Foundations

civil techniques

Jet Grout Soil Nailing

abbu riyaz 1 May, 2023

The Jet Grout Soil Nailing method use for eroding the soil for creating holes in the slope surface. Steel bars install in this hole and grout with concrete. It provides good corrosion protection for the steel bars. Soil nailing is a technique in which soil slopes, excavations or retaining walls are reinforced by the insertion of steel reinforcing bars.

Soil nailing uses to stabilize existing slopes and excavations. The top-to-bottom construction is advantageous compares to the other retaining wall systems.

As construction proceeds from the top to bottom, shotcrete or concrete applies to the excavation face to provide continuity. In short Soil, Nailing increases the shearing resistance of soil by acting in tension.

In the present construction times, soil nailing employes large in railway construction work. It uses for the stabilization of side lopes in existing track-road. And laying of new tracks adjoining to an existing one.

Types of Jet Grout Soil Nailing

There are three types of Jet Grouting Soil Nailing, they are,

Single fluid jet grouting
Double fluid jet grouting and
Triple fluid jet grouting.

1. SIngle fluid jet grouting

In this Single fluid jet grouting, the grouting takes place by using grout. In this method of the single jet grouting, the grout force into the soil with the very high-speed mechanism. And grouting carries out.

2. Double fluid jet grouting

In Double fluid jet grouting, the grouting takes place by using Air and grout. In this method of the double jet grouting, the grout and air force into the soil with the very high-speed mechanism.

3. Triple fluid jet grouting

In Triple fluid jet grouting, the grouting takes place by using Air, Water, and grout. In this method of the triple jet grouting, the grout, air, and water forces into the soil with the very high-speed mechanism.

civil techniques

Soil Nailing

abbu riyaz 1 May, 2023

Soil nailing is a construction technique to reinforce soil to make it stable and strong. Soil nailing technique uses for slopes and excavations alongside highways, railway lines. It uses for, excavations, retaining walls slopes, to make it more strong and stable.

The soil reinforces with slender elements like reinforcing bars name as nails. These reinforcing bars install into pre-drill holes and grouts. The nails install at an inclination of ten to twenty degrees with vertical reinforcement.

Soil Nailing employes when requiring slopes for excavation cannot provide due to space constraints. And employes in the construction of retaining wall. It is an alternative to retaining wall structures.

At excavation, the shotcrete, concrete and grouting materials apply to the excavation face to grout the reinforcing steel and nails. It provides stability to the steep soil slope.

Types of Soil Nailing:

There are various types of soil nailing techniques:

Grouted Soil Nailing
Driven Nails
Self-drilling Soil Nail
Jet Grouted Soil Nail
Launched Soil Nail

1. Grouted Soil Nailing

In this type, the holes drills in walls or slope face and nails inserts in the pre-drill holes. These holes fill with grouting materials like concrete and shotcrete.

2. Driven Nails:

Driven nailing use for temporary stabilization of soil slopes. In this method, the nails drive in the slope face at the time of excavation. This method is very fast. It does not provide corrosion protection to the reinforcement steel and nails.

3. Self-drilling Soil Nail:

In this method, the hollow bars use. Hollow bars drills into the slope surface and grout inject simultaneously during the drilling process. This method of soil nailing is faster than grout nailing. This method provides more corrosion resistance to nails than driven nails.

4. Jet Grouted Soil Nail:

In this method, jets use for eroding the soil for creating holes in the slope surface. Steel bars install in this hole and grouts with concrete. It provides good corrosion protection for the steel bars and nails.

5. Launched Soil Nail:

In this method, the steel bars force into the soil with high speed using compressed air mechanism. The installation of soil nails is fast. And control over the length of bar penetrating the ground is difficult.

civil techniques

Footings

abbu riyaz 1 May, 2023

Footings designs to resist the shear force causes by imposing loads. Footings constructs in open space and known as open foundations. It provides with natural slopes on all sides. It employs for a depth up to 5 m. The base of the structure enlarges or spreads to provide individual supports. These type of foundations provides for the structure of moderate heights built on the dry ground.

