CHAPTER 3: COMMERCIAL AND INDUSTRIAL BUILDINGS
LESSON 12: BASEMENT
12.0 INTRODUCTION
In civil engineering, a basement is defined as a subterranean or partially subterranean level of a
building, located either entirely or partially below the ground level. It's essentially the lowest
floor of a building, built below the natural grade line (the surface of the surrounding land).
12.1 FUNCTIONS OF A BASEMENT
Basements serve numerous functions in buildings, depending on the building type and the
specific design requirements. Here are the primary functions from a civil engineering and
building utilization perspective:
1. Foundation and Structural Support:
• Load Transfer: The basement acts as a critical part of the foundation, transferring the building's
weight (live and dead loads) to the underlying soil.
• Stability and Anchorage: It provides stability to the structure, resisting uplift from wind or
earthquake forces. It can also serve as an anchorage point for foundation systems.
• Deep Foundation Option: In areas with unstable or expansive soils, a basement can act as a
deep foundation, reaching deeper into stable soil strata.
2. Space for Utilities and Mechanical Systems:
• Housing Essential Infrastructure: Basements are commonly used to house essential building
systems, including:
* HVAC (Heating, Ventilation, and Air Conditioning) Equipment: Furnaces, boilers, air
handlers, and ductwork.
* Electrical Panels and Wiring: Main electrical service panels, transformers, and wiring
conduits.
* Plumbing Systems: Water heaters, pumps, pipes, and sewage ejector systems.
* Fire Suppression Systems: Sprinkler system components, water tanks, and pumps.
* Data and Communication Equipment: Servers, routers, and other communication
infrastructure.
• Accessibility for Maintenance: Basements provide easy access for maintenance, repairs, and
upgrades to these essential systems.
3. Usable Living or Functional Space:
• Additional Living Space: Basements can be finished to provide additional living space,
including:
* Bedrooms
* Bathrooms
* Living rooms or recreation rooms
* Home offices
* Home theaters
• Storage Space: They often serve as a valuable space for storage, reducing clutter on upper
floors.
• Functional Space: They can be used for laundry rooms, workshops, wine cellars, or other
specialized uses.
4. Protection and Environmental Control:
• Thermal Insulation: Basements can provide natural insulation, helping to regulate building
temperature and reduce heating and cooling costs. The earth surrounding the basement maintains
a relatively stable temperature.
• Protection from the Elements: They offer protection from wind, rain, snow, and extreme
temperatures.
• Protection from Natural Hazards: Properly designed and constructed basements can offer some
protection during storms or even mild seismic events.
• Sound Dampening: They can help reduce noise transmission between floors.
5. Flood Control (With Proper Design):
• Flood Mitigation: In flood-prone areas, raised basements or properly designed waterproof
basements can reduce the risk of flood damage. However, they must be designed with adequate
drainage and waterproofing features.
6. Economic Considerations:
• Increased Property Value: A finished basement can add significant value to a property.
• Efficient Space Utilization: Basements allow developers to maximize usable space on a limited
footprint.
12.2 DIFFERENT TYPES OF BASEMENT TYPES
Key Considerations for Basement Types:
• Site Conditions: Soil type, groundwater level, and slope of the land influence the selection of
basement type.
• Building Design: The building's size, intended use, and layout determine the appropriate
basement type.
• Budget: Different types of basements have varying construction costs.
• Local Building Codes: Compliance with regulations on egress, ventilation, and waterproofing.
• Functionality: The intended use of the basement (storage, living space, utilities, etc.) dictates its
design.
In Civil Engineering, understanding these basement types is essential for:
• Proper structural design and foundation stability.
• Effective waterproofing and drainage planning.
• Efficient use of space and integration with the building design.
• Compliance with safety regulations.
12.2.1 Retaining Walls
a) Definition: A retaining wall is a structure designed to hold back soil or other loose materials
that would otherwise collapse or erode due to gravity. It's used to create a change in elevation,
stabilize slopes, or support earth embankments.
b) Functions of a Retaining Wall:
• Soil Stabilization: Prevents soil from slumping, sliding, or collapsing.
