| 1. |
- Ekström, Ingvar, et al.
(författare)
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Adapting Ligga to higher design flood, spillway channel modification through physical & numerical modeling
- 2007
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Konferensbidrag (refereegranskat)abstract
- As part of Vattenfall’s dam-safety program, Ligga dam is to be rebuilt for higher safety level. Besides diverse measures, the spillway channel will be modified. The channel is bounded by natural bedrock. Spillway operations during the past years have evidenced severe erosion and damages in the fractured rock. Rock instability becomes visible even at moderate spillway discharges 800 – 900 m3/s. The updated design-flood of the dam is in the order of the magnitude of 2000 m3/s. To adapt the dam to the higher flood, the spillway channel has to be re-shaped, so that the flood is safety released and the structural integrity of the embankment dam is maintained. As a cost-effective alternative, excavation is recommended, as a large volume of rock material is required for stabilizing the dam and for replacing the slope protection upstream. To achieve satisfactory flow behaviors, hydraulic model tests are made to examine and optimize excavation possibilities. The re-shaping of the waterway is complicated by the fact that the existing channel bends in plan and the excavation must follow roughly the same curvature. Considerations are also given to exemption of the dam toe from erosion and the forest on the left riverside from being flooded. Computer simulations of water-rock interaction are made with the commercial code UDEC. Against previous flood release records, the numerical model of rock erosion is calibrated and uses measured water level, flow velocity and dynamic water pressure in the model as input data. Results show that the new waterway configuration provides proper flow patterns and the rock foundation after reinforcement is not subjected to unacceptable damage at spillway discharges up to the design flood.
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| 2. |
- Ekström, Ingvar, et al.
(författare)
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Improving spillway discharge safety at Bergeforsen
- 2011
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Konferensbidrag (refereegranskat)abstract
- Bergeforsen is a 35 m high embankment dam. The technical discharge capacity of the existing spillway is 2300 m3/s at full reservoir retention level (FRRL). To meet new design flood criteria a first major rehabilitation was carried out 2003, which allowed discharge of an extreme flood at a water level higher than the FRRL. Recent underwater inspections of the spillway and energy converter have however revealed a need for rehabilitation and adaptation of the concrete structures to the design flood flow conditions. To make it possible to take the spillway out of operation for the time period required for adequate repairs it has been decided to rebuild the dam, adding an alternative spillway structure that will serve as discharge facility during the upgrade of the existing spillway. For this reason, a new 25-m gated spillway, with a stilling basin followed by a curved tunnel section, will be constructed in the left river bank. Once the existing spillway is rehabilitated the combined discharge capacity will make it possible to safely pass the revised design flood at a reservoir level not exceeding the FRRL. A physical model was built to asssit in the design decision, the purpose of which is to verify and optimize engineering solutions for increased discharge capacity, so that the design flood is released without jeopardizing the stuctural integrity of the dam.
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| 3. |
- Ekström, Ingvar, et al.
(författare)
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Large-scale shear box tests to determine rockfill parameters
- 2016
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Ingår i: Association of State Dam Safety Officials Annual Conference 2016. - Lexington, Kentucky : Association of State Dam Safety Officials. - 9781510830752 ; , s. 828-845
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Konferensbidrag (refereegranskat)abstract
- A 160 (525 ft) m high asphalt concrete core rockfill dam is developed in an area of very high seismicity in Cetin, Turkey. Topographical constraints of the dam footprint impose a steep outer geometry of the dam, requiring the geotechnical properties of the rockfill to comply with certain minimum limits. Test blasting in a potential quarry and rockfill rolling compaction trials suggest that the tested gneiss/schist rock material to a large extent is weathered and weak. The friction angle of the rockfill is a decisive parameter for both the static and dynamic stability of the dam slopes and especially for the deformation of the dam crest due to strong earthquakes. The suggested rock fill material has therefore undergone detailed testing. To this end, large-scale shear tests with a 1000 mm diameter sample cylinder have been carried out at the Luleå Technical University in Sweden.
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| 4. |
- Ekström, Ingvar, et al.
