Abstract
Designed by Opus, Double Tracking and Electrification Works between MacKay’s Crossing and Waikanae at Kapiti Coast north of Wellington, New Zealand required 14 km length of up to 4 m high new railway embankments, ground improvement, up to 30 m high cut slopes and slope stabilisation works to be built alongside the existing North Island Main Trunk Railway embankment. Approximately 4 km length of the new railway embankments had to be built over a very soft peat within a narrow designation corridor located between the high steep eastern hills and State Highway 1. The project had to be built within a short timeframe and the existing Main Trunk Railway Line had to remain operational during the construction. The design and construction techniques used had to address a number of geotechnical challenges: construction on peat with undrained shear strength of 7 kPa to 15 kPa, insufficient room for stabilising berms, large (up to 1.5 m) settlements of the new railway embankments and frequent re-levelling of the existing railway tracks during construction, construction of upslope protection works to stabilise steep cuttings. Finite element modelling of the new and existing railway embankments was undertaken to predict the settlements and the required frequency of relevelling of the existing railway tracks. Lateral and vertical deformations of the new and existing embankments as well as pore pressures in the peat were closely monitored during the construction phase. The project was successfully completed in February 2011. Keywords: peat, railway embankment, settlement, preloading, stabilising berm, trackbed.
Highlights
Теория расчета строительных конструкций– settlement of the existing railway embankment due to the load from the new embankment;
Designed by Opus, Double Tracking and Electrification Works between MacKay’s Crossing and Waikanae on the Kapiti Coast required a 14 km length of up to 4 m high new railway embankments to be built alongside the existing railway embankment
The existing rail line is a section of the North Island Main Trunk Railway and was a single track
Summary
– settlement of the existing railway embankment due to the load from the new embankment;. – where the railway corridor was narrow, retaining walls were required to support the new fill embankment, these were founded on peat and had to be designed to tolerate large settlement;. Bedrock is exposed along the eastern side of the railway corridor It forms the steep hill slopes and is typically mantled by colluvium or rock talus. Boreholes were drilled at the locations where peat layer thickness was the largest, the peat was softer than at other locations and where high new fill embankments were required. The peat parameters were chosen based on the consideration of the field and laboratory test data, previous case studies for similar ground conditions in the area and were refined based on the results of the construction monitoring. The modulus E of the peat is very low due to its soft nature and high void ratio
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