CIVIL 3811 Lecture Slides - Week 4 - 2022 PDF

Foundations and Retaining walls CIVL3811 Engineering Design and Construction School of Civil Engineering | Faculty of Engineering THE UNIVERSITY OF SYDNEY The University of Sydney Page 1  Introduction Definition Foundation: The structure, that transmits the load of the building to...

Foundations and Retaining walls CIVL3811 Engineering Design and Construction School of Civil Engineering | Faculty of Engineering THE UNIVERSITY OF SYDNEY The University of Sydney Page 1  Introduction Definition Foundation: The structure, that transmits the load of the building to the underneath soil. superstructure substructure column or wall load Footing undisturbed soil The University of Sydney Page 2  Introduction Selection of a Foundation type Selection of a foundation type depends on ; › ground conditions › ground water level › site environment (buildings nearby) › type of structure that needs to be supported by the foundation system Structural requirements ; › need to transfer the loads into the undisturbed soil › need to provide sufficient safety to the structure Constructional requirements: › use minimal resources › constructed with a minimal cost › time efficient construction techniques The University of Sydney Page 3 1. The area investigated versus size and nature of development. 2. Degree of uncertainty in characterizing the site versus the cost of the investigation. 3. Potential for optimization of foundation design. Geotechnical investigation can cost 0.5 to 5% of project value but result in significant savings. PILES SOFT SOIL ROCK The University of Sydney Page 4 The University of Sydney Page 5 The University of Sydney Page 6 The University of Sydney Page 7 The University of Sydney Page 8 The University of Sydney Page 9 The University of Sydney Page 10  Introduction Types of Foundations – Shallow Foundations Pad foundation Strip foundation Beam foundation The University of Sydney Page 11 Mat/ Raft foundation The University of Sydney Page 12 The University of Sydney Page 13 The University of Sydney Page 14 The University of Sydney Page 15 The University of Sydney Page 16 The University of Sydney Page 17 The University of Sydney Page 18 The University of Sydney Page 19  Introduction Types of Foundations – Shallow Foundations Raft foundation The University of Sydney Page 20  Raft foundation The University of Sydney Page 21  Soil Properties Allowable Soil Bearing Capacities Typical allowable bearing capacities for different types of soil is given in the following table. However, a thorough investigation on soil condition at the site need to be performed prior to the selection of bearing capacities for critical soil conditions and large structures. Allowable bearing capacity of soil , 𝒒𝒒𝒂𝒂 = 𝒒𝒒𝒖𝒖 ⁄𝑭𝑭. 𝑺𝑺 1 𝑞𝑞𝑢𝑢 - ultimate bearing capacity of soil 𝐹𝐹. 𝑆𝑆 - factor of safety Material Allowable bearing capacity (kPa) Soft clay 50-100 Medium dense clay 100-200 Stiff clay 200-400 Loose fine sand 𝟔𝟔 M 𝑒𝑒 = 𝑞𝑞𝑚𝑚𝑚𝑚𝑚𝑚 𝑞𝑞𝑚𝑚𝑚𝑚𝑚𝑚 𝑞𝑞𝑚𝑚𝑚𝑚𝑚𝑚 𝑞𝑞𝑚𝑚𝑚𝑚𝑚𝑚 3(L/2 − 𝑒𝑒) 𝑁𝑁 𝑞𝑞𝑚𝑚𝑚𝑚𝑚𝑚 = 6 𝑁𝑁 𝑀𝑀𝑦𝑦 3 𝐿𝐿 𝑞𝑞 = ± 3 2 𝑏𝑏 2 − 𝑒𝑒 𝑏𝑏𝑏𝑏 𝐼𝐼 To begin the design of an isolated footing, the vertical 𝑁𝑁 6𝑀𝑀 column load 𝑁𝑁 and the moment 𝑀𝑀 are estimated for 𝑞𝑞𝑚𝑚𝑚𝑚𝑚𝑚 = + 4 𝑏𝑏𝑏𝑏 𝑏𝑏𝐿𝐿2 service load condition. The dimensions 𝑏𝑏 and 𝐿𝐿 are 𝑁𝑁 6𝑀𝑀 then chosen so that the maximum calculated pressure 𝑞𝑞𝑚𝑚𝑖𝑖𝑖𝑖 = − 5 does not exceed the allowable bearing pressure of 𝑏𝑏𝑏𝑏 𝑏𝑏𝐿𝐿2 The University of Sydney soil. 