Abstract:In this study, the strength expressions of horizontal and circular composite soils reinforced with rigid plastic belts were derived using experiments and theoretical analysis by considering the strength of the reinforcement material and the reinforcement material/soil ratio. Results revealed that the reinforced composite soil has greatly increased cohesion compared with plain soil. If there are grass roots in the soil inside the ring, a secondary reinforcement effect would form, and its strength would further improve. Good agreement between the calculated curve and the experimental curve was found, with a maximum error of 5.1%. However, the mobilization of the reinforced material is within 1%-7.5%. Lastly, analysis was performed on the strength indicators of the reinforced soil. Results showed that compared with plain soil, the cohesion and maximum internal friction angle of the reinforced composite soil are increased by 2.75-5.35 times and 21.7%, respectively. The cohesion values of the horizontal and circular reinforced soils are increased by 0.5-2.767 times and 0.732-3.417 times, respectively, while the maximum internal friction angle is increased by 2.2°. It is proposed that the combination of “four circular + three horizontal” reinforcement has the best reinforcement effect, followed by the combination of “two circular + four horizontal” reinforcement. In practice, the above two reinforcement forms can be referred to for the reinforcement and repair of the slope and foundation.

Abstract:In this study, considering one subway tunnel section in the Zhengzhou area as the research object, the tunnel structure was simulated with the three-dimensional fine segment, and orthotropic circular lining models were employed for the simulation of the tunnel structure, and the operation load of the metro train was simplified as the artificial excitation function. Afterward, the dynamic response of short-distance vertical overlapping tunnels during metro train operation was analyzed by the generated numerical model. The vertical vibration response, influence range, and dynamic stress of adjacent overlapping tunnels in terms of different factors (train position, tunnel structure, train speed, and tunnel clearance distance) were examined. The results revealed the remarkable impact of the running train in the upper tunnel on the vibration of the arch of the lower tunnel, the small impact of the running train in the lower tunnel on the vibration of the upper close tunnel, but a relatively small impact on other areas. The use of staggered assembly can reduce the vibration impact of short-distance vertical overlapping tunnels in the overlapping section. The train running in the upper tunnel has a large impact on the acceleration of the arch of the lower tunnel during the two stages of starting acceleration and reaching the maximum speed. With the decreasing net distance of the tunnel, there is a substantial increase in the vertical acceleration of the arch of the lower tunnel caused by the train on the upper tunnel, as well as the strongest overall vibration in the overlapping area. When the distance from the overlapping section is one time of the tunnel diameter, the influence of the net distance on the acceleration value can be neglected.

Abstract:In this study, to investigate the effect of the sinking depth of the source and receiver (hydrophone cable) on single-channel seismic exploration, a ghost wave influence model was developed. The Ricker wavelet was employed to simulate the source wavelet, and the impact of ghost waves, which arise as a result of the sinking depth of the source and receiver, on the primaries was analyzed. The conclusions were confirmed by the empirical data collected at different depths. The results exhibited that there exists an inverse correlation between the resolution of the seismic profile and the total depth of both the source and receiver. As the sinking depth of the source or hydrophone cable increases, the resolution of the seismic profile decreases, and the energy of the received seismic wave increases from a low value to the maximum value and then slowly decreases to a stable value. When the sinking depth of the hydrophone cable is less than 168.8/f (m), the fluctuation of the received seismic wave energy with the sinking depth of the source is relatively gentle. However, when the sinking depth is extremely small, the received seismic wave energy is greatly weakened, and the effective penetration depth of the seismic wave is substantially reduced. When the sinking depth of the source is approximately 292.3/f (m), the peak values of the primary and the source ghost wave overlap and the received seismic wave energy is the largest. When the sinking depth of the source is greater than 584.6/f (m), the increase in the sinking depth of the source has no impact on the increase in the received seismic wave energy if not considering the attenuation of the seismic wave energy in the water.

