What is a Micropile? Micropile Construction Method

Micropiles Introduction

Micropiles were introduced as an efficient and cost-effective alternative to traditional piles. The main advantage of micropile is its ability to be applied in very congested and low clearance areas and on any soil types. Micropiles are best suited for piling, foundation underpinning works, slope engineering, soil stabilization, etc. Another important feature of micropiles is their ability to work with minimal disturbance to existing structures and people around the area. Micropiles have been widely used as a very reliable and cost-effective alternative in the evolution of urban development.

What are Micropiles?

Micropiles, also known as mini piles, root piles, and pin piles, are small-diameter bored grouted friction piles, which are high-performance, high-capacity bored load-bearing components, and their pile diameters are generally less than 300mm. Each pile consists of steel elements, usually cemented with grout, into load-bearing soil or rock. Micropiles usually adopts pressure grouting, the pile and the soil around the pile can be closely combined, the virtual soil and bearing layer under the pile tip are cemented and reinforced, and pressure grouting can significantly improve the mechanical properties of the soil around the pile and increase the bearing capacity of a single pile.

Sinorock micropiles meet EN 14199 standard, anchor rod material and thread standard meet ISO 10208, ASTM A615 standard, etc.

micropile foundation

Structure of Micropile

The types of micro piles are gradually increasing with the development of the industry , but the basic structure is generally the same. A typical micropile structure is mainly composed of steel casing, reinforcement, grouting body and accessories.

Reinforcement: usually full-threaded round steel or steel pipe, this type of reinforcement can ensure the bonding force with the grouting body.

Hex nut: It is mainly used to fix the force transmission plate on the top of the pile to ensure that the load on the top of the pile is transmitted to the pile body.

Pile top force transmission plate: Its function is to effectively transmit the pile top load to the pile body. Sometimes in order to improve the local pressure bearing capacity of the pile top part, spiral reinforcement is set on the pile top part to strengthen.

Steel casing: The role of the steel casing is not only to follow the retaining wall when drilling, but also sometimes as a part of the micropile.

 micropile 1

In recent years, with the development of geotechnical technology, self-drilling anchor bolts can also be used as micro piles. Its structure mainly includes self-drilling anchor rod, drill bit, nut, coupler, bearing plate and centralizer. The hollow bar anchors can be used not only as a drill string but also as a grouting pipe. It can realize simultaneous drilling and grouting functions without casing, which can bring great cost-effectiveness to project construction.

Construction of Micropiles

Traditional micropiles construction process:

Drilled into bedrock, micropiles combine with the rock channel walls to transfer loads. Drilling rigs for micropiles can be portable, for narrow interior facilities, or tracked machines weighing up to 40 tonnes, for larger construction sites.

l  As the pile is drilled into the bedrock, the casing of the micropiles is advanced.

l  Remove the drill pipe. So each micropile is set in bedrock.

l  Reinforced load bars are lowered into the enclosure to increase capacity.

l  Cement grout is pressed into the casing and rock socket to ensure bonding.

l  The casing of the micropile is raised to the top of the bedrock, allowing it to bond with the rebar.

l  Cut excess steel from the top of the micropiles. The piles are capped to the engineer's design.

l  Load testing of a selected number of piles to demonstrate engineering load design.

Self drilling anchor bolt construction process:

The installation procedure for mircropile is similar to bored piling it’s using drilling method.

l  Check whether the functions of the drilling rig are normal. After ensuring that there is no problem, thread the self drilling anchor bolt to be used with the drill bit.

l  Drilling and grouting: Connect the rod body and the grouting pipe to the drilling rig through the rotary grouting adapter, and perform grouting during the drilling process to achieve simultaneous completion of drilling and grouting.

l  If the length of a single self-drilling anchor bolt does not reach the design drilling depth, the length of thecoupler can be used to meet the design requirements;

l  Install the backing plate and nut.

l  Reinforcement Result Test

Advantages of Self drilling Micropiles

l  Surface friction is 20% higher than casing drilling

l  Construction is possible with small and lightweight equipment

l  low noise and vibration

l  Suitable for tension and pull loads

l  Fast and efficient installation, high output

l  Limited construction area can achieve high capacity bearing capacity

l  Suitable for all soil types, ideal for collapsible soils


Sinorock team has many years of experience in providing complete geotechnical engineering services. If you have any needs or questions about self-drilling anchor systems and their applications, please feel free to contact us at sinorock@sinorockco.com.

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