This paper deals with the effect of layer height randomness on the seismic response of a layered soil. These parameters are assumed to be lognormal random variables. The analysis is carried out via Monte Carlo simulat...This paper deals with the effect of layer height randomness on the seismic response of a layered soil. These parameters are assumed to be lognormal random variables. The analysis is carried out via Monte Carlo simulations coupled with the stiffness matrix method. A parametric study is conducted to derive the stochastic behavior of the peak ground acceleration and its response spectrum,the transfer function and the amplification factors. The input soil characteristics correspond to a site in Mexico City and the input seismic accelerations correspond to the Loma Prieta earthquake. It is found that the layer height heterogeneity causes a widening of the frequency content and a slight increase in the fundamental frequency of the soil profile,indicating that the resonance phenomenon is a concern for a large number of structures. Variation of the layer height randomness acts as a variation of the incident angle,i.e.,a decrease of the amplitude and a shift of the resonant frequencies.展开更多
To investigate the seismic response of the steel-strip reinforced soil retaining wall with fullheight rigid facing in terms of the acceleration in the backfill, dynamic earth pressure in the backfill, the displacement...To investigate the seismic response of the steel-strip reinforced soil retaining wall with fullheight rigid facing in terms of the acceleration in the backfill, dynamic earth pressure in the backfill, the displacements on the facing and the dynamic reinforcement strain distribution under different peak acceleration, a large 1-g shaking table test was performed on a reduced-scale reinforced-earth retaining wall model. It was observed that the acceleration response in non-strip region is greater than that in potential fracture region which is similar with the stability region under small earthquake,while the acceleration response in potential fracture region is greater than that in stability region in middle-upper of the wall under moderately strong earthquakes. The potential failure model of the rigid wall is rotating around the wall toe. It also was discovered that the Fourier spectra produced by the inputting white noises after seismic wave presents double peaks, rather than original single peak, and the frequency of the second peak trends to increase with increasing the PGA(peak ground amplitude) of the excitation which is greater than 0.4 g. Additionally,the non-liner distribution of strip strain along the strips was observed, and the distribution trend was not constant in different row. Soil pressure peak value in stability region is larger than that in potential fracture region. The wall was effective under 0.1 g-0.3 g seismic wave according to the analyses of the facing displacement and relative density. Also, it was discovered that the potential failure surface is corresponds to that in design code, but the area is larger. The results from the study can provide guidance for a more rational design of reinforced earth retaining walls with full-height rigid facing in the earthquake zone.展开更多
Urochloa brizantha (synonymous of Brachiaria) is the most spread species of grass in the tropical world, primarily in regions with acid and low fertility soils. This study was conducted to investigate changes in the s...Urochloa brizantha (synonymous of Brachiaria) is the most spread species of grass in the tropical world, primarily in regions with acid and low fertility soils. This study was conducted to investigate changes in the soil chemical properties of a Typical Acrudox submitted to a strategy of grazing with rotational stocking, liming and nitrogen fertilisation. Treatments involved combinations of two pre-grazing heights (25 and 35 cm) with two rates of nitrogen (50 and 200 kg·ha-1·year-1). All combinations received lime, P and K fertilization and an untreated control group was allocated according to a complete randomised block design, five replications. Soil sampling was done in layers of 0-5, 5-10, 10-20, 20-30 and 30-40 cm deep in pastures of U. brizantha Marandu (Palisade grass). The samples were analysed for pH, H+ + Al3+, soil organic matter (SOM), P, K+, Ca2+, Mg2+, exchangeable and calculated CEC, BS% and aluminium saturation. Liming and fertilisation improve the soil fertility. The highest organic matter contents were obtained for the 0-5 cm layer, with a nitrogen fertilisation of 200 kg·N·ha-1. The management practice for the pre-grazing height of 25 cm, regardless of the nitrogen, is the best strategy for soil quality and livestock production.展开更多
文摘This paper deals with the effect of layer height randomness on the seismic response of a layered soil. These parameters are assumed to be lognormal random variables. The analysis is carried out via Monte Carlo simulations coupled with the stiffness matrix method. A parametric study is conducted to derive the stochastic behavior of the peak ground acceleration and its response spectrum,the transfer function and the amplification factors. The input soil characteristics correspond to a site in Mexico City and the input seismic accelerations correspond to the Loma Prieta earthquake. It is found that the layer height heterogeneity causes a widening of the frequency content and a slight increase in the fundamental frequency of the soil profile,indicating that the resonance phenomenon is a concern for a large number of structures. Variation of the layer height randomness acts as a variation of the incident angle,i.e.,a decrease of the amplitude and a shift of the resonant frequencies.
基金founded by the National Natural Science Foundation of China(Grant No.51708163)Research Program of the Ministry of Transport of the People’s Republic of China(Grant No.2013318800020)Doctoral Innovation Fund Program of Southwest Jiaotong University(Grant No.D-CX201703)
文摘To investigate the seismic response of the steel-strip reinforced soil retaining wall with fullheight rigid facing in terms of the acceleration in the backfill, dynamic earth pressure in the backfill, the displacements on the facing and the dynamic reinforcement strain distribution under different peak acceleration, a large 1-g shaking table test was performed on a reduced-scale reinforced-earth retaining wall model. It was observed that the acceleration response in non-strip region is greater than that in potential fracture region which is similar with the stability region under small earthquake,while the acceleration response in potential fracture region is greater than that in stability region in middle-upper of the wall under moderately strong earthquakes. The potential failure model of the rigid wall is rotating around the wall toe. It also was discovered that the Fourier spectra produced by the inputting white noises after seismic wave presents double peaks, rather than original single peak, and the frequency of the second peak trends to increase with increasing the PGA(peak ground amplitude) of the excitation which is greater than 0.4 g. Additionally,the non-liner distribution of strip strain along the strips was observed, and the distribution trend was not constant in different row. Soil pressure peak value in stability region is larger than that in potential fracture region. The wall was effective under 0.1 g-0.3 g seismic wave according to the analyses of the facing displacement and relative density. Also, it was discovered that the potential failure surface is corresponds to that in design code, but the area is larger. The results from the study can provide guidance for a more rational design of reinforced earth retaining walls with full-height rigid facing in the earthquake zone.
文摘Urochloa brizantha (synonymous of Brachiaria) is the most spread species of grass in the tropical world, primarily in regions with acid and low fertility soils. This study was conducted to investigate changes in the soil chemical properties of a Typical Acrudox submitted to a strategy of grazing with rotational stocking, liming and nitrogen fertilisation. Treatments involved combinations of two pre-grazing heights (25 and 35 cm) with two rates of nitrogen (50 and 200 kg·ha-1·year-1). All combinations received lime, P and K fertilization and an untreated control group was allocated according to a complete randomised block design, five replications. Soil sampling was done in layers of 0-5, 5-10, 10-20, 20-30 and 30-40 cm deep in pastures of U. brizantha Marandu (Palisade grass). The samples were analysed for pH, H+ + Al3+, soil organic matter (SOM), P, K+, Ca2+, Mg2+, exchangeable and calculated CEC, BS% and aluminium saturation. Liming and fertilisation improve the soil fertility. The highest organic matter contents were obtained for the 0-5 cm layer, with a nitrogen fertilisation of 200 kg·N·ha-1. The management practice for the pre-grazing height of 25 cm, regardless of the nitrogen, is the best strategy for soil quality and livestock production.
