A case history of monitoring a wide pile group Part I: geology, single pile analysis and testing, and monitoring data

This is the first of two papers on a wide pile group. In this part, the geology and a geotechnical model of the site are presented, along with the design of a single pile, analysis of a static loading test, and some dynamic tests. The response of the piled foundations comprising 399 bored piles supporting three 70-storey towers on a common mat was monitored over nine years. The records consist of results of a static loading test to 3.5 times the sustained load, dynamic tests of four piles, and monitoring the development of load in 15 piles and settlement of 40 points during construction and nine years following. At end of construction, the perimeter piles received more load from the towers than did the interior piles and the mat settled on average 90 mm. At the end of the monitoring period, due to the general subsidence, the average settlement of the mat had increased by 50 mm. Most of the settlement is considered to originate from the compression of the soil layers below the pile toe level. A subsequent paper will present the analysis and design of the wide pile group, and the numerical analysis of the static loading test on a single pile and of the wide pile group.