Engineering geological characteristics and processes of permafrost along the Qinghai–Xizang (Tibet) Highway

Engineering geological problems of thaw-settlement and frost-heave occur frequently along the Qinghai–Xizang (Tibet) Highway (QXH) line and produce an adverse impact on roadbed stability. Eight monitoring sites were established along the QXH to investigate the engineering geological characteristics and environmental process of permafrost, including the upper and lower boundary of the active layer under the natural surface, the seasonal freeze–thaw depth under the asphalt pavement, the permafrost table temperature and roadbed stability. The investigation results show that the active layer thickness and permafrost table temperature under an asphalt pavement are higher than under a natural surface due to the absorption heat and reduced evaporation capability of the asphalt pavement. The implication for highway design and construction in permafrost areas are discussed.     

Reducing ground vibrations caused by underground blasts in LKAB Malmberget mine

Due to the large-scale sub-level caving in Malmberget mine and the short distance between the mine and Malmberget town, the ground vibrations in the town have reached a high level since the year 2001 when large scale caving mining started. In order to control and reduce the high vibrations, LKAB launched a research project on active reduction of vibrations in Malmberget by using the wave interference or wave superposition method with electronic detonators. By means of this method, the vertical vibrations were reduced by 10% and the total vibration time for a ring blast was reduced by 80% according to five ring tests in the mine. For a further reduction of the vibrations, a second method, named changing initiation sequence in ring blasts, was developed on the basis of stress wave theory and the geographic conditions of the town and the mine. The second method has so far been applied in all of the drifts near the town, and the vibrations measured at the town show that the vertical vibrations caused by production blasts in the mine have been reduced by more than 31% on average. In addition, a third method, dividing a ring into two parts during blasting, was developed and used to reduce the ground vibrations from a number of very large rings in the mine. The results indicate that the vibrations have been reduced by more than 33%, and a more interesting and surprising result is that ore extraction has been increased by the third method.     

Influence of total charge in a blast on the intensity of ground vibrations—field experiment and computer simulation

A number of factors influence the generation, propagation and intensity of ground vibrations. However, there are conflicting opinions with regard to the influence of the blast size on the intensity of ground vibrations. This paper discusses the experiments conducted in an opencast coal mine in India and a simulation study carried out to establish the influence of total charge in a blast on the intensity of ground vibrations. Studies clearly indicate that the total explosive charge in a blast has insignificant influence on the intensity of ground vibrations for distances between 100 m and 3000 m.     

Seismic hazard analysis for critical infrastructures in California

California is in a highly seismically active region, and structures must be designed and constructed to withstand earthquakes. Seismic hazard analysis to estimate realistic earthquake ground motions and surface fault rupture offsets is done for various mitigation measures. The best policy is to avoid constructing structures crossing seismogenic faults. Because earthquake timings are unpredictable within our current understanding, the best method is time-invariant deterministic seismic hazard analysis (DHSA) to assess effects from the largest single earthquake called Maximum Credible Earthquake (MCEs) expected from seismogenic faults. Time-dependent hazard estimates such as those arrived at through probabilistic seismic hazard analysis (PSHA) are inherently unreliable. Hazard analyses based on MCEs have been in continuous use for the design and construction of highways and bridges in California for over 30 years.

This paper presents an alternative to other methods of analysis, e.g., Abrahamson (2000) [Abrahamson, N.A., 2000. State of the practice of seismic hazard evaluation. Melbourne: proceedings of GeoEng, 2000].     

山西大同市地裂缝的分布特征及其发展趋势

地裂缝是地下断裂构造现今活动在地表土层形成的痕迹，地裂缝灾害能够造成严重的经济损失和社会影响，叙述了山西大同市地裂缝的现状、灾害情况及地裂缝的基本特征，并对其成因进行了分析，对其发展趋势进行了预测。     

高邮台地电阻率异常与地震

应用差分能量法和归一化月速率方法处理了江苏省高邮台的地电阻率观测资料。结果表明，高邮台地电阻率观测对附近的中等以上地震和远距离的台湾强震有一定的映震信息检测能力。     

Ground cracks in Ethiopian Rift Valley: facts and uncertainties

No accurate relationship has been obtained in this study between ground cracks in Ethiopian Rift Valley and the most common causes of earth fissures such as aquifer-system compaction and increased horizontal seepage stresses. This is due to the fact that the level of groundwater withdrawal responsible for these processes is still negligible in Ethiopia. If aquifer-system compaction and increased horizontal seepage stresses have a certain role, then it should be through the long-term effect of groundwater flow from basins to neighboring lakes. The ground cracks appeared also not to have a direct link with active faulting or distant earthquakes. Structurally, the Ethiopian Rift Valley is dominated by NE–SW-trending tensional faults, but no evidence is obtained in this study to associate the process of surface cracking with major tectonics. However, an aseismic elastic strain, which originates at depth and propagates upward through sediments without the formation of bedrock faults, could result in conditions conducive to the development of cracks. Then, fissures might ultimately be created after heavy rainfalls by near-surface processes such as piping and hydrocompaction along water-line sources.     

Multipath mitigation by conventional antennas with ground planes and passive vertical structures

An antenna ground plane (GP) plays a major role in the mitigation of multipath coming from underneath the antenna. A distinct trend in user antenna size and weight reduction has been observed during recent years. With this focus in mind, an overview of conventional flat conductive and impedance GP is provided. Results of modern developments of passive vertically stacked structures are discussed. The possibility of obtaining a reasonable level of multipath mitigation with vertical structures of several centimeters is shown.     

In situ experiments and seismic analysis of existing buildings. Part II: Seismic integrity threshold

The interest of in situ measurements (presented in Part I paper) for a seismic assessment of existing buildings is analysed in this paper. It is shown that the experimental modal characteristics obtained on regular concrete structures are described successfully by suited Timoshenko beam modelling. For a given structure, taking into account the experimental data, the corresponding beam model, and choosing the maximum tensile strain of concrete as damage criterion for key structural elements, a maximum level of the ground acceleration can be determined. This so‐called seismic integrity threshold is directly related to the onset of structural damages. This new approach is illustrated on one of the studied buildings. The advantages of using ambient vibrations survey for the vulnerability assessment of existing buildings are discussed. Copyright © 2005 John Wiley & Sons, Ltd.