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| 2. |
- Vinck, Ken, et al.
(författare)
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Advanced in-situ and laboratory characterisation of the ALPACA chalk research site
- 2022
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Ingår i: Geotechnique. - : ICE Publishing. - 0016-8505 .- 1751-7656.
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Tidskriftsartikel (refereegranskat)abstract
- Low-to-medium density chalk at St Nicholas at Wade, UK, is characterised by intensive testing to inform the interpretation of axial and lateral tests on driven piles. The chalk de-structures when taken to large strains, especially under dynamic loading, leading to remarkably high pore pressures beneath penetrating CPT and driven pile tips, weak putty annuli around their shafts and degraded responses in full-displacement pressuremeter tests. Laboratory tests on carefully formed specimens explore the chalk’s unstable structure and markedly time and rate-dependent mechanical behaviour. A clear hierarchy is found between profiles of peak strength with depth of Brazilian tension (BT), drained and undrained triaxial and direct simple shear (DSS) tests conducted from in-situ stress conditions. Highly instrumented triaxial tests reveal the chalk’s unusual effective stress paths, markedly brittle failure behaviour from small strains and the effects of consolidating to higher than in-situ stresses. The chalk’s mainly sub-vertical jointing and micro-fissuring leads to properties depending on specimen scale, with in-situ mass stiffnesses falling significantly below high-quality laboratory measurements and vertical Young’s moduli exceeding horizontal stiffnesses. While compressive strength and stiffness appear relatively insensitive to effective stress levels, consolidation to higher pressures closes micro-fissures, increases stiffness and reduces anisotropy.
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| 3. |
- Ahmadi Naghadeh, Reza, 1982, et al.
(författare)
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A laboratory characterisation of the response of intact chalk to cyclic loading
- 2022
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Ingår i: Geotechnique. - : Thomas Telford Ltd.. - 0016-8505 .- 1751-7656. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports the cyclic behaviour of chalk, which has yet to be studied comprehensively. Multiple undrained high-resolution cyclic triaxial experiments on low- to medium-density intact chalk, along with index and monotonic reference tests, define the conditions under which either thousands of cycles could be applied without any deleterious effect, or failure could be provoked under specified numbers of cycles. Intact chalk's response is shown to differ from that of most saturated soils tested under comparable conditions. While chalk can be reduced to putty by severe two-way displacement-controlled cycling, its behaviour proved stable and nearly linear visco-elastic over much of the one-way, stress-controlled loading space examined, with stiffness improving over thousands of cycles, without loss of undrained shear strength. However, in cases where cyclic failure occurred, the specimens showed little sign of cyclic damage before cracking and movements on discontinuities led to sharp pore pressure reductions, non-uniform displacements and the onset of brittle collapse. Chalk's behaviour resembles the fatigue response of metals, concretes and rocks, where micro-shearing or cracking initiates on imperfections that generate stress concentrations; the experiments identify the key features that must be captured in any representative cyclic loading model.
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| 4. |
- Jones, Robert P., et al.
(författare)
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Patterns of Recurrence After Resection of Pancreatic Ductal Adenocarcinoma : A Secondary Analysis of the ESPAC-4 Randomized Adjuvant Chemotherapy Trial
- 2019
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Ingår i: JAMA Surgery. - : AMER MEDICAL ASSOC. - 2168-6254 .- 2168-6262. ; 154:11, s. 1038-1048
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Tidskriftsartikel (refereegranskat)abstract
- Importance: The patterns of disease recurrence after resection of pancreatic ductal adenocarcinoma with adjuvant chemotherapy remain unclear.Objective: To define patterns of recurrence after adjuvant chemotherapy and the association with survival.Design, Setting, and Participants: Prospectively collected data from the phase 3 European Study Group for Pancreatic Cancer 4 adjuvant clinical trial, an international multicenter study. The study included 730 patients who had resection and adjuvant chemotherapy for pancreatic cancer. Data were analyzed between July 2017 and May 2019.Interventions: Randomization to adjuvant gemcitabine or gemcitabine plus capecitabine.Main Outcomes and Measures: Overall survival, recurrence, and sites of recurrence.Results: Of the 730 patients, median age was 65 years (range 37-81 years), 414 were men (57%), and 316 were women (43%). The median follow-up time from randomization was 43.2 months (95% CI, 39.7-45.5 months), with overall survival from time of surgery of 27.9 months (95% CI, 24.8-29.9 months) with gemcitabine and 30.2 months (95% CI, 25.8-33.5 months) with the combination (HR, 0.81; 95% CI, 0.68-0.98; P=.03). The 5-year survival estimates were 17.1% (95% CI, 11.6%-23.5%) and 28.0% (22.0%-34.3%), respectively. Recurrence occurred