# A Case Study on Distresses of Concrete Pavements Supported on a Retaining Wall
## 6 Conclusions  
This case study presented a comprehensive evaluation of continuously reinforced concrete pavement (CRCP) supported on an in-service MSE wall. The subject section showed various types of distresses, such as lane separation, faulting, settlement, and lateral movement of the MSE wall. Extensive field investigations were performed to assess the conditions of the pavement structures and MSE wall, including FWD tests, coring, DCP tests, CPTs, LiDAR surveys, and soil borings. Extensive analyses of results from field and laboratory tests led to the following major conclusions:  
* The distresses observed in the subject section are believed to be primarily caused by the high plasticity of the backfill soils, which are prone to shrink and swell with moisture  
Figure 19: Graphical illustrations of the potential distress mechanisms: (**a**) expected condition of the subject section immediately after construction, (**b**) initial settlement of the MSE wall, (**c**) lane separation and tensile failure of tie-bar due to the lateral movement and tilting of the MSE wall caused by water infiltration, (**d**) softened sub-base support and formation of voids due to the continuous infiltration of water, (**e**) faulting, settlement and lane separation due to the loss of sub-base support, and (**f**) further lane settlement and shear failure of tie-bar under repeated heavy traffic.  
variations. Additionally, the increased lateral pressure behind the MSE wall due to water infiltration and the low hydraulic conductivity of CH soils appears to have accelerated the progress of distress. Furthermore, the continuous water infiltration behind the MSE wall is attributed to the weakened embankment soils and material washout.
* The resilient moduli of the backfill soils, estimated via DCP tests conducted at the locations where major distresses were observed, were significantly smaller than those at control locations. In particular, the resilient moduli of the backfill soil were less than 8 ksi (55.1 MPa) where severe pavement distresses were observed.
* FWD testing results revealed that the overall slab deflections in the area where distresses were observed were significantly greater than the typical deflection values for well-performing 12 in (30.5 cm) CRCP in Texas.
* Core samples taken through the pavement structure showed excellent concrete quality. For one core sample extracted from a location where exceedingly high slab deflections were observed, there was a layer of polyurethane foam directly beneath the concrete, suggesting the existence of a significant void in the past due to the washout of the base materials.
* The cone penetration tests (CPTs) were utilized to evaluate the conditions of backfill materials for the entire MSE wall height and identify the boundary of the soft backfill soils. The resilient moduli of the backfill soils, estimated through the correlation between the results of DCP tests and CPTs, indicated that the entire backfill materials were in poor conditions, except for near the bottom of the MSE wall. Accordingly, the adopted repair strategy was to remove the existing materials and replace them with cement-treated backfills from the pavement surface to 2.9 ft (0.9 m) above the MSE wall base.  
Conceptualization, PC. and HS.; methodology, HL. and N.K.; validation, PC. and H.S.; writing--original draft preparation, HL. and N.K.; writing--review and editing, HL. and HS.; supervision, H.S. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.