• Grade Change: Allows for the creation of level areas on sloping terrain, useful for construction
or landscaping.
• Water Management: Can sometimes be incorporated to control water flow and prevent erosion.
• Support for Structures: Provides lateral support to foundations, pavements, and other
structures.
• Aesthetic Purposes: Can be designed for visual appeal, often used in landscaping or
architectural design.
c) Types of Retaining Walls:
• Gravity Retaining Walls: Rely on their own weight to resist soil pressure. Typically
constructed of concrete, stone, or masonry. Effective for lower walls with smaller loads.
• Cantilever Retaining Walls: Use a reinforced concrete base and a vertical wall that cantilevers
out from the base. Widely used for various wall heights, very common.
• Counterfort Retaining Walls: Similar to cantilever walls, but with vertical supports
(counterforts) on the back of the wall for added stability, used for taller walls with greater loads.
• Buttress Retaining Walls: Similar to counterfort, but with supports on the front (visible side) of
the wall, not as common as counterforts.
• Sheet Pile Retaining Walls: Constructed using interlocking sheets of steel or concrete driven
into the ground, used in temporary support for excavations or permanent waterfront structures.
• Gabion Retaining Walls: Made from wire cages filled with rocks, used for erosion control,
landscaping, or retaining slopes.
• Anchored Retaining Walls: Used when additional lateral resistance is needed. Can use soil
anchors, tiebacks, or geogrids to improve stability.
Figure 1.2 Retaining wall terminology
d) Design Considerations:
• Soil Properties: Understanding the type of soil (e.g., clay, sand, gravel), its density, cohesion,
and angle of internal friction is crucial.
• Surcharge Loads: Accounting for additional loads on the soil behind the wall, like vehicles,
buildings, or stored materials.
• Water Pressure: Designing for hydrostatic pressure if groundwater is present.
• Stability: Ensuring the wall is stable against sliding, overturning, and bearing failure.
• Drainage: Implementing proper drainage behind the wall to prevent water buildup.
• Material Selection: Choosing durable and suitable materials based on structural requirements
and aesthetic preferences.
12.2.2 Raft Basements (Mat Foundations)
a) Definition: A raft basement, also known as a mat foundation, is a large, continuous concrete
slab that covers the entire footprint of a building and acts as both the foundation and the
basement floor. It's used to distribute the building's load over a wide area.
b) Functions of a Raft Basement:
• Load Distribution: Distributes the building's load uniformly over a large area, minimizing the
stress on the underlying soil.
• Foundation for Unstable Soil: Effective in situations with weak or compressible soil, where
traditional footings would not be adequate.
• Uniform Settlement: Helps to prevent differential settlement of the building, which can lead to
structural damage.
• Waterproofing and Moisture Barrier: Acts as a base layer for waterproofing and can help to
prevent moisture intrusion from the ground below.
• Base for a Basement: Provides the floor of the basement and transfers structural loads to the
soil below.
c) When to Use a Raft Basement:
• Weak Soil: Used when the soil bearing capacity is low or variable.
• High Water Table: Can help to prevent water intrusion if properly designed.
• Heavy Buildings: Suitable for large, heavy structures with significant loads.
• Uniform Settlement Required: When it's essential to prevent uneven settlement.
• Small Footprint Buildings: Can be very useful when the building's footprint does not allow for
traditional strip footings.
d) Types of Raft Foundations (Based on Structural Design):
• Flat Slab Rafts: A simple, uniform-thickness concrete slab used for relatively light loads.
• Thickened Slab Rafts: Increased thickness at specific locations, such as under load-bearing
walls, for better support of concentrated loads.
• Ribbed Rafts: Consist of a concrete slab with ribs or beams that improve its stiffness and load
distribution. Suitable for heavier loads or weaker soils.
• cellular Rafts: A cellular raft foundation consists of two slabs with two-way interlocking
ground beams. The upper (suspended) slab and the lower (ground-bearing) slab are usually
incorporated within the beams to form I-sections, with voids between them.
