Secant Pile Wall Design and Analysis Example

Secant Pile Wall Design and Analysis example

Secant Pile Wall Design & Analysis example DeepXcav software program (Version 2011) (ParatiePlus within Italy) Document Version 1.0 Issued: 13‐January‐2012 Deep Excavation LLC www.deepexcavation.com

Created by Deep Excavation LLC, Astoria, New York

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Secant Pile Wall Design and Analysis example A. Problem description We are going to design a 12 m excavation between two secant pile walls. The distance between the two walls is 8 m. There wall depth will be 16 m. The minimum required dewatering level is ‐1 m below maximum excavation level. In this model we will use strut supports, Metric Pipes with Diameter = 0.6 m. Concrete cube strength: 40 N/mm2, so we will use concrete C 32/40. Figure 1 presents the construction site and Figure 2 presents the Design Section AA, which is marked in Figure 1 and will be analyzed. Tables 1 and 2 present the soil properties and the wall properties respectively.

Figure 1: Site plan and Design Section AA.


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Figure 2: Design Section AA. Table 1: Soil parameters. Soil Layer MDS VDS

φ’ C’ γ (deg) (kPa) (kN/m3) 34 0 19 41 0 19.5

Design parameter KY ELOAD γ KX (m/s) (m/s) (kN/m2) (kN/m3) 19 1.15 E‐5 1.15 E‐5 30000 19.5 1.15 E‐5 1.15 E‐5 60000

ERELOAD (kN/m2) 90000 180000

Table 2: Wall parameters. Pile diameter (D) Pile spacing Pile length Concrete Steel Rebars Number of rebars per pile Shear reinforcement Shear reinforcement spacing

0.6 m 0.6 m 16 m C 32/40 S 500 D25 10 Spiral Reinf D10 250 mm


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Secant Pile Wall Design and Analysis example B. Modeling in DeepXcav Now we will present how this model can be designed using DeepXcav. In DeepXcav we can add construction stages by pressing the Add Stage button in the Model tab. Stage 0:

First, we modify our soil layers. In the General tab of DeepXcav we press the button (Figure 3). In the dialog that appears we choose to change the general elevation to the elevation 7.2 m, and to apply this change to all boreholes (Figure 4). Next, we press the button in the model tab in order to add a second wall to the model (Figure 5). We right click on each wall and we choose to Deactivate it for this stage.

Figure 3: The General tab of DeepXcav and the Move model Elevations button.

Figure 4: The Move Elevations dialog. Created by Deep Excavation LLC, Astoria, New York

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Figure 5: The two walls, deactivated in Stage 0. Next, we will apply the soil properties. To do so, we go to the Model tab of DeepXcav and we press the button in order to modify our stratigraphy. When we do so, the Edit Borings and Soils dialog appears (Figure 6). Here we choose to add a new soil with the top elevation of 0. We press the Edit button next to each soil layer in order to edit the layer properties. Then the Edit soil data dialog appears (Figures 7 and 8).

Figure 6: The Soil Layers dialog. Created by Deep Excavation LLC, Astoria, New York

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Figure 7: The Edit soil data dialog.

Figure 8: Soil model and Loading – Reloading Elasticity parameters. Created by Deep Excavation LLC, Astoria, New York

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Secant Pile Wall Design and Analysis example Next, we edit the wall properties. We double click on each wall and we apply the changes (Figure 9). To edit the wall section properties, we press the Edit Section button. In the dialog that appears, we choose to use secant pile walls and we apply our preferences (Figures 10 and 11).

Figure 9: The Edit wall data dialog.

Figure 10: The Edit wall section properties dialog.


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Figure 11: The concrete and rebar properties. Stage 1: In this stage we will modify the soil inclinations in order to design our model. To create the bench surfaces, we right click on our model, first on the left side of the left wall and next on the right side of the right wall, and we choose to “Set left bench surface” and “Set right bench surface” respectively (Figure 12). Then the Modify surface section dialog appears, and we apply our preferences (Figure 13).

Figure 12: The available surface options.


