Showing papers in "Bulletin of Engineering Geology and the Environment in 2006"

Landslide hazard and risk zonation—why is it still so difficult?

Abstract: The quantification of risk has gained importance in many disciplines, including landslide studies. The literature on landslide risk assessment illustrates the developments which have taken place in the last decade and that quantitative risk assessment is feasible for geotechnical engineering on a site investigation scale and the evaluation of linear features (e.g., pipelines, roads). However, the generation of quantitative risk zonation maps for regulatory and development planning by local authorities still seems a step too far, especially at medium scales (1:10,000–1:50,000). This paper reviews the problem of attempting to quantify landslide risk over larger areas, discussing a number of difficulties related to the generation of landslide inventory maps including information on date, type and volume of the landslide, the determination of its spatial and temporal probability, the modelling of runout and the assessment of landslide vulnerability. An overview of recent developments in the different approaches to landslide hazard and risk zonation at medium scales is given. The paper concludes with a number of new advances and challenges for the future, such as the use of very detailed topographic data, the generation of event-based landslide inventory maps, the use of these maps in spatial-temporal probabilistic modelling and the use of land use and climatic change scenarios in deterministic modelling.

Engineering geology maps: landslides and geographical information systems

Abstract: IAEG Commission No. 1—Engineering Geological Maps—is developing a guide to hazard maps. Scientists from 17 countries have participated. This paper is one of a series that presents the results of that work. It provides a general review of GIS landslide mapping techniques and basic concepts of landslide mapping. Three groups of maps are considered: maps of spatial incidence of landslides, maps of spatial–temporal incidence and forecasting of landslides and maps of assessment of the consequences of landslides. With the current era of powerful microcomputers and widespread use of GIS packages, large numbers of papers on the subject are becoming available, frequently founded on different basic concepts. In order to achieve a better understanding and comparison, the concepts proposed by Varnes (Landslide hazard zonation: a review of principles and practice, 1984) and Fell (Some landslide risk zoning schemes in use in Eastern Australua and their application 1992; Landslide risk assessment and acceptable risk. Can Geotech J 31:261–272, 1994) are taken as references. It is hoped this will also add to the international usefulness of these maps as tools for landslide prevention and mitigation. Six hundred and sixty one papers and books related to the topic are included in the references, many of which are reviewed in the text.

Challenges and trends for geological modelling and visualisation

Abstract: The successful execution of both large and complex construction projects and environmental and natural hazard assessments requires a precise definition of subsurface conditions. Over the past two decades, a series of sophisticated 3-D modelling technologies—collectively identified as geoscientific information systems, or GSIS—have been developed to address this subsurface characterisation need. Existing commercial systems reflect their historical origins. The modelling and visualisation process remains technically challenging. Rapid development of computer hardware and software, modern data base design concepts and expanded information transmission capabilities across the Internet are encouraging the greater use of GSIS technologies as they become cheaper and easier to use and integrate within corporate decision-support systems. The integration of GSIS with broader information management systems is not common, but limited initial experiences suggest that large benefits are likely to result.

The behaviour of organic matter in the process of soft soil stabilization using cement

Abstract: In some projects where cement is used to stabilize soft soil foundations, it is found that the organic matter influences the stabilization effect. As a consequence, extra admixtures are added to accelerate the reactions of cement and improve the stabilization effect. In this study, different kinds of extra admixtures were used with cement to stabilize a soft soil with a high organic content. Direct shear and unconfined compression tests were undertaken and the mechanical indices in different conditions obtained. The total amount and components of the organic matter in every sample were also determined. The results show that the addition of extra admixtures improves the properties of cement-stabilized soils and that different extra admixtures play a different role.

