Soil Tunnel Test Section: Case History Summary

The strong influence of construction procedures was demonstrated by comprehensive field measurements of initial lining behavior and of ground movements for a soil tunnel. Plowing movements for the first tunnel shield created much of the ground loss and settlement. Much less settlement was observed for the second tunnel construction with a shield of an improved design. Volume changes in the soil played an important role in the entire pattern of ground movement. During first tunnel construction, significant increases in soil volume resulted in less surface settlement than the actual amount of lost ground about the shield. The opposite was observed for the second shield where significant compression of soils took place, particularly in the pillar between the two tunnels and in the previously disturbed soils over the first tunnel. The rib and lagging initial lining was demonstrated to be truly flexible. A ground reaction curve was established on the basis of analysis and measurement of load. The initial lining was observed to be carrying less than half of the full overburden load.