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The tight oil/gas reservoirs in China have showed the great exploration prospects and high production potential, with the characteristics of low porosity, low permeability, and significant heterogeneity in formation rocks. It remains a challenge to sort out the relations between reservoir wave responses and rock physical properties, and the further studies on the wave response patterns of tight reservoirs are in an urgent demand. The shear modulus and S- (shear) wave attenuation of rocks are affected by the properties of pore fluid and confining pressure. The ultrasonic wave experiments are performed on eight partially-saturated tight sandstone samples at different confining pressures, and we estimate S-wave attenuation with the spectral-ratio method. Results show that S-wave attenuation decreases with increasing confining pressure, and the water saturation case shows more loss compared to the oil saturation case, while the gas saturation case gives the lowest attenuation. We observe the S-wave relaxation peak at an intermediate water saturation for the gas-water partial-saturation case in general. S-wave attenuation increases with increasing porosity or permeability. Based on the measured rock physical properties, and combined with the Voigt–Reuss–Hill (VRH) average, differential effective medium (DEM) model and squirt-flow model, a tight rock attenuation model is proposed for analyzing the attenuation characteristics of fluid-saturated rocks at different confining pressures. The model reasonably describes the S-wave attenuation characteristics. The model predictions of S-wave attenuation show apparent pressure- and fluid-sensitivity at full saturation and partial saturation conditions. For sample TS1-19 at full saturation with different confining pressures, the S-wave peak attenuation predicted by the model ranges from 11.6 to 69.5, and decreases with confining pressure, while the relaxation frequency shifts to high frequency end. For the partial saturation condition of the sample, the predicted S-wave peak attenuation ranges from 15.5 to 39.8 at a confining pressure of 30 MPa and increases with water saturation, while the relaxation frequency shifts to low frequency end. For all the samples at 30MPa confining pressure, the predicted S-wave attenuation ranges from 5.6 to 38.6. At the full-saturation case, the predicted S-wave attenuation increases with porosity and decreases with confining pressure. For the partial saturation case, the S-wave attenuation predicted with the model and the Voigt and Reuss bounds generally increases with water saturation, whereas the experimentally-measured attenuation exhibits the peak attenuation at an intermediate saturation. [ABSTRACT FROM AUTHOR]

The dynamic characteristics of the filler are intricately linked to the stability of the subgrade. In this investigation, relying on Haoji (Haolebaoji-Ji'an, China) heavy-haul railway engineering, cyclic triaxial tests were executed to scrutinize the dynamic attributes exhibited by the 3%–5% cement-stabilized expansive soil (CSES) across a series of diverse cyclic stress, confining pressures, and frequencies. Concurrently, in situ vibration trials were undertaken to dissect the dynamic characteristics inherent to the CSES subgrade. The outcomes of cyclic triaxial tests indicate that the augmentation in both the dynamic shear strength and modulus of CSES by a factor of 2–3, coupled with an escalation of the critical dynamic stress threshold by five tosix times, is attributed to the heightened internal structural density within the CSES compared to virgin expansive soil. In identical settings, it is noteworthy that the mean critical dynamic stress threshold observed for CSES surpasses that of Group A filling by a factor of 1.5–1.7. Furthermore, the maximum critical dynamic stress exhibited by CSES achieves a 1.2-fold superiority over its lime-stabilized expansive soil (LSES). The outcomes gleaned from the in situ vibration tests elucidate that, when subjected to the passage of a high-velocity train traveling at 120 km/hr, bearing the load of 25–30 tons per axle, the subgrade surface exhibits dynamic stress ranging from 98.57 to 116.07 kPa. Meanwhile, the dynamic stress undergoes a notable escalation due to rainfall infiltration, intensifying by a factor of 1.02–1.28 times its original magnitude. The influence depth of dynamic stress extends 1.4–1.6 times beyond the designed subgrade bed thickness of 2.5 m. Notably, the critical dynamic stress of the filler surpasses the dynamic stress at the same position, underscoreing the capacity of 3%–5% CSES filling for heavy-haul railways to ensure long-term dynamic stability. [ABSTRACT FROM AUTHOR]

This study examines the widespread practice of upstream tailings dam construction in metallurgical mines in China, conducting comprehensive testing and research on tailings from various depositional zones of the Caijiagou tailings pond. Analysis of the test results from three types of tailings reveals a systematic relationship between the mechanical characteristics of tailings and their depositional zones: the farther from the dam, the finer the tailings particles, categorized as silty clay tailing, silt tailing, and sandy silt tailing. Consistent patterns were observed in the consolidated-drained shear strength and consolidated-undrained effective shear strength of these tailings. Among these, sandy silt tailing exhibited the highest strength, whereas silty clay tailing displayed the lowest. The dynamic stress–strain relationships of all three tailings types are described using the Hardin equivalent viscous-elastic model, where the initial dynamic shear modulus and the maximum dynamic shear stress in the model increased with effective confining pressure. The damping ratios exhibited a three-stage trend with increasing dynamic strain: gradual increase, rapid growth, and then gradual stabilization. Under various consolidated stress conditions, the ratio of the damping ratio to the maximum damping ratio versus the reduction in dynamic shear modulus showed a favorable linear relationship. Under vibration conditions, the dynamic shear stress corresponding to tailings failure increased with higher effective confining pressure and consolidated stress ratio. Finally, this study summarizes the parameters and indicators related to the saturated tailings of iron mines used in the research. Our work provides a foundation and reference for the design of tailings dams and the development and utilization of abandoned tailings ponds. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of clayey loess is strongly affected by the soil structure, but although anisotropy has been identified in loess by some, the anisotropy of small-strain behaviour is rarely reported. This paper presents an experimental study on the inherent and stress-induced small-strain shear stiffness anisotropy of a clayey loess from China. Both undisturbed and reconstituted specimens were tested with bender elements under isotropic compression and shearing conditions. Under an isotropic stress state, an inherent anisotropy was found for undisturbed specimens, while the reconstituted specimens prepared by moist tamping behaved isotropically. During shearing, the ratio of horizontal to vertical shear moduli of the undisturbed specimens decreased due to both an increase of stress anisotropy and the destruction of the intact structure. In contrast, the stiffness ratio of the reconstituted specimens only decreased due to stress anisotropy and it became more anisotropic at the critical state. This study reveals the influence of intact structure and inherent anisotropy on the behaviour of loess soils, which cannot be reproduced by compaction, thus highlighting the importance of characterising the undisturbed loess. [ABSTRACT FROM AUTHOR]

Until the Mw 6.6 Luding earthquake ruptured the Moxi section of the Xianshuihe fault (XSHF) on 5 September 2022, the region had not experienced an Mw >6 earthquake since instrumental records began. We used Global Positioning System (GPS) and Sentinel-1 interferometric synthetic aperture radar (InSAR) observations to image the coseismic deformation and constrain the location and geometry of the seismogenic fault using a Bayesian method We then present a distributed slip model of the 2022 Mw6.6 Luding earthquake, a left-lateral strike-slip earthquake that occurred on the Moxi section of the Xianshuihe fault in the southwest Sichuan basin, China. Two tracks (T26 and T135) of the InSAR data captured a part of the coseismic surface deformation with the line-of-sight displacements range from ∼−0.16 m to ~0.14 m in the ascending track and from ~−0.12 m to ~0.10 m in the descending track. The inverted best-fitting fault model shows a pure sinistral strike-slip motion on a west-dipping fault plane with a strike of 164.3°. We adopt a variational Bayesian approach and account for the uncertainties in the fault geometry to retrieve the distributed slip model. The inverted result shows that the maximum slip of ~1.82 m occurred at a depth of 5.3 km, with the major slip concentrated within depths ranging from 0.9–11 km. The InSAR-determined moment is 1.3 × 1019 Nm, with a shear modulus of 30 GPa, equivalent to Mw 6.7. The published coseismic slip models of the 2022 Luding earthquake show apparent differences despite the use of similar geodetic or seismic observations. These variations underscore the uncertainty associated with routinely performed source inversions and their interpretations for the underlying fault model. [ABSTRACT FROM AUTHOR]