𝑞𝑞𝑚𝑚𝑚𝑚𝑚𝑚 < 𝑞𝑞𝑎𝑎 7 Page 25  Combined Footings Why we need Combined footings In situations where two columns are fairly close to each other or neighbouring isolated footings over lap, a combined footing can be used. When a structure has an edge column closer to the boundary where symmetry of the column footing cannot be achieved, a combined footing with adjacent interior column would provide a simple design solution. The University of Sydney Page 26  Combined Footings Soil pressure distribution 𝑁𝑁𝐴𝐴 = 𝑁𝑁𝐵𝐵 𝑁𝑁𝐴𝐴 ≠ 𝑁𝑁𝐵𝐵 𝑁𝑁𝐴𝐴 𝑁𝑁𝐵𝐵 𝑁𝑁𝐴𝐴 𝑁𝑁𝐵𝐵 𝐿𝐿1 𝐿𝐿1 𝑞𝑞1𝑚𝑚𝑚𝑚𝑚𝑚 𝑞𝑞𝑚𝑚𝑚𝑚𝑚𝑚 𝑞𝑞2,𝑚𝑚𝑚𝑚𝑚𝑚 𝑅𝑅 𝑅𝑅 𝑏𝑏 𝑏𝑏 𝐿𝐿 𝐿𝐿 Constant pressure Varying pressure The University of Sydney Page 27  Combined Footings Selection of Dimensions The line of reaction force acting through the geometric centroid of the plate 𝑁𝑁𝐴𝐴 𝑁𝑁𝐵𝐵 The width (b) and the length (L) of the footing can be 𝐿𝐿1 estimated from 𝐿𝐿 × 𝑏𝑏 × 𝑞𝑞𝑚𝑚𝑚𝑚𝑚𝑚 = 𝑁𝑁𝐴𝐴 + 𝑁𝑁𝐵𝐵 8 𝑞𝑞𝑚𝑚𝑚𝑚𝑚𝑚 Take first moment of area about left hand edge of the footing to estimate length (𝑑𝑑𝐴𝐴 ) of the footing. 𝑑𝑑𝐴𝐴 𝑁𝑁𝐴𝐴 + 𝑁𝑁𝐵𝐵 𝑥𝑥 = 𝑁𝑁𝐴𝐴 𝑑𝑑𝐴𝐴 + 𝑁𝑁𝐵𝐵 (𝐿𝐿1 + 𝑑𝑑𝐴𝐴 ) 9 𝑏𝑏 𝑥𝑥 𝐿𝐿 where 𝑥𝑥 = provides a symmetrical pressure 2 𝐿𝐿 distribution in the footing. The University of Sydney Page 28  Combined Footings Selection of Dimensions The line of reaction force acting with an offset to the geometric centroid of the plate 𝑁𝑁𝐴𝐴 𝑁𝑁𝐵𝐵 𝑁𝑁𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝑀𝑀𝑦𝑦 𝑞𝑞 = ∓ 𝑥𝑥 10 𝐿𝐿1 𝐴𝐴 𝐼𝐼𝑥𝑥 1 𝐴𝐴 = 𝐵𝐵 × 𝐿𝐿 𝐼𝐼𝑥𝑥 = 𝐵𝐵𝐿𝐿3 12 𝑞𝑞1𝑚𝑚𝑚𝑚𝑚𝑚 𝑞𝑞2,𝑚𝑚𝑚𝑚𝑚𝑚 𝑀𝑀𝑥𝑥 = 𝑁𝑁𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 × 𝑒𝑒𝑦𝑦 11 𝑅𝑅 𝑒𝑒𝑦𝑦 𝑏𝑏 𝑞𝑞2,𝑚𝑚𝑚𝑚𝑚𝑚 < 𝑞𝑞𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 𝑏𝑏 𝐿𝐿/2 𝐿𝐿 The University of Sydney Page 29  Combined Footings Determination of Moments and Tension Reinforcement 𝑁𝑁𝐴𝐴 𝑁𝑁𝐵𝐵 𝑁𝑁𝐴𝐴 𝑁𝑁𝐵𝐵 𝑞𝑞𝑢𝑢𝑢𝑢𝑢𝑢,𝑚𝑚𝑚𝑚𝑚𝑚 Bending moment diagram 𝑞𝑞𝑢𝑢𝑢𝑢𝑢𝑢,𝑚𝑚𝑚𝑚𝑚𝑚 Required reinforcement ratio (𝑝𝑝) can be estimated from Eq.(12) where 𝑀𝑀∗ is in 𝑘𝑘𝑘𝑘𝑘𝑘 Shear Force diagram and 𝑑𝑑 is in 𝑚𝑚𝑚𝑚. Note that the amount is given by the following equation is for 1m wide strip. 𝑀𝑀∗ 𝑝𝑝 = 2.7 × 2 12 𝑑𝑑 The University of Sydney Page 30  Combined Footings Determination of Moments and Shear Forces Longitudinal bending 𝑀𝑀1 𝑀𝑀2 𝑀𝑀5 𝑀𝑀3 𝑀𝑀4 0.7𝑎𝑎𝑠𝑠𝑠𝑠𝑠𝑠 0.7𝑎𝑎𝑠𝑠𝑠𝑠𝑠𝑠 𝑑𝑑 𝑑𝑑 𝑆𝑆1 𝑆𝑆2 𝑆𝑆3 𝑆𝑆4 𝑑𝑑 𝑑𝑑 𝑑𝑑 𝑑𝑑 Plan view of the footing Part elevation of the footing Critical sections for longitudinal bending , 𝑀𝑀1 - 𝑀𝑀5 Critical sections for flexural shear, 𝑆𝑆1 - 𝑆𝑆4 The University of Sydney Page 31  Design of RAFT Foundation Why we need RAFT foundations In situations where isolated or combined footings aren’t capable of bearing the pressure due to the large column loads, the use of a Raft foundation is opted. Raft foundations, much like combined footings, are required to be checked for bearing pressure. In addition, settlement and punching shear of the columns are also critical factors when the design of a raft foundation is considered. Raft foundation The University of Sydney Page 32  Design of RAFT Foundation Types of Raft foundations Flat plate Plate with drop panels Flat with Pedestals Waffle slabs The University of Sydney Page 33  Design of RAFT Foundation Soil pressure acting on the raft 𝑁𝑁 𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 𝐻𝐻 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 𝑞𝑞 𝛾𝛾 = Unit weight of soil 𝑁𝑁𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝑞𝑞 = − 𝛾𝛾𝛾𝛾 𝐴𝐴 The University of Sydney Page 34  Design of RAFT Foundation Rigid method approach › The RAFT is infinitely rigid, and therefore, the flexural deflection of the mat does not influence the pressure distribution. › The soil pressure is distributed in a straight line or a plane surface such that the centroid of the soil pressure coincides with the line of action of the resultant force of all the loads acting on the foundation 𝑁𝑁𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 𝑁𝑁1 𝑁𝑁2 𝑁𝑁3 𝑁𝑁4 𝑞𝑞𝐴𝐴,𝑚𝑚𝑚𝑚𝑚𝑚 