WHAT IS SOIL CEMENT- TYPES, ADVANTAGES, DISADVANTAGES AND APPLICATIONS.

Soil Cement

Soil cement is a construction material, a mix of pulverized natural soil with small amount of Portland cement and water, usually processed in a tumble, compacted to high density. Hard, semi-rigid durable material is formed by hydration of the cement particles.

Soil cement is frequently used as a construction material for pipe bedding, slope protection and road construction as a sub base layer reinforcing and protecting the sub grade. It has good compressive and shear strength but is brittle and has low tensile strength so it is prone to forming cracks.

Soil cement mixture differs from Portland cement concrete in the amount of paste.While in Portland cement concretes the paste coats all aggregate particles and binds them together in soil cement the amount of cement is lower and therefore there are voids left, and the result is a cement matrix with nodules of uncemented material.

Types Of Soil Cement

1. Cement Modified Soil
2. Cement Treated Base
3. Soil Cement Base
4. Acrylic Copolymer

1. Cement Modified Soil (CMS)

Cement modified soil  is a sub base solution that blends cement and water with native (in-situ) soils to improve undesirable soil properties. The engineered mix forms a weather-resistant work platform for construction operations and a stronger, permanent sub grade for enhanced pavement support and capacity. Silt and clay soils, particularly when they are wet, can lead to construction problems. These soils can be soft, plastic, and difficult to compact. Cement modified soil is used to improve the engineering properties and construction characteristics of silt and clay soils by reducing this plasticity and enhancing the compaction and strength of the treated soil.

2. Cement Treated Base (CTB)

Cement treated base is a strong frost resistance base for a concrete or asphalt pavement wearing surface.Cement treated base is a mixture of aggregate materials or granular soils combined with measured amounts of Portland cement and water that hardens after compaction and curing to form a  durable paving material.

3. Soil Cement Base (SCB)

Soil cement base contains high amount of cement compared to cement modified base.It is commonly used as a cheap pavement base for roads, streets, airports and material handling areas. A seal coat is required in order to keep the moisture out. To avoid wear and tear a final coat of asphalt concrete is placed for pavement construction. 

4. Acrylic Copolymer

Acrylic copolymer is also called as rhino snot.It is a water-soluble acrylic polymer. This gains a property to penetrates the soil or sand mix and bind together.This is hence used instead of cement.When the whole mixture dries up, it become waterproof, UV resistant, solid bond which binds the soil together and reducing the dust. In higher concentration it creates a durable surface that can withstand heavy traffic, allowing existing soil to be used for roads, parking lots, trails and other heavy traffic areas.

Advantages Of Soil Cement

• Improve strength.
• Highly economical.
• Improve performance.
• Better weather resistant.
• Maintenance cost is less
• Reduce plasticity/cohesiveness.

Disadvantages Of Soil Cement

• Required proper supervision.
• Not suitable for some soil.
• Cracks may form in soil cement.
• Harmful for environment.
• Required more labor.

Applications Of Soil Cement

• Soil cement bricks.
• Airport pavements.
• Parking lots.
• City roads.

6 TYPES OF ROLLERS USED FOR CONSTRUCTION WORK

 Types Of Rollers

Rollers are the construction equipment used for the compaction of soil, sand, gravel and crushed stone etc.There are mainly 6 types of rollers:

1. Cylindrical Rollers
2. Sheepsfoot Rollers
3. Vibratory Rollers
4. Pneumatic Rollers
5. Smooth Wheeled Rollers
6. Grid Rollers

1. Cylindrical Rollers

Cylindrical rollers are light weight roller and are pushed by a person.The size varies but it is generally about 1 meter in diameter and about 1.5 meter long.These rollers are used mainly for small and private projects.It is made of iron, stone or concrete.The ground pressure generated by this type of roller is about 7 kg/cm2.

2. Sheepsfoot Rollers

Sheepsfoot rollers is also known as padfoot or tamping rollers.It consists of a drum having many round or rectangular shaped feet or lugs on it.It is available in different diameters and width of drum and different lengths and shapes of feet.Sheepsfoot rollers are good for compacting cohesive soils and silty clay in road construction work.