Assessing the nonlinearity of a site plays a crucial role in earthquake engineering. For some building structures and lifeline projects that need safety assessment after earthquakes, the analysis of nonlinear degree of sites can help accurately revealing the amplification effect of sites and evaluating the damage degree of buildings which is convenient for subsequent reinforcement and demolition work. The quantitation of nonlinear threshold of sites is an important method to evaluate the degree of site nonlinearity. In this paper, a nonlinear characteristic index reflecting the degradation of shear modulus is proposed based on the instantaneous frequency of the site calculated by using the vector auto-regression moving average (VARMA) model. Then, seismic records of class I, II, III and IV sites specified as per code for seismic design of buildings in China are selected from the KiK-net network in Japan, and the threshold value of ground motion acceleration characterizing the nonlinear response of sites are provided. Finally, the variation of the nonlinear characteristic index (shear modulus degradation) vs. different (peak ground acceleration) PGA for four types of sites are presented. [ABSTRACT FROM AUTHOR]

To apply the discrete element method (DEM) to simulate the interaction process between soda saline–alkali soil and subsoiling component in Northeast China, establishing the soda saline–alkali soil particle model and selecting more accurate simulation parameters are important. In this paper, we studied the soda saline–alkali soil of the Songnen Plain in China. First, we studied the geometric shape of soda saline–alkali soil particles and proposed a modeling method for single soil particles based on the multisphere combination method. Considering the cohesion of soda saline–alkali soil particles, the Hertz–Mindlin with JKR (JKR) model was used as the contact model between soil particles. Then, the calibration method was used to obtain simulation parameters of soils that are difficult to obtain experimentally. We conducted soil angle of repose (AoR) tests, the Plackett–Burman (PB) tests, and steepest ascent (SA) tests in turn to perform a sensitivity analysis for microscopic contact parameters and select the parameters that have a significant effect on the response value (static AoR), i.e., soil surface energy, soil–soil static friction coefficient, and soil–soil rolling friction coefficient. Then, the optimal combination of simulation parameters was obtained via the Box–Behnken (BB) tests, using ANOVA to optimize the multiple regression equation. Finally, the optimal parameter combination was verified by the AoR test and the direct shear (DS) test. The results showed that the parameters had good adaptability for the AoR test. However, the simulation results of the DS test were significantly different from the experimental values. Therefore, the contact model needs to be further modified by adding Bonding bonds between soil particles based on the JKR model and further correcting for Rayleigh time step, shear modulus, and surface energy. By comparing the simulation and the experimental results, it was found that the simulation results obtained from both the DS test and AoR test had relatively small errors relative to physical tests, the two trends are the same, and the values are similar. This verified the feasibility and effectiveness of the soda saline–alkali soil particle modeling method and parameter selection proposed in this paper. [ABSTRACT FROM AUTHOR]

In southern China, granite residual soil (GRS) is widely used as road base material. Thus, it is important to study the effects of hot and rainy climates and cyclic loads generated by trains on the dynamic properties of GRS. In this work, by means of dynamic triaxial tests, the effects of the number of drying and wetting (D–W) cycles, fines content and number of load cycles on the hysteresis curve, dynamic shear modulus Gd and damping ratio λ of GRS are systematically investigated. The experimental results illustrate the changes in the morphology of the hysteresis curve and dynamic parameters with the numbers of load and D–W cycles, as well as the fines content. Namely, the area S, center offset d, and residual strain εsp of the hysteresis curve decrease with the increase of load cycle number, increase with the growth of fines content, and first decrease with the increase of D–W cycle number, then slowly increase to stabilized values. However, the major axis gradient k exhibits exactly the opposite relationships. Meanwhile, the dynamic shear modulus Gd increases with the growing load cycles and decreases with the addition of fines content, and the damping ratio λ shows the opposite behavior. It is also shown that Gd and λ vary linearly with respect to logN, where N is the number of D–W cycles. The dynamic properties of GRS are mostly affected by the number of load cycles, which is followed by the fines content and then the number of D–W cycles. The influence of the latter two factors on the dynamic properties of GRS may be primarily due to contact form changes between soil particles. [ABSTRACT FROM AUTHOR]

Seismic petrophysics is an important link between seismic elastic properties and reservoir physical properties. Based on the petrological and microstructure characteristics of shale in the Qingshankou formation of Sanzhao sag in the north of Songliao Basin, this paper presents an anisotropy petrophysical model with complex pore structure suitable for organic shale constructed with the use of the Voigt-Reuss-Hill average model, an anisotropy self-consistent approximation+differential effective medium model, and the layering of clay and kerogen is simulated by using the Voigt-Reuss-Hill average and bond transform to achieve the simulation of shale anisotropy. Based on the proposed model, the effects of the organic volume fraction, porosity, and pore aspect ratio on rock elastic properties are discussed. The result shows that with the increase of matrix porosity, all elastic parameters show a decreasing trend; with the increase of the organic volume fraction, except shear modulus, other elastic parameters show an increasing trend. Through comparative analysis, the elastic parameters (Lamé impedance and Shear impedance) sensitive to the organic volume fraction and porosity are optimized; the seismic petrophysical cross-plot template with core calibration is constructed. The application shows that the predicted S-wave velocity based on the proposed model is in good agreement with the S-wave velocity derived from dipole source logging. Combined with the high-precision prestack elastic parameter inversion, the "sweet spot" characteristics can be well described, and the research could contribute to a better "sweet spot" description and provide a better support for shale exploration in Sanzhao sag. [ABSTRACT FROM AUTHOR]

In this study, a series of resonant-column experiments were conducted on marine clays from Bohai Bay and Hangzhou Bay, China. The characteristics of the dynamic shear modulus (G) and damping ratio (D) of these marine clays were examined. It was found that G and D not only vary with shear strain (γ), but they also have a strong connection with soil depth (H) (reflected by the mean effective confining pressure (σm) in the laboratory test conditions). With increasing H (σm) and fixed γ, the value of G gradually increases; conversely, the value of D gradually decreases, and this is accompanied by the weakening of the decay or growth rate. An intelligent model based on a back-propagation neural network (BPNN) was developed for the calculation of these parameters. Compared with existing function models, the proposed intelligent model avoids the forward propagation of data errors and the need for human intervention regarding the fitting parameters. The model can accurately predict the G and D characteristics of marine clays at different H (σm) and the corresponding γ. The prediction accuracy is universal and does not strictly depend on the number of neurons in the hidden layer of the neural network. [ABSTRACT FROM AUTHOR]

