Basement construction report

BASEMENT CONSTRUCTION AND WATERPROOFING.

1.  
  
 
BASEMENTS  
REPORT- BUILDING CONSTRUCTION  
─  
SUBMITTED TO:  
DR. MEENAKSHI SINGHAL  
SILIA GROVER  
SUBMITTED BY:  
ANKITA ARORA(17071978168)  
BHAVIKA GOYAL(17071978180)  
SECTION B; SEMESTER 4.  
 
 
 

2. 1  
 
INTRODUCTION  
●The term “basement” has been regarded as synonymous to the term “deep pit”, which  
applies to excavations over 4.5 m deep.   
●The main purpose of constructing  
basements are:   
(a) to provide additional space,  
(b) as a form of buoyancy raft,   
(c) in some cases, basements may be needed   for  
reducing net bearing pressure by the  
removal of the soil.  
 
A basement can be defined as a building  
storey built below the ground level.   
The basement walls are in fact retaining walls   to  
withstand the soil and hydraulic pressures.  
A basement can be constructed either by choice or compulsion.  
BASEMENT CONSTRUCTION BY CHOICE  
It can be constructed by choice if the plot area is quite large, does not violates by-lawsand  
plenty   
funds are available.  
Basements are common in large and tall buildings and often used as car parks, stores,  
underground shopping complexes etc.  
In most cases, the main function of the basement in a building is to provide additional  
space for the owner, and the fact that it reduces the net bearing pressure by the weight of  
the displaced soil may be quite incidental. In cases where basements are actually needed  
for their function in reducing net bearing pressure, the additional floor space in the  
substructure is an added bonus.  

3. 2  
 
BASEMENT CONSTRUCTION BY COMPULSION  
When the house is built on a low lying plot, construction of the basement is regarded better  
than resorting to earth filling below the floors. The house builder may do all sorts of  
compaction of earth filed below the floors but the threat of settlement of floors over the time  
remains.  
When the natural ground level is more than 6ft below the road level, technically, one should  
opt for a basement instead of landfill. In such cases basement construction can be considered  
as a compulsion.  
 
TYPES OF BASEMENTS   
CATEGORIES OF BASEMENT   
● Basic utility (car parking, plant rooms (excluding electrical equipment, workshops)  
● Better utility (workshops and plant rooms requiring drier environments )  
● Habitable (ventilated residential and commercial areas)   
● Special (archives, requiring controlled environments).  
 
 
 
 

4. 3  
 
BASEMENT MATERIALS   
Poured reinforced concrete basements:  
(Used in high water table areas)   
● Solid concrete is better able to resist  
cave-ins caused by lateral pressures of  
water, earth, and wind.  
● More fire resistance-because solid  
concrete is dense and is joint free.  
● More resistant to water since  
concrete has fewer and smaller voids than  
concrete blocks.  
Masonry block basements:( Used in low water table areas)   
● The basement walls are  
made with masonry block units.  
● There are many joints  
where the masonry units connect  
and thus the walls need to be  
properly and adequately  
waterproofed (not damp proofed)  
to avoid water seepage.  
 

5. 4  
 
 
Precast panel basements   
●The precast basement panel  
can be created in much the  
same way as the poured  
concrete basement.  
● In this method, basement walls  
are generally molded at a  
location other than the building  
site.  
● The walls can then be transported to the building location and placed on the  
footer.  
●While the integrity of the walls may be similar to the poured concrete wall, a crane  
will be needed to place the walls on the footer. The cost for such major  
equipment can increase the total cost of the basement construction.  
BASEMENT DESIGNS   
●A basement is one or more floors of a building  
that are either completely or partially below the  
ground floor.   
 
 
●A Semi-basement is an architectural term for a  
floor of a building that is half below ground,  
rather than entirely such as a true basement or  
cellar.   
 

6. 5  
 
● A Lower ground floor is the lowest level of a building partially below the surface  
of the ground.   
 
