publicatie: Construction and Survey Accuracies for the execution of rockworks

1 Introduction

1 Introduction

Wherever coastal and embankment protection works are being executed, dredging and rock dumping play an important factor in the work. The accuracy with which these activities are to be carried out are subject to the requirements specified in a contract. Those requirements arise from considerations of, amongst other aspects, the function that the completed work must fulfill. Additionally, there are practical limits to the placement accuracy that can be achieved. In practice, it is impossible to make the surface of a dredged area or a dumped rock site completely flat, even if cost is not a consideration. This can create a certain tension between the requirements from the designer, those which the contractor can achieve (even with the application of maximum effort) and economic considerations. Furthermore, during monitoring of the completed works surveying errors, either systematic or not, are always present; their nature and extent can be the source of vigorous discussions among the parties involved. A specification writer should have a sound understanding of these aspects in order to be able to prevent troublesome clashes between the clients and the contractors for this type of work. In addition, it is important that the clients and contractors themselves have the necessary understanding of these topics. In the past contractual problems have arisen during the execution of dredging and dumped rockworks as a result of unrealistic, unachievable, and/or unnecessarily strict requirements in the specifications.

These problems could probably have been avoided if the parties involved had a better understanding of construction and surveying at the start of the entire process. As a result of these issues the steering committee Dredging, Coastal and Embankment Works of SBRCURnet SBRCURnet, an independent research network for the entire construction industry.established a working group in 2000 to investigate and systematize these issues. That working group presented its findings in a technical report. However, that report was not deemed suitable for clients, contractors and the specification writers who are not yet familiar with this subject. Therefore in 2001 the booklet ‘Construction and survey accuracies for the execution of dredging and stone dumping works’ [22] was published, which gave a brief summary of the most important factors. The present guideline is an update of the 2001 booklet. This update includes a more extensive view on survey technology and on construction considerations. Also included are the results of pit trials conducted for the Maasvlakte 2 Project, the 2000 ha port extension project for the Port of Rotterdam. This guideline is intended primarily to provide information for the clients, contractors, specification writers and engineers.

This guideline contains the following structure:

  • Construction aspects
  • Measurement aspects
  • Evaluation aspects

In Chapter 2 a brief summary is given of common construction methods in the marine environment, along with a description of the main factors that determine the quality of the rockwork structures. The concept of construction accuracy is explained, with a qualitative and quantitative examination of this accuracy in relation to the various dredging and rock dumping methods.

In Chapter 3 a similar explanation if provided on the concept of surveying accuracy in relation to the various systems for the determination of position and levels.

Chapter 4 addresses the evaluation of completed marine structures. Examples are given illustrating the evaluation of the average layer thickness, the minimum layer thickness and the highest absolute level of a rock layer. Lastly, some concluding remarks and recommendations for the contractual setting between clients and contractors are given. For many of the parties involved it will mainly be this last part that will be of interest.

The quantitative information provided must be seen as indicative, as it applies only to the specified situation. Deviations from these indications are certainly not inconceivable for other project or working methods.