Corrective measure to check pile foundation failure

Pile foundation contains sound bearing strength, good durability and small differential settlement with regards to other foundation types.

Pile foundations are normally provided in the following conditions :-

1. Low bearing strength of soil.
2. Non-existence of perfect bearing stratum at shallow depths.

3. Greater loads from the super structure for which shallow foundation may not become inexpensive or feasible.

But pile foundations become damaged and collapse specifically throughout earthquakes because of the following purposes.

1. Inadequacy of sufficient boring
2. Improper soil grouping
3. Soft strata under tip of pile
4. Insufficient driving formula (wrong data)

5. Imperfect size of hammer leads to deficient penetration, too light or get damaged if too heavy
6. Misapprehension of load
7. Damaged of encased piles
8. Buckling of piles
9. Cracking of piles
10. Vibration that leads to lateral or vertical movement
11. Flowing strata resulting from adjoining excavation or bank sloughing
12. Tension failure of concrete pile for shortage of reinforcement
13. Eccentricity because of bowing or falling out of plumb
14. Deterioration caused by lower ground water level
15. Insect and marine borer attack and erosion

16. Detachment of concrete caused by poor quality of concrete or reactive aggregate
17. Failure of the thin shell of the piles
18. Overweight owning to earthfill.

Corrective measures to get rid of failure of pile foundation:

1. Preliminary repair like encasement or replacement
2. Extraction of partial load
3. Underpinning

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Published By
Rajib Dey
www.constructioncost.co
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Definition of building substructure and its constituents

The primary constituents of a building substructure belong to the foundation and plinth beam. These components securely transmits the load from the superstructure to the ground.

Foundation: The foundation means the structure situated under the ground level that gets in touch with the superstructure directly. The foundation transmits the dead loads, live loads and all other loads operating on it to the foundational soil.

The construction process of foundation is done in such a manner that the soil over which it stands is stressed inside its safe bearing strength. Any failure of foundation leads to the failure of the building structure.

Therefore, different building structure requires various types of foundations like shallow or deep foundations.

Preliminary, the soil profile is checked with a geotechnical engineer prior to complete a proper foundation for the building structure. The following types of foundation are normally utilized for building structure:

1. Strip Foundation (Shallow Foundation)
2. Raft Foundation (Shallow Foundation)
3. Pile Foundation (Deep Foundation)

1. Strip Foundation: Strip foundation or strip footing offers support for linear structures like a wall or tightly spanned column, in the shape of strips. It is suitable for the soils having strong bearing strength as well as ability to support light structural loading. The size and location of the strip foundation are based on the width of the wall.

2. Raft Foundation: Raft foundation is also known as a mat foundation. It expands over the total building area and combats severe structural loads.

A raft foundation transmits the total load from the building area to the total floor area. As a result, the stress operating on the soil is significantly decreased that results in lessening the scope for shear failure of soil.

3. Pile Foundation: Pile Foundation stands for a type of deep foundation that transmits heavy loads from the superstructure to hard strata underneath the ground. Pile in a pile foundation refers to a deep reinforced concrete column that meets the hard rock strata far below the ground.

Plinth Beam: Plinth beam belongs to a beam that is developed in the plinth level among the wall and the foundation.

The purpose of this type of reinforced concrete beam is to resist the circulation of cracks from the foundation to the walls.

A plinth beam can allocate the load uniformly from the walls to the foundation. These are essential for construction projects planned in the areas susceptible to earthquake.

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Published By
Rajib Dey
www.constructioncost.co
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Reasons for collapsing of foundation

There are several reasons for collapsing of foundation which range from poor soil condition, structural faults etc. Given below, some of the major causes for collapsing of foundation :-

1. Collapsing of Foundation because of surpassing the bearing strength of soil
2. Collapsing of Foundation because of withdrawn of moisture from Soil all of a sudden
3. Collapsing of Foundation because of differential or unequal settlement
4. Collapsing of Foundation because of uneven progress and pattern of construction
5. Collapsing of Foundation because of movement of adjacent soil.

