Micropile Foundation: What is It? Applications | Types | Installation | Design

Time:2022-10-09From:sinorock View:

As urbanization is speeding up, land resources are becoming more valuable, resulting in the deeper foundations under buildings and the construction of underground works in dense building complexes is becoming more and more common. This is due to the restricted environmental conditions around the foundation, limited space for sloped excavation, and no construction surface for large construction machinery operations. The large diameter jet-grouted piles and the traditional form of soil-nailing wall support cannot meet the needs of the project. For this reason, micropile was born. Micropile is a high-strength, economical and practical support structure with strong applicability to environmental conditions. It can be flexibly arranged for small construction operation surface needs, has high strength, can meet engineering needs and solve engineering problems, and is now more and more widely applied.

What is Micropile?

Micropile, also called mini-piles, pin-piles, or root piles, is a high-performance and high-capacity deep foundation drilling material. The pile diameter is usually less than 300mm, and the length is not less than 30m and can achieve a working load of 200 tons or more. Micropile is a type of grouted pile that uses a drilling and pressure grouting construction process.

Mini piles originated in Italy in the early 1930s and began to be used in the United States in the 1940s, and developed very rapidly. It has been widely used in recent years and is now applicable to small and medium-sized industrial and civil buildings, especially for project sites with narrow sites.

Common Types of Micropiles

For different construction processes, it is divided into four categories:

l Type-A: Cement slurry only gravity filling

l Type-B: Pressure grouting (0.5 – 1Mpa)

l Type-C: The use of a secondary grouting process (Type-A step first, followed by re-infusion of the cement slurry at a pressure of 1 MPa before the gravity-filled cement slurry hardens) results in a higher bearing capacity compared to the same volume of grouted piles. However, it should be noted that the extra pressure generated by this can cause bypass expansion.

l Type-D: Repeat grouting.

Common Application of Mini Piles

l Foundation Support

l Underpinning of existing structures

l Reinforcement for Slope Stabilization and Settlement Reduction

l Permanent Retaining Walls

l Structural Support of Directly Loaded Piles

Advantages and Features of Micropiles

l Capable of penetrating various obstacles and suitable for different soil conditions.

l Provide structural support

l Enhance soil stability

l Small size and lightweight, relatively cheap

l Easily installed within confined spaces. The construction can be implemented with a 0.6*1.8m plan view size, and 2.2m headroom.

l No harmful vibrations or noise to surrounding structures.

l Small pile hole, minimal additional pre-stress on the foundation, and little impact on the original building.

l Works in compression and tension with a relatively high load capability

l The micropile can reduce the additional stress of the soil layer in a certain depth range and reduce the deformation and settlement of soil.

l Lightweight rotary percussive equipment can be used

l Low emissions or electric drive equipment, less pollution to the environment.

Micropile vs Typical Pile

l Small construction equipment, suitable for narrow construction areas.

l Suitable for complex geological conditions.

l Micropile can be used on the existing foundation, which is one of the simplest and most feasible schemes in the foundation restoration and reinforcement project.

l Micropile can be used for slope stabilization and different soil reinforcement, and it is suitable for different types of ground improvement projects.

How Does Micropile work?

According to the active mode, can be divided into two types:

1. As the main stress structure, it can resist the water and soil pressure generated in the process of foundation excavation

2. It is mainly used as an advanced support structure

Installation Process

The construction of micropile is generally carried out according to the following procedures:

drill holes - hole clearing - anchor bolts placement – grouting

1. Preparation

Check all kinds of construction machinery and supporting equipment for drilling and grouting, focusing on checking whether the drilling rig and grouting pump can work normally, and whether the size of the drill bit meets the requirements.

2. Dilling

The micro piles are drilled using an engineering geological drilling rig. Drilling is done in sections. The drill bit can be an alloy bit.

3. Hole cleaning

After drilling to the design depth, inject water to clear the hole until the hole is flooded with water. The pressure should be controlled during grouting to make the slurry injected evenly.

4. Pile body grouting

Use pressure grouting machine for grouting.

Self-drilling Anchor Bolts Used As Micropile

l Works in compression and tension

l Without temporary casing

l Grouting while drilling provides a potential for densification of insitu soils

l High construction efficiency

l The most efficient form of micropile in confined spaces

l Lightweight rotary percussive equipment can be used

l Self-drilling micropile load range from 110KN to 3660KN

Practical Application of Self-drilling Mini-pile in Building Construction

l Private residences with street frontage.

self drilling minipile used in private residences

The basement building makes full use of self-drilling mini-piles, which cause less disturbance to the original residence.

l Foundation restoration of the building.

self drilling minipile foundation restoration

Since the foundation of ancient buildings does not have a reinforced concrete support structure, the foundation base is prone to settlement. Self-drilling mini-piles can be used to suppress soil deformation.

l Pile set for supporting structure to support the existing foundation

self drilling minipile for existing foundation support

l New building foundation reinforcement

l Emergency reinforcement.

For the softening and collapse of soil caused by strong rainfall in the rainy season, the self-drilling anchor bolt construction work surface is small and there is no need to excavate and remove the soil used for counter-pressure. After grouting, it can reinforce the geotechnical soil at the collapse site. The self-drilling anchor bolt can be flexibly combined with other support structures.

Summary

In foundation support, micro-piles have many advantages, which can be widely used in projects around the foundation that are under limited environmental conditions, and need to do emergency reinforcement. It has excellent economic and environmental benefits.

When self-drilling anchor system is used as a micro-pile in building foundation engineering, it becomes increasingly popular because of their simplicity and convenience, reliability and practice, and high efficiency

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