Micropile: An Overview of The History And New Development

Overview History of Micropile

The emergence of steel pipe piles as a new type of pile is inseparable from the steelmaking and rolling technologies in the steel processing industry. The earliest use of steel piles was in the United States in 1908, and then in Europe in 1930, steel pipe piles were gradually used. In the 1950s, Japan began to use a large number of micro steel pipe piles. At that time, due to the rapid development of Japan and its limited land area, the government actively expanded the construction field in coastal areas, which further promoted the development of steel pipe piles.


The characteristics of the steel pipe pile determine its good bearing performance. It can withstand large horizontal stress, and the design can be flexibly adjusted to connect with the upper structure. The required construction space is small and the construction progress is fast. These advantages prompted the rapid development of steel pipe piles in the 1960s.


Italian Femando Lizzi clearly proposed the concept of Micropile in the 1950s. Micropiles are small-diameter drilled columns, also known historically as reticoli di pali radice (root piles). Such systems comprise multiple vertical and inclined micropiles interlocked in a three-dimensional network, creating a laterally confined soil/pile composite structure



source: earth-engineers


Micropile New Development

The diameter of the micropile is only 70-300mm. Due to its small diameter, in actual engineering, the holes are usually drilled first and then insert into the prestressing tendon and grouting.

In landslide prevention projects, the diameter of micropiles is mostly 90~180mm, and 150mm is the most common. In addition, the application of micropiles in landslide prevention has shown diversified development. The number of rows of micropiles is variable, mostly in 2-5 rows, and the layout of pile groups is mostly in the shape of a plum blossom.


In foundation support projects, micropiles have shown many advantages, and can be widely used in projects such as limited areas and emergency reinforcement, and have good economic and environmental benefits. The material of the micropile has also been newly developed. When the self-drilling anchor bolt is used as a micropile in the construction foundation project, the drilling and grouting can complete at one time, which is more convenient and efficient.

Micropiles also used for slope stabilization, reinforcement of quay walls, protection of buried structures, and other soil and structure support and ground reinforcement applications.


micropile application structure
source: earth-engineers

In addition to control landslides, micropiles are also commonly used in engineering in combination with other relatively mature support technologies, which can be mainly summarized as follows:

(1) Combination of micropile and pressure grouting

In application, micro-steel pipe piles are usually used. Firstly, holes are drilled, and then steel floral tubes are put in for pressure grouting to strengthen the rock and soil around the pipe body. At the same time, since the grout penetrates into the cracks of the rock-soil mass, the slide-resistant performance of the rock-soil mass itself is improved.


(2) Combination of micropiles and prestressed cable anchor

If the sliding surface is buried deep, the lower part of the micro-pile group often needs to be driven into a relatively stable rock layer. At this time, the pile body of the bearing section above the sliding surface may bear a large horizontal load. At this time, the pile body of the load-bearing section above the sliding surface may bear a relatively large horizontal load. So, generally, a connecting beam will be erected on the top of the pile, and with a prestressed cable anchor structure. This kind of combined structure combines the advantages of micropiles, and can also avoid shortcomings, showing a more obvious reinforcement effect.


(3) Micropile gravity retaining wall

This technology is to combine the traditional anti-sliding retaining wall and the micro-pile group. Firstly, the micro-pile group is arranged in the vertical direction, and then the upper part of the micro-pile group is connected with the retaining wall masonry. The lower part of the micropile group is anchored in a stable rock formation. This structural form can effectively overcome the anti-overturning and slide-resistant properties of traditional retaining walls. In addition, this form has less disturbance to the actual engineering landslide and can be widely used in small and medium-sized layer landslides and dynamic landslides.


(4) Combination of micropiles and ordinary slide-resistant piles

This treatment technology is to install micropiles at the bottom of the ordinary slide-resistant piles and anchors them in a relatively stable rock and soil layer. Combining the micropiles and surrounding rock and soil can effectively increase the stability of the slide-resistant piles and can also better overcome the inconvenient construction of ordinary slide-resistant piles.


The above is a review of the history and research development of micro piles. If you have any questions about self-drilling anchor bolts, micropiles and foundation engineering, or slope reinforcement engineering, welcome to contact us.

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