Abstract:There is an urgent need for the safe operation of highways, considering the development degree of geological disasters along the highway after earthquakes. In this work, a risk evaluation system based on the risks of geological disasters and novel protection engineering technology was established for highways in mountainous areas. In the proposed evaluation system, the damaged highway was scored in two stages, and the total disaster risk score was calculated from the corresponding evaluation index and weight coefficient of each stage to determine the geological hazard risk level threatening the highway. As a case analysis, the proposed system for geological disasters of highways in mountainous areas was applied on the Chuanzhusi—Jiuzhaigou highway after a typical debris flow disaster to confirm its applicability. The results exhibited that the evaluation system proposed in this work has good practicability and reliability in the reconstruction of the Chuanzhusi—Jiuzhaigou highway after the earthquake.

Abstract:As a strategic area for the development of the Hainan Free Trade Port's science and technology, further elucidation of the geological environment of Yazhou Bay in Sanya is a fundamental requirement for the development planning of science and technology. By selecting eight influencing factors, such as water depth, slope, sediment quality, area of ancient channels or ancient lakes, area of sand waves, area of sand ridges, area of soft soil, and thickness of soft soil, the suitability of the study area was quantitatively analyzed and evaluated via the K-means clustering method, analytic hierarchy process, and entropy weight method. The study area was divided into the following five suitability levels: good, relatively good, moderate, relatively poor, and poor. The impact of the different influencing factors on the suitability of Yazhou Bay was analyzed, and the geological environmental characteristics of the five zones were summarized. Results revealed that the area with the best suitability is located in the central-northern part of the study area, followed by the central-southern part; furthermore, the geological environmental quality of the two wings is the worst, and the moderate zone is distributed along the outer edge of Yazhou Bay. It is recommended to prioritize the planning and development of zones with good suitability, followed by the zones with relatively good suitability. In this study, the K-means clustering method was first employed to classify the influencing factors, and then the analytic hierarchy process and entropy weight method were utilized for the calculation of the subjective and objective weights of the evaluation factors, forming a scientific evaluation method combining the subjective and objective aspects. This method, when applied to the suitability evaluation of development in the geological environment, can effectively identify preferred areas. The results of this study can be used as references as well as offer a geological basis for development planning and disaster prevention in the study area.

Abstract:Dingxi City, Gansu Province, situated at the intersection of two tectonic systems, namely, the Qi—Lü—Helan tectonic system and the Hexi tectonic system, is susceptible to geological hazards such as landslides, collapse, and debris flow. To reduce these risks, systematic analysis of meteorology and hydrology, topography, geological structure, and various geological problems associated with highway construction was performed by using geological survey data and planning and survey data of existing and new roads. The analysis results revealed a close link between the diverse meteorological, hydrological, and geomorphological phenomena in the region and its unique geographic location and geological environment. The Dingxi area is categorized based on climate characteristics into a hilly-gully loess plateau in the north of the Weihe River and a high-cold and humid region to the south. The former is susceptible to geological problems such as landslides, collapses, and loess sinkholes, while the latter is prone to debris flows and widespread occurrence of landslides and collapses. Furthermore, special rock and soil properties, such as collapsible loess, soft rock fragmentation and severe deformation, loose sandstone, and other adverse geological conditions, considerably hampered the geological safety of road alternatives, the selection of a highway corridor, and the layout and construction of structures. This work offers a detailed discussion of the distribution law and development characteristics of these geological problems along the highway, as well as proposes comprehensive investigation and prevention measures to provide sound foundation and theoretical support for engineering construction and disaster prevention and mitigation in the region.

Abstract:Currently, earthquakes are impossible to predict accurately. Thus, determining the correlation between earthquakes and certain physical quantities by actively investigating earthquake-generating mechanisms is of great significance. The Earth plate above the asthenosphere rotates with the Earth, and changes in the Earth's rotation may trigger major earthquakes. In this paper, the relationship between major global earthquakes with magnitudes above M_W7.9 and the Earth's rotation period, polar motion, and nutation after the year 2000 was examined. A strong correlation was found between major global earthquakes and a change in length of day (LOD) with a period of approximately 13-15 days, polar motion with a period of approximately 1 year, and irregular nutation with a period of approximately 10 days. Analysis using Bayes theorem revealed that the probability of the occurrence of a large earthquake at the inflection point of LOD is three times that of random probability, while probabilities at the inflection points of X-direction pole motion, Y-direction pole motion, and nutation are six, three, and two times, respectively, that of random probability. The inflection point does not have a strictly fixed cycle because it is subject to irregular drifts caused by various perturbations. Major global earthquakes often occur at the inflection points of the aforementioned periodic changes. The study findings are expected to provide useful information for the prediction of large earthquakes.

