Purpose and principle of pre-loading

A surcharge usually consists of a temporary load of sand or other material, which is placed on top of the reclaimed area that needs to be consolidated. Once sufficient consolidation (usually expressed in terms of settlement or dissipation of excess pore pressure) has taken place, the surcharge can be removed and construction activities may start. The thickness of a surcharge may vary considerably, but will generally be in the range of 2-10 m (i.e., a surcharge of approximately 35 kPa 180 kPa when placed above the water table). 

A surcharge consisting of sand is generally easy to place and the most cost-effective method to accelerate the settlement process. This is particularly true if the material 

Method Techniques Soil types Application depth depth 

Consolidation Pre-loading with clay, peat, silt, but Drains at depth. up to 

During the design phase analyses have to be made to predict the settlements (see section 8.5.3.2) as a function of the time and the surcharge load and, if applicable, the spacing of the vertical drains (see section 7.4.2). Input for these calculations has to be derived from the results of site investigations and laboratory testing (see section S.4.2.2). 

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