Many research studies made on hundreds of MSE walls have shown that in order to get lower values of lateral earth pressure coefficients from an active condition on the backfill soil, thus lower exerted loads and stresses on the reinforcement, the wall needs to yield. This is typical of extensible polymer-based wall systems, such as geosynthetics. Steel systems, on the other hand, are very rigid and do not allow enough deformation on the wall to generate the active condition. For this research, steel reinforcement for MSE walls that behaves similar to geosynthetics was developed. This was done by using crimps on steel bars that would allow the wall to deform as the crimps straighten. A pullout box was designed and constructed, where tensile and pullout tests were performed on the crimped reinforcement. Different crimp geometries on different bar diameters were tested under a range of confining pressures. From this, force-displacement curves were developed for these crimp geometries that could be used to predict deflections on walls with crimped reinforcement. In addition, the pullout resistance of the crimps in the straighten process was evaluated. This way, the crimps would not only be used to allow the wall to yield, but also as a pullout resistance mechanism. The pullout resistances per crimp for different tensions on the crimp and under a range of overburden pressures were evaluated. By combining the pullout resistance of the crimps and the force-displacement curves, a new internal stability design method was introduced where crimped reinforcement is used to resist both pullout and rupture failure. Also presented here are the pullout resistances of round bars with improved deformations of different diameters. These were found to have the same pullout resistance of square deformed bars with the same cross-sectional area. Round bars are preferred over square bars because they are more corrosion resistant and have longer design life.

Current design codes of Mechanically Stabilized Earth (MSE) Walls allow the use lower lateral earth pressure coefficient (K value) for designing geosynthetics walls than those used to design steel walls. The reason of this is because geosynthetics walls are less rigid permitting the wall to deform enough to work under active pressures instead of at rest pressures as in steel walls. A new concept of crimped steel bars was recently introduced. This new type of bar was tested for tension and pullout behavior. Results on tests made on crimped bars show that putting those crimps in the steel bar will give us a better pullout behavior and a more flexible tensile behavior. This new type of steel bar will behave more like geosynthetics, allowing the wall to deform sufficiently to reach the necessary deflection to reach the active condition. The use of steel by current design codes is pushing MSE walls to be designed with more steel than needed. Measurements of the force in different walls showed that the steel is not being used even close to the maximum stress allowed by the code which is 50%. The proposed design methodology using crimped bars will help us save around 52% of steel volume compared to the actual design procedures. This means a huge improvement in the usage of steel versus actual designs. This improvement is obtained because of the efficient behavior of rounded bars under corrosion and because of the flexibility in the bars obtained with the crimps that will allow us to reach the active condition.

Large scale static lateral load tests were completed on a pile cap with wingwalls under several different sand backfill configurations: no backfill, loosely compacted unconfined, loosely compacted slip plane wall confined, loosely compacted MSE wingwall confined, and densely compacted MSE wingwall confined. The relative compaction of the backfill was varied during each test to observe the change in passive resistance provided by the backfill. The wall types were varied to observe the force placed on the walls and the wall displacement as a result of the laterally loaded pile cap and backfill relative compaction. Passive force-displacement curves were generated from each test. It was found that the densely compacted material provided a much greater passive resistance than the loosely compacted material by 43% (251 kips) when confined by MSE walls. The outward displacement of the MSE walls decreased noticeably for the dense MSE test relative to the loose MSE test. Backfill cracking and heave severity also increased as the relative compaction level of the backfill increased. As the maximum passive force was reached, the reinforcement reached their peak pullout resistance. Correlations were developed between the passive pressure acting on the pile cap and the pressure measured on the MSE wingwalls as a function of distance from the pile cap for both loose and dense backfills. The pressure measured on the wingwalls was approximately 3 to 9% of the pressure acting on the pile cap. As the distance from the pile cap increased, the pressure ratio decreased. This result helps predict the capacity of the wingwalls in abutment design and the amount of allowable wall deflection before pullout of the backfill reinforcement occurs. Three methods were used to model the measured passive force-displacement curves of each test. Overall, the computed curves were in good agreement with the measured curves. However, the triaxial soil friction angle needed to be increased to the plane strain friction angle to accurately model both the loose and dense sand MSE and slip plane wall confined tests. The plane strain friction angle was found to be between 9 to 17% greater than the triaxial friction angle.

Large scale static lateral load tests were performed on a pile cap under varying sand backfill configurations: no backfill, full-width dense sand backfill, dense sand slip plane confined backfill, and two configurations of dense sand MSE wall confined backfills. Efforts were made to maintain the relative compaction of the backfills for each of the tests near the same value. The MSE wall panel arrangement was varied to determine the effect of different reinforcement configurations on the passive resistance and wall panel displacement. Passive force-displacement curves were generated from each test. It was found that the MSE design manual provided reasonable estimates of pullout resistance of bar mats in dense sand, and that the passive resistance of a soil backfill confined by MSE walls can be calculated with an increased friction angle using a log-spiral approach. Also, the amount the triaxial friction angle can be increased depends on how much the MSE wall panels displace outward. Correlations were developed between the pressure on the pile cap and that on the MSE wall panels near the pile cap. Generally, the pressure on the wall panels was less than 10% of that which was on the adjacent pile cap, and decreased as the distance from the pile cap increased. Finally, it was found that while limiting the backfill width decreases the ultimate passive resistance of the backfill, if the backfill is confined in a plane strain configuration the passive resistance per unit width is higher than that for an unconfined backfill.

