What is Micropiles? | How Does Micropiles Work? | Micropile Design, Size and Installation
What is Micropiles? Advantages and Disadvantages of Micropiles |Micropile Sizes
What is Micropiles?
Micropiles are a type of foundation structure that is used in ground improvement and stabilization. They are typically installed by drilling small holes, or micropiles, into the soil to depths of up to 200 feet.
These piles can be made out of steel, concrete or wood and have many advantages over traditional types of foundations.
For instance, they can withstand high seismic activity because they don’t rely on the strength of soil as much as other structures do. This makes them ideal for areas where earthquakes are common like Japan and California.
Micropiles also offer an efficient way to stabilize slopes in order to prevent landslides from happening; this is especially true for unstable terrain where it might not be possible to create a stable slope using conventional methods such as adding
They have been used for over 50 years and were developed as a cost-effective way to construct foundations during earthquakes.
Micropiles are typically less expensive than other types of foundations, but they require more time to install.
There are many benefits to micropile construction, such as how it doesn’t limit building height or size because there is no need for deep excavation before installation begins.
The results can be seen in places like Japan where buildings have remained standing after powerful earthquakes thanks to this innovative technology!
Micropiles are a type of foundation piling. They can be used for the construction of residential or commercial buildings, bridges and other infrastructure projects.
Micropiles have been around for over four decades and have become an increasingly popular solution to stabilizing soft soils and meeting the needs of project owners who need more space on which to build.
Traditional methods of deep foundation installation such as piling, or the use of helical piles can be time consuming and cost prohibitive to install.
Micropile technology is a relatively new option that offers an alternative solution to traditional methods in order to solve many difficult geotechnical problems, including soft soils and contaminated soils.
How Does Micropiles Work?
Micropiles move structural loads from inappropriate soil layers to solid foundation soils. Loads are transmitted from the foundation to the micropile’s steel and grout and then shed to the surrounding rock or soil via high friction values.
Reinforcing steel, generally an all-thread bar, is placed into the micropile casing, followed by the injection of high-strength cement grout.
The casing may extend to the whole depth or may terminate above the bond zone, with the reinforcing bar continuing to the full depth.
Capacity varies according on micropile size and subsurface topography, but compressive capacities of over 500 tons have been attained.
Micropile Design and Installation
A micropile is a friction pile with a narrow diameter that may be bored or drilled and placed at an angle to handle axial and lateral stresses.
Depending on the soil conditions and use, micropiles can be cased or uncased. The central reinforcing bar and cementitious grout, once placed, facilitate weight transmission into the bearing soil or rock.
The quality of the connection between the central reinforcement, grout, and the kind of soil/rock determines load bearing capacity.
Micropiles are commonly installed using down-the-hole hammers and rotary-percussion (top hammer).
Bar with a Hollow Micropiles are drilled into the earth using a sacrificial drill/grout tip while pressure grout is poured down the hollow bar
The technique of drilling that will be utilized is determined by the soil type, rock conditions, and application.
They may be placed in soil, rock, cobbles, and boulders, as well as in man-made obstacles or in locations with high water tables, to depths of more than 60 meters (200 feet).
Micropiles may be utilized in almost any soil condition, and load is acquired by bond tension between the grout and the surrounding soils.
Micropiles have the distinct benefit of being the only piling method capable of piercing obstacles during installation. For various soil conditions, a broad range of drilling tips are offered.
Micropile Sizes
Micropiles are a construction technique that is often used in the geotechnical engineering field to support and stabilize earth structures. They are typically installed when there is not enough soil or rock available on site for traditional foundation footings.
The micropile method uses excavated material from other parts of the site, such as bedrock, rather than using dirt piles which can be less stable.
The micropiles are inserted vertically into this material and then grouted with cement to stabilize them in place.
Micropiles are deep foundation components with diameters ranging from 5 to 12 inches that may stretch to depths of 200 feet and reach operating loads of more than 200 tons. High-strength steel casing, rebar, and grout are used to construct micropiles.