Collapsing of Foundation because of surpassing the bearing strength of soil:-

Ultimate bearing strength means ultimate load intensity that a soil can bear devoid of any shear failure of the Soil. The size of the footing with regard to length, breadth and diameter, is primarily based on the bearing strength.

A foundation/ footing of a structure must contain adequate size in order that the intensity of load directing via that footing from the structure to the soil below should not raise the bearing strength of that soil. If the bearing strength of soil is low or load operating is heavy and the size of the footing is relatively small than actual requirement then the load intensity (i.e. load per unit area say KN/sq.m. etc.) conveyed on the soil may be greater as compared to the bearing strength of the soil, for this reason a shear failure of soil will occur.

To provide perfect footing size, the safe bearing strength rather than ultimate bearing strength should be applied to obtain margin of safety against any accidental loading as well as abnormal behavior of the soil due divergence in its bearing strength. Safe bearing strength is nothing but ultimate bearing strength divided by a appropriate factor of safety usually varying from 2 to 4.

Collapsing of Foundation because of withdrawn of moisture from Soil all of a sudden :

It is one of the most crucial factors that should not be neglected. Moisture withdrawn occurs in the following ways :-

a) By draining water from the adjacent well through pump
b) By dewatering adjacent Pond
c) Reduction of ground water table close to the ground previously.

Since the soil usually comprises of soil solid, water and air and super structural load on soil is carried by the both soil solid and pore water, as soon as the pore water is withdrawn, it will produce voids inside the soil system around and at the bottom of the foundation soil that leads to subsidence of the soil together with supporting structure. As a result, the collapsing of foundation happens.

To get more details about other reasons for failure, go through the following link www.mycivil.engineer



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Published By
Rajib Dey
www.constructioncost.co
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Details of Cast in Situ Concrete Piles and their advantages

Cast In Situ belongs to a construction item or structural member similar to a beam or in this case a Pile that should be built up, assembled or poured at site instead of prefabrication in a factory. Normally, in cast in place or cast in situ construction, concrete is delivered from a batch plant to site where it is poured and compressed into the formwork that is fixed in required shape and dimensions at site.

Cast in situ or cast-in-place piles are cast in position inside the ground; generally in such type of piles, drilling of necessary diameter and depth into the ground is done with an auger drilling device or a drill bit.

There is a helical screw blade generally known as a “fighting blade” inside the device that functions as a screw conveyor to eliminate the drilled out material. Besides, auger drilling an old method known as percussion drilling is also applied for excavating the hole. Under this method, a heavy cutting or hammering bit affixed to a roper or cable is lowered in the open hole or inside a temporary casing.

After entering deep into the ground, a temporary steel casing is lowered in the borehole to safeguard loose soil from dropping in the borehole.

The verticality of the casing should be examined precisely prior to start. Once the optimal depth is attained, the reinforcement cage with vertical rebars and stiffeners is lowered within the borehole, and the upper part is hanged at the top. The concreting is generally performed with Tremie method of concrete piling.

There are normally 6 types of cast in situ piles as below:-

1. Simplex Pile, 2. Franki Pile, 3. Vibro Pile, 4. Vibro Expanded Pile, 5. Raymond Pile, 6. Mac Arthur Pedestal Pipe

Benefits of Cast In Situ Concrete Piles: The cast in situ piles are set up with pre-excavation and reduce the vibration because of driving as in case of driven piles.

In housing area, sound pollution may occur if the piles are entered by hammering. To get rid of this issue, situ piling is suitable in such areas.

For water logged area, cast in situ piling with permanent casing is very effective.

The skin friction resistance with the ground is fully used in cast in situ piles throughout the design phases that is not recommended in case of driven piles where only the end bearing is applied.

Normally, there is no need of any foreign materials and tools and the original equipments and materials will meet the requirements of a project, as a result the cast-in-situ piles become as a cost-effective and adjustable type of pile foundation.

Precast piles should be designed to satisfy the handling and driving stresses thus enhancing the essential reinforcement that does not happen in the case of cast in situ piles and therefore, the amount of necessary reinforcement is minimized.