The purpose of this study was to extract galvanized steel wire reinforcement coupons from mechanically stabilized earth (MSE) walls along I-15 and determine the rate of corrosion that has taken place since Phase I, which was conducted by Gerber and Billings (2010). The galvanized steel reinforcement analyzed in this study has been in place for 19 to 20 years at the time of extraction. A total of 85 coupons were extracted and laboratory analysis was performed to determine the thickness of remaining zinc galvanization on each coupon. Soil samples were obtained from each one-stage wall extraction location to determine moisture content for correlation with corrosion. After laboratory testing was performed, the measured zinc coating thickness was compared to that determined in Phase I. An average corrosion rate of approximately 0.032 oz/ft²/year has occurred since Phase I. According to the AASHTO (2017) design corrosion rate of 0.35 oz/ft²/year for the first two years and 0.09 oz/ft²/year until the depletion of the zinc, the zinc coating would have been completely depleted after 16 years. Based on the results of laboratory testing, the initial galvanization coating was likely greater than the specified thickness of 2.0 oz/ft² (86 μm). The zinc galvanization is corroding at a slower rate than the AASHTO design rate. The AASHTO design rate for depletion of zinc coating and subsequent corrosion of the steel reinforcement is conservative for the corrosion conditions present in the MSE wall reinforcement coupons tested. The integrity of the steel reinforcement that is currently in place is not likely to be compromised by corrosion.

Mechanically Stabilized Earth (MSE) walls retain soil on steep, unstable slopes with crest loads. Over the last decade, they are becoming quite popular due to their low cost-to-benefit ratio, design flexibility, and ease of construction. Like any civil infrastructure, MSE walls need to be continuously monitored according to transportation asset management criteria during and after the construction stage to ensure that their expected serviceability measures are met and to detect design and/or construction issues, which could lead to structural failure. Current approaches for monitoring MSE walls are mostly qualitative (e.g., visual inspection or examination). Besides being time consuming, visual inspection might have inconsistencies due to human subjectivity. Other monitoring approaches are based on using total station, geotechnical field instrumentations, and/or Static Terrestrial Laser Scanning (TLS). These instruments are capable of providing highly accurate, reliable performance measures. However, the underlying data acquisition and processing strategies are time-consuming and are not scalable. This research focuses on a comprehensive strategy using a Mobile LiDAR Mapping System (MLS) for the acquisition and processing of point clouds covering the MSE wall. The strategy produces standard serviceability measures, as defined by the American Association of State Highway and Transportation Officials (AASHTO) – e.g., longitudinal and transversal angular distortions. It also delivers a set of recently developed measures (e.g., out-of-plane offsets and 3D position/orientation deviations for individual panels constituting the MSE wall). Moreover, it is also capable of handling MSE walls with smooth or textured panels with the latter being the focus of this research due to its more challenging nature. For this study, an ultra-high-accuracy wheel-based MLS has been developed to efficiently acquire reliable data conducive to the development of the standard and new serviceability measures. To illustrate the feasibility of the proposed acquisition/processing strategy, two case studies in this research have been conducted with the first one focusing on the comparative performance of static and mobile LiDAR in terms of the agreement of the derived serviceability measures. The second case study aims at illustrating the feasibility of the proposed strategy in handling large textured MSE walls. Results from both case studies confirm the potential of using MLS for efficient, economic, and reliable monitoring of MSE walls.

A Mechanically Stabilized Earth (MSE) wall is a vertical grade separation that uses earth reinforcement extending laterally from the wall to take advantage of earth pressure to reduce the required design strength of the wall. MSE wall systems are often prefabricated to reduce construction time, thus improving constructability when compared with conventionally cast-in-place reinforced wall systems. However, there is a lack of knowledge for predicting the service-life of MSE retaining wall systems when recycled backfill materials such as Recycled Asphalt Pavement (RAP) and Crushed Concrete (CC) are used instead of Conventional Fill Material (CFM). The specific knowledge missing is how these recycled materials, when used as backfill in MSE wall systems, affects the corrosion rate of the reinforcing strips. This work addresses this knowledge gap by providing recommendations for MSE wall systems backfilled with CC or RAP, and provides a guide to predict the service-life based on corrosion rate test data obtained from embedding steel and galvanized-steel earth reinforcing strips embedded in MSE wall systems backfilled with CC, RAP, and CFM. Experimental data from samples emulating MSE wall systems with steel and galvanized-steel reinforcing strips embedded in CC and RAP were compared to samples with strips embedded in CFM. The results of the testing provide data and methodologies that may, depending on the environmental exposure conditions, justify the use of RAP and CC for the construction of MSE walls. If these backfill materials are obtained from the construction site, this could provide a significant cost savings during construction.