Four Common Problems in Micropiles Design

Time:2023-01-13From:sinorock View:

Micropiles were proposed by Lizzi in Italy in the 1950s. They were initially used for the reinforcement of historic buildings and monuments and were gradually extended to Europe and North America. The pile diameter of the micropile is generally less than 300mm, and the pile is formed by pressure grouting after the hole is formed. Due to the characteristics that other slide-resistant structures do not have, micropile has gradually been paid attention to in landslide control projects. However, due to the relatively short application time of micro piles in landslide prevention and control engineering, there is still no thorough knowledge of its slide-resistant mechanism, and no relatively mature calculation theory has been formed, so there are still some controversies. This article will analyze several common problems in the design of micropiles.

1. About the slide-resistant effect of micropiles

In order to verify the role of micropile in landslide prevention and control engineering, the micropile research group of Chang'an University has successively carried out several sets of model tests. Single pile test, single row pile test and pile group test were carried out.

Experimental details

The landslide model used in the test is composed of loess artificially rammed and filled, and the sliding surface is artificially preset. In the test, the micropile single-pile test and the micro-pile group test were used respectively. Through the test, after setting the micro-piles at the foot of the slope, in order to cause the slope to slide, a larger load must be added to the top of the landslide, which shows that the addition of micro-piles improves the sliding resistance of the landslide.

Arrangement of micropiles

A total of 5 rows of micropiles were arranged in the experiment, the pile spacing was 0.6m, the row spacing was 0.15m, the length of a single pile was 4m, and the pile diameter was 60mm. During the test, the pressure was continuously applied on the top of the slope until the micropile was damaged, and the loading amount reached 48kPa in total. It shows that the sliding resistance effect of micropiles is obvious. The data analysis in the test shows that setting the micropile before the landslide can increase the stability coefficient of the landslide model from 1.0 to 1.27.

2. About the reinforcement of micropiles

If micropiles are used as compression members, it is reasonable to reinforce them according to the pile core. In landslide control projects, micropiles are used as lateral force members to bear the bending moment. While using pile core reinforcement, the reinforcement should be arranged at the centroid of the flexural section. Theoretically, the reinforcement rods at this time do not bear the bending moment. Therefore, in the landslide control project, the micropiles should be reinforced with steel cages or steel pipes as reinforcement materials.

3. About the number of rows of micropiles

During the sliding process of soil landslides, the stress on the micropiles is uneven.

The force on the first row is the largest and gradually decreases on the rear rows.

In terms of stress, it is best to arrange the piles in 3 to 5 rows, and connect the top with connecting beams to give full play to the space function of the pile group. If there are more than 5 rows, it is recommended to increase the spacing of micropiles, which is better than increasing the number of rows of micropiles.

For rock landslides, especially hard rock, a uniform distribution is a good design plan since the landslide thrust distributed to each row of micropiles is roughly equal, The number of rows of piles can be determined according to the force value of landslide thrust. The arrangement on the plane is preferably no less than 3 rows.

4. About the parameter design of micropile

The parameter design content of micropiles includes pile spacing, pile length, the row number of piles, water-cement ratio, etc.

（1）Pile spacing. According to theoretical analysis and engineering experience, it is suggested that the pile spacing can be considered as 3 to 10 times the pile diameter. When the rock and soil conditions are good, the value takes the upper limit, and when the rock and soil conditions are poor, takes the lower limit.

(2) Pile length. Considering the bending resistance of the micro-pile, when the pile body reaches a certain length, increasing the length of the pile has little significance for slide-resistant. However, considering the stress state of the pile body after cracking, it is recommended that the length-to-diameter ratio of the embedded section should generally not be greater than 12:1.

(3) The number of rows of piles.

In the design of micro piles, it is suggested that the number of rows of micropiles arranged in parallel should be 3 to 5 rows.

(4) Water-cement ratio.

If the grouting process is adopted, it is recommended that the water-cement ratio be controlled at 0.35~0.4.

The above are the 4 common problems in micropile design. Sinorock as a professional ground support expert and years of experience in manufacturing self-drilling anchor bolt, has many practical slope reinforcement and foundation support projects experience. If you have any question or requirements, welcome to contact us at sinorock@sinorockco.com.

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