Advantages of Micropiles
- There are less or no vibrations.
- There is no need for dewatering; it may be put in a high-water table environment.
- Load displacement is small.
- Installed in places where other traditional deep foundation techniques do not function effectively due to sloping rock.
- Capability to install in restricted access installations (5ft wide) and with limited headroom (8ft high)
- Methods of installation are similar for all ground situations.
- Installation of a drill and grout at the same time
- Can be combined with other techniques to meet unique or complex project requirements cost-effectively and efficiently
Disadvantages of Micropiles
Except in the case of shallow pile termination depth, the sole drawback of micropiles is their comparatively high cost in comparison to other piling methods.
Micropiles FAQs
1. Why is Micropiles required?
Micropiles are typically utilized when the ground conditions are challenging, such as natural or man-made obstacles, sensitive ground with nearby structures, restricted access/low headroom, and/or karstic geology.
They are frequently used to repair failing foundation systems, for structural rehabilitation, to support structures impacted by nearby development, for seismic retrofitting, or for in-situ reinforcing such as embankment, slope, and landslide stabilization.
2. How is micropiles installed?
When complicated site circumstances and design criteria exist, micropiles are often used in conjunction with other ground modification techniques.
A high-strength steel casing is typically drilled down to the design depth during the installation procedure. A reinforcing bar is placed into the casing, and high-strength cement grout is poured into it.
The casing may reach the whole length of the pile, or it may just extend a portion of the length, with the reinforcing bar extending the entire length.
A detachable bit or a sacrificial head to the steel casing can be used to drill.
In certain situations, the steel casing is removed entirely or partially, and more grout is poured in under pressure.
3. What are some advantages of micropiles
- Micropiles are small and lightweight.
- Micropiles are cost effective.
- The low level of vibration and noise creates little disruption.
- Piling rigs can be low-emission or even powered by electricity.
- They are useful for installation in ecologically demanding settings, such as wind turbine towers, because they can be put through nearly any ground condition.
- They may be installed while bypassing existing utilities, eliminating the need for costly utility re-routing.
- They may be erected near existing walls with limited headroom and on crowded sites.
- They can withstand compressive, tensile, and lateral stresses and have a high load capacity.
4. How much do micropiles cost?
The cost of micropiles depends on the site characteristics and the technical complexity of the project. In general, micropiles cost about $120 per linear foot.
5. What are the methods used for drilling micropile?
There are two common hand-drilled pile methods: solid-stem auger and hollow-stem auger.
With solid-stem auger drilling, a perforating bit or drilling stick drills both ends of the casing to a depth of 6 to 12 inches.
The steel casing is buried in soil or rock and the grout is forced into both ends of the casing by using a counterweighted drill string. The grout is then filled with cement over the entire casing length.
With hollow-stem auger drilling, a steel drill string is used to drill down to the depth of the rotary table.
The grout is then pumped through a hollow steel stem into both ends of the casing. The stem is exposed and filled with grout.
6. How does micropiles work?
Micropiles are filled to their design depth by pouring grout into a steel casing that has been pre-drilled.
A steel core is then inserted into the grout and then is cemented into place. The steel casing is buried in soil, rock, or concrete.
Steel casing with a tapered surface, micropiles can be grouted through cut-outs in the wall. The micropile acts as a construction unit that will support the weight of a structure or project on its own during curing.
7. What is the use of micropiles in foundation design?
Micropiles are almost always used to strengthen the weak areas of the existing soil. Micropiles can also be used as a load-displacing element in connection with other foundations.
In many instances, they may serve as a very economical replacement for more involved but effective foundation systems.
8. What type of soil can be used in Micropiles foundation?
When the ground conditions are challenging, such as natural or man-made obstacles, sensitive ground with nearby structures, restricted access/low headroom, and/or karstic geology.
9. What is the depth of micropiles?
The length of the casing is typically from 12 to 200 feet long. The length of the steel casing will depend on a number of factors including soil properties and depth requirements for penetration.
