2. Foundations and basements

1. 2. Foundations and basements Building Technology (EG 626 CE)

2. Definition of foundation • It is the lowest part of structure. It provides base for super structure. It transmits loads to soil below. It is a part that is below the ground level. Function of foundation • To transmit all superimposed loads (wind, vibration, dead and live loads). • To withstand against all kinds of settlements (against failure of underlying soil). • To give stability to structure by resisting in firm base. • To prevent lateral movement of supporting materials. Characteristics • Wide enough section to distribute weight over larger base area within safe bearing capacity. • Evenly loaded condition that prevents unequal settlement. • Deep enough preventing overturning and increasing stability. Foundation

3. Types of foundation • Shallow foundation • Deep foundation • Shallow foundation • The depth of the foundation is less than or equal to its width. • It is placed immediately below the lowest part of the superstructure. • Deep foundation • It is relatively deep and need special precautions • The purpose of deep foundation is to attain bearing stratum deep inside the ground in case of weak soil. Foundation

4. Spread footing • Independent footing • Combined footing • Continuous footing • Strip footing • Wall footing • Inverted arch footing • Eccentrically loaded footing • Offset and Strap (cantilever) footing • Raft foundation • Slab (solid)-up to 30 cm • Slab and beam- slab > 30 cm • Cellular- slab >90 cm • Grillage foundation • Timber grillage • Steel grillage Shallow foundation

5. Independent Combined Continuous Spread footing Shallow Foundation

6. t 2t + 2J Strip footing wall Inverted arch Eccentric Shallow Foundation

7. Raft Foundation Cellular Slab & beam Slab Raft Shallow Foundation

8. Timber grillage Steel grillage Grillage Foundation Shallow Foundation

9. Pile foundation • Well foundation (caissons) • Piles • Pile is the pillar like structure driven deep in to the ground to strengthen strength of soil below, It acts as support to the spread footing, It is used individually or in cluster through out wall. • Uses of piles • in very poor soil condition, • in waterlogged soil (high water table), • in filling areas, • in areas with heavy loads, • in compressible soil, • in the areas where the mat or grillage foundations are not possible. • as the anchor in docks, Deep Foundation

10. Decking Sheet Anchor Bearing Fender Batter • Types of piles • According to the uses; • Bearing piles • Friction piles • Sheet piles • Anchor piles • Batter piles • Compaction piles • Fender piles Deep Foundation

11. Types of Piles • According to material use; • Steel piles (H-beam, Box piles, pipe piles, screw piles and disc piles) • Cement concrete piles • Cast-in-situ piles • Cased: Raymond, Mcarthor, Monotube, BSP base driven, Swage etc. • Uncased: Simplex, Franki, Vibro, Vibro-expanded, Pedestral, Pressure etc. • Pre-cast piles • Pre-stressed piles • Timber piles • Composite piles • Sand piles Deep Foundation

12. Methods of pile driving • Drop hammer • Stem hammer • Water jet • Boring • Selection of types of pile • Nature of structure • Loading in structure • Ground water table • Length of pile required • Availability of material and equipments • Factors causing deterioration of piles • Cost of piles Deep Foundation

13. Well foundation • Well foundation is the water tight box structure of wood/ RCC/steel and mostly used in the foundation of the bridges. • Purpose: to develop an enclosure below for plumb and provide access shaft to reach a deep tunnel transmitting the loads to hard bearing strata. • Types of well foundations (Caissons) • Box caissons • Well foundation or open caissons- single, double or cylindrical • Pneumatic caissons Deep Foundation

14. Soil and its properties • Soil is uncemented geological deposits • It is the basis of foundation • Property of soil decides the type of foundation • Types of soil: Cohesive and Cohesion less • Sub-soil exploration • Very important phase in construction and determines the characteristics of underlying soil. • Soil investigation is must before undertaking construction works. • Acquires general picture of geology of area. • Objectives of soil exploration: • To determine the value of safe bearing capacity of soil. • To select economic types of foundation. • To determine the depth of proposed foundation. • To predict likely settlement and make allowance for that in design. • To know underground water level and its problem Soil and soil exploration

15. Inspection • Naked eye observation • Test pits • Helps to know type of soil at small depth, pit size: 1.5*1.5 m² and depth 1.5m. • Probing • Hollow tube of 35-50 mm is driven to ground at about 30 cm at a time. • Boring • Auger • Deep: percussion and rotating boring. • Wash: case tube is driven along with this a wash jet is inserted, this washes the soil below and bring it to the surface. • Test piles • Wood/steel piles are driven under hammer blows. • Geo-physical methods • Electrical method • Electric current is passed through cathode and anode in soil and the flow of current through cathode to anode is the measure of soil below. • Seismic methods • Vibrations are caused by artificial explosions and the movement of these vibration waves measures the soil characteristics. Method of soil exploration

16. It is the ability of soil to support the load coming over it. • It is the strength of soil to resist minimum load coming to its unit area causing no failure. • Maximum bearing capacity of soil = W/ A • Safe bearing capacity = W/(A*f) where, W is Total load including self weight A is area of sole plate and f is factor of safety Bearing capacity of soil

17. Mechanical stabilization • Mixing different graded soil • Change of grading of soil • Mixing different graded soil • Use of roller • Cement stabilization • Mixing soil, cement and water • Lime stabilization • Mixing soil, lime and water • Bituminous stabilization • Mixing of bitumen with soil • Chemical stabilization • Calcium chloride, Sodium chloride, Polymers, Chrome Lignin, Sodium silicate • Thermal stabilization • Heating, Freezing • Electrical stabilization • Grouting under pressure • Geo-textile and fabric stabilization • Sheet piling • Sub-soil drainage Methods of improving bearing capacity of soil

