Site Characterization Program Research Articles

Risk-Informed Design of RCC Dams under Extreme Seismic Loading

The existing Scoggins Dam and reservoir are in Washington County, Oregon, and the title is held by the U.S. Bureau of Reclamation (Reclamation). Reclamation has previously identified dam safety concerns related to the existing embankment dam. Regional project sponsors, including Clean Water Services, have identified the need for expanded storage capacity in the reservoir to meet growing water demands and address water quality issues in the Tualatin River downstream of the dam. As part of efforts to resolve dam safety issues and increase the water storage in the reservoir, a comprehensive feasibility level design of a new 185-foot-high Roller Compacted Concrete (RCC) dam. Extraordinary seismic hazards have been identified in the region associated with the Cascadia Subduction Zone (CSZ). Further, any dam alternative carried forward for funding, final design, and construction will have to meet the Public Protection Guidelines (PPG) of Reclamation that require a formal quantitative risk analysis. A risk-informed design approach was adopted to configure the layout and cross-section properties of the dam. A multi-phase site characterization program and preliminary RCC mix design program were performed to support the design. In addition, models were developed, and an extensive suite of both (two-dimensional) 2D and (three-dimensional) 3D structural analyses were performed for seismic loadings with total durations of over 200 s, strong shaking of over 140 s, and peak ground accelerations of over 2 gravitational accelerations (g) (up to 50,000-year return period event). This paper describes the feasibility design configuration of the dam, including the seismic hazard characterization, structural analysis models, and seismic response modeling results. The expected performance of the dam relative to the risk-informed design criteria and Reclamation PPGs will be generally described.

Landslide susceptibility mapping based on rainfall scenarios: a case study from Sao Paulo in Brazil

<abstract> <p>Mass movement susceptibility mapping from rainfall data and in situ site characterization constitute an important approach for preventing geological-geotechnical accidents on railroads and highways. A comprehensive site characterization program was conducted to identify slopes with mass movements along the 44 km of SP-171 road in the state of Sã o Paulo, Brazil. Ninety-two slopes with some degree of instability were found along this section of the road, including rupture scars, active erosive processes and the presence of unstable rock blocks. Two scenarios for mass movement susceptibility (100 mm and 500 mm of accumulated rainfall) were defined by overlaying thematic maps of relief, soil type, geology, accumulated rainfall and declivity using geographic information system-based techniques. The results for both scenarios identified the regions with high and medium susceptibility to mass movements; for the scenario of 100 mm of accumulated rainfall; we found that 27% and 73% of the land area of SP-171 is respectively highly and moderately susceptible to landslide events. For the scenario of 500 mm, we found 58% and 40% to be highly and moderately susceptible areas. This study also allowed us to identify the main geotechnical problems along the 44 km of this road, and thus can be used to guide actions and decisions to avoid or minimize such problems.</p> </abstract>

Geotechnical Characteristic Assessments of Floodplain Soils Using SCPTU Data in Nanjing, China

In order to improve the understanding of such floodplain sediments and determining the validity of the tests, an extensive series of multifunctional seismic piezocone tests with pore pressure dissipation phase have been performed and supplemented with conventional borings, standard penetration, laboratory testing, and so forth. Sounding results from SCPTU were used to determine the stratigraphic profiles and the soil characteristics of two anchorage sites. A comparison of the boring and laboratory results with the CPTU profiles showed that the CPTU provided excellent information on soil stratigraphy and good guidance for determination of behavior and engineering implications of recent Yangtze River floodplain. At an area where local correlations based on modern SCPTU do not exist, methods for estimating coefficient of earth pressure at rest (K0), hydraulic permeability (kh), and equivalent stiffness (G0) associated with bridge foundation design are presented, compared, and verified. Results also illustrate the complexity and variability of the floodplain stratigraphy and soil properties, which means that the suggestions in this study should be updated when more local experience is obtained. This case study suggests that such enhanced seismic piezocone test should be considered as a potential tool and the instrument of first choice in site characterization programs for design of bridges founded on complicated soils in China.