(författare)
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Large-scale Sonic drilling to determine supporting fill parameters
- 2019
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Ingår i: Dam Safety 2019, Conference Proceedings. - : Association of State Dam Safety Officials. ; , s. 384-397
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Sonic drilling has been carried out in the upstream support fill zone of the 101 m (332 ft) high and 1800 m (5900 ft) long Messaure embankment dam located in northern Sweden. The purpose was to investigate the upstream fill material and obtain samples to perform laboratory tests for further geotechnical characterization of the material. The support fill material zone consists of cobbles, gravel, and sand of hard rock types, and modification of the drilling equipment to suit the purpose of the drilling was required. A Sonic drilling rig was identified in Europe, which could drill holes inclined and recover samples in steps of up to 178 mm (7") diameter and 3 m (10 ft) length. Holes were by this method drilled, cored and cased by vibrations combined with rotation at high power resonant sonic frequencies, without adding fluid that disturbs the quality of the recovered material. To make the sampling of the coarse-grained friction material successful, a new catcher for the sampling tube (core barrel) was constructed. An anchor plate was developed, to prevent the casing from drifting and the process to mount and remove the casing was adapted. After a process of repeated trial drillings in a test area, during which the equipment was gradually developed to meet the requirements, the drill rig was moved to site. Drilling was conducted in the upstream direction from the crest at full reservoir level. Samples of the complete gradation of the supporting fill could successfully be recovered from up to 45 m (150 ft) long holes at an angle of 43-45° from the vertical axis. The retracted casing left a 279 mm (11") diameter hole that was backfilled during closely monitored conditions. The grout mix was balanced to avoid excess penetration and grout loss into the fill, at the same time as hydraulic fracturing had to be avoided in the drill holes close to the slope. This paper describes the drilling investigation and the used equipment, the drilling conditions and the experiences gained.
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| 5. |
- Ferdos, Farzad, et al.
(författare)
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Hydraulic Conductivity of Coarse Rockfill used in Hydraulic Structures
- 2015
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 108:2, s. 367-391
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Tidskriftsartikel (refereegranskat)abstract
- Internal erosion is a major cause of embankment dam failure. Unravelling and instability of the downstream slope, initiated by internal erosion and leakage through the dam core, is one of the most likely breach mechanisms for large, zoned embankment dams. To be able to model this mechanism, the relationship between the hydraulic gradient and the flow velocity for the coarse rockfill material must be understood. Because most studies of this topic have focused on the flow parameters in gravel-size materials with Reynolds (Re) numbers lower than 25,000, permeability measurements are needed coarser rockfill material under heavily turbulent flow regimes prevailing in rockfill material under certain design flow scenarios. This paper presents the set-up and results of a series of field and laboratory experimental studies and the subsequent data interpretation, from which relevant hydraulic conductivity parameters, defined in applicable flow laws, were extracted. This study demonstrates that the exponent of a power flow law relating the hydraulic gradient and the flow velocity is Re number dependent for pore Re numbers 60,000. The power remains constant (Re number independent) above this Re number threshold for the fully developed turbulent regime. This validity threshold as well as the constant behaviour also applies if the flow law is written in a quadratic form. The aforementioned threshold lies beyond the ranges investigated experimentally by previous researchers. The experiments in this study examined Re numbers as large as 220,000 for grain-diameter distributions in the range 100-160 mm and as large as 320,000 in the range 160-240 mm.
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| 6. |
- Ingvar, A., et al.
(författare)
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No association between infections, HLA type and other transplantrelated factors and risk of cutaneous squamous cell carcinoma in solid organ transplant recipients
- 2012
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Ingår i: Acta Dermato-Venereologica. - : Medical Journals Sweden AB. - 0001-5555 .- 1651-2057. ; 92:6, s. 609-614
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Tidskriftsartikel (refereegranskat)abstract
- Recipients of solid organ transplants are at a markedly increased risk of cutaneous squamous cell carcinoma (SCC). We investigated potential associations between post-transplant infections, HLA type, and other transplant-related factors and risk of SCC, taking immunosuppressive treatment into account. A population-based case-control study was conducted. All patients who developed SCC during follow-up (1970-1997) were eligible as cases (n = 207). Controls (n = 189) were individually matched to the cases on age and calendar period of transplantation. Detailed exposure information was collected through an extensive, blinded review of medical records. Odds ratios were computed with conditional logistic regression. There were no significant associations with any infectious agents, or with number and timing of infections, specific HLA-type, donor characteristics, or other transplant characteristics and risk of post-transplant SCC. These results suggest that risk of post-transplant SCC is neither closely related to specific post-transplant infectious disorders, nor to the infectious load or specific HLA types.
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| 7. |
- Ingvar, Åsa, et al.
