at the test end,the peak load and ductility coefficient of the specimen have no obvious correlation with the screw diameter, and the elastic stiffness increases significantly with the increase of the screw diameter. With the increase of screw end distance from 15 mm to 25 mm, the elastic stiffness of the specimen did not change significantly, while the peak load and ductility coefficient increased by about 35%. With the increase of plate thickness from 12 mm to 20 mm, the peak load of the specimen is increased by about 40%, the elastic stiffness is increased by about 90%, and the ductility coefficient is reduced by about 30%. Compared with the specimen with a loading angle of 0°, when the loading angle is 45°, the elastic stiffness of the specimen is increased by about 100%, and the peak load and ductility coefficient do not change significantly. When the loading angle is 90°, the elastic stiffness and peak load of the specimen do not change significantly, and the ductility coefficient is reduced by about 40%.

Abstract:In order to explore the change of wood properties of ancient building members under natural aging, a part of larch (Larix principis-rupprechtii Mayr) timber member of ancient building, which is about 350 years old, and a new timber with the same species and similar annual wheel width were used in this study. Small clear specimens were processed to measure the material properties (color, dry density and material mechanics property parameters) and non-destructive testing (NDT) parameters (micro-drill resistance value and velocity of ultrasonic wave). The nondestructive testing, physical and mechanical properties parameters of specimens were compared to analyze the variation and distribution, and then the multiple regression model for the physical and mechanical properties of ancient building timber were established based on the parameters measured in this study. The study results showed that the measured material property parameters and NDT parameters of the natural ageing wood specimens were significantly attenuated. And there is a highly significant difference in the color of natural aging specimens and new timber specimens. It was also found that the coefficients of variation of the parameters of natural aging specimens were all higher than those of new timber specimens, but both of them conformed to a normal distribution. Moreover, the developed model for the evaluation of physical and mechanical property parameters of larch timber members has a good evaluation performance.

Abstract:The structure health monitoring of high voltage transmission tower was very important to ensure the safe operation of the transmission line. When the transmission tower structure was damaged, the gusset plate bolts would be loosened first. The multiscale model of the transmission tower structure is established by using ABAQUS finite element analysis software. The energy change rate of the wavelet packet was taken as the damage index. The damage identification was carried out under different working conditions when bolt looseness of a joint plate at the tower leg. The signal transmission equipment was a sensor based on Internet of Things technology. The data acquisition equipment was PVDF piezoelectric film strain gauge. Applying excitation loads at the bottom of the actual transmission tower structure, the dynamic strain of the measured points on the gusset plate was extracted to verify the damage identification method. The test results show that the damage index can accurately identify the damage degree of the gusset plate. It is also sensitive to bolt looseness near the measuring point.

Abstract:Orthotropic steel deck (OSD) in a long-span cable-stayed bridge is vulnerable to fatigue damage at the rib-to-deck (RD) joints due to traffic vehicle load. An algorithm for fatigue damage evaluation simulation of long-span bridge based on mesoscale damage model is presented in this paper. Firstly, the fatigue damage evolution model of steel deck based on microscopic damage mechanics is derived. Combined with the measured traffic data, the random traffic flow simulation is realized based on Monte-Carlo method. Finally, it is applied to estimate the damage accumulation of a multi-span cable-stayed bridge. The results indicate that the fatigue damage accumulation at the rib-to-deck (RD) joints is greater than other areas of the OSD. The cumulative rate of fatigue damage at the rib-to-deck (RD) joints shows a strong nonlinear trend. The results are also compared with those estimated by the linear Miner,s model. The predicted fatigue life is far less than that by the linear Miner,s model.

Abstract:Under long-term loading, the deformation of reinforced concrete flexural members is an important evaluation index and it is one of the checking contents of the serviceability limit state. To study the degradation law of bending stiffness of marine high-performance concrete beams after action of repeated loads, a total of 10 test beams were designed and fabricated. After exposure to the repeated load test, the chloride solution dry-wet cycle test and their coupled test, the mid-span deflection development and stiffness degradation of the test beams were evaluated using the four-point bending test. A modified method for the code formula of beam short-term stiffness is proposed. The test results indicate that when the load level is determined according to the moment of the beam’s pure bending section equal to 0.4M_u, the damage degree in concrete approaches 15% after 30 cycles of repeated load. For the test beams exposed only to the chloride solution dry-wet cycles, their mid-span deflection develops slower than that of the reference beam. After the action of repeated loads, the mid-span deflection of these test beams develops faster than that of the reference beam. When the damaged beams were exposed to chloride solution dry-wet cycles, their degradation of bending stiffness became more obvious. Based on the experimental results, the damage effect reduction factors were proposed to revise the calculation formula of beam,s short-term stiffness. The rationality and effectiveness of the revised formula are verified by the test data.

