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# 3D Stratigraphy in Deep Excavations

### Automatic generation with DeepEX 3D Finite Element Analysis

1. Introduction

In deep excavation projects, understanding the subsurface conditions is crucial for effective design and execution. Geotechnical reports, derived from borehole data, provide insights into soil properties and stratigraphy. However, in large project areas, significant variations in soil layer elevations can occur, posing challenges in accurately modeling the 3D stratigraphy. Traditionally, engineers resort to using the closest boring data or design for the most critical scenario, which can be inefficient and time-consuming. Estimating the actual 3D stratigraphy involves complex mathematical models and assumptions, often requiring considerable effort.

DeepEX 3D Finite Element Analysis revolutionizes this process by enabling rapid and precise estimation of 3D stratigraphy. This article explores how DeepEX leverages borehole data to automatically generate 3D stratigraphic models, simplifying the design process for geotechnical engineers.

Figure 1: 3D stratigraphy in DeepEX

2. 3D Stratigraphy Generation in DeepEX 3D FEM

DeepEX 3D FEM software allows for the swift generation of 3D stratigraphic models using borehole data. Engineers can import borehole information into the software, which then performs soil interpolation and extrapolation to define the stratigraphy.

Interpolation: This involves connecting two known surface points of the same soil type, extracted from borehole data, to calculate the elevation (z-value) for any point within the defined area. Linear interpolation creates a triangular mesh, often resulting in angular surfaces, while bicubic interpolation uses a smoother, curve-based approach for more realistic modeling.

Extrapolation: This process estimates soil elevations beyond the area defined by the boreholes, within the limits of the 3D FEM design. The nearest neighbor method assigns the elevation of the closest borehole to these points, while linear extrapolation uses lines passing through boreholes to determine elevations, extending the triangle mesh approach beyond the borehole-defined area.

3. Example: 3D Stratigraphy for a Braced Excavation 3D FEM model with DeepEX

To illustrate the capabilities of DeepEX, we consider a cantilever excavation model using the 3D Finite Element analysis method, showcasing the automatic 3D stratigraphy generation.

Step 1: Define Boreholes

In DeepEX, a series of boreholes are defined, specifying the position for each boring (X and Y coordinates). In this example, we use six boreholes.

Figure 2: Borings, boring location and soil layers in DeepEX

Step 2: Generate and Analyze a 2D Excavation Model

A 2D model of a 6 meters deep excavation with one level of struts is created, analyzed, and optimized in DeepEX.

Figure 3: 2D excavation model - 2D Finite Element Analysis in DeepEX

Step 3: Generate the 3D Frame Model

Using the DeepEX 3D Frame wizard, the 3D frame model is generated, displaying all borehole locations on the project plan view.

Figure 4: DeepEX 3D Frame Model with all boring locations

Step 4: Generate the 3D Finite Element Model

By selecting the corresponding button in the 3D FEM tab in DeepEX, the 3D Finite Element model is generated automatically, including all construction stages. Model limits and the density of the 3D FEM mesh can be adjusted.

Figure 5: Generated 3D FEM model in DeepEX with a single boring

Step 5: Apply 3D Stratigraphy Options

The 3D Stratigraphy options in DeepEX allow the selection of multiple borings for stratigraphy generation. Interpolation and extrapolation options are chosen, such as bicubic interpolation and nearest neighbors extrapolation.

Figure 6: 3D Stratigraphy options for the DeepEX 3D FEM

Figure 7: 3D stratigraphy, automatically generated on the DeepEX 3D FEM model

DeepEX generates the 3D FEM mesh based on the selected mesh density. The software can display soil, wall, and support displacement and settlement shadings, moment and shear shadings for walls, support axial reactions, moments, and structural checks for struts, tiebacks, and walers according to selected structural codes.

Figure 8: Generated 3D FEM mesh in DeepEX

Figure 9: Surface settlements shadings & structural checks from DeepEX 3D FEM analysis

4. Conclusion

DeepEX 3D Finite Element Analysis software significantly enhances the efficiency and accuracy of 3D stratigraphy generation in deep excavation projects. By automating the interpolation and extrapolation of borehole data, DeepEX allows geotechnical engineers to quickly create realistic 3D models, reducing the time and effort traditionally required. This innovative approach not only improves the design process but also ensures more reliable and optimized excavation solutions, addressing the complexities of varying soil conditions across large project areas.

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