Project Description

In March 1996 cracks and displacements were observed in approximately 250 rigid concrete pavement panels along the express toll route highway. There was longitudinal and some transverse and diagonal cracking, plus spalling along the joints. Differential movements of up to 100 mm (4 inches) were recorded locally due to frost action. The localized pavement distress occurred prior to the highway being opened to sustained traffic loads, therefore a geotechnical investigation was carried out to establish the probable causes and suggested remedial action.

The field investigation studies involved visual condition surveys, crack surveys, concrete coring, joint examination, ten boreholes with continuous split spoon sampling and Standard Penetration testing, three test pits, insitu density measurements using calibrated nuclear gauges, concrete compressive strength testing, laboratory grain size analyses, pavement thickness measurements, aggregate sampling and testing, groundwater level monitoring in six standpipe piezometers, inspection of subsurface drain tile systems and surface drainage ditches.

The findings showed 300 mm (12 inches) concrete thickness with a minimum compressive strength of 35 MPa (5000 psi), 100 mm (4 inches) of an open graded drainage layer (OGDL), and 155 mm (6 inches) of well compacted Modified Granular A, as specified, on a poor draining and low plasticity silty sand to silt and clay subgrade with high moisture contents. The load transfer efficiency of the joints between the concrete slabs was found to be above 85%.

Additional subsurface and surface drainage measures were recommended for the frost susceptible subgrade soils subjected to seasonal freezing temperatures and high water levels.