Abstract:Performance-based design is a frontier scientific topic in the seismic design of retaining structures. In this study, the deformation mode of a modular reinforced soil retaining wall (RSRW) was investigated via the shaking table test. The displacement calculation methods of the retaining wall were collected and summarized, and the distribution laws of the yield acceleration coefficient under different failure modes were analyzed. Subsequently, a comparison of the consistency between the measured and calculated values of different calculation methods was done. The findings revealed that the displacement mode of the retaining wall is a rotation-based coupling of translation and rotation; moreover, the yield acceleration coefficients under the different failure modes solved by the safety factor method decrease with increasing input acceleration amplitude, and those obtained by the simple and energy methods are constants. Afterward, the yield acceleration coefficients were substituted into the different displacement calculation methods, and the displacements under different peak accelerations were calculated using the Richards and Elms upper bound method (less than 0.4g), Cai and Bathurst mean upper bound method (0.4g-0.6g), Newmark upper bound method (0.6g-0.8g), and Whitman and Liao mean fit method (0.8g-1.0g). Finally, the seismic design process of the modular RSRW was summarized.

Abstract:Examining the gravity anomaly characteristics, geological structure, and fault structure of the North China block and surrounding areas is significant for assessing earthquake risk and long-term mineral resource formation in this region. Based on the Bouguer gravity anomaly data from the North China block and surrounding areas, the wavelet approximations and details of the Bouguer gravity anomaly, Moho depth, and gravity anomaly derivatives are obtained via multiscale wavelet decomposition, Parker-Oldenburg iterative inversion, and gravity anomaly derivative methods. The key results are as follows: (1) the wavelet approximations and details show that the North China block can be divided into two subunits, namely, the Ordos Craton block in the west and the North China ring-like rift basin in the east. (2) The Moho depth is in the range of 28-52 km; it strikes NNE and gradually decreases from west to east, with obvious “east-west zoning.” In the Ordos Craton block and the North China ring-like rift basin, the Moho depth inside the block remains stable, whereas that below the block boundaries changes drastically. (3) Thirteen block boundaries and major fault zones in the study area are identified and corrected based on the derivative results of gravity anomaly.

Abstract:A dam breach accident occurred in a tailings pond in Jiaokou County, Shanxi Province, on March 17, 2022, which led to great economic losses. To investigate the reasons behind the dam breach, surcharge, dam deformation, and capacity change analyses were conducted retrospectively based on the stereo image pair data from multitemporal optical satellites and remote sensing techniques such as SBAS-InSAR. Additionally, the Slope/W module of GeoStudio software was employed to analyze the stability of the slope before the dam breach. It was revealed that (1) the capacity of the tailings pond reached its maximum value before September 2019, and it was surcharged to 960 000 m³ before December 2021 in the subpond behind dam 2^#, which exceeded the design capacity by 48 000 m³, thus reducing the stability of the dam. (2) The source of material of the dam breach mainly derives from the area above dam 2^#. The areas between dams 2^# and 1^#, as well as from dam 1^# to the gully, mainly contain accumulated material. (3) Furthermore, the dam breach is a typical seepage field-induced instability of the tailings dam, and the safety factor of the slope stability is reduced from 1.125 to 0.991 due to tailings loading, which is the direct inducing factor of the dam breach of the tailings pond.