Bring Your A-GaME!

The Federal Highway Administration (FHWA), in collaboration with industry partners, is helping state DOTs take their existing geotechnical site characterization programs to the next level. Technolo...

Best Practices For Geotechnical Site Characterization: Have We Regressed from Decades Past?

The objective of a geotechnical site-characterization program is to determine soil and rock stratigraphy, in-situ pore water pressure conditions, and soil and rock properties for analysis and design of geotechnical engineering infrastructure. It is best conducted using an integrated approach that combines various geo-disciplines to describe, evaluate, and determine expected site characteristics. The extensive advancement of tools and procedures in recent decades provides an opportunity to execute effective and thorough site-characterization programs routinely in practice. Yet, this is often not the case, and some may argue that today’s state-of-practice has regressed in recent decades. While contractual structures and budget restrictions may contribute to this lower level and quality of characterization, the technical knowledge and pragmatic strategies available are not always implemented.

Geospatial Statistics Elucidate Competing Geological Controls on Natural CO2 Seeps in Italy

Site selection for the geological storage of CO2 for long timespans requires an understanding of the controls on containment, migration, and surface seepage of subsurface CO2 fluids. Evidence of natural CO2 migration from depth to the surface is documented at 270 sites from Italy, a prolific CO2 province. Previous studies indicate that CO2 delivery to and from buried structures that host CO2 accumulations is fault controlled but competing controls on the CO2 flow pathways affect the location and style of CO2 release. Here, we conduct a meta-analysis using a novel geospatial approach to statistically determine the relationship between the geological setting and structures and the CO2 seep spatial distribution and characteristics (morphological type, flux, and temperature) in Central Italy. We find that seep distribution differs on two spatial scales corresponding to the geological setting. On large scales (>5 km), seeps are isotropically distributed and align with regional structures such as anticlines, decollements, and extensional faults. On local scales (<5 km), seeps cluster and align with subsidiary geologic structures, including faults and lithological boundaries. The detailed location and flux of seeps within clusters are influenced by the regional structural domain: in the Tyrrhenian, seeps tend to be located along fault traces, whereas seeps are located as springs in the tip and ramp regions of fault scarps in the Apennines. Thus, our geospatial approach evidences, at a regional scale, how macrocrustal fluid flow is governed by deep extensional and compressional features but once CO2 reaches shallower structures, it evidences how smaller scale features and hydrogeological factors distribute the CO2 fluids in the near surface, dependent on the geological setting. This work not only demonstrates useful application of a novel geospatial approach to characterize competing crustal controls on CO2 flow at different scales but also informs the design of appropriate site characterization and surface monitoring programs at engineered carbon stores.

Variation of horizontal in situ stress with depth for long-term performance evaluation of the Deep Geological Repository project access shaft

A site characterization program was carried out for a proposed Deep Geological Repository (DGR) project for Ontario Power Generation’s (OPG) low- and intermediate-level nuclear waste repository near Kincardine, Ontario. The repository is proposed to be constructed at approximately 680 m below ground surface within the competent argillaceous limestone of the Cobourg Formation. The in situ stress state at the project site will have significant impact on both the short- and long-term performance of repository openings, such as emplacement caverns and access shafts. As part of the site characterization program, an evaluation of the in situ stress state of the project site was conducted which consisted, primarily, of a review and synthesis of existing stress measurements conducted at various locations throughout Ontario and the midwestern U.S. Based on geomechanics data from deep boreholes and stress measurement data, a simplified FLAC3D model of the full stratigraphic profile was developed and used to simulate the influence of regional tectonic strain in the project area. In particular, this method takes into account the rock properties, such as stiffness, for discrete units at the DGR site. The model was calibrated on the basis of in situ stresses measured at Norton Mine, in a similar geological environment as the DGR site, and with site-specific borehole televiewer observations (i.e., breakouts). The model-predicted horizontal in situ stress profile showed general agreement with the observations and also showed the significant influence of discrete rock unit stiffness.

