Roller Types Soil Compaction Equipments For Backfilling

Roller Types Soil Compaction Equipments For Backfilling

There are different types of rollers and other soil compaction equipments available. Use of these compacting machines depends on soil types and moisture conditions.

Following are different types of Compaction Equipments for different soil types:

The soil compaction equipments can be divided into two groups:

• Light soil compacting equipments
• Heavy soil compacting equipments

1. Light Soil Compacting Equipments:

These equipments are used for soil compacting of small areas only and where the compacting effort needed is less. Below are light equipments for soil compaction:

(i) Rammers:

Rammers are used for compacting small areas by providing impact load to the soil. This equipment is light and can be hand or machine operated. The base size of rammers can be 15cm x 15cm or 20cm x 20cm or more.

Rammers for soil compaction

For machine operated rammers, the usual weight varies from 30kg to 10 tonnes (6 lbs to 22000 lbs). These hammers with 2- 3 tonnes (4400 to 6600 lbs)weights are allowed to free fall from a height of 1m to 2m (3ft to 7ft) on the soil for the compaction of rock fragments.

Rammers are suitable for compacting cohesive soils as well as other soils. This machine in areas with difficulty in access.

(ii) Vibrating Plate Compactors:

Vibrating Plate Compactor

Vibrating plate compactors are used for compaction of coarse soils with 4 to 8% fines. These equipments are used for small areas. The usual weights of these machines vary from 100 kg to 2 tonne with plate areas between 0.16 m2 and 1.6 m2.

(iii) Vibro Tampers:

Vibro tampers is used for compaction of small areas in confined space. This machine is suitable for compaction of all types of soil by vibrations set up in a base plate through a spring activated by an engine driven reciprocating mechanism. They are usually manually guided and weigh between 50 and 100 kg (100 to 220 lbs).

2. Heavy Soil Compaction Equipments:

These compacting machines are used for large areas for use on different types of soils. The heavy compaction equipments are selected based on moisture content of soil and types of soil. Following are different types of these equipments:

I) Smooth Wheeled Rollers:

Smooth wheeled rollers are of two types:

• Static smooth wheeled rollers
• Vibrating smooth wheeled rollers

The most suitable soils for these roller type are well graded sand, gravel, crushed rock, asphalt etc. where crushing is required. These are used on soils which does not require great pressure for compaction. These rollers are generally used for finishing the upper surface of the soil. These roller are not used for compaction of uniform sands.

Smooth Wheeled Rollers

The performance of smooth wheeled rollers depend on load per cm width it transfers to the soil and diameter of the drum. The load per cm width is derived from the gross weight of the drum.

The smooth wheeled rollers consists of one large steel drum in front and two steel drums on the rear. The gross weight of these rollers is in the range of 8-10 tonnes (18000 to 22000 lbs). The other type of smooth wheel roller is called Tandem Roller, which weighs between 6-8 tonne (13000 to 18000 lbs).

The performance of these rollers can be increased by increasing the increasing the weight of the drum by ballasting the inside of drums with wet sand or water. Steel sections can also be used to increase the load of the drum by mounting on the steel frame attached with axle.

The desirable speed and number of passes for appropriate compaction of soil depends on the type of soil and varies from location to location. About 8 passes are adequate for compacting 20 cm layer. A speed of 3-6 kmph is considered appropriate for smooth wheel rollers.

Vibrating smooth wheeled rollers

In case of vibrating smooth wheeled rollers, the drums are made to vibrate by employing rotating or reciprocating mass.

These rollers are helpful from several considerations like:-

• Higher compaction level can be achieved with maximum work
• Compaction can be done up to greater depths
• Output is many times more than conventional rollers

Vibrating smooth wheeled rollers

Although these rollers are expensive but in the long term the cost becomes economical due to their higher outputs and improved performance. The latest work specifications for excavation recommends the use of vibratory rollers due to their advantage over static smooth wheeled rollers.

