基于信号包络线相似性的特定场地地下爆炸识别方法研究

基于信号包络线相似性, 本文提出了特定场地地下爆炸的识别方法, 并将其用于一个特定场地地震事件分析, 以评估该方法对特定场地爆炸事件的识别效果. 结果表明, 在误警率约为6.3%的情况下, 事件间距小于15 km的爆炸事件漏检率约为0.5%, 事件间距在15—30 km范围内的爆炸事件漏检率约为5.0%. 与波形互相关方法相比, 本文方法大幅扩大了有效识别特定场地爆炸事件的空间范围.      

Full-scale experimental modal analysis of an arch dam: The first experience in Iran

Forced vibration field tests and finite-element studies were conducted on the Shahid Rajaee concrete arch dam in Northern Iran to determine the dynamic properties of the dam–reservoir–foundation system. The first forced vibration tests on the dam were performed with two different types of exciter units, with a limited maximum force, bolted on the dam crest for alternative in-phase and out-of-phase sequencing. Because of an insufficient number of recording sensors, two arrangements of sensors were used to cover sufficient points on the dam crest and one gallery during tests. Two kinds of vibration tests, on–off and frequency sweeping, were carried out on the dam. The primary natural frequencies of the coupled system for both symmetric and anti-symmetric vibration modes were approximated during on–off tests in two types of sequencing of exciters, in phase and out-of-phase, with a maximum frequency of 14 Hz. The principal forced vibration tests were performed at precise resonant frequencies based on the results of the on–off tests in which sweeping around the approximated frequencies at 0.1 Hz increments was performed. Baseline correction and suitable bandpass filtering were applied to the test records and then signal processing was carried out to compute the auto power, cross power and coherence spectra. Nine middle modes of vibration of the coupled system and corresponding damping ratios were estimated. The empirical results are compared against the results from calibrated finite-element modeling of the system using former ambient vibration tests, considering the dam–reservoir–foundation interaction effects. Good agreement is obtained between experimental and numerical results for eight middle modes of the dam–reservoir–foundation system.     

Inelastic seismic behavior of soil–pile raft–structure system under bi-directional ground motion

Performance based design of structure requires a reasonably accurate prediction of displacement or ductility demand. Generally, displacement demand of structure is estimated assuming fixity at base and considering base motion in one direction. In reality, ground motions occur in two orthogonal directions simultaneously resulting in bidirectional interaction in inelastic range, and soil–structure interaction (SSI) may change structural response too. Present study is an attempt to develop insight on the influence of bi-directional interaction and soil–pile raft–structure interaction for predicting the inelastic response of soil–pile raft–structure system in a more reasonably accurate manner. A recently developed hysteresis model capable to simulate biaxial interaction between deformations in two principal directions of any structural member under two orthogonal components of ground motion has been used. This study primarily shows that a considerable change may occur in inelastic demand of structures due to the combined effect of such phenomena.     

Liquefaction-induced deformation of earthen embankments on non-homogeneous soil deposits under sequential ground motions

Damage of embankments during earthquakes is widely attributed to the liquefaction of foundation soil. Previous studies have investigated the dynamic response of embankments by mainly considering uniform sand foundation and a single earthquake event. However, the foundation of an embankment consists of many sublayers of soil from liquefiable sand to relatively impermeable layer, and during earthquakes a mainshock may trigger numerous aftershocks within a short time which may have the potential to cause additional damage to soil structures. Accordingly, the investigation of liquefaction-induced deformation of earthen embankments on various liquefiable foundation conditions under mainshock–aftershock sequential ground motions is carried out by a series of dynamic centrifuge tests in this study. The liquefiable foundation includes uniform sand profile, continuous layered soil profile, and non-homogeneous soil profiles. Effects of various foundation conditions on embankment deformations are compared and analyzed. From the test results, it is found that the embankment resting on non-homogeneous soil deposits suffer more damage compared to the uniform sand foundation of same relative density. The test results also suggest that the sequential ground motions have a significant effect on the accumulated deformation of embankment.     

Effect of a forced harmonic vibration pile to its adjacent pile in layered elastic soil with double-shear model

A new model named double-shear model based on Pasternak foundation and Timoshenko beam theory is developed to evaluate the effect of a forced harmonic vibration pile to its adjacent pile in multilayered soil medium. The double-shear model takes into account the shear deformation and the rotational inertia of piles as well as the shear deformation of soil. The piles are simulated as Timoshenko beams, which are embedded in a layered Pasternak foundation. The differential equation of transverse vibration for a pile is solved by the initial parameter method. The dynamic interaction factors for the layered soil medium are obtained by the transfer matrix method. The formulation and the implementation have been verified by means of several examples. The individual shear effects of soil and piles on the interaction factors are evaluated through a parametric study. Compared to Winkler model with Euler beam, the present model gives much better results for the dynamic interaction of piles embedded in stiff soil with small slenderness ratios. Finally, the effect of a forced long pile to a short pile embedded in multilayered soil medium is studied in detail.     

浙江长兴深井地电台建设

随着人类的活动,地电阻率和地电场观测受到更多干扰。介绍浙江省长兴深井地电台建设过程,并讨论建设中存在的问题,初步分析地电观测资料,证明井下地电阻率和地电场观测在一定程度上可以屏蔽干扰,由此可见建设深井地电台的重要性。     

强夯法加固夹砂粘土吹填场地的现场试验研究

江苏省连云港赣榆港区陆域采用航道和港池的疏浚土方吹填形成作业港区,吹填工艺以绞吸式疏浚为主,疏浚涉及土层为粘土和砂土,由此形成了粘土和砂土的混合土地基。为了提高地基承载力和均匀性,采用了强夯法对地基进行加固,但是目前对夹砂粘土地基强夯加固的理论和实践较少。为此,以砂夹粘土构成的混合土地基为对象,测试了多种能量单点夯击时的地基土夯沉量、孔压和夯坑周围土体强度等参数,探讨了强夯法加固该类地基的加固深度和水平影响范围。结果表明：对于该类地基而言,有效加固深度修正系数取0.35~0.5为宜;强夯过程中,孔压与强度的增长范围不对应,即孔压影响范围远大于强度影响范围。     

渗流作用下河岸深基坑支护结构稳定性分析

河水径向渗流会对河岸基坑稳定性及支护结构内力产生显著影响。以某深基坑工程为背景进行了三维流固耦合数值模拟分析,研究了渗流对深基坑土体及支护结构受力与变形的作用规律。研究结果表明：1初始水位时,渗流作用对土体水平应力与土体剪应力的影响较小,但水位上升后,坑底处土体水平应力明显增大,在坑壁拐角处应力集中现象突出,土体剪应力在开挖面以下的底脚处最大;2土体水平位移与竖向位移均在水位上升时呈递增趋势;3桩身弯矩与剪力在水位上升初期有较大增加,之后增长速度减小;4上层、下层锚杆的自由段和锚固段轴力在水位上升初期均有明显增加,但之后增加幅度很小;5安全系数在水位上升初期降低较多,之后以较小速度呈线性减小。     

混凝土的入模温度和水化热对青藏直流输电线路冻土桩基温度特性的影响

施工过程中混凝土的入模温度和水化热对多年冻土区桩基施工期间的热稳定性具有重要影响. 针对该问题,利用有限元方法定量研究了±400 kV青藏直流输电线路冻土区锥柱基础入模温度、水化热和含冰量对桩基回冻过程、温度场变化和桩底融化深度的影响规律. 结果表明：水化热影响下,桩基中心温度在第3天达到最高,桩底滞后1 d,基坑表面受其影响较小,主要受环境温度影响;第24天,桩底出现最大融化层,随着入模温度增加,融化层厚度相应增加,入模温度为6℃时融化层厚度为34 cm,15℃时为55 cm;入模温度越高,回冻时间越长,当入模温度为6℃时,完全回冻需经历52 d,15℃时,回冻时间将增加7 d. 含冰量对桩底融化深度有影响,含冰量越大底部融化深度越小;冻土年平均地温是影响桩底融化深度的重要因素,少冰高温（-0.52℃）、低温（-1.5℃和-2.5℃）冻土条件下,最大融化层厚度分别为38 cm、34 cm和25 cm. 基于上述结果,在多年冻土地区的桩基工程,建议混凝土入模温度为6~8℃,底部碎石垫层至少40 cm.