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The most common type of deep foundation is a pile, which is also called a pile foundation. A pile foundation is a relatively tall, slender, column-like structure that, when placed inside the soil as a foundation, is responsible for transferring the load of the upper floors to more suitable layers of soil at lower depths. The pile foundation is actually the column that is placed inside the soil. The pile passes the loads on the structure deep into the soil and transfers it to the stronger soil. In grounds that can not withstand the loads from the structure and also surface excavation is not cost-effective, the load transfer of the building to the ground is done by a deep foundation.

pile foundation – Istasazeh Co
pile foundation – Istasazeh Co

Types of pile foundation

Depending on the ground condition, the groundwater level and the type of load to be transported, different types of piles are used in construction work. pile foundation have the following types depending on the materials from which they are made:

pile foundation types depending on the materials:

  • Steel piles
  • Concrete piles
  • Timber piles
  • Composite piles
Types of foundation piles
Types of foundation piles

Types of construction piles
Types of construction piles

Types of foundation pilesSteel piles

Steel piles are one of the types of precast foundation piles that are used to build foundations and have a high execution speed. Precast piles are classified into two groups: small hollow piles and solid piles.

Small hollow piles are made of steel tubes that are suitable for foundation, and solid piles are made of H-shaped steel tubes.

Classification of steel piles

In general, steel piles can be classified as follows:

  • Screw piles
  • Disc piles
  • H-shaped piles
  • Plate piles

The steel piles used have an H-shaped steel section or a tubular section. Tubular piles have an open or closed end that is driven into the ground. Piles with an L-shaped or plate cross section can also be used as a pile base.

H-shaped piles are preferred for pile driving under foundations because they are thicker than L-shaped piles.

Types of foundation piles - H-shaped steel piles
Types of foundation piles – H-shaped steel piles

H-shaped piles are classified into two groups according to whether they are connected by welding or riveting. In fact, steel piles can be welded or riveted as needed.

The ends of steel piles may also have a flat or conical surface. In this type of connection, welding must be used.

In order to facilitate pile driving in hard soils (soft rock and dense sand), piles with different cross sections are used, which are determined according to the type of soil.

Types of steel piles

1. Tubular piles

Tubular piles are used as friction piles to support the load of the structure. These piles are seamless, stainless steel tubes that are welded together and divided into two categories:

  • Open end piles
  • Closed end piles
Tubular steel pile
Tubular steel pile

Open end pile:

Open end piles are mostly used to penetrate hard rock soils. These piles, after sinking into the soil or rock, move the soil inside the iron tube out using compressed air. Then, with the help of a water jet, the inside of the tube is cleaned and after guiding the steel tube to the required depth, the inside of the tube is filled with concrete with standard specifications.

Closed end pile:

In closed end piles, a conical element is made of steel or cast iron and is connected to the end of the steel tube using welding. At the end, after guiding the tube into the soil, the tube is filled with a sufficient amount of concrete.

The diameter of the tube used in closed end piles can vary from 0.25 to 1.2 m. The thickness of these piles varies from 8 to 12 mm.

2. Screw piles

Screw piles are made of iron or cast iron. These piles are made of a long rod with a screw or spiral end. The rod used in screw piles can also be hollow or solid.

The base diameter of screw piles is between 0.45 to 1.5 m. The spiral-shaped floor of the pile is transferred into the soil using an electric motor, which facilitates the process of easy penetration of the pile into the subsoil.

Screw piles are very useful in clay soils and are also economical. On the other hand, the use of screw piles in this type of soil helps to increase productivity. Also, installing the pile base in this type of soil is made easier by metal columns and screws.

3. Disc piles

Disc piles are similar to screw piles, except that in disc piles, the cast iron disc is connectec to the bottom of the iron rod. To facilitate the dewatering process, a hole is made in the bottom of these piles.

This type of pile can also be used in soft or sandy soil because it allows disc piles to sink during the dewatering process.

Disc piles are mostly used for marine constructions, because these areas need more penetration into the soil.

