What are Micropiles?
Micropiles (also referred to as Mini-Piles) are deep foundation, small diameter grouted piles typically consisting of a central steel reinforcement member and commonly includes steel casing. Micropiles can be designed to carry very high capacity loads, with design loads commonly on the order of 250 kips and higher depending on project requirements.
Loads are typically achieved through skin friction between the grout and surrounding soil or rock. In limited situations, loads can be achieved in end-bearing where the piles are terminated in competent rock formations. Unlike a Drilled Pier, Micropiles derive a large percentage of their load from the steel reinforcement. This, coupled with achieving their load in skin friction, makes micropiles excellent for both tension and compression loads. Steel casing can also be added to address lateral loading requirements.
Micropiles are typically used in limited access areas, such as low overhead clearance, and can be accessed through a typical man door. Micropiles are a cost effective solution in areas with Karst topography and sloping rock.
With a typical Drilled Pier foundation, significant cost overruns can occur due to extra rock coring. This is because Drilled Piers are extended along the face of sloping rock, or when voids are encountered in the rock formation near the design bearing elevation of the drilled piers and extra rock coring is required. Micropiles reduce this risk as micropiles typically extend down into the rock formation so the load is transferred in skin friction and potential voids in the rock are identified. This eliminates the risk of voids below the bottom of the Drilled Pier.
Micropile System Applications
Micropiles can be used in a variety of applications. Particularly useful when projects are launched in areas with limited access or weak soil, Micropiles have become a preferred method of deep foundation stabilization for their reliability, versatility, and efficiency.
Before you can decide if Micropiles are the best option for your project, it’s important to understand how they work and are applied. For an overview of Micropiles, their components, and practical uses, review this brief guide:
Uses for Micropiles
- Deep foundation Projects: Micropiles are a convenient option for establishing a deep foundation because they do not require pre-drilling. Establishing a deep foundation is necessary on job sites of high capacity loads, on-site barriers, or poor soil.
- Foundation Rehabilitation & Repairs: When existing foundations are compromised the use of Micropiles helps fortify the foundation’s stability. The structural load is transferred to the Micropiles to a more suitable and stable soil layer. Micropiles are a cost-efficient option in comparison to foundation replacement.
- Foundation Stabilization of Adjacent Structures: Micropiles can be used in projects with nearby structures, or for structures sharing adjacent walls that may interfere with the stability of your project.
Micropile Jobs and Considerations
Micropiles can be used on a variety of projects, including the fortification or creation of foundations for bridges, towers, and new buildings. The versatility of Micropiles has led to their increased popularity and their use in tough construction conditions. When faced with areas of low clearance, restricted access, or collapsing soil types, Micropiles are an ideal solution.
When compared to other foundation products, Micropiles are customizable and cost efficient and they eliminate the need for additional steps during installation. Because Micropile installation can be completed without pre-drilling, project completion time is not compromised. Micropiles offer the following features and capabilities:
- Helps control corrosion caused by soil
- Provides consistent results in a variety of applications
- Installed quickly
- High load capacity when compared to other options
- Pre-drilling not a required step for Micropile installation
- Cost and pricing: Unlike other foundation options, Micropiles are budget friendly and built to last. Their ability to be quickly installed factors into the overall cost since additional hours are not needed to complete installation, reducing staff expenses.
Components of Micropile
Each part of a Micropile works together to reinforce the strength of a foundation system. Available in cased and uncased varieties, Micropiles typically include the following parts.
- Extension and lead displacement plates: Separated by the square or round staff extension, lead and extension displacement plates are applied once the Micropile is in the soil. Displacement plates are essential in the creation of space around the shaft.
- Steel casing or reinforcement rod: Stabilizing a Micropile’s ability for high-capacity loads, steel casing or a steel-reinforcing rod serves as the strengthening element.
- Standard lead section: Placed at the deepest part of the soil, the standard lead section enters the ground first, making way for the Micropile.
Types of Micropile Systems
- Cased Micropiles and Uncased Micropiles: Available in both cased and uncased versions, Micropiles are made to ideally match each project. Uncased Micropiles need only grout for installation, while cased alternatives combine grout and a casing material to stabilize or build foundations.
- Hollow Bar: Ideal for collapsible soils, hollow bar Micropiles produce increased bond stress when applied.
- Helical Pulldown Micropile: Used primarily for deep foundations and high capacity loads, the Helical Pulldown Micropile combines skin friction and end-bearing to support foundations.
Micropiles are available in multiple varieties, but all are cost-efficient, quick to install, and useable in limited access or low-headroom areas. For help in determining the type of Micropile that is best for your project based on your specific needs, contact MDTI today.