The foundation or foundation of a structure is responsible for transferring the building loads to the ground. Therefore, its condition plays an important role in building safety. Earthquakes, liquefaction phenomena, illegal settlement in foundation soil, reduction of bearing capacity, etc. are some of the things that threaten the integrity of the foundation. Reinforcement using microbubble is one of the ways to improve the mechanical properties of the soil, reducing the possibility of damage to the foundation due to the weight of the structure and destructive movements of the ground. In this article, we will learn about the details of the Naqwiyah method for a building or structure with a micro-pillar (with micro-pillars.)
What is Micropile?
Micro column or micropillar refers to elements with a diameter of 10 to 30 cm that are carried out vertically or obliquely around the foundation. Reinforcement using Micropil is combined with mild steel reinforcement and cement mortar injection. Microcolumns are load-bearing members that, by penetrating deeper than the depth of the foundation, transfer loads to more resistant parts and resist settlement.
Candles can be placed in the ground in two ways: movable and replaceable. In the moving form, the candles are driven into the ground by hammering or shaking. Microcolumns are a set of replaceable shafts that are driven into the drilling site by injection of high-pressure cement slurry, usually reinforced.
Where is the Micropile method applied?
When there is not enough space around the foundation for candles, micropillars are used to increase the bearing capacity of the foundation. In granular soil, it is necessary to consolidate and compact the soil mass through the transmission of kinetic and vibration energy. The energy needed for this work is provided through the process of hammering micropillars.
Liquefaction is a phenomenon that, when it occurs, the shear resistance of the soil is greatly reduced and large asymmetric settlements are created in the wake of the structure. As a result of this accident, the building can suffer serious damage and even collapse. One way to stabilize soil in areas prone to liquefaction is to strengthen the soil with microbeads.
Other applications of micropile are:
Improving the foundations of new and old buildings
Install the slope of the ground
Controlling the bearing capacity of the foundation and increasing its capacity
Build a firewall
How does Micropil work?
Micropile is carried out in four stages: drilling, pipe perforation, injection and reinforcement. In this section, we explain the main steps of applying Micropil.
holes
In some cases, due to factors such as ground construction, dense soil layer, concrete, etc., precision column pipes cannot be carried out by hammering method. In this case, the drilling process must be carried out by a rotary or rotary percussion method. Excavation must be done to a depth that can be used for roads, sometimes the entire micropile height is excavated.
Pipe drilling
In the pipe drilling stage, micro-columns are installed in the well. The microcolumn tubes are connected and hammer-tossed in series. Threaded bushings and pipe welding on the edge of the bushings are used to completely connect the pipes together. If the microbubble tube sinks less than 10 cm into the soil after 30 successive blows, hammering is stopped and after drilling to the design depth, the tubes are installed in the well.
Injection
The cement mortar must be carefully prepared and grouted so that the soil around the foundation is strong enough at the end of the process. Usually, Type 2 or Type 5 Portland cement is used in the grouting process depending on the chemical conditions of the place.
Grout grouting should be prepared using standard equipment, with a water-cement ratio of 0.5 to 1.5 and mixed for at least 30 seconds with a special mixer. The cement slurry is then injected with a special injection pump on site. The grouting process must be carried out at high pressure (up to 10 atmospheres) so that the cement slurry penetrates the soil layers.
Installation of reinforcement and flange
In the last step, the hardener must be placed inside a micropile tube. The appropriate time to install reinforcement is before the cement sets. If necessary, edge welding is used in the hardener to create a complete connection between the foundation concrete and the micropil and also to prevent the micropil head from cutting into the concrete.
What are the advantages and disadvantages of the micropillar method?
Reinforcement using micropel, like any other strengthening method, has advantages and disadvantages. In the following, we will examine the strengths and weaknesses of this method.
Advantages
Stability control: The presence of fans and a thick steel wall causes the load to be transferred and distributed to the lower resistant layers. Deep soil reinforcement and high steel hardness reduce soil stability.
Improving soil mechanical properties: Cement slurry injection increases the desired mechanical properties of soil, including hardness, compressibility, adhesion, coefficient of friction, bearing capacity and shear resistance.
Consolidation and compaction of granular soil through vibration: Compaction of granular soil is not easy and must be accompanied by vibration. The method of operation and methods of fine columns provides the vibration and energy necessary to compact the granular soil.
Low cost: Materials required for reinforcement using microbubble size. Low workshop setup costs and short project implementation time are other reasons for the cost effectiveness of this method.
Easy and quick implementation (even in the presence of groundwater): In this method, various operations can be performed without causing interference in the work. Also, due to the small size and size of the machines used, they can be easily carried and used.
Defects
Vertical microcolumns have limited lateral and axial load due to their small diameter.
Vertical microcolumns have a high implementation cost with limited bearing capacity.
Reinforcement cannot be used with fine columns in the grounds of ancient monuments and historical buildings without special arrangements
conclusion
Although strengthening with micropil has many advantages for establishing structures in weak soils, before doing so, you should pay attention to factors such as budget and the effectiveness of this method in the project environment. The type of land, depth of penetration, number of micropillars, machines and materials required, etc. are some of the factors that affect the cost of implementing a microbubble. Also, to evaluate the performance of these elements, the results of compressive loading, tensile loading and lateral loading tests should be checked