4. H-shaped piles

H-shaped steel pile driving is one of the new technologies developed in the pile driving industry. H-shaped piles can withstand high pressures to a high degree. These types of piles are often used to penetrate an area with rock or any other hard layer. They can also make the soil easier to move.

H-shaped steel pile
H-shaped steel pile

Advantages of H-shaped piles

They occupy less storage space.

  • Easier to transport
  • They have easier permeability based on the structure of the area.
  • The amount of computational error in the target area is less than other methods.
  • They have an easier assembly process.
  • The maximum penetration depth for these piles is 100 m.
  • They simultaneously perform permeability and compaction operations.
  • The main application of this pile is in the construction of highways and retaining walls of dams.

Corrosion of steel piles

Steel piles, regardless of their type, are more likely to corrode the soil. In such cases, the piles can be coated with charcoal or corrosion-resistant coating. Sometimes they are coated with chemicals or special substances on the concrete to prevent corrosion.

Steel pile preparation operation:

  • Cleaning the steel surface (rust removal)
  • Painting
  • Construction and assembly

Concrete piles

Concrete piles are used in two ways:

  • Precast piles
  • Cast in-place piles

Precast piles can be made using ordinary rebars. Their cross section is square or octagonal. The bars are used to make the pile resistant to the bending produced during transport, lifting and applying a lateral force to the pile, as well as increasing the compressive strength. Precast piles are made to the desired length and are made under wet conditions to achieve the desired strength. They are then transported to the place of compacting. Precast piles can be prestressed using high-strength prestressing cables. Cast in-place concrete piles are currently made by first drilling a well in the ground by hand or machine and then placing the reinforcement cage inside the well and filling it with concrete. Today, cast in-place piles are made in different ways and types, and most of them are monopolized by the specific company that originally invented them.

Cast in-place pile well drilling machine
Cast in-place pile well drilling machine

Cast in place piles fall into two main groups:

  • With casing
  • Without casing

Both groups can have a flattened tip (pedestal). Casing cast in-place pile is executed in such a way that first a steel tube is compacted to the ground and after reaching the desired depth, its internal materials are emptied and the inside of the tube is filled with concrete. The tube can be compacted by placing a mandrel inside it and after reaching the desired depth, the mandrel can be removed. To flatten the pile (create a pedestal), after pouring some concrete on the tip of the pile, releasing the weight from the height, it is compacted to spread it on both sides. To execute a pile without a casing, the casing is first compacted in the ground and then the casing is gradually pulled out at the same time as concreting inside the casing.

Deep pedestals and box foundations are actually cast in-place concrete piles that are larger than about 750 mm in diameter and can be armed or unarmed, with or without a pedestal (furnace).

A deep pedestal is a large-diameter concrete pile that is done to drill a well in the ground and then a bar shelf is driven into it (if armed) and finally filled with concrete. Depending on the soil conditions, a casing or a metal shield may be used to prevent the well wall from collapsing. The diameter of the deep base hole is usually large enough for an inspection person to enter.

There are usually advantages to using deep foundations:

  • A deep pedestal alone can replace several piles, thus eliminating the need to use a head pile cap.
  • In dense sand and gravel deposits, it is much easier to use deep pedestal than pile driving.
  • As a result of vibration from pile driving can endanger adjacent buildings. While in the execution of deep foundations there is no such risk.
  • Pile driving on clay soils can cause soil swelling or lateral movement of driven piles. Deep foundations do not contain such complications.
  • There is no noise created by driving the pile when executing deep foundations.
  • Due to the possibility of widening the tip of the deep base (creating a furnace), deep bases can show considerable tensile strength against the interaction forces.
  • In deep foundations, it is possible to visually inspect the condition of the walls as well as the bottom of the well, which provides the strength of the base tip.
  • Deep basea are more resistant to lateral loads than piles due to their larger diameter.

In addition to the above advantages, the use of deep basea has several disadvantages:

  • Concreting deep bases requires careful monitoring.
  • In bad weather, concreting operations may be delayed.
  • Like anchored trenches, deep excavation for pedestals may cause settlement of surrounding ground and damage adjacent buildings to the foundation.

