THE PROBLEM
Detailed analysis of the ground was necessary to predict settlement calculations and anticipated consolidation time required. The clays in the foundation soils could cause problems with long term settlement. Ground cover sediments included strata of clays and sand - the clays were typically of medium and low plasticity. Due to the surcharge imposed by the new bridge structure, it was necessary to address the issue of settlement caused by the structure.
THE SOLUTION
A Tensar MSL was introduced as basal reinforcement to the bridge abutment to help in mitigating differential settlement. TensarTech Earth Retaining Systems were proposed for the bridge abutment and wing wall construction. The bankseat bears directly on the reinforced soil block with the near vertical TensarTech TW1 modular block wall system providing a hard and durable facing. To speed up the consolidation process and limited post construction settlement the bridge abutment was preloaded. For design purposes the MSL provided predictable soil parameters for the foundation.
PROJECT DESCRIPTION
The Tensar MSL was installed using three layers of Tensar TriAx® geogrid and granular fill to form a relatively stiff mattress below the foundation level of the TensarTech TW1 Wall. The TensarTech TW1 modular block wall system comprises dry laid concrete facing blocks together with Tensar RE geogrids.
A high efficiency polymer connector is used to connect the facing blocks to the geogrid reinforcement. For the maximum retained height of 4.95m, the design called for geogrid reinforcement lengths from 8.5m to 10m to accommodate the bridge bank seat loadings. The total length of the TW1 Walls were 68m and 71m respectively and direct sections in front of bank seats measured 31.5m and 34m.
The TensarTech TW1 system was also chosen as a solution because of its structural flexibility. Due to the dry laid construction of the facing, any anticipated post construction settlement could be accommodated without causing undesirable aesthetic facing issues.
