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The importance of laboratory proficiency testing schemes in assessing and improving uncertainty
Get PDFAny site characterisation relies on at least some laboratory tests, and some of those test results (often from basic tests such as Liquid Limit and Plastic Limit) are used in initial design calculations based on correlations. However, the reliability of those correlations is heavily dependent on the uncertainty in the results of those laboratory tests. There is an inter-laboratory proficiency testing scheme that has been running for over fifteen years in the UK, with many worldwide participants. This paper presents a compilation of the scheme’s findings to allow an assessment to be made regarding the reliability of different tests. As an example, repeatability within a single laboratory for the Liquid Limit test by cone penetrometer has been shown to be ± 1 %, but between different laboratories this has risen to ± 6 %. Similar ranges have been found in the Plastic Limits which, taken together with the uncertainties from the Liquid Limits, could give rise to significant concerns over using correlations based on the Plasticity Index. Other examples of results from various test methods are given in this paper and it is argued that much of the uncertainty comes not from the test method itself, but from other factors including basic equipment maintenance, calibration, technician training and competence. It will be seen that laboratory proficiency testing schemes are crucial in highlighting these problems and giving an opportunity to allow better assessment of the quality of both test results and, arguably, the laboratories that produce them
Numerical Simulations of Cone Penetration Response via Accounting for State-Dependence and Full-Strain-Range Non-Linearity of Sand
Get PDFThe penetration response of CPT is not only related to the stress and density states of sand but also influenced by the nonlinear stress-strain relations of soils from very small (10-5) to relatively large (10-1) strain levels. Appropriate considerations of the above key soil behaviours can be crucial for accurate numerical simulations of CPT response. For this purpose, an intergranular strain (IGS)-based elastic model is introduced into a critical-state-based, state-dependent plasticity model to capture the state-dependence and full-strain-range non-linearity behaviour of sand. A numerical model of the CPT penetration process is then established by combining the aforementioned constitutive model and the arbitrary Lagrangian-Eulerian (ALE) large deformation finite element technique. The latter is adopted to handle the problems of large deformations of soil and mesh distortion. Then the computed response of CPT is compared against centrifuge test observations, and the numerical model is utilized to analyse the influences of the full-strain-range non-linearity behaviour of sand on the penetration response of CPT. The results indicate that the non-linear stress-strain relations at small strains can have noticeable impacts on the tip resistance of CPT, in particular for loose sand, while having a relatively small influence on the penetration depth required to reach a steady-state penetration resistance. The above influences might be attributed to a rapid decay of soil strains with the distance from the cone tip, and consequently high stiffness and strong constraints effects of far-field soils on core soils adjacent to the cone ti
PLENARY LECTURE - The Legacy of Michele Jamiolkowski to Geotechnical Engineering
No full textMichele Jamiolkowski was deeply interested in many topics in geotechnical engineering. The link between his many contributions to the discipline was his deep appreciation for the need to develop techniques for predicting the performance of real structures. This focus on real structures was pervasive in all of his research, and led to his attention to experimental investigation of natural soils. Jamiolkowski recognized the importance of in situ tests to site characterization of natural soils, and consequently this paper focuses on this topic. Jamiolkowski was involved in many challenging projects, and he always considered each project as an occasion to improve the state of the art, to develop novel approaches in site characterization, to develop new in situ test interpretation methods, and to obtain quality experimental data. The paper summarizes major improvements to the state of the art that resulted from his contributions, as well lessons learned from major and iconic projects in which Jamiolkowski was involved
Interpretation of the undrained pressuremeter test in unsaturated condition