in 479 patients (65.6%); another 78 patients (10.7%) died without recurrence. Local recurrence occurred at a median of 11.63 months (95% CI, 10.05-12.19 months), significantly different from those with distant recurrence with a median of 9.49 months (95% CI, 8.44-10.71 months) (HR, 1.21; 95% CI, 1.01-1.45; P=.04). Following recurrence, the median survival was 9.36 months (95% CI, 8.08-10.48 months) for local recurrence and 8.94 months (95% CI, 7.82-11.17 months) with distant recurrence (HR, 0.89; 95% CI, 0.73-1.09; P=.27). The median overall survival of patients with distant-only recurrence (23.03 months; 95% CI, 19.55-25.85 months) or local with distant recurrence (23.82 months; 95% CI, 17.48-28.32 months) was not significantly different from those with only local recurrence (24.83 months; 95% CI, 22.96-27.63 months) (P=.85 and P=.35, respectively). Gemcitabine plus capecitabine had a 21% reduction of death following recurrence compared with monotherapy (HR, 0.79; 95% CI, 0.64-0.98; P=.03).Conclusions and Relevance: There were no significant differences between the time to recurrence and subsequent and overall survival between local and distant recurrence. Pancreatic cancer behaves as a systemic disease requiring effective systemic therapy after resection.Trial Registration: ClinicalTrials.gov identifier: NCT00058201, EudraCT 2007-004299-38, and ISRCTN 96397434. This secondary analysis of a randomized clinical trial investigates patterns of recurrence after adjuvant chemotherapy in pancreatic cancer and the association with survival.
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| 5. |
- Liu, Tingfa, et al.
(författare)
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Cyclic Characterisation of Low-to-Medium Density Chalk for Offshore Driven Pile Design
- 2023
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Konferensbidrag (refereegranskat)abstract
- Project-specific advanced laboratory testing is employed increasingly frequently in site investigations for major offshore projects. Such testing needs to focus on characterising properties under in-situ conditions, while also catering for the effects of foundation installation and subsequent service conditions, including cyclic loading. Low-to-medium density chalk, a variable soft biomicrite, can be de-structured to soft paste under dynamic percussion or large-strain repetitive shearing, posing significant challenges and uncertainties for driven pile design. This paper draws on key outcomes from undrained cyclic triaxial test programmes on both intact chalk and dynamically de-structured (putty) chalk. The cyclic response of intact chalk resembles the fatigue behaviour of hard rocks and develops little sign of damage before sharp pore pressure reductions and brittle collapse occurs. In contrast, fully de-structured chalk develops both contractive and dilative phases, as seen with silts. The associated effective stress reductions vary systematically with the number of cycles and cyclic stress ratio. A laboratory-based global axial cyclic predictive method is proposed from the experiments and employed to predict the outcomes of field axial cyclic loading pile tests. The research provides then basis for robust cyclic design guidance for piles driven in low-to-medium density chalk.
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| 6. |
- Liu, Tingfa, et al.
(författare)
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Laboratory investigation of the cyclic loading behaviour of intact and de-structured chalk
- 2023
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Ingår i: Proceedings of the 8th International Symposium on Deformation Characteristics of Geomaterials (IS-PORTO 2023).
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Konferensbidrag (refereegranskat)abstract
- Chalk is a soft biomicrite composed of silt-sized crushable CaCO3 aggregates. Chalk’s response to cyclic loading depends critically on its sensitive micro fabric and state, which may be altered significantly by high-pressure compression, dynamic impact or prior large-strain repetitive shearing. This paper reports high-resolution undrained cyclic triaxial experiments on low- to medium-density intact chalk and chalk de-structured by dynamic compaction to model the effects of percussive pile driving. The intact chalk manifested stable and nearly linear visco-elastic response under a wide range of the one-way, stress-controlled cyclic loading conditions imposed. However, high level cycling led to sudden failures that resembled the fatigue response of metals, concretes and rocks, with little sign of cyclic damage before sharp pore pressure reductions, non-uniform displacements and finally brittle collapses. However, the de-structured chalk’s response to high-level undrained cycling resembles that of silts, developing both contractive and dilative phases that led to pore pressure build-up, leftward effective stress-path drift, permanent strain accumulation, cyclic stiffness losses and increasing damping ratios. Results from exemplar tests are presented to illustrate these key features and demonstrate how chalk’s undrained cyclic shearing characteristics depend also on effective stress level. The experimental outcomes provide significant scope for developing constitutive and empirical relationships or predictive tools to enable the interpretation and design of driven pile foundations in chalk and other chalk-structure interaction related problems under cyclic loading.
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