Evaluation and Recommendations for Flowfill and Mechanically Stabilized Earth Bridge Approaches

2008 ◽  
Vol 2045 (1) ◽  
pp. 51-61
Author(s):  
Naser M. Abu-Hejleh ◽  
Dennis Hanneman ◽  
Trever Wang ◽  
Ilyess Ksouri
Keyword(s):  
Filter Material ◽  
Soil Mass ◽  
Reinforced Soil ◽  
Mechanically Stabilized Earth ◽  
Repair Costs ◽  
Bridge Approach ◽  
Class B ◽  
Class 1 ◽  
Backfill Materials ◽  
Mechanically Stabilized

To alleviate the common bridge bump problem, the Colorado Department of Transportation (CDOT) has employed three new alternatives for bridge abutment backfill since 1992: flowfill, mechanically stabilized earth (MSE) using well-graded granular Class 1 backfill (reinforced soil mass as in MSE walls), and MSE using free-draining Class B filter material. However, the occurrence of bridge bump problems is still reported. A study evaluated CDOT current practice for design and construction of bridge approaches and then developed recommendations to improve this practice (improve performance and reduce costs) on the basis of the results of the following: (a) best practices for bridge approaches collected from CDOT staff and reported in the literature, (b) evaluation of the performance and cost-effectiveness of Colorado's MSE and flowfill bridge approaches, and (c) identification of the causes of significant bridge approach settlement problems observed in some of Colorado's MSE and flowfill bridge approaches. Evaluation procedures and forensic investigations were developed and applied to obtain the information needed for the first two items. Flowfill should remain a viable alternative for certain field and construction scenarios that justify its higher costs. MSE approaches with both Class B and Class 1 backfill materials should be routinely used in future CDOT projects with documentation of their performance and cost (construction and repair costs) for a future evaluation. Comprehensive recommendations are presented to mitigate the observed bridge approach settlement problem; the most important recommendations are for improved support and drainage systems for the sleeper slab where the settlement problem occurs.

A Process for Optimizing Gradation of Marginal Backfill of Mechanically Stabilized Earth Walls to Achieve Acceptable Resistivity

2018 ◽  
Vol 2672 (52) ◽  
pp. 251-257 ◽  
Author(s):  
Jose Luis Arciniega ◽  
W. Shane Walker ◽  
Soheil Nazarian ◽  
Kenneth L. Fishman
Keyword(s):  
Corrosion Rate ◽  
Fine Sand ◽  
Coarse Sand ◽  
Mechanically Stabilized Earth ◽  
Mechanically Stabilized Earth Walls ◽  
Texas Department ◽  
Backfill Materials ◽  
Mechanically Stabilized ◽  
Sand And Gravel ◽  
Earth Walls

The service life of mechanically stabilized earth walls depends on the corrosion rate of the metallic reinforcement used in their construction. The resistivity of the backfill aggregates needs to be measured accurately to estimate realistically the corrosion rate of the reinforcement. Resistivity testing is usually performed using the traditional soil box on the portion of the aggregates that passes a No. 10 or No. 8 sieve to either select or reject the backfill. For a more reasonable characterization of the corrosivity of coarse backfills, it is desirable to use their actual gradations. To that end, several resistivity boxes that were double and quadruple the dimensions of the original box were constructed. In addition to the three standard gradations specified by the Texas Department of Transportation, over 20 backfill materials sampled from sources throughout Texas were fractionated to fines, fine sand, coarse sand, and gravel. Resistivity tests were performed separately on each of these four constituents for each backfill. The results were used to evaluate a relationship that would allow the estimation of the resistivity of any desired backfill gradations from the resistivity values of these four constituents. The proposed model looks promising since the resistivity of the backfill composed of the actual gradation can be estimated with reasonable certainty. The results of this study can potentially help highway agencies and contractors use a number of local quarries that are currently disqualified based on the resistivity values obtained from only testing materials that pass a No. 8 or No. 10 sieve.

Temperature Distribution in Mechanically Stabilized Earth Wall Soil Backfills for Design Under Elevated Temperature Conditions

2015 ◽  
Vol 7 (2) ◽  
Author(s):  
Andrew M. Kasozi ◽  
Raj V. Siddharthan ◽  
Rajib Mahamud
Keyword(s):  
Las Vegas ◽  
Temperature Data ◽  
Measured Temperature ◽  
Mechanically Stabilized Earth ◽  
Ansys Fluent ◽  
Design Procedures ◽  
Model Predictions ◽  
Mse Wall ◽  
Mechanically Stabilized Earth Wall ◽  
Mechanically Stabilized

Two-dimensional (2D) transient numerical thermal modeling was undertaken using ansys fluent v12.1 software to estimate distribution of soil backfill temperatures in a typical mechanically stabilized earth (MSE) wall. The modeling was calibrated using field-measured temperature data from the Tanque-Verde MSE wall in Tucson, Arizona (AZ) in which computed temperature data were found to be within ±5% of the field data. The calibrated model predictions for Las Vegas, Nevada (NV) showed an overall average soil backfill temperature of 34.3 °C relative to a maximum outside surface temperature of 51.6 °C. Such a high average soil backfill temperature calls for modification of design procedures since conventional designs are based on geosynthetic tensile strength determined at 20 °C.

scholarly journals Characterization of the New Metallo-β-Lactamase VIM-13 and Its Integron-Borne Gene from a Pseudomonas aeruginosa Clinical Isolate in Spain

2008 ◽  
Vol 52 (10) ◽  
pp. 3589-3596 ◽  
Author(s):  
Carlos Juan ◽  
Alejandro Beceiro ◽  
Olivia Gutiérrez ◽  
Sebastián Albertí ◽  
Margalida Garau ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Pcr Amplification ◽  
Class 1 Integron ◽  
Negative Results ◽  
New Variant ◽  
Class B ◽  
Class 1 ◽  
Encoding Gene ◽  
Good Agreement

ABSTRACT During a survey conducted to evaluate the incidence of class B carbapenemase (metallo-β-lactamase [MBL])-producing Pseudomonas aeruginosa strains from hospitals in Majorca, Spain, five clinical isolates showed a positive Etest MBL screening test result. In one of them, strain PA-SL2, the presence of a new bla VIM derivative (bla VIM-13) was detected by PCR amplification with bla VIM-1-specific primers followed by sequencing. The bla VIM-13-producing isolate showed resistance to all β-lactams (except aztreonam), gentamicin, tobramycin, and ciprofloxacin. VIM-13 exhibited 93% and 88% amino acid sequence identities with VIM-1 and VIM-2, respectively. bla VIM-13 was cloned in parallel with bla VIM-1, and the resistance profile conferred was analyzed both in Escherichia coli and in P. aeruginosa backgrounds. Compared to VIM-1, VIM-13 conferred slightly higher levels of resistance to piperacillin and lower levels of resistance to ceftazidime and cefepime. VIM-13 and VIM-1 were purified in parallel as well, and their kinetic parameters were compared. The k cat/K m ratios for the antibiotics mentioned above were in good agreement with the MIC data. Furthermore, EDTA inhibited the activity of VIM-13 approximately 25 times less than it inhibited the activity of VIM-1. VIM-13 was harbored in a class 1 integron, along with a new variant (Ala108Thr) of the aminoglycoside-modifying enzyme encoding gene aacA4, which confers resistance to gentamicin and tobramycin. Finally, the VIM-13 integron was apparently located in the chromosome, since transformation and conjugation experiments consistently yielded negative results and the bla VIM-13 probe hybridized only with the genomic DNA.

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