The document discusses strengthening substructures. It defines a substructure as including the foundation and supporting elements below ground level. Common reasons for needing to strengthen substructures include changes in building loads, foundation settlement, aging infrastructure, and seismic vulnerability. Failure can result from poor soil conditions, improper foundation design, construction issues, water-related problems, environmental factors, overloading, lack of maintenance, and age-related deterioration. Key factors that influence substructure strength are identified as well as common causes of failure. Various methods for strengthening substructures are outlined, including underpinning, grouting, micropiles, soil nailing, and tiebacks.

1. DEPARTMENT OF CIVIL
ENGINEERING
Presented by:
Nandhini V (23SE09)
M.E – Structural Engineering
Strengthening of substructures
P23STP01 – MAINTENANCE AND
REHABILITATION OF STRUCTURES

2. STRENGTHENING OF SUBSTRUCTURES
Introduction:
 The substructure typically includes the foundation and any supporting elements
below ground level.
 The methods of strengthening the substructure depends on the nature of the
existing substructure issues, soil conditions, and the requirements of the
structure.
 The strength of a substructure, which includes the foundation and supporting
elements below ground level, is influenced by various factors, coupled with
proper engineering analysis and design, is essential for creating a strong and
stable substructure for a building or any other structure.

3. TYPES OF FOUNDATION
End Bearing Pile
Friction Pile
Under Reemed Pile
Both End Bearing and
Friction Pile

4. Why Strengthening of substructure need?
 Changes in Building Use or Load Requirements
 Foundation Settlement or Movement
 Aging Infrastructure
 Structural Damage or Distress
 Seismic Vulnerability
 Changes in Soil Conditions
 Increased Environmental Loads
 Upgrading to Meet Building Codes

5. Causes for substructure failure:
1. Poor Soil Conditions:
 Inadequate Bearing Capacity: If the soil beneath the foundation lacks the
necessary bearing capacity to support the structure's loads, settlement or failure
may occur.
 Expansive Soils: Swelling or shrinking of expansive soils due to changes in
moisture content can lead to differential settlement and foundation movement.
2. Improper Foundation Design:
 Incorrect Type of Foundation: Choosing an inappropriate foundation type for
the specific soil conditions or building loads can result in failure.
 Inadequate Depth: Foundations that are not deep enough may experience
settlement or instability, especially in regions with variable soil conditions.

6. Contd…
3. Construction Issues:
 Poor Construction Practices: Inadequate compaction of fill material, improper
concrete curing, or faulty construction techniques can compromise the strength
and stability of the substructure.
 Insufficient Reinforcement: Inadequate reinforcement in the foundation
elements, such as footings and piles, can lead to structural failure under heavy
loads.
4. Water-related Issues:
 High Groundwater Levels: Elevated groundwater levels can reduce the bearing
capacity of the soil and lead to settlement or instability.
 Poor Drainage: Inadequate drainage around the foundation can result in water
accumulation, soil erosion, and other water-related problems.

7. Contd…
5. Environmental Factors:
 Freeze-Thaw Cycles: In regions with freezing temperatures, the expansion
and contraction of water in the soil can cause heaving and settlement,
affecting the substructure.
 Seismic Activity: Earthquakes can induce lateral forces and ground
movement, potentially causing foundation failure.
6. Structural Overloading:
 Excessive Loads: Overloading the structure beyond its design capacity can
lead to stress and deformation in the substructure.
 Unanticipated Loads: Changes in building use or renovations without proper
consideration of the additional loads can contribute to failure.

8. Contd…
7. Lack of Maintenance:
 Neglected Repairs: Ignoring signs of foundation distress or failing to
address minor issues in a timely manner can lead to more severe
problems.
 Vegetation Growth: Roots from nearby trees and shrubs can exert
pressure on foundations and cause damage over time.
8. Geological Factors:
 Natural Subsidence: Some areas may experience natural subsidence due
to geological processes, leading to settlement and structural issues.
 Karst Formation: In regions with karst topography, dissolution of
soluble rocks can result in the formation of sinkholes and instability.

9. Contd…
9. Age-related Deterioration:
 Material Degradation: Over time, concrete and other construction
materials may degrade due to environmental exposure, leading to a
reduction in strength and stability.

10. Factors governing strength of substructure:
1. Soil Characteristics
 Type of Soil
 Soil Bearing Capacity
2. Foundation Type
 Type of Foundation
3. Load Characteristics
 Vertical Loads
 Lateral Loads

11. Contd…
4. Structural Design
 Building Design
 Materials Used
5. Environmental Conditions
 Climate
 Groundwater Level
6. Geotechnical Investigations
 Site Investigation
 Subsurface Conditions

12. 7. Construction Techniques
 Excavation and Backfilling
 Compaction
8. Regulatory Requirements
 Building Codes and Standards
9. Monitoring and Maintenance
 Monitoring Systems
 Regular Maintenance
Contd…

13. Steps involved in strengthening of substructure:
 Structural Assessment
 Determine Causes of Distress
 Load Analysis
 Conceptual Design
 Detailed Engineering Design
 Geotechnical Design
 Material Selection
 Construction Planning
 Site Preparation
 Implementation of Strengthening Measures
 Quality Control and Monitoring
 Post-Strengthening Assessment
 Documentation
 Maintenance and Monitoring

14. Methods used for strengthening substructures:
 Bracing System for Piers
 Micro-Reinforcement with Fibers
 Localized Foundation
Strengthening
 Underpinning
 Grouting
 Micropiles
 Soil Nailing
 Jet Grouting
 Sheet Piling
 Reinforcement with Geotextiles
 Chemical Stabilization
 Slope Stability Measures
 Foundation Replacement
 Tiebacks or Ground Anchors
 Base Isolation
 Concrete Jacketing
 Carbon Fiber Reinforcement
 Steel Plate Bonding
 Strengthening of bridge piers

15. Micro-Reinforcement
with Fibers
Bracing System
for Piers
Methods used for strengthening substructures:

16. Methods used for strengthening substructures:
Underpinning
Localized Foundation
Strengthening

17. Grouting

18. Micropiles

19. Soil Nailing

20. Jet Grouting

21. Sheet Piling
Tiebacks or
Ground Anchors

22. Strengthening of bridge piers