Pilot-scale CO2 Sequestration Test Site in the Sulcis Basin (SW Sardinia): Preliminary Site Characterization and Research Program

The deep aquifer located at a depth of about 1000-1500 m within fractured carbonate in the Sulcis coal basin (South-West Sardinia, Italy) constitutes a potential reservoir to develop a pilot-scale CO2 storage site. The site is well known in terms of stratigraphy and structural settings, due to the data available from the coal mining activity. On the basis of these data, a potential deep reservoir and the caprock can be recognized; more in detail, in the southern sector of the basin, the top of the potential reservoir reaches a suitable depth for storage. At the same time, the already existing infrastructures (the Sotacarbo Research Centre on carbon capture, utilization and storage), coupled with some peculiar features (as the low natural seismicity, the hydrogeological system, etc.) makes the Sulcis area a potential experimental site capable to further develop CO2 storage technologies, such as low-cost drilling, site monitoring, and experimental studies on CO2 diffusion and leakage.In this context, Sotacarbo (in cooperation with ENEA, the Universities of Cagliari and Rome “La Sapienza”, OGS, INGV and RSE) is leading a very ambitious research program, funded by both the Italian and the Sardinian Regional Governments within two different and complementary projects, to characterize the Sulcis coal basin as a potential site for the development of CO2 geological storage technologies. The research activities are structured in two different phases: (i) site characterization, including the construction of an underground and a fault laboratories and (ii) the installation of a test site for small-scale injection of CO2. In particular, the underground laboratory will host geochemical and geophysical experiments on rocks, taking advantages of the buried environment and the very well confined conditions in the galleries; in parallel, the fault laboratory will be constructed to study CO2 leakage phenomena in a selected fault.Overall, the project, which is currently ongoing, will allow to characterize the Sulcis basin and to develop a permanent infrastructure (know-how, equipment, laboratories, etc.) for advanced international studies on CO2 storage.This work describes the whole Sulcis CO2 storage project, highlighting its current status, some of the preliminary results of site characterization phase, planned activities and the links with the research activities on carbon capture and utilization.

The influence of different supports on the properties of the excavation damaged zone along the FE tunnel in the Mont Terri Underground Rock Laboratory

Abstract Permeability and its spatial distribution around an underground opening in a geological formation are important for the interpretation of thermal, hydraulic and mechanical findings from an in situ demonstration experiment. Within the site characterization programme of the Full-scale Emplacement (FE) experiment, permeability measurements with nitrogen gas have been conducted from six short boreholes. Four of them were located in a section without shotcrete support and two in a section with a three-layer-shotcrete lining. As expected, the extension of the zone with an increased permeability was larger (up to 2 m) in the area without shotcrete support than that in the section with a shotcrete lining (less than 1.5 m). The water content in the sections with or without shotcrete linings also showed different behaviour over long-term monitoring. The water content in the deep borehole section in the area with a shotcrete lining stayed almost constant, while the water content in the deep borehole section in the area without shotcrete tended to continuously decrease. In general, the water content close to the tunnel is influenced by the seasonal change in the temperature and relative humidity within the tunnel, especially in the section without a shotcrete lining. Analysis of the abovementioned observations/findings was done by performing FEM (finite-element method) calculations with OpenGeoSys (OGS) software using a coupled hydromechanical model. Owing to the high stiffness of shotcrete, the displacement in the section with a shotcrete lining was smaller. This, in turn, results in a smaller extension in the excavation damaged zone (EDZ). However, shotcrete has a relatively high suction capacity and high initial water content: thus, the interface between the shotcrete and the Opalinus Clay becomes more saturated. Therefore, the excavation-induced fractures in the Opalinus Clay close to the shotcrete can be sealed by swelling. The water content decreases continuously, as a result of desaturation occurring during the operational phase and the associated change in porewater pressure.

