Applications of a GIS-based geotechnical tool to assess spatial earthquake hazards in an urban area

A geotechnical information system (GTIS) was constructed within a spatial geographic information system (GIS) framework to reliably predict geotechnical information and accurately estimate site effects at Gyeongju, an urban area in South Korea. The system was built based on both collected and performed site investigation data in addition to acquired geo-knowledge data. Seismic zoning maps were constructed using the site period (T _G) and mean shear wave velocity to a depth of 30 m (V _S30), and these maps were presented as a regional strategy to mitigate earthquake-induced risks in the study area. In particular, the T _G distribution map indicated the susceptibility to ground motion resonance in periods ranging from 0.2 to 0.5 s and the corresponding seismic vulnerability of buildings with two to five stories. Seismic zonation of site classification according to V _S30 values was also performed to determine the site amplification coefficients for seismic design and seismic performance evaluation at any site and administrative subunit in the study area. In addition, we investigated the site effects according to subsurface and surface ground irregularities at Gyeongju by seismic response analyses in time domains based on both two- and three-dimensional spatial finite element models, which were generated using spatial interface coordinates between geotechnical subsurface layers predicted by the GTIS. This practical study verified that spatial GIS-based geotechnical information can be a very useful resource in determining how to best mitigate seismic hazards, particularly in urban areas.     

Numerical and analytical investigation of compressional wave propagation in saturated soils

In geotechnical earthquake engineering, wave propagation plays a fundamental role in engineering applications related to the dynamic response of geotechnical structures and to site response analysis. However, current engineering practice is primarily concentrated on the investigation of shear wave propagation and the corresponding site response only to the horizontal components of the ground motion. Due to the repeated recent observations of strong vertical ground motions and compressional damage of engineering structures, there is an increasing need to carry out a comprehensive investigation of vertical site response and the associated compressional wave propagation, particularly when performing the seismic design for critical structures (e.g. nuclear power plants and high dams). Therefore, in this paper, the compressional wave propagation mechanism in saturated soils is investigated by employing hydro-mechanically (HM) coupled analytical and numerical methods. A HM analytical solution for compressional wave propagation is first studied based on Biot’s theory, which shows the existence of two types of compressional waves (fast and slow waves) and indicates that their characteristics (i.e. wave dispersion and attenuation) are highly dependent on some key geotechnical and seismic parameters (i.e. the permeability, soil stiffness and loading frequency). The subsequent HM Finite Element (FE) study reproduces the duality of compressional waves and identifies the dominant permeability ranges for the existence of the two waves. In particular the existence of the slow compression wave is observed for a range of permeability and loading frequency that is relevant for geotechnical earthquake engineering applications. In order to account for the effects of soil permeability on compressional dynamic soil behaviour and soil properties (i.e. P-wave velocities and damping ratios), the coupled consolidation analysis is therefore recommended as the only tool capable of accurately simulating the dynamic response of geotechnical structures to vertical ground motion at intermediate transient states between undrained and drained conditions.     

Effect of sampling plan and trend removal on residual uncertainty

ABSTRACT

The ground is one of the most highly variable of all engineering materials. As a result, geotechnical designs depend upon a site investigation to estimate the ability of the ground to perform acceptably. For example, when a shallow foundation is being proportioned to avoid a bearing capacity failure under a certain applied load, the frictional and cohesive properties of the ground under the foundation must first be estimated through a site investigation. Questions which arise are: How does the quality and intensity of the site investigation affect the design? Is more investigation cost effective? If the site is sampled at one location and the foundation placed at a different location, how does this mismatch affect the target design and the reliability of the final foundation? By modelling the ground as a spatially variable material, questions such as the above can be investigated through Monte Carlo simulation and sometimes theoretical probabilistic models. Using such tools, this paper looks specifically at how the intensity (frequency and spatial distribution) of a site sampling plan, and how the samples are used, affects the understanding of the ground properties under a foundation. Interestingly, it is found that removing the sample mean outperforms removing the best linear unbiased estimate (BLUE) when the actual field correlation length is small but the BLUE correlation length is assumed equal to the field size. Recommendations are made regarding number of samples and the type of trend to best characterise the field.

