MWH and Dura Vermeer Milieu BV were jointly asked to provide input on the organisation of earthmoving operations in connection with the construction of an underground railway line in Delft. In consultation with the client, it was decided to have the excavated soil BRL 9335-certified. The project concerns a tunnel track with a length of 2.4 km, to yield an estimated 1.2 million m3 of excavated soil of variable quality. The project will be carried out over the next ten years and is using models that factor in the soil composition and any soil pollution past or present.
The future railway tunnel
The railway tunnel will cut directly through Delft, running past several historic monuments and buildings constructed on footings. Consequently, this places high demands on the workmanship and construction methods used. Part of the railway tunnel will be constructed using the walls/roof method, which causes less vibration and noise and involves diaphragm walls being set at a depth of 24 metres below ground level. Where possible, the work will be done using a standard excavated sheet pile cofferdam.
A number of important preparatory activities were required before actual tunnel construction began. In the run-up to construction, extensive research was done on the soil composition and state of the groundwater. This drew in part on existing lithological data, supplemented with new drilling data. An expected soil quality map (verwachtingswaardenkaart) was compiled based on the data on soil composition and known existing ground pollution. This map was also intended as a guide for earthmoving work over the course of the project. The entire line was also inspected for any possible unexploded explosives, the presence of material suspected of containing asbestos, protected flora and fauna and the nature and quantity of foreign materials in the soil.
The BRL 9335 certification process includes the performance of random checks to ascertain if the information generated by the expected soil quality map corresponds with the situation on-site. This involved the inspection of individual 2,000-tonne soil samples for each soil quality classification, in accordance with the Dutch Soil Quality Decree (Besluit bodemkwaliteit). These inspections determined that the topsoil can be classed as ‘Industry’ and the subsurface as ‘AW2000’. A quality manual for excavated soil was drawn up on the basis of this data, which manual was audited and approved by KIWA. The BRL 9335 certificate allows for the reliable and environmentally sound qualification of soil from large-scale projects of this kind while at the same time boosting efficiency and yielding significant cost savings.
Digital subsurface model
A unique feature of this project is its use of an online subsurface model input with a combination of soil composition data and specifics of the execution. The subsurface model provides insight into where and when the various soil types such as clay, peat, loam and sand will be excavated. This information was elaborated through the interpretation of data from various coordinated as well as specific research reports. The various stakeholders (including the client, soil flows coordinator and competent authorities) were given access to this information to ensure that everyone involved would know which soil would be excavated where and when. A model was also used to determine the scale of the existing pollution.
MWH supplied custom solutions for this extensive, multifaceted project. The project encompassed a wide variety of disciplines that all had to be coordinated, with MWH drawing on its specific soil and infrastructure expertise. The works started in 2010. Soil will be excavated in phases, which are expected to continue until the end of 2014.
- Data collection
- Modelling of surface lithology
- Interpretation of data
- Compilation of expected soil quality map
- Performing soil sample inspections
- Certification assessment
- Compilation of quality manual
- Coordination of soil flows
- Supervision of excavation work
- Soil decontamination
- Work-related health and safety
- Project support
- Build solutions
- Delft, Netherlands
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