No full textThe pressuremeter measures both the pressuremeter modulus and the limit pressure, which are used to estimate the bearing capacity of the foundation according to different standards. The results of the pressuremeter test include the pLM limit pressure and the EM pressuremeter modulus. These quantities cannot be directly input as data for geotechnical calculations using Finite Elements or Finite Differences in the study of civil engineering structures such as retaining walls, tunnels, embankments, and excavations. These modern calculation methods require, at a minimum, knowledge of the mechanical characteristics of the soil, including elasticity (with Young’s modulus (E) and the Poisson ratio ()) and resistance (with cohesion (c’) and the angle of friction (’)). This study is devoted to the interpretation of the pressuremeter test so that it is possible to use it for the determination of the mechanical characteristics of the soil. When the pressuremeter test is carried out into clay, it appears pore pressure during the test when only shearing is applied. In summary, understanding pore pressure and interpreting measurements to determine the effective shear modulus are crucial for geotechnical engineering and subsurface exploration. Effective shear modulus can differ significantly from the value determined solely based on total pressure. This study provides the theoretical value of the Skempton coefficient B. Additionally, it proposes an interpretation theory for the pressuremeter test in clay. Finally, the theory is validated through a comparison with tests performed in London clay at a depth of 20.6 meter
Calculation of heights for local datum points of tide gauges in Albania referred to the average sea level and albageo program
Get PDFThe accurate measurement and monitoring of sea levels are of paramount importance, especially for coastal regions like Albania, where sea level changes can have significant impacts on various aspects of life, including coastal infrastructure, ecosystems, and human settlements. This abstract provides an in-depth overview of a study focused on the calculation of heights of local datum points at tide gauges in Albania with reference to the average sea level, using the ALBAGEO3 program. Tide gauges play a crucial role in understanding the dynamic nature of sea levels. These instruments measure the height of the sea surface relative to a reference point, which is typically known as the local datum. The calculation of heights of local datum points is crucial for several reasons. Firstly, it provides insights into the relative sea level changes at different locations in Albania. It allows for the identification of areas that may be more vulnerable to such events, enabling betterinformed decision-making in terms of coastal management and disaster preparedness. Furthermore, accurate knowledge of local datum heights is essential for navigation and maritime activities. It ensures that nautical charts are up to date and that ships can safely navigate Albanian waters without the risk of running aground or encountering obstacles related to sea level changes. In summary, the study on the calculation of heights of local datum points at tide gauges in Albania, utilizing the ALBAGEO3 program, plays a pivotal role in advancing our understanding of sea level variations in this coastal nation. The accurate and reliable data generated through this research benefits not only the scientific community but also provides actionable insights for policymakers, urban planners, and other stakeholders involved in the sustainable development and protection of Albania's coastal areas
Evaluation of the challenges present in the obtaining, processing and interpreting useful data from offshore seismic cone penetration testing
Get PDFThe Seismic Cone Penetration Test (SCPT) is an essential tool for establishing in-situ shear wave velocity (ð£ð ), which is then used to establish profiles of Small Strain Shear Modulus (ðºððð¥), a direct input parameter to the design of offshore wind turbine foundations. Performance of SCPT offshore presents greater challenges than on land and each offshore site investigation contractor uses their own different non-standard equipment to try to address these challenges. This contributes to the multiple areas of uncertainty in the assessment of wave arrival time and distance, which can result in less reliable data sets. Additionally, a variety of data processing and interpretation methods are used across the industry, the benefits and limitations of which must be understood if one is to specify, plan or undertake such testing. The authors provide a review of methods of acquiring data, the equipment required and the different processing and interpretation methods available, specifically comparing true interval straight ray analyses with pseudo interval true ray path analyses and the different processing steps which can be taken to increase reliability in datasets
Multi-method in situ geophysical testing in a high porosity chalk mass