3. Vibratory Rollers

Vibratory rollers are most commonly used road rollers.This type of roller are fitted with one or two surface steel wheels 0.9 to 1.5 m in diameter and 1.2 m to 1.8 m in width.A vibratory roller is used for compacting granular base courses.It sometimes used for asphaltic concrete work.Self propelled vibratory rollers are now available weighing from 4 to 6 tonnes.

4. Pneumatic Rollers

Pneumatic roller has a number of rubber tires at the front and at the rear end. Empty spaces left in between the two tires that make 80% coverage area under the wheels. Pneumatic roller has the ability to exert contact pressure ranges from 500 - 700 Kpa. Pneumatic tired roller can be used for highways, construction of dams and for both fine grained and non-cohesive soils.It is also for smoothening of finishing bitumen layer on highways, roads, streets etc.

5. Smooth Wheeled Rollers

Smooth wheeled rollers consists of a large steel drum in front and one or two wheels or drum on the rear end.These are either tandem or three wheel rollers. Smooth wheel rollers are ideal for gravel, sand, ballast and surface dressings. They are not effective in compacting embankments and softer turf, but they are the most effective in compacting silty or sandy soils with the fewest passes. The weight of tandem roller varies from 2 to 8 tonnes and that of two wheeled roller varies from 8 to 10 tonnes. The ground pressure exerted by tandem rollers is about 10 to 17 kg/cm2

6. Grid Rollers

Grid rollers have a cylindrical heavy steel roller consisting of a network of steel bars coming together to form a grid like pattern. The grid may also be ballasted with concrete blocks for additional contact pressure. These rollers are ideal for compacting most coarse grained soils, since they provide little kneading action with high contact pressure. They are generally towed units and can operate at speeds between 5 and 24 km/hr and its weight varies between 5 tonnes net and 15 tones ballasted. 

WHAT IS PNEUMATIC CAISSONS AND ITS ADVANTAGES.

 Pneumatic Caissons

A pneumatic caisson is a rigid, inverted box with open at the bottom and close at the top. A working chamber is provided at its bottom to keep the caisson free of water and mud by use of compressed air. The design of a pneumatic caisson is similar to that of an open caisson is similar to that of an open caisson in many respect. The ultimate load carrying capacity, the design of walls, concrete seal and cutting edge are similar to that of open caissons. Pneumatic caisson is specially used at the place where it is not possible to construct the well. It is suitable for the depth of the water more than 12 m. However following differences should be clearly noted.

1. Working Chamber

The working chamber is made up of mild steel. It is about 3 m high and consists of a strong roof at its top.The chamber is air tight and the air in chamber is kept at a specified pressure to prevent entry of water and soil into it. The wall of the chamber should be thick and leak proof. To keep the frictional resistance low the outside surface of the walls are made smooth.

2. Air Shaft

An air shaft is a vertical passage which connects the working chamber with an air lock at the top.The shafts are made up of steel tubes and the joints of the tubes are provided with rubber gaskets to make them leak proof.It provides an access to the working chamber for workmen and also used to transport the excavated materials to the ground surface. In large caissons two separate air shaft are provided one for the passage of workmen and other for the transportation of materials.

3. Air Lock

An air lock is a steel chamber provided at the upper end of the air shaft above water level.The purpose of provided an air lock is to permit the workmen and materials to go in or to come out of the caisson without releasing the air pressure in the caisson. The steel chamber of air lock is provided with two airtight doors, one of which opens to the shaft and the other opens to the outside atmosphere.

Advantages Of Pneumatic Caissons

• Excavation and pouring of concrete is done in the dry.
• The soil can be inspected and the soil samples can be taken if required.
• Bearing capacity of soil can be determined by conducting in-situ test in the working chamber.

Disadvantages Of Pneumatic Caissons

• It is very expansive.
• Large number of manual work required which increase the cost.
• The penetration depth below water table is limited to 30 m to 40 m.
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WHAT IS SITE INVESTIGATION

Site Investigations

Site investigation or sub surface explorations are done for obtaining the information about subsurface conditions at the site of proposed construction.Site investigation consist of determining the profile of the natural soil deposits at the site, taking the soil samples and determining the engineering properties of the soils.It also includes in-situ testing of the soils.