𝑞𝑞𝐵𝐵,𝑚𝑚𝑚𝑚𝑚𝑚 𝑞𝑞𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 The University of Sydney Page 35  Design of RAFT Foundation Develop shear and bending moment diagrams for each strip by considering the modified loads and the pressure obtained from the previous step. Shear force diagram Bending moment diagram The University of Sydney Page 36  Introduction Types of Foundations – Deep Foundations Cast-in situ bored piles Driven piles The University of Sydney Page 37 The University of Sydney Page 38 The University of Sydney Page 39 The University of Sydney Page 40 The University of Sydney Page 41 The University of Sydney Page 42 The University of Sydney Page 43  Cast-in-Place Piles Information on Drawings – Maximum pile loads and moments – Contract Levels – Requirements for socket material – Minimum length of the socket – Reinforcement and concrete details – Details of the permanent casing and driving shoe The University of Sydney Page 44 Pile caps and spread footings Proper detailing of the pile cap https://www.carrabay.com.au/pile-cages/ https://www.thestructuralworld.com/2018/07/20/pile-cap-design/ The University of Sydney Page 45 Pile caps and spread footings Pile caps and spread footings might be designed using the strut and tie method, or if their width is large relative to their thickness, they can be designed as beams. https://ryanrakhmats.wordpress.com/2021/07/03/simplified-pile-caps-design-with-strut-and-tie-methods/ https://www.researchgate.net/publication/233087801_ Evaluation_of_the_shear_strength_of_four_pile_cap_ using_strut_and_tie_model_STM/figures?lo=1 The University of Sydney Page 46  Numerical methods P d L P = working load factor of safety = Pu/P = 2.5 The load-deformation response of piles under axial load has been extensively studied using numerical methods. The University of Sydney Page 47  Numerical methods Based on the results, charts can be developed. Settlement of a pile depends on the various parameters of pile geometry and stiffness and soil stiffness. The University of Sydney Page 48  Numerical methods https://www.midasbridge.com/en/solutions/substructure s https://www.midasbridge.com/en/solutions/substructures The University of Sydney Page 49  Pile group settlement P L d ELEVATION PLAN Settlement is the limiting design criterion for pile groups in both sands and clays. The University of Sydney Page 50 Pile Function – Piles transfer loads on the bridge superstructure and substructure to the foundations. – Pile loads are calculated during the bridge design process. – https://www.constructioncost.co/bridge-pile-cap-construction-details.html The University of Sydney Page 51 Pile Resistance Pile resistance is derived from friction on pile sides and from bearing on the bottom of the pile – Driven piles are used where they can be driven some distance into the soil to the required resistance, or to refusal on rock – Usually cheaper than cast-in-place piles – Cast-in-place piles used where rock is close to the surface, or where vibration and noise of pile driving operation is unacceptable Cast-in-place piles for Driven piles for bridges bridges https://www.iceusa.com/blog/dooker-hollow-bridge-driven-piles/ https://www.geotech.net.au/capabilities/foundation-piling/bored-cast-in-situ.html The University of Sydney Page 52  Driven Steel H-Piles – Steel H piles – Suitable for rural applications – If there are no aggressive soil conditions (or preventative measures are taken), then major advantages for : Hard driving conditions High tensile forces and bending moments Very long piles – Limits on driving stresses Conflicting views: range 0.85 Fy to 1.4 Fy Recommendations in