Foundations

civil techniques

PILE TYPES

abbu riyaz 1 May, 2023

PILE TYPES BASED ON CONSTRUCTION METHOD

Three pile types of pile foundations according to their construction methods:

Driven piles,
Cast-in-situ piles, and
Driven and cast-in-situ piles.

1. Driven Pile Foundations:

It is of concrete, steel or timber. These piles are prefabricating before placing at the construction site. If drive piles are of concrete, they are precast. These piles are drive using a pile hammer.

When piles drive into the granular soils, they displace the equal volume of soil. This helps in compaction of soil around the sides of piles and results in the densification of soil. The piles which compact the soil adjacent to it is compaction pile. This compaction of the soil increases its bearing capacity.

Saturated silty soils and cohesive soils have poor drainage capability. So these soils are not compacts when piles are drill through it. The water is to be a drain on the soil to be compact. Stresses develop adjacent to the piles have to be borne by pore water only. This results in an increase in pore water pressure and a decrease in bearing capacity of the soil.

2. Cast-in-situ Pile Foundations:

Cast-in-situ piles are the concrete pile. These piles construct by drilling holes in the ground to the required depth. And then filling the hole with concrete. Reinforcements utilize in the concrete as per the requirements. These piles are of small diameter compare to drill piers.

Cast-in-situ piles are straight bore piles or with one or more bulbs at intervals are cast. The piles with one or more bulbs are under-reamed piles.

3. Driven and Cast-in-situ Piles

Driven and cast-in-situ piles have the advantages of both driven and cast-in-situ piles. The procedure of installing a driven and cast-in-situ pile is as follows:

A steel shell of the diameter of a pile driven into the ground with the aid of a mandrel inserting into the shell. After driving the shell, the mandrel removes and concrete pours into the shell.

The shell is of corrugate and reinforces thin sheet steel or pipes. The piles of this type are shell type piles.

The shell-less type formes by withdrawing the shell while the concrete places. In both the types, the bottom of the shell is close to a conical tip which separates from the shell. By driving the concrete out of the shell an enlarge bulb form in both the types of piles. Th shells left in place and the tube concretes. This type of pile is very much use in piling over water.

civil techniques

Pile cap

abbu riyaz 30 Apr, 2023

A pile cap is a mass concrete structure contains more piles embeds in it. A group of pill drives into clay, soft, and loose soils to provide a strong, stable and suitable foundation.

The pile designs considering the punching shea around the heads of the piles and column base. It also designs for bending moment due to the transmission of loads from columns to the individual piles.

Pile cap Necessity

Pile is necessary when the bearing capacity of soil below the structure is insufficient for a spread footing. It transfers the load to deeper, firmer strata. Piles used where the soil particularly affects by seasonal changes, to transfer the load below the level of such influence.

The load support exceeds the bearing capacity of a single pile, a group of piles uses.

The group capped by a spread footing or a cap to distribute load to all piles in the group. Where there are a large number of closely space piles, provide individual caps. It is more economical to provide just one large cap, forming a piled raft.

SHAPES

The shape and plan dimensions of the pile cap depend on two factors.

Number of piles in the group and
The spacing between each pile.

The most common shapes are

1. Number of piles in the group

A group of piles accommodates in a pile cap.

Two pile

In two pile cap, two piles are embeds in one pile cap. The picture shows a two and one pile cap PCC arrangments for pile cap.

Three pile

The picture shows a typical three pile arrangement PCC for pile cap.

Three pile cap

The image shows a three pile cap concreting.

The shapes of the pile caps minimize the plan area for symmetrical pile arrangement about the load.

It is overhand the outer piles by at least 150mm and not excessive. And not more than the diameter of the pile diameter.

There are different shapes of pile caps according to the number of piles.

DEPTH

The overall depth provides sufficient bond length for the pile reinforcement and the column reinforcement.

The depth decides by the following criteria.

Punching shear.
Pile anchorage.
Shrinkage and swelling of the soil.
Frost attack.
Groundwater table.

The most important thing is a shear capacity of the pile which affects the selection of the pile depth.

SECONDARY REINFORCEMENT:

The secondary reinforcement provides to prevent the piles from splaying outwards from the pile cap.

This reinforcement provided at the bottom of the pile cap running around the longitudinal reinforcement. Projecting from the piles into the pile cap.
The direction of the secondary reinforcement is changing at the head of each pile.