Get PDFChalk is a silt-sized soft biomicrite rock often encountered as a low to medium density, high porosity, structured material within a fractured mass. In recent years, there has been increased interest in the behaviour of chalk and the development of new design procedures for pile foundation installation design, motivated by several large-scale onshore and offshore infrastructure projects. Recent modelling has demonstrated the importance of accurately characterising the operational stiffness of the chalk mass. While several methods exist to measure the chalk’s stiffness in situ, they are often subject to significant scatter, with no guidance available to the end user on interpretation or on which method should be used as a baseline. A new programme of multi-method in situ geophysical testing in chalk at a well-characterised onshore test site in Southern England is described that forms part of a wider research project. The chalk deposit is shown to be relatively uniform with depth which provides a unique opportunity to apply multiple methods and interpretations without the influence of significant layering. The experimental programme is described and the interpretation and selected results of downhole geophysical tests at depths up to 40m are presented. The chalk’s remarkably high shear stiffnesses are shown to be highly repeatable and consistent when rigorous test execution and analysis is applie
Development of a Calibration Chamber System for Testing at High Confining Pressures
Get PDFCone penetration testing with pore pressure measurement (CPTu) represents a state of practice tool to assess the in situ state parameter, strength, and liquefaction susceptibility of sandy soils and mine tailings. Many techniques for the interpretation of CPTu data are based on the results of calibration chamber test programs on sand and, more recently, mine tailings. While these efforts have led to the current methods to interpret CPTu data, two factors relevant to CPTu interpretation require consideration: (i) the available calibration chamber data is dominated by tests with consolidated mean effective stresses < 200 kPa; and (ii) tailings storage facilities are being constructed to heights such that in situ effective stresses are far higher than those of the available calibration chamber test database. While much of CPTu interpretation is carried out in a dimensionless framework, there is evidence that existing relationships between stressnormalised tip resistance and state parameter are dependent on effective stress. This stress-dependence has been attributed to a variation in shear rigidity with effective stress, which is not accounted for in many interpretation techniques. However, at high stresses, other factors such as the curvature of the critical state line in an e-log(p’) plane may contribute. To assess CPTu of sands at high stresses, a novel small-scale calibration chamber employing a miniature cone capable of testing soils consolidated to a mean effective stress up to 2,000 kPa is outlined. Test results are presented for tests carried out over a range of mean effective stresses up to 1,000 kPa
The influence of soil structure on CPTu and SDMT results
Get PDFThe natural structure of clays has a significant influence on its mechanical behaviour and can be characterized using insitu and laboratory tests. It was reported by Robertson (2016) that soil structure leads to an increased tip resistance (qc) and shear wave velocity (Vs) when performing seismic cone penetration tests. However, only limited studies investigated changes in soil structure by means of in-situ tests. Sensitive, marine clays were investigated within the research project "VIBE – Sustainable Ground Improvement Solution for Oslo" at the Norwegian Geo-Test site Onsøy (Gundersen et al. 2019). Possibilities and limitations of the vibro replacement method were studied for very soft ground conditions based on a full-scale field test. The influence of soil structure on in-situ measurements of piezocone penetration tests (CPTu) and seismic flat dilatometer tests (SDMT) are further studied by intentionally disturbing the soil structure by a vibrator. Results of CPTu and Medusa SDMT, executed before and after treatment, are compared to characterize changes in soil structure. The results indicate that the vibration-induced destructuration led to a significant decrease of CPTu measurements, namely tip resistance (qc), sleeve friction (fs) and measured pore pressure (u2), within medium to high sensitive clays. As the decrease in fs is more significant compared to the decrease in qc, a significant decrease in friction ration (Rf) was observed. In analogy, SDMT resulted in a decrease in shear wave velocity (Vs), horizontal stress index (KD) and dilatometer modulus (ED) after the vibro treatment. It was further shown that the soil behaviour type chart according to Robertson (2016) leads to no sufficient characterization of soil structure in soft, marine clays
Construction of the W2Power tower demonstrator
Get PDFDeliverable 6.2 is a demonstrator of the tower of the W2Power floating windturbine at scale of 1/6. The demonstrator made of GRP will have a estimated dimension of 10m with a diameter of 1.5m. This demonstrator should be built by month 24. This deliverable will be public