Geotechnical Survey Research Articles

Estimation of In-Situ Shear Strength Parameters of Weathered Granitic (MASADO) Slopes Using Lightweight Dynamic Cone Penetrometer

ABSTRACT A major problem in the geotechnical approach to the stability of natural slopes is that there is usually little information on the in-situ geotechnical conditions, because of the extreme difficulty associated with ground investigations of steep slopes covered with vegetation. In this study, a lightweight dynamic cone penetration test (LWDCPT) has been introduced for a geotechnical survey of natural weathered granitic (Masado) slopes. Based on a series of direct shear tests, the internal friction angle and the apparent cohesion of reconstituted Masado soil were found to be fairly closely related to the void ratio and the degree of saturation in the soil. From the laboratory calibration tests, an equation was created to relate the dynamic cone resistance (qd) and the void ratio of reconstituted Masado under different degrees of saturation. Equations were developed to calculate the internal friction angle and the apparent cohesion from the value of qd for Masado at a known degree of saturation. LWDCPT and direct shear tests were carried out on undisturbed samples taken from a natural Masado slope. The estimated internal friction angle and the apparent cohesion calculated with the value of qd in the LWDCPTs agreed fairly well with those of tests on the undisturbed samples obtained in laboratory shear tests.

Numerical modelling of seismic site effects incorporating non-linearity and groundwater level changes

In the past decades, the necessity for detailed earthquake microzonation studies was recognized worldwide. Therefore, different approaches were established and applied. Unfortunately, the majority of these approaches are not based on pre-existing field data but require extensive seismic measurements and investigations. Furthermore, these approaches incorporate non-linearity inadequately and cannot take groundwater level changes into account. For this purpose, notably numerical models are most suitable. These models require a good knowledge of the local geological conditions (especially of the uppermost unconsolidated units), information about the geotechnical parameters of these units, and a hydrogeological model of the investigated area. Most of this information can be obtained from geotechnical investigations and surveys that have already been carried out in most densely populated areas. In a case study for Bucharest City, non-linear analyses were performed using software that is based on the visco-hypoplastic constitutive law. The results indicate that groundwater level changes have an important influence on duration and amplitude of ground response and thus should be considered for seismic microzonation studies. This approach can be used to display site effects and to identify different microzones taking different earthquake magnitudes and groundwater levels into account.

Comparison among SASW, ReMi and PS-logging techniques: Application to a railway embankment

Results obtained by SASW and PS-logging (in-hole) seismic techniques are compared with the relatively new ReMi (Refraction microtremor) method at a common site with a well-known soil profile: a recently constructed high-speed railway embankment. PS-logging is the most accurate technique in identifying the soil profile of the embankment followed by Re-Mi and SASW. Mean shear wave velocity estimations are also higher for PS-logging, followed by SASW and ReMi, while mean deviation is similar in each technique. The ReMi technique has provided very accurate results in the study of the embankment profile, which in addition to its high operability and its fast data processing, makes it a very convenient technique for extensive geotechnical surveys.

Aplicação de métodos de agrupamento para definição de famílias de descontinuidades

This work had the purpose of applying numerical and classical methods of clustering for the definition of discontinuity sets in order to use the results in rock slope stability studies. In general classical methods are employed, involving the use of pole density diagrams to define these sets. However there can be uncertainties in family sets interpretation, especially when discontinuity family frequency is very distinct. In these cases the use of numerical methods to define family sets, associated to classical methods in order to interpret, validate and represent the sets is interesting, as they complement each other. Data used in this work was obtained from geotechnical surveys along a mine, an urban slope and a road slope, where discontinuity orientations were measured. Softwares developed in FORTRAN language were used in the definition of discontinuity sets. Average values of orientation and dispersion parameters of discontinuity sets were calculated, as the distribution probability data function was obtained. Field observations demonstrated the reliability of the clustering method used.