The amount of secondary reinforcement changing its direction at the head of each pile. And is not less than 20% of the main tensile reinforcement and well bond.

civil techniques

Steel corrosion control methods

abbu riyaz 30 Apr, 2023

Steel Corrosion control methods are essential to prevent damage and the failure of structures. 40% of failure of structures are by corrosion of inner steel. Steel corrosion control methods carry mostly in the structure that locates in coastal areas. And steel structures like tower transmission lines, cell phone towers, etc.

There are many causes of corrosion. It relates to the quality of concrete and quality of construction. The first step in corrosion of steel is to provide good quality of concrete. The quality of concrete materials, mixing and compaction and workmanship help to control the steel corrosion.

Quality in construction reduces corrosion. There are various methods, they are

Steel corrosion control methods

Cement-Polymer Composite Coated Rebars (CPCC)
Fusion Bonded Epoxy Coated Rebars (FBEC)
Corrosion Resistant Steel Deformed Rebars (CRSD)

1. CPCC

It set in concrete surrounds by an alkaline medium. A cement base coating is more useful for steel corrosion control. Apply two coats of cement polymer on rebar.

Products in CPCC are:

De-rusting Solution
Alkaline Powder
Phosphating Jelly
Inhibitor Solution
Sealing Solution

2. FBEC

It produces from 100% solid finely ground fuse powder particles. At heating, it melts to form an adherent film. There is no primer film provide in FBEC rebars. It makes a medium of weakness in the path of a bond between rebar and concrete.

Epoxy coats the rebar by

Melts
Flows
Gels
Cures
Cools
Stick to coat

3. CRSD

Corrosion begins with the formation of an initial layer of rust. On common rust on normal rebars, the CRSD rust is self-renewing. The protective oxide is fine texture, tightly stick and a barrier to moisture, oxygen, carbon dioxide, Sulphur dioxide. And chloride prevents corrosion.

Use corrosion resistance bars to prevent corrosion of concrete structures, damage, and failure of structures. This increases the strength and lifespan of structures.

civil techniques

Plastic formworks for concrete construction

abbu riyaz 30 Apr, 2023

Plastic formworks for construction is to keep fresh concrete in position to gain strength. With the help of formworks, concrete is easily made into various shapes and size. And the structure constructs.

There is different material uses to make formworks. Mainly timber and steel. Plastic gives a number of advantage compares to other materials. some are durability, cost-effectiveness, and flexibility.

The construction of formworks takes time. And it spent about 20 to 25% of the total cost of the structure. It is a major factor that affects the success of construction in terms of safety, cost, quality, and speed. Using of Plastic formworks reduces the setting time. And it is easy to fix. And remove easily after concrete gets strong. It reduces the time to fixing and removing. It requires low manpower.

Advantages of Plastic Formworks in Concrete Construction

Plastic formworks have many advantages like durability, cost, and flexibility. Formworks expend large labor force and total cost of the project. Efforts have made to introduce a formwork system which is cost-effective. And assembles, dismantle and handle easily by labor.

There are many advantages make by plastic formworks in concrete construction. some of them are as follows,

Cost-effective
Labor-friendly
Eco-friendly
Low maintenance

1. Plastic Formwork

It makes from specific high-grade plastic. Other materials do not stick to it. And no chemical reactions occur between pour material and the plastic. And there are no scratches on the surface. This is the main cause of using Plastic formwork in modern construction.

2. leakages

Leakages are the main factor to consider in the construction of structures. Leakages in formwork lead to segregation. It causes honeycomb in the concrete structures. By using Plastic formwork water and fresh concrete leakages from different parts of the form prevents. It is by the perfect fitness of parts of the Plastic formwork system.

3. labor-friendly

It is the most labor-friendly system. It fits and plugs easily and considerably lightweight compares with other types of formwork systems.

4. Nailing and oiling

Nailing and oiling plates not require. As in the other types of formwork like steel and wood, it is necessary to oil it. And it sets by nailing. The erection of formwork is by nailing. But in this type of Plastic formwork, it does not requires. Auto-leveling of plugging system make plates level automatically. And take less time to install and dismantle. This makes Plastic formwork a major material in modern construction.

5. cleaning

Cleaning of formwork is an important thing.The formworks are clean and neat it gives a long life of the material. As the formworks are in large numbers it’s difficult to clean properly. And cleaning takes more time. It requires more manpower to clean formwork. Plastic forms are clean with water easily. This makes Plastic formwork a major material in modern construction. Plastic formwork to be handled properly. It breaks by bad handling. And using low voltage hot air gun to seal it.

