Understanding the Key Differences Between Driven & Drilled Soldier Piles

Introduction:

Soldier pile walls are a versatile and widely used method for retaining soil and preventing erosion in construction and civil engineering projects. Among the various techniques for installing soldier piles, two stand out as popular choices: driven and drilled soldier piles. In this article, we'll explore the fundamental differences between these two methods and when each is most suitable.

Driven Soldier Piles:

Driven soldier piles involve installing vertical piles into the ground by physically driving them into the soil. Heavy machinery, such as pile drivers or hydraulic hammers, are used to force the soldier piles into the ground. Piles are typically made of steel or concrete and are designed to withstand the driving process.

Driven soldier piles are often used for temporary excavations and situations where a quick and cost-effective solution is required. They may not be suitable for sites with hard or rocky soil, as driving piles into such conditions can be challenging.

Advantages:

1. Fast installation.

2. Cost-effective for temporary structures.

3. Minimal site disturbance.

Limitations:

1. Limited to relatively shallow walls.

2. May not be suitable for hard or rocky soil conditions.

Drilled Soldier Piles:

Drilled soldier piles are installed by drilling holes into the ground and then placing the piles into these holes. Drilling equipment is used to create holes for the soldier piles, typically using augers or drilling rigs. Piles are then inserted into the holes, and the annular space is backfilled with grout or concrete.

Drilled soldier piles are suitable for both temporary and permanent retaining walls. They are often used in areas with challenging soil conditions, including hard or rocky terrain.

Advantages:

1. Suited for deeper and taller walls.

2. Versatile and adaptable to various soil conditions.

3. Provides a more stable and long-lasting solution.

Limitations:

1. Slower installation compared to driven piles.

2. Can be more expensive due to the use of drilling equipment and concrete.

Choosing the Right Method:

Selecting between driven and drilled soldier piles depends on several factors, including:

- Project requirements (temporary or permanent).

- Soil conditions (soft or hard soil, rock, etc.).

- Wall height and loadbearing capacity.

- Budget considerations.

A Case Study

Below we present a comparative analysis, depth optimization, and cost estimation for a 20-foot deep excavation model, employing one level of ground anchors. The analysis is conducted using the cutting-edge DeepEX – Shoring design software , leveraging both the conventional Limit Equilibrium analysis method (LEM) and the innovative Non-Linear analysis approach with soil springs (NL).

Case 1: Driven Soldier Piles - Efficiency in Simplicity

Our first scenario involves the utilization of W21x101 driven soldier piles strategically placed at 8-foot intervals. This method showcases the simplicity and speed associated with driven piles, making it a suitable choice for many construction applications.

Case 2: Drilled Soldier Piles - Precision and Stability

In the second scenario, we employ the same structural section for the wall. However, we opt for a more intricate approach by placing the soldier piles within 2.5-foot diameter drilled holes filled with concrete grout. This method underscores the precision and enhanced stability achievable through drilled soldier piles.

Within our DeepEX software, we have the flexibility to adjust pressure widths beneath the excavation, accounting for arching effects on passive pressures. Figure 5 provides a visual representation of pressure width recommendations for soldier pile walls, offering valuable insights into optimizing design parameters. Figures 6 and 7 show the results of our analysis, with the Limit Equilibrium and Non-linear analysis methods, respectively, shedding light on the structural performance of both driven and drilled soldier pile systems. Lastly, Figure 8 presents the cost estimation outcomes, assuming uniform operational costs and project dimensions for both cases.

Key Findings:

Embedment Length: Driven steel beams require roughly 30% more wall embedment length to achieve the minimum recommended wall embedment Factor of Safety (FS) of 1.5 compared to the drilled soldier piles. This highlights the efficiency of the latter in achieving the desired level of safety.

Structural Performance: The calculated wall moment and support reaction results are consistent across both analysis methods in each case. However, the wall displacement of the drilled soldier pile systems is notably smaller, demonstrating their enhanced stability and structural integrity.

Cost Considerations: It's essential to note that while drilled soldier piles offer superior performance and precision, the total project cost is marginally higher compared to driven soldier piles. This is a trade-off to consider when making your project decisions.

Conclusion:

In the world of soldier pile walls, understanding the differences between driven and drilled soldier piles is essential for making the right choice for your construction project. While driven piles offer speed and cost savings for temporary structures, drilled piles provide versatility and stability, making them suitable for a wider range of applications. By considering your specific project needs and site conditions, you can make an informed decision that ensures the success and longevity of your retaining wall.