(ii) Sheep foot Roller:

Sheep foot rollers are used for compacting fine grained soils such as heavy clays and silty clays. Sheep foot rollers are used for compaction of soils in dams, embankments, subgrade layers in pavements and rail road construction projects.

Sheep foot rollers are of static and vibratory types. Vibratory types rollers are used for compaction of all fine grained soils and also soil with sand-gravel mixes. Generally this roller is used for compaction of subgrade layers in road and rail projects.

Sheep foot Roller Compacting Equipment

As seen in picture above, sheep foot rollers consist of steel drums on which projecting lugs are fixed and can apply a pressure upto 14kg/sqcm or more. Different types of lugs are namely spindle shaped with widened base, prismatic and clubfoot type.

The weight of drums can be increased as in the case of smooth wheeled rollers by ballasting with water, wet sand or by mounting steel sections.

The efficiency of sheep foot rollers compaction can be achieved when lugs are gradual walkout of the roller lugs with successive coverage. The efficiency is affected by the pressure on the foot and coverage of ground obtained per pass. For required pressure and coverage of ground, the parameters such as gross weight of the roller, the area of each foot, the number of lugs in contact with the ground at any time and total number of feet per drum are considered.

The compaction of soil is mainly due to foots penetrating and exerting pressure on the soil. The pressure is maximum when a foot is vertical.

(iii) Pneumatic Tyred Rollers:

Pneumatic tyred rollers are also called as rubber tyred rollers. These rollere are used for compaction of coarse grained soils with some fines. These rollers are least suitable for uniform coarse soils and rocks. Generally pneumatic tyred rollers are used in pavement subgrade works both earthwork and bituminous works.

Pneumatic Tyred Rollers

Pneumatic rollers have wheels on both axles. These wheels are staggered for compaction of soil layers with uniform pressure throughout the width of the roller.

The factors which affects the degree of compaction are tyre inflation pressure and the area of the contact. The latest rollers have an arrangement to inflate the tyre to the desired pressure automatically. The total weight of the roller can be increased from 11.0 tonne to 25.0 tonne or more by ballasting with steel sections or other means.

(iv) Grid Rollers:

Grid rollers are used for compaction of weathered rocks, well graded coarse soils. These rollers are not suitable for clayey soils, silty clays and uniform soils. The main use of these rollers are in subgrade and sub-base in road constructions.

Grid Rollers

As the name suggests, these rollers have a cylindrical heavy steel surface consisting of a network of steel bars forming a grid with squire holes. The weight of this roller can be increased by ballasting with concrete blocks.

Typical weights vary between 5.5 tonnes net and 15 tonnes ballasted. Grid rollers provide high contact pressure but little kneading action and are suitable for compacting most coarse grained soils.

(v) Pad Foot / Tamping Rollers:

These rollers are similar to sheep foot rollers with lugs of larger area than sheep foot rollers.

Pad Foot / Tamping Rollers

The static pad foot rollers also called tamping rollers have static weights in the range of 15 to 40 tonnes and their static linear drum loads are between 30 and 80 kg/cm. These rollers are more preferable than sheep foot roller due to their high production capacity, and they are replacing sheep foot rollers.

The degree of compaction achieved is more than sheep foot rollers. The density of soil achieved after compaction with this roller is more uniform.

These rollers operate at high speeds, and are capable to breaking large lumps. These rollers also consists of leveling blades to spread the material.

Pad foot or tamping rollers are best suitable for compacting cohesive soils.

Pile Foundations Requirements and Functions in the Construction Industry

Pile Foundations Requirements and Functions in the Construction Industry

Pile foundation is required when the soil bearing capacity is not sufficient for the structure to withstand. This is due to the soil condition or the order of bottom layers, type of loads on foundations, conditions at site and operational conditions.

Many factors prevent the selection of surface foundation as a suitable foundation such as the nature of soil and intensity of loads, we use the piles when the soil have low bearing capacity or in building in water like bridges and dams

A pile foundation consists of two components: Pile cap and single or group of piles. Piles transfers the loads from structures to the hard strata, rocks or soil with high bearing capacity. These are long and slender members whose length can be more than 15m.