Variability of the engineering properties of rock masses quantified by the geological strength index: the case of ophiolites with special emphasis on tunnelling

Abstract: The paper presents a quantitative description, using the Geological Strength Index (GSI), of the rock masses within an ophiolitic complex including types with large variability due to their range of petrography, tectonic deformation and alteration. This description allows the estimation of the range of rock mass properties and the understanding of the dramatic changes in behaviour which can occur during tunnelling, from stable conditions to severe squeezing within the same formation at the same depth. The paper presents the geological model in which the ophiolitic complexes develop, their various petrographic types and their tectonic deformation, mainly due to overthrusts. The structure of the various rock masses includes all types from massive strong to sheared weak, while the conditions of discontinuities are in most cases fair to poor or very poor due to the fact that they are affected by serpentinisation and shearing. Serpentinisation also affects the initial intact rock itself, reducing its strength. Associated pillow lavas and tectonic melanges are also characterised. Based on the GSI, a classification of the behaviour in terms of tunnelling is presented, including stable conditions, structural instability, mild overstressing, stress dependant instability, squeezing and ravelling.

Assessing landslide hazard in GIS: a case study from Rasuwa, Nepal

Abstract: A slope stability analysis on a regional scale is presented for the northern part of the Rasuwa district in Nepal, covering 409 km2. A physically based slope stability model coupled to a simplified groundwater flow model was used to estimate soil wetness, and safety maps were generated for three steady state and two quasi-dynamic conditions. The results show that only about half of the soils are unconditionally stable, characterised by slopes smaller than 22°. Some 7% of the study area is prone to failure under completely saturated conditions, where the slopes exceed 30° and the land-use is predominantly agricultural. Some deficiencies in the model are discussed, but nevertheless the study shows that based upon relatively coarse and limited data, useful landslide hazard information on a regional scale can be obtained.

Cohesion of unsaturated residual soils as a function of volumetric water content

Abstract: Soil cohesion changes with the moisture state of a soil. This paper presents an empirical equation to predict the cohesive component in the shear strength of unsaturated residual soils as an exponential function of volumetric water content. The formulation originated from a multiple linear-regression analysis for data sets obtained from shear tests using undisturbed soils with varying moisture contents. The empirical equations can realistically predict the reduction in soil cohesion due to wetting (R 2=0.88, 0.93). The methodology described in this paper provides a convenient alternative to the quantitative estimation of unsaturated shear strength, especially in an engineering practice such as a slope stability analysis as no matrix suction data are required.

Three and more dimensional modelling in geo-engineering

Abstract: Full three-dimensional modelling has been developed and is implemented for many sites where engineering structures are built. Such computer models of the subsurface allow for a more sophisticated handling of subsurface data leading to, for example, better dimensioning of geotechnical units, the evaluation of hazard and risk, foundation design, tunnel routing, planning and building, etc. Other applications are the back-analysis for completed civil engineering projects to verify the correctness of assumed and estimated ground models and parameters, the verification of the correctness of constitutive models for ground behaviour and the use of back analysis to improve building methodologies or equipment. The paper illustrates some of these advantages with a number of state-of-the-art applications of three-dimensional modelling in engineering geology and geotechnical engineering, highlighting a number of key issues when computer-aided 3D modelling is used: the definition of geotechnical (homogeneous) zones, scale and detail, uncertainty and likelihood of the developed model.

Comparison of geophysical methods for sub-surface mapping of faults and fracture zones in a section of the Viggja road tunnel, Norway

Abstract: Results from site investigations, 2D resistivity, refraction seismic and VLF on a section of tunnel near Trondheim, show that 2D resistivity data are most valuable for interpreting geological structures in the sub-surface. VLF only identifies zones and does not indicate thickness, width or dip direction. The method is also sensitive to technical installations. Refraction seismic is valuable for mapping depth to bedrock, location and width of fracture zones but cannot indicate the depth or dip direction of such zones. With 2D resistivity, the position of a zone is well identified. This method may also provide information on the depth and width of the zone as well as the dip direction. In most cases 2D resistivity clearly identifies zones in the bedrock that can be observed as fault and/or fracture zones in the tunnel. The results described in this paper show a good correlation between the resistivity profiles, mapped structures on the surface and mapped zones in the tunnel.

