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EARTHWORKS IN BUILDINGS.pdf

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1 Introduction: A building is a man-made structure with a roof and walls standing more or less permanently in one place, such as a house or factory. Buildings come in a variety of shapes, sizes and functions, and have been adapted throughout history for a wide number of factors, from building materials available, to weather conditions, to land prices, ground conditions, specific uses and aesthetic reasons. To better understand the term building compare the list of nonbuilding structures. Earthworks are engineering works created through moving or processing of part of earth surface involving the quantities of soils, rocks and other sediments. If we apply the earthworks in building construction there are three involved Components: Foundation Water System (such as groundwater, drainage etc.) Basement
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  • 1

    Introduction:

    A building is a man-made structure with a roof and walls standing more or less permanently in one place,

    such as a house or factory. Buildings come in a variety of shapes, sizes and functions, and have been

    adapted throughout history for a wide number of factors, from building materials available, to weather

    conditions, to land prices, ground conditions, specific uses and aesthetic reasons. To better understand the

    term building compare the list of nonbuilding structures.

    Earthworks are engineering works created through moving or processing of part of earth surface involving

    the quantities of soils, rocks and other sediments.

    If we apply the earthworks in building construction there are three involved Components:

    Foundation

    Water System (such as groundwater, drainage etc.)

    Basement

  • 2

    Earthworks in Buildings

    Components of the Building:

    1. Superstructure

    Construction above the basement or foundation

    supported by an infrastructure which in turn is

    supported by the substructure.

    2. Substructure

    Basic framework or foundation that supports a

    superstructure, and is supported by an

    infrastructure.

    3. Foundation

    The foundations of the building transfer the

    weight of the building to the ground. While

    'foundation' is a general word, normally, every

    building has a number of individual

    foundations, commonly called footings.

  • 3

    Process and parts of Building Construction ( Superstructure and Substructure)

  • 4

  • 5

    Earthworks in buildings

    Foundation

    Major component of building earthworks. The structure, that transmits the load of the building to the soil.

    Choosing a kind of foundation depends on:

    the ground conditions the groundwater conditions the site, the environment (the buildings nearby) the structure of our building

    Requirements:

    structural requirements: safe, be able to carry the load of the building constructional requirements: schedule, minimal resources, minimal cost

    Foundation Components

  • 6

    Steps in establishing Foundation

    1. Site Preparation

    Remove trees and any debris Remove top soil (4-6 below surface)

    2. Site Layout

    Ensure lot lines are known & setbacks are complete Layout building perimeter Use batter boards Establish building corners & building perimeter Use surveying instruments

    3. Excavation Excavate foundation along line created by batter boards

    Excavate remainder of soil inside perimeter

    Dont excavate inside soil if slab on grade

    If deep foundation, taper edges to prevent collapse

    If soil unstable, or very deep - use shoring

    4. Pour Footings

    Construct formwork (if required)

    Install reinforcement (rebar) for footings

    (protrudes above footing to tie-into foundation wall)

    Pour concrete footings

    Smooth / finish surface

  • 7

    Types of Foundation:

    1. Shallow Foundation

    also called spread footings or open footings. The 'open' refers to the fact that the foundations

    are made by first excavating all the earth till the bottom of the footing, and then constructing

    the footing.

    During the early stages of work, the entire footing is visible to the eye, and is therefore called

    an open foundation.

    The idea is that each footing takes the concentrated load of the column and spreads it out over

    a large area, so that the actual weight on the soil does not exceed the safe bearing capacity of

    the soil.

    Several kinds of shallow footings

    a. Individual footings

    Individual footings are one of the most simple and common types of foundations. These are used

    when the load of the building is carried by columns. Usually, each column will have its own footing.

    The footing is just a square or rectangular pad of concrete on which the column sits. To get a very

    rough idea of the size of the footing, the engineer will take the total load on the column and divide it

    by the safe bearing capacity (SBC) of the soil.

  • 8

    c. Raft Foundations Raft Foundations, also called Mat Foundations, are most often used when basements are to be constructed. In a raft, the entire basement floor slab acts as the foundation; the weight of the building is spread evenly over the entire footprint of the building. It is called a raft because the building is like a vessel that 'floats' in a sea of soil.