 
 
BASIC REQUIREMENTS  
●Care should be taken to build a damp proof basement that doesn't allow ingress  
of water or moisture.  
●Design should allow maximum possible light and ventilation.  
●The local bylaws should be followed and carefully studied before any type of  
construction.  
●No objection certificate from the owners of the neighbouring plots should be  
secured.  
●Basements should not increase the risk of flooding from any source and are not  
being encouraged in areas that are prone to flooding.   
● Basements should have adequate Fire Safety measures and Means of Escape.  
●Avoid adversely affecting drainage and run-off or causing other damage to the  
water environment.  
●If groundwater is present, the levels should be monitored for a period of time.  

7. 6  
 
NBC GUIDELINES RELATED TO  
BASEMENT CONSTRUCTION  
●The minimum height of the basement should be 2.5 metres and the maximum  
height 4.5 metres.  
●The ceiling height should be a minimum of 0.9 metres and maximum of 1.2  
metres above the road surface.  
●Ventilation is must for the basement and could be in the form of blowers, exhaust  
fans, air-conditioning, etc.  
●Surface drainage should not enter the basement.  
●The basement’s walls and floors must be water-proof.  
●The basement should not be accessed directly from the road. It should be  
accessed only from the main entrance or an alternative staircase that provides  
access to the building.  
●Only when a projecting basement is flush with the ground, or if the authority  
allows, can the basement be permitted to touch the adjacent property.  
WATERPROOFING OF BASEMENTS   
Waterproofing a basement is applying a membrane to the basement wall that has the  
ability to bridge  
cracks if they should  
occur in the  
basement wall. If the  
site has a high water  
table or poor soil  
conditions then a  
waterproofing system  
should be used.  

8. 7  
 
However although the soil drains well many people waterproof the basement walls  
anyway for extra protection against water getting into the basement.  
 
CARE FOR INSERTS  
Certain electric conduits and boxes need to be placed in RCC walls before casting them.  
All conduits’ location must be pre planned and should be secured in their positions.  
It is not possible to provide conduits and electrical boxes after the RCC walls. Binding  
wire should be wrapped in helical fashion around the PVC conduit pipes for creating  
their bond with concrete. The conduits and boxes are to be provided along the inner  
face of the wall.  
BASEMENT WALLS  
●The walls should ideally be cast in RCC.  
●In certain areas the practice of raising half brick walls and then leaving a gap  
between them is followed.   
●This “Desi” practice should be avoided as it reduces work of shattering for the  
contractors.  
●The concrete used should be rich, ideally M25.  
●Vertical reinforcement should be provided on both the faces of RCC walls for  
basements. In addition, horizontal bars should run inside vertical bars on both  
faces.  
●The RCC walls are designed to bear vertical loads from the structure above and  
the earth pressure on the outer face of walls.  
●The vertical steel bars should be provided in staggered fashion.  

9. 8  
 
THE MAJOR DESIGN  
CONSIDERATIONS  
The major design considerations for deep excavation is divided into five sections :  
1. Planning of surface investigation and laboratory testing.  
2. Evaluation of foundation of adjacent properties and their tolerance.  
3. Selection of type of retaining wall.  
4. Selection of type of support system.  
5. Size of excavation and scale of work  
6. Type of soil.  
7. Water table level.  
8. Contractor preference.  
9. Cost factor.  
 
SLURRY WALLS  
 
 
 
 
 
 
 
 

10. 9  
 
BRACING  
CONSTRUCTION METHODS  
There are essentially three general methods of constructing a basement:   
(1) Open cut method.  
(2) Cut and cover method.  
(3) Top down method.  
OPEN CUT METHOD  
This is the simplest and most straightforward technique of providing an excavation to  
the required depth. The sides of the excavation are sloped to provide stability, with  
possible slope protection to maximise the angle of the slope. Upon excavating to the  

11. 10  
 
required depth, the basement is constructed from bottom upwards. After the  
completion of the basement, the remaining excavated areas between the basement  
and the side slope are backfilled .  
ADVANTAGES  
●Because there are no additional support operations and equipment, it is the  
economical choice.   
● The open trench provides easy access to the work because equipment and  
construction materials are minimized.materials are minimized.   
● The open cut method is suitable for most ground conditions, except for oozing mud  
and running sands.  
 
