Design and analysis of deep excavation geotechnical engineering

At the end of the project a student should be able to: 

• Design and analyse deep excavations to Eurocode 7. 

• Use numerical analysis tools exemplified by OptumG2. 

• Present your work (calculations and text) in report format to a professional standard. 

COURSEWORK BRIEFING SHEET 

Background This coursework involves the analysis and design of a propped excavation in a sandy soil as shown in Figure 1. The excavation is 12 m deep and 15 m wide and is supported by steel sheet piles. The embedment depth is 4 m. The walls are connected by props with a spacing of 5m at the ground level. On the left side of the excavation a surcharge of 20 kN/m2 (permanent) applies. 

Figure 1: Propped excavation. 

Soil data 

φk (°) φd (°) γ (kN/m3) E (MPa) ν ψk (°) K0 37 31 18 40 0.2 7 0.4 

Design parameters are to be used for ULS analyses while characteristic parameters are to be used for SLS analyses. 

Question 1 [10/100] Sketch the earth pressure distributions corresponding to “free earth support” conditions at the front and back of the left wall (with maximum values indicated). The earth pressure coefficients are to be determined from the diagrams or tables in Appendix 1. 

Question 2 [20/100] Assuming that the wall strength is sufficient, show that the prop strength is sufficient. Hint: use horizontal equilibrium to show that the necessary prop force is less than the maximum one. 

Question 3 [20/100] Assuming that the wall strength is sufficient, show that the embedment depth is sufficient. Hint: use moment equilibrium about the top of the wall to show that an external moment with the appropriate sign is necessary to bring the wall to failure. 

Question 4 [25/100] Using OptumG2, determine the minimum allowable wall strength assuming ULS conditions. 

Question 5 [25/100] Using an AZ 25-800 steel sheet pile profile (see specifications below), perform an excavation analysis to determine the maximum deflection of the left wall. The walls and the props can be wished in place and the surcharge acts from the beginning. Use 2 m excavation steps and plot the maximum deflection of the left wall as function of excavation depth. The stiffness of the props can be set to EA = 420,000 kN. Figure 2: AZ 25-800 steel sheet pile profile. 

You are to submit a report in PDF format. The report must be of a professional standard. All assumptions, results, etc should follow from the report. Results without proper documentation will be ignored. 

Appendix 1: Earth pressure coefficients 

The active and passive earth pressure coefficients are given in the diagrams and tables below and function of the friction angle, f, and the soil-wall interface roughness, d/f. 

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