An increasing amount of waste seashells in China has caused serious environmental pollution and resource waste. This paper aims to solve these problems by using waste seashells as modified materials to prepare high-performance modified asphalt. In this study, seashell powder (SP) and stratum corneum-exfoliated seashell powder (SCESP) were adopted to prepare 10%, 20% and 30% of seashell powder-modified asphalt (SPMA) and stratum corneum-exfoliated seashell powder-modified asphalt (SCESPMA) by the high-speed shear apparatus, respectively. The appearance and composition of two kinds of SPs were observed and determined by the scanning electron microscope (SEM). The types of functional groups, temperature frequency characteristics, low temperature performance and adhesion of SPMA were tested by the Fourier-transform infrared (FTIR) spectrometer, dynamic shear rheometer (DSR), bending beam rheometer (BBR) and contact angle meter. The results show that the SP and SCESP are rough and porous, and their main component is CaCO3, which is physically miscible to asphalt. When the loading frequency ranges from 0.1 Hz to 10 Hz, the complex shear modulus (G*) and phase angle (δ) of SPMA and SCESPMA increase and decrease, respectively. At the same load frequency, SCESPMA has a larger G* and a smaller δ than SPMA. At the same temperature, SCESPMA has a larger rutting factor (G*/sin δ) and better high-temperature deformation resistance than SPMA. SP and SCESP reduce the low-temperature cracking resistance of asphalt, of which SCESP has a more adverse effect on the low-temperature performance of asphalt than SP. When SP and SCESP are mixed with asphalt, the cohesion work (Waa), adhesion work (Was) and comprehensive evaluation parameters of water stability (ER1, ER2 and ER3) of asphalt are improved. It is shown that both SP and SCESP have good water damage resistance, of which SCESP has better water damage resistance than SP. These research results have important reference value for the application of waste biological materials in asphalt pavement. [ABSTRACT FROM AUTHOR]

Diatomite is a widespread geological substance found in coastal and lake areas worldwide. Although diatomites are increasingly used in geotechnical engineering construction, a significant knowledge gap exists regarding their mechanical responses to static and dynamic loadings, particularly in high-speed railway projects. This study investigates the static and dynamic behaviors of diatomites through extensive experiments, considering both natural and remolded states. It focuses on representative diatomite specimens obtained from the Shengzhou region in China, an area intersected by the Hang-Shao-Tai high-speed railway. The results of uniaxial compression and undrained triaxial shear tests show that the structural degradation of diatomite significantly impacts its stress-strain responses, failure patterns, and mechanical parameters under static and dynamic loading conditions. The structural effects of natural diatomite tend to degrade as the confining pressure level increases, resulting in corresponding changes in its mechanical parameters. Undrained triaxial shear tests conducted on natural diatomite reveal that the inclinations of the shear band closely correspond to those predicted by the Mohr-Coulomb solution. Additionally, we present a modified hyperbolic-type model to evaluate the damping ratio of diatomites. Furthermore, a power-law model based on Hardin's formula was used to predict the maximum shear modulus of diatomites under varying stress levels and void ratios. Microstructural and chemical analyses were conducted using scanning electron microscopy and X-ray diffraction to gain insights into the observed structural effects at the microscale. • Investigated static/dynamic properties of Shengzhou diatomite for Hang-Shao-Tai railway geotechnics enhancement. • Shengzhou diatomite transitions from localized to homogeneous deformation, indicating high-strength weakening. • Shengzhou diatomite's strength is notably affected by structural degradation, particularly concerning cohesion. • Revealing Shengzhou diatomite's geomechanical properties in China enriches diatomite understanding databases. [ABSTRACT FROM AUTHOR]

The small-strain stiffness of soil is significant in the accurate prediction of the deformation caused by interactions between foundation soil and structures. Considering the whole range of small strain (10−6~10−3), a bending element-resonant column (BE-RC) combined test system was developed to conduct continuous tests on the shear modulus of unsaturated soil. Under the dehydration path, it was used to investigate the small-strain shear modulus of unsaturated silty-fine sand in Hangzhou Bay, China. The results show that the shear modulus under different net stresses and matrix suctions appeared to non-linearly decay with the increase in strain until stable values were reached at a large strain. At the beginning from the saturated state, the Gmax value increased slowly with decreasing saturation and reached its maximum value at the optimum saturation (Sr)opt; then, it rapidly decayed to the level in the saturated, once the saturation degree decreased to a level lower than (Sr)opt. Additionally, an improved prediction model was proposed for the Gmax of unsaturated sand, considering different saturations. Based on the mesoscopic evolution of internal pore water morphology and the variation in intergranular stress caused by capillary action, the variation in the Gmax could be divided into three segments of saturation: the boundary effect stage, the transition stage and the unsaturated residual stage. [ABSTRACT FROM AUTHOR]

This paper presents results from a series of stress-controlled undrained cyclic triaxial tests on the undisturbed marine silty clay, silt, and fine sand soils obtained from the Bohai Sea, China. Emphasis is placed on the major factors for predominating the dynamic shear modulus (G) and damping ratio (λ) in the shear strain amplitude (γa) from 10−5 to 10−2, involving depth, sedimentary facies types, and water content of marine soils. The empirical equations of the small-strain shear modulus (Gmax) and damping ratio (λmin) using a single-variable of depth H are established for the three marine soils. A remarkable finding is that the curves of shear modulus reduction (G/Gmax) and the damping ratio (λ) with increasing γa of the three marine soils can be simply determined through a set of explicit expressions with the two variables of depth H and water content W. This finding is validated by independent experimental data from the literature. At the similar depths, the G value of the marine soils of terrestrial facies is the largest, followed by the neritic facies, and the G value of the marine soils of abyssal facies is the smallest. The sedimentary facies types of the marine soils have slight effect on the λ value. Another significant finding is that the shear modulus reduction curves plotted against the γa of the three marine soils at the similar depths are significantly below those of the corresponding terrigenous soils, while the damping curves plotted against γa are just the opposite. The results presented in this paper serve as a worthful reference for the evaluation of seabed seismic site effects in the Bohai Sea due to lack of experimental data. [ABSTRACT FROM AUTHOR]

Offshore wind power construction is currently experiencing rapid growth worldwide, with China leading in the number of offshore wind turbines. Approximately 60 % to 70 % of these turbines are situated in the offshore area of the South Yellow Sea, Jiangsu Province. Despite its frequent exposure to waves and earthquakes, this region lacks comprehensive studies on the dynamic characteristics of local marine soils, which hinders the development of marine engineering design. This study addresses this gap by conducting a series of tests on marine silty sand using a combination of resonant column and dynamic triaxial tests. The investigation examined various dynamic parameters at both small and large strain scales, taking into account the soil's relative density, dynamic loading frequency, and cyclic stress ratio (CSR). The experimental results revealed that the attenuation of dynamic shear modulus aligns well with the classic H-D model. Moreover, the damping ratio exhibited an increase with cyclic loading until reaching a peak value at dynamic shear strains between 0.5 % and 0.8 %, followed by a rapid decrease due to liquefaction. Additionally, the failure behavior of the marine silty sand was found to be more sensitive to relative density than dynamic loading frequency under undrained shearing condition. The critical CSR for soil with a relative density of 73 % was approximately 0.18. Whereas for soil with a relative density of 53 %, it was about 0.12. The experimental findings provide valuable insights and parameters for the design of offshore engineering in this area. [ABSTRACT FROM AUTHOR]