Cellular raft foundations are very rigid, making them suitable for heavy loads or loose soil that
can be subject to uneven settlement.
e) Design Considerations:
• Soil Properties: Analyzing the soil's bearing capacity, compressibility, and settlement
characteristics.
• Building Loads: Determining the building's weight and any additional loads that will be
imposed on the raft.
• Slab Thickness: Designing for adequate strength and stiffness to resist bending and shearing
forces.
• Reinforcement: Using reinforcing steel (rebar) to provide tensile strength and prevent
cracking.
• Waterproofing: Incorporating waterproofing measures to prevent water intrusion.
• Drainage: Implementing drainage systems to divert water away from the foundation.
12.2.3 Box Basements
a) Definition: A box basement, also known as a "box-type" or "rigid frame" basement, is a
foundation system constructed from reinforced concrete walls and a concrete base slab, forming
a rigid, box-like structure below ground. The walls are typically connected monolithically (cast
as a single unit) to the base slab, providing a high degree of structural integrity.
b) Characteristics:
• Rigid Structure: The interconnected walls and base slab create a very strong, rigid box that can
withstand significant soil and hydrostatic pressures.
• Monolithic Construction: The walls and base slab are typically cast as a single unit, ensuring a
strong, continuous connection.
• Watertight Construction: Designed with a focus on creating a watertight enclosure, making it
suitable for areas with high water tables.
• Good Load Distribution: The box structure distributes the building's load evenly to the
foundation soil.
• Suitable for Poor Soil: Often used when dealing with soft or unstable soils that cannot support
typical foundations.
• Can be Multilevel: Can be designed with multiple levels for underground parking, storage, or
other specialized uses.
c) Advantages:
• High Structural Strength and Stability: Provides exceptional resistance to soil pressures and
settlement.
• Watertight Construction: Effective in preventing water infiltration, making it suitable for high
water table conditions.
• Suitable for Poor Soils: Allows construction on sites with soft or unstable ground.
• Good Load Distribution: Ensures uniform load distribution and minimizes differential
settlement.
• Can Support Heavy Loads: Well-suited for supporting large and heavy buildings.
d) Disadvantages:
• Higher Construction Cost: Compared to simpler foundations, box basements are more
expensive due to their complexity.
• Requires Skilled Construction: Requires specialized expertise and precise construction
techniques.
• Complex Design: Design requires detailed engineering and analysis.
e) Common Uses:
• High-rise buildings, especially those with underground parking.
• Buildings located in areas with soft or unstable soil.
• Buildings located in areas with a high water table.
• Structures requiring a watertight underground space.
• Buildings requiring high structural integrity and stability.
12.2.4 Cellular Basements
a) Definition: A cellular basement, also referred to as a "honeycomb" or "waffle slab" basement,
consists of a grid of interconnected concrete walls and slabs, creating a series of cells or
compartments within the foundation structure. It's a reinforced concrete system that provides
enhanced strength and stiffness.
b) Characteristics:
• Cellular Structure: The grid-like formation of walls and slabs creates a series of cells or
compartments.
• Lightweight: While it is strong, the cellular structure uses less concrete than solid slabs,
making it relatively lightweight.
• High Stiffness and Strength: Provides high structural integrity due to the interconnected walls
and slabs.
• Efficient Load Distribution: The cellular design efficiently distributes loads across the
foundation.
• Suitable for Large Spans: Ideal for covering large areas and supporting heavy loads.
• Can be Precast: Elements can be precast, speeding up on-site construction.
c) Advantages:
• High Strength and Stiffness: Provides significant structural strength and resistance to
deformation.
• Lightweight Compared to Solid Slabs: Reduces the total weight of the foundation.
• Efficient Load Distribution: Distributes loads evenly, reducing stress on the soil.
• Suitable for Large Spans: Enables the construction of wide, open basements.
•Can Reduce Concrete Use: Reduces the amount of concrete required compared to solid slabs,
leading to cost savings.
d) Disadvantages:
• More Complex Construction: More complex to form and construct than solid concrete slabs.
• Can Be Labor Intensive: Requires skilled labor and careful formwork construction.