Abbreviations: BLUE: best linear unbiased estimate; MCS: Monte Carlo simulation; LAS: local average subdivision     

Bayesian assessment of site‐specific performance of geotechnical design charts with unknown model uncertainty

Soil properties are indispensable input parameters in geotechnical design and analysis. In engineering practice, particularly for projects with relatively small or medium sizes, soil properties are often not measured directly, but estimated from geotechnical design charts using results of some commonly used laboratory or in situ tests. For example, effective friction angle ?′ of soil is frequently estimated using standard penetration test (SPT) N values and design charts relating SPT N values to ?′. Note that directly measured ?′ data are generally not available when (and probably why) the use of design charts is needed. Because design charts are usually developed from past observation data, on either empirical or semi‐theoretical basis, uncertainty is unavoidably involved in the design charts. This situation leads to two important questions in engineering practice: 1 how good or reliable are the soil properties estimated in a specific site when using the design charts? (or how to measure the performance of the design charts in a specific site?); and 2 how to incorporate rationally the model uncertainty when estimating soil properties using the design charts? This paper aims to address these two questions by developing a Bayesian statistical approach. In this paper, the second question is firstly addressed (i.e., soil properties are probabilistically characterized by rationally incorporating the model uncertainty in the design chart). Then, based on the characterization results obtained, an index is proposed to evaluate the site‐specific performance of design charts (i.e., to address the first question). Equations are derived for the proposed approach, and the proposed approach is illustrated using both real and simulated SPT data. Copyright © 2016 John Wiley & Sons, Ltd.     

“Tunnel Information and Analysis System”: A Geotechnical Database for Tunnels

Existing experience from the design and construction of underground works is of major importance for the improvement of the construction methods and procedures in tunnelling, especially under adverse and complex geological and geotechnical conditions. This experience can be of great value to geotechnical engineers and engineering geologists, if data acquired through the ground investigation, the design and the construction is systematically collected, categorized and stored in a properly structured database that enables a targeted access to it, as well as to proceed to correlations and analysis, based on engineering criteria. Such a database should be carefully designed to “connect” all available data through all the phases of a tunnel project and premises deep knowledge from the geological and geotechnical investigation to the final design and construction. In order to make substantial use of the experience accumulated from the construction of a great number of tunnels, a database named Tunnel Information and Analysis System (TIAS) was developed. The data source for TIAS database was 62 tunnels of the Egnatia Highway in northern Greece, many of which have been constructed under difficult geological conditions in weak rock masses. The data processed by TIAS came from a variety of sources such as geological mapping, boreholes, laboratory and in situ testing, geotechnical classifications, engineering geological behaviour, groundwater, design parameters, information concerning immediate support measures, construction records and cost. The purpose of the system, besides incorporating extended and multi-source data for easy access, is to provide a tool for turning data into usable information for the comparison of anticipated and encountered geological and geotechnical conditions, the evaluation of geotechnical classification and design methods and the relations regarding rock mass conditions and behaviour and immediate support methods and types.     

A study of ground‐structure interaction in dynamic plate load testing

A mathematical treatment is presented for the forced vertical vibration of a padded annular footing on a layered viscoelastic half‐space. On assuming a depth‐independent stress distribution for the interfacial buffer, the set of triple integral equations stemming from the problem is reduced to a Fredholm integral equation of the second kind. The solution method, which is tailored to capture the stress concentrations beneath footing edges, is highlighted. To cater to small‐scale geophysical applications, the model is used to investigate the near‐field effects of ground‐loading system interaction in dynamic geotechnical and pavement testing. Numerical results indicate that the uniform‐pressure assumption for the contact load between the composite disc and the ground which is customary in dynamic plate load testing may lead to significant errors in the diagnosis of subsurface soil and pavement conditions. Beyond its direct application to non‐intrusive site characterization, the proposed solution can be used in the seismic analysis of a variety of structures involving annular foundation geometries. Copyright © 2002 John Wiley & Sons, Ltd.     