Hard petroleum asphalt, which is a high modulus asphalt binder material, is used for improving asphalt pavement rutting distress. This property is attributed to the good high-temperature rheological characteristics of hard petroleum asphalt. The study investigates the performance of hard petroleum asphalt and Styrene-Butadiene-Styrene polymer modified asphalt (SBSPMA) based on three aspects: asphalt oil source, asphalt grade, and aging degree. The short-term and long-term aging of four hard petroleum asphalts and SBSPMA of comparative samples were measured using the rolling thin film oven test (RTFOT) and the pressure aging test (PAV). Firstly, the viscosity-temperature curve of hard petroleum asphalt was obtained using the Brookfield viscosity test at different temperatures combined with the improved REFUTAS formula. The complex shear modulus ( G ∗), phase angle (δ), and rutting factor ( G ∗ / sin δ) of each asphalt sample were then measured by the dynamic shear rheometer test (DSR). Furthermore, the temperature sensitivity of each asphalt sample was calculated using the complex modulus index method (GTS). The compaction and paving temperature ranges of each asphalt were then confirmed. The results showed that the high-temperature rheological characteristics of hard petroleum asphalt were similar to those of SBSPMA. The temperature sensitivity of hard petroleum asphalt was basically the same as that of SBSPMA, while the influence of aging on the G ∗ of hard petroleum asphalt was greater than that of SBSPMA. In addition, the hard petroleum asphalt construction temperature was lower than that of SBSPMA. [ABSTRACT FROM AUTHOR]

Most potato harvesting in China requires haulm removal. The properties of the tubers change after haulm removal. Investigating the effects of different haulm removal times on the physical mechanics and collision damage characteristics of potato tubers during the harvest period can provide a reference for reducing the damage rate of potato tubers during mechanical harvesting. The Longshu No. 7 potato, which is widely grown in northwest China, was selected as the experimental object in this study. The tuber parameters of the physical mechanics and collision damage characteristics for four different haulm removal dates (0, 7, 10 and 14 days before harvesting) were experimentally determined. The results showed that with the increase in haulm removal time before harvesting, the rupture pressure, Young's modulus, and shear modulus increased significantly. The coefficient of restitution decreased significantly. Additionally, when multiple potato tubers fell on the steel plate in the EDEM simulation test, the maximum force of a single tuber with the largest resultant force and the maximum contact force of all tubers were affected significantly. Both showed significant downward trends. The results of this study can provide a reference for discrete element simulation parameters related to potato harvesting machinery. It can also provide a reference for determining the time to haulm removal during the actual harvest. [ABSTRACT FROM AUTHOR]

Small strain shear modulus plays a fundamental role in the evaluation of site response parameters. The Standard penetration test (SPT) and Seismic Piezocone Penetration Test (SCPTU), which can quickly get the density and shear wave velocity (Vs), were rarely used in small strain shear modulus estimating. In this study, an attempt has been made to develop the regression relationship between standard penetration test (SPT) N values and the small strain shear modulus (Gmax). For this purpose, field investigations SPT and seismic piezocone penetration test (SCPTU) data from locations in Su-Xin Expressway of China have been used, which were also used for ground improvement project. The in-situ density of soil layer was estimated using undisturbed soil samples from the boreholes. The Vs profiles with depth were obtained for the locations close to the boreholes. The values for small strain shear modulus have been calculated by measured Vs and in situ soil density. About 50 pairs of SPT-N and Gmax values were used for regression analysis. The differences between measured and corrected values which were used in fitted regression relations were analyzed. Most of the existing correlations were developed based on the studies carried out in Japan and in India, where N values are measured with hammer energy of 78%, which may not be directly applicable for other regions because of the variation in SPT hammer energy which in China is about 55%. A new correlation has been generated using the measured values in silts of China. From this study, it is found that uncorrected values of N and modulus give the best fit regression relations when compared to corrected N and corrected modulus values. With most equation was used for sand and clay, the regression relations between corrected values of N and modulu gives the equation of silts in China. [ABSTRACT FROM AUTHOR]

Uncertainties of the ground motions and structural parameters are the main factors that limit the accuracy of embankment seismic fragility assessment. In response to the uncertainties of the ground motions, artificial synthesizing method of the near-fault pulse-like ground motions was proposed, and 15 ground motions with the rupture fault distances ranging from 1 to 15 km were synthesized by taking the Chi-Chi earthquake in Taiwan, China, as an example. The Xi'an-Baoji expressway K1125 + 470 embankment was taken as the research object, and a total of 12 structural parameters were selected as the design variables, namely, the elastic modulus, bulk modulus, shear modulus, density, cohesion force, and internal friction angle of the embankment fill and soil foundation, respectively. In response to the uncertainties of these parameters, 3 principal components with large impacts on the embankment seismic fragility were extracted based on the principal component analysis. Mapping relationships among the principal components and embankment seismic damages were analyzed using the uniform design response surface method, and the seismic fragility assessment was carried out and the fragility curves were plotted. The research results are consistent with the actual embankment seismic damage conditions of the Chi-Chi earthquake, indicating that the proposed method is scientific and reasonable. It also shows that it would obviously overestimate the seismic performance in the embankment seismic fragility assessment without considering the uncertainties of the ground motions and structural parameters. [ABSTRACT FROM AUTHOR]

Acoustic and electrical methods are commonly used to evaluate hydrate saturation based on P-wave velocity (Vp) and resistivity, respectively. We evaluate hydrate saturation using petrophysical parameters directly related to the presence of hydrates. Five petrophysical parameters sensitive to hydrate saturation were first analyzed using the equivalent medium rock physical model, logging intersection plots, and petrophysical parameter inversion. The simulated annealing global optimization method was then used to estimate the hydrate saturation profile in the Shenhu Area, China. The petrophysical parameters Vp, λρ, and λμ, which are associated with the rock elastic and shear moduli, are highly sensitive to hydrate saturation for an estimated saturation range of 0.1–0.44. This range is consistent with that obtained from the original well diameter curves. However, the parameters Vs and μρ, which are only related to the rock shear modulus, yield high hydrate saturation estimates of 0.22–0.43 and exhibit some deviations from the real-time data. Owing to its sensitivity, the Poisson's ratio is least desired for hydrate evaluation among the studied parameters. The sensitivity of hydrate saturation depends on the petrophysical model used for studying hydrate physical properties and storage analysis. [ABSTRACT FROM AUTHOR]

Higher‐precision determinations of hydrate reservoirs, hydrate saturation levels and storage estimations are important for guaranteeing the ability to continuously research, develop and utilize natural gas hydrate resources in China. With seismic stereoscopic detection technology, which fully combines the advantages of different seismic detection models, hydrate formation layers can be observed with multiangle, wide‐azimuth, wide‐band data with a high precision. This technique provides more reliable data for analyzing the distribution characteristics of gas hydrate reservoirs, establishing velocity models, and studying the hydrate‐sensitive properties of petrophysical parameters; these data are of great significance for the exploration and development of natural gas hydrate resources. Based on a velocity model obtained from the analysis of horizontal streamer velocity data in the hydrate‐bearing area of the Shenhu Sea, this paper uses three VCs (longitudinal spacing of 25 m) and four OBSs (transverse spacing of 200 m) to jointly detect seismic datasets consisting of wave points based on an inversion of traveltime imaging sections. Accordingly, by comparing the differences between the seismic phases in the original data and the forward‐modeled seismic phases, multiangle coverage constraint corrections are applied to the initial velocity model, and the initial model is further optimized, thereby improving the imaging quality of the streamer data. Petrophysical elastic parameters are the physical parameters that are most directly and closely related to rock formations and reservoir physical properties. Based on the optimized velocity model, the rock elastic hydrate‐sensitive parameters of the hydrate reservoirs in the study area are inverted, and the sensitivities of the petrophysical parameters to natural gas hydrates are investigated. According to an analysis of the inversion results obtained from these sensitive parameters, λρ, Vp and λμ are simultaneously controlled by the bulk modulus and shear modulus, while Vs and μρ are controlled only by the shear modulus, and the latter two parameters are less sensitive to hydrate‐bearing layers. The bulk modulus is speculated to be more sensitive than the shear modulus to hydrates. In other words, estimating the specific gravity of the shear modulus among the combined parameters can affect the results from the combined elastic parameters regarding hydrate reservoirs. [ABSTRACT FROM AUTHOR]

