Proper estimation of soil reinforcement loads and strains is key to accurate internal stability design of reinforced soil structures. Current design methodologies use limit equilibrium concepts to ...estimate reinforcement loads for internal stability design of geosynthetic and steel reinforced soil walls. For geosynthetic walls, however, it appears that these methods are excessively conservative based on the performance of geosynthetic walls to date. This paper presents a new method, called the K-stiffness method, that is shown to give more accurate estimates of reinforcement loads, thereby reducing reinforcement quantities and improving the economy of geosynthetic walls. The paper is focused on the new method as it applies to geosynthetic walls constructed with granular (noncohesive, relatively low silt content) backfill soils. A database of 11 full-scale geosynthetic walls was used to develop the new design methodology based on working stress principles. The method considers the stiffness of the various wall components and their influence on reinforcement loads. Results of simple statistical analyses show that the current American Association of State Highway and Transportation Officials (AASHTO) Simplified Method results in an average ratio of measured to predicted loads (bias) of 0.45, with a coefficient of variation (COV) of 91%, whereas the proposed method results in an average bias of 0.99 and a COV of 36%. A principle objective of the method is to design the wall reinforcement so that the soil within the wall backfill is prevented from reaching a state of failure, consistent with the notion of working stress conditions. This concept represents a new approach for internal stability design of geosynthetic-reinforced soil walls because prevention of soil failure as a limit state is considered in addition to the current practice of preventing reinforcement rupture.Key words: geosynthetics, reinforcement, walls, loads, strains, design, K-stiffness method.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The paper describes a new working stress design methodology introduced by the writers for geosynthetic reinforced soil walls (K-Stiffness Method) that is now extended to steel reinforced soil walls. ...A large database of full-scale steel reinforced soil walls (a total of 20 fully instrumented wall sections) was used to develop the new design methodology. The effects of global wall stiffness, soil strength, reinforcement layer spacing, and wall height were investigated. Results of simple statistical analyses using the ratio of measured to predicted peak reinforcement loads (i.e., method bias) demonstrate the improved prediction accuracy. The AASHTO Simplified Method results in an average method bias of 1.1 with a coefficient of variation (COV) of 45%, whereas the proposed K-Stiffness Method results in an average bias of 0.95 and a COV of 32%. Soil strength was found to have limited influence on reinforcement loads for steel reinforced soil walls, especially for high shear strength soils, while global wall stiffness and wall height had a major influence on reinforcement loads.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The paper provides a synthesis of work by the writers that has the objective of developing a new working stress method for the calculation of reinforcement loads in geosynthetic reinforced soil ...walls. As a precursor to this objective, careful back-analyses of a database of instrumented and monitored full-scale field and laboratory walls are used to demonstrate that the current American Association of State Highway and Transportation Officials (AASHTO) Simplified Method used in North America results in excessively conservative estimates of the volume of reinforcement required to generate satisfactory long-term wall performance. The new design method captures the essential contributions of the different wall components and properties to reinforcement loads. The method is calibrated against measured in situ wall reinforcement loads using a careful interpretation of reinforcement strains and the conversion of strain to load using a suitably selected reinforcement stiffness value. A novel feature of the method is to design the wall reinforcement so that the soil within the wall backfill is prevented from reaching a failure limit state, consistent with the notion of working stress conditions.
We present a new analysis of previously published SuperCDMS data using a profile likelihood framework to search for sub-GeV dark matter (DM) particles through two inelastic scattering channels: ...bremsstrahlung radiation and the Migdal effect. By considering these possible inelastic scattering channels, experimental sensitivity can be extended to DM masses that are undetectable through the DM-nucleon elastic scattering channel, given the energy threshold of current experiments. We exclude DM masses down to 220 MeV/c2 at 2.7 x 10-30 cm2 via the bremsstrahlung channel. The Migdal channel search provides overall considerably more stringent limits and excludes DM masses down to 30 MeV/ c2 at 5.0 x 10-30 cm2.
We measured the nuclear-recoil ionization yield in silicon with a cryogenic phonon-sensitive gram-scale detector. Neutrons from a mono-energetic beam scatter off of the silicon nuclei at angles ...corresponding to energy depositions from 4 keV down to 100 eV, the lowest energy probed so far. The results show no sign of an ionization production threshold above 100 eV. In conclusion, these results call for further investigation of the ionization yield theory and a comprehensive determination of the detector response function at energies below the keV scale.
We reviewed our experience in 79 children who had unrelated cord blood transplant (UCBT) between 1996 and 2007 with a major focus on GVHD, comparing both traditional and National Institute of Health ...(NIH) criteria. The cumulative incidence (CI) of acute GVHD (aGVHD, by day +100) was 0.42 for grade II-IV and 0.22 for grade III-IV. The CI of all aGVHD (NIH, that is, no time limit) at 1 year was 0.45 for grade II-IV and 0.32 for grade III-IV. Infused CD34 cell dose (>1 × 10(5)/kg), pretransplant bacterial infection and nonmalignant disorders were risk factors for grade II-IV aGVHD on univariate analysis. Infused CD34 cell dose remained significant on multivariate analysis. At 1 year, the CI of chronic GVHD (cGVHD) using the Seattle criteria was 0.27, whereas that for cGVHD (NIH) was 0.08. By NIH criteria, the classic form of cGVHD was uncommon (5%) after UCBT. Instead, the acute (71%) and overlap (24%) GVHD variants predominated. Grade II-IV aGVHD was a significant risk factor for cGVHD by both Seattle and NIH criteria. We conclude that GVHD after day +100 after UCBT typically carries features of aGVHD. Moreover, and in marked contrast to adult unrelated donor hematopoietic stem cell transplantation, the GVHD observed in this series did not adversely affect survival.
We present the design and characterization of a cryogenic phonon-sensitive 1-gram Si detector exploiting the Neganov-Trofimov-Luke effect to detect single-charge excitations. This device achieved ...2.65(2) eV phonon energy resolution when operated without a voltage bias across the crystal and a corresponding charge resolution of 0.03 electron-hole pairs at 100 V bias. With a continuous-readout data acquisition system and an offline optimum-filter trigger, we obtain a 9.2 eV threshold with a trigger rate of the order of 20 Hz. The detector's energy scale is calibrated up to 120 keV using an energy estimator based on the pulse area. The high performance of this device allows its application to different fields where excellent energy resolution, low threshold, and large dynamic range are required, including dark matter searches, precision measurements of coherent neutrino-nucleus scattering, and ionization yield measurements.
A series of fluorinated high density polyethylene (f-HDPE) geomembrane (GM) samples of different thickness (1, 1.5 and 2.5
mm) was exhumed from the backfill immediately upstream of a barrier system ...constructed to contain a hydrocarbon spill in the Canadian Arctic. The samples were tested for oxidation induction time (OIT), crystallinity, melt index (MI) and tensile properties. The results of these tests are reported and it is shown that the durability of the GM was maintained well beyond the initial 3-year design life of the barrier system. Based on 7 years of field data, the std-OIT depletion time for the 1.5
mm thick GM used in the barrier system was inferred to be over 140 years while the antioxidant depletion time based on the HP-OIT is estimated to be about 200 years. No significant temporal changes in the crystallinity, MI or tensile properties of the exhumed GM samples were detected.
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