Engineering geological assessment of the proposed Uru Dam, Turkey

This paper describes the results of the engineering geological investigations and rock mechanics studies carried out at the proposed Uru Dam site. Analyses were carried out in terms of rock mass classifications for diversion tunnel, kinematic analysis of excavation slopes, permeability of the dam foundation and determination of rock mass strength parameters.Uru Dam is a rock-filled dam with upstream concrete slab. The dam will be built on the Suveri River in the central part of Turkey. The foundation rocks are volcanic rocks, which consist of andesite, basalt and tuff of Neogene Age. Studies were carried out both at the field and the laboratory. Field studies include engineering geological mapping, intensive discontinuity surveying, core drilling, pressurized water tests and sampling for laboratory testing.Uniaxial, triaxial and tensile strength tests were performed and deformation parameters, unit weight and porosity were determined on the intact rock specimens in the laboratory. Rock mass strength and modulus of elasticity of rock mass are determined using the Hoek–Brown empirical strength criterion. Rock mass classifications have been performed according to RMR and Q systems for the diversion tunnel.Engineering geological assessment of the proposed dam and reservoir area indicated that there will be no foundation stability problems. Detailed geotechnical investigations are required for the final design of the dam.     

Ground Investigations for Changi East Reclamation Projects

Geotechnical ground investigation is important in all construction works particularly, land reclamation projects. The Changi East reclamation project is a mega project that involves creation of land space as large as 3,000 hectares in multiple phases between 1991 and 2005. Ground investigation plays a critical role in the Changi project which involved substantial amount of ground improvement works after reclamation by sand filling. One important aspect of the investigation was to evaluate the geotechnical characteristics of the underlying compressible soils beneath the original seabed for the selection of suitable methods of ground improvement. The other important aspect of the investigation was to characterize and verify the compactness of the reclaimed sand fill. Many types of in situ tests were extensively used in the project. The field vane shear test provides correlations between the undrained shear strength and depth for the upper and the lower marine clay strata in the Northern part and the Southern Part of the reclaimed site. Combined with laboratory undrained shear strength tests, the field vane strength profiles allow the derivation of the undrained shear strength over effective stress ratios for the upper and the lower marine clays. In addition, results from three other in situ tests, the piezocone cone penetration test, the flat dilatometer test, and the self boring pressuremeter test provided useful verification of these correlations. A field-performance based method of assessing degree of consolidation in the underlying clay was developed by combining field monitoring, laboratory testing and conventional as well as specialized in situ testing. An effective use of in situ testing methods for assessment, the outcome of ground improvement and for fill quality control in the densification of granular soils is illustrated with field observation data collected at the project site.     

Geotechnical site investigations for possible urban extensions at Suez City, Egypt using GIS

With the development of economic activities in the world, the construction activities have also increased. A proper surface and subsurface investigation is made to assess the general suitability of the site and to prepare an adequate and economic safe design for the proposed work. The main purpose of the current study is to create a spatial model of the geotechnical conditions and considerations by using geographic information systems (GIS) techniques to develop and analyze a site model and to plan site activities at the new extension of Suez City (SC). In the geotechnical site evaluations, GIS can be used in four ways, data integration, data visualization and analysis, planning and summarizing site activities, and data presentation. The integrated data can be displayed; manipulated and analyzed using tools build into the GIS programs, thus creating the geotechnical site model of the study area. Decisions can be made for further site activities and the results of the site activities can be integrated into the GIS site model. Interpretation of geotechnical data frequently involves assimilating information from many sites each with a unique geographical location. Interpretation of these data requires the spatial location to incorporate into the analysis. Weights are assigned to different of mechanical, physical soil properties, geological, hydrogeological, and other ancillary data. Finally, the weighted maps are integrated using a GIS based on the construction purposes for the new extension of SC for significant cost savings in design, construction and longevity. The ideal and good zones’ highest regime has been observed towards central and western regions with sporadic pockets. The marginal zones to average zones are moderately suited for shallow foundation.     

