Analysis of Blast Vibration Characteristics Across a Trench and a Pre-Split Plane   总被引：3，自引：0，他引：3  

A. J. Prakash  P. Palroy  D. D. Misra 《Fragblast: International Journal for Blasting and Fragmentation》2004,8(1):51-60

This paper presents the influence of various discontinuities, natural or artificial, on magnitude and frequencies of blast induced ground vibrations. These discontinuities were geological faults, a pond, a shaft incline, a trench and a pre-split plane interposed in the path of vibration propagation. In the post-trench region, ground vibrations in terms of peak particle velocity were significantly reduced and dominant frequencies in higher bands were consequently observed. Depth of trench with respect to blastholes were varied and consequent vibration characteristics were analyzed. The techniques of creating a trench and pre-split plane were successfully implemented in controlling vibration and in increasing the explosives charge to meet the scheduled production target of an opencast mine. Comparisons of ground vibration characteristics affected by a trench and a pre-split plane of the same depth are described in the text. The findings lead to the conclusion that such experimental data are necessary for production blasting in open cast mines under constrained conditions.  相似文献   

长江干流主要营养盐含量的变化特征——1998~1999年日中合作调查结果分析   总被引：18，自引：0，他引：18  

徐开钦  林诚二  牧秀明  村上正吾  徐保华  渡边正孝 《地理学报》2004,59(1):118-124

根据1998年和1999年秋季在长江干流从重庆至长江口进行的纵向采样和分析,对长江干流的各态氮、磷含量的沿江变化进行研究。从整体上了解长江干流的水质变化特性,特别是营养盐含量的分布状况。研究结果表明,长江干流的SS浓度很高,介于50~400 mg/l。TN、TP浓度分别在70~110 滋mol/L、2~25 滋mol/L之间,前者以NO3-N为主,后者以PTP为主,PO4-P含量仅占TP的10%~20%。DIN/PO4-P的比值在70~160之间,远高于浮游植物生长P限制值,表明长江口及临近海域中P可能是生物生命活动的主要限制因素。葛洲坝水库对SS、TP、TN、NH4-N、BOD、COD等水质有一定的净化作用。长江水体在通过各大城市以及两大湖泊时,BOD、NH4-N负荷的增加迅速,特别是通过重庆、武汉、南京、上海及洞庭湖和鄱阳湖之后尤为明显。N、P含量的上升与人口增长、生活污水排放量及流域内化肥施用量增加有关。洞庭湖和鄱阳湖水系以及周围的面源负荷,对长江流域的营养盐变动有很大的影响。  相似文献   

Long-term bed load transport rate based on aerial-photo and ground penetrating radar surveys of fan-delta growth, Coast Mountains, British Columbia     

Channa P. Pelpola  Edward J. Hickin   《Geomorphology》2004,57(3-4):169-181

Sequential aerial photography, sonar bathymetry, ground-penetrating radar (GPR), and sediment sampling and analysis provide the basis for calculating the volumetric and mass rate of progradation of the delta of Fitzsimmons Creek, a steep, high-energy, debris-flow-dominated channel draining about 100 km² of the southern Coast Mountains of British Columbia. Fitzsimmons Creek is typical of small mountain rivers in the region. GPR imaging is used to define the pre-depositional morphology of the receiving basin, a technique that improves the accuracy of the volumetric survey. The 52-year record (1947–1999) of progradation yielded an average annual volumetric transport rate of 1.00±0.16×10⁴ m³ year⁻¹ for bed load, corresponding to a mass transport rate of 1.60±0.28×10⁴ Mg year⁻¹. Bed load yields are consistent with those obtained in hydrogeomorphically similar basins in the region and elsewhere. Decade-based annual rates, which vary from 0.64±0.11×10⁴ to 2.85±0.38×10⁴ Mg year⁻¹, provide poor estimates of the 52-year average. Indeed, the 52-year record may also not be long enough to fully integrate the significant fluctuations in the sediment efflux from Fitzsimmons Creek. The methodology proposed in this paper can be transferred to other comparable mountain environments worldwide.  相似文献   

Simulation of seismic response in a city-like environment   总被引：1，自引：0，他引：1  

Jean-Philippe Groby  Chrysoula Tsogka  Armand Wirgin   《Soil Dynamics and Earthquake Engineering》2005,25(7-10):487-504

We study the seismic response of idealized 2D cities, constituted by non-equally spaced, non-equally sized homogenized blocks anchored in a soft layer overlying a hard half space. The blocks and soft layer are occupied by dissipative media. To simulate such response, we use an approximation of the viscoelastic modulus by a low-order rational function of frequency and incorporate this approximation into a first-order-in-time scheme. Our results display spatially variable, strong, long-duration responses inside the blocks and on the ground, which qualitatively match the responses observed in some earthquake-prone cities of Mexico, France, the USA, etc.  相似文献   

