# A Case Study on Distresses of Concrete Pavements Supported on a Retaining Wall
## 4 Potential Distresses Mechanisms  
Although there is a limited understanding of the mechanisms underlying lane separation and faulting occurrences in concrete pavement, [PERSON] et al. [52] suggested the following mechanism:  
\"Over time environmental changes due to temperature and moisture cause curling and warping in the slab. In areas with poor drainage and expansive soils, differential movement of the pavement lowers or lifts the outside edge of the shoulder slab, creating a lever arm that is restrained by the tie-bars. These cyclic changes allow free water and non-compressible debris into the joint, increasing the stress on the tie-bar with every significant cycle. Meanwhile, the free moisture in the joint continues to slowly corrode the tie-bar until its reduced section ruptures or pulls out of the concrete. Once several tie-bars in a row have failed, the slabs are free to move \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\
\begin{tabular}{c} **Sample** \\ **Location** \\ \end{tabular} } & **Soil** & **Soil** & **Soil** & **Water** & **\% Passing \#200** & **LL [40]** & **PI [40]** \\  & **Classification** & **Classification** & **Content (\%)** & **\%** & **\%** & **\%** \\ \hline \multirow{2}{*}{In MSE wall} & \multirow{2}{*}{CH} & \multirow{2}{*}{A-7-6} & 30–39.4 & 90–03.6 & 64–75 & 32–43 \\  & & & (34.4) [40] & (92.6) [40] & (70) [40] & (37) [40] \\ \hline \multirow{2}{*}{
\begin{tabular}{c} **Beneath MSE** \\ wall \\ \end{tabular} } & \multirow{2}{*}{CH} & \multirow{2}{*}{A-7-6} & 22–40.6 & 90.7–99.7 & 38–84 & 22–48 \\  & & & (32) [40] & (96.7) [40] & (70) [40] & (40) [40] \\ \hline \hline \end{tabular} Notes: [40] LL = liquid limit; PI = plasticity index; [40] Values in parentheses indicate averages.  
\end{table} 
Table 2: Summary of laboratory test results. Figure 18: Resilient moduli of backfill materials and founding soils determined via CPT (CPT8 is a control). apart from each other. This can allow more water into the joint, resulting in a softening of the sub-base support. After vertical friction is lost between the two slabs at the longitudinal joint, the slabs will no longer effectively transfer wheel loads across the joint. Then, as traffic wheel loads cross the longitudinal joint, the two adjacent slabs will move independently. The slab carrying most of the wheel loads will deflect more than adjacent slabs, creating a pumping action from traffic in wet weather. As water infiltrates the failed, separated joint, pumping removes waterborne fines from the sub-base, replacing them with more water. This cycle continues until enough sub-base is softened and removed to create a large enough void beneath that the pumping slab begins to permanently subside, or fault\" (Pages 1 and 2, [PERSON] et al. [52]). The mechanism proposed by [PERSON] et al. [52], in conjunction with the results of the investigations performed in this study, provide valuable insights into the potential distress mechanism of the subject section, which is graphically illustrated in Figure 19. Figure 19 presents the appearance of the subject section immediately after construction. The presence of high plastic clays inside and beneath the MSE wall, combined with repeated traffic loading and environmental factors, causes the settlement of the MSE wall (Figure 19b), perhaps partially dragging down the riprap. Differential movements of pavement due to cyclic changes in temperature and moisture can allow free water to enter the joint, and the water infiltration into the backfill soils of the MSE wall induces greater lateral pressure behind the MSE wall, causing lateral movement and tilting (Figure 19c). Such lateral movement and tilting of the MSE wall causes not only the further settlement of riprap but also lane separations, thus imposing very large tensile stress on tie-bars. The free moisture in the joint continues to slowly corrode the tie-bars until its reduced section fails in tension due to the large tensile stress induced via the lateral movement and tilting of the MSE wall.