Abstract:Instability of reservoir landslides can cause serious harm and inflict severe economic losses. Interferometric synthetic aperture radar (InSAR) has become a key tool in landslide identification. Time-series InSAR technology has the capacity to identify potential landslides; however, challenges exist, such as long data processing time and low efficiency with mass data. Thus, in this study, an InSAR phase gradient stacking-based approach to the rapid identification of potential landslides was proposed. The modified Sobel operator was employed for the calculation of the gradient of the InSAR differential interferometric phase. After error removal, the gradient superposition method was adopted to quickly identify the areas with deformation. Twenty-three potential landslides were successfully and rapidly identified in the Maoergai reservoir using this method, indicating high reliability and good detection ability of weak deformation. The identification speeds of the proposed method were 1.4 and 1.9 times faster than those of Stacking-InSAR and SBAS-InSAR, respectively. This proposed method, which can quickly and accurately identify potential landslides from massive data, offers guidance for the rapid identification of potential landslides in a wide area.

Abstract:After the Wenchuan earthquake, a large number of landslide dams were formed in debris flow channels in the mountainous areas of western China, which were prone to collapse and form outburst floods under heavy rainfall events. The intense erosion and scouring of downstream loose deposits by floods could exacerbate or trigger debris flow disasters and cause severe damage to downstream engineering structures. In this study, indoor flume experiments were performed to explore the responses of soil-water parameters and dynamic parameters in the deposits and behind the dam, which were utilized for the analysis of the initiation mechanism of erosion and scouring of loose deposits and the interaction mechanism between the deposits and the dam. A formula to compute the impact force of debris flow based on pore water pressure was derived. The findings revealed that (1) during the scour initiation process, lateral erosion and retreated erosion are the main modes of the deposits, with volumetric water content and pore water pressure increasing first and then decreasing and matric suction fluctuating and decreasing. (2) During the impact process of debris flow on the dam, two impact peaks appear behind the dam; moreover, the first peak results in unimpeded water discharge and an acceleration of 1.29 m/s², the second peak results in blocked drainage and an acceleration of 1.22 m/s², and the peak debris level reaches 95 mm. (3) The overall impact force of debris flow on the dam is composed of both dynamic and static parts; the static impact force is proportional to the pore water pressure behind the dam, and the dynamic impact force is proportional to the square of the flow velocity. This work offers theoretical and technical support to understand the scour initiation mechanism of gully loose deposits and the prevention of debris flow disasters after earthquakes.

Abstract:Luojing Gully is located southeast of Detuo Town, Luding County, Sichuan Province, and approximately 11 km from the gully opening to its southeast is the Dagangshan hydropower station. To effectively prevent the threat and damage caused by debris flow in Luojing Gully to the operation and maintenance of the Dagangshan hydropower station, the distribution characteristics of the materials in Luojing Gully after the “9·5” Luding earthquake and the motion evolution process of debris flow under different rainfall cycles were analyzed. From on-site survey and remote sensing image interpretation of LiDAR aerial photography before and after the Luding earthquake, it was concluded that 37 landslides with a total area of about 0.125 km² took place in Luojing Gully, and the actual amount of loose deposits was 155 200 m³. Thus, combined with precise material source, refined terrain, and 5%, 2%, and 1% rainfall frequencies, OpenLISEM numerical calculation was performed to characterize the motion evolution of the debris flow in Luojing Gully. The results revealed that during the recurrence periods of 5%, 2%, and 1% rainfall, the maximum mud depths and maximum flow velocities are 6, 8, and 11 m and 5, 7, and 10 m/s, respectively. At 5% and 2% rainfall frequencies, debris flow has a small blocking degree to the Dadu River, and at 1% frequency, it can cause a half blocking state.