Data integration, reservoir response, and application

The microseismic activity observed in and around a geologic formation undergoing carbon dioxide (CO2) injection is a combination of natural, or “background”, microseismicity plus that activity which is induced by injection operations. Since injection pressure within storage target formations are maintained safely below fracture pressure this induced activity typically originates at natural pre-existing zones of mechanical weakness presented by structural or stratigraphic features. The combination of mechanical properties and in situ stresses dictate the focal mechanism for microseismic emissions, an understanding of which facilitates the use of observed microseismicity for regulatory compliance and project management.Under favorable conditions microseismic activity may be unambiguously correlated with structural and/or stratigraphic features directly observed in seismic data, thus providing strong constraints to interpretation of observed microseismicity for focal mechanisms. However, in many cases, such as at the Illinois Basin–Decatur Project (IBDP), this direct correlation is elusive and other indirect support is required. Analysis of microseismicity at IBDP has been performed within the context of the integrated reservoir and mechanical earth models developed as part of the site characterization and monitoring program. The IBDP integrated modeling workflow involved continuous and geotechnically consistent data integration for geologic modeling, calibrated flow simulation, three-dimensional (3D) mechanical earth model, and coupled hydro-mechanical simulation. Using the coupled model, scenario-based forward modeling of microseismicity was performed for hypothetical focal mechanisms inferred from observed data.The experience gained at IBDP illustrates the importance of integrated modeling in the interpretation of microseismic activity for focal mechanisms and provides valuable insights into critical data gaps which could be the target of future basic research efforts.

High Resolution Site Characterization as key element for proper design and cost estimation of groundwater remediation

Substantial amounts of money are spent each year on cleaning up ground water contaminations that were caused by historical industrial site activities. Too often, however, remedial objectives are not achieved within the anticipated time frame. Moreover, remedial budgets which were estimated prior to the start of remediation turn out to be largely insufficient to meet the remedial objectives. This situation, very common, creates significant troubles for all the stakeholders involved in the remediation project. The reason for not meeting remedial regulatory closure criteria or exceeding remedial budgets is often due to an incomplete conceptual site model. Having conducted high resolution site characterization programs at numerous sites where remediation was previously conducted, ERM has found several recurring themes: • Missed source areas and plumes; • Inadequate understanding of source area and plume architectures (i.e., three-dimensional contaminant distribution); • Inadequate understanding of the effects of site (hydro)geologic conditions on the ability to access contamination (i.e., via remedial additive injections of groundwater/soil gas extraction). This paper explains why remediations often fail and what the alternatives to prevent these failures (and exceeding remedial budgets) are. More specifically, it focuses on alternative investigation methods and approaches that help to get to a more complete (high resolution) conceptual site model. This more complete conceptual site model in return helps a more focused remedial design with a higher remedial efficiency. As a minimum, it will take away a lot of (financial) uncertainty during the decision making when selecting a remedial alternative. Contaminants that have a greater density then water are known to have a greater complexity in terms of both investigation as well as remediation. Therefore, they will be the main focus of this paper.

Solar Astronomy at High Altitude

A major project called the National Lar ge Solar Telescope (NLST) has been proposed for pursuing Solar Astronomy at High Altitude. The project envisages the development of a state-of-the-art 2-m class telescope to carry out high-resolution studies of the solar atmosphere. This project is led by the Indian Institute of Astrophysics and has national and international partners. Its geographical location will fill the longitudinal gap between Japan and Europe and is expected to be the lar gest solar telescope with an aperture lar ger than 1.5 m till ATST and EST come into operation. NLST is an on-axis alt-azimuth Gregorian multi-purpose open telescope with the provision of carrying out nighttime stellar observations using a spectrograph at the Nasmyth focus. The telescope utilizes an innovative design with low number of reflections to achieve a high throughput and low polarization. High order adaptive optics is integrated into the design that works with a modest Frieds parameter of 7-cm to give diffraction limited performance. The telescope will be equipped with a suite of post-focus instruments including broad and narrow band imagers, a high-resolution spectrograph and a polarimeter . A comprehensive site characterization programme has demonstrated the presence of at least two excellent sites for setting up observational facilities for solar astronomy at high altitude in India.

