Using Seismic Tomography and Holography Ground Imaging to Investigate Ground Conditions

Unforeseen, variable subsurface ground conditions present the greatest challenge to the heavy construction and civil engineering industry in the design, construction, and maintenance of large projects. A detailed, accurate site investigation will reduce project risk, improve construction performance and safety, prolong the life of the tunnel or structure,and prevent waste in over - design. Presently, site characterization and geotechnical engineering are limited by the inability to adequately describe these subsurface ground conditions.NSA Geotechnical Services has successfully applied seismic tomography and holography ground imaging technologies on tunneling and heavy civil excavations worldwide. Seismic signal waveforms traveling through a complex medium consist of various arrivals from refractions, reflections, scattering, and dispersion. Tomography and holography are proven inversion technologies for estimating location and extent of material property variations causing changes in signal waveforms.ent attenuation rates and velocities. Seismic waves will travel faster through competent material and be generally less attenuated than through broken/fractured ground or voids.encounters an interface between ground zones possessing different seismic properties. Most geologic structures, anomalies,and changes in lithology provide detectable seismic reflections if they are within a reasonable distance of the seismic source.This paper will present various applications of these technologies, illustrating how seismic imaging can provide accurate information regarding ground conditions associated with tunneling projects. With this information, engineers can complete projects safely, within time and budget constraints.     

地震层析成像及全息岩土成像岩土工程地质条件调查

在大型工程项目的设计、施工和维护阶段,复杂多变的地下岩土工程条件对大型建筑和土木工程产业带来的巨大挑战令人难以想象.具体而言,通过准确的现场勘察可以降低工程风险,改善施工作业,确保施工安全,延长隧道或建筑结构的使用寿命,防止超设计的浪费.显然,由于缺乏对地下岩土工程地质条件进行合理描述的手段,限制了工程现场地质条件的表征和岩土工程技术的发展.NSA大地工程有限公司成功地将地震层析成像及全息岩土成像技术应用于隧道工程和大型土木工程开挖领域.经复杂介质传播的记录地震信号是由折射、反射、散射、弥散等多类波形所组成,层析成像和全息成像是常用的利用信号波形变化来估计介质性质变化的位置和范围的反演技术.·岩石三维图像(Rock Vision3DTM)技术的基本原理是基于地震能量在不同种类介质中以不同的衰减率和速度传播.通常,与破碎或裂隙发育的岩土体或空洞条件相比,地震波在完整坚硬的介质中传播时,具有更高的传播速度和更低的衰减.·TRTTM技术的基本原理是利用了地震波在岩土体中传播过程中遇到具有不同震动特性的岩土区带间的界面时部分地震波能量将产生反射的特性.绝大多数地质结构异常及岩性变化,在地震信号可及的距离范围内,均可形成可探测的地震反射.文章介绍了上述技术的各种应用条件,分析了地震成像技术在隧道工程施工中所能提供的与隧道工程施工有关的岩土工程地质条件方面的准确信息.根据这些信息,工程建设者可以按期在预定计划内安全地完成工程施工.     

用三维模型计算整体活塞机械变形及应力的研究

本文以16V240ZJ型柴油机结构改进后的整体薄壁球铁活塞为例,用三维有限元模型计算了在最大气体爆发压力作用下,其机械变形和应力的分布规律,研究了一些结构参数的变化对其应力分布的影响,并对活塞顶部应力较高的部位进行了二次细算,揭示了销座部分的结构非轴对称性对活塞顶部环向各点应力分布规律的影响,为活塞的改进设计提供了依据。     

Cycle Network Planning: Towards a Holistic Approach Using Temporal Topology

ABSTRACT

Current cycle-network planning (CNP) at the local level tends to be dominated by a subjective-pragmatic approach in which it is only possible to consider a limited number of route alignment possibilities and development-sequencing scenarios. Although this method may produce acceptable results, it may also be true that the final design could be improved – and the construction efficiency could be enhanced – by a more comprehensive review of the available options in relation to the objectives of the intervention. Such objectives may include accident reduction, modal shift in favour of cycling, health benefits or strategic expansion of a network. This article presents work undertaken to demonstrate a holistic approach to CNP, based on a logically defined spatio-temporal model and allowing some semi-automated multiobjective optimization of network designs in a GIS-based decision-support system. The model is introduced briefly before a case study applying this model to development of a cycle network in a small town in northeast England is described. The results obtained from this case study and the implications of this research for cycle network planners are discussed.