Cast in situ piles are attached over the ground with a pile cap that applies a monolithic approach. The top ground is excavated up to pile cut off level from where the slushy low quality concrete is eliminated with hand hilty to retain developed rebars into the pile cap.

Because of this monolithic connection, cast in situ pile provides good resistance against the earthquake and wind forces.

As soon as the piles are casted, no maintenance is required.

Since the materials and machinery applied are obtained from the local community, local contractors can perform the job and not any skilled labor is required for cast in situ piles.

No serious consideration should be provided for joints in cast in situ piles with regards to precast driven piles.



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Published By
Rajib Dey
www.constructioncost.co
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Shaft3D – A powerful software for foundation design and analysis

Shaft3D software is created for simplifying the pile design process specifically for the drilled shafts or caisson type foundations. The software will allow you to perform multi tasking like shaft axial capacity analysis, lateral analysis and concrete design etc.

With Shaft3D, it is possible to design caisson foundations for windmills, transmission lines, utility lines or any other structure requiring drilled pier foundations quickly.

Shaft3D can enhance your productivity considerably through its windows-based, easy-to-learn graphical interface and its capacity to offer a complete solution for different types of analyses.

Given below, some useful features of the software :-

• International Design Codes: Compatible with various concrete design codes to finish your global projects efficiently.
• User Defined Parameters: There are various design options like shaft boundary conditions, choice of safety factors in end bearing, skin friction and pullout, choice of axial capacity methods and lot of others to fulfill numerous project specifications.
• Graphical Input of Soil Profile: Facilitates input of unrestricted number of soil layers, each with various unique set of soil properties graphically permitting you to visualize your soil profile.
• Soil Property Values: Offers a series of values of soil properties like cohesion, angle of internal friction with selection of the soil type authorizing you to complete a preliminary design devoid of detailed soil report.

• Load Cases and Combinations: Produces generally used load cases and combinations for shaft design that saves design time considerably.

• Multiple Analyses: Accomplishes axial capacity analysis, lateral analysis and concrete design in one combined surrounding.
• Axial Capacity Methods: Facilitates to choose from several axial capacity methods so that it is possible to fulfill the need of your company or client.

• Lateral Analysis: Accomplish lateral analysis with finite element analysis demonstrating vital information like deflections, shears, bending moments along the length of the shaft allowing you to explore with different “what-if” scenarios.
• Concrete Design: Execute concrete capacity design for axial loads and biaxial bending that offers you a complete geotechnical and structural solution.
• Rebar Layouts: Generates several rebar layouts with customization options.

• Material Quantities: Produces material quantities to perform precise cost estimates for your customers each time at each phase of the project.
• Detailed Design Sketches: Creates a detailed design sketch with plan, elevation and section to sum up the completed design efficiently.

• Multiple Reporting Options: Produces various types of customizable reports to utilize them for your internal or client requirements.

To know the additional features, go through the following link dimsoln.com

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Published By
Rajib Dey
www.constructioncost.co
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A live demonstration on Raft versus Pile Foundation

If the gaps of footing are nearer, a raft foundation is recommended. Often, basements are created for particular purpose imposing to implement raft foundation. Usually, a raft foundation refers to a floating foundation that includes the ground completely to disperse load.

Pile foundation is mostly used if the spacing of footing is big & soil is costly in nature & it is not reasonable to excavate complete depth of this costly soil below the footing. If the spacing of column is big, raft foundation becomes expensive.

A raft foundation is ideal for feasibly inconstant soils, or soils which are extremely flexible. The raft system decreases the pressure on foundational soils. In some cases, a pile foundation is utilized in equivalent situations as a raft foundation. Piles should be set up intensely to spread to a strong strata of material, like gravel or bedrock.

A raft system will be perfect in some conditions where the depth of silt, sand or fine soil is very deep to develop a pile foundation. A spread footing is also ideal for feasibly unsteady soils. A spread footing needs excavating to a specific depth under the site grade, and considerably wider as compared the footprint of the house, and backfill with condensed, structural gravel fill. As soon as it is positioned, a standard concrete foundation is founded on the structural fill.

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Published By

Rajib Dey

www.constructioncost.co

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