Formwork materials like wood, steel, produce many disadvantages. The use of wood is costly. And it creates environmental impacts of deforestation.

Other formworks cost high makes it not suitable to use. Plastic forms are recyclable. And it is eco-friendly. It reduces handling time. And provides great reusability index.

civil techniques

RCC Columns Pedestals and Footings

abbu riyaz 30 Apr, 2023

RCC Columns Pedestals and Footings is to give good strength and durability to structural members. Improper concrete leads to corrosion of steel by pores, cracks in concrete. This cause concrete not to achieve its strength in the setting. This leads failure of columns, pedestals, footings during occupancy of the structure.

RCC Columns Pedestals and Footings work inspection

Inspection for strength, leakage, and finish.
Reinforcement inspection, lap length, correct lapping.
Inspection of concrete cover.
Alignment of the structural member.
Availability of sufficient construction material at the site.
Availability of vibrators.
Proper safety PPEs and safety measures.
A Proper ratio of mix
Availability of slump testing equipment.
Availability of cube casting equipment.

After the inspection concreting work starts.

1. Concrete cover

Concreting of RCC columns, pedestals and footings starts from the center of vertical bars and go towards the ends.

2. Vibration

Vibrate concrete at regular intervals to spread evenly on all sides. Avoid Over vibration of concrete. Over vibration of concrete leads to segregation of coarse aggregates which settles at the bottom making the mix weak.

3. key

Provide proper keys in the center of column reinforcement and walls. This is to provide a proper grip between concrete of stem part with footing, walls, foundations. Apply 1:1 ratio of cement and sand slurry. This avoids separation of stem/ wall where a cold joint forms.

4. Starters

After concreting of the footing in a day or two starters for column and wall to cast with proper alignment. And again the upper surface of starter is making rough. In green concrete, place coarse aggregate outside and part goes inside by the spread and light press. This measure provides a proper grip on the surfaces.

5. Dowel

Dowel to Insert between the outer main bar of wall and column. It provides grip between old and new concrete surfaces. This dowel is 600 to 800 mm cut pieces of bars. Inserts in green/wet concrete such a way that half-length is projecting and half-length is inside concrete.

civil techniques

Repairing Concrete Column Cracks and Damages

abbu riyaz 30 Apr, 2023

Repairing concrete column cracks and damages is essential. The column concrete damages are becoming critical in mass structures like shopping malls, commercial buildings. To carry out the column repair identify the axial dead load, live load, and horizontal load.

Repairing concrete columns are two category

Surface or cosmetic – covers local deterioration
structural repair – strengthens the affected columns.

Repairing Concrete Methods for cracks and damages

1. Unloading Columns

unloading the column is necessary. Entire cross-section of the repair column is capable of carrying the reintroduce design load. Without unloading, new repair does not carry any load. Drying shrinkage of new material reduces the share of the load.

2. Redistribution of the Load

In corrosion of reinforcement and concrete deterioration, Redistribute a load of column concrete with alternative supports for repair.

3. Supplemental Reinforcing Steel

The supplemental vertical bar to fix outside the original cage with extra ties. Provide adequate cover and Place Apartment’s bars outside the tie bars to increase column dimensions. Use Hairpin ties, of stainless steel laterally to support the supplemental bars. Column ties cannot disturb at the repair of the longitudinal bars as it causes buckling.

4. Concrete Removal

Remove concrete within a column cage and unload the column. If not, the longitudinal bars are buckle and compression failure of column take place.

5. Corroded Reinforcing Steel

It’s not necessary to remove the corrode reinforcing bar with the reduce cross-sectional area if the loss is supplement with additional reinforcing bars. The partially corrode reinforcing bars are thoroughly clean by sandblasting to obtain the bare metal. The bars with excessive corrosion is replacing with fresh reinforcement having full laps on both sides.

6. Corroded Ties

Replace the corrode ties by adding stainless steel hairpin ties that are anchor into the concrete. It is often necessary to deposit extra material around columns to provide an adequate cover over the supplemental ties.

7. Low-strength Concrete

Where the concrete strength is low, resulting in insufficient load-carrying capacity, several alternatives are available:

Shore the column and remove and replace the in-place concrete.
Shore column and increase the size of the column to reduce bending stresses, and increase confinement on placed weak concrete.
Wrap the column with carbon- or glass-reinforced plastic.
Install a supplemental column.