Hydrogeochemical characterisation and modelling of groundwaters in a potential geological repository for spent nuclear fuel in crystalline rocks (Laxemar, Sweden)

Two sites in the eastern coast of Sweden have been investigated by the Swedish Nuclear Fuel and Waste Management Company (SKB), within the framework of the site characterisation programme, as possible candidates for hosting the proposed repository for the long-term storage of spent nuclear fuel: Forsmark and Laxemar. This study presents the main results concerning the hydrogeochemical characterisation of the groundwaters in the second site, Laxemar. The distribution of the main chemical variables in groundwaters are shown and interpreted in combination with the results from speciation–solubility and reaction-path simulations, together with the available mineralogical information. The results indicate that the main processes determining the overall geochemical evolution of the Laxemar groundwaters are advective/diffusive mixing and water–rock interactions driven by past and present climatic changes inducing the input of different recharge waters over time (glacial meltwater, old marine water and modern meteoric water) and affecting the preexisting very old saline groundwaters in the bedrock. The superimposed effects of these mixing events, deduced from the behaviour of the conservative elements (Cl and δ18O), have generated a rather steep salinity gradient in the groundwater system, with diluted waters in the upper part, brackish waters in the middle, and saline waters in the lower part of the bedrock.The resultant successive disequilibrium states imposed by mixing have conditioned the water–rock interaction processes that have affected the non-conservative elements to different degrees. The main chemical reactions found to be important in controlling some of the variability of these elements and some important parameters like pH and alkalinity, are: aluminosilicate and carbonate dissolution/precipitation, quartz and fluorite equilibrium, cation exchange, and gypsum dissolution. These reactions and their importance in the system are presented in this paper.Once the main hydrogeochemical features of the Laxemar groundwaters and the potentially controlling water–rock interactions in the system have been identified and justified with the help of thermodynamic simulations, a general geochemical conceptual model has been proposed. This model will be used as the basis for predicting the future evolution of the groundwater chemistry as an essential part of the safety assessment of the future repository.

Paleohydrogeologic simulations of Laurentide ice‐sheet history on groundwater at the eastern flank of the Michigan Basin

AbstractA deep geologic repository (DGR) for low‐ and intermediate‐level waste has been proposed by Ontario Power Generation for the Bruce nuclear site in the Municipality of Kincardine, Ontario, Canada. As envisioned, the proposed DGR would be constructed at a depth of about 680 m below ground surface within the argillaceous Ordovician limestone of the Cobourg Formation. Within the geologic setting of southern Ontario, the Bruce nuclear site is positioned along the eastern flank of the Michigan Basin. The regional‐scale domain for the modeling undertaken in support of the DGR program encompasses an area of approximately 18 000 km2 and extends to the deepest points in Lake Huron and Georgian Bay. The conceptual model for the ground water system was developed using data from the DGR site characterization program. Hydraulic parameters for the model hydrostratigraphic units were defined using data from the DGR site boreholes and from lab analyses of cores. Borehole data included hydraulic conductivities from straddle‐packer hydraulic tests and pressure measurements from the Westbay MP38 and MP55 multilevel groundwater monitoring system. Data from this system indicate that units of the Salina and the Ordovician sediments are under‐pressured relative to hydrostatic levels associated with ground surface at the DGR site. The Silurian Niagaran Group is slightly over‐pressured while the Cambrian Formation sandstone is significantly over‐pressured. The pressure distribution in the sedimentary rock of the Bruce site was analyzed using a hydromechanical model that assumed homogeneous loads and no lateral strain. Layer dependent specific storage coefficients and one‐dimensional loading efficiencies were calculated based on testing of core samples. The impact of glaciation and deglaciation on the groundwater system was investigated in paleohydrogeologic scenarios. The model results indicated that basal meltwater does not penetrate vertically below the units of the Salina at the DGR site. A suite of paleohydrogeologic scenarios were investigated in this study. Based on these analyses, glaciation and deglaciation were unable to yield the abnormal pressure patterns observed in the DGR boreholes for the Ordovician formations. Models that included the presence of a gas phase were found to produce under‐pressures that are similar to field observations.