Relationship between microstructure and bowing properties of calcite marble claddings

Abstract: The use of thin (20–40 mm) marble as cladding for building facades has increased substantially during the last few decades Many of the marble facades perform but some durability problems have occurred, especially with calcite marble, when the cladding starts to bow indicating a decrease in strength This study considers the influence of the microstructure on the bowing of the calcite marble using adjacent grains analysis Samples with a granoblastic texture all had six adjacent grains while those with a more complex microstructure had up to 13 adjacent grains The samples with a granoblastic texture had the greatest degree of bowing, suggesting that the microstructure is a crucial parameter for the durability of marble and that adjacent grains analysis could be a fast and easy method to assess the suitability of marble for cladding purposes

The effect of the pH of the testing liquid on the slake durability of gypsum

Abstract: It is known that foundation problems are caused by the dissolution of gypsum due to both chemical and mechanical processes. In order to investigate the combined effect of physico-chemical agents on the erodability of gypsum, a series of slake durability tests were carried out on eight different types of gypsum using testing solutions with different pH values. XRD, chemical and petrographical analyses, and basic strength tests such as unconfined compression, Brazilian tensile, and point load were performed on the eight rock types. The slake durability results ranged from medium to very high under the different pH conditions but it was concluded that the slake durability of gypsum is independent of the pH of the testing solution. Mineralogical composition and fabric are considered to have a greater influence on the slake durability of gypsum.

Probabilistic assessment of earthquake hazard in Sinai in relation to the seismicity in the eastern Mediterranean region

Abstract: Sinai is surrounded by the most active seismic trends in Egypt and earthquake risk reduction has become an important ongoing socio-economic concern. Twenty-five earthquake source zones were used to define the seismicity of the eastern Mediterranean region. Peak ground acceleration (PGA) values with a 90% probability of not being exceeded in 50 and 100 years were determined for the Sinai and Dead Sea regions. These indicated the highest relative levels of ground motion are expected in regions neighbouring the Gulf of Aqaba, the Dead Sea and the southern part of the Gulf of Suez. Other regions were characterized as having a relatively low to intermediate level of PGA values. The PGA values obtained will be useful for civil engineers, regulators and planners, in order to mitigate the effects of earthquakes and to plan earthquake resistant designs.

Disaster risk management in development projects: models and checklists

Abstract: In Latin America and the Caribbean, the available information about the causes and consequences of risk is scarce and barely meets the needs of project engineers and decision makers. Although local governments and communities typically who bear the brunt of the losses, they do not participate in the definitions and are not informed about the “acceptable” level of risk or how to reduce it. The formulation and adoption of risk management criteria (supported by engineering geological modelling), throughout the cycle of development/investment projects, should take account of the affected communities and how they can play a part in the decision making. This requires an increased awareness and understanding of both natural hazards and vulnerability. The paper analyses best practices based on experiences from Latin America and the Caribbean, which may be useful for the evaluation of hazards and vulnerability and lead to proactive risk management.

Investigating epikarst using low-frequency GPR: example from the Gran Sasso range (Central Italy)

Abstract: A realistic 3D view of the epikarst is key to understanding karst groundwater phenomena. Ground penetrating radar proved to be highly effective for investigating the epikarst of a sinkhole located in the Gran Sasso karst range (central Italy). Two different low-frequency antennae (100 MHz bistatic shielded and 40 MHz bistatic unshielded) were used. The radar signal interpretation was correlated with field observations of the epikarst and borehole data. Two radar anomaly surfaces were identified, which were correlated with the top and bottom of the epikarst surface. The shape of the two surfaces correlates well with the surface topography of the study sinkhole and with the orientation of its main joints and karren. The work indicated that such a 3D reconstruction could be usefully applied to karst aquifer vulnerability studies.

Discontinuity networks in mudstones: a geological approach

Abstract: Although usually masked by a veneer of weathered products, a discontinuity network has been observed in mudstones dated from the Lower Cambrian to the Miocene, principally in pits and quarries. Its origin is attributed to an early hydraulic fracturing of the initial muds with their drainage and progressive compaction. In contrast no natural discontinuities have been observed in the galleries of underground nuclear waste laboratories in Boom Clays at Mol, Belgium, and in Opalinus Clays at Mont Terri, Switzerland, or in deep reconnaissance borings. However, the observations were made immediately after the works. At depth, natural discontinuities are closed by the stress field. As there is no cement and with the temperatures of diagenesis being too low to allow any re-crystallization, they are sealed but not healed. They could reopen with the release of stress and/or desiccation.