Site investigation are performed to obtain information on the physical properties of soil and rock around a site to design earthworks and foundations for proposed structure and for repair of distress to earthworks and structures caused by subsurface conditions.This type of investigation is called a site investigation.Additionally site investigations are also used to measure the thermal resistivity of the soils or backfill materials required for underground transmission lines, oil and gas pipelines, radioactive waste disposal and solar thermal storage facilities.

Site investigation are generally done to obtain the information that is useful for one or more of the following purposes:

• To determine the bearing capacity of the soil.
• To select the type of foundation for a given structure.
• To select the depth of the foundation  a given structure.
• To select the suitable construction techniques.
• To determine the ground water level and properties of water.
• To predict the lateral earth pressure against retaining walls.
• To estimate the probable maximum and differential settlements.
• To investigate the safety of the existing structures and to suggest the remedial measures.

Stages Of Site Investigation

1. Site Reconnaissance 
2. Preliminary Explorations
3. Detailed Explorations

Site Reconnaissance

Site reconnaissance is the first step in a site investigation.It includes a vist to the site and to study the maps and other relevant records.It helps in deciding future programme of site investigation, scope of work, methods of exploration to be adopted, type of sample to be taken and the laboratory testing and in-situ testing.

Preliminary Exploration

The main purpose of preliminary exploration is to determine the depth, thickness, extent and composition of each soil stratum at the site.The depth of the bed rock and the ground water table is also determined.The preliminary explorations are generally in the form of a few borings or test pits.Tests are conducted with cone penetrometers and sounding rods to obtain information about the strength and compressibility of soils.

Preliminary site exploration is carried out for small projects, light structures, highways, airfields, etc. The main objective of preliminary exploration is to obtain an approximate picture of sub-soil conditions at low cost. It is also called general site exploration.

Detailed Explorations

The main purpose of detailed explorations is to determine the engineering properties of the soils in different strata.It includes an extensive boring programme, sampling and testing of the sample in a laboratory.Detailed exploration is preferred for complex projects, major engineering works, heavy structures like dams, bridges, high rise buildings, etc. A huge amount of capital is required for a detailed site exploration hence, it is not recommended for minor engineering works where the budget is limited. For such type of works, data collected through preliminary site exploration is enough.

In this stage, numerous field test such as Vane shear test, plate load test and permeability tests are conducted to determine the properties of the soils in natural state.

TYPES OF SOIL SAMPLE

 Soil Sample

Soil sample are obtained during sub-surface exploration to determine the engineering properties of the soils and rocks.Soil sample are generally classified into two categories:

1. Disturbed Sample
2. Undisturbed Sample

Disturbed Sample

Disturbed sample are the sample in which the natural structure of the soil gets disturbed during sampling.However, these samples represent the composition and the mineral content of the soil.Disturbed samples can be used to determine the index properties of the soil, such as grain size, plasticity characteristics, specific gravity.Disturbed soil sample do not retain in-situ properties of the soil during the collection process.Engineers do not consider these sample to be  representative of underground soils except for geotechnical testing that do not rely on the structure of the soil itself.Scientist commonly test disturbed soil samples for soil type and texture, moisture content nutrient and contaminant analysis, among other evaluations.

Undisturbed Sample

Undisturbed sample are the samples in which the natural structure of the soil and the water content are retained.However, it may be mentioned that it is impossible to get truly undisturbed sample.Some disturbance is inevitable during sampling, even when the almost care is taken.Even the removal of the sample from the ground produces a change in the stresses and causes disturbances.

Undisturbed samples are used for determining the engineering properties of the soil, such as compressibility, shear strength and permeability. Some index properties such as shrinkage limit can also be determined.The smaller the disturbance, the greater would be the reliability of the results.

Undisturbed soil sample retain the structural integrity of the soil and have a high recovery rate within the sample.Collecting a perfectly undisturbed sample is difficult and the samplers may contain a small portion of undisturbed soil at the top and bottom of the sample length. Undisturbed samples allow an engineer to determine the geotechnical properties of the strength, permeability, compressibility and fracture patterns among others.