Radionuclide migration at experimental polygon at Red Forest waste site in Chernobyl zone. Part 2: Hydrogeological characterization and groundwater transport modeling

Abstract This article represents the second of two articles, which review the main results of the international radioecological projects: Chernobyl Pilot Site Project (1999–2003) and Experimental Platform in Chernobyl (2004–2008). These projects studied radionuclide migration from the near-surface radioactive waste trench at the Red Forest waste dump in the Chernobyl zone, which contained nuclear fuel particles. This article presents results from the comprehensive hydrogeological site characterization program including the following issues: geological structure of the study site, hydraulic properties of the deposits, tracer tests in the aquifer, results of groundwater monitoring and unsaturated zone regime studies, as well as data on the 90Sr distribution in the unsaturated zone and aquifer, and analyses of 90Sr sorption behavior. The derived parameters were used to develop and calibrate 1D (flow tube) and 2D (cross-section) models describing the migration of 90Sr from the studied waste trench to the unsaturated zone and aquifer over a 16-a period (1986–2002). The models involved the following sub-models: (1) the geostatistical (structural) model for radioactivity distribution in the trench (using GSLIB); and (2) the radionuclide source term model (STERM1D) describing dissolution of fuel particles and a 1D of radionuclide redistribution in the trench body and unsaturated zone. The MODFLOW – MT3D codes were used to model the 2D 90Sr transport in the aquifer cross-section. Calibration of the 1D model with respect to Kds and dispersivities allowed quite accurate reproduction of 90Sr migration behavior for the early period (1995–1998). The less perfect fit between the 1D and 2D modeling results and monitoring data for the later period (1999–2002) suggests the need to improve the conceptual radionuclide migration model (i.e. to account for transient hydraulic and geochemical regimes of the waste site).

Aerosol optical properties retrieved using Skyradiometer at Hanle in western Himalayas

A Skyradiometer was installed at Hanle in Ladakh, in October 2007 as a part of the site characterization program for the proposed National Large Solar Telescope project. Aerosol optical depth (AOD), single scattering albedo (SSA), volume size distribution, and refractive indices were retrieved at five spectral channels, using measurements of direct and diffuse solar irradiation. At 500 nm, the yearly average values of AOD and SSA were found to be 0.05 and 0.965, respectively. The volume size distribution shows a general bimodal behavior with two peaks at around 7–10 and 0.1 – 0.2 μ m with an occasional tri-modal behavior.

Distinguished multiple events of fracture mineralisation related to far-field orogenic effects in Paleoproterozoic crystalline rocks, Simpevarp area, SE Sweden

Detailed investigations of fracture minerals have been carried out in the Simpevarp area, SE Sweden, in order to reveal the low-temperature evolution of the site and to discern different events of deformation, especially in the brittle regime. The study is part of the site characterisation programme for a potential deep-seated repository for spent nuclear fuel. The bedrock in the area is composed of generally un-metamorphosed 1.8 Ga crystalline rocks. Detailed SEM investigations of cross-cutting fracture mineralisations have revealed several generations of fillings formed at gradually lower temperatures during repeated events of fracturing and reactivation from the Paleoproterozoic until the Quaternary. 40Ar/ 39Ar geochronology and fracture orientation analyses have been used to relate each fracture filling generation to geological events, such as far-field effects from orogenies, as well as more local effects related to intrusions. Fracturing and formation of different fracture mineral parageneses during at least four different orogenies have been indicated: the waning stages of the Svecokarelian orogeny (> 1.75 Ga), the Danopolonian orogeny (~ 1.47–1.44 Ga), the Sveconorwegian orogeny (~ 1.1–0.9 Ga) and the Caledonian orogeny (~ 0.5–0.4 Ga). The fracture minerals and greisen related to the Danopolonian orogeny mainly formed in relation to the intrusion of two indicatively Danopolonian-related granites nearby. Furthermore, periods of extension are indicated in the area by the presence of late-Sveconorwegian dolerites. Fractures filled with lower Cambrian sandstone are plausibly formed in relation to far-field extensional effects of the opening of the Iapetus Ocean. Fracture minerals of Paleozoic age or younger show influence of loading and unloading cycles. The youngest fracture minerals identified indicate precipitation from waters of similar composition as the present groundwater.