Chemical and mineralogical transformations in three tropical soils due to permeation with acid mine drainage

Abstract: The chemical and mineralogical compositions of three tropical soils, before and after permeation with 19–24 pore volumes of acid mine drainage (AMD), were assessed using X-ray diffraction and chemical analyses, in order to consider their potential value as clay liners. After permeation the CEC of one soil (Soil K) was reduced, partly due to structural modification of smectite by AMD. Conversely, the other soils (Soils A and H) showed increased CEC values due to structural changes in mixed layer vermiculite minerals, resulting in the formation of vermiculite as a separate phase in the soils. The specific surfaces of the soils were reduced. AMD caused changes in the variable charge properties of the soils due to the composite effects of soil pH and organic matter reduction and the changes in composition of exchangeable ions. Dolomite, gibbsite, diaspore, magnesioferrite and hydroxy apatite were dissolved from the soils. Chlorite was mildly altered but kaolinite was structurally resistant to AMD attack. Jarosites were, however, formed in all the soils. It was concluded that the tropical soils studied could be effective sinks for zinc and nickel from AMD, but that Soils A and H would be the most desirable clay liners for acid mine waste containment due to their low hydraulic conductivity, high sorptive capacity and compatibility with AMD.

Study of the micro-mechanical behaviour of the Opalinus Clay: an example of co-operation across the ground engineering disciplines

Abstract: The high degree of scientific cross-fertilisation possible between the three geo-engineering disciplines soil mechanics, rock mechanics and engineering geology, is demonstrated by means of a micro-mechanical model of the Opalinus Clay. After a brief review of Terzaghi’s effective stress principle and the importance of micro-mechanical models in general, a conceptual study of a micro-mechanical model of a claystone is presented in some detail. The model is based on the Particle Flow Code (PFC) developed by Itasca Corp. It introduces into the model the pertinent composition and structure of the Opalinus Claystone established in the local engineering geology of Switzerland and SW Germany. This includes elongated clay platelets, various layers of densified water around the platelets, free water in the pores and a specific texture of the platelets after consolidation. The model is numerically subjected to a series of loading stages. It is shown that the micro-mechanical model reproduces a number of features which have been known for a long time in soil and rock mechanics but which are often intractable in conventional generic models. The features include non-linear stress–strain curves with pre-failure damage and post-failure strain softening, a non-linear increase of the particle contacts with loading, distinct clustering of deformations, clustering of micro cracks leading to the development of shear bands and hysteresis in cyclic loading. It is concluded that micro-mechanical models are promising tools for further development of our understanding of the mechanical behaviour of geological materials. They offer an excellent opportunity for scientific co-operation between engineering geologists and soil and rock mechanics engineers.

Highway failure over talc–tremolite schist terrain: a case study of the Ife to Ilesha highway, South Western Nigeria

Abstract: Several failure stretches along the newly completed Ife–Osu–Ilesha highway in South Western Nigeria have been studied. The sub-grade as well as the borrow materials are schist-derived, residual micaceous soils which contain abundant talc and hydromica. The flaky structure of these soils means it is difficult to achieve adequate field compaction. Extensive deposits of amphibolite-derived residual soils also occur in the area, which would provide a more suitable sub-base/fill material. The case study highlights the importance of an engineering geological appreciation of the ground conditions prior to design and construction.

Groundwater recharge via deep boreholes in the Patras Industrial Area aquifer system (NW Peloponnesus, Greece)

Abstract: The economic development of the Patras Industrial Area is influenced by both the availability and the seasonal variability of water resources. Groundwater from the deep confined aquifer is the major source of water for the industries located in this area. During the 1980s, over-pumping combined with prolonged dry periods has lowered the groundwater level. The paper presents the results of groundwater recharge testing in the confined aquifer using three deep boreholes and injection rates ranging from 30.5 to 63.5 m3/h. The groundwater level rose by more than 3.5 m in the recharge boreholes and 1 m in those 0.5 km away. The field experiments provided useful guidance on the proper planning of pilot tests, data monitoring and analysis, which can also be applied to other regions with similar conditions. Based on the hydrogeological conditions a groundwater flow model was successfully used to predict the aquifer system response. The work confirms that aquifer recharge is an environmentally acceptable solution, as part of an integral water resources management plan.