    Mat Foundations are used where the soil is week, and therefore building loads have to be spread over a large area, or where columns are closely spaced, which means that if individual footings were used, they would touch each other.

    b. Strip footings

    Strip footings are commonly found in

    load-bearing masonry construction,

    and act as a long strip that supports

    the weight of an entire wall. These

    are used where the building loads are

    carried by entire walls rather than

    isolated columns, such as in older

    buildings made of masonry.

  • 9

    2. Deep Foundations

    The load-bearing layer is in deeper location

    The loads of the building are too heavy

    Kinds of Deep Foundation

    a. Pile Foundation

    A pile is basically a long cylinder of a strong material such as concrete that is pushed into the

    ground so that structures can be supported on top of it.

    Pile Materials

    Steel; H- piles, Steel pipe

    Concrete; Site cast or Precast

    Wood; Timber

    Composite

    Pile foundations are used in the following

    situations:

    1. When there is a layer of weak soil at the surface.

    This layer cannot support the weight of the

    building, so the loads of the building have to

    bypass this layer and be transferred to the layer

    of stronger soil or rock that is below the weak

    layer.

    2. When a building has very heavy, concentrated

    loads, such as in a high rise structure.

    Pile foundations are capable of taking higher

    loads than spread footings.

    Top View of the Materials

  • 10

    There are two types of pile foundations, each of which works in its own way.

    Pile Construction:

    End Bearing Piles In end bearing piles, the bottom end of the pile rests on a layer of especially strong soil or rock. The load of the building is transferred through the pile onto the strong layer. In a sense, this pile acts like a column. The key principle is that the bottom end rests on the surface which is the intersection of a weak and strong layer. The load therefore bypasses the weak layer and is safely transferred to the strong layer. Friction Piles Friction piles work on a different principle. The pile transfers the load of the building to the soil across the full height of the pile, by friction. In other words, the entire surface of the pile, which is cylindrical in shape, works to transfer the forces to the soil.

    A. CFA technology

    Drilling continuously until planned depth

    (using guiding tube if necessary) Placing the concrete and removing

    the drill Placing reinforcement (vibration)

    (CFA= Continuous Flight Auger)

  • 11

    b. Slurry walls

    A deep, narrow trench filled with

    concrete (and reinforcement)

    Functions

    Retaining wall during excavation

    (can be watertight)

    Foundation

    Wall of the basement

    B. Soil-Mec technology

    Boring until planned depth (using a guiding tube)

    Using bentonite mud (slurry) under the groundwater level

    Placing reinforcement Placing the concrete and removing the

    guiding tube

    C.Franki technology (bulb pile or compacted concrete

    pile)

    Filling concrete in a steel pipe (creating a plug)

    Pushing down the pipe using a heavy drop hammer

    Fastening the pipe and creating the foot Placing the concrete and compacting while

    removing the pipe (reinforcing)

  • 12

    Excavation

    In general, excavation means to loosen and .take out materials leaving space above or below ground.

    Sometimes in civil engineering term earthwork is used which include backfilling with new or original

    materials to voids, spreading and levelling over an area.

    Excavation and earthmoving plants

    Advantages of using mechanical plant in excavation :

    a) work done quicker,

    b) avoid dangerous condition of work by human workers, say, existence of ground water or collapse of soil,

    c) achieve greater depth,

    d) use fewer manpower and work done in lower cost (for larger scale work only)

    Disadvantages

    a) involve larger running and maintenance costs,

    b) require a larger operating area,

    c) access provision to working area,

    d) less flexible in work planning,

    e) idling time increase cost of work

    Excavation in most situations nowadays is done by mechanical means. However, the exact method to be adopted still depends upon a number of factors:

    1. Nature of subsoil affect type of machine used and the necessity of soil protection.

    2. Size of excavation affect type of machine used and method to excavate.

    3. Scale of work large volume of excavation may involve complicated phasing arrangement and work

    planning

  • 13

    4. Ground water condition affect degree of protection (watertight sheet piling or dewatering may

    required.)