Piles can be made from concrete, wood or steel depending on the requirements. These piles are then driven, drilled or jacked into the ground and connected to pile caps. Pile foundation are classified based on material of pile construction, type of soil, and load transmitting characteristic of piles.

The use of pile foundations as load carrying and load transferring systems has been for many years. Timber piles were used in early days, driven in to the ground by hand or holes were dug and filled with sand and stones. The use of steel pile started since 19th century and concrete piles since 20th century.

With the change in technology and industrial revolution, many advance systems have been devloped for pile driving from the invention of steam and diesel pile driving machines.

The use of pile foundations is increasing day by day due to non-availability of land for construction. Heavy multi-storyed building are being constructed, and load from these structures can not be directly transferred to ground due to low bearing capacity issue and stability issues of building during lateral load application. So, demand for use of pile foundations are increasing day by day. Due to this demand for piles, there have been many improvements in piles and pile driving technology and systems. Today there are many advanced techniques of pile installation.

Pile Foundation Functions

Function of Pile Foundation:

As other types of foundations, the purpose of pile foundations is:

• To transmit the buildings loads to the foundations and the ground soil layers whether these loads vertical or inclined
• To install loose cohesion less soil through displacement and vibration.
• To control the settlements; which can be accompanied by surface foundations.
• To increase the factor of safety for heavy loads buildings

The selection of type of pile foundation is based on site investigation report. Site investigation report suggests the need of pile foundation, type of pile foundation to be used, depth of pile foundation to be provided. The cost analysis of various options for use of pile foundation should be carried out before selection of pile foundation types.

Unless the ground condition is rocks, for heavy construction and multi-storied buildings, the bearing capacity of soil at shallow depth may not be satisfactory for the loads on the foundation. In such cases, pile foundation has to be provided. The number of piles in a pile groups required is calculate from the pile capacity of single pile and the loads on the foundation. Piles are a convenient method of foundation for works over water, such as jetties or bridge piers.

Environmental Considerations in Site Investigations

Site investigation is carried out before the start of a new construction projects. Environmental considerations in site investigation is of much importance to investigate the site suitability for the given project. This investigation refers to the local conditions and resources both natural and those already existing including the infrastructure. A preliminary site reconnaissance should be carried out as early as possible utilizing available data, in order to consider the surroundings in relation to the project. Aerial photographs can be a valuable aid. The principal investigation that should be carried out are given below:

(1) Topography – Suitability of surface features at the site on land or over water.

Topography Surveying

(2) Public and private services – Availability of a suitable workforce, transportation facilities for access, water supply, power and telecommunications, sewerage and drainage, disposal of wastes.

(3) Living amenities – Facilities available or required for accommodation during construction and afterwards. The extent and standard of the community services either existing or planned.

(4) Geology – The local ground conditions at the site and in the surrounding area would normally be indicated sufficiently at this stage from the geological survey maps where available, otherwise by a site visit and/or an enquiry addressed to the local public authority. Check for adverse natural conditions such as unstable ground, underground caverns and subsidence potential.

(5) Construction materials – If in situ deposits are of interest refer to the geology or earlier uses of the site (e.g. old tips). For new roads in virgin country use aerial survey and remote sensing.

(6) Hydrology – Surface and groundwater conditions, river and tide levels, currents and stream flow, flood levels and drainage conditions. Periodic occurrence of springs.

(7) Other uses of site area – Past, current and proposed other uses at and around the site, such as mine workings (underground or open-cast), tunnels and underground bulk storage. Former industrial areas, refilled gravel pits, refuse tips, reclamation, waste and spoil dumps, buried pipelines, services, drains, pollution, radioactivity and other hazards. Ecological and conservational impacts. Consider both the site and its surroundings.