Abstract:Owing to the rise and fall of reservoir water levels and rainfall events, several soil landslides show periodic step deformation. The deformation mechanism of such landslides is complex, and forewarning and forecasting of landslides are difficult. With the Woshaxi landslide as the research object, the deformation mechanism of secondary sliding mass was revealed, and the thresholds of rainfall and reservoir water level were revealed through more than 10 years of field inspection, 13 years of artificial monitoring data, and 4 years of automatic monitoring data. It was found that (1) the main factors controlling the deformation of secondary sliding mass change from reservoir water level drop and reservoir water immersion to continuous rainfall. (2) Continuous rainfall gives rise to slope deformation; the time of the “peak-value delay” effect of the deformation rate caused by rainfall is about 1-2 days, and the decay time of the displacement rate lasts about 5-9 days. (3) The cumulative rainfall threshold for 30 days is 150 mm, and 1-day rainfall before deformation is 40 mm; moreover, within 3 days after the deformation initiation, the accumulated rainfall exceeding 50 mm will accelerate the slope deformation and prolong the deformation time. The cumulative rainfall of 30 days before the reservoir water level decreases to 146 m is 115 mm, and the decline rate threshold of the reservoir water level is 0.8 m/d. This work offers a reference for monitoring and early warning of similar landslides.

Abstract:Quantitative studies on active faults based on tectonic geomorphology are essential for understanding the activity history and predicting future behavior. Currently, fault dislocations are mainly obtained by measuring tools, which should be analyzed for their reliability and applicability. In this study, three commonly used measuring tools (LaDicaoz, 3D_Fault_Offsets, and MCSST) were employed. Subsequently, based on the high-precision DEM obtained by the UAV photogrammetric technique, MCSST was applied to measure the vertical dislocation of fault scarps along the Danghe reservoir fault, and the LaDicaoz and 3D_Fault_Offsets were applied to measure the horizontal dislocation of the Huangxianggou fault. MCSST was used in this study to perform a detailed steep ridge vertical dislocation measurement of the Danghe reservoir fault. LaDicaoz and 3D_Fault_Offsets were utilized for accurate measurement of the horizontal dislocation of the Huangxianggou fault, and the reliability of these three measuring tools was further examined using the cross-checking method. Lastly, based on the extraction process and results, the automation degree, ease of use, repeatability, and other characteristics of the three software programs were compared and analyzed, and their advantages and disadvantages were summarized. Analysis results indicated that LaDicaoz and 3D_Fault_Offsets have high accuracy and decent application in horizontal displacement measurement, and MCSST is better applicable in vertical displacement extraction. However, the automation degree of the three tools needs improvement. This study may further enhance the development of scientific and practical measurement software tools.

Abstract:Grotto stability and visitor safety are threatened by the development of dangerous rock mass. Monitoring and analysis of the deformation characteristics of dangerous rock mass in grottoes play a crucial role in the stability assessment of rock mass. Considering the North Grotto Temple in Qingyang, Gansu Province, as the example, Global Navigation Satellite System deformation monitoring, joint meter, and noncontact fissure monitoring techniques were applied for analysis of the deformation characteristics of dangerous rock mass in three scales, namely, the regional geological body, cliff body, and key blocks of the North Grotto Temple. During the monitoring period, the displacement of the upper regional geological body presented a sudden change, with a settlement of 5.2 mm after continuous rainfall, the displacement of the central bedrock recovered gradually after a slow growth, and the deformation was within ±1 mm. The deformation at the bottom of tectonic fissures in cliff increased in fluctuating form, with the highest value in January—February of the following year. With decreasing temperature, the deformation rate in the middle of the fissure was quicker than that at the bottom. The deformation of superficial fissures in cave 32 fluctuated near 0 mm in the range of ±2 mm. Deformation of the regional geological body was highly correlated with rainfall, and that of the cliff was negatively correlated with temperature; moreover, the deformation of key blocks was also susceptible to temperature, humidity, and human disturbance. Current deformations of the rock masses at the three scales varied within a small range, with little influence on each other and no synergy. This study can provide reference data for the stability assessment and predictive analysis of the North Grotto Temple.

Abstract:To further investigate the mechanical properties of solidified loess, specimens with different solidified agent content were prepared with loess in Zhengzhou area, and cured to the test age under standard curing conditions before they were saturated. Using GDSTTS standard stress path triaxial apparatus, a series of consolidated-undrained (CU) shear tests were carried out, and the influences of confining pressure, solidified agent content, and curing age on the mechanical properties of solidified loess were studied. The experimental results show that the solidified loess in Zhengzhou area has remarkable structural characteristics; the stress-strain curves are characterized by strain softening and can be described by three-parameter expression of hump type. In addition, the peak stress and residual stress of solidified loess increase with the increase in the confining pressure, the content of curing agent, and the curing age. However, the influence of the curing age on the strength of solidified loess weakens after curing for more than a certain time.