Abstract:In this experiment, by comparing the compressive strength values and internal pore structure of five different aerated concrete test blocks at different ages under the conditions of negative temperature curing and standard curing, the development law of the compressive strength of aerated concrete is analyzed based on the (-5 ℃) curing condition, and the range of less harmful pores under this condition is further clarified based on the relationship between the pore size and the pore water; and the inherent lack of strength of aerated concrete is analyzed from a microscopic point of view. The experimental results show that the continuous (-5 ℃) curing has an obvious restraining effect on the growth of the compressive strength of aerated concrete, and the strength is less than the standard curing test block at the same content; under the same curing conditions, the strength and content are affected by the air-entraining agent. There is a negative correlation between them; based on the negative temperature curing environment, the high content of aerated concrete will reduce the compactness of the concrete due to the increase in the number of pores in the slurry, which will affect the compressive strength of the concrete to a certain extent, but it will cause the resistance of the aerosol to the negative temperature environment cannot be ignored. In order to analyze the balance between the negative temperature environment and the amount of air-entraining agent, the pore structure development law and strength growth system of cement-based materials under negative temperature are used to ensure that the compression the strength of aerated concrete is low and the pore structure is relatively optimized. Under the premise of finding the content of aerated concrete under the condition of negative temperature (-5 ℃).

Abstract:In order to study the properties of straw fiber reinforced foam concrete, fiber-reinforced foam concrete was prepared by the physical foaming method with ordinary Portland cement as the main cementitious material, silica fume, metakaolin and fly ash as the supplementary cementitious materials, and rice straw fiber as reinforcement material. The effects of straw fiber content on the density, water absorption, compressive strength, flexural strength, splitting tensile strength and frost resistance of foam concrete were investigated by full factorial tests at different water-to-binder ratios and foaming agent dosages. The results showed that the density, compressive strength and splitting tensile strength of straw fiber reinforced foam concrete increased first and then decreased with the increase of fiber content for different water-to-binder ratios and foaming agent dosages. The compressive strength increased with density as a power function. The splitting tensile strength increased exponentially with the increase of compressive strength. When the water-to-binder ratio was 0.45, the flexural strength increased first and then decreased with the increase of fiber content. When the water-to-binder ratio was 0.50, the flexural strength increased with the increase of fiber content. The incorporation of fiber increased the pore size and water absorption rate of foam concrete, and reduced its frost resistance.

Abstract:The electric flux tests, scanning electron microscope and mechanical tests were carried out respectively on cementitious composites with single mixing and compound mixing CaCO₃ whisker and PVA fiber to investigate chloride ion resistance of multi-scale fiber reinforced cementitious composites. The effects and mechanisms of different fiber sizes, amount of admixture and mixing ratios on the chloride ion resistance and basic mechanical properties of cementitious composites were analyzed. In addition, the calculation method of the depth of chloride ion erosion was proposed. The results showed that different types of fibers can enhance cementitious composites at different structural levels, and the chloride ion resistance of multi-scale fiber reinforced cementitious composites is much better than that of single fiber reinforced cementitious composites. The compressive strength of composites is inversely proportional to the depth of chloride ion erosion and the electric flux. When the compressive strength of the composite was increased by 13.6%, the depth of chloride ion erosion and the electric flux were decreased by 39.1% and 44.7%, respectively. Based on the experimental data, a calculation model of chloride ion erosion depth considering the influence of compressive strength is established, which can be used to evaluate the chloride ion penetration and erosion resistance of cement-based materials reinforced by multi-fiber composite.

Abstract:Previous studies show that the fly ash geopolymer concrete cured at room temperature can be significantly improved if mixed into a small dosage of ordinary Portland cement. However, this modified material has rarely been compared with the traditional fly ash geopolymer concrete, cured at high temperature and not mixed with any ordinary Portland cement. In order to meet the needs of practical engineering applications, the basic mechanical properties, including Poisson,s ratios, were tested and compared between two different materials, i.e., the thermally cured fly ash polymer concrete without cement and the room temperature cured fly ash geopolymer concrete with a small dosage of cement particles. Also, to clarify the mechanism in results of the mechanical tests, the microscope and chemical elements tests, including SEM, EDS, XRD, FTIR and CT, are performed. The results show that the mechanical properties of room-temperature cured fly ash polymer concrete containing a little cement are close to those of thermal cured FGC without cement particles. Before compressive failure of prism specimens, the lateral to the vertical strain ratio is close to 1.0, exhibiting a significant lateral deformation capability. After adding 8% cement particles, the degree of polymerization reaction at room temperature is close to that of high temperature curing measures without cement. In forming a more reasonable microscopic pore structure, the samples cured at room temperature are better than those cured at high temperatures.

Abstract:On September 5th, 2022, an earthquake with magnitude 6.8 happened in Luding, Sichuan Province, which caused severe geological disasters and brought heavy workload for rescue. It was urgent to find out the damaged roads in the disaster-hit area and assess the difficulty of rescue work. Multiple damaged roads were investigated and 507 damaged points were found. Characterized by large number, small scale, and continuous distribution, landslides and collapse accounted for more than 90% of the total damage. The severity of highway damage was positively correlated with the seismic intensity, while it was negatively correlated with the distance from fault zones and rivers. Under the combination of adverse impact, the degree of disasters on high way significantly increased. In some regions, even 92.5% roads were damaged. During the road reopening and recovery, a strategy of using the water transport resources in the reservoir area of Longtoushi and Dagangshan Hydropower Station to quickly establish five wharves and a green pathway to the epicenter was proposed. The reconstruction of the transportation network made full use of the water way instead of focusing on the road grade and indicator, aiming to improve the road resistance to natural disasters.

Abstract: