The Frequency Content of Ground Vibration

A detailed examination of the frequency content of ground vibration is presented in terms of the so-called instantaneous frequency and time-frequency analysis. These techniques, and others, are applied to the surface vibration from a mass blast that triggered a large seismic event and to an earthquake vibration measured in the walls of a massive dam. As an associated issue it is shown that the relationship between peak levels of acceleration and velocity also reveals information on the frequency content of ground vibration. It is demonstrated quite clearly that the popular zero-crossing method cannot be used to obtain the frequency associated with the peak vibration level. In fact it is a false notion that one particular frequency can be associated with the peak level except for the ideal (and impractical) case of a single sinusoid. Realistically, there is a distribution of frequencies associated with the peak level, and a technique of sliding filters is suggested in order to examine the dependence of the peak level upon this frequency content. In light of the sliding filter approach, a new frequency dependent criterion for allowable levels of vibration is presented. This criterion is a completely continuous and well-defined function of frequency and so is more realistic than the current criteria which are only piecewise continuous and based upon an ill-defined frequency. The new criterion is applied to vibration data obtained from quarries and underground operations and is also applied to a model of resonant vibrations in urban dwellings.     

Numerical Analyses of the Influence of Blast-Induced Damaged Rock Around Shallow Tunnels in Brittle Rock

Most of the railway tunnels in Sweden are shallow-seated (<20 m of rock cover) and are located in hard brittle rock masses. The majority of these tunnels are excavated by drilling and blasting, which, consequently, result in the development of a blast-induced damaged zone around the tunnel boundary. Theoretically, the presence of this zone, with its reduced strength and stiffness, will affect the overall performance of the tunnel, as well as its construction and maintenance. The Swedish Railroad Administration, therefore, uses a set of guidelines based on peak particle velocity models and perimeter blasting to regulate the extent of damage due to blasting. However, the real effects of the damage caused by blasting around a shallow tunnel and their criticality to the overall performance of the tunnel are yet to be quantified and, therefore, remain the subject of research and investigation. This paper presents a numerical parametric study of blast-induced damage in rock. By varying the strength and stiffness of the blast-induced damaged zone and other relevant parameters, the near-field rock mass response was evaluated in terms of the effects on induced boundary stresses and ground deformation. The continuum method of numerical analysis was used. The input parameters, particularly those relating to strength and stiffness, were estimated using a systematic approach related to the fact that, at shallow depths, the stress and geologic conditions may be highly anisotropic. Due to the lack of data on the post-failure characteristics of the rock mass, the traditional Mohr–Coulomb yield criterion was assumed and used. The results clearly indicate that, as expected, the presence of the blast-induced damage zone does affect the behaviour of the boundary stresses and ground deformation. Potential failure types occurring around the tunnel boundary and their mechanisms have also been identified.     

A Feasibility Study on Controlling Ground Vibrations Caused by Blasts in Malmberget Underground Mine

In order to control or reduce the ground vibrations caused by underground blasts in Malmberget mine, a number of blast tests were carried out during production blasts and a series of single shot waveforms were obtained. Then the single shot waveforms from the same ring or different rings were analysed and compared with each other. The results showed that the single shots are reproducible, meaning that the ground vibrations caused by underground blasts can be controlled by means of the interference of the vibration waveforms measured. Finally, a formal test using electronic detonators and employing an optimum delay time of 8 ms was done in production. The test for an 11-borehole ring shows that the maximum vertical ground vibrations are reduced to the maximum vertical vibrations of a single shot. Particularly, the total vibration history for the 11-borehole-ring blast is shortened to about 200 ms over a velocity of 2 mm/s. However, the total vibration history of a normal production blast of 11-borehole ring is always 1400 ms over a velocity of 2 mm/s, namely the total vibration time of a production blast can be reduced to one seventh of that of the common production blasts by using the vibration control method. This indicates that the vibration control method introduced in the paper is feasible for underground mining blasts.     

Response of Concrete and Masonry Dams to Ground Vibration due to Blasting

The safety and stability of concrete and masonry dams is a great concern when blasting has to be conducted close to these dams in order to construct small hydro-electric projects. There is a danger of ground vibration amplification to those residential-type buildings that are built close to these dams.

Responses of three concrete and masonry dams were measured directly by conducting a number of blasts and by monitoring vibration in the ground as well as on the dams. The amplitudes and frequencies of the motions were analysed and vibration attenuation relations were derived. These relations were used to compare the vibration levels on the dams with those in the ground.

Because of close-in construction blasts that produced high frequency ground vibrations, there was no amplification of the ground vibrations by these dams. The measured amplitudes of ground vibration were comparable to those of the dams.     

强夯地基处理振动效应的研究

强夯法是地基处理的重要方法之一,在进行强夯地基处理时要评价强夯振动效应,评价的基础正是强夯振动振幅和振动衰减规律。以昌平区沙岭新村工程场地为例,通过对回填场地进行强夯振动监测,分析了强夯振动最大振幅及其随距离的衰减规律,并用频率的四次多项式表示场地介质衰减指数。在场地介质作用谱和强夯激励谱的基础上,通过计算得到介质作用函数和强夯激励函数。通过不断积累强夯振动效应资料,建立起不同性质岩土体与场地介质作用函数之间的关系,进而明确工程岩土体的物理力学性质和动力学表现之间本构关系。     

大气重力波布阵探测灾害性冰雹过程的研究

1995－1997年在冰雹灾害频繁的贵州省中西部进行了灾害性冰雹过程的大气重力波布阵探测研究，结果表明使用动态谱分析技术的大气重力波三测点布探测方法不仅可以在冰雹灾害发生3－24小时以前获得可靠的预警信息，而且可连续跟踪监测波原所在方位，为冰雹过程发生发展的理论机制及预报方法和研究和人工防雹作业提供了一些新的线索和一种新的技术手段。     

地埋管换热器钻孔长度计算方法研究

地埋管换热器钻孔长度计算是土壤源热泵系统设计的核心。为规范地埋管换热器钻孔长度计算,从《地源热泵系统工程技术规范》基本要求出发,以合肥市某土壤源热泵工程为例,进行了地埋管换热器钻孔长度计算和校核模拟计算。研究表明,热干扰对地埋管换热器钻孔长度有较大的影响,不考虑热干扰影响的钻孔长度计算结果偏小;由于热堆积的影响,地埋管换热器流体平均出口温度呈现逐年上升趋势。校核模拟计算结果表明地埋管换热器钻孔计算长度能够满足规范的要求。     

软地层中斜拉群锚特性的研究

为了研究上海地区土层锚杆的群锚效应，本文以明德林（Ｍｉｎｄｌｉｎ）解为基础，通过引用根据试验所得的锚杆非线性传递函数，对软地层中斜拉锚杆的长度、间距、入土深度、压浆等因素对群锚效应的影响进行了探讨，得出一些有价值的结果。     

Numerical and Experimental Study of Free Vibration Characteristics of a Cable-Stayed Bridge

INTRODUCTIONUnderstanding dynamic response andits correla-tion to the effects of traffic , wind and earthquake hasbecome one of the engineering challenges of cable-stayed bridges , since the cable-stayed bridges arepresently extending to medium- and long-spanlengths .Investigations of both the aerodynamic sta-bility and earthquake response of cable-stayed bridgesare dependent upon knowledge of the dynamic char-acteristics ,such as natural frequencies , mode shapesand modal damping values ,…     

Effect of Pile Driving on Ground Vibration in Clay Soil: Numerical and Experimental Study

Geotechnical and Geological Engineering - In this study, peak particle velocity (PPV) values for driving three piles with diameters of 40&nbsp;cm, 50&nbsp;cm, and 70&nbsp;cm in a clayey...     