Aplicação de métodos de agrupamento para definição de famílias de descontinuidades

This work had the purpose of applying numerical and classical methods of clustering for the definition of discontinuity sets in order to use the results in rock slope stability studies. In general classical methods are employed, involving the use of pole density diagrams to define these sets. However there can be uncertainties in family sets interpretation, especially when discontinuity family frequency is very distinct. In these cases the use of numerical methods to define family sets, associated to classical methods in order to interpret, validate and represent the sets is interesting, as they complement each other. Data used in this work was obtained from geotechnical surveys along a mine, an urban slope and a road slope, where discontinuity orientations were measured. Softwares developed in FORTRAN language were used in the definition of discontinuity sets. Average values of orientation and dispersion parameters of discontinuity sets were calculated, as the distribution probability data function was obtained. Field observations demonstrated the reliability of the clustering method used.

Mobility of potentially harmful metals in latosols impacted by the municipal solid waste deposit of Londrina, Brazil

The contamination of soils by metals issuing from municipal solid waste (MSW) disposal in tropical environments has hardly been studied with regard to the particular problems associated with them, i.e., generally a high permeability of soils despite the abundance of clay, and the role of reactive Fe compounds. From a previous geotechnical and chemical survey, three latosol profiles differently affected by MSW leachates in the region of Londrina (Paraná, Brazil) were selected. The aims were to evaluate the extent of their contamination, to better understand the fate of potentially harmful metals in tropical soils and rank the determining factors. Samples between 0.5 and 7 m depth were analyzed for their physical, mineralogical and chemical properties, and their micro-morphology was described by optical and transmission electron microscopy. Two steps of a sequential extraction procedure helped to assess the mobility of elements and to better discriminate between metals originating from pedogenesis and issued from MSW. These combined approaches showed that exposed soil profiles have been impacted at various depths, down to 7 m, through increased metal content, especially enhanced mobility of Zn, Co, Mn, Cu and Fe, and through increased salinity and organic matter. The mobility of potentially harmful metals should decrease with pH, which significantly increased in some impacted horizons, but other factors can reverse this trend.

Recognition of shallow karst water resources and cave potentials using thermal infrared image and terrain characteristics in semi-arid regions of Iran

Shallow karst water resources and caves may influence land surface temperatures due to cold transfer property of rocks and evaporation from buried karst. The objective of this research was to develop a method for recognition of karst areas based on evaluating the surface characteristics that manifest itself by low land surface temperature in the satellite images. Investigation of thermal ETM+ image of the study region in Iran showed that parts of carbonate rocks that bear karst water are relatively cooler compared to areas with similar terrain conditions. Relational modeling provided useful information on spatial distribution of areas that have the potential to hold karst water resources and/or caves. Further inspection of ASTER images, along with geotechnical, geophysical and geological field surveys verified the approach. Significant correlation was found between electrical resistivity and thermal band values. The method may be used as a primary exploratory tool for shallow karst water explorations in similar areas.

Strike-slip deformations in the West Siberian Basin and their impact on exploration and development of oil and gas reservoirs

Extensive 3D seismic exploration has revealed in much of the West Siberian petroliferous basin area a special type of faults and deformations within the sedimentary cover, caused by low-separation basement strike-slip faults. A geologic phenomenon associated with strike-slip fault structures is something new to the understanding of the subsurface structure of West Siberia. Complex morphology, intense disjunctive faulting, block arrangement and enormously wide stratigraphic range of oil and gas presence are characteristic of numerous hydrocarbon fields within the zones of strike-slip fault structures. It would certainly be a risky endeavor to design field development-andproduction projects, drill production wells and conduct geotechnical surveys without confident geomechanical and kinematic models for structure-forming, fluid-conductive and sealing dislocations caused by strike-slip faults in the basement.

Seismic reflection characteristics of naturally-induced subsidence affecting transportation

High-resolution seismic reflections have been used effectively to investigate sinkholes formed from the dissolution of a bedded salt unit found throughout most of Central Kansas. Surface subsidence can have devastating effects on transportation structures. Roads, rails, bridges, and pipelines can even be dramatically affected by minor ground instability. Areas susceptible to surface subsidence can put public safety at risk. Subsurface expressions significantly larger than surface depressions are consistently observed on seismic images recorded over sinkholes in Kansas. Until subsidence reaches the ground surface, failure appears to be controlled by compressional forces evidenced by faults with reverse orientation. Once a surface depression forms or dissolution of the salt slows or stops, subsidence structures are consistent with a tensional stress environment with prevalent normal faults. Detecting areas of rapid subsidence potential, prior to surface failure, is the ultimate goal of any geotechnical survey where the ground surface is susceptible to settling. Seismic reflection images have helped correlate active subsidence to dormant paleofeatures, project horizontal growth of active sinkholes based on subsurface structures, and appraise the risk of catastrophic failure.