• Cost May Be High Can be more costly than simpler solutions for smaller projects.
e) Common Uses:
• Large buildings, including commercial and industrial structures.
• Buildings on soft or unstable soil.
• Buildings requiring large, open basement spaces without columns.
• Structures with significant vertical loads.
• Underground parking garages, auditoriums and theaters.
12.2.5 Piled Basements
a) Definition: A piled basement is a foundation system that combines a traditional basement with
a deep foundation system using piles or piers. The piles transfer the building's load to deeper,
more stable soil strata when the surface soil is inadequate to support the structure directly.
b) Characteristics:
• Deep Foundations: Piles or piers extend deep into the ground to reach stable soil.
• Combined Foundation System: Integrates a basement slab with a piling system for additional
support.
• Used in Poor Soils: Designed for situations with very weak or unstable soil.
• Supports Heavy Loads: Capable of supporting substantial structural loads.
• Reduces Settlement: Minimizes settlement and differential settlement issues.
• Can be Complex Design and Construction: Requires specialized engineering knowledge and
piling equipment.
c) Types of Piles Used in Piled Basements:
• Driven Piles: Piles driven into the ground using pile drivers. Materials include steel, concrete,
or timber.
• Bored Piles: Piles created by drilling a hole into the ground, filling it with concrete, and
sometimes reinforcement.
• Micro-Piles: Small-diameter piles used in situations with limited access or sensitive
surroundings.
d) Advantages:
• Suitable for Very Poor Soils: Enables construction on sites with soft, unstable, or expansive
soils.
• Reduces Settlement: Minimizes settlement and differential settlement.
• Supports Heavy Loads: Can handle substantial structural loads.
• Versatile Application: Suitable for diverse soil and building conditions.
e) Disadvantages:
• Higher Construction Cost: Piling is typically an expensive foundation option.
• Specialized Equipment and Skills: Requires specialized equipment and skilled labor for
installation.
• Can be Noisy and Disruptive: Pile driving can generate significant noise and vibrations.
• Complex Design and Analysis: Requires a detailed geotechnical investigation and engineering
design.
f) Common Uses:
• High-rise buildings in areas with poor soil conditions.
• Buildings located in earthquake-prone zones.
• Structures near waterfronts or other unstable areas.
• Buildings with heavy loads requiring deep foundation support.
In Summary:
• Box basements provide a rigid, watertight structure for stable and secure foundations, often
chosen when high strength and water tightness are essential.
• Cellular basements are lightweight yet stiff systems that distribute loads efficiently, especially
useful in supporting large areas with limited columns.
• Piled basements utilize piles to reach stable ground, enabling construction on sites with very
poor soil conditions and high loads.
CONSOLIDATION EXERCISES:
1) What is basement
Answer: A basement is defined as a subterranean or partially subterranean level of a building,
located either entirely or partially below the ground level.
2) Give 4 functions of a basement
Answer: • Load Transfer: The basement acts as a critical part of the foundation, transferring the
building's weight (live and dead loads) to the underlying soil.
• Stability and Anchorage: It provides stability to the structure, resisting uplift from wind or
earthquake forces. It can also serve as an anchorage point for foundation systems.
• Deep Foundation Option: In areas with unstable or expansive soils, a basement can act as a
deep foundation, reaching deeper into stable soil strata.
• Thermal Insulation: Basements can provide natural insulation, helping to regulate building
temperature and reduce heating and cooling costs. The earth surrounding the basement maintains
a relatively stable temperature.
3) List 3 types of retaining walls
Answer: • Gravity Retaining Walls: Rely on their own weight to resist soil pressure. Typically
constructed of concrete, stone, or masonry. Effective for lower walls with smaller loads.
• Cantilever Retaining Walls: Use a reinforced concrete base and a vertical wall that cantilevers
out from the base. Widely used for various wall heights, very common.
• Counterfort Retaining Walls: Similar to cantilever walls, but with vertical supports
(counterforts) on the back of the wall for added stability, used for taller walls with greater loads.
ASSIGNMENT:
1) Draw the different types of piled basements
Answer: