# A Case Study on Distresses of Concrete Pavements Supported on a Retaining Wall
## 3 Evaluation of the Performance of the Subject Section
### Evaluation of Concrete Pavement Structure  
#### 3.1.1 Slab Deflection  
To minimize traffic closure time, the authors selected an FWD test because it is fast and does not involve the removal of pavement material. FWD tests have been widely used for characterizing the mechanical response of the pavement system and assessing the structural capacity [40; 41; 42; 43]. In this study, FWD tests were conducted on the inside shoulder (IS), inside lane (IL), and middle lane (ML) on Day 1 and the outside lane left wheel path (OL LWP), outside lane right wheel path (OL RWP), and outside shoulder (OS) on Day 2. The deflections at 9000 lb (40 kN) loading were evaluated along all of the lanes, covering a total length of 600 ft (183 m) each. Figure 5 shows FWD drop locations performed in the subject section.  
Figure 2: Typical pavement section in the project site.  
Figure 3: Types of distresses observed in the subject section: (**a**) lane separation, (**b**) tie-bar failure, (**c**) lane settlement and faulting, and (**d**) lateral movement of the MSE wall.  
Figure 6a shows slab deflections versus DMI (distance measuring instrument) in feet along the subject section obtained via FWD tests. Slab deflections on the inside shoulder and inside lane ranged between 0.8 mils (0.020 mm) and 3.8 mils (0.097 mm), whereas slab deflections on the middle lane ranged between 0.4 mils (0.010 mm) and 24 mils (0.610 mm) (note that although the maximum deflection value of 24 mils (0.610 mm) was measured at about DMI 42 ft (12.8 m), slab deflections on the middle lane overall ranged between 4 mils (0.102 mm) and 9 mils (0.229 mm)). This clearly indicates that the inside shoulder and inside lane have better slab performance than the middle lane. Along the outside lane, slab deflections ranged between about 1 mils (0.025 mm) and 19.3 mils (0.490 mm), showing much greater overall deflections than the inside shoulder and inside lane. Slab deflections on the outside shoulder ranged between 1 mils (0.025 mm) and 26.8 mils (0.681 mm), but the larger deflection values were limited to a zone between DMI 41 ft (12.5 m) and 60 ft (18.3 m). Other than the localized zone, slab deflections on the outside shoulder were less than 3 mils (0.076 mm).  
To summarize, the inside shoulder, inside lane, and outside shoulder showed much better slab support conditions than the middle lane and outside lane. Also, higher deflections occurred between DMI 0 and 350 ft (106.7 m), particularly between DMI 30 ft (9.2 m) and 60 ft (18.3 m). Figure 6b, showing a colored profile map of slab deflections, with the green color indicating the slab deflections less than 3 mils (0.076 mm) and the red and yellow colors indicating slab deflections greater than 12 mils (0.305 mm), summarizes the overall slab support conditions in the subject section.  
According to [PERSON] et al. (2014), the statewide average deflection of well-performing 12 in (30.5 cm) CRCP in Texas is about 1.7 mils (0.043 mm). Figure 6 clearly shows that slab deflections at the subject section well exceed this value, indicating poor performance. In particular, very large deflection values near DMI 40 ft (12.2 m) indicate the possible presence of voids beneath the slab.  
Figure 4: Distress map showing an overview of the locations where major distresses were found.  
Figure 5: FWD testing locations conducted on the subject section.