Discontinuities, such as joints and beddings, usually play a significant role in the seismic response and corresponding failure process of slopes, especially for anti-dip rock slide according to ...field observations. Shaking table tests associated with numerical analyses are carried out in this paper to explore the effect of seismic wave on response of jointed anti-dip rock slopes. Shaking table tests involve anti-dip rock slope models with different rock types and different excitation intensities. Ten accelerometers are installed inside each slope model to monitor the dynamic response and spectrum shifting characteristics. It is found that the area of failure zone in the soft rock anti-dip slope is approximate 1.5 times the size of that in the hard rock anti-dip slope. Meanwhile, the width and ridge number of the fast Fourier-transformation spectrum along the slope surface can reveal the internal damage features within the anti-dip rock slopes, and the multiple failure planes can also be recognized according to the variation of distance between the innermost and outermost ridges in the fast Fourier-transformation spectrum. Moreover, the distinct element method incorporating a damage model is used to interpret the test results and to identify the main influencing factors for seismic instability. It is found that the failure pattern of a jointed anti-dip rock slope is more sensitive to bedding inclination than to joint inclination.
Irrigation with reclaimed water is becoming a common practice in many cities around the word. One of the main concerns regarding the use of reclaimed water in urban green land is soil salinity ...accumulation. Field investigations in the seven parks of Beijing were conducted to study the accumulation of soil salinity under different reclaimed water irrigation history. The accumulation trend and distribution pattern of soil salinity in a 100 cm soil profile were evaluated by the ENVIRO‐GRO model. Field investigation results showed that average soil salinity in the plots irrigated with reclaimed water was higher than that irrigated with tap water by 19.2% at the depth of 0–20 cm. Difference of average soil salinities at the depth of 0–20 cm between field measurement and model simulation was quite small, less than 15.0%. Under irrigation water salinity of 0.6, 1.2, and 2.4 dS/m, simulated annually average soil salinity decreased/increased from initial value of 1.62 dS/m, to 1.53, 2.75, and 4.66 dS/m, respectively, at the equilibrium state. Accumulation of soil salinity in clay loam was 3 times of that in sandy loam. A mild to moderate soil salinization could appear under higher irrigation water salinity, lower irrigation water amount, and heavy soil texture. Irrigation practices and soil hydraulic properties were dominated factors affecting soil salt accumulation. It is not recommended to use water‐saving irrigation and irrigate on heavy soils as well as plant with a salinity stress threshold less than 1.85 dS/m under reclaimed water irrigation in Beijing.
Key Points
Field investigations were similar to these under the default model simulation
Soil salinization appeared with extreme irrigation cases and heavy soil
Soil salinity is mainly affected by irrigation practice and hydraulic property
In order to investigate the seismic response of steep bedding and toppling rock slopes, a large-scale shaking table test was performed taking into consideration a variety of factors such as slope ...type and input seismic excitation. Diverse seismic responses, including acceleration and earth pressure at several locations, were analyzed in terms of the test results. It was found that the slope type has a significant impact on the failure mechanism and response norm of different kinds of rock slopes. Firstly, the slide surface of the steep bedding rock slope is basically parallel to the slope surface, while that of toppling rock slope skews the rock layer under seismic load. The failure zone area of the toppling rock slope is smaller than that of the bedding rock slope, which is mainly because it consumes plenty of seismic energy to break through the rock layer of the toppling rock slope. In addition, for acceleration along the vertical direction, an abrupt amplifying effect exists at the top slope when the peak input motion acceleration (PIMA) exceeds a certain value: 0.6 g for a bedding rock slope and 0.4 g for a toppling rock slope. Meanwhile, for acceleration along the horizontal direction, the acceleration amplifying factors of toppling rock slopes are larger at the slope surface but smaller at the inner slope portion than that of bedding rock slopes. Furthermore, the acceleration amplifying factor is larger than the earth pressure amplifying factor at the slope surface. The earth pressure amplifying factor at the top surface for a toppling rock slope is close to that of a bedding rock slope with an increase in PIMA. This novel experiment reveals the different failure mechanisms between steep bedding and toppling rock slopes, as well as being of help to the conduct of further study on seismic hazard early warnings.