A box foundation is a foundation that executes in a wet environment such as a river, lake or coastal. To create a box foundation, a hollow or box shaft places to the desired location on the ground to reach the solid layer on which the foundation is to be built. To make it easier for the box to sink into the soft ground, a blade edge is placed at the bottom of the box. After placing the lower edge on the solid layer, the materials inside the box are emptied and after placing the reinforcement shelf inside the box, it is concreted inside. The middle and side bases of bridges, coastal walls and coastal protection structures can be placed on box foundations.

Precast concrete piles with tubular cross section
Precast concrete piles with tubular cross section

Stages of execution of concrete piles in place:

  • Primary drilling with bentonite mud injection
  • Casing to a depth beyond the failed layer
  • Re-drilling from inside the casing
  • Creating a storage at the end of the pile (for pedestal piles)
  • Reinforcement shelf placement
  • Placement of termie and funnels and concreting
  • Pull out the casing
  • Completing the pile execution

Advantages of in-situ concrete piles:

  • No diameter limit
  • Possibility to increase the pile cross section at the end and increase the bearing capacity
  • Easier procurement of drilling machines than pile driving
  • Suitable for use in urban environments due to less noise
  • Completing studies and identifying soil during drilling

Disadvantages of in-situ concrete piles:

  • Impossibility to control the quality of concrete used, especially when it is below groundwater level.
  • The need to use casing tubes and drilling mud
  • Possibility of moving the central axis of the pile during execution
  • Possibility of casing tube remaining after concreting
  • The effect of weather conditions on the execution process
  • Contamination of the drilling environment and concrete poured in the well due to the use of drilling mud

Special points for compacting concrete piles:

  • Concrete curing is required before compacting.
  • The cshelfing of concrete during compacting must be controlled.
  • There is a need to correct the head pile due to damage caused by hammer blows.

What is a pile hammer?

A mechanical machine is used to place piles in the ground to improve the foundations of buildings or structures. The pile hammer has a heavyweight that moves freely up and down in a single line that can be lifted hydraulically, diesel and steam. When the weight reaches the highest point, the mechanical energy is converted into potential energy and stored there, and when the weight is released, the stored potential energy is converted into kinetic energy, which causes the piles to be placed on the ground.

The piles are first placed in the desired location with a crane and then a hammer is placed on them and the compacting operation is performed.

Vertical pile compacting operation:

First the pile is allowed to sink under its own weight, then the pile driving is done. Light hammers (wind or vibrating hammers) are commonly used at the beginning of a pile sink. The direction of the pile should be controlled with a surveying camera. Sometimes the deviation can be corrected, otherwise the pile must be pulled out.

Types of pile hammer:

  • Fall
  • Single stage (wind, steam)
  • Diesel
  • Multi-stage
  • Vibrating

Methods of bearing the weight of the hammer during pile driving:

  • By rig
  • Placing a hammer on the pile

Important points about foundation piles

1- Geotechnical studies

Based on geotechnical studies, the following results are obtained:

  • Determining the task of using or not using pile foundations
  • Subsurface and environmental conditions
  • Economic considerations
  • Selecting the type of deep foundation (in place/compacting)
  • Material of piles
  • Equipment and facilities for construction and execution
  • Pile depth

2- Preparation of drilling site

  • The drilling site should be completely flat and compacted with materials with adequate drainage capability and have sufficient rigidity to perform operations.
  • It should be having enough space to move the drilling and concreting machine.
  • During drilling operations, the drilling soil should be removed from the platform surface regularly.
  • In riverbeds and in places that are exposed to surface water, surface water should be prevented from entering the drilling site by a sheet pile around the drilling site.

3- Marking the execution place of the pile

At this stage, the exact location of the pile is determined and marked by the surveying team.

