DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 1

Circular Shaft Example – Secant Pile Wall (English units)

Deep Excavation LLC Software program: DeepEX 2018

Document version: 1.0 January 4, 2019

www.deepexcavation.com www.deepex.com

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 2

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.

Figure: Project model.

Table 1: Soil properties.

Soil Layer Soil Type Design parameter

φ’ (deg)

C’/Su (psf)

γ (pcf)

γdry (pcf)

ELOAD

(ksf) ERELOAD

(ksf)

F Fill 25 0 120 120 300 900

C Clay 29 1300 116 116 400 1200

S1 Sand 32 0 130 130 600 1800

S2 Sand 34 10 135 135 900 2700

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

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 3

Table 4: Wall parameters.

Pile diameter 1.72 ft

Steel pile section W12x96

Secant pile spacing 1.22 ft

Steel A50

Wall depth 40 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

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 4

B. Modeling with DeepEX

The model will be created using the DeepEX Model Wizard:

Define Analysis Methods:

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.

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 5

Define project type and dimensions

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).

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 6

Define soil types and stratigraphy

Figure: Soil Properties and Soil Layers in DeepEX Wizard.

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.

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 7

Define wall type and wall section properties

Figure: Wall types in DeepEX Wizard.

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.

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 8

Supports

Figure: Support Types in DeepEX Wizard.

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.

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 9

Define Stages – Support Elevations

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.

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 10

Define Surcharge

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.

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 11

Define structural codes:

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.

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 12

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:

Figure: Generated Model – Stage 3.

C. Results in DeepEX

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 EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 13

Table: DeepEX critical results/stage – Hoop Results

Figure: Wall moment and hoop force, Stage 3.

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