Abstract:Using the strong motion record database of the Loess Plateau, 1 209 items of strong motion records were selected from 144 strong motion stations, and a simplex algorithm was employed for calibration of the response spectrum to investigate the relationship between the characteristic period of the site design response spectrum and the epicenter distance and magnitude in the Loess Plateau region. The results revealed the following: (1) on the class II site, there is a relationship established between the characteristic period of the design response spectrum and the epicenter distance; furthermore, the horizontal characteristic period gradually increases with increasing epicenter distance, while the vertical characteristic period remains nearly constant with the changing epicenter distance (M≤6.5). (2) At the class II site, the characteristic period of the horizontal design response spectrum is positively correlated with the earthquake magnitude (4.0＜M＜7.0); moreover, when the epicenter distance varies between 90 km and 150 km, the relationship between the characteristic period and the magnitude can be expressed by T_g=0.054M -0.017 (EW), and T_g=0.066M -0.085 (NS). (3) Compared with the characteristic period values of the ground motion acceleration response spectra for sites in Table 3.2.3 of the Specification for Seismic Design of Buildings (DB 62/T 3055—2020), the characteristic periods of the design response spectra for class II sites in the Loess Plateau region given in this study are lower than the specified values of the first and second groups of design earthquakes; however, they are higher than the specified values of the third group when the magnitude is greater than 6.0. This work can offer guidance for determining the characteristic period of the design response spectra of engineering sites in the Loess Plateau region.

Abstract:In this work, an artificial seismic wave fitting method was proposed based on embedded baseline drift correction, which is different from the traditional frequency domain method. First, a nonstationary displacement expression was generated to derive the time-history expressions for velocity and acceleration. Subsequently, the envelope function can be obtained from the zeroing condition satisfied by each expression. Then, combined with the analytical formula for the harmonic response of a system with a single degree of freedom, the target response spectrum fitting problem can be transformed into a set of nonlinear equations to establish the amplitude spectrum. Finally, the efficient iteration algorithm for nonlinear equations was employed to acquire the acceleration, velocity, and displacement time histories at the same time. The standard spectrum of Rg1.60, the floor spectrum of a nuclear island, and the design spectrum in the Code for Seismic Design of Buildings were utilized to confirm the efficiency and accuracy of the proposed method. Therefore, the novel method proposed in this work can be employed for the fast fitting of artificial seismic waves.

Abstract:In this study, the seismic performance of concrete columns confined by corroded stirrups after reinforcement was studied. Sixteen reinforced concrete (RC) rectangular columns were designed, and the corrosion-accelerated specimens were strengthened with enveloped steel and carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP). Finally, low-frequency cyclic loading tests were performed to investigate the effects of different reinforcement materials, different reinforcement wrapping methods, and different bonding materials on the hysteresis curve, skeleton curve, stiffness attenuation, ductility performance, and energy dissipation capacity of the RC columns confined by corroded stirrups. The findings revealed that (1) compared with the noncorroded column, the strengthened corroded column is dominated by bending shear failure. The CFRP-strengthened specimen has a higher bearing capacity than the GFRP-strengthened specimen, but its ductility is lower than that of the GFRP-strengthened specimen. (2) Compared with the noncorroded column, the energy dissipation capacities of the enveloped steel-strengthened specimen, the CFRP-strengthened specimen, and the GFRP-strengthened specimen are increased by 222.3%, 123.9%, and 98.5%, respectively as well as their ductility coefficients by 45.3%, 22.3%, and 25.6%, respectively. Therefore, enveloped steel reinforcement offers the greatest improvement in seismic performance of stirrup-corroded columns; moreover, CFRP reinforcement is superior to GFRP reinforcement, whole-clad reinforcement is better than ring-clad reinforcement, and epoxy resin adhesive has slightly better bonding than cement-based grout.