Resistivity and offset error estimations for the small-loop electromagnetic method

Handheld frequency-domain electromagnetic (EM) instruments are being used increasingly for shallow environmental and geotechnical surveys because of their portability and speed of use in field operations. However, in many cases, the quality of data is so poor that quantitative interpretation is not justified. This is because the small-loop EM method is required to detect very weak signals (the secondary magnetic fields) in the presence of the dominant primary field, so the data are inherently susceptible to calibration errors. Although these errors can be measured by raising the instrument high above the ground so that the effect of the conducting ground is negligible, it is impracticable to do so for every survey. We have developed an algorithm that simultaneously inverts small-loop EM data for a multidimensional resistivity distribution and offset errors. For this inversion method to work successfully the data must be collected at two heights. The forward modeling used in the inversion is based on a staggered-grid 3D finite-difference method; its solution has been checked against a 2.5D finite-element solution. Synthetic and real data examples demonstrate that the inversion recovers reliable resistivity models from multifrequency data that are contaminated severely by offset errors.

A geographical information system managing geotechnical data for Athens (Greece) and its use for automated seismic microzonation

This article presents a geographical information system (GIS) which manages geotechnical data obtained from detailed geotechnical surveys as well as from in situ observations in Athens, Greece. Thoroughly examined data from more than 2,000 exploratory boreholes and trial pits located in the wider area of Athens have been incorporated using a relational database system. From the analysis of these results, thematic maps are compiled to illustrate the distribution of engineering geological information (e.g. the depth of the “Athens schist” head). In addition, a methodology for an automated GIS-aided seismic microzonation study is outlined and is being employed taking into account the aforementioned geotechnical and engineering geological information, as well as existing seismological data to estimate the variability of seismic ground motion for the southern part of Athens.

A Comparative Evaluation of the Geotechnical Index Properties of Clayey Sediments along the West Coast of India

Sediment core samples collected during geotechnical surveys along the West Coast of India in the near shore areas of Arabian Sea have generated data on the geotechnical index properties of clayey sediments up to nearly 5 m depth below seafloor. A comparative study of three sectors within themselves is attempted before carrying out a final evaluation between the sectors. Cohesive clayey sediments of Gujarat sector are comparable though widely variant in a few aspects; in the Maharashtra-Goa-Karnataka sector though, plasticity levels and clay type vary, and activity and consistency levels are quite similar. Though broadly comparable, the clayey sediments of Kerala-Tamilnadu sector have quite diverse characteristics that fail to conform to any particular pattern as each area has an exclusive set of geotechnical properties.

Calibration techniques and sampling resolution requirements for groundtruthing multibeam acoustic backscatter (EM3000) and QTC VIEW™ classification technology

Both acoustic and sediment surveys were carried out in the Broughton Archipelago, British Columbia, in order to map a former aquaculture site and calibrate acoustic surveys with georeferenced sediment properties. The acoustic surveys included EM3000 Multibeam (including backscatter) and QTC VIEW™ (Series IV) technologies, while the geotechnical survey entailed Van Veen grab sampling of surface sediments and associated analyses. The two acoustic technologies were consistent in their ability to identify distinct regions of seafloor characterized by rock outcrops, consolidated substrates, or gel-mud depositional fields. Both multibeam backscatter data and QTC VIEW™ number-coded classifications were extracted across a range of circular areas located at each georeferenced sampling station (radii: 2, 3, 4, 5, 8, 12, 16, 20 m). Statistical correlations were observed between backscatter and certain geotechnical properties, such as sediment porosity, sediment grain size fractions (<2 μm, silt content), and particulate sulfur concentration. The areal resolution of backscatter extraction was explored in terms of determining a sensitive calibration technique between backscatter and sediment properties. In general the highest r 2 values between backscatter and sediment variables were observed across extraction radii between 8 and 20 m. Such groundtruthing techniques could be used to interpolate seafloor characteristics between sampling stations and provide a steering tool for sampling designs associated with benthic monitoring programs.

