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Secant Pile Wall - Anchored Excavation Design Example

Secant Pile Wall with Tiebacks Supporting a 40ft Excavation


In this example we will design an anchored secant pile wall (1.7ft Secant Piles with W12x96 beams), with three levels of ground anchors, supporting a 40ft excavation. The model is created and analyzed with DeepEX - Shoring Design Software.


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.



Table 2: Stratigraphy.



Table 3: External loads.



Table 4: Wall parameters.



Table 5: Support parameters.



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.


  • 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.


  • 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.


  • 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.


  • 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.


  • 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.


  • 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.


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.


C. Anchored Wall 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 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.


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




















Figure: Wall embedment safety factors, Stage 7.



 


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