Pervious concrete (also called porous concrete, permeable concrete, no fines concrete and porous pavement) is a special type of concrete with a high porosity used for concrete flatwork applications that allows water from precipitation and other sources to pass directly through, thereby reducing the runoff from a site and allowing groundwater recharge.
A pervious concrete street
Pervious concrete is made using large aggregates with little to no fine aggregates. The concrete paste then coats the aggregates and allows water to pass through the concrete slab. Pervious concrete is traditionally used in parking areas, areas with light traffic, residential streets, pedestrian walkways, and greenhouses.[1][2] It is an important application for sustainable construction and is one of many low impact development techniques used by builders to protect water quality.
2. Contents
Introduction
Alterations of ground after formation
Need for Ground Improvement
Ground Improvement potential
Improvement techniques
Modern Techniques
3. Introduction
• Soil improvement is the alteration of any property of a soil to improve
its engineering performance which may either be a temporary process or
a permanent
• This can be done by reducing the pore water pressure, by reducing the
volume of voids in the soil, or by adding stronger materials.
• The result of an application of a technique may be increased strength,
reduced compressibility, reduced permeability, or improved ground water
condition
4. Alterations of Ground after formation
Major causes of alterations are
– Seasonal moisture variation
– Water seepage and surface erosion
– Vegetation
– Temperature variation
– Vibration
– Mining subsidence and pumping
– Construction operation
5. Need for ground improvement
• Rapid urbanisation and industrial growth driving demand for land . In
order to meet this demand, land reclamation & utilization of unsuitable or
environmentally affected lands have been taken up
• Where poor ground conditions make traditional forms of construction
expensive, it may be economically viable to attempt to improve the
engineering properties of the ground before building on it
• To improve load bearing capacity and shear strength
6. Ground Improvement potential
All ground conditions may not be the same but different in varieties and
generally of three types:
Hazardous: A regional/local field condition is such that a regular design
approach or an economical treatment technique may not be feasible and
construction in such a location may result in ultimate disaster. As far as
possible such location must be avoided
Poor: A local condition including regional conditions which may require
special design &/or special treatment for development
Favorable: A local condition including regional conditions for which normal
design and ground treatments are suitable
8. Mechanical Compaction
• This method utilizes mechanical compactors and rollers which reduce
voids
• This method has very low depth of influence and hence can be used only
for shallow soils
• In the event of weak soil being present up to certain depth, the same is
replaced with a layer of good soil
• Sheepsfoot roller and vibratory rollers are used for cohesive and
cohesionless soils respectively
9. Soil stabilization techniques
• This method can be used only for shallow soils which includes:
– Mechanical: This method employs mixing and re-
proportioning of soils with sandy/gravely material
– Chemical: This method employs the use of lime, calcium & sodium
chlorides, admixtures like lignin, water-proofers, aggregants,
dispersants, natural and synthetic polymers
– Cementing: This method employs use of Cement. Lime and/or Flyash
and/or bituminous (asphalt) material may be used
10. Dynamic Compaction
• This method has a higher depth of influence as compared to mechanical
compaction methods and hence can be used for deeper soils
• This method includes:
– Vibration methods
– Impact methods
– Micro-Blasting
12. Impact methods
1. The depth up to which soil can be compacted is 10-12 m
2. All types of soil except clay-bearing and soil having high water table, can
be compacted
3. The Depth of influence/improvement is given by : D = n(W*H)0.5
where ‘n’ is a constant which depends on various factors like:
– Material to be compacted
– Applied force
– Contact area
– Presence of energy absorbing layers
13. These methods are:
• Rapid Impact compaction: In this method, the soil is compacted
under the pounding action of heavy hammer
• Dropping of heavy weight: In this method, steel or concrete weight
around 500-600kN is dropped from a height of 40-50m with the help of a
crane
Animation
Animation
14. Micro-blasting
• The micro-blasting technology is used for the improvement of subsoil
under civil and hydro engineering structures.
• It employs high-energy explosions to modify the surrounding soil.
• The energy generated by the explosion of 1 kg of TNT = the energy of 5
tons of tamper falling free from a height of 100m.
• Applications: harbour areas, reclaimed islands, breakwaters, road
embankments and airfield pavements, nuclear power plants, dams, etc.
Loose soil before
blasting
Densified soil
after blasting
Underwater explosive
compaction
explosive compaction with
surface charges
16. Pre-loading
• It is used to densify sanitary landfills
• Pre-load is applied in the form of an imposed earth-fill left for a long period
over an area to be compacted
• When soil is being laid on the garbage and kept for long period, the leachate
present in it is squeezed out, as a result, there is reduction in volume of
garbage and more space is available
17. Drainage Methods
• This is includes several methods like:
– Dewatering systems: these include methods like construction of
sumps/ditches/trenches and well-point system
– Drains: these include open, closed, horizontal and vertical drains
18. Diaphragm wall
• It’s the generalized term used for stone columns, vertical sand drains
• In which a vertical wall is constructed to prevent collapse of sides by
resisting the lateral pressure and add to stability of structure of soil
• Thus Diaphragm wall include :
a) Sand Drains
b) Stone columns
19. Grouting & Injection
• Grouting is normally done to fill the cracks present in soil or rock strata
• It proves effective in following situations
– When foundation is to be below ground water table
– When site is located in an area where direct access is restricted
– When design of foundation is restricted by no. of boundaries & contact zones
– Excavation is not possible besides the proposed structure
• The grout used may be a combination of cement slurry with different
admixture
• Bentonite slurry may be commonly used grout, it is basically a highly
plastic clay which has 2 advantages
– Due to its highly plastic nature it can enter into even its smallest present crevice
– It compacts quickly & forms a monolithic structure
– It is costly and hence used in special situations like to protect the sides of tunnels from
collapsing
23. Electrical methods
• Electro-osmosis
– This method is employed for cohesive soils (clays)
– Metal strips are inserted and a well point system is also employed
– The current is passed through metal strips thus becoming the anode
and well point system as cathode
– Water being charged with anions flows to well point system and is
pumped out
24. Thermal Stabilisation by Heating
Temperature
Formation of
Thermal
Gradient in soil
Flow of pore
water
Dielectric
Constant
Particle Electric
Repulsion
Strength of soil
25. Thermal Stabilisation by Cooling
Temperature
Pore water in
soil freezes
Ice is formed
Soil is reinforced
Non-vibration
sensitive
barriers/walls are
formed
Soil Strength
26. Rock Anchors
• Rock bolts are tensile units employed to keep rock mass in compression
• It is installed as nearly perpendicular to joints as practicable
• The ordinary types consist of rods installed in drill holes by driving and wedging, by
driving and expanding, or by grouting with mortar or resins
• Bolt heads are then attached to rod and twisted against a metal plate to impose
the compressive force on mass
• Fully grouted rock bolts, provide more permanent bolts than ordinary types
• Rock bolts are used in slope stabilization, open excavations, in tunnels, caverns,
mines, concrete dam foundations to provide resistance to uplift and sliding
27. Geo-products
• These include use of Geo-textiles, Geo-membranes,
Geo-grids, Geo-spacers, geo-webs, geo-composites,
etc
• These in general are porous of polypropylene
polyester, nylon or PVC and their variations
• The main functions of these are :
1. Separation
2. Fluid transmission
3. Reinforcement
4. Filtration
5. Containment
6. Barrier
