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DESIGN OF A RETAINING WALL SYSTEM AS PART OF A ROAD SCHEME

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Introduction

UNIVERSITY OF NEWCASTLE UPON TYNE Department of Civil Engineering and Geosciences COURSEWORK- CIV964/CW/2005 DESIGN OF A RETAINING WALL SYSTEM AS PART OF A ROAD SCHEME BY: Mr Godwin Eton A59089203 TABLE OF CONTENTS 1.0 introduction and project brief ... ... ... ... ... ... ... 2.0 subsurface condition ... ... ... ... ... ... ... ... 3.0 laboratory and field investigations, results ... ... ... ... ... 4.0 foundation design option analysis ... .... ... ... ... ... ... 5.0 foundation type option recommenced ... ... ... ... ... ... 6.0 shallow foundation options ... ... .. ... ... ... ... ... 7.0 settlement and rates of settlements ... ... ... ... ... ... 8.0 deep foundation options ... ... ... ... ... ... ... ... 9.0 summary and recommendations ... ... ... ... ... ... ... 10.0 cost implications ... ... ... ... ... ... ... ... ... LIST OF FIGURES Figure 1: Cross-section showing the subsurface profile at the project site ... ... Figure 2: Plan view of the project site showing column spacing ... ... ... Figure 3: Schematic representation of the proposed square pad ... ... ... foundation with vertical load Figure 4: Schematic representation of the proposed of embedment of the piles along the longitudinal axis of the proposed building ... ... ... Figure 5: Penetration of single pile into the subsurface ... ... ... ... Figure 6: Load on a pile group arrangement ... ... ... ... ... ... Figure 7: Penetration of pile group into the subsurface at case #1 ... ... ... Figure 8: Pile cap over four piles to be employed at the project site ... ... ... Figure 9: Schematic representation of the settlement based on the ... ... ... equivalent raft concept... ... ... ... ... ... ... ... List of Tables Table1: Summary of geotechnical properties of the subsurface at the project site ...

Middle

A potential slip surface was assumed to lie within the laminated clay layer hence; it was taken as the boundary between the upper and the lower soil layers. Slope analysis took place in two stages, first the stability of the existing slope was analysis and after which stability was analyzed with the retaining wall in place to assess for possibility of failure. Results from computer Run Following the above analysis, results showed that the existing slope is stable with a Factor of Safety of 4.03. For the slope with the retaining wall no failure plan was obtained below depth of 8.00 meters implying that the wall is stable at a depth of 15.00 meters of embedment. A Factor of Safety of 1.33 was obtained. Results of the computer runs are presented in figures 3 and 4 below. Figure 3: Slope Stability analysis for the Existing Slope before the emplacement of the wall Figure 4: Slope Stability analysis for the Existing Slope after the emplacement of the wall 6.0 3.0 OPTION ANAYSIS Remarks DISCUSSION IN RELATION TO THE DESIGN AND CONSTRUCTION OF THE RETAINING WALL AT THE PROJECT SITE Retaining Wall Options Analysis and Recommendation. The most common types retaining whish can be employed for the proposed project include: Gravity concrete wall, cantilever T-reinforced concrete wall, cantilever with sheet pile base and embedded wall (propped or un-propped) The stratigraphic arrangement over the whole plan area of the site, led to the early decision to use a single-propped embedded Diaphragm wall as retaining wall system to provide both temporary and permanent support. Alternative considerations were Cantilever free standing wall system, Cantilever wall system on pile foundations and gravity wall. These were quickly discarded because of cost implications, restricted access at proposed road below the wall, proposed retained height of 6.50 meters, enormous earthworks that will be involved and unfavourable subsurface conditions. Gravity wall was not considered because of height restriction of which Clayton et all (1993)

Conclusion

Design Philosophy The limit state design philosophy is adopted and it is assumed that the design will satisfy both the ULS and SLS. Different methods are employed to calculate the Factor of Safety. Determination of Depth of Embedment The detailed calculations involved assessment of the depth of embedment at both the two axes namely the eastern and southern axes. (figure 6a) The worst case (with the thick layer of laminated clay) is considered for detailed calculations (Figure 6b). Computer runs for the western side are also included in this report. N S q kN/m2 (surcharge) = 10 kN/m2 Proposed engineering fill q Figure 6: Cross section of the Single-propped Diaphragm Wall proposed for the project site Note: The position of the prop is chosen as 3.5m below the new ground surface in order to avoid the two made grounds which are likely to reduce the prop force when installed. However, additional prop can be installed at a shallower depth for added stability of the proposed wall. 5.0 Summary And Concluding Remarks Remarks A retaining wall system involving Reinforced concrete diaphragm wall has been proposed for used as a retaining structure at the proposed project site. The wall should be installed at an embedment depth of 8.50 and 11 meters corresponding to a Factor of Safety of between 1.5 - 2.0, and a retained height of 6.50 meters. A single propped should be installed at a depth of 3.50 meters from the top of the fill level. In addition, 0.5 meter allowance was made the proposed road pavement. Summary of the calculated Factor of Safety (FoS) for the various stages of work are presented in table 4 below. Table 3: Summary of Calculated Factor of Safety Stage of work Permanent works Temporary short term Temporary long term Remarks Fos (8.5m) West East West East West East 1.9 1.5 1.8 1.2 2.0 2.2 OK Fos 11.4 m - 2.0 - - - - OK Finally, it is believed that the above findings, comments, discussions and recommendations would be of assistance in the deliberations and decisions in the process of constructing the envisaged structures.

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