Abstract:With the growth of the nuclear power industry and the reduction in high-quality sites, the third-generation AP1000 semi-active tube-ring hybrid nuclear power plant is likely to build on non-bedrock sites, facing near-site vibration. Therefore, it is crucial to research near faults comprehensively and evaluate the seismic performance and reliability of near-fault nuclear plant sites. In this study, the dual effects of the hard soil foundation and horizontal displacement limiter on the structure were first considered. According to ATC-63, 15 groups of far-field and 14 groups of near-field ground motions were selected, and the material strain was taken as the damage index. Then, the seismic damages of the AP1000 tube-ring hybrid workshop with and without a base-isolation device were compared and analyzed. Next, different effects of base-isolation measures of the building structure under near-field and far-field earthquakes were explored. Results showed that the base-isolation measures for the tube-ring hybrid workshop have an obvious isolation effect under a near-field earthquake action, which is smaller than that under far-field earthquakes. Under the near-field ground motion, the fourth-level damage safety of the workshop with the base-isolation device is greater than that without the base-isolation device. However, the fourth-level damage safety still meets code requirements. Therefore, constructing a workshop on non-bedrock sites in near-fault areas is feasible.

Abstract:On January 8, 2020, a strong magnitude M6.9 earthquake occurred in Menyuan County, Qinghai Province, resulting in damage to the Ming Great Wall in Shandan County, Gansu Province. This study aimed to examine the dynamic response and damage characteristics of the rammed earth walls under this earthquake by surveying the seismic site. Using the recorded seismic waves after amplitude equivalent processing as input ground motions, numerical analysis was conducted on the dynamic response of the rammed earth walls under bidirectional seismic loading. The maximum displacement, peak acceleration, and wall stress distribution characteristics of different measuring points were analyzed, and the main internal cause of the earthquake damage was discussed. The findings reveal that the wall displacement and peak ground acceleration (PGA) gradually increase with increasing height under bidirectional seismic load; however, the PGA amplification effect is not apparent within a height range of 0.5 m from the bottom of the wall. The maximum displacement and acceleration take place at the crack position on the top of the wall. The ground motion response of walls under horizontal seismic load is more obvious. The maximum principal stress and maximum shear stress emerge in the overhanging part at the bottom of the wall where there are cracks, and the stress concentration is evident in the position of wall cracks, rammed lap joints, and excavated overhangs. The amplification effect of cracks on the ground motion of the rammed earth wall exhibits a weakening effect within a certain height range but gradually changes to a strengthening effect with increasing height. Cracks can substantially improve the seismic response at the top of the wall, which is probably the main internal cause of the wall damage induced by this earthquake. This work can contribute to a scientific basis for the reinforcement and repair of ancient city wall sites.

Abstract:The interface connection between carbon fiber-reinforced polymer (CFRP) plates and steel beams has an influence on the reinforcement effect and bearing performance of steel beams. To better determine problems regarding debonding, an effective approach to qualitatively identi-fying the interface debonding position was examined. In this study, the bonding and debonding specimens of CFRP plate-reinforced steel beams were fabricated. Sound signals were acquired by locally knocking on specified positions, and then, Welch power spectral density (PSD) estimation and fast Fourier transform (FFT) were employed for analysis of the spectral characteristics of sound signals. The findings exhibited that the difference between the peak values of two curves from the Welch PSD estimation is distinct within the low-order vibration frequency range of 0-500 Hz, and the frequency at the peak of the PSD curve with debonding damage is obviously shifted to zero compared with the corresponding frequency at the normal part. The average first-order vibration frequency extracted from PSD curves under the first working condition quantitatively shows the change in frequencies at the debonding damage and normal parts, which corresponds to the decrease in local stiffness after debonding. Compared with the traditional FFT damage location method, the peak values of the PSD curves are greatly different from those of the FFT curves; therefore, it is easier to determine whether the debonding damage has occurred at the position. Moreover, the influence of hammerheads with different attributes on the experiment results was investigated, thus providing a reference for practical engineering.