The 2001 Adana landslide and its destructive effects, Turkey

The current study deals with a catastrophic landslide that occurred due to heavy rainfall in Adana, Southern Turkey in 2001. The research area, which is one of the largest populated districts in Adana, and one of the most tropical places between the Middle East and southern Europe, has about 25,000 people. On the basis of geological and geotechnical surveys, the landslide phenomena and the effects of landslide are examined. To understand the slide mechanism of the landslide, ground reconnaissance, laboratory and in situ tests are conducted. It is observed that the clayey and silty layers of the site are heavily saturated due to extreme rainfall in winter, and consequently sheared. The landslide consists of a block sliding in the upper portions and a debris flow/soil flow component around the margins of the sliding blocks in the middle parts and at the toe. Although there was no loss of human life, it has caused significant economic losses. Besides, it is determined that if precautions are not taken around the landslide area, larger landslides could definitely occur in the future.

Geological-geophysical study for the disign of a hazardous waste landfill in Albania

Industrial wastes in Albania belong to four main groups: i) wastes from the industrial hot spots, ii) wastes from the old chemical storages, Hi) wastes from mining and ore processing and iiii) wastes from present and future industries. The landfill for hazardous waste is intended as a facility to enable the clean-up of old mostly abandoned industrial sites (the hot spots and other sites), storages of obsolete chemicals and treat and dispose of hazardous waste presently generated in Albanian industry. The technical design of the landfill was anticipated by complex geological study including the geological, geophysical, geotechnical and hydrogeological surveys. All the above surveys aimed to find the best clay terrains with suitable geotechnical and hydrogeological features for the landfill design

Primary influential factors in the management of public transportation projects in Taiwan

The primary influential factors must be screened out to improve the efficiency of management of public projects. This study synthesizes 91 possible influential factors in the management of transportation projects in Taiwan. Following the procedures of the multicriteria evaluation method and the fuzzy analytic hierarchy process (FAHP), the primary influential factors are screened out and ranked in order of priority. After analysis, it was found that the top five primary influential factors for responsible entities are (i) introduction of the earned value analysis, (ii) efficiency of the geotechnical survey, (iii) environmental laws and regulations of the local government, (iv) price-index fluctuation, and (v) on-site safety management. The top five factors ranked by the supervisory entities are (i) manpower, (ii) revision of laws and regulations, (iii) price-index fluctuation, (iv) traffic conditions, and (v) mistakes or faults of design. In the contractor phase, the top five factors are (i) bidding price, (ii) scope of the contractor, (iii) price-index fluctuation, (iv) management education and training system, and (v) government procurement act.Key words: management, influential factors, transportation project, fuzzy analytic hierarchy process (FAHP), Taiwan.

On the evaluation of unsaturated flow in a natural slope in Rio de Janeiro, Brazil

Geotechnical engineers and geologists are frequently concerned with the complex phenomenon of rainstorm-induced landslides in mountainous tropical regions. This paper analyses the hydrological conditions that contributed to a huge deep-seated slide of a slope in Rio de Janeiro, Brazil. The slope failure occurred after a short period of intense rainfall, buried cars, and caused structural damages to an adjacent building. On the following day, the failure surface was completely saturated, despite the fact that no groundwater was observed within the slope. Understanding a rain-induced landslide is a considerable challenge. In the present case, there was an extra question to be answered: why were no slope movements observed a few months earlier, when a more intense rainfall reached the slope? Geological and geotechnical surveys were carried out aiming at determining complete soil profile characterization, piezometric levels and hydraulic parameters. Field investigations indicated a variable thickness unsaturated residual soil layer overlying a gneissic rock. The transition between the saprolitic soil and the sound rock consisted of a highly fractured and weathered rock. 3D flow modelling has shown that the amount of rain infiltration was insufficient to produce positive pore-water pressures. It was likely that development of preferential infiltration paths could explain the hydrological conditions of the slope during landslide. Water infiltration through the fractured soil–rock transition induced a rapid development of positive pore water within the soil mass. This favourable scenario might have been created by the lack of maintenance of the crest drainage channel, adjacent to the slide area. It is a common engineering practice to try to associate rainfall amounts to the risk of slope failure. The role that bedrock plays in generating pore pressure is seldom considered. The numerical analyses presented in this paper pointed out at the complexity of flow modeling of rain infiltration through unsaturated residual soil slopes. It essentially revealed that flow mechanisms other than rain infiltration over the slope surface might play a major role on hydrological pattern of slopes.

