Deep Excavation model in Abu Dhabi, UAE

Excavation Model Comparison between DeepEX, FREW and PLAXIS 2D

Deep excavations in urban coastal environments present significant geotechnical and structural challenges, particularly when groundwater conditions, wall stiffness, and support system interaction strongly influence excavation performance. Reliable prediction of wall movements and support reactions is therefore essential for both safety and serviceability.

This article revisits the performance of a deep excavation constructed for the Emirates Pearl Tower and Bab Al Qasr Hotel project in Abu Dhabi. The excavation was originally presented by Walid Jaber and Amr Al Degwe during the DFI Annual Conference 2015 as a case study evaluating excavation performance and instrumentation data.

The project involved a 20 m deep excavation supported primarily by a 1.0 m thick reinforced concrete diaphragm wall with three levels of ground anchors. In one corner of the excavation, the support system transitioned to two levels of steel struts.

The original publication compared measured excavation performance against numerical predictions using FREW and PLAXIS 2D. In this study, the excavation was reanalyzed using the DeepEX platform to evaluate the correspondence between computed and observed behavior.

Excavation Support System

The excavation support system consisted of:

·         A 1.0 m thick reinforced concrete diaphragm wall

·         Three levels of prestressed ground anchors

·         Localized steel strutting in one corner region

·         Groundwater control measures

·         Instrumentation for wall displacement and support load monitoring

Because the excavation was constructed in a coastal environment with significant groundwater influence, both soil and seepage behavior played a critical role in the overall response of the system.

Figure 1 presents the DeepEX model developed for Section A, including the diaphragm wall geometry, anchor layout, groundwater conditions, and the resulting wall bending moment and displacement distributions at the final excavation stage.

Figure 1. DeepEX numerical model for Section A used to evaluate diaphragm wall behaviour, support loads, and excavation-induced deformations.

Numerical Modeling Approach

The published excavation was reanalyzed using modeling assumptions consistent with those presented in the original study. Where information was unavailable, reasonable engineering assumptions were adopted based on available geotechnical data and published literature.

The evaluation focused on comparison of:

·         Wall displacements

·         Support reactions

·         Wall bending moments

·         Groundwater flow response

Both nonlinear soil response and staged excavation effects were considered in the DeepEX analysis.

Comparison with Measured Performance

The comparison showed that the DeepEX model produced wall displacements that were closest to the measured inclinometer data when compared with the previously published numerical analyses.

Support reactions predicted by DeepEX, FREW, and PLAXIS 2D were generally in reasonable agreement with the field measurements. However, instrumentation data indicated that maximum support loads occurred only locally and during limited excavation stages.

The DeepEX nonlinear analysis also produced smaller wall bending moments than FREW and moments comparable to those obtained from PLAXIS 2D.

Table 1 compares the maximum wall bending moments, support reactions, and horizontal wall displacements obtained from the DeepEX analysis against the results reported using FREW and PLAXIS 2D, as well as the available field measurements.

Table 1. Comparison of maximum wall bending moments, support reactions, and horizontal wall displacements predicted by DeepEX, FREW, and PLAXIS 2D against field measurements

Because the measured wall displacements were lower than many of the predicted values, the DeepEX bending moment distribution was considered more representative of the actual wall behavior.

Importance of Groundwater Flow Modeling

One of the most important findings of the reanalysis was the influence of groundwater conditions on excavation response.

The study demonstrated that realistic representation of groundwater table conditions and seepage flow was essential to accurately capture:

·         Lateral wall movements

·         Anchor and strut loads

·         Effective stress redistribution

·         Overall excavation response

In this case, full-flow groundwater analysis was necessary to obtain realistic predictions. Simplified groundwater assumptions produced noticeably different wall forces and deformation behavior.

This observation is particularly important for excavations in coastal or high groundwater environments, where pore pressure changes can significantly alter wall performance.

Figure 2 illustrates the overall excavation response at the final construction stage, including wall deformation profiles and bending moment distributions along both diaphragm walls.

Figure 2. Predicted bending moments and wall displacements at the final excavation stage illustrating the overall excavation response and soil–structure interaction. Modeling recommendations.

For deep excavations in coastal urban environments, the analysis should carefully consider:

·         Staged excavation and support installation

·         Groundwater flow and seepage conditions

·         Diaphragm wall stiffness and embedment

·         Nonlinear soil behavior

·         Anchor and strut stiffness

·         Soil–structure interaction effects

·         Comparison with field instrumentation data

·         Sensitivity analysis for groundwater assumptions

Field measurements remain one of the most valuable tools for validating excavation models and calibrating numerical assumptions.

Conclusion

The Abu Dhabi excavation case study demonstrates the importance of realistic groundwater and soil–structure interaction modeling in deep excavation analysis.

The DeepEX reanalysis showed good agreement with measured wall displacements and support reactions while producing realistic bending moment distributions comparable to advanced finite element analysis results. The study also highlighted how groundwater flow conditions can significantly influence excavation behavior and should be carefully incorporated into the numerical model.

For complex urban excavations, combining staged analysis, nonlinear soil response, and seepage modeling can substantially improve prediction accuracy and provide engineers with greater confidence in excavation performance assessments.

References

Walid Jaber and Amr Al Degwe (2015). Deep Excavation Performance for Emirates Pearl Tower and Bab Al Qasr Hotel, Abu Dhabi. Proceedings of the DFI Annual Conference 2015.

Clough, G.W., and O’Rourke, T.D. (1990). Construction Induced Movements of In-Situ Walls. ASCE Specialty Conference on Design and Performance of Earth Retaining Structures.

Ou, C.Y. (2006). Deep Excavation: Theory and Practice. Taylor & Francis.

Let us show you how to reduce your design time by up to 90%!

Free Web Presentation - Meet our Experts

30min

Book Now