The effect of bed mobility on resistance to overland flow     

Shixiong Hu  Athol D. Abrahams 《地球表面变化过程与地形》2005,30(11):1461-1470

When sediment grains are transported as bed load in overland flow, there is a net transfer of momentum from the flow to the grains. When these grains collide with other grains, whether on the bed or in the flow, streamwise flow velocity decreases and resistance to flow increases. Resistance to flow generated in this manner is termed bed‐load transport resistance. Resistance to flow f over a plane bed may be partitioned into grain resistance f_g and bed‐load transport resistance f_bt. We use the symbols f_btf and f_btm to denote f_bt for flows over fixed beds and over mobile beds, respectively, and we compute the effect of bed mobility on flow resistance f_mob by subtracting f_btf from f_btm. The data for this study come from 54 flume experiments with fixed beds and 38 with mobile beds. On average f_mob is approximately equal to half of f_btm, which is about one‐quarter of f. Hence, f_mob is about one‐tenth of f. Predictive equations are developed for f_btf, f_btm and f_mob using dimensional analysis to identify the relevant independent variables and regression analysis to evaluate the coefficients associated with these variables. Values of f_mob are always positive which implies that mobile beds offer greater resistance to flow than do fixed beds. Evidently bed‐load grains colliding with mobile beds lose more momentum to the bed than do grains colliding with fixed beds. In other words, grain collisions with mobile beds are less elastic than those with fixed beds. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Green''''s functions for uniformly distributed loads acting on an inclined line in a poroelastic layered site   总被引：4，自引：0，他引：4  

梁建文  尤红兵 《地震工程与工程振动(英文版)》2005,(2)

Based on one type of practical Biot's equation and the dynamic-stiffness matrices of a poroelastic soil layer and half-space, Green's functions were derived for uniformly distributed loads acting on an inclined line in a poroelastic layered site. This analysis overcomes significant problems in wave scattering due to local soil conditions and dynamic soil-structure interaction. The Green's functions can be reduced to the case of an elastic layered site developed by Wolf in 1985. Parametric studies are then carried out through two example problems.  相似文献   

SEDIMENT TRANSPORT, DELTA GROWTH AND SEDIMENTATION IN LAKE NIGARDSVATN, NORWAY     

GUNNAR ØSTREM  NILS HAAKENSEN  HANS CHR. OLSEN 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):243-258

ABSTRACT. The retreat of Nigardsbreen, an outlet glacier from the ice-cap Jostedalsbreen in south-central Norway, from its largest extent during the Little Ice Age, uncovered a proglacial lake during 1936–1967. This lake, Nigardsvatn, has been studied since 1968 in order to obtain data on solid material carried by the meltwater stream from the glacier, both in suspension and as bottom load. Between 70 and 85% of the suspended sediment has been deposited on the lake bottom, forming annual varves. The coarse material has been deposited in a delta, the formation of which started in 1968. Its growth, and hence the volume of total annual bottom load, has been surveyed annually for the past 36 years. In 1969 the entire bottom load was collected by building a fence-like net across the river. Material >3 cm was caught by this net, and formed approximately half the amount of suspended sediment transport during the same three-week period. Annual average deposition on the delta was 11800×10³ kg for the period 1968–2003. This is almost the same amount as carried in suspension from the glacier on an annual mean basis for the 36-year period. If conditions remain constant, the lake will be completely filled in about 500 years. The glacier erosion is calculated to be 0.3 mm/a.  相似文献   

沉降-时间曲线呈“S”型的证明及其应用——从土体本构关系   总被引：6，自引：0，他引：6  

梅国雄  宰金珉  殷宗泽  赵维炳 《岩土力学》2005,(Z1)

从土体本构关系出发,严格证明了在线性加载或近似线性加载情况下(这和岩土工程实际加载相类似),沉降-时间曲线呈“S”型,并由此建立了新的沉降-时间预测模型,工程应用证明了该模型的合理性。  相似文献   

Proof of settlement-time curve appearing “S” shape with ramp load and its application base on stress-strain relationship   总被引：1，自引：0，他引：1  

MEI Guo-xiong  ZAI Jin-min  YIN Zong-ze  ZHAO Wei-bing 《岩土力学》2005,26(Z1):21-24

Based on stress-strain relationship of soil, the proof is made for that s-t curve appears “S” shape when the load is increased linearly, which is similar to construction process. A new model of forecasting the relation of settlement-time is presented. Case history shows the rationality of the method.  相似文献   

Influence of transducer-ground coupling on vibration measurements   总被引：1，自引：0，他引：1  

G. R. Adhikari  A. I. Theresraj  R. N. Gupta 《Fragblast: International Journal for Blasting and Fragmentation》2005,9(2):79-92

Various methods of transducer mounting provide varying degrees of coupling between the transducer and the measurement surface. The influence of four of these methods on vibration measurements was studied. For this purpose, the first transducer was placed freely on a horizontal surface, the second one was 'sandbagged', the third one was 'spiked' and the fourth one was completely buried in soil. These transducers were mounted side by side and ground vibrations were monitored for 14 blasts at an opencast coal mine.

Ground vibrations in terms of peak particle velocity, peak vector sum and frequency with different mounting methods were analysed. Assuming the data of the buried transducer as the most acceptable one, relative values of other transducers were determined and plotted. For the given tolerance for instrumental and human errors, anomalous readings were found in some cases. The waveforms of the buried transducer were then compared with those of others. Clear distortion in the waveforms or a very low correlation coefficient between two waveforms was suspected poor coupling.

The results indicate that decoupling is most likely with the surface transducer. However, the sandbagged and spiked transducers are also prone to decoupling. Decoupling can result in higher or lower ground vibration. Therefore, burial should be the preferred method for mounting of transducers in soil.  相似文献