Hydraulic conductivity variability of the Boom Clay in north-east Belgium based on four core drilled boreholes

The hydraulic conductivity of the Boom Clay is investigated since many years in Belgium in the framework of the site characterisation programme supporting the performance assessment of potential geological disposal of high-level radioactive waste in this formation. In this paper, the variability of the hydraulic conductivity is assessed in a large part (1100 km 2) of the deposition area of the Boom Clay. It is based on numerous vertical and horizontal hydraulic conductivity measurements ( K v and K h ) performed with permeameter-type experiments on clay cores from four distant boreholes, i.e. Doel-2b, Zoersel, Mol-1 and Weelde-1. A thorough analysis of the results of the grain-size measurements is performed and its relationship with the hydraulic conductivities is examined through multiple regressions. This approach allows deriving site-specific empirical relationships to predict vertical hydraulic conductivities from the grain-sizes used as soft data. This increases our confidence in the global value of the vertical hydraulic conductivity at the scale of the formation and enhances the overall assessment of the variability of this parameter at the regional scale. Further efforts should be done to evaluate the variability of the hydraulic conductivity with relationships that are suitable for the whole depositional area. This would make the method more attractive for the overall assessment of a potential host-formation for geological disposal.

Deformation of a soft estuarine deposit under a geotextile reinforced embankment

This paper presents a case history of a geotextile reinforced highway embankment constructed on a soft estuarine deposit installed with prefabricated vertical drains. The case history documents the geotechnical site characterization, embankment construction, and monitoring program. The loading response of the soft estuarine soil was monitored during construction using hydrostatic profile gauges, settlement plates, pneumatic piezometers, and slope inclinometers. Settlements of up to 1.3 m were measured under the 4 m high embankment. The deformation behaviour was interpreted qualitatively from the monitoring data using the general framework of elastic-plastic soil models. The effectiveness of the monitoring program is also briefly discussed. The paper provides performance details that make this case history useful to researchers studying the loading response of soft soils under a geotextile reinforced embankment.Key words: case history, embankment, soft clay, vertical drainage, reinforcement.

Data-worth analysis for multiobjective optimal design of pump-and-treat remediation systems

The design and the management of pump-and-treat (PAT) remediation systems for contaminated aquifers under uncertain hydrogeological settings and parameters often involve decisions that trade off cost optimality against reliability. Both design objectives can be improved by planning site characterization programs that reduce subsurface parameter uncertainty. However, the cost for subsurface investigation often weighs heavily upon the budget of the remedial action and must thus be taken into account in the trade-off analysis. In this paper, we develop a stochastic data-worth framework with the purpose of estimating the economic opportunity of subsurface investigation programs. Since the spatial distribution of hydraulic conductivity is most often the major source of uncertainty, we focus on the direct sampling of hydraulic conductivity at prescribed locations of the aquifer. The data worth of hydraulic conductivity measurements is estimated from the reduction of the overall management cost ensuing from the reduction in parameter uncertainty obtained from sampling. The overall cost is estimated as the expected value of the cost of installing and operating the PAT system plus penalties incurred due to violations of cleanup goals and constraints. The crucial point of the data-worth framework is represented by the so-called pre-posterior analysis. Here, the tradeoff between decreasing overall costs and increasing site-investigation budgets is assessed to determine a management strategy proposed on the basis of the information available at the start of remediation. The goal of the pre-posterior analysis is to indicate whether the proposed management strategy should be implemented as is, or re-designed on the basis of additional data collected with a particular site-investigation program. The study indicates that the value of information is ultimately related to the estimates of cleanup target violations and decision makers’ degree of risk-aversion.