Risk-oriented seismic microzoning study of an urban settlement

A methodology is presented to evaluate the local seismic response of an urbanized site and to realize cost-effective seismic microzoning studies on a quantitative basis with the aim to provide more insights for the choice of risk mitigation measures. The methodology makes use of an integrated deterministic and probabilistic seismic hazard analysis to select the reference earthquake and the related ground motion used to assess the local seismic response. Amplified response spectra, related to local site effects, are obtained after the investigation of the local geological conditions carried out through integrated geological, geophysical and geotechnical surveys. The amplified response spectra are then converted into reference ones, to match the shape of conventional response spectra provided by many international seismic codes such as Eurocode 8 ( Design of structures for earthquake resistance). A vulnerability analysis provided the distribution of the buildings’ typology in the urban centre and allowed for computing the expected damages. The outcome is a zoning of the investigated site matching the correlation between the severity of the expected seismic actions as modified by the local seismic response and the structural features of the buildings present in the urban area. The resulting seismic microzoning is more informative than conventional ones, having the potential to be used for the adoption of risk mitigation measures such as the seismic retrofitting of buildings and the formulation of emergency plans for civil protection purposes.

Correlations between geotechnical and electrical data: A case study at Garchy in France

Geophysical (Electrical Resistivity Tomography, Ground Penetrating Radar profiles and seismic refraction) and geotechnical (dynamic penetrometer, in situ vane test) surveys were carried out at Garchy (Nièvre, France). The main objective of this study was to establish qualitative and quantitative correlations between electrical and geotechnical data from this site in a simple geological context. Concerning qualitative correlations, geotechnical tests and Electrical Resistivity Tomography sections are consistent with a three-layers model: a fine soil with a significant clay fraction sandwiched between a low moisture sandy soil and oolitic limestones. Despite the usual difficulty to locate clearly interfaces in inverted ERT sections, both methods provide consistent depths of the substratum top. Moreover, this study confirms that correlations between reflectors of GPR profiles and vertical geotechnical property variations are mainly explained by vertical water content changes. As far as quantitative correlations are concerned, no clear relationship between cone resistance and inverted resistivity extracted from ERT sections has been observed. Nevertheless, if we do not consider the upper sandy soil composed with gravels, the couple inverted resistivity–cone resistance would be a lithological discriminator. This lithological discrimination is enhanced when inverted resistivity values obtained from extracted 1D soundings are considered. This original result should be validated in other sites. Moreover, a satisfactory quantitative correlation between inverted resistivity values and measured water content values has been obtained; this correlation demonstrates once more that resistivity is a good indirect predictor of water content.

Definition of subsoil structure and preliminary ground response in Aigion city (Greece) using microtremor and earthquakes

An extensive campaign—including detailed geologic and geotechnical surveys both existing and news as well as noise measurements—was conducted along a cross-section in order to define both geometry and soil properties (mainly the shear wave velocity) of the main formations in Aigion city. Aigion city is located in the Gulf of Corinth, Greece, a highly seismic region of the Aegean Sea. The main objective of the accurate 2D soil model is its use in site response modeling and in the interpretation of observations from a vertical down-hole accelerograph array. This model revealed a complex geologic structure with a multi-faulted shear zone related to the Aigion fault. The defined subsurface structure offered the possibility for its correlation with estimated site effects, in terms of spectral ratios. Two different data sets, earthquakes recorded at down-hole accelerograph network and noise measurements at 17 sites, were used. To translate the empirical transfer functions with the geologic structure, the 1D estimates were also computed. All these results are consistent, indicating a satisfactory correlation between the soil model and preliminary site response.