一种新型板桩码头结构的离心模拟

卸荷式地连墙板桩结构码头是国内自主创新的深水码头结构,为了深入认识这一板桩码头结构在设计荷载下的工作性状和土与结构共同作用机制,结合某一拟建码头泊位的卸荷式地连墙板桩码头结构设计方案验证需要,进行了3组大型土工离心模型试验研究。其中2组为重复性的模型试验,以验证设计方案的可行性;第3组则模拟了无卸荷平台结构的地连墙板桩码头结构设计方案,以比较有无卸荷平台的板桩码头来揭示全直桩卸荷平台结构的卸荷效果。并且介绍了码头结构离心模拟技术,包括模型设计、模型制作和模型测量及试验步骤等关键内容。     

Framework for assessing probability of exceeding a specified liquefaction-induced settlement at a given site in a given exposure time

This paper presents a framework for assessing the probability of exceeding a specified liquefaction-induced settlement at a given site in a given exposure time. This framework deals not only with the effect of liquefaction (in terms of settlement) but also with probabilistic characterization of all possible ground motions at a given site (in terms of a joint distribution of a_max and M_w). Additionally, a new concept, referred to herein as liquefaction-induced settlement hazard curve, is introduced for assessing the annual rate of settlement exceedance at a given site. This settlement hazard curve concept has the potential to be a very useful tool in the field of geotechnical earthquake engineering. Satisfactory results are obtained in the demonstration examples analyzed with the proposed framework. Whereas the proposed framework is simple and effective, further refinements to this framework, especially on the treatment of epistemic uncertainty, are warranted.     

Numerical simulation of evapotranspiration using a root water uptake model

The abstraction of ground water by vegetation and its influence on the behaviour of geotechnical structures such as pavements, foundations and slopes has been researched for many years. In recent years, the use of numerical methods in geotechnical engineering has rapidly increased. A major challenge for numerical modelers involves the specification of the surface flow boundary condition to model root water uptake by vegetation. The abstraction of ground water by roots is a complex process which involves the interaction of the atmosphere, vegetation and the ground. Accurate prediction of the pore water pressure changes induced by vegetation requires the development of algorithms which can mimic the process of transpiration by vegetation in the continuity equation of fluid flow. This paper presents a root water uptake model which has been coded into a finite element program that can perform coupled (mechanical and fluid flow behaviour) analyses. The input data includes rainfall, potential evapotranspiration and maximum root depth. The key features of the model are discussed first, followed by a presentation of results from a series of parametric studies.     

曙光雷达数据处理软件系统

针对岩土工程探测对象的隐蔽性与复杂性,开发了曙光雷达数据处理软件系统,实现了不同类型雷达数据的共享数据处理、分形处理、偏移、联合反演、小波变换等功能;现场验证及试用结果表明,该软件系统可以改善地下目的物探测的分辨率和真实度,可为岩土工程施工提供较准确的地下障碍物资料。     

Engineering-geological model of the Segura River flood plain (SE Spain): a case study for engineering planning

This article presents a sedimentological and geotechnical study of the surficial sediments in the Segura River valley (SE Spain). We formulate an engineering-geological model consisting of four zones, each characterized by its geotechnical properties and by various geotechnical problems (namely low bearing capacity, significant ground settlement and liquefaction of sandy sediments). The model quantifies the geotechnical properties and potential problems in each zone. It serves as a useful tool for preliminary geotechnical investigations. The model also enables a better design of field surveys as well as optimal selection of geotechnical investigation techniques for future civil engineering works.     