The dynamic shear modulus G is one of the vital parameters for the dynamic properties of marine soils and is crucial for marine geotechnical engineering design. In order to investigate the G characteristics of various marine soils, a series of resonant column tests were performed on undisturbed marine soils with various depths taken from Bohai Bay, Yangtze River estuary, and Jintang Strait, respectively. In addition, the maximum dynamic shear modulus G max and strain-compatible G of the tested marine soils were compared with the marine and terrestrial soils from the published literature. A remarkable finding is that, compared with terrestrial soils, the marine soils in different sea area present the stronger nonlinear behavior with lower shear modulus due to the special depositional environment. With the increasing of H , G in each strain range increase, and the dynamic characteristics of the marine soils gradually transition from nonlinear to linear, the G max and reference shear strain γ 0 value of marine soils in different sea areas increases linearly with the increasing H , but the G max and γ 0 growth rate varied with the sea environment and soil type. Based on the quantitative prediction equation of the G max and G attenuation relationship (G / G max ∼ γ) of various marine soils, a new prediction equation can be also established to predict G value in different depth and strain levels of various marine soils. The proposed equation are validated by independent experimental data of marine and terrestrial soils from the literature. In this regard, the proposed procedure provides a significant advantage in the evaluation of dynamic properties of marine soils in practice. • The marine soils in different seas represent more nonlinearity compared with those of the terrestrial soils. • A stress-dependent G / G max ∼ γ prediction method for marine soils was proposed considering the variation law of A , B, and γ 0. • A stress-dependent G max and G prediction method is established for marine soils in different sea areas. [ABSTRACT FROM AUTHOR]

For undisturbed loess with water sensitivity and dynamic vulnerability, which is often in a state of damage accumulation due to the influence of natural factors (the fluctuation of groundwater level, rainfall infiltration/evaporation, and seismic load), the impact of relevant engineering problems is significant, and the disaster-causing process is complex. Cyclic simple tests were used to illustrate the behaviour of the dynamic shear modulus of loess exposed to various factors of dry-wet(D-W) cycles and stress conditions (D-W cycles times N , lower limit water content w 1 , and consolidation stress σ v). Using scanning electron microscopy (SEM), we assessed the inherent damage mechanism under D-W cycles. The findings show that the D-W cycles considerably affect the dynamic shear modulus of undisturbed loess, with the strongest effect occurring during the first D-W cycles. Based on the Hardin hyperbolic model, the stress exponent n is a specific parameter of w 1. In addition, the relationship between N and G 0 / P a /(σ v / P a) n is a power function, and G 0 / P a /(σ v / P a) n drops as w 1 and N increase. The fitting parameters a of the dynamic shear modulus ratio normalization model are not sensitive to σ v / P a , D-W cycles times N , and lower limit water content w 1. Based on the dynamic shear modulus, a damage degree prediction method considering N , w 1 , and σ v is established. The results can provide a theoretical reference for earthquake disaster prediction in collapsible loess areas. [Display omitted] • Dry-wet cycles test, cyclic simple shear test, and SEM test were carried out. • The behavior of dynamic shear modulus under the coupled action of dry-wet cycles and dynamic load was investigated. • Method were proposed and verified to predict dynamic shear modulus under dry-wet cycles. • This study can provide reference for earthquake disaster prediction in loess area. [ABSTRACT FROM AUTHOR]

Across the globe, the formation of large oil and gas fields is always associated with a wide range of anhydrite cap rocks. Thus, an accurate analysis of the dynamic and static mechanical properties of anhydrite rocks is required. A deep thick anhydrite cap rock is developed in the Paleogene formation of the southwestern Tarim Basin, NW China. In this paper, we designed mechanical and acoustic synchronization tests and acquired the corresponding parameters. The effects of stress and mineral composition on the dynamic and static mechanical properties of the anhydrite rock were analyzed systematically. The results indicate that under uniaxial conditions, the anhydrite rock showed obvious brittle rupture characteristics, while under triaxial conditions, the shear rupture characteristics were obvious. The stress–strain curves of the anhydrite rocks under triaxial conditions can be divided into five stages: initial compression stage, linear elasticity stage, nonlinear steady extension stage, nonlinear unsteady extension and failure stage and post-peak stress stage. An increase in the anhydrite content can delay the weakening time of the anhydrite rocks, greatly improving the rock strength. Under high-stress conditions, the anhydrite mineral particles can accumulate large amounts of energy, exhibit a long period of creep behavior and produce significant additional stresses. The anhydrite composition can improve the strength and rigidity of the anhydrite rocks. However, anhydrite rock with a high anhydrite content will also have strong plasticity. The greater the stress environment that the anhydrite rock bears, the stronger its plasticity will be. The anhydrite component can improve the ability of the anhydrite rocks to resist shear rupture. Compared to the anhydrite mudrocks (AMR), argillaceous anhydrite rocks (AR) have higher VP, VS and VP/VS values. There is a very good positive correlation between VP/VS and the anhydrite content. A regression model of the longitudinal and shear wave time differences of the anhydrite rocks is obtained, which can be used for the prediction of the shear wave time difference. The dynamic Young's modulus, Poisson's ratio and shear modulus of the AR are higher than those of the AMR. The regression models of dynamic and static mechanical parameters of the anhydrite rocks are also obtained. These models will be valuable in the evaluation of mechanical characteristics for similar types of anhydrite rocks worldwide. [ABSTRACT FROM AUTHOR]

Quaternary silt is widely distributed in China and easily liquefies during earthquakes. To identify the influence of the dry density on the liquefaction behaviour of Quaternary silt, 40 cyclic triaxial liquefaction tests were performed on loose silt (dry density ρd=1.460 g/cm3) and dense silt (ρd=1.586 g/cm3) under different cyclic stress ratios (CSRs) to obtain liquefaction assessment criteria, determine the liquefaction resistance, improve the excess pore water pressure (EPWP) growth model and clarify the relationship between the shear modulus and damping ratio. The results indicate that the initial liquefaction assessment criteria for the loose and dense silts are a double-amplitude axial strain of 5% and an EPWP ratio of 1. The increase in the anti-liquefaction ability for the dense silt is more significant under lower confining pressures. The CSR of loose silt falls well within the results of the sandy silt and Fraser River silt, and the dense silt exhibits a higher liquefaction resistance than the sand-silt mixture. The relationships between the CSR and loading cycles were obtained at a failure strain of 1%. The EPWP development in the dense and loose silts complies with the “fast-stable” and “fast-gentle-sharp” growth modes, respectively. The power function model can effectively describe the EPWP growth characteristics of the dense silt. Finally, based on the liquefaction behaviour of silt, a suggestion for reinforcing silt slopes or foundations is proposed. [ABSTRACT FROM AUTHOR]