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Figure 13: The modify surface section dialog. Next, in the Model tab we choose to excavate between the 2 walls to the Elevation 4 m (Figure 14) and by right clicking on each wall we choose to activate it. Figure 15 presents the model of this stage.

Figure 14: Model tab: Excavate between the two walls to Elevation 4 m. Created by Deep Excavation LLC, Astoria, New York

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Figure 15: Model, Stage 1. Stages 2 to 8: In these stages we excavate and apply the strut supports step by step. To excavate, we change the Layer elevation between the 2 walls (Figure 14). We are careful to keep the water table at least 1 m below the excavation. Table 3 presents the soil and water table elevation in each construction stage. Table 3: Soil and Water table elevations. Stage Stage 2 Stage 4 Stage 6 Stage 8

Soil Elevation (m) 3.4 ‐1.1 ‐4.6 ‐8

Water table elevation (m) 1 ‐2.1 ‐5.6 ‐9

In the stage that follows each excavation, we add a strut support to the model. To do so, we click on the button in the toolbar on the left side of the screen, and then we click first on the left and next on the right wall. In the dialog that appears we can define the strut properties (Figure 16). Table 4 presents the strut and excavation levels when each strut is first installed. Table 4: Soil and Water table elevations. Stage Stage 3 Stage 5 Stage 7

Soil Elevation (m) 3.7 ‐0.8 ‐4.3


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Figure 16: Edit Strut properties dialog. In Stage 3 we add a surface load on the left wall of 15 kPa. To do so, we click on the tool button on the left vertical tool bar. Then we click on the left point and next to the surface point next to the wall. When we do so, the dialog on Figure 16B appears. Here we select the "Treat as surface load option" and change the vertical surcharge intensity to 15kPa on both point 1 (left) and point 2 (right).


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Figure 16B: Surcharge dialog In the Analysis tab of DeepXcav we apply our analysis options (Figure 17).  

We choose to use the Beam on Elastoplastic Foundations Analysis Mode (non‐linear) We choose to apply wall friction as a percentage of soil friction on both walls (66%)

Figure 17: Analysis options. Finally, we go to the Design tab of DeepXcav and we apply a Wall Safety Factor of 1.5 (Figure 18).


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Figure 18: Wall Safety Factor. Stage 9: We add this last stage to the model in order to change the water behavior to a full flownet for this stage (in all other stages we will keep a Simplified flow). In the Analysis tab, we choose to use a flownet and to apply this change only to the current Stage (Figure 19).

Figure 19: Flownet. Created by Deep Excavation LLC, Astoria, New York

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Secant Pile Wall Design and Analysis example C. Results After we perform the calculations we can see the results in the results tab of DeepXcav. We can see various results for each construction stage: 

Wall moments

Figure 20: Wall moment diagrams for stage 8 and 9 respectively (red line is wall capacity). 

Wall shear forces

Figure 21: Wall shear diagrams for stage 8 and 9 respectively (dark red line is wall shear capacity). Created by Deep Excavation LLC, Astoria, New York

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Secant Pile Wall Design and Analysis example 

Wall displacements

Figure 22: Wall displacements for stage 8 and 9 respectively. 

Effective vertical stresses

Figure 23: Effective vertical stress for stage 7 and 8 respectively.


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Secant Pile Wall Design and Analysis example 

Water Pressure shadings (Stage 9 – Flownet analysis)

Figure 24: Water pressure shadings. 

Embedment Safety Factors

Figure 25: Embedment safety factors. From the results above, we come to the following conclusions: a. The shear capacity of the wall is not enough for this model, so we suggest reducing the shear reinforcement spacing. b. The wall embedment is not enough, so we should increase the pile length. c. We should increase the dewatering depth beneath the excavation surface. Created by Deep Excavation LLC, Astoria, New York

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Secant Pile Wall Design and Analysis example We will perform the following actions and recalculate the model:   

We will increase the wall depth to 22 m. We will decrease the shear reinforcement spacing to 125 mm and shear reinforcement diameter to D12. We will set the dewatering level to the elevation ‐10 m for the stages 8 and 9.


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Secant Pile Wall Design and Analysis Example

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