Norwegian Geotechnical Institute (NGI) Digital Archive
Not a member yet
1356 research outputs found
Sort by
Multiscale synchrotron microtomography imaging of kerogen lenses in organic-rich shales from the Norwegian Continental Shelf
Get PDFpublishedVersio
Structural instrumentation and monitoring of the Block Island Offshore Wind Farm
Get PDFpublishedVersio
Towards improved characterization of the fate and impact of hydraulic fracturing chemicals to better secure regional water quality
Get PDFacceptedVersio
Developing a relationship between static Young’s modulus and seismic parameters
Get PDFMechanical properties of petroleum reservoirs can be determined via static techniques based on laboratory triaxial tests
under reservoir conditions. Dynamic approaches represent an alternative in cases where such static laboratory data are
unavailable. Dynamic elastic properties are calculated using ultrasonic wave measurements in the laboratory or in situ well
logging. Different relationships have been proposed to estimate static properties from dynamic ones based on the available
data from a particular reservoir. However, these relationships are often reservoir-specific, making them inadequate for general
seismic inversion purposes. This research proposes a method for developing relationships between seismic parameters
and static Young’s modulus in carbonate reservoirs by integrating ultrasonic measurements, well logging data, and rock
mechanic tests. A multistage triaxial test simulating the reservoir conditions was used to fully control the stress and strain
during the geomechanical experiments. Static Young’s modulus was cross-correlated with a broad spectrum of seismic
parameters that can be extracted from seismic inversion (e.g., acoustic impedance, shear impedance, Lambda–rho, and
mu–rho). Separate analytic relationships were proposed to convert dynamic Young’s modulus and seismic parameters into
static Young’s modulus. Analysis of variance was used to evaluate the results and study the applicability and reliability of
the obtained relationships. Furthermore, the reliability of the obtained relationships was successfully confirmed by well
logging data and blind well analysis. The proposed methodology can be used to predict rock behavior for geomechanical
and structural modeling
CPT 3 – Quantitative risk assessment: Remarks on the uncertainty in the delimitation of hazard zones based on historical observations
Get PDFThe Norwegian building code regulates the societal acceptable risk from avalanches for three building classes (S1, S1, and S3). The corresponding highest allowed nominal annual probabilities of avalanches reaching the building for these classes are set as 1/100, 1/1000 and 1/5000 respectively (TEK17, 2017). That is, avalanches should not reach a building, or the accompanying outdoor area and cause (considerable) damage more often than the building class permits. These hazard classes are used for delineation of avalanche hazard zones for land use planning (TEK17, 2017). For the assessment of the quantitative risk of avalanches reaching existing settlements only limited methods are available. Thus, historical observations can be of special importance, as they may be direct indicators for the real hazard in the area of interest. To a certain degree, they can also provide an indication of a possible change of hazard over time due to environmental changes. However, historical observations are affected by inherent uncertainties and many questions remain open. Here, we aim to combine results from several work packages to develop a more consistent method of using historical observations that may help improve quantitative hazard assessments and evaluation of the uncertainties involved.NVE (Norges vassdrags- og energidirektorat
K0 as a Function of Changes in Stress and Strain Conditions during Consolidation, Unloading and Reloading
Get PDFThere are several examples in the literature that describe empirical correlations for the coefficient of earth pressure at rest, K0, and undrained shear strength, su, in normally consolidated and overconsolidated clays as a function of index properties like plasticity index, overconsolidation ratio, OCR, and friction angle. However, a physical understanding of the reason why the coefficient of earth pressure at rest varies as a function of these parameters is still lacking, which causes an uncertainty in the value of K0 to use in geotechnical analyses and in design. This paper investigates the relationship between deformation and mobilization of friction. At the same time, it considers that the unloading process has to be looked at as a stability problem where a static, stabile equilibrium needs to be maintained, thus requiring that the mobilized shear strength equals the applied shear stress. The resulting values of coefficient of earth pressure at rest, K0, interpreted from effective stress paths alone, give realistic results, also in agreement with recent statistical evaluations on the K0-value in Norwegian clays. The new interpretation contributes to explain the widely used empirical correlations presented in the literature
Vane Shear Strength in Terms of Effective Stresses
Get PDFExperience with the shear strength determined with the field vane has shown that the measured values of the strength, normalized with the effective overburden stress, suv/σ'vo, are often lower than 0.1 for normally consolidated quick clays of low plasticity. This undrained shear strength ratio is less than one third of the corresponding undrained strength measured in a triaxial active test in the laboratory. For more plastic clays and overconsolidated clays, however, the difference between field vane and triaxial active shear strength is found to be less. The ratio of the two strengths might even be close to unity in some cases. The explanation for this phenomenon is not that the insertion of the field vane causes disturbance and remoulding in soft, sensitive clays. With a revised failure criterion for soft, contractant clays, it is possible to express the vane strength in terms of effective stresses, and thus to explain the differences in the shear strengths measured by the vane and in the laboratory. It is concluded that the directly measured vane shear strength values do not constitute, in most cases, a representative strength for stability analysis, for instance for embankments and excavations. Amethod for correcting the vane shear strength for stability analysis in practice is proposed