    5. Surrounding condition impose certain restrictions and precautions (eg. diversion of a government

    drain, or underpinning work to the nearby building foundation)

    Deep excavation

    Deep excavation, unlike a shallow one, often requires to protect the sides of cut using

    suitable support. Besides, the problem of ground water cannot be avoided. There are methods

    to overcome this, such as:

    1. Dumpling method

    This is used where there are buildings or street in the proximity. The method is to construct a

    series of retaining wall in trench, section by section, around the site perimeter ,leaving a

    centre Called "dumpling"

    2. Diaphragm walling

    This method need to construct a R.C. retaining wall along the area of work. Because the wall

    is designed to reach very great depth, mechanical excavating method is employed. Typical

    sequence of work includes:

    a. Construct a guide wall guide wall is two parallel concrete beams running as a guide to the

    clamshell which is used for the excavation of the diaphragm wall.

    b. Excavation for the diaphragm wall In normal soil conditions excavation is done using a

    clamshell or grab suspended by cables to a crane. The grab can easily chisel boulder in soil

    due to its weight.

  • 14

    c. Excavation support excavation for the diaphragm wall produces a vertical strip in soil which can

    collapse easily. Bentonite slurry is used to protect the sides of soil. Bontonite is a naturally

    occurring clay which, when added to water, forms an impervious cake-like slurry with very large

    viscosity. The slurry will produce a great lateral pressure sufficient enough to retain the vertical soil.

    d. Reinforcement reinforcement is inserted in form of a steel cage, but may require to lap and

    extend to the required length.

    e. Concreting - concreting is done using tremie. As Concrete being poured down, bontonite will be

    displaced due to its density is lower than concrete. Bontonite is then collected and reuse. Usually

    compaction for concrete is not required for the weight of the bontonite will drive most of the air

    voids in concrete.

    Joining design for the diaphragm wall Diaphragm walling cannot be constructed continually for a

    very long section due to tremendous soil pressure. The wall is usually constructed in alternative

    section. Two stop end tubes will be placed at the ends of the excavated trench before concreting. The

    tubes are withdrawn at the same time of concreting so that a semi-circular end section is formed. Wall

    sections of this type are built alternatively leaving an intermediate section in between .

  • 15

    Cofferdams

    A cofferdam may be defined as a temporary box structure constructed in earth or water to exclude soil or

    water from a construction area, such as for foundation or basement works.

    Use of cofferdam suitable for excavation of larger scale can be of :

    a) Sheet pile cofferdam Also known as single skin cofferdam. Interlocking type steel sheet pile is used

    and can use for excavation up to 15m. Sheet pile in this case acts as a cantilever member to support the

    soil therefore adequate depth of pi le or suitable toe treatment may be required. In addition, cofferdams are

    need to be braced and strutted or anchored using tie rods or ground anchors.

    b) Double skin cofferdam This works similarly like the sheet pile to form a diaphragm. However, the

    diaphragm is double-skinned using two parallel rows of sheet pile with a filling material placed in the void

    between. This creates somewhat a gravity retaining structure and increase the ability to counteract the soil

    behind. However, more working space is required.

  • 16

    Sheet Steel Piling

    Steel, amongst other materials such as timber, is most effective to be used as sheet pile due to its high

    tensile as well as their interlocking ability. It can be used as timbering to excavation in soft and/or

    waterlogged soils especially in congested site where there is no enough space for complicated shoring.

    Ground anchor

    Ground anchor is basically a pre-stressing tendon embedded and anchored into soil or rock to provide

    resistance to structural movements by a tying back" principle.

    Common applications are :

    1. General slope stabilization

    2. Tying back/stabilizing a retaining structure

    3. Tying back/stabilizing for diaphragm walls, but for a temporary nature during excavation

    4. Tying back the entire building from up possible uplifting

    Ground anchor can be classified into:

    1. Rock anchor for anchorage in rock

    2. Injection anchor suitable for most cohesive and non-cohesive soils

    Method to form a ground anchor

    A hole is predrilled on soil or rock in position carefully calculated. For rock anchor, an anchor bar with

    expanded sleeves at the end is inserted into the hole. A dense high strength grout is injected over a

    required length to develop sufficient resistance to hold the bar when it is stressed. Stressing is by hydraulic

    mean and when the stress is developed, the head of the bar is hold by an end plate and nut.

    For injection anchor, a hole should be bored usually with an expanded end to increase anchorage ability.

    The pre-stressing bar is placed into the bore hole and pressure grouted over the anchorage length.