Previous researches on the mechanical model of toppling failure mainly concentrated on two-dimensional mechanical model (TwDM) analysis. The TwDM analysis assumes the width of the slab beam is unit ...width without considering the lateral constraint force. The assumed conditions are obviously different from the site conditions, thus there is a certain difference between the calculated results and the field work. A three-dimensional mechanical model (ThDM) of toppling failure was established, considering that the slab beam was mainly subject to self-weight, the frictional resistance of interlayer and lateral constraint force. Due to the progressive characteristics of toppling failure, the concept and the formula of the first fracture depth (FFD) of toppling was raised and constructed. The case study indicates that the ThDM is more effective and can be accurately used to calculate the toppling fracture depth of the slab beam. The FFD decreases proportionally with the increase of slab beam width. FFD grows fast when the slab beam width is less than 2.0 m and it tends to be stable when the slab beam width is above 2.0 m. The FFD decreases with the increase of the lateral constraint coefficient, indicating that the boundary condition of the free space is positively correlated with the stability and depth of toppling. This is a good explanation of the free space effect. This study provides a reference for the stability evaluation and prevention-control design of toppling slope in the future.
Predicting the failure time of a landslide is considered as challenging work in the field of landslide research, and inverse velocity is proved to be an effective and convenient method. The onset of ...acceleration (OOA) has a crucial effect on the prediction failure time from the inverse velocity method. However, a simple method to identify OOA points is lacked, and most of the identifications rely on expert experience. Therefore, this study presents an application of a simple framework developed to identify the OOA by analyzing monitoring velocity data in three steps, including selection of the absolute value of velocity, reliable area identification and OOA identification. A new parameter based on exponential moving average (EMA) is developed to identify the landslide OOA. The framework is applied to three historical case studies to test its practicability and effectiveness. The forecasting results show a good correspondence between the accuracy rate and the coefficient of determination (
R
2
). The predicted failure time according to the linear extrapolation starting from the identified OOA points is acceptable with a high
R
2
and high accuracy.
Recently, various toppling slopes have emerged with the development of hydropower projects in the western mountainous regions of China. The slope on the right bank of the Laxiwa Hydropower Station, ...located on the mainstream of the Yellow River in the Qinghai Province of Northwest China, is a typical hard rock slope. Further, its deformation characteristics are different from those of common natural hard rock toppling. Because this slope is located close to the dam of the hydropower station, its deformation mechanism has a practical significance. Based on detailed geological engineering surveys, four stages of deformation have been identified using discrete element numerical software and geological engineering analysis methods, including toppling creep, initial toppling deformation, intensified toppling deformation, and current slope formation. The spatial and time-related deformation of this site also exhibited four stages, including initial toppling, toppling development, intensification of toppling, and disintegration and collapse. Subsequently, the mechanism of toppling and deformation of the bank slope were studied. The results of this study exhibit important reference value for developing the prevention-control design of toppling and for ensuring operational safety in the hydropower reservoir area.
Engineering experience shows that outward dipping bedded rock slopes, especially including weak interlayers, are prone to slide under rainfall conditions. To investigate the effect of inclined weak ...interlayers at various levels of depth below the surface on the variation of displacements and stresses in bedded rock slopes, four geo- mechanical model tests with artificial rainfall have been conducted. Displacements, water content as well as earth pressure in the model were monitored by means of various FBG （Fiber Bragg Grating） sensors. The results showed that the amount of displacement of a slope with a weak interlayer is 2.8 to 6.2 times larger than that of a slope without a weak interlayer during one rainfall event. Furthermore, the position of the weak interlayer in terms of depth below the surface has a significant effect on the zone of deformation in the model. In the slope with a high position weak interlayer, the recorded deformation was larger in the superficial layer of the model and smaller in the frontal portion than in the slope with a low position weak interlayer. The slope with two weak interlayers has the largest deformation at all locations of all test slopes. The slope without a weak interlayer was only saturated in its superficial layer, while the displacement decreased with depth. That was different from all slopes with a weak interlayer in which the largest displacement shifted from the superficial layer to the weak interlayer when rainfall persisted. Plastic deformation of the weak interlayer promoted the formation of cracks which caused more water to flow into the slope, thus causing larger deformation in the slope with weak interlayers. In addition, the slide thrust pressure showed a vibration phenomenon o.5 to 1 hour ahead of an abrupt increase of the deformation, which was interpreted as a predictor for rainfall-induced failure of bedded rock slopes.