Types of footings

Wall Footing
Isolated footing
Combined footing
Inverted footing
Continous footing
Cantilever footing
Grillage footing

1. Wall Footing

Footings are of simple or stepped on wall footing. The base course of the footings is of concrete or other material. These footings employ only for simple structures. It has one projection beyond the width of the wall on sides. The width of the concrete base is equal to twice the width of the wall. In single footings, the brick footing is widely employing.

2. Isolated or column footing

It uses to support individual columns. It is in step or has a projection in the concrete base. In heavy loads, steel reinforcement provides in both directions in concrete bed. An offset of 15 cm provides on all sides of the concrete bed. In brick masonry, offset is of 5 cm on all sides in regular layers.

3. Combined footing

A combined footing supports more columns in a row. The combined footing is of rectangular shape if both the column carry equal loads. In unequal loads it of trapezoidal shape. It is rigid and resisting on the homogeneous soil.

4. Inverted arch footing

Inverted arch footing use on the soft soil to reduce the depth of foundation. Loads above an opening transmit from supporting walls through inverter arches of soil. In this type of footing, the end columns are stable enough to resist the outward pressure causing by arch section.

5. Continuous footings

In this type of footing, a single continuous R.C. slab provides a foundation of more columns in a row. It is suitable for locations liable to earthquake activities. This prevents differential settlements in structure. To have a better stability deeper beam constructs in between columns.

6. strap or cantilever footing

It consists of more individual footings connects by a beam known as a strap and known as cantilever footing. This type of footing uses where the distance between the column is greater. It serves to transfer column loads on the soil with equal and uniform soil pressure.

7. Grillage footing

This type of footings uses to transmit heavy loads from steel columns to the soils having low bearing power. This type of arrangements avoids deep excavation. And provides a necessary area at the base to reduce the intensity of pressure. Grillage footings are of roll steel joists and name as grillage beams to providing in single or double tires.

civil techniques

Retaining Walls

abbu riyaz 1 May, 2023

Retaining walls

Retaining wall prevents the earth from sliding or eroding away. And to resist the material pressure of the material that it is holding back. It constructs with heavy blocks, angled stones, offset cinder blocks, wood or reinforced concrete frames backfilled or filled with the well-graded stone designed to create the geological resistance or mass required to counteract the earth pressures and surcharge loading. And also, anchor into the ground with steel I beam vertically inserted into the ground and reinforced with concrete and linked in between with planks or reinforced, Pre-fabricated concrete blocks.

Types of Retaining wall

Classification of retaining walls:

Following are the different types of retaining walls based on the shape and the mode of resisting the pressure.

Gravity wall-Masonry or Plain concrete
Cantilever retaining wall-RCC (Inverted T and L)
Counterfort retaining wall-RCC

1. Gravity wall – Masonry or Plain concrete

Gravity retaining Wall constructs of concrete, stone or brick masonry and are thicker in section. The geometry of these walls also helps them to maintain the stability. Mass concrete walls are suitable for retained heights of up to 3 m. The cross-section shape of the wall affects by stability, the use of space in front of the wall, the require wall appearance and the method of construction.

2. Cantilever retaining wall-RCC (Inverted T and L)

A cantilever retaining wall is one that consists of a wall which connects to the foundation. They are the most common type engages. Cantilever wall rest on a slab foundation. A cantilever wall holds back a significant amount of soil. It consists of a stem, toe slab, and heel slab.

