MSE WALL AND REINFORCEMENT TESTING AT MUS-16-7.16 BRIDGE SITE

The assumptions involved in the current method recommended in the FHWA Design Manual and the Coherent Gravity method for design of reinforced earth walls resulted in many discrepancies. These most influential assumptions are (i) the treatment of the reinforced soil mass as a rigid block, (ii) the assumption of strain compatibility between the reinforcement and the soil, (iii) the assumption of no frictional stresses along the soil horizontal slices, and (iv) the ignorance of the effects of the reinforcement lengths and stiffness on the vertical and horizontal stresses and the working forces of the reinforcements. These assumptions resulted, in many cases, in either overestimating or underestimating the working forces in the reinforcement, as well as the vertical and lateral earth pressures within the reinforced soil mass. They were also responsible for the errors in obtaining the reinforcement resistance to pullout, and the active and effective lengths of reinforcements. The main objective of this research is to carry out an instrumentation monitoring and field-testing program on a newly constructed 52 ft (15.85 m) high MSE abutment wall on the Old Schoolhouse Road in Muskingum County, Ohio. The instrumentation plan included strain gages spot-welded to pre-selected reinforcement strips, earth pressure cells located at the bottom of the reinforced soil mass, and contact pressure cells embedded in the concrete facing. Four field pullout tests have also been conducted corresponding to four different overburden depths. The research resulted in the development of a new method that can be used to accurately analyze and effectively design the reinforced earth walls. This method, called the Virtual Soil Wedge (VSW) method, has been theoretically developed to account for the influences of the reinforcement spacing, length, and location relative to the height of the wall in the calculation of the working forces of the reinforcement, the lateral earth pressures, and the pullout factors of the reinforcements. This method has introduced two new factors: an embracement factor that relates the reinforcement layouts to the lateral earth pressures, and a scaling factor that accounts for the roughness, type and shape of the reinforcement, and the type and size of the backfill soil. The scaling factors for different soil and reinforcement combinations should be evaluated using field measurements or experimental data. The field measurements made at the Schoolhouse Road wall were compared with the method recommended by the FHWA Design Manual and the VSW method developed in this research. The FHWA recommended method was shown to be only convenient for the case of walls with simple geometry. However, for walls with slopping backfill surcharge, significant errors were observed. The VSW method, on the other hand, was shown to be capable of accurately predicting the measured maximum reinforcement forces and their locations, the lateral earth pressures, and the pullout resistance of the reinforcement. The presence of reinforcements has influenced the vertical earth pressure values throughout the construction period. This, in turn, has influenced the distribution of the pullout factors, F, with the overburden depth. Combining the VSW method with the basic equation defining the pullout resistance of the reinforcement, resulted in the development of a relationship defining the pullout factors of the reinforcement as a function of the reinforcement spacing, length and locations within the reinforced earth walls.