The mechanical parameters of shale are some of the most significant assessment indices for shale gas exploitation. The development of element logging offers an opportunity to study the correlations between the elemental concentrations and the mechanical characteristics of shale. Using the Lower Cambrian shale in the Cen'gong area, Guizhou Province, China, as an example, 490 data sets are extracted using formation element and mineralogy (FEM) and cross multipole array acoustic (XMAC) logging. Through Spearman correlation analysis, the correlations between the major elements (Si, Ca, Fe, S, Ti, Mn, Mg, Al, and K) and the mechanical parameters (Young's modulus, Poisson's ratio, shear strength, shear modulus, and brittleness index) are studied. The effects of the Si content on the mechanical parameters (positive/negative correlations, magnitude and significance of the correlations) are discussed based on X-ray diffraction analyses of the minerals in 146 samples. When 1.84% < C Si (Si content) < 28.08%, Young's modulus and the brittleness index decrease with increasing Si content, and Poisson's ratio increases. When 28.08% < C Si < 31.32%, there is no significant correlation between the Si content and the mechanical parameters. When 31.32% < C Si < 44.24%, Young's modulus and the brittleness index increase with increasing Si content, and Poisson's ratio decreases. Thus, it is not reasonable to determine the mechanical properties of shale based only on the elemental composition in different regions. [ABSTRACT FROM AUTHOR]

A new type of composite pile called a sand-filled nodular (SFN) pile has been increasingly used as a foundation element in the southeast coastal region of China. This paper derives an analytical solution of the vertical dynamic impedance of a SFN pile in saturated soil. The accuracy of the derived solution was verified by degenerating the SFN pile into a general pipe pile. The feasibility of incorporating the thin-layer assumption in Biot theory was then examined and the results suggested that for soft soils with shear modulus less than 5 MPa, the thin-layer solution is sufficiently accurate to estimate the vertical dynamic impedance of a pile in saturated soil. A parametric study was further conducted to provide insight into the influences of pile geometries and sand fill properties on the vertical dynamic impedance of the pile. The results indicated that the pile geometries have considerable influence on the vertical dynamic impedance of SFN piles where pile rib length plays a most significant role. • For soft soils, the thin-layer assumption is feasible in Biot theory. • The geometry of a sand-filled nodular pile considerably affects its complex impedance. • The effect of the pile rib length on complex impedance is much marked. • The sand-filled nodular pile is superior in elastic wave energy dissipation. [ABSTRACT FROM AUTHOR]

The offshore wind farm industry in China has been growing exponentially in recent years, and suction bucket foundations are increasingly applied as an effective solution. This paper presents a comprehensive site investigation and outlines the key soil parameters for offshore suction bucket foundation design, by taking the Houhu wind farm in southern China as an example. The in-situ cone penetrometer (CPTU) tests and sampling borehole were carried out to investigate the geotechnical features of soils. The soil conditions are characterized by multilayers and complicated sediment components. The classification and mechanical properties, such as stress history, static and cyclic shear strengths, and shear modulus of soils were obtained and compared by CPTU interpretation and advanced laboratory tests. Then the probable foundation optimization design solution from the perspective of soil parameters in the light of set up effect and cyclic behavior was discussed and highlighted. Based on the experience of this project and other projects in offshore China, some common challenges were summarized and the relative recommendations were proposed finally. The main objective of this study is to provide more reliable guidance of geotechnical investigation for the rapid development of wind farms in offshore China. • A comprehensive site investigation was carried out for the offshore suction bucket foundation design in southern China. • The classification and mechanical properties of soils were obtained and compared by CPTU interpretation and advanced laboratory tests. • The probable foundation optimization design solution was discussed and highlighted. [ABSTRACT FROM AUTHOR]

Owing to the coupled influences of traffic loading, freeze-thaw cycles, and salt expansion, saline silt subgrades easily suffer from the frost boiling disaster, which compromises the stability of subgrades. In this study, to analyze the coupled influences on the dynamic behavior of saline silt, cyclic triaxial tests were conducted on thawed saturated saline silt from the Yellow River Delta in China. The evolution of dynamic behavior was analyzed considering the existence of salt and freeze-thaw cycles. The results suggested that the cyclic shear stress decreased with increasing salt content and freeze-thaw cycles at the same cyclic shear strain. The dynamic shear modulus decreased and the damping ratio increased with increasing salt content and freeze-thaw cycles. Empirical formulas were established and verified to predict the dynamic shear modulus and damping ratio of the thawed saturated saline silt. This study provides a useful guideline for evaluating and designing saline silt subgrades in seasonal frozen regions. • Cyclic triaxial tests were conducted on thawed saturated saline silt from the Yellow River Delta in China. • The evolution of dynamic behavior was analyzed considering salt content and freeze-thaw cycles. • Empirical formulas were established to predict the dynamic shear modulus and damping ratio of the thawed silt. [ABSTRACT FROM AUTHOR]

Optimal whole-life design for marine structures requires an accurate assessment of how their underlying geo-materials respond to various static and cyclic loads. This study experimentally investigates the undrained shear behavior and stiffness characteristics of intact, soft marine clay that outcrops an offshore wind farm in southeast China. A series of monotonic and cyclic triaxial tests were conducted on the highly compressible marine clay, and the test results were interpreted within the critical state framework. The elastic shear modulus measured using bender elements in triaxial tests was compared with the secant modulus that gradually degraded with the strain during monotonic and cyclic loading. An interesting finding was that the elastic stiffness measured at various loading stages increased exponentially with the mean effective stress; a power-law increasing trend was also observed in the secant modulus normalized by the void ratio at various strain levels. It was also demonstrated that the intact sample under cyclic loading is stiffer than that under monotonic loading at the same strain level. Furthermore, a close correlation between the nonlinear undrained shear stiffness and the elastic stiffness measured during monotonic or cyclic loading was observed, which is of vital importance when evaluating the stiffness degradation behavior of natural soils over strain ranges relevant to major engineering works. • Undrained monotonic and cyclic behavior of intact soft marine clay is experimentally studied. • The elastic modulus measured using bender elements is compared with the secant modulus. • The shear moduli at different strain levels correlate well with the mean effective stress. • The nonlinear undrained shear stiffness has a close correlation with the elastic stiffness. [ABSTRACT FROM AUTHOR]

Periodic freezing–thawing is recognized as a real threat to the mechanical properties of reinforced loess, which has been used in the recent construction of high-speed railways in northwest China; however, the performance of these materials under periodic freezing–thawing and dynamic loading has rarely been investigated. In this work, dynamic triaxial tests were conducted on fly ash- and polypropylene fiber-reinforced loess with different blend ratios and freeze–thaw cycles. The dynamic shear modulus and damping ratio were investigated. The results revealed that cyclic freezing–thawing had a remarkable effect on the dynamic shear modulus and damping ratio, which demonstrated considerable reductions and increases, respectively, after cyclic freezing–thawing. Additionally, the dynamic shear modulus increased notably with the fly ash content and confining pressure and decreased with the water content. Meanwhile, the damping ratio increased with the fiber content and water content and decreased with the fly ash content and confining pressure. Comparatively, the effects of polypropylene fiber on dynamic behavior were found to be not significant. Furthermore, novel models were established to predict the dynamic shear modulus and damping ratio for reinforced loess. The results provide more information towards infrastructure design in seasonal frozen regions. [ABSTRACT FROM AUTHOR]

