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Element testing of soft soils is challenging due to the large strains attained in the pre-failure range. Besides the heterogeneity of natural samples, the set-up configuration is the main driving factor for non-homogenous response. Stress, strain and pore pressure non-uniformities induced by the loading system affect the observed behaviour and complicate proper interpretation of the results. Among the difficulties encountered in the interpretation of laboratory data, the unexpected decrease of the stress ratio frequently observed on Dutch organic soft clays on the wet side of critical state is investigated by numerically back-analysing the triaxial test set-up. A 3D finite element simulation using an advanced constitutive model for soft clays developed at TU Delft was performed to clarify the nature of the response. The results indicate that a decrease in the deviatoric stress up to critical state may be interpreted as a true feature of the soil response. However, the response at large strains is very much influenced by the triaxial shear apparatus, in particular, by the rotation of the top cap which triggers geometrical instability. Practical recommendations are given to limit the effects of the set-up configuration on the determination of the undrained shear strength to be used for field applications., Geo-engineering

Ground borne vibrations generated by the passage of underground trains may change over time due to objective causes, such as increasing weight and speed of trains or ageing of the infrastructure components, as well as a variation in the dynamic response of the soil surrounding the tunnel. Among the possible causes of changes in the soil dynamic response, its hydrologic state has been seldom investigated. In this contribution, the role played by the conditions of the soil above the water table is addressed, starting from a case history in the city of Milano. Two-dimensional plane strain numerical models have been developed for the infrastructure. The models were calibrated on the results of two geophysical investigations performed at the same site in the city centre, but at two different times, which allowed distinguishing different dynamic responses. The system was excited by a synthetic load time history, matching a reference dynamic load spectrum included in Italian recommendations. Limitations of using this input on a 2D plane strain model were assessed by comparing the computed vibrations with experimental acceleration records collected on the tunnel. The results of the two numerical models are compared with those of a simulation performed assuming fully dry conditions above the water table. Overall, the set of analyses shows that even small changes in the dynamic response of the soil, interpretated as a consequence of variable saturation, may result in a change of a few decibels in the acceleration levels. Much larger accelerations are predicted on average with the simpler dry model, clearly showing the advantages of a more accurate modelling strategy., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Geo-engineering

Monitoring structural behavior of earth structures during construction and in service is a common practice done for safety reasons, consolidation control and maintenance needs. Several are the techniques available for measuring displacements, water pressures and total stresses, not only in these geotechnical structures but also at their foundations. Materials testing has been used for calibrating models for structural design and behavior prediction, and these models can be validated with instrumentation data as well. Relatively recent investigation on the behavior of these materials considering their degree of saturation focuses on monitoring the evolution of water content or suction as function of soil-atmosphere interaction, necessary to predict cyclic and/or accumulated displacements, and has huge potential to predict the impact of climate changes on the performance of existing geotechnical structures. This new need justifies the investment on developing sensors able to be used for in situ monitoring of water in the soils, such as those presented here. Testing and monitoring becomes even more important nowadays when, for sustainability purposes, traditional construction materials are replaced by other geo-materials with unknown behavior and long-term performance (mainly accumulated displacements). Existing experimental protocols and monitoring equipment are used for such cases, however new techniques must be developed to deal with particular behaviors. Three case studies are presented and discussion is made on monitoring equipment used and how monitored data helped understanding the behaviors observed., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Geo-engineering

A relevant part of the geotechnical infrastructure in the north of Europe and overseas is built on soft organic soils, including peat. Peat is extremely vulnerable to climate-related hazards as increased temperature accelerates drying, shrinkage and decomposition of the organic matter. Peat exhibits dramatic changes in volume with changes in water content. As the material deforms, the pore space evolves and changes the water retention response. The evolution of the pore space leads to a hysteretic relationship between suction, water content, and void size distribution. In this work, data from free shrinkage-swelling and suction measurements on natural fibrous peat subjected to drying and wetting cycles are presented and discussed. The water retention and shrinkage behaviour of the samples are modelled by accounting for capillarity and considering the evolution of the pore size distribution. X-Ray computer tomography was used to explore the change in the pore space upon shrinkage and drying. The experimental evidence shows that peat experiences distinct shrinkage zones including one where accelerated contraction occurs. Such behaviour is explained as a consequence of the interactions of an aggregated fabric. This is supported by the conceptual modelling approach that highlights the pivotal role of the evolving pore space., Geo-engineering