(8) Meteorology – Regional temperature, rainfall, humidity, prevailing winds and fog. Seasonal effects. Local microclimatical conditions before and after construction of the project.

Different Types of Foundations and Its Uses - Concrete RCC Foundation

There are different foundation types and uses of these depends on the soil condition and loads from the structure. It is advisable to know suitability of each foundation types before making any decision for their selection in any construction project.

Following are the foundation types and their uses:

1. Spread footings and wall footings:

Spread footings are those whose base is more wider than a typical load bearing wall foundations. This is used in case of buildings. The wider base of this footing type spreads the weight from the building structure over more area and provides better stability.

Spread Footing

Spread Footing

Spread footings and wall footings are generally used for individual columns. walls and bridge piers. These footings are used where the bearing soil layer is within 3m (10 feet) from the ground surface. The soil bearing capacity must be sufficient to support the weight of the structure over the base area of the structure.

These foundations should not be used on soils where there is any possibility of ground flow of water above bearing layer of soil which may result in scour or liquefaction.

2. Mat Foundations:

Mat foundations are those which are spread across the entire area of the building to support heavy structural loads from columns and walls.

Mat Foundation

Mat Foundation

The use of mat foundation is for columns and walls foundations where the loads from the structure on columns and walls are very high. This type of foundation is used to prevent differential settlement of individual footings, thus designed as a single mat (or combined footing) of all the load bearing elements of the structure.

This type of foundation is suitable for expansive soils whose bearing capacity is less for suitability of spread footings and wall footings. This type of footing is economical generally when one-half area of the structure is covered with individual footings and wall footings is provided.

These foundations should not be used where the ground water table is above the bearing surface of the soil. Use of foundation in such conditions may lead to scour and liquefaction.

3. Pile Foundations:

Pile foundation is a type of deep foundation which is used to transfer heavy loads from the structure to a hard rock strata much deep below the ground level.

Pile Foundation

Pile Foundation

Pile foundations are used to transfer heavy loads of structures through columns to hard soil strata which is much below ground level and where shallow foundations such as spread footings and mat footings cannot be used. This type of foundation is also used to prevent uplift of structure due to lateral loads such as earthquake and wind forces.

Generally used for soils where soil conditions near the ground surface is not suitable for heavy loads. The depth of hard rock strata may be 5m to 50m (15 feet to 150 feet) deep from the ground surface. The pile foundations resists the loads from structure by skin friction and by end bearing. Use of pile foundations also prevents differential settlement of foundations.

4. Drilled Shafts:

Drilled shafts is also a type of deep foundation and has action similar to pile foundations discussed above, but are high capacity cast-in-situ foundations. It is also called as caissons. It resists loads from structure through shaft resistance, toe resistance and / or combination of both of these. The construction of drilled shafts or caissons are done using an auger.

Drilled Shafts or Caisson Foundation

Drilled Shafts or Caisson Foundation

This foundation can transfer column loads larger than pile foundations. It is used where depth of hard strata below ground level is location within 10m to 100m (25 feet to 300 feet). This foundation is not suitable when deep deposits of soft clays and loose, water-bearing granular soils exists. It is also not suitable for soils where caving formations are difficult to stabilize, soils made up of boulders, artesian aquifer exists.

Soil stabilization with lime and fly ash - Principles of Soil Stabilization

The term soil stabilization means the improvement of the stability of bearing power of the soil by the use of controlled compaction, proportioning under the addition of suitable admixtures or stabilizers. Soil stabilization deals with physical, physicochemical and chemical methods to make the stabilized soil serve its purpose as pavement component material.

Soil Stabilization

Principles in soil stabilization:

• Evaluating the properties of given soil.
• Deciding method of supplementing the lacking property by the effective and economical method of stabilization.
• Designing the stabilized soil mix for intended stability and durability values.
• Considering the construction procedure by adequately compacting the stabilized layers.

Soil stabilization may result in any one or more of the following changes:

Increase in stability, change in physical properties like density or swelling, change in physical characteristics.