  • 17

    Earthwork in Basements:

    CONSTRUCITON OF BASEMENT USING TRADITIONAL METHODS

    Construction of basement is difficult for it must be carried out below deep ground in adverse condition such

    as existence of ground water, muddiness or limited working space. Besides, works are needed to be done

    amidst layers of props, struts, walings and shores, which cannot be removed until the permanent works are

    completed and capable of carrying the final loads. For each case of basement construction, the method of

    soil support, sub-soil condition, structure of the basement as well as the layout requirement of the entire

    building must be taken into consideration before designing the method of works.

  • 18

    Method of constructing ordinary basement

    One of the most effective methods to construct ordinary basement is by the use of diaphragm wall or sheet

    pile wall (cut-off) which serves as a retaining structure during excavation and as the sides of the basement

    walls. When the central soil is removed during excavation, the cut-off wall should be properly supported for

    works. Below are some method suggested.

    1. Use of lattice beams

    A series of lattice beams or steel trusses

    are installed so that they span between the

    top of opposite diaphragm walls enabling

    them to act as propped cantilevers. The russ

    trusses can be removed after the internal

    floors have been constructed and

    receiving all the lateral forces from soil.

    2. Use of Ground Anchors

    Diaphragm walls are exposed by carrying out

    the excavation in stages and ground anchors

    are provided to stabilize the walls as the works

    proceeds. This method is most effective for

    basement of very large span or without

    intermediate floors as lateral support

    Basement Excavation Support using Lattice Truss

    Basement Excavation Support using Ground Anchors

  • 19

    3. Construct floor slab as support floor slab as support (top-down method)

    After the perimeter diaphragm walls

    have been constructed, the ground

    floor slab and beams are cast

    providing tip edge lateral support to

    the walls. An opening is left in the slab

    for labours, material or plant as access

    to continue excavation to the lower

    stages. This is repeated until the

    required depth is reached.

    4. cast the centre basement slab to support struts

    Centre area between the diaphragm walls

    can be excavated leaving an earth berm

    around the perimeter to support the walls

    whilst the lowest basement floor in centre

    can be constructed. Slots to accommodate raking struts acting

    between the wall face and the floor slab

    are cut into the berm. Final excavation and

    construction of the remaining of the

    basement can take place in stages around

    the raking struts.

    Basement Excavation Support using Ground floor slab

    (top-down method)

    Basement Excavation Support using Shore or Strut

    from a Central Basement Slab cast in advance phases

  • 20

    Waterproofing the basement

    A water-tighted basement wall is an essential element to waterproof a basement. |However, due to the

    basement walls are often constructed under complicated phases to match with the excavation sequences

    and this may increase the possibility of leaking, therefore, careful construction joining design is essential to

    ensure the basement structure is perfectly water-proved. Very often the providing of water stops into these

    joints is helpful. However, the most widely used method to water-proof a basement is to provide a cavity to

    the wall of the basement (by building a skin wall to the sides). The ground water leaks into the basement

    can then be collected through concealed channel to a sump pit and remove by pumps.

    Earthworks in a Water System

    The spacing between drains will vary between 10m for

    clay soils to 50m for sand. Subsurface drains are usually

    formed from buttjoined clay pipes laid in narrow

    trenches. In cases where it is desirable to catch water

    running on the surface, the trench is back-filled nearly to

    the top with rubble either continuously along the trench

    or in pockets. A trench filled with rubble or broken stone

    will provide passage for water and is effective in dealing

    with flows on the surface. Pipes and trenches belonging

    to the main site drainage system may cause uneven

    settling if allowed to pass close to or under buildings.

    Where needed a separate drain, that surround the

    building and installed not deeper than the footing, is

    used to drain the foundation trench.

  • 21

    References

    http://cee.engr.ucdavis.edu/faculty/boulanger/

    http://en.wikipedia.org/wiki/Foundation_(engineering)

    http://www.foundationengineering.info/photo_galleries/08/footing_construction/

    www.wikipedia.org

    http://www.wikihow.com/ How to build a concrete foundation in 7 steps/

    Civil Engineering Construction by J.M. Antill, Paul Ryan and G.R. Easton (McGraw Hill 1988)

    Civil Engineering Technology by B.G. Fletcher and S.A. Lavan; (Butterworths 1982);

    Introduction to Civil Engineering Construction by Roy Holmes (College of Estate Management, 1996)


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