Evaluation of seismic diagenetic facies is an effective interpretation procedure to characterize the spatial distribution of diagenetic facies in deep tight sandstones in offshore sparse well areas. Based on petrographic and seismic data, research on seismic diagenetic facies was used in the proposed workflow to predict the spatial distribution and distribution characteristics of seismic diagenetic facies for the third (H4c) sub-member of the fourth (H4) member of the E 3 h Formation in the Xihu Sag, East China Sea Basin, Eastern China. Herein, two discriminant functions between the core-derived diagenetic facies and the seismic elastic parameters of shear modulus, p-wave impedance, and porosity data volume were established using the supervised learning method, and seismic data X and seismic data Y containing diagenetic facies information were evaluated. Based on the linear function between seismic data X and seismic data Y, a new seismic data volume was calculated and a comprehensive index of diagenetic facies was proposed to describe the distribution of diagenetic facies. The comprehensive index of diagenetic facies can better identify the spatial distribution of diagenetic facies. The results of seismic diagenetic facies research mainly focused on (1) the spatial distribution of diagenetic facies and (2) the distribution characteristics of diagenetic facies. Based on core-derived diagenetic facies, typical stratal slices, and sedimentary microfacies, the spatial distribution of seismic diagenetic facies in the two sublayers of the H4c sandstone was accurately interpreted. The northern part of the H4c1 and H4c2 sublayers mainly developed quartz-cemented facies and a small amount of chlorite-coated quartz facies. The southern part and the surrounding areas of the H4c1 and H4c2 sublayers primarily developed tightly compacted facies. The area near four (F1, F2, F3, and F4) faults in the H4c1 sublayer mainly developed a small amount of dissolution facies, whereas the area near the F2 and F4 faults in the H4c2 sublayer primarily developed a small amount of dissolution facies. Furthermore, the distribution characteristics of seismic diagenetic facies were investigated from the perspective of sedimentary microfacies and diagenetic facies. The chlorite-coated facies is mainly distributed in the subaqueous distributary channel sedimentary microfacies. The dissolution facies is primarily distributed in the subaqueous distributary channel and sheet sand sedimentary microfacies near the faults. This study shows that the research of seismic diagenetic facies using petrographic data and seismic data can better predict the spatial distribution of diagenetic facies of deep tight sandstone. • The relationship between core-derived diagenetic facies and seismic elastic parameters was established. • A diagenetic facies comprehensive index was proposed. • Seismic diagenetic facies distribution was interpreted. • Distribution characteristics of diagenetic facies was investigated. [ABSTRACT FROM AUTHOR]

Based on the background of the development of China's South China Sea, few studies can provide a reference for pile foundation construction in calcareous sand layers. In this paper, one-dimensional impact tests were conducted on three uniformly graded (0.25–0.50 mm, 0.50–1.00 mm, and 1.00–2.00 mm) and one mixed graded (0.075–2.00 mm) calcareous sand and silica sand specimens with the aid of a split Hopkinson pressure bar (SHPB) system, while several sets of mixed graded specimens with different moisture contents and relative densities were studied for comparison. Each specimen was impacted at least 10 times. The results of the tests based on the effect of the number of impacts, particle size, moisture content and relative density on the dynamic behavior of calcareous sand are summarized as follows. The dynamic apparent stiffness of calcareous sand is approximately 1/8–1/9 that of silica sand due to their different particle shapes and mineral compositions. The dynamic/bulk/shear apparent modulus of calcareous sand decreases with an increase in the mean diameter, d 50. After repeated impact, the apparent modulus of specimens with different particle sizes continued to increase and decreased with an increase in d 50. For calcareous sand, with increasing particle size, the compression index C c increases, and the yield pressure is approximately 40% that of silica sand under the same conditions. Compared to silica sand, calcareous sand reaches a better energy absorption capacity at a lower stress. Under the same axial stress, the energy absorption efficiency increases with increasing particle size and decreases with an increase in the number of impacts. • Effects of numbers of impacts, particle size, moisture content and relative density on dynamic behavior is studied. • Impact stress-strain, one-dimensional compressive behavior and energy-absorption of sand is studied. • Differences in the dynamic behavior of calcareous sand and silica sand under impact loading are compared. • Given a reference for pile driving in calcareous sand layer. [ABSTRACT FROM AUTHOR]

Site investigations of the soils are considered very important for evaluation of the site conditions, as well as the design and construction for the project built in it. Taihu tunnel is thus far the longest tunnel constructed in the lake in China, with an entire length of over 10 km. However, due to the very insufficient site data obtained for the lacustrine clay in the Taihu lake area, a series of self-boring pressuremeter (SBPM) field tests was therefore carried out. Undrained shear strengths were deduced from the SBPM test, with the results showing generally higher than those obtained from the laboratory tests, which may be attributed to the disturbance to the soil mass during the sampling process. Degradation characteristics of the soil shear modulus (Gs) were mainly investigated, via a thorough comparison between different soil layers, and generally, the shear modulus would cease its decreasing trends and become stable when the shear strain reaches over 1%. Meanwhile, it was found that a linear relationship between the plasticity index and the shear modulus, and between the decay rate of the shear modulus and the plasticity index as well, could be developed. Further statistical analysis over the undrained shear strength and shear modulus distribution of the soils shows that the undrained shear strength of the soils follows a normal distribution, while the shear modulus follows a log-normal distribution. More importantly, the spatial correlation length of the shear modulus is found much smaller than that of the undrained strength. [ABSTRACT FROM AUTHOR]

The Zhuanghe wind farm is under development offshore China. The site investigation campaign was completed in 2019. Both monopiles and suction buckets are considered as foundation types, and they are presently in the design phase. Soil testing was carried out at both the HDEC and the NGI laboratories. Soil parameters obtained from the laboratory tests are interpreted and discussed in this paper. Important soil parameters for foundation design, such as static and cyclic shear strengths, shear modulus and thixotropy from the tests on the Zhuanghe soil are compared with available databases in the literature, and soil parameters for foundation design are recommended. The purpose of this study is to provide a realistic reference for research and practice in the offshore wind energy industry offshore China where very few advanced tests for windfarm development are available. • Details of soil conditions and soil parameters for an actual wind farm location offshore China is provided. • Representative soil parameters that can be used for foundation design at the Zhuanghe offshore wind farm site is recommended • Static strength is evaluated based on both laboratory tests and in situ CPTU tests, and a reasonable cone factor is suggested • Shear modulus and thixotropy are recommended based on laboratory tests and discussed according to available database in the literature. [ABSTRACT FROM AUTHOR]

Loess is a typical soil with the characteristic of water sensitivity, and in the study of water-induced geological disasters of loess distribution areas worldwide, special attention must be paid to the influence of this sensitivity. Hence, quantitative study of the water sensitivity of loess has been a basic scientific issue of wide concern. In this study, the water sensitivity characteristics of loess in the South Jingyang Tableland of China are investigated through oedometer tests and triaxial shear tests, and the variation in the structural strength, deformation modulus, and strength parameters of intact samples with different water contents is studied. It is found that the structural yield stress, initial deformation modulus and cohesion are sensitive to the water content, i.e., decreasing in the form of a power function or an exponential function with increasing initial water content. An analysis shows that the above parameters can be used to normalize the compression curves, stress-strain curves and critical state lines of loess. According to the quantitative formula of water sensitivity in the field of petroleum exploration, a new method to assess the water sensitivity of loess by analogy is proposed, which involves the structural strength, deformation modulus and shear strength parameters in the natural and humidified states. The analysis further indicates that the water sensitivity index proposed in this paper is a reasonable, sensitive and effective way to quantify the water sensitivity of loess. • The compression curves, stress-strain curves and critical state lines of loess can be normalized. • A new method for assessing the loess water sensitivity index is proposed. • A geomechanical model reflecting the micro-structural mechanical response process of water sensitive loess is presented. [ABSTRACT FROM AUTHOR]