Strain rate dependent strength and stress–strain characteristics of a welded tuff

Abstract: Results of 61 uniaxial compression tests on the welded Topopah Spring tuff are presented. The tests were carried out under constant strain rates at room temperature. Stress–strain analysis indicates that dilatancy and compaction start at about 50% of ultimate strength. A sudden stress drop occurs at about 90% of the ultimate strength, which indicates the onset of specimen failure. Both strength and peak axial strain decrease with strain rate as power functions. Based on the strain rate dependence of strength and peak axial strain, it is inferred that the elastic modulus is strain rate dependent. A relationship between stress, axial strain, and axial strain rate is developed. The parameters in this relation are estimated using multivariate regression to fit stress–axial strain–strain rate data.

Engineering geological mapping of heterogeneous rock masses in the Northern Apennines: an example from the Parma Valley (Italy)

Abstract: Most of the geological formations in the Northern Apennines are made up of flysch and tectonic melanges. A general characterization of the most common rock masses cropping out in the Val Parma is presented in this paper, using the Marinos–Hoek classification based on the Hoek–Brown criterion. Three groups were identified: heterogeneous rock masses essentially controlled by single discontinuities with strengths much lower than the main rock mass (HH); truly heterogeneous rock masses with approximately equal alternations of hard and weak horizons which fail through the weaker materials (TH) and a rock mass in which the majority of the material is weak, tending to soil-like behaviour (WH). A general engineering geological map of the study area is presented, highlighting the spatial distribution of the three different groups.

Rôle des fluides dans le comportement hydromécanique des roches fracturées hétérogènes: Caractérisation in situ et modélisation numérique

Abstract: Les processus de couplages hydromecaniques dans un massif rocheux fracture sont etudies a travers des experimentations in situ et des simulations numeriques. L'approche experimentale consiste a mesurer simultanement la pression de fluide et le deplacement mecanique en differents points d'un reservoir carbonate tout en controlant les conditions aux limites hydrauliques. Ces mesures sont analysees par modelisation couplee hydromecanique. A l'echelle du massif, mesures et modeles montrent que le couplage hydromecanique est controle par un comportement hydraulique de double permeabilite de fractures associe a un comportement mecanique de double rigidite de fractures. A l'echelle de la fracture unique, des mesures dynamiques par capteurs a fibre optique realisees lors d'un pulse de pression montrent une reponse pression/deplacement presentant une boucle caracteristique dont l'evolution est differente entre les phases d'augmentation et de chute de pression. A partir de ces donnees in situ, les parametres hydromecaniques des fractures et de la matrice rocheuse sont retro analyses par les modeles numeriques. Ces modelisations montrent que la sensibilite de la reponse hydromecanique de la fracture pressurisee est fortement dependante de la raideur normale et de l'ouverture hydraulique de la fracture, de la raideur de la matrice rocheuse et de la geome trie du reseau de fractures.

Common ground in engineering geology, soil mechanics and rock mechanics: past, present and future

Abstract: Engineering geology, together with soil mechanics and rock mechanics, is commonly considered to be one of the three fundamental scientific disciplines in ground engineering. Historically, the interrelation between these three disciplines has never been free of ambiguity. This, for instance, is highlighted by the fact that both Karl von Terzaghi, the founder of soil mechanics, and Leopold Muller, the founder of rock mechanics, considered themselves foremost as engineering geologists without, however, succeeding in establishing engineering geology as a free-standing discipline with autonomous intellectual merits, methods and procedures. This situation has changed recently as evidenced in Knill’s fundamental publication (2002) on Core Values in Engineering Geology and by the fact that the relevant three International Societies are currently in the process of moving together towards a “Federation of Geo-Engineering Societies”.