18. Basis of foundation design • Total loads of building • Nature and bearing capacity of sub-soil. • A good foundation is judged by; • Firm location • Stability of structure • Free from settlements Suitability of different types of foundation

19. Black cotton soil • Good for agriculture and bad for structure. • High shrinkage value due to change in moisture content. • Volume varies as 20-30% of original volume. • Develops very wide and deep cracks due to excessive shrinkage • Very weak in saturation. • Problematic for foundation. Foundation in black cotton soil

20. Precautions for foundations in black cotton soil • Foundation depth be enough below from cracks to hard strata. • Measures to be applied to avoid water reaching to bottom of foundation. • Prevent foundation from direct contact with black cotton soil. • If thickness of black cotton soil is high, foundation is to be laid on piles. • Raft foundation is the choice in this condition. • Tie-beam in plinth is important. Foundation in black cotton soil

21. Causes of foundation settlement • Consolidation of soil particles • Reduction of moisture content • Heaving of soil due to pressure • General earth movement • Effects of unequal settlements • Stresses in structure • Distortion of structure fabrics • Failure of structure • Prevention of undue unequal settlements • Proper foundation design • Proper soil investigation Settlement of foundation

22. Unequal settlement of sub-soil • Unequal load distribution • Horizontal movement of soil adjoining structure • Lateral pressure tending overturn • Shrinkage due to withdrawal of moisture from soil • Atmospheric action • Lateral escape of soil below foundation • Nearby building construction • Trees etc. Causes of foundation failure

23. Definition • It is a process of improving and strengthening existing foundation • It facilitates to support structure and assist in transferring loads to better soil strata • Necessity • Occurrence of excessive settlement • Increasing load bearing capacity of foundation • Change of functional use • Addition in loading pattern • Permitting to lower adjacent ground below existing foundation • Construction of new basement nearby Underpinning of foundations of existing building

24. Operation to be carried out before underpinning • Survey of structure • Marking of Settlement if any • Noticing neighbors (adjacent building) • Setting indicators to identify probable cracks while underpinning • Carrying out corrective measures for cracks etc. • Investigate sub-soil Underpinning

25. Sequences of operation • Suitable holes driven through the wall and a needle beam is inserted & supported on the jack • Excavation is started below foundation and footing of the foundation is reached • The offset of the foundation is cutoff and removed & excavation is reached to the defined depth • New foundation is laid in the desired depth up to the underside of the existing foundation • This process is repeated in stages • Final layer of pinning work just underside of existing foundation should be done with the mortar from rapid hardening cement • Precautions • Excavation in one time done for less than one fourth of length, for weak soil it is done for less than one fifth to one seventh of length, normally length of one bay is taken as 1.5 m • To be carried out slowly in stages and not at a time Underpinning

26. Pit method • Ordinary • Cantilever • Pile method • Improving of foundation by grouting and chemical consolidation Methods of underpinning

27. wall wall weight Needle beam Needle beam Jack Existing foundation Existing foundation New foundation New foundation wall wall Perforated pipe GL GL Pile cap pile consolidation Hard strata Methods of underpinning

28. Basement is a space, a storey or a floor immediately below the adjacent ground level. • Retaining wall is essential component of basement. Basement

29. Retaining wall • Structural wall that resists lateral thrust of earth mass, pressure of sub-soil water & support vertical loads. • Function of retaining wall • Strength, stability and Durability • Resistance to overturn and horizontal slide • Resistance to overstress in the materials of construction • Resistance to overstress in the soil on which the wall rest Basement

30. Active earth pressure • Lateral pressure that tends to move or overturn the wall at all times • This is the result of earth wedge retained and any hydrostatic pressure of ground water • Passive earth pressure • The reactionary pressure that builds up to resist any forward movement of the wall, because any forward movement will compress the soil in front and reaction to counteract this movement builds up. • Angle of repose • The natural slope taken up by any soil and given in terms of the angle to the horizontal base line • Varies from 450 to 00 angle for wet clay, but for most soils, this angle of repose is 300. • Wedge of soil • The mass of soil resting on the upper plane of the angle of repose • Surcharge • The additional mass of soil above the top surface of wall • Frictional force Forces acting on the retaining walls

31. surcharge Mass of wall Active earth pressure Weep hole Angle of repose Friction at interface Ground pressure Forces acting on the retaining walls

32. Effect of ground water • The sub-soil ground water reduces soil shear strength. • Reduces bearing of the base and the soil • Subsoil drainage is the solution for this. • Effect of inadequate passive earth resistance • The passive earth resistance at the front of the wall resists sliding • Insufficient passive pressure is not able to resist sliding • Provision of ribs under the head and toe increased passive pressure Factors affecting strength, stability and durability of retaining wall

33. Gravity or mass retaining wall • Cantilever or L-Shaped Retaining wall (max H=6 m) • Base entirely in front of stem • Base partly in front and partly behind the stem • Base wholly behind the stem • Counterfort retaining wall (max H=8 m ) Types of retaining walls

34. Cantilever Retaining wall Gravity or Mass Retaining Wall Types of Retaining wall

35. Design principle of retaining wall • Overturning does not occur • Sliding does not occur • The soil beneath the wall is not overloaded • The materials in the wall are not overstressed • Factors to be considered during design • Nature and type of soil • Height of water table • Sub-soil water movements • Types of wall • Materials used in the wall Retaining wall