Discrimination of fluid properties in tight fractured reservoirs plays a significant role in seismic reservoir characterization for a fracture-induced horizontal transversely isotropic (HTI) medium. From a perspective of low-frequency anisotropic Gassmann's theory, we propose a new anisotropic fluid indicator coupling an isotropic fluid/porosity term and a dry term of normal fracture weakness by the use of linear slip theory and weak-anisotropy (WA) analytic assumption. The accuracy of WA approximation with and without the coupled anisotropic fluid indicator are demonstrated in application to the tight gas-bearing fractured reservoirs with relatively low values of fracture properties. Integrating the perturbations in WA elastic stiffness components of fluid-saturated fractured porous media and the scattering function, we then derive a linearized and weakly anisotropic PP-wave reflection coefficient in terms of isotropic fluid/porosity term, shear modulus, density, coupled anisotropic fluid indicator, and fracture weaknesses. Based on the sensitivity analysis of coupled anisotropic fluid indicator and two fracture weaknesses for the difference of PP-wave reflection amplitudes in two orthogonal azimuths, we find that the coupled anisotropic fluid indicator is less sensitive to the azimuthal amplitude differences than the fracture weaknesses. Combining the Bayesian framework with two regularization constraint terms of Cauchy sparse and initial model, we finally propose an iterative singular-value- decomposition (SVD)-based inversion method of seismic amplitude difference between two orthogonal azimuths to estimate the coupled anisotropic fluid indicator and two fracture weaknesses. Tests with noisy synthetic seismic gathers demonstrate that the estimated model parameters can be reasonably inverted from two azimuthal seismic data with three angles of incidence containing a moderate level of noises. Field data acquired over Sichuan basin in China is used to further confirm that the proposed inversion approach can get geologically reasonable estimates of coupled anisotropic fluid indicator and fracture weaknesses. Consequently, the coupled anisotropic fluid indicator is more sensitive to the gas-bearing fractured reservoirs than the conventional fracture weaknesses, which may provide a more effective manner for the fluid identification of tight gas-bearing fractured reservoirs. • A new and low-frequency coupled anisotropic fluid indicator is proposed. • PP-wave reflection coefficient containing fluid and fracture indicators is derived. • SVD-based iterative inversion method is proposed to perform the fluid identification. [ABSTRACT FROM AUTHOR]

The quickly accumulated crayfish shell waste in China has led to severe environmental issues and recycling pressure. This study aims to build an efficient protocol by utilizing waste crayfish shell powder in the production of high-performance and sustainable asphalt binder. The asphalt binder modified with different contents of crayfish shell powder (5%, 10% and 20% mass ratio to control asphalt, respectively) were first prepared at the temperature of 140oC–150 °C. Then the softening point and the penetration of the prepared samples were implemented to compare the stiffness difference between the modified and original asphalt binder. The results indicated that the added shell powder increased the softening point and decreased the penetration of the control asphalt. Furthermore, the high-temperature stability of the asphalt binder was examined by the dynamic shear rheometer (DSR) tests. The DSR results revealed that adding shell powder could enhance the rutting resistance of the asphalt binder by decreasing the phase angle δ, increasing the dynamic shear modulus |G∗| and finally enhancing the rutting factor |G∗|/sinδ. After that, to compare the creep performance between the control and modified asphalt binder, the multiple stress creep recovery (MSCR) tests were employed. The results of the MSCR test showed that at the same temperature, the percent recovery was higher while the non-recoverable creep compliance J nr of modified asphalt was lower than those of the control binder. These results indicated that the added crayfish shell powder could increase the stiffness, improve the high-temperature stability and creep resistance of the asphalt binder. Finally, fourier transform infrared spectroscopy (FT-IR) test results implied that the added CS would not affect the chemical structure of the asphalt binder, and the modification was mainly a physical process. The novelty and limitation of this study have also been detailedly explained in the discussion part. The test results could provide a reference for the engineering application of the crayfish shell powder modified asphalt material and lead to both a cleaner and greener product. [ABSTRACT FROM AUTHOR]

• The initial strain and the shear modulus are revealed with moisture contents. • A method for obtaining the long-term strength of loess specimens is proposed. • A modified Burgers creep models is proposed. Understanding the creeping behavior of loess is of great importance as large-scale loess landslides are closely related with creep behavior. At present, it is still challenging to predict and estimate the long-term stability of such landslides. This is in a large degree due to the poor understanding of moisture control on creep behavior of loess. The purpose of this study is to decipher the loess creep behavior under various moisture contents (MCs) using loess specimens obtained from Baqiao landslide, Xi'an of China, using multi-loading triaxial creep tests under different MCs of 9%, 12%, 15%, 18% and 21%. Based on the laboratory test results, a series of relationships between the creep rate at the steady-state creep stage and the initial strain and initial shear modulus are revealed. Meanwhile, a method for obtaining the long-term strength of loess specimens, namely, the Steady-state Creep Rate Slope Method (SCRSM), is proposed. SCRSM resolves the issue in several conventional methods such as the Isochronous Stress-Strain Curve Method, the Tangent Method of Steady Creep Rate when MCs are of concern. Such an improvement is primarily due to a better way of finding the inflection point of the steady-state rate. It is found that SCRSM is robust and accurate to determine the long-term strength of loess specimens. Furthermore, we propose a modified Burgers model with a newly introduced nonlinear parameter n to overcome deficiencies of conventional creep models. This modified Burgers model is flexible to fit the creep test curves of loess, and can describe the curves at the accelerated creep stage more accurately. Lastly, the main factors triggering the Baqiao landslide is analyzed considering stratum lithology, rainfall and excavation. In general, this study provides a basis for understanding the evolutional process of loess landslides as well as guidelines for prevention, controlling and prediction of loess landslides. [ABSTRACT FROM AUTHOR]

With the rapid development of high-speed railways (HSRs) in seasonally frozen regions in China in recent years, there is an increasing need for better understanding of how the construction materials behave. In particular, the dynamic behaviours of coarse-grained materials (CGMs) used for China's HSRs subjected to combined actions of cyclic loading and freeze-thaw (F-T) cycles has attracted much attention. In this study, a series of cyclic triaxial tests were performed to investigate the characteristics of CGMs considering the effects of number of F-T cycles (N FT), confining pressures (σ 3), dynamic stress amplitude (σ ¯ d), and fines content (FC). Representative test results of accumulative axial strain (ε acc), resilient modulus (M r), dynamic shear modulus (G d) and damping ratio (D) are then presented and discussed. Empirical models are proposed and validated for predicting the evolution of ε acc and M r for CGMs under the cyclic loading. In addition, the evolution models of G d and D were established, which can be used for computing the response of CGMs under various influencing factors. Overall, this study provides further insights into the cyclic behaviours of CGMs in seasonally frozen regions. • Cyclic triaxial tests were carried out on prepared thawed coarse-grained materials. • Effects of freeze-thaw cycles, confining pressure, dynamic stress amplitude, and fines content were discussed. • Models for accumulative strain, resilient modulus, dynamic shear modulus and damping ratio were proposed and validated. [ABSTRACT FROM AUTHOR]