Objectives: The objective of the study was to carry out an analysis of the methodological quality of clinical trials (effects of exercise on frailty in older people) based on ACSM recommendations. ...Methods: The search scope included PubMed, Embase, Web of Science, Cochrane, and literature that cannot be retrieved from the database. The topic was the impact of exercise on frailty in elderly people. Changes in five outcome measures (FP, BI, SPPB, GS, and BMI) were assessed using mean differences (MD) and 95% confidence intervals (95% CI). A random effects model (RE) was used to conduct a meta-analysis and compare the results between subgroups. Results: The intervention effects of exercise on the five outcome indicators of frailty in elderly people were all significant (p < 0.05). The effect of a high-consistency subgroup on outcome indicators FP and GS was more significant than that of the low- or uncertain-consistency subgroup (MD: −1.09 < −0.11, MD: 2.39 >1.1). There was no significant difference in the intervention effect as reflected in the outcome measures SPPB and BMI in the high-consistency subgroup (p = 0.07, p = 0.34). There was no significant difference in the impact of the intervention on the outcome measure BI between the two subgroups (p = 0.06, p = 0.14). Conclusions: Exercise prescriptions with high consistency with ACSM recommendations may be more effective in both FP and GS interventions than those with uncertain or low consistency. However, it is essential to note that the data derived from the meta-analysis is still subject to the small number of studies, the unknown degree of consistency of participants in individual studies, and the different mix of cases in the studies.
This study aimed to investigate the effects of dietary supplementation with dl-methionine (dl-Met) and dl-methionyl-dl-methionine (dl-Met-Met) in breeding pigeons on the carcass characteristics, meat ...quality and antioxidant activity of squabs. A total of 324 pairs of breeding pigeons were selected and allotted to 9 treatments in a completely randomized design, and the birds were fed dietary treatments for 45 d, including a Met-deficient basal diet (BD, crude protein = 15%, Met = 0.25%) and BD + 0.15%, 0.30%, 0.45%, or 0.60% dl-Met or dl-Met-Met diets. Compared with the diet fed to the BD group, dietary dl-Met or dl-Met-Met supplementation effectively increased the carcass yield, semieviscerated yield, eviscerated yield, breast muscle yield, thigh muscle yield, a* value, catalase activity, total superoxide dismutase activity and glutathione peroxidase activity, but decreased the L* value, malonaldehyde concentration, drip loss and cooking loss of squabs (p < 0.05). The relative bioavailability values of dl-Met-Met relative to those of dl-Met were 467% and 376% based on carcass yield and breast muscle yield, respectively (p < 0.001). Moreover, dl-Met-Met was more effective than dl-Met in decreasing the drip loss and improving the antioxidant activity of the breast and thigh muscles of squabs (p < 0.05). As a source of Met, dl-Met-Met, rather than dl-Met, was more beneficial to squabs.
The objective of this research was to assess the characteristics of seismic induced damage and the deformation patterns of pre-stressed cement-grouted cables that are used for rock slope ...stabilization projects subjected to quasi-static cyclic loading.The experimental configuration includes the installation of 15 pre-stressed cables in a slope model made of concrete blocks（theoretically rigid rock mass） on top of a pre-existing sliding surface.The study showed that：（i） The pre-stressed cables exhibited great seismic performance.Rapid displacement of the model blocks was observed after the complete loss of the initial pre-stress load under continued applied cyclic loads and exceedance of the state of equilibrium,which implies the higher the initial pre-stress load,the better the seismic performance of the rock anchor;（ii） The failure of the pre-stressed cables was due to fracture at the connection of the tendons and cable heads under cyclic loading.The sequence of failure had a distinct pattern.Failure was first observed at the upper row of cables,which experienced the most severe damage,including the ejection of cable heads.No evidence of de-bonding was observed during the cyclic loading;（iii） The stress distribution of the bond length for pre-stressed cables was highly non-uniform.High stress concentrations were observed at both the fixed end and the free end of the bond length both before and immediately after the state of equilibrium is exceeded.The results obtained can be used to evaluate the overall performance of pre-stressed rock anchors subject to seismic loading and their potential as rockfall prevention and stabilization measures.
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