DISADVANTAGES  
●The slope of the bank requires more excavation and backfill volume than the other  
options.  
● The only bank support is the strength of the soil. If drying, flooding, or change of  
soil properties weakens the soil, then sloughing and collapse can happen with  
little or no warning.  
●The sloped banks require a wider work area.  
● The bank slopes may force the use of larger equipment because the distance to  
reach into the trench is increased and a greater volume of soil must be excavated  
and backfilled.  

12. 11  
 
CUT AND COVER METHOD  
This technique is usually employed in constrained sites where ground movements to  
the adjacent surrounding have to be kept to the minimum.   
Retaining walls are required to support the excavation with the provision of bracing as  
the excavation proceeds downward until the deepest basement level. The basement is  
then constructed in the conventional way, bottom upwards in sequence with removal of  
the temporary struts .  
●The main disadvantages of a cut and cover tunnel are its disruptive effects in  
congested urban environments.   
● Cost of cut and cover construction increases sharply with increased depth.   
●Tunnel driving costs are usually higher per meter of tunnel that costs than the  
average shallow cut and cover tunnel.  
 

13. 12  
 
 
 
 
 
 
 
TOP DOWN METHOD  
●Similar to the cut and cover technique, permanent perimeter walls are first  
constructed. Reverse method of bottom up.   
●Prefounded columns are then constructed, followed by the construction of the  
ground floor slab.Steel stanchion/H-sections are inserted and concrete pumped in  
to slightly over the lowest basement slab level. The holes are then backfilled with  
soil. This lower part of the stanchions embedded in concrete will later form the  
integral part of the foundation for the structure. The upper part of the stanchions  
not embedded in concrete serves as the column supports for the subsequent  
basement floors.  
● Excavation then proceeds downward and basement slabs are constructed while  
construction of the superstructure proceeds simultaneously .   
●Excavation proceeds without the need for strutting to support the excavation as  
the slabs act as the permanent horizontal supports. When the formation level is  
reached, pile caps and ground beams are constructed.   

14. 13  
 
●The obvious advantage of utilising top down construction technique is that the  
superstructure can proceed upwards from ground level simultaneously with the  
excavation downwards.   
●Ground movement to the adjacent area is minimised as excavation is always  
strutted during construction. The main difficulties are the limited headroom for  
excavation, restricted access for material handling, dust and noise problems.   
●Cost of construction is high as it involves installation of more sophisticated  
temporary support such as prefounded columns.   
●Provision of mechanical ventilation and artificial lighting is necessary during  
construction.  
 
 
 
 
 
 
 
 
 
Whichever method is chosen, it is essential that the excavation is adequately supported,  
and the groundwater properly controlled. Shoring should be provided for any  
excavation that is more than 1.8 m deep. The three common methods of supporting an  
excavation either in isolation or combination are:  
● Excavations supported by sheet piling.   
●Excavation supported by reinforced concrete diaphragm wall constructed in  
advance of the main excavation.   
●Excavations supported by contiguous bored piles or secant piles  
constructed in advance of the main excavation.  

15. 14  
 
Construction in Excavations Supported by Sheet Piling   
●This is a suitable method for sites where the space around the excavation is insufficient  
for sloping back the sides.   
●If the soil conditions permit withdrawal of sheet piling for re-use elsewhere, this  
method of ground support is very economical compared with the alternative of a  
diaphragm wall.   
●Sheet piling comprises a row of piles which interlock with one another to form a  
continuous wall which may be temporary or permanent. It consists of rolled steel  
sections with interlocking edge joints.   
 
