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Effect of Surcharge Analysis on Cantilever Excavation Design

A. Introduction

Selecting the appropriate surcharge method can have a significant impact in cantilever sheet pile design.

In this article we examine the impact of several external surcharge distribution approaches on the design of a cantilever excavation system.

Different scenarios for an external distributed surcharge and a 3-Dimensional load are considered. The wall embedment and sheet pile section is optimized for each case with our shoring design software – DeepEX.


Tables 1 and 2 summarize assumed soil layer and initial wall section properties respectively.

Figure 1 presents the generated model in DeepEX.


Table 1: Soil Layers (Stratigraphy) – Soil Properties

Table 2: Default Wall Properties


Figure 1: Cantilever Sheet Pile Wall – DeepEX Model


B. Examined External Surcharge Cases


The following cases are evaluated:


Case 1: Distributed Surface Load – Elasticity Equations (Boussinesq etc.)


Case 2: Distributed Surface Load – 2-Way Distribution Method


Case 3: Distributed Surface Load – 1-Way Distribution Method


Case 4: Distributed Surface Load – Elasticity Equations x2 (AREMA Specifications)


Case 5: 3D Load (Footing) – Distributed Load – Elasticity Equations


Case 6: 3D Load (Footing) – Distributed Load – 2-Way Distribution from Soil Friction


The following figures illustrate the related settings both for the external strip load and for the 3-D Footing load in DeepEX Software.

Figure 2: Distributed Load Settings & External Load Analysis Options – DeepEX Software


Figure 3: 3D Footing Load Settings & Analysis Options – DeepEX Software


C. Analysis Settings

All the examined case models will be analyzed with the Free Earth Method for cantilever excavations (LEM approach) assuming a wall-soil interface friction angle at 33% of the soil friction angle.

Figure 4: Analysis Settings in DeepEX Software


Wall embedment will be optimized by requiring a minimum wall embedment FS of 1.5 on rotation.

Figure 5: Automatic Depth Optimization Options in DeepEX



D. Analysis Results & Wall Optimization

Figure 6: Case 1 – Elasticity Equations: Wall Embedment FS, Wall Moment & Surcharge Pressure Diagrams


Figure 7: Case 2 – 2-Way Distribution: Wall Embedment FS, Wall Moment & Surcharge Pressure Diagrams, Pile Section Optimization Options


Figure 8: Case 3 – 1-Way Distribution: Wall Embedment FS, Wall Moment & Surcharge Pressure Diagrams


Figure 9: Case 4 – Elasticity x2 (AREMA): Wall Embedment FS, Wall Moment & Surcharge Pressure Diagrams


Figure 10: Case 5 – 3D Footing – Elasticity Equations: Wall Embedment FS, Wall Moment & Surcharge Pressure Diagrams


Figure 11: Case 6 – 3D Footing – 2-Way Distribution from Soil Friction: Wall Embedment FS, Wall Moment & Surcharge Pressure Diagrams


E. Analysis Summary & Conclusions

Table 3 summarizes the calculated maximum moments, the minimum required wall embedment depths and the optimum structural section for each load case.


Table 3: Analysis Summary

​Optimum Wall Embedment


​Min Wall Embedment FS

​Optimum Structural Section

​Maximum Moment

​Moment Check Ratio

​Case 1

​18.5 ft

​1.569

​AZ12-770

​45.6 ksf

​0.788

​​Case 2

​18 ft

​1.6

​AZ12-770

​37.7 ksf

​0.651

​​Case 3

​18.5 ft

​1.569

​AZ12-770

​41.9 ksf

​0.723

​​Case 4

​22 ft

​1.57

​AZ20-800

​74.5 ksf

0.803

​​Case 5

​15.5 ft

​1.572

​AZ12-770

​27.8 ksf

​0.48

​​Case 6

​16 ft

​1.581

​AZ12-770

​27.8 ksf

​0.48

From all the above examined scenarios it is clear that the selection of the surcharge distribution approach can have a big impact on the design project’s cost.

Our clients and our workshop participants already know the best method!

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