(författare)
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Immunosuppressive treatment after solid organ transplantation and risk of post-transplant cutaneous squamous cell carcinoma
- 2010
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Ingår i: Nephrology, Dialysis and Transplantation. - : Oxford University Press (OUP). - 0931-0509 .- 1460-2385. ; 25:8, s. 2764-2771
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The risk of cutaneous squamous cell carcinoma (CSCC) is found to be substantially increased after organ transplantation. The association with specific immunosuppressive regimens has been previously investigated, but results are not concordant. We aimed to clarify the relationship between separate immunosuppressive drugs, drug load, timing and risk of post-transplant CSCC. METHODS: A population-based nested case-control study was performed in the Swedish organ transplantation cohort (n = 5931). All patients who developed CSCC during the follow-up (1970-97) were eligible as cases (n = 207). Controls (n = 189) were randomly selected from the cohort and individually matched to the cases on follow-up time, age at and calendar period of transplantation. Exposure information was collected through extensive and standardized review of medical records. RESULTS: The median time to CSCC was 6.7 years. Post-transplant azathioprine (Aza) treatment considerably increased the risk of CSCC during all time periods analysed, and the risk augmented with increasing dose and duration. Patients who after the entire follow-up period had received a high accumulated dose of Aza had an 8.8-fold increased risk of CSCC in multivariate analysis (P < 0.0001), compared to patients never treated with Aza. Additionally, a high accumulated dose of corticosteroids during the same period conferred a 3.9-fold elevated risk of CSCC (P = 0.09), compared to the lowest accumulated dose of corticosteroids. Cyclosporine treatment was not associated with the risk of CSCC post-transplantation. CONCLUSIONS: This study provides evidence that Aza treatment, but not cyclosporine treatment, is strongly associated with post-transplant CSCC risk. The results suggest that the risk of CSCC after organ transplantation is not only an effect of the immunosuppressive load per se.
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| 8. |
- Molinder, Gabriella, et al.
(författare)
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Reliability-based safety factors for earth dam stability calculations
- 2019
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Ingår i: Sustainable and Safe Dams Around the World. - : Canadian Dam Association. ; , s. 229-237
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Konferensbidrag (refereegranskat)abstract
- Probability based stability analysis is of rising prevalence in dam safety aroundthe world, though it is most commonly used for concrete structures. The stability of a Swedishrockfill dam has been analyzed with deterministic and probabilistic stability analyses. The probabilisticanalysis was made using the Rosenblueth method (point estimation method), where thesafety factor and reliability index β has been calculated for circular slip surfaces. A comparisonbetween deterministic and probabilistic stability analysis concludes that reliability-based stabilityanalysis is a useful method for integrating uncertainties into a stability analysis. However, itin our opinion is more suitable as a complement to deterministic analysis rather than as areplacement. High quality material data and a deep understanding of both geotechnical engineeringand probability theory is essential for reliability index β to be useful.
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| 9. |
- Shahrivar, Mehrnoosh, et al.
(författare)
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Low-dose aspirin use and colorectal cancer survival in 32,195 patients : A national cohort study
- 2023
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Ingår i: Cancer Medicine. - : John Wiley & Sons. - 2045-7634. ; 12:1, s. 315-324
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Results from previous studies indicate that use of aspirin may improve colorectal cancer (CRC) survival. The aim of this study was to assess whether use of aspirin influences overall survival or CRC-specific survival in an unselected cohort of patients diagnosed with CRC.METHODS: The study was performed using the Colorectal Cancer Data Base Sweden (CRCBaSe), a mega-linkage originating from the Swedish Colorectal Cancer Register, with additional linkages to other national health care registers. All patients diagnosed with primary CRC stage I-III treated with curative surgery, aged 18-85 years at diagnosis, from 2007 through 2016 were identified. Information on low-dose aspirin use was extracted from the Swedish Prescribed Drug Register. Exposure was defined as dispensed prescription for at least 6 months. Aspirin exposure was analyzed at the time of surgery (yes/no) and as a time-varying exposure during follow-up. Follow-up was restricted to a maximum 6 years, to model 5-year survival. Cox regression models were fitted to estimate hazard ratios (HRs) with 95% confidence intervals (CIs). Adjustments were performed for sex, age, year of diagnosis, Charlson comorbidity index, hypertension, and ASA score as potential confounders.RESULTS: A total of 32,195 patients diagnosed with CRC were included. 6764 (21%) were exposed to aspirin at the time of CRC surgery. The median time of follow-up was 4.2 years. Aspirin use at the time of surgery was not associated with all-cause (adjusted HR = 1.03, 95% CI: 0.97-1.08) nor CRC-specific mortality (adjusted HR = 0.99, 95% CI: 0.91-1.07). Aspirin use during follow-up was associated with increased all-cause (adjusted HR = 1.09, 95% CI: 1.04-1.15) but not CRC-specific mortality (adjusted HR = 0.98, 95% CI: 0.91-1.06). A CRC-specific effect associated with aspirin was noted from approximately 3 years following surgery.CONCLUSIONS: In this large nation-wide cohort study there was no convincing association between aspirin use after CRC and OS or CRC-specific survival.
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| 10. |
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