  • Surveying operations
  • Marking the exact location of the pile

4- Selecting the type of drilling machine

5- Deployment of drilling machine

After preparing the execution place for the pile, the drilling machine will be located on the site. The location of the drilling rig is determined to meet the following conditions:

  • There is no need to move until the end of drilling a pile, because if the drilling machine is moved and re-installed, it will disturb the level and verticality of the drilling machine.
  • Applying the least dynamic impact to the piles executed in the previous stags as much as possible.
  • Creating minimum work barriers to the movement of machinery related to drilling operations (cranes, truck mixers, loaders, etc.).

6- Providing the necessary facilities to prevent the wall collapsing of the drilling site

If it is possible for the walls of the pile drilling site to collapse due to soil or water pressure, the wall collapsing should be prevented by one of the following methods:

Use of bentonite mud or similar materials:

Due to the amount of pore water and also the mechanical structure of the materials, mainly the pile wall does not have the necessary stability during drilling and the use of stabilizing materials such as bentonite with a viscosity of at least 30 s and a maximum of 50 s/l is applicable. Bentonite slurry is a mixture of a type of soft clay suspended in water, which must be prevented from settling by using a stirrer. By transferring bentonite slurry into the well and due to the thixotropic properties of the clay, a shell is created on the wall of the pile that prevents the wall from collapsing or water from penetrating. Bentonite should be thoroughly mixed with water so that the mixture does not become lumpy. Bentonite mud should be able to create a coating or smooth cake on the well wall and keep smaller drilled particles (about 6 mm) suspended.

Bentonite mud is made with suitable concentration in ponds or in special machines for making bentonite mud and is transferred to the drilling well by tube and pump. To prevent wastage of bentonite mud when the drilling well overflows, it can be directed to the pond by installing a pond near the drilling site and returned to the well by separating larger suspended particles with a sieve.

In some stages of drilling operations, if the fall is due to collision with alluvial layers with fine-grained sand structure that does not have the necessary adhesion, bentonite slurry alone is not responsible for stabilization and adding 400 kg grade cement slurry to bentonite slurry at the drilling well site. It is recommended that after adding the cement slurry, the executive operation be stopped for the initial trapping time of the cement (approximately 25 to 35 minutes) and then the drilling operation continues.

It should also be noted that in cases where bentonite or similar materials are used to maintain the wall of the drilling well, these materials, if they have a high concentration, can be placed in parts of concreting by creating a coating layer on the concrete to stop the pile of concrete cohesion.

Use of casing:

The casing is used in lands where there is a possibility of excessive soil fall or deformation into the empty space of the well. The casing is also used in cases where dewatering the well wall from the entry of groundwater is desired. It is not necessary to use casing along the entire length of the well, but if only a certain depth of the well has fallen soil, the casing can be continued until it passes that depth.

In most cases, a casing tube 3 to 5 m in the initial depth of the pile is used to prevent the drilling well from collapsing.

Execution of pile foundation by casing method
Execution of pile foundation by casing method

 

How to install the casing:

1. First, drill the well to the depth that we pass through the fall layer, and then place the casing tube in it. Continued drilling is done from inside the casting tube.

2. Before starting the drilling, we drive the casing tube with a vibrator to the desired depth (passing through the fall layer) in the ground and in the next stage, we start drilling inside the tube. This method is mostly used in loose soils such as coasts.

Today, rotary machines have the ability to drive the casing tube in the ground in a circular manner and do not need a vibrator.

7- Drilling

After placing the casing, drilling continues through the tube and, if necessary, bentonite mud injection is continued in the well. In the upper part of the casing, the necessary supports should be installed to hold it in the entrance of the drilling well and pull it out. The casing can be left in place or pulled out.

The casting tube should be pulled out after concreting and before the initial trapping of the concrete. In cases where the dimensions of the casting are large, the casting is usually pulled out at the same time as the last concreting stags.

Creating a storage at the end of the pile (especially for pedestal piles):

If the diameter of the end section of the pile is larger than the diameter of the well, it is called a storage pile or flat floor (pedestal). Storage can be created in stable and non-fall soils and if the groundwater level is low to increase the bearing capacity of the pile.

Pedestal piles are used when there is a strong layer of soil or a weak layer of rock at the end of the pile. Otherwise, in piles whose ends are on a hard rock layer, most of their bearing capacity is equal to the strength of pile concrete and they do not need the end storage.