 
 
 
 
 
 
 
Construction in Excavations Supported by Reinforced Concrete Diaphragm Wall   
●A diaphragm wall is constructed by excavation in a trench which is temporarily  
supported by bentonite slurry.   
●On reaching founding level steel reinforcement is lowered into the trench,  
followed by concrete to displace the bentonite.   

16. 15  
 
●This method is suitable for sites where obstructions in the ground prevent sheet  
piles from being driven and where the occurrence of groundwater is  
unfavourable for other methods of support.   
 
●The bentonite slurry has the following properties:   
-Supports the excavation by exerting hydrostatic pressure on the wall.  
- Provides almost instantaneously a membrane with low permeability.   
-Suspends sludgy layers building up at the excavated base.   
-Allows clean  
displacement  
by concrete,  
with no  
subsequent  
interference  
with the bond  
between  
reinforcement  
and set  
concrete.   

17. 16  
 
●Excavation is carried out within the bentonite slurry immersion which  
supports the excavation by exerting hydrostatic pressure on the trench  
walls.   
Construction in Excavations Supported by Contiguous Bored Pile  
●Contiguous bored pile wall is a line of bored piles installed close together or  
touching.   
●The typical sequence of construction is such that the next pile is to be constructed  
more than 3 m away from the previous one.   
●This method is useful in: built-up areas where noise and vibration should be  
limited;in industrial complexes where access, headroom and/or restriction on  
vibration may make other  
methods such as steel sheet piling  
or diaphragm walling less suitable.   
●The male piles are reinforced  
while the female piles are not.   
 
 
DEWATERING  
●Dewatering is the process of removing water from an excavation.  
●Dewatering may be accomplished by lowering the groundwater table before the  
excavation work.  
● This method of dewatering is often used by placing pipelines in areas with high  
groundwater levels.  
●There are four basic methods for controlling groundwater:   
Open pumping — Water is permitted to flow into an excavation and collected in  
ditches and sumps before being pumped away.   
Pre Drainage — Lower groundwater table before excavation using pumped wells,  
wellpoints, ejectors and drains.   

18. 17  
 
Cutoff — Water entry is cut off with steel sheet piling, diaphragm walls,  
contiguous bored pile and secant pile walls, tremie seals or grout.   
Exclusion — Water is excluded with compressed air, a slurry shield, or an earth  
pressure shield. These methods are frequently used for tunnelling work.  
WATERTIGHT BARRIER WALLS  
●Keep water out  
●Barriers must  
reach an  
impervious  
strata.  
●Types- slurry  
walls and  
sheeting with  
pumps  
●Must resist  
hydrostatic  
pressure.  
 
 
 
 

19. 18  
 
CONTROLLING GROUNDWATER  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

20. 19  
 
BASEMENT FOUNDATION  
Depending upon the superstructure loads/moments transmitted to foundations and  
soil characteristics, the raft foundation could be of following types  
●Raft of uniform thickness(flat plate type)  
●Raft of uniform thickness with additional thickness under columns( flat slab type)  
●Cellular raft  
●Rigid frame raft  
●Raft supported on piles (piled raft)  
 

21. 20  
 
FLAT PLATE TYPE RAFT   
●This is the simplest form of raft foundation.
● This type of mat is used when the columns and walls are uniformly spaced at small intervals
and the subjected loads are relatively small.
●Reinforcement is
placed in both directions and
more reinforcement is required
at the column locations and
load-bearing walls.
●The thickness of this
type of raft foundation is
generally restricted within
300mm for economic reasons.
A thicker slab would not be
economical.

 
FLAT SLAB TYPE FOUNDATION  
When the columns and load        
bearing walls are subjected to        
heavier loads, the slab is        
thickened under the columns       
and walls and extra        
reinforcement is provided to      
resist against diagonal shear        
and negative reinforcement.  