AS 2159 – H section piles: 0.85 Fy https://theconstructor.org/structural-engg/foundation-design/steel-piles/40266/ The University of Sydney Page 53  Trench-box excavation shoring systems for sewer installation – Usually for shallow narrow excavations where the excavation base is stable, and water is not present. These types of shoring systems are prefabricated and pushed into the ground. The trench walls are typically supported by connected braces. These systems should generally not be used when ground deformation control is important. https://www.deepexcavation.com/en/resources/excavation-shoring-systems The University of Sydney Page 54 The University of Sydney Page 55  Sheet pile excavation shoring systems – Steel or vinyl sheet piles are commonly installed when groundwater is an issue and where the ground allows installation of the sheet piles without causing damage to adjacent structures. http://projectmanagement123.com/wp-content/uploads/2016/01/Method-Statement-Temporary- Sheet-Piling-Sheet-Shoring.jpg https://www.keller.com.au/expertise/techniques/sheet-piles The University of Sydney Page 56  Sheet Pile Walls – Application: Temporary shoring and retention of deep soils above and below water table. – Usually restrained by multiple rows of anchors or bracing/struts – Relatively low cost – Can be withdrawn and re-used. Disadvantages -Noise and vibration. -Cannot penetrate rock. -Relatively flexible, so can cause damage (cracking) to adjacent structures. -Some leakage through clutches. The University of Sydney Page 57 The University of Sydney Page 58 The University of Sydney Page 59  Soldier Pile Walls – Applications: For the retention of vertical excavations in stiff clay or weak rock, above the groundwater table. – Typically bored concrete piles/piers with infill shotcrete panels. – May be restrained by “tie-back” ground anchors. Advantages -Relatively low cost shoring system -Can socket into rock for restraint (cantilever). Disadvantages -Local instability of panel material between piles The University of Sydney Page 60 Soldier Pile Walls The University of Sydney Page 61 Soldier piled walls are a form of embedded retaining wall that is used to retain the soil behind to allow the ground level in front of the wall to be lowered, the retained height can be increased with the use of propping or anchoring. Soldier Pile Walls with Tiebacks https://www.deepexcavation.com/en/resources/retaining- systems/soldier-pile-lagging-walls https://www.keller.com.au/expertise/techniques/soldier-and- The University of Sydney Page 62 contiguous-pile-retaining-walls  Contiguous Pile Walls Application: Retention of dry soils, above the water table to provide a stiffer wall adjacent to neighbouring properties or utilities (e.g. buildings) Formed by bored or CFA (grout or concrete-injected) piles. Minimal shotcrete surface usually applied to exposed face, with strip drains squeezed into the (25mm) gaps, if required. The University of Sydney Page 63 https://www.keller.co.uk/expertise/techniques/contiguous-pile-walls The University of Sydney Page 64  Secant Pile Walls Application: Retention of soils below the water table for watertight basement construction. Formed by CFA (grout or concrete-injected) piles. Can be either ‘hard-soft’ or ‘hard-hard’ piles. ‘Hard-soft’ walls formed by primary, reinforced (structural) piles and unreinforced or low strength grout. https://railsystem.net/secant-pile-walls/ The University of Sydney Page 65  https://railsystem.net/secant-pile-walls/ The University of Sydney Page 66  Secant Pile Walls The University of Sydney Page 67  Diaphragm Walls Applications: -Permanent retaining wall