In pedestal piles, belling buckets are used to increase the cross section of the end of the pile. At the end of these buckets are articulated arms equipped with blade teeth that cone the soil. As the bucket rises, the arms contract. Due to executive problems, the concrete on the side of the storage is considered unreinforced.

8- Reinforcement (reinforcement shelf or steel core)

At this stage, if the pile concrete is reinforced, the reinforcement shelfs are established according to the technical specifications and transported by crane and transferred to the drilled well. Usually, the length of each shelf is 12 meters. Due to the depth of the pile, if more shelves need to be added, the first shelf is kept in the opening of the drilling well. According to the specifications of the reinforcement, the necessary overlap is done and they are connected by the reinforcement and after the connection, the shelves are placed in the drilling well.

Note that the reinforcement shelf should never go down to the bottom of the well as it is necessary to observe the minimum concrete cover between the shelf and the bottom of the well. Concrete rollers installed on transverse reinforcements are used to observe the concrete cover between the shelf and the wall of the pile. Sometimes steel profiles (in the pile axis) are used instead of reinforcement shelves.

9- Concreting

Concreting in the drilled place of the pile is done continuously by a special tube (tremie). In this way, the tremie tubes in different dimensions of 2 to 5 m and a diameter of 10 to 20 cm are connected to the depth of the pile and are placed inside the drilling well and a funnel is installed in the upper part to enter the concrete.

Now we start pouring concrete in the funnel and by lowering the tremie tube up and down, it is emptied from the tremie tube by a concrete crane and poured into the drilling well. To prevent drilling mud (bentonite slurry and similar materials) from entering the concrete, the end of the tremie tube should always remain in the concrete. This will keep the drilling mud on the concrete because it is lighter than the concrete and prevent it from penetrating the concrete.

Gradually, when the concrete rises in the drilling well to shorten the tremie tube from the upper part and without the end of the tremie tube tube coming out of the concrete, we separate the initial part and start re-concreting by installing the funnel again.

Drilling completion time to start concreting should not exceed 6 hours. If this period increases for unpredictable reasons, due to the deposition of suspended solids or the collapse of the well wall, contaminants may accumulate at the bottom of the well, which must be drained with appropriate equipment before concreting begins.

To ensure the continuity of pile concrete, the volume of wells and concrete used after concreting should be controlled.

Concreting should continue above the final level of the pile concrete. Additional concreting height, if concreting is done below the water level, is equal to 1.5 to 3 m and if concreting is done in a dry place, it is equal to 7.5 to 30 cm (due to mixing drilling mud with final part concrete). Additional concreting height should be specified in private surveyings and technical specifications.

10- Destruction of excess concrete

After concreting the pile, the piles should be soaked for 7 days and then the top of all the piles should be destroyed as needed. Under no circumstances should excess concrete on the pile be destroyed before 7 days.

Timber piles

Timber piles are the trunks of healthy, smooth and tall trees whose leaves have turned yellow and their surface has been carefully shaved after peeling. The maximum length of most timber piles is between 10 and 20 m. The wood used as the pile must be straight, seamless, and intact.

Timber piles are divided into the following three groups:

  • Group A piles: These piles carry heavy loads. The minimum diameter of the head of such piles is 350 mm (14 inches).
  • Group B piles: These piles carry light loads. The minimum diameter of the head of these piles is between 305 to 330 mm (12 to 13 inches).
  • Group C piles: These piles are used for temporary construction work. The minimum diameter of the head piles is 305 mm (12 inches). In no case should the diameter of the head pile be less than 150 mm (6 inches). When the entire length of the pile is in the groundwater aquifer, these piles can be used to carry permanent loads.