3. Counterfort retaining wall-RCC

counterfort types adapted to larger heights. It consists of a stem, toe slab and heel slab as in case of cantilever retaining wall. But it also consists of counterforts are a regular interval which divides the stem. The stem with the combination of counterfort behaves like a tee-beam with varying width. The stem and heel slabs are effectively fixed to counterforts so that the stem bends horizontally between the counterforts due to lateral earth pressure. Thus the thickness of stem and the heel slab is considerably reduced due to the reduction of the moment due to fixity of these slabs between counterforts.

civil techniques

Pile Driving Equipment

abbu riyaz 1 May, 2023

Pile Driving Equipment

Pile Driving Equipment uses to drive piles in the weak soil for providing strong grip to foundations. The process of forcing a pile into the ground is pile driving. The piles drive vertically into the earth.

The equipment required for pile driving is as follows

Pile frames
Pile hammers
Leads
Winches and
Miscellaneous.

1. Pile frames

The pile frames are generally of steel having a height varying from ten to twenty-five meters and more. Pile frames are light and easy to transport. It consists of platforms for supporting drivers, engines, winches, etc.

2. Pile hammers

The function of hammers is to impart energy to drive the pile into the soil. These hammers guides between two steel members known as leads. Heavy conventional hammers drive pile by an impact. Vibratory hammers evolve as to avoid noise pollutions by driving piles by vibration.

3. Leads

Leads employ to guide hammers and piles. For drop hammers, fixed leads are uses. Leads are movable and adjustable as per use. Leads are more convenient.

4. Winches

Winches require for lifting the hammer and pile. These are of a light type with a single drum or heavy type with a double or triple drum. And it fits with reversing gears. Drop hammers, pneumatic hammers, winches operate by diesel, petrol, and electric engines. For steam hammers, use steam-power winches to lift the hammer and pile.

5. Miscellaneous

The other equipment requires for the process of pile driving are pile extractors, followers, jetting equipment, steam engines, air compressors.

pile extractors are for pulling piles from the ground after its impaction to a connection of reinforcement to foundations.
followers are connecting pieces of wood or steel between hammer and top of a pile. It is to transmit energy from the hammer to pile in underwater pilling.
jetting equipment is necessary to discharge water jets at high pressure to assist driving piles into sand or fine gravel.

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.

civil techniques

Methods of Ground Water Control in Excavations

abbu riyaz 30 Apr, 2023

The Methods of Ground Water Control in Excavations explains in this post. These techniques use to prevent groundwater entering into construction like, piling for bridges, tunneling, marine structures, underground structures. The groundwater causes extreme geotechnical problems in excavations like sand running for most of the construction projects. These issues caused by groundwater increase construction budget and extend construction time.

Methods of Ground Water Control in Excavations

There are two major Methods of Ground Water Control in Excavation explains as follows,

Pumping technique
exclusion technique

1. Pumping technique

It is highly expensive by Utilization of large capacity pumps which are not economical to consider in the critical situations.

2. Exclusion Methods to Control Ground Water in Excavations

There is a number of techniques by which groundwater exclusion are obtaining:

Forming impervious barriers

Chemical consolidation for controlling groundwater in excavation

Groundwater control by compressed air

Freezing groundwater control.

In these, we provide methods to prevent groundwater entering in construction by using Forming impervious barriers.

3. Forming impervious barriers

In this technique, permeability reduces by creating an impervious barrier.

An impervious barrier with lower end close by expandable plug & upper end seals on the surface drives into the soil. And grout is force into the pipe and drive out the plug and wide fissures with grout.

Application

Drill a hole in advance, insert a lance for grouting to carry out by a bottom-up method or top-down method.
Gout upper part by a lance inserted into the hole. After its setting time grout lower part of the pipe.
After grouting, preventing groundwater from entering into the excavation of piling, the normal procedure implies out for constructions.

Chemical consolidation for controlling groundwater in excavation

Chemical consolidation method is suitable for sandy gravels and fine grading sands. The most usual chemical material used for chemical consolidation is the sodium silicate.

Control Ground Water in Excavation by Compressed Air Method

There are several factors that motivate the application of compressed air to control groundwater in excavations. Compress air techniques are for controlling groundwater in excavations of tunnels and shafts.