南京地铁应用人工地层冻结法的可行性研究

人工地层冻结技术用于采矿凿井在国外有100余年的历史,在中国也有40余年,然而,它在其它岩土工程中的应用尚处于起步阶段。本文以南京地铁珠江路—鼓楼区间为例,探讨了冻结法施工的可行性、设计方法、技术要点及其可能遇到的环境岩土工程问题。     

天然地基承载力可靠度研究

采用 Ｈａｎｓｅｎ 公式的计算模式,运用可靠度基本理论建立了天然地基承载力可靠度分析的概率模型,通过一个实际场地的可靠度研究,得出了相应于现行总安全系数的可靠度指标和设计验算点,并在此基础上探讨了基本变量互相关对可靠度指标的影响,得出了有益的结论     

刚性桩复合地基垫层对桩土应力比影响分析

从极限平衡理论角度对刚性桩复合地基中垫层作用机理进行分析,提出桩顶垫层厚度、垫层材料内摩擦角等参数对桩土应力分担的控制公式,推导出在已知表面应力情况下考虑桩土共同作用的桩土沉降计算公式,在此基础上提出一种桩土应力比的迭代计算方法。编制程序实现对算例的计算,总结分析计算结果并与实测值进行对比验证。     

地下水控制性关键水位研究初探

分析和探讨了地下水控制性关键水位的类别划分以及蓝、黄、红区的划分依据和原则,并结合西北、华北和东部沿海地区普遍存在的地下水问题,提出了西北型、华北型和东部沿海型地下水蓝线水位和红线水位等具体分析成果,为加强水资源的量化管理和地下水"水量与水位"综合管理等提供了重要依据.     

粉喷桩处理软基固结计算方法的探讨

根据实际的地基结构,在Terzaghi一维固结理论的基础上,建立粉喷桩复合地基桩间土的固结模型并求解;结合高等级公路粉喷桩加固路基工程实例,将理论计算值与现场试验结果进行沉降计算对比分析。     

打桩振动对周围环境的影响

在城市建筑物密集区进行振动沉管施工,引起震动对周围环境的影响已成为地基处理施工中一个突出的问题,通过对某项工程水泥粉煤灰碎石柱(CFG)桩施工振动对周边建筑物影响的测试和分析,对地基处理方法的选型及如何有效减轻和控制施工振动对周围环境的影响,均具有一定意义。     

充水预压法加固油罐软土地基数值分析

利用有限差分程序FLAC3D对充水预压法加固油罐地基进行了数值模拟,详细分析了大型油罐地基的变形特性及形状,得出了一些有用结论,并将结果和监测数据进行了对比分析,显示了很好的一致性。     

非开挖HDD地表变形数值模拟及DCRP识别技术研究

采用非开挖水平定向钻进技术近地表施工时,由于地层及钻井液压力等原因易产生地表变形。结合美国梅萨市一处通信管道施工实例,对0-0.9 MPa钻井液压力作用下的地表变形程度进行了数值分析,得到地表最大隆起量为26 mm。采用DCRP技术及水准仪方法对该变形区域钻井液压力作用前后的地表进行位移检测,得到地表最大隆起量分别为28 mm和30 mm,表明数值模拟分析结果同现场检测结果比较吻合。同时,在现场所布置的26个检测点中,两种方法检测到的隆起量最大相差2.7 mm,表明其精度比较接近。此外,由于DCRP技术属于非接触式三维检测,受施工现场条件及人员操作限制少,故具有较为理想的应用前景。     

季节冻土层对房屋地震破坏的影响

冬期地面形成一坚硬的季节冻结层,从而在一定程度上改变了地基土的动力特性,也就改变了地表层的卓越周期．１９８６年黑龙江省德都地区冬、夏两次地震震害调查发现,冬期地震对较刚性房屋破坏严重,而夏期刚好相反,即相对柔性结构房屋地震破坏严重．通过实地观测与室内分析计算,进一步研究了这一问题．     

Spatial-Temporal Ground Deformation Study of Baotou Based on the PS-InSAR Method

Ground subsidence is an emerging geological hazard in Baotou,Inner Mongolia.Four areas of Baotou with relatively large subsidence range and rate were selected for analysis.Focusing on investigation of ground subsidence using PS-InSAR technology,a total of 43 frames of ALOS PALSAR images yielded a SAR data span from December 2006 to January 2011,allowing ground subsidence scope,subsidence velocity,time-series deformation to be obtained.Major causes and influencing factors of the ground subsidence are closely related to soft soil consolidation and compaction and the decrease in the level of groundwater caused by increased development and utilization of groundwater.