Abstract:The seismic safety of lifeline infrastructure is of great importance for disaster prevention and mitigation and earthquake relief work in China, as railway bridges are more associated with the safety and stability of personnel transfer and material transportation. Based on the analysis of the seismic data and seismic damage investigation of railway bridges in earthquake areas, combined with practical experience from seismic design of railway bridges in China and relevant scientific research results, three issues of the Code for Seismic Design of Railway Engineering have been successively published in China. This paper reviewed the 60-year development history of codes for seismic design of railway bridges in China and classified the historical periods in which seismic design work for railway bridges has been performed in China. A comparison and summary of the sections regarding railway bridges in the 1977, 1987, and 2009 issues of the Code for Seismic Design of Railway Engineering revealed that the code series gradually embodies the concept of performance-based design, with more refined site classification, more scientific consideration of seismic effects, and more explicit provisions for seismic structural measures of railway bridges. Thus, the objective of this study is to offer a reference to improve and refine the methods for predicting seismic damage of railway bridges in seismic zones.

Abstract:Viscous dampers can be destroyed due to a certain limit state during large earthquakes. However, existing research on viscous dampers for cable-stayed bridges has mostly focused on the parameter optimization of dampers, and only a few studies have considered the impact of damper failure on the seismic performance of cable-stayed bridges. In this paper, a finite element model of a three-tower cable-stayed bridge and a simplified model of viscous dampers were established based on the OpenSees platform, taking into account the bearing capacity and travel limit. The influence of the damping coefficient and the damping index of the viscous damper on the seismic response of the cable-stayed bridge was studied, and the values of the damper parameters were determined. Nonlinear time-history analysis of the cable-stayed bridge was conducted, and the seismic responses were compared for the following conditions: without dampers, with dampers but not considering the limit state, and with dampers and considering the limit state. Results show that the energy dissipation capacity and the damping effect of the damper would be significantly decreased by considering their limit states during large earthquakes. The seismic capacity of cable-stayed bridges with energy dissipation design will be overestimated if the failure of dampers as a result of reaching their limit states is not taken into consideration.

Abstract:The influence of seismic excitation on the dynamic response of high-speed vehicle-simply supported box girder bridge system is related to the operation safety of high-speed railway. Based on the theories of vehicle-rail coupling dynamics and train-rail-bridge dynamic interaction, the dynamic model for vehicle-rail-bridge coupling system in high-speed railway bridge section was established by using the finite element and multi-body dynamics methods, and the dynamic response of vehicle-rail-bridge coupling system of high-speed railway under the action of artificial seismic waves was analyzed. Results show that the influence of seismic excitation on the lateral vibration characteristics of track slab, support layer, and bridge is higher than that on the vertical vibration characteristics, and the sensitivity of bridge structure to seismic excitation is higher than that of track structure. The influence of vehicle speed on the vertical vibration characteristics of system is higher than that on the lateral vibration characteristics. The study results can provide a theoretical basis for the safe operation of high-speed railway under seismic load.

Abstract:To consider the impact of structural parameter uncertainties on the seismic fragility of nuclear power plants, a seismic fragility analysis based on the first-order second-moment method (FOSM) was carried out in this research. The uncertainties of the four concrete parameters of nuclear power structures were investigated: the density, elastic modulus, Poisson's ratio, and tensile strength of the concrete material. A finite element model was established, and the results were compared with test results to verify the model accuracy. Based on the finite element numerical simulation, dynamic responses of the nuclear power plant model under multiple seismic records with different peak accelerations were calculated using the incremental dynamic analysis method. Meanwhile, the logarithmic standard deviation under parameter uncertainties was obtained on the basis of FOSM to evaluate the seismic fragility curves of nuclear power structures. Results indicated that structural parameter uncertainties have certain influences on nuclear power structures, and seismic fragility results that overlook such uncertainties underestimate structural failure probabilities. This method can provide a theoretical basis and offers practical value for the fragility analysis of nuclear power structures considering parameter uncertainties.