Change in chemical properties:

Retaining the desired minimum strength water proofing.

Based on the above properties the various techniques of soil stabilization may be grouped as follows:

Proportioning Technique:

Various locally available soils and aggregates are mixed in suitable proportions and compacted to serve desired objective.

Cementing Agents:

The strength of the stabilized soil can considerably be increased by the addition of cementing agents like Portland cement, lime or lime-fly-ash. Bituminous materials also impart binding effect to non-cohesive soils.

Modifying Agents:

If the stabilizer added in small proportion could modify the undesirable properties of certain soils (such as highly clayey soils) making them more useful as construction material, such stabilizers may be called modifiers. The most common modifier used in the case of highly plastic soils is lime. Portland cements also acts as modifier in some cases.

Water Proofing Agents:

A compacted soil mass which is stable enough may become weaker or softer by the ingress of water or when subjected to soaking conditions. If the absorption of water can be stopped or retarded by means of some water-proofing agent, it will be possible to make use of such materials with advantage. The most common method of water proofing is by the use of bituminous materials.

Water Retaining Agents:

Some-non-cohesive soils have sufficient stability when the compacted layer possesses slight moisture content, but the soil may become loose and less stable when completely dried. In such cases use of materials with deliquescent properties, like calcium chloride is likely to be useful to retain some moisture to impart some apparent cohesion and thus retain the stability. This incidentally can also reduce the dust nuisance in un-surfaced roads.

Water Repelling Agents:

Almost the same function as water proofing agent may be performed by the water repelling or retarding agents like organic compound (Vinsol resin and other resinous materials).

Heat Treatment:

Thermal stabilization has different useful aspects as regards clayey soils. There are desirable changes in some of the properties and heat treated soil may be used in a number of ways.

Chemical:

There are several chemicals, which when added single or in combination, even in trace quantities (less then 0.5 percent by weight of soil) may impart useful changes in certain types of soils. However considerable investigation and care is needed before adopting any of costly chemicals.

In all the above methods, adequate compaction of the stabilized layers is the most essential requirement.

How to determine the minimum depth of foundation required - Foundation Depth Calculator

Many factors affects the determination of depth of foundation. Calculation for foundation depth is done based on type of soil, ground water table, loads from structure, bearing capacity of soil and other factors.

• General factors to be considered for determining depth of foundation are:
• Load applied from structure to the foundation
• Bearing capacity of soil
• Depth of water level below the ground surface
• Types of soil and depth of layers in case of layered soil
• Depth of adjacent foundation

The minimum depth of foundation should be considered to ensure that the soil is having the required safe bearing capacity as assumed in the design. However, it is advised to carry out soil investigation before deciding on depth of foundation. Soil investigation report will suggest the foundation depth based on the type of structure, soil properties, depth of water table, and all other variable that should be considered. Soil investigation report provides bearing capacity of soil at different levels and at different locations.

Determine Minimum Required Depth of Foundation

When the soil investigation report is not available, the depth of foundation should be selected such that it is not affected by swelling and shrinking of soil due to seasonal changes. Depth of foundation should also consider the depth of water table to prevent and scour below the ground.

For foundation near existing foundation, It must be ensured that pressure bulbs of foundations do not coincide if the depth of new foundation has to be taken below the depth of existing foundation.

The foundation should not be contracted at shallow depth considering the frost action in cold countries.

Rankine’s formula provides the guidance on minimum depth of foundation based on bearing capacity of soil.

Where, h = minimum depth of foundation

p = gross bearing capacity

 = density of soil

  = angle of repose or internal friction of soil.

The above formula does not consider the factors discussed above and just provides the guidance on minimum foundation depth, assuming that the foundations are not affected by factors such as water table, frost action, types and properties of soil etc. as discussed above. This formula does not consider the loads from the structure on the foundation.

In the Rankine’s formula, it can be seen that foundation depth depends on the bearing capacity of soil, so, if the bearing capacity of soil increases, the depth of foundation also increases.