Assessing the Long-Term Performance of Mechanically Stabilized Earth Walls (2012)

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45 • “Use the right technology for the right application. For example, consider need and possibility to achieve various settlement/rigidity constraints and match service level to appropriate cost for application.” • “Providing a sound and firm foundation for support of the wall; and providing proper drainage within the wall sys- tem and adjacent to the wall geometry.” • “Performance depends on quality of construction and quality of retained backfill materials.” • “Make sure the contractor is using the specified reinforced fill material and is constructing according to plans.” • “By having a formal wall approval process we have lim- ited the use of modular block wall systems and the deterio- ration of these facing elements due to deicing chemicals.” • “The systems can last forever but must be designed and built correctly.” • “Electrochemical property requirements for backfill material were not specified for one wall built in the late 70s. As a result, the wall failed due to corrosion of the steel reinforcements when it was about 25 years old.” • “You need to have an inventory and know where all the walls are that you own.” • “For the most part, NYSDOT has had very few problems with MSE Structures. We do know that great care must be taken in constructing these structures. If you start wrong in the beginning you’ll always be seeing problems in the walls.” • “The inadequate durability of modular block MSE wall facings in locations affected by winter roadway salt application.” • “Prevent surface runoff or other external water sources from inundating reinforced zone.” • “I think we are so conservative in our designs that we have not had any problems with our long term stability of our MSE walls.” • “This is an issue which has not been addressed by the agency.” • “Lesson(s) learned—‘The outside may get ugly—it’s the inside that matters.’ We had an MSE ride a landslide downslope 32 ft back in the 1970’s. It deformed signifi- cantly, but is still in service today. We have had several lose foundation support. But as long as they were able to move and readjust the stresses through deformation, with no loss of backfill, they have all been able to stay in ser- vice, some for decades. However, excessive consolida- tion settlement and internal drainage failures have lead to issues with cavities and retainment loss. These MSE failed within months and had to be replaced. Amazing[ly] flex- ible, but only up to a limit. It’s what’s inside that counts.” • “Quality of construction. Drainage, drainage, drainage (including erosion). Corrosion of metallic reinforcement.” • “Ensure corrosion monitor readings are performed at a regu- lar inspection rate. If a failure occurs then notify appropriate subsection.” • “We don’t have a lot of MSE walls relative to other states, so this question is difficult to answer. We have not had problems that I am aware of with our MSE walls.” • “Put tight requirements on the modular blocks. Make sure the wall is well drained internally and externally.” • “So far have performed very well.” • “Proper drainage within the wall and proper external drainage behind and in front of the wall.” • “Use of fine-grained select fill has resulted in the migra- tion of material out from behind walls. We have thou- sands of square foot of wall that was backfilled with this type of material. Many walls have shown distress as a result. We have coarsened up the gradation of select fill to lessen the potential of fill migration.” • “We have had some failures and problems that have shown the need for an assessment, inventory, and inspec- tion program.” • “Drainage, drainage, drainage.” • “W-a-t-e-r: from any and all directions and sources.” • “Following proper construction procedures and follow- ing material specifications.” • “Performing and adequate geotechnical subsurface investigation.” • “Settlement.” • “Investigate and address identified problems quickly.” • “The recognition that most MSE wall problems are almost always related to a combination of deficiencies, hardly ever just one single issue. The ‘devil is always in the details,’ so to speak. It is important to keep in mind that most walls are categorized as a Series Engineering System, as opposed to a Parallel Engineering System with respect to external and global stability consider- ations. Using ‘averaged’ shear strengths along a Linear/ Series Wall System can actually cause a real stability failure within a known weak design reach . . . as the weakest link will most assuredly show up as a stability issue on any shallow wall foundation. There is typically no benefit from a redundant parallel system as in most other structure types. Also, we have learned the hard way that MSE Wall reinforcing details around obstruc- tions must be identified early-on in the design phase, as it is always a hassle to deal with during construction. And last, but certainly not the least, wall drainage is a huge component in any MSE Wall project, both during construction and throughout the lifetime of the struc- ture. In summary . . . external/global stability, internal reinforcing details and drainage should be high on any engineer’s checklist of important considerations neces- sary for the successful performance of any MSE Wall Project.” • “Freeze and thaw of block wall, surface run-off seep into the wall.” • “Improve Specifications, Approved Products List, Inspector and contractor training.” APPENDIX C “Most Signficant Lesson(s) Learned” as Reported by Agencies

46 • “None of our installations have reached an age where failure would be anticipated. To date, no significant per- formance issues have been identified.” • “[ . . . N]eed to model to predict the life of the reinforce- ment.” • “Performance of nearby drainage culverts can have signifi- cant impacts on wall performance. In our case, a collapsed culvert resulted in local groundwater table above the height of the wall. Other lessons: the bench at the base of the MSE wall is important to maintain.” • “[Our agency] has been using MSE walls for over 30 years with great success. Our only problems have been poor construction practices which are found and corrected before walls are accepted from the Contractor. We attribute our suc- cess to good geotechnical design, quality backfill required and only using pre-approved walls systems that meet AASHTO requirements.” • “To make sure the ends of the wall where the access trails to build the wall are properly compacted.” • “We have to get beyond our reactive mentality and be pro- active in monitoring these walls.”