![]() ![]() Its removal impracticable while leaving it in and constructing the embankment directly onto it would have Variability of the thickness and extent of the peat made The piles driven into the glacial deposits underlying the In the areas where layers of peat were found it wasĭecided to support the embankment on a piled raft Likely the band drain system will work satisfactorily. Atterberg limits and bulk density against depth below ground level. Yet to be placed but from the results of the first lift it isįIG. Time of writing the second lift of the embankment had The first embankment lift these were 600-700 mm. Within the range predicted on the basis of laboratory Settlement of the embankment was monitored using This variation was found to affect the rate of excess pore pressure dissipation in the alluvium, and as the 26 000 bandĭrains penetrated the sand and gravel by 0.5 m, itĬonfirmed there was good hydraulic continuity between the band drains and the sand and gravel. The piezometric level in the sand and gravel underlying the alluvium varied seasonally rising to withinĠ.5 m of ground level during the winter and falling toġ m below ground level during the summer. The field coefficient of consolidation decreased to 2.0 m2/year. Nearly a 10-fold decrease in the field coefficient ofĬonsolidation as the alluvium pre-consolidation pressures were exceeded. ![]() The response of the piezometers during theĬonstruction of the first embankment lift indicated Monitor the performance of the installed drainage Installed in the alluvium between the band drains to Two lifts with a minimum 12-month consolidation The embankment was designed to be constructed in Increasing effective stress and a lower bound laboratory value of 1.2m2/year was used to determine the The coefficient of consolidation was found to decrease significantly with Laboratory consolidation and in situ permeability tests were used to measure the consolidationĬharacteristics of the alluvium. Time to a minimum and to reduce po st-construction In this area it was decided to promote primaryĬonsolidation using band drains to keep construction Typical plot of the Atterberg limits and bulk densityĪgainst depth clearly shows the presence of the three Some partly decomposed woodįragments were also found in the lower layer. The upper layer, except it contained small pockets and Sand partings and the lower layer was very similar to Geological sections along centre line between (a) Chainage 9000 and 10 000 and (b) 10 000 and 11 000. Site location for the Afon Ganol Valley section of the A55.į~G. Vertical root stems, the middle layer contained fineįIG. ![]() Silty clay in which three main layers were identified,Įach 4-5 m thick. Sampling of the alluvium proved it to be a soft grey To a low level rotary interchange, the alluvial clay was Resulted in two completely different forms of embankmentĪt the western end where the e m b a n k m e n t was highest and widest in order to accommodate two slip roads ![]() Ground conditions along the length of the road embankment The road embankment, which in thisĪrea varies in height from 2 to 7 m, is constructed over softĪlluvial clays and peat, up to 15 m (Fig. Travers Morgan & Partners, 21 Station Road, Colwyn Bay, Clwyd LL29 8BPĪ 2-km length of the North Wales Coast Road (A55) between Colwyn Bay and Conwy runs along the floor of theĪfon Ganol Valley which once formed part of the RiverĬonwy estuary (Fig. Section of the North Wales Coast Road (A55) 335-337.Ī technical note on the design and construction of the Afon Ganol Valley ![]()
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