below water table. -Stiff retention system; fewer anchors needed. -Can socket wall into rock, for cut-off wall. -Over 30m depth with good verticality control. The University of Sydney Page 68  https://link.springer.com/article/10.1007/s40515-021-00208-0/figures/1 The University of Sydney Page 69  Types of Retaining Wall Gravity walls Rely on their weight for the stability of the wall Embedded walls Mobilise earth pressures in the ground to provide resistance The University of Sydney Page 70  Retaining Walls Gravity walls Gabion walls Crib walls Cantilevered walls The University of Sydney Page 71  Introduction Retaining Walls Buttress wall Bridge abutments Reinforced earth walls The University of Sydney Page 72  Abutments in bridges The abutment provides the connection between the bridge deck and the approach road. It refers to both the vertical or sloping face between the upper and lower ground levels, and also the concrete support for the bridge superstructure. https://civilengineeringbible.com/article.php?i=261 https://www.beco-bermueller.de/en/applications/civil-engineering/bridge-abutments/ https://www.semanticscholar.org/paper/Stress-Distribution-on-Bridge-Abutment-due-to-Live-Saranya- Umashankar/6158130f3cd8fa576e461d8af434011ede773a98 The University of Sydney Page 73  Reinforced Earth Retaining Structure – This is a type of retaining system for soil that uses artificial reinforcement imbedded into soil or rock to stabilise a wall at the face of the soil that holds it in place. The University of Sydney Page 74  Gabion Caged Stone Wall – Gabions cages are rectangular box shaped cages made of thin wired steel mesh (similar to chicken mesh) which may be filled with rocks. These may then be stacked and tied together with steel wire. The University of Sydney Page 75  General Guidelines AS 4678 : 2002 This standard is applicable to retaining structures and reinforced soil structures that are commonly constructed for engineering works and infrastructure. Such structures are typically up to 15 m in height. Structures of unusual shape, of large retained heights (in excess of 15 m) or founded in unusual ground conditions (such as soft ground, land slips, steep sides or deeply inclined gullies), together with structures subject to sustained cyclic loading, are outside the provisions of this Standard. Structures shall be classified in accordance with following table. Structures where failure would result in minimal damage and loss of access where the wall height (H) is greater than 1.5 m are deemed to be classification B structures. The University of Sydney Page 76 Soil Types Cohesive soil: Sticky soil such as clay or clayey silt whose strength depends on the surface tension of capillary water. Cohesionless soil: Any free-running type of soil, such as sand or gravel, whose strength depends on friction between particles. (a) (b) The University of Sydney Page 77  Soil Properties General soil properties can be classified as in Table D4: AS 4678. However, it is required to obtain accurate data from the site geotechnical report. AS 4678-Section D3 The University of Sydney Page 78  Soil Properties Unit weight (𝛾𝛾) of soil and similar materials are given in Table D1: AS 4678. AS 4678-Section D2 The University of Sydney Page 79  Cantilevered Walls Failure Modes Overturning Sliding Global overturning Bending of components The University of Sydney Page 80  Cantilevered Walls Typical Section Finished ground surface Stem / wall Temporary excavation line Backfill height backfill Existing ground Toe Heel Typical drainage system The University of Sydney Page 81  Cantilevered Walls The University of Sydney Page 82