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Privacy and Cookies

We may change this privacy notice from time to time by updating this page.

What information do we collect?

When you use this website, we may collect the following information:

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We do this by using cookies, which are small files that help us track how our visitors use the website and enable us to understand where we can improve your experience. If you would like to find out which cookies we use and the information they track see our Cookies Policy.

Once you submit or register information through our website we will know who you are and your activities on this website and information about you and/or your company may be recorded on our systems. For example, we may ask for personal information when you download our software including:

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We may share your personal information with companies acting on our behalf who will only use the information to provide that service. However, we will retain control of your data and any third party service provider that we use must act in accordance with our instructions. We may also share your personal information with a purchaser or potential purchaser of our business.

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You may request details of the personal information that we hold about you under data protection laws. If you would like a copy of the information held about you please write to us at oasys@arup.com or at: Data Protection Officer, 13 Fitzroy Street, London, UK, W1T 4BQ. Please note that we may charge a small £10 administration fee for information requests.

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Data Security

We are committed to ensuring that your information is secure. In order to prevent unauthorised access or disclosure we have put in place suitable physical, electronic and managerial procedures to safeguard and secure the information we collect, including locked cabinets, electronic password protection and pass card access to buildings.

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Website Terms and Conditions

The contents of this web site are protected by copyright and other intellectual property rights under international conventions. No copying of any words, images, graphic representations or other information contained in this web site is permitted without the prior written permission of the webmaster for this site.

Oasys accepts no responsibility for the content of any external site that links to or from this site.

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Software Licensing Terms

Terms and Conditions of Purchase

The full conditions of purchase and maintenance for all Oasys software are set out in the Oasys Software Licence and Support Agreement. All prices are subject to TAX at the current rate.

Prices and specifications are subject to change without notice – please ask for a written quotation.

Although every care has been taken to ensure the accuracy of all information contained herein, the contents do not form or constitute a representation, warranty, or part of any contract.

Superseded Versions of Terms and Conditions

Oasys keeps copies of all superseded versions of its terms and conditions.

Maintenance & Support Services

Support and maintenance is included with all subscription licences for their full duration.

Annual maintenance contracts are available for software under a perpetual licence, prices are based on a percentage of the most recent list price.

This service includes:

  • telephone/fax/email/web based support
  • free software updates available via internet download
  • personalised output header for many products

Advanced Cut and Cover Tunnel Analysis

Software Used on this Project

Project Overview


Following the construction of cut and cover tunnel sections, concerns were raised by the Client about drainage pipes cast into the base slab of the cut and cover tunnel segments. Various additional justification calculations have been carried out by the contractor but there had been no resolution of the issue. Consequently, additional analyses were proposed based on more rigorous methods.

Raison Foster Associates were asked by the contractor to investigate the stresses within the tunnel section base slab for a cut and cover tunnel.

The project is confidential in nature and, as such, the location and specifics of the project has not been included but, the analysis methods and outcome of analysis will be discussed.


Drainage pipes have been cast into the base slab and the client wanted to understand the stresses on these pipes. Consequently, the client required more rigorous analysis using finite element analysis (FEA) methods.

How Oasys proved invaluable


To carry out the FEA check, Raison Foster used Oasys SAFEt (Version 19.0). This program is designed to carry out finite element computations for a wide range of geotechnical situations. The program computes soil stresses, strains and deformations through one more sequences of events allowing staged construction to be considered directly. Time dependent consolidation and steady state seepage can also be modelled. The program provides displacements, total and effective stresses, strains and pore water pressures as either tabulated or plotted output.


A section that was representative of the deeper cut and cover tunnels was chosen for the analysis, The section has been prepared on the basis of as built drawings and a review of the local site investigation boreholes. For the SAFE analyses, a half section has been adopted as shown for an axisymmetric analyses. At this location the excavation is approximately 23m wide with parallel 1.2m wide diaphragm walls providing the temporary works support with or two levels of 1320mm diameter tubular steel props. Excavation at this chainage was taken to 15.5m depth prior to construction of the reinforced concrete tunnel section and backfilling.

Materials and Soil Modelling

Although a range of material models are available, this analysis used the linear elastic model for the structural elements (tunnel segments, diaphragm wall, temporary props e.t.c.) and the elastic Mohr-Coulomb model for the different soils.

The soil stratigraphy along the tunnel is shown below.

The analyses are intended to investigate most probable behaviour under service conditions with final stages to represent service limit (SLS) and ultimate limit (ULS) conditions. Soil design parameters are therefore unfactored for all stages of the analysis. Both drained and undrained soil behaviour was modelled.

Construction Sequence

0.      Initial conditions
1.      Install diaphragm wall and excavate to 5m depth
2.      Prop and excavation to 10.5m depth with dewatering
3.      Prop and excavation to 15.5m depth with dewatering
4.      Construction and delay at formation level with dewatering
5.      Place drainage layer and cast tunnel base slab
6.      Remove lower prop
7.      Complete tunnel segments
8.      Backfill above tunnel to underside of upper prop
9.      Remove upper prop
10.  Backfill above tunnel to ground level
11.  Construct road formation inside tunnel
12.  SLS long term conditions
13.  ULS long term conditions

Alternate analyses have been carried out assuming a construction delay (Event 4) sufficient to allow fully drained behaviour and full dissipation of negative pore water pressures following completion of the excavation.


It was possible to compare the maximum computed bending moment taken from the various SAFE output for comparison with the ultimate bending moment capacity and cracking moment for the diaphragm wall. In all cases the margin between the ultimate bending moment capacity and computed values is sufficient to ensure adequate king term durability and performance of the diaphragm walls. This will ensure any long term support provided by the retaining walls is likely to remain for the design life of the tunnel.

SAFE computed deflections for the tunnel base slab were also reviewed. Net movements were reviewed for the period between casting the base slab and the long term SLS case.

Additional outputs were extracted from the SAFE computations to investigate the likely bearing pressures between the tunnel base slab and the underlying ground. Plotted output for the SLS and ULS analysis stages are shown. For both analysis cases, it is shown that the available bearing capacity exceeds the computed bearing pressure by a sufficient margin.

The drainage pipe in embedded in the base slab about 1.25m from the side of the wall. Maximum computed bending moments, shear force and thrust were extracted from the SAFE results to assess the capacity of the pipe.


Geotechnical Engineer: Raison Foster Associates

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