Anchored Wall Example Secant Pile Wall with Tiebacks

DEEPEX EXAMPLE: SECANT PILES WITH TIEBACKS

DEEP EXCAVATION 1

Anchored Wall Example – Secant Pile Wall with Tiebacks (English units)

Deep Excavation LLC Software program: DeepEX 2018

Document version: 1.0 September 3, 2018

www.deepexcavation.com www.deepex.com


DEEP EXCAVATION 2

A. Project description In this example we will design an anchored secant pile wall with 3 tieback rows, supporting a 40ft 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


DEEP EXCAVATION 3

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 diameter 1.72 ft

Steel pile section W12x96

Secant pile spacing 1.22 ft

Steel A50

Wall depth 60 ft

Table 5: Support parameters.

Tieback 1 Tieback 2 Tieback 3

Tieback elevation on wall -10 ft -20 ft -30 ft

Tieback spacing 6 ft 6 ft 6 ft

Angle 20 deg 20 deg 20 deg

Free length 27.3 ft 22.5 ft 17.8 ft

Fixed length 35 ft 35 ft 35 ft

Support section 5 Strands x 0.525in 5 Strands x 0.525in 5 Strands x 0.525in

Prestress 70 kips 70 kips 70 kips


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 Limit Equilibrium Analysis method to our model. 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.


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 an anchored wall model). Next, we define the project dimensions (final excavation depth, walls depth, excavation width, top of the wall elevation and water table). Finally, we define the support properties (in this case tieback spacing and the tieback structural section). The software will use the same properties (spacing, structural sections etc) for all created supports. Later we can access each support on the model area (double-click on the support) and edit the specific support properties.


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.


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.


DEEP EXCAVATION 8

• 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.


DEEP EXCAVATION 9

• 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.


DEEP EXCAVATION 10

• 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.


DEEP EXCAVATION 11

The software automatically creates all project construction stages, according to our selections in the Model Wizard. The following Figures present the models in Stages 5 and 7 respectively:

Figure: Generated Model – Stage 5.

Figure: Generated Model – Stage 7.


DEEP EXCAVATION 12

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 following figures present some graphical results from the results tab of DeepEX.

Table: DeepEX critical results/stage

Figure: Wall moment and shear diagrams, Stage 7.


DEEP EXCAVATION 13

Figure: Wall deflections and soil pressures diagrams, Stage 7.

Figure: Wall embedment safety factors, Stage 7.

Documents

Anchored Wall Example Secant Pile Wall with Tiebacks