Karst Remediation in the Variant to the National Road 9 Between Cascais and Abuxarda, Portugal

Abstract

In the final stages of the contract for the construction of the Variant to the National Road 9 between Abuxarda and Cascais, Portugal, in September 2006, a collapse in the platform occurred, resulting from the presence of an underlying karstic cavity. A treatment solution was implemented, which consisted in cleaning the cavity and filling it with stone materials. However, remaining the doubt about the existence of similar cavities under the road platform and taking into account the vicinity of an overpass, it was conducted additional site investigation, establishing a scenario where a karst system is present, at depths that did not guarantee conditions of functionality and safety of these infrastructures. This scenario led to postpone the entry into service of the road. Considered different options for the treatment of these cavities, it has developed a solution that provided the use of grout injection techniques and /or high viscosity mortars trough, boreholes made from the platform surface and on the perimeter of the Overpass foundations. In order to dispel any doubts about the suitability for the treatment solution, the Owner of Work, appealed an independent Consultant, which, after the analysis of all available information, recommended the partial opening to traffic, conditioned in terms of weight and speed of vehicles. The contract for karst remediation works was held during the first semester of 2008. A closer supervision to this contract, allowed managing and complete the works on schedule and under budget contractually, fulfilling the objectives defined in the project.