The primary objective of this study was to determine whether concrete lug anchors retarded pavement movement on steep grades. Minnesota Department of Transportation's policy is that grades in the 3 to 5 percent and greater range are steep and may require lug anchors. Standard lug anchor spacing varies from 150 feet, center to center, for 3 percent grades to 75 feet, center to center, for 5 percent and greater grades.
During the initial study of lug anchors on State Project 0702-49 it was observed that pavement settlement was occurring at these lug anchor locations. Settlement of up to 1 1/2 inches was observed. It was felt that this settlement was being caused by surface water entering the pavement structure, flowing in a down hill direction via the base aggregates, being trapped at the lug anchors and finally, due to traffic loads, being pumped out, thereby causing loss of base fines and some subgrade soil fines. End result was pavement settlement. Therefore, a second phase of this study, utilizing 2 inch perforated pipe to control surface water was initiated on S.P. 0702-51 This report covers both studies.
Conclusions based on this study are: 1) that lug anchors do prevent the downhill movement of the concrete pavement; 2) that when lug anchors are used a perforated pipe system also be built to collect the surface water that enters the pavement structure thus eliminating the anticipated base pumping and pavement settlement.