If a timber pile is driven into completely saturated soil, its life will be almost infinite. However, in marine climate, timber piles are attacked by various organisms and serious damage occurs within a few months. Timber piles above the surface of groundwater are attacked by insects. Some modifications, such as protecting them with Creosote oil, can extend their life.

pile foundation -Timber piles
pile foundation -Timber piles

Composite piles

In composite piles, the upper and lower parts of the pile are made of two different materials. For example, composite piles may be made of steel and concrete or wood and concrete. The composite steel and concrete piles are composed of the lower part of steel and the upper part of concrete in place. This type of pile is used when the length of the pile required to provide the bearing capacity exceeds the capacity of the concrete pile in a simple place. The composite wood and concrete piles have a timber lower part that is permanently in the groundwater aquifer and their upper part is made of concrete. In any case, it is difficult to make a connection at the intersection of two materials, which is why composite piles are not widely used.

The composite steel piles and concrete piles
pile foundation – The composite steel piles and concrete piles

Types of pile foundation in terms of performance

End-bearing pile:

If the rock bed or rock-like layer (very dense) is located at a regional depth, the pile can be extended to that layer. In this case, the bearing capacity of the pile will completely depend on the bearing capacity of the rock bed in front of the tip of the pile. That is why these piles are called end-bearing. In such a case, considering the depth of the rock bed from the drilled boreholes, determining the length of the pile will not be so difficult. If instead of a rock bed, a hard and relatively dense layer is located at a regional depth, the pile can be continued for several meters in the hard layer.

Friction pile:

If the depth of the bed rock or rock-like layer is high, the length required for the end-bearing pile will be uneconomical. In such cases, the pile is driven to a suitable depth in the upper soft layer without reaching the hard layer. The choice of the friction name for these piles stems from the fact that most of their strength is provided by wall friction. Of course, this name can sometimes be misleading, because the strength of piles that are driven in the clay layer depends on the adhesion between the pile wall and the clay. The length required for a friction pile depends on the shear strength of the soil, the load applied and the size of the pile. Determining the required pile length requires a good understanding of the soil-pile interaction, engineering judgment and experience.

Compaction piles:

In some special cases, piles are driven in granular layers to create good compaction in the topsoil. These piles are called compaction piles.

The length of compaction piles depends on the following factors:

  • Relative soil compaction before compaction
  • Relative compaction required after compaction
  • Depth required for compaction

Compaction piles are usually short, but some field tests are needed to determine their proper length.

Application of pile foundation in buildings

  • When the surface layers of the soil are too compact, or too weak, so that the surface foundation can not be used to distribute the load on the building; piles are used to transfer loads to a stronger bottom layer or bedrock.
  • When the structure is very heavy, for example in high-rise buildings, bridges or water tanks
  • The groundwater level in the lower soil should fluctuate a lot.
  • Executing large-scale foundations is very costly or practically impossible.
  • The structure is located on the coastal or riverbed.
  • They may be designed to withstand lateral forces or uplift pressures.
  • Dealing with tensile forces in foundations that are below the water surface or overturning of tall structures.
  • Control of seepage and landslide and increase the stability of slopes.

The information needed to design a pile foundation is divided into four general categories:

  • General knowledge, type and physical properties of layers such as granulation, Atterberg limits, soil type classification, density and percentage of natural soil humidity and groundwater level
  • Soil resistance parameters including internal friction angle and adhesion in both drained and non-drained states
  • Subsidence parameters such as modulus of elasticity, consolidation coefficients, swelling, initial porosity as well as over consolidation ratio (OCR)
  • Determination of chlorine concentration and PH of chemical tests to check and control corrosion of pile materials such as sulfate determination tests

In-situ tests of pile foundation

Due to the fact that in natural tests, the natural conditions of the soil changeless, it is more appropriate to use the results of these tests in determining the bearing capacity of piles. The use of standard penetration testing and, if possible, cone penetration testing is recommended in the study program. The cone penetration test provides accurate and useful results to the designer, especially if combined with a measurement of pore water pressure. In addition to the above tests, according to the geotechnical consultant, other tests such as percimeter, flat dilatometer and blade cutting in soft and saturated clay layers can also be used.

Criteria for selecting the type of pile foundation

The type of pile and the method of execution should be determined by the geotechnical consultant or design consultant and taking into account the following four basic criteria.