 

22. 21  
 
 
 
 
 
 
 
 
 
 
 
 
BEAM AND SLAB TYPE RAFT  
●Raft system consists of an inverted beam and slab system, beams carry heavy loads and  
moments.  
●Adopted where in non uniform column loads likely to induce differential settlements.  
● Rigid beams connecting the columns reduce differential settlements.  
●Soil pressure carried by slabs transmitted to beams.  
●Space between beams over slabs filled up. These spaces used as sumps for basement drainage.  
●Filling can provide counter weight against buoyancy of groundwater.  
●Usually costly and time consuming compared to slab type.  
 

23. 22  
 
CELLULAR RAFT  
●Cellular raft foundation is  
also known as box type  
raft foundation or rigid  
frame raft foundation.   
●In this type of foundations,  
boxes like structures are  
formed where the walls of  
each box acts as beams  
and these are connected  
by slabs at top and  
bottom.   
●The beams and slabs are  
united in such a way that  
their cross section looks  
like an I-section.   
●This type of foundation  
can resist very high bending stresses and is suitable for loose soils where settlement is  
uneven.  
 
RIGID FRAME RAFT  
●In this type of raft, the foundation  
walls act as a deep beam.  
● Rigid frame mat is referred when  
columns carry extremely heavy  
loads and the connecting beams  
exceed 90cm depth.   
●Here two concrete slabs are  
placed, one on top of another  
and connected with foundation  
walls in both directions and thus  
forms a cellular raft foundation.   

24. 23  
 
●This type of raft is very rigid and is economical when the required slab thickness is  
very high.  
PILED RAFT  
●This type of raft foundation is
supported on piles.
● A piled raft is used when the soil at a
shallow depth is highly compressible
and the water table is high.
●Piles under the raft help in reducing
settlement and provide resistance
against buoyancy.

 
PILE CAPS AND STITCHING SLAB SYSTEM  
●Group of piles provided under columns.  
●Pile caps bottom connected through stitching slab to provide continuous base.  
●Stitching slab system span between pile caps and resist uplift pressure.  

25. 24  
 
 
WATERPROOFING  
 
 
 
 
 
 
 
 
 
 
To achieve the performance level required, one or a combination of the following  
waterproofing systems may be adopted:   
●Membrane system   
●Integral system  
● Cavity/drainage system  
Waterproofing vs Damp-proofing  
● Waterproofing prevents the passage of water in the presence of  
hydrostatic pressure.   

26. 25  
 
●Damp-proofing retards the absorption of moisture in the absence of  
hydrostatic pressure.  
Why waterproof a basement ?   
● Hydrostatic Pressure   
● Concrete cracks   
● Capillary Action    
●Vapor Transmission  
●Condensation  
HYDROSTATIC PRESSURE  
 
 
 
 
 

27. 26  
 
Hydrostatic pressure can cause =  
Basement flooding + structural damage  
+  
Property damage  
 
 
 
CAPILLARY ACTION  
Moisture infiltration results in=  
Unhealthy air + dampness + wall assembly  
damage  
 
 
CAPILLARY DEVELOPMENT  

28. 27  
 
CONCRETE CRACKS  
 
VAPOR TRANSMISSION  
 
 
 
 
 
 
 
 
 
 
 
What Is A Quality Waterproofing System?   
● Preventing the passage of liquid water in the presence of hydrostatic pressure.   
●A drainage system reducing hydrostatic pressure.  

29. 28  
 
 
METHODS OF WATERPROOFING  
BASEMENTS  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

30. 29  
 
 

31. 30  
 
1. Surface & Groundwater Control  
 
2. Application of waterstops at construction joints  
 
 

32. 31  
 
 
3. Cementitious system  
 
4.Structurally Integral Protection System  
 

33. 32  
 
5.Tanked or membrane cement  
 
 
 
 
6. Drained Cavity protection System  
 
 
 

34. 33  
 
7.Applying Ferrocement on Shore Piles  
 
 
 
 
 
 
 
 
 
 
 
 
8.MEMBRANE SYSTEM  
 
 
 
 
 
 
 
 
 
 
 
 
 

35. 34  
 
 
9. WELLS FOR WATERTABLE  
 
 
 
 
 
 
 
 
 
THANKYOU!