Increasing frequency and intensity of extreme weather events in the Netherlands is raising attention on the unsaturated response of geo-infrastructures, promoting research projects to provide an overview of the impact of unsaturated conditions on the response of shallow soil layers and embankments, and to better address maintenance and mitigation measures. As part of this effort, we discuss the results of standard laboratory tests performed on initially unsaturated samples retrieved from the field and tested in natural conditions, as well as after controlled drying and wetting. The variation of the "undrained"(i.e. at constant water content) shear strength with the degree of saturation obtained from the laboratory tests aligns well with CPT measurements performed in the field. An elastic-plastic constitutive model with mixed isotropic-rotational hardening developed for saturated soft soils was extended to unsaturated conditions by following a robust approach previously developed for compacted clayey soils. Coupling between the mechanical and the hydraulic behaviour is provided by the water retention curve. The model nicely captures the response observed in the laboratory, until extreme dry conditions, which possibly alter the structure of the soil, the peak stress, and the brittleness after failure. The model is capable of reproducing the effects of the previous hydraulic history on the stress-strain behaviour observed from the laboratory tests over a wide range of degree of saturation., Geo-engineering

Peats are encountered in waterlogged deltaic areas, where degradation is delayed by favourable environmental conditions. The recent increase in frequency and severity of droughts is expected to accelerate peat degradation, in turn increasing subsidence and flood risk, urging better understanding of the response of peats to drying events. To this aim, compression tests on natural and reconstituted peat samples were performed, supported by X-ray micro-computed tomography. The peat fabric was found to be the key factor in the response to drying, with fibres playing the most significant role. Drying in peats starts affecting the macro-fabric, with an irreversible reduction in volume and disruption of the fibrous network occurring under saturated conditions until a threshold void ratio is reached, below which desaturation occurs of the intra-fibres and intra-peds pores. The first drying stage dramatically decreases the compressibility, while the hydraulic conductivity is hardly affected due to the enlargement of macropores. Secondary compressibility is affected by the peat fabric besides the organic content. The total organic content does not change substantially during drying; hence, it is not the best proxy to describe the consequences of drying on the response of fibrous peats. The fibre content can be better used to serve the aim., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Geo-engineering

Purpose: The aim of this study was to evaluate the cost-effectiveness and net monetary benefit of olaparib maintenance therapy compared with no maintenance therapy after first-line platinum-based chemotherapy in newly diagnosed advanced BRCA1/2-mutated ovarian cancer from the Italian National Health Service (NHS) perspective. Methods: We developed a lifetime Markov model in which a cohort of patients with newly diagnosed advanced BRCA1/2-mutated ovarian cancer was assigned to receive either olaparib maintenance therapy or active surveillance (Italian standard of care) after first-line platinum-based chemotherapy to compare cost-effectiveness and net monetary benefit of the 2 strategies. Data on clinical outcomes were obtained from related clinical trial literature and extrapolated using parametric survival analyses. Data on costs were derived from Italian official sources and relevant real-world studies. The incremental cost-effectiveness ratio (ICER), incremental cost-utility ratio (ICUR), and incremental net monetary benefit (INMB) were computed and compared against an incremental cost per quality-adjusted life-year (QALY) gained of €16,372 willingness-to-pay (WTP) threshold. We used deterministic sensitivity analysis (DSA) and probabilistic sensitivity analysis (PSA) to assess how uncertainty affects results; we also performed scenario analyses to compare results under different pricing settings. Findings: In the base-case scenario, during a 50-year time horizon, the total costs for patients treated with olaparib therapy and active surveillance were €124,359 and €97,043, respectively, and QALYs gained were 7.29 and 4.88, respectively, with an ICER of €9,515 per life-year gained, an ICUR of €11,345 per QALY gained, and an INMB of €12,104. In scenario analyses, considering maximum selling prices for all other drugs, ICUR decreased to €11,311 per QALY and €7,498 per QALY when a 10% and 20% discount, respectively, was applied to the olaparib official price, and the I

Conventional triaxial tests on peats are strongly criticised due to the very high shear strength parameters obtained from standard data elaboration, leading to unrealistic factors of safety when used in geotechnical design and assessment. Various operational approaches have been proposed in the literature to overcome this difficulty; however, they seem to lack consistent mechanical background. Some of the issues related to the shear strength evaluation of peats from triaxial tests come from the non-uniform stress and strain states developing in the samples well before failure is attained, due to end restraint effects. Undrained triaxial compression tests were performed on reconstituted peat to examine the influence of end restraint on the deviatoric stress, excess pore pressure and deviatoric strain response. Samples were tested with standard rough end platens and with modified platens to reduce the friction between the sample and bottom and top caps. Four different initial height-to-diameter ratios were examined, to reduce the consequences of rough end platens on the sample response. The results indicate that end restraint contributes dramatically to overestimating the shear strength of peat, due to the increase in both the calculated deviatoric stress and the measured excess pore pressure at the bottom of the sample. Suggestions are given to quantify the influence of end restraint in the interpretation of standard data, in an attempt to suggest viable procedures to determine more reliable effective and undrained shear strength parameters from standard triaxial tests., Accepted Author Manuscript, Geo-engineering