  • Superstructure specifications including type of loading, use, degree of importance of the structure, economic justification and project schedule
  • Equipment and facilities for the installation of piles and project operating conditions
  • Bed conditions including soil profile, layer properties as well as groundwater and its fluctuations
  • Corrosion rate, performance and durability of pile materials

Corrosion protection

In order to protect the pile from corrosion, according to the project conditions and the economic justification of the project, one of the methods such as increasing the deterioration of the pile, bitumen coating, epoxy, painting, increasing the concrete coating, metal plating or cathodic protection should be used.

Depending on the corrosion rate in the environment and the duration of service, the deterioration of the pile body can be increased. This amount of deterioration is called sacrificial deterioration. Before coating, the steel surface must be thoroughly cleaned. The bitumen coating (as a method of protection) must be approved by a consultant or monitoring body.

Steel piles without concrete caps should be coated with a bitumen coating 1 m low and 322 mm above the final ground surface. Piles connected to the concrete cap should be lined up to one meter below the level of the bitumen cap. Protective coatings below the minimum water level will not be required, taking into account tidal fluctuations and water turbulence. The above recommendations are related to the normal conditions of execution time and adjustment of the pile length.

If the pile remains near the coastal for a long time due to operational delays, due to the high capability of environmental conditions, the necessary measures should be considered in coordination with the monitoring body.

If the exact depth of penetration of the piles in the soil is not assured, before insulating and protecting the piles from corrosion, the penetration depth should be determined by the test piles. If this is not possible due to emergencies, it is necessary to increase the length of the protected area or other measures should be considered.

construction Pile tests

In general, construction pile tests are performed to control the quality and integrity of the pile, to check the driven stresses, to evaluate the driven equipment and accessories, to determine the driven stop criterion, and to determine the bearing capacity of the pile. These tests may be performed at the time of design, during execution, or after execution.

Test of foundation pile

At the discretion of the consultant or the monitoring body, depending on the conditions of the site or project, test of piles are executed and tested within the site. On these piles, static and dynamic tests are performed in order to check the bearing capacity of the design, evaluate the method and equipment of execution, verify the required and applicable length and other execution aspects according to the diagnosis of the monitoring body.

Tests performed on construction piles
Tests performed on pile foundation

Executive pile foundation

A number of main piles are tested for loading or integrity control at execution time. The number or percentage of tests and their type can be reflected in the execution contract documents. The number of these tests and the introduction of the relevant piles for the test should be verified and finalized based on the findings recorded at the time of execution and diagnosis of the monitoring body.

Environmental considerations in pile foundation operation

In order to reduce the environmental effects and potential damage caused by pile driving operations to the environment, distances should be set as minimum values from residential areas, hospitals, public and industrial buildings and buildings with sensitive facilities. Determining these distances will depend on the hammer energy, the length and dimensions of the pile, as well as the material of the soil layers. In addition, the amount of vibration resulting from the pile driving operation should be considered and, if necessary, the cost of installing instruments such as geophones at certain intervals should be determined to control the amount of vibration.

Precast concrete piles should be designed so that the discarded part is minimized. The discarded part of the piles must be moved to a suitable place by the contractor. Environmental considerations should be considered in the selection of drilling mud to limit the number of harmful pollutions to the minimum or permissible values introduced by the relevant organizations.

Safety principles in different stages of pile foundation execution

During the execution of piles, especially driven piles, the contractor is obliged to provide all the necessary conditions to ensure adequate safety. All workshop personnel should wear safety shoes and helmets and be aware of potential hazards such as collapsing piles when moving, ruptured crane cables and spilling hot oil, especially diesel hammers. During the execution of compacting and on-site piles, it is necessary to determine the safety zone by using the danger bar to prevent accidents caused by the overturning of the pile hammer or pile, as well as to prevent the movement of irresponsible people.

The contractor is obliged to provide a sufficient number of first aid kits in the workshop. Fire extinguishers are also required in the workshop. If the pile pad ignites or smokes during compacting, it should be turned off immediately and moved to a suitable place.

Related contents:

Federal Highway Administration (FHWA)

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