Secant Pile Wall - Circular Shaft Design Example

Circular Shaft - Secant Piles - 20ft Excavation

In this example we will design a secant piles circular shaft, supporting a 20ft excavation. The model is created and analyzed with DeepEX - Shoring Design Software.

A. Project Description

In this example we will design secant pile wall circular shaft, supporting a 20ft excavation. The Figure below presents the project model. Tables 1 and 2 present the soil properties and the stratigraphy respectively. Table 3 presents the external loads. Tables 4 and 5 present the wall and support properties respectively. The general ground surface is at El. 0ft and the general water table is at El. -50 ft.

Deep Excavation - Circular Shaft Model in DeepEX

Figure: Project model.

Table 1: Soil properties.

 

Soil Layer

Soil Type

Design parameter

φ’ (deg)

C’/Su (kPa)

γ (kN/m3)

γdry (kN/m3)

ELOAD (kPa)

ERELOAD (kPa)

F

Fill

25

0

19

19

15000

45000

C

Clay

29

65

18.5

18.5

20000

60000

S1

Sand

32

0

20.5

20.5

30000

90000

S2

Sand

34

5

21

21

45000

90000

 

Table 2: Stratigraphy.

Soil Layer

Elevation (ft)

OCR

Ko

F

-0

1

0.577

C

-5

1

0.515

S1

-18

1

0.47

S2

-27

1

0.441

 

Table 3: External loads.

Load

Load Type

Start Point

End Point

Load Magnitude

Load 1

Strip Surcharge

(-51,0)

(-1,0)

0.6 kips

 

Table 4: Wall parameters.

Pile width

1.72 ft

Steel pile section

W12x96

Secant pile spacing

1.22 ft

Steel

A50

Wall depth

60 ft

 

Table 5: Support parameters.

 

Cap Beam

Ring Beam

Thickness

3 ft

1.5 ft

Depth

3 ft

1.5 ft

Elevation on the wall

Top of the wall

-10 ft

B. Modeling with DeepEX

The model will be created using the DeepEX Model Wizard:

  • Define Analysis Methods:

DeepEX Model Wizard - Analysis Methods and Options

Figure: Analysis Methods in DeepEX Wizard.

In this dialog, we choose to apply the combination method to our model (Limit Equilibrium and Non-Linear). For the classical earth pressures in design stages with multiple support levels we define FHWA apparent pressures and for the beam analysis we choose CALTRANS method. The combination method will first run the Limit Equilibrium Analysis and calculate the wall embedment FS, and then will run the Non-Linear Analysis and present these results on the tables and on the model area graphically.

  • Define project type and dimensions

DeepEX Model Wizard - Project Type and Support Section Options

Figure: Project Type and Dimensions in DeepEX Wizard.

In this dialog we select the project type (in this case we select the option to create a circular shaft model). Next, we define the project dimensions (final excavation depth, walls depth, excavation width, top of the wall elevation and water table). 

  • Define soil types and stratigraphy

DeepEX Model Wizard - Soil Properties and Stratigraphy (Borings)

Figure: Soil Properties and Soil Layers in DeepEX Wizard.

 

DeepEX Model Wizard - Soil Type - Soil Properties and Soil Layers

Figure: Soil Properties and Soil Layers dialogs in DeepEX.

In these dialogs we can define the required soil types and the properties for each created soil, as well as, the model stratigraphy by defining the top of the soil layer elevation and the soil type in each layer.

 

  • Define wall type and wall section properties

DeepEX Model Wizard - Wall Type Selection

Figure: Wall types in DeepEX Wizard.

DeepEX Model Wizard - Wall Section Settings and Properties

Figure: Wall Sections dialog in DeepEX.

In these dialogs we select the wall section type (in this case secant pile wall), the steel pile section, the wall spacing and the concrete – steel materials.

  • Supports

DeepEX Model Wizard - Cap Beam and Ring Beam Supports

In this dialog, we define the dimensions of the supports we wish to use in the model. We will use a cap beam and a ring beam at EL: -10 ft. We check the support types and we define the support dimensions.

  • Define Stages – Support Elevations

DeepEX Model Wizard - Construction Stages Generation Options

Figure: Support Elevations in DeepEX Wizard.

In this dialog, we define the depth from the surface or each support level, as well as, the depth below each support level where we wish to excavate in the stages, before the support is installed. The software automatically calculates all elevations (excavations and support installation levels) of these defined depths and generates all intermediate construction stages.

 

  • Define Surcharge

DeepEX Model Wizard - External Load Options

Figure: Support Elevations in DeepEX Wizard.

In this dialog we define the surcharge type and properties, as well as the surcharge modeling options. In this case we will use a 0.6 kips strip surcharge, developed for 50 ft, starting 1ft behind the left wall. After the model is automatically generated by the software wizard, we can access the stages in the model area and add any required additional loads graphically, using the Draw Loads options in the General tab of DeepEX.

 

  • Define structural codes:

DeepEX Model Wizard - Structural and Geotechnical Design Codes and Standards

Figure: Structural Codes in DeepEX Wizard.

In this dialog, we can define the structural and geotechnical design codes that we wish to assign to this model. In this case, we will use US allowable settings for steel design and ACI for concrete.

The software automatically creates all project construction stages, according to our selections in the Model Wizard. The following Figures present the models in Stage 3:

 

 

DeepEX Model - Excavation Model in Stage 3 - Final Excavation

Figure: Generated Model – Stage 3.

C. Circular Shaft Analysis and Results

 

Since the model is ready, we can choose to calculate the design section, pressing on the button .

After the analysis is succeeded, the Summary table appears. The table below includes some critical checks and values for each construction stage. The last columns of the Analysis and Checking summary Table, present the Circular Shaft results (Hoop Buckling Safety actor, Hoop Force etc). The following figures present some graphical results from the results tab of DeepEX.

Table: DeepEX critical results/stage

DeepEX Analysis Results - Analysis and Checking Summary Table

Table: DeepEX critical results/stage - Hoop Results

DeepEX Analysis Results - Analysis and Checking Summary Table - Hoop Forces

DeepEX Analysis Results - Wall Moment and Hoop Force Diagrams

Figure: Wall moment and hoop force diagrams, Stage 3.

DeepEX Analysis Results - Wall Displacements and Soil Pressures Diagrams

Figure: Wall deflections and soil pressures diagrams, Stage 3.

Presentations_DeepEX_Projects.png

 

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