Assessing groundwater contamination risk using the DASTI/IDRISI GIS method: coastal system of western Mamora, Morocco

Abstract: In this study, the DASTI method was used to evaluate vulnerability to groundwater pollution in the vicinity of Rabat, western Morocco. The model is based on the characterization of five intrinsic parameters: unsaturated zone thickness, saturated zone thickness and lithology, soil texture, topography and hydraulic gradient. A system of classes of the hydrogeological characteristics was applied to evaluate relative vulnerability to groundwater contamination and a susceptibility map was prepared based on land use and the vulnerability index map. The study showed the DASTI method (applied using IDRISI software) can serve as a tool to evaluate vulnerability to pollution and thus facilitate programs to protect groundwater resources.

A linear graphical method to predict the effect of compaction on the hydraulic conductivity of clay liners and covers

Abstract: It is proposed to present compaction relationships by plotting the inverse of the dry density versus the molding water content. In the proposed graph, the curves for equal degree of saturation become straight lines. The proposed new graph is shown to be very convenient to assess the saturated hydraulic conductivity, k sat, of non-swelling compacted clay, using a dual porosity model. The value of k sat depends on the secondary porosity between clay clods. The equation developed for equal k sat value appears also as a straight line in the proposed graph. It facilitates the prediction of k sat from field compaction data and thus the prediction of field performance of clay liners and covers.

Numerical analysis of stresses and displacements for the Tafjord slide, Norway

Abstract: Numerical modelling has been used for analyzing stresses and displacements for the very steep and more than 1,000 m high Heggura rock slope near Tafjord, Norway where a disastrous 3 million m3 rock slide occurred in 1934. It is shown that very anisotropic stresses exist near the slope surface and displacements of the remaining slope as result of the 1934 slide have been calculated to up to 210 mm. Such considerable displacements are believed to have a significant impact on the present and future stability of the Heggura slope.

The provision of digital spatial data for engineering geologists

Abstract: Until recently most spatial geological information was in analogue (mainly paper) form, which made it expensive to store and often difficult to use because of its increasing fragility. However, with the rapid advances in information technology in the last 20 years, not only has it become relatively easy to digitise or digitally scan historical information but, increasingly, data suppliers are, themselves, producing the raw data in digital form. This brings with it a host of new problems for the acquisition, management and dissemination of the information. These issues include data collection (what, where, how and by whom), data management and security (metadata, validation, backup, access), data access (how, where and at what price) and the provision of value-added products based on the data tailored to the needs of specific users. For engineering geologists, the historical acquisition of geological data in various forms is on the verge of delivering a whole range of new products that should alter the way in which site investigation is carried out.

Geological and geotechnical characteristics of Xiaolangdi dam, Yellow River, China

Abstract: In order to construct a 154 m high, 1,650 m long earth filled dam across the Yellow River at Xiaolangdi, China, site investigations including in situ and laboratory tests, Landsat imaging, geological mapping, geophysical survey and drilling were undertaken. Two special investigation techniques were employed. To ensure full recovery of the intercalated clays and siltstones in the Permian and Triassic deposits, a sleeve drilling technique was introduced while to establish the long-term stress conditions in the tunnels, radial resistance testing was undertaken. The paper focuses on the geotechnical characteristics of the Quaternary sands and gravels, which in the channel of the valley are up to 70 m thick, and discusses the influence of the Triassic and Permian bedrock.

Modelling of seismic hazard for the El-Dabaa area, Egypt

Abstract: This paper reviews the likely ground acceleration related to a seismic event for the location of a nuclear power site at El-Dabaa, Egypt. More recent data have been integrated into the design philosophy developed some 20 years ago and seismic hazard assessment was carried out using probabilistic techniques. The maximum possible earthquake magnitude Mmax was estimated for the area surrounding El-Dabaa and the hazard parameter peak ground acceleration (PGA) calculated for given zones. The iso-acceleration map of the El-Dabaa area for a return period of 400 years indicates PGA values of 0.15 g, slightly above those for a 100-year return period. The results are in general very similar to those obtained using the deterministic approach of El-Sayed. The differences in some zones may be related to the fact that the probabilistic methods are very sensitive to the completeness of the data and use simple attenuation laws that oversimplify the wave’s propagation phenomena. The work on the estimation of PGAs will contribute to the determination of national seismic codes, giving guidance on which buildings must take seismic risk into consideration and the necessity to re-appraise the seismic risk for existing buildings.