Hydraulic In situ Testing for Mining and Engineering Design: Packer Test Procedure,Preparation, Analysis and Interpretation

Hydraulic in situ measurement of rock mass permeability by packer (Lugeon) testing is an inherent and integral element of many engineering, hydrogeological and mining investigation. This paper describes and discusses geotechnical testing in the design process from a consulting practitioner’s perspective. This study focuses on the Packer testing planning, procedure, results & interpretation. Packer test system is an optimum method for obtaining values of hydraulic conductivity in wells that are difficult to analyse using conventional slug test systems. Packer tests are carried out to assess the variability of a borehole as it intersects various hydrogeological units. It gives vertical distribution of hydraulic properties and water quality in the aquifer and usually cheaper than a nest of wells and gives more continuous record and this knowledge can often be essential for a proper design. The role, objectives, types and interpretation of testing, limitations and recommended good practices as part of the geotechnical design process are outlined through the examination of test data from a case record.     

黄河源区高寒植被主要特征初探

位于青藏高原东北部多年冻土与季节冻土交错带的黄河源区高寒生态环境及其变化一直备受关注. 气候变暖、冻土退化条件下,为了解黄河源区不同冻土区植被状况,在源区布设了4个场地：查拉坪（CLP,源区南部连续低温多年冻土区）;扎陵湖南岸（ZLH,源区中南部岛状多年冻土区）;麻多乡（MDX,源区西部的不连续多年冻土区）;鄂陵湖北岸（ELH,源区中北部季节冻土区）. 结合植被调查和场地监测,分析了源区各冻土区植被的差异. 结果显示：总体上低温多年冻土区植被盖度、多样性指数高,表现为连续多年冻土区（查拉坪）>不连续多年冻土区（麻多乡）>季节冻土区（鄂陵湖北岸）,其中岛状多年冻土区（扎陵湖南岸）例外,该场地平均盖度最低,多样性指数介于查拉坪和麻多乡之间,局部植被退化较严重. 均匀度指数均表现为扎陵湖南岸最高,查拉坪次之. 地上生物量调查结果显示：查拉坪>麻多乡>扎陵湖南岸>鄂陵湖北岸,且鄂陵湖北岸出现指示植被退化的植物. 尽管黄河源区高寒植被研究为理解冻土退化条件下的生态环境变化提供了一些基础数据,评估气候变化和冻土退化的生态和水文效应需要更系统的调查和监测研究.     

平果铝厂厂区岩溶地基处理方法

在充分收集和研究平果铝厂厂区岩土工程条件的基础上,阐述了厂区的岩溶发育特征,总结研究了平果铝厂的岩溶地基处理方法,为系统研究岩溶地区地基处理措施提供科学依据。     

Determination of silica sand stiffness

Site investigation and evaluation of properties of soil or rock are important aspects of geotechnical design. Determination of the ground stiffness is one of the important parameters in geotechnical engineering. Since the measurement of shear modulus is very sensitive to soil disturbance, especially for sand, determination of the stiffness of soil in the field is more reliable than in laboratory tests on sampled specimens. Measurement of shear modulus is one of the most common applications of self-boring pressuremeter testing. As an in situ device, the pressuremeter provides a unique method for assessing directly the in situ shear modulus of a soil. This paper describes a laboratory study of silica sand stiffness, which varies with stress level and strain amplitude. The results show that the elastic shear modulus value is mainly dependent on the value of the mean effective stress and relative density.     

天津地区岩土工程勘察中地震效应重点问题分析

场地和地基的地震效应评价是岩土工程勘察的一项重要任务。结合天津地区工程地质条件和岩土工程勘察现状,对场地和地基的地震效应评价所涉及的抗震设防烈度的确定、场地类别的划分、抗震地段的划分、液化判别、软土震陷、场地稳定性和适宜性评价等重点问题进行了探讨。