Q.1 Past site investigation reports are often very useful and can often save time and money in site investigations. The Geotechnical Information Unit of the Geotechnical Engineering Office(GEO) contains numerous records of boreholes from throughout the Territory, as will as useful records of landslides, rainfall and piezometric data, and laboratory test results on soil and rock samples. Relevant data can be readily accessed by geographical location of the site. Past construction records for both the site and for adjacent properties are useful for site investigation. Several government departments posses valuable information for the planning and execution of the site investigation. They are the Civil Engineering Department, Building Ordinance Office, Highways Department, Water Supplies Department, Drainage Services Department, and Architectural Services Department. Non-government agencies such as Mass Trainsit Railway Corporation and other utility companies can also provide valuable information on past construction records. Services records are also an essential part of the desk study, necessary to locate hidden services such as electricity cables, sewers and telephone wires. This in formation is usually provided free of charge by the relevant service provider. A suggested list of sources is: Water Supplies Department, Drainage Services Department, Mass Trainsit Railway Corporation, The Hong Kong Electric Company, Hong Kong & China Gas Company, all telecom company etc… Aerial photographs can be used in the preparation and revision of maps and plans, and they can assist in the identification and general assessment of natural and man-made features, including geology, geomorphology, hydrology and vegetation on or in relation to a site. They are particularly useful in the assessment of site history (i.e. changes in form, materials and land use) and can provide valuable information for the assessment of slope stability. Reference: GEOTECHNICAL ENGINEERING OFFICE, (1987). Guide to Site Investigation. Hong Kong: The Government of the Hong Kong Special Administrative Region. p. 33.

Q.2 We had some major performance requirements that a foundation must satisfy. Such as the foundation must be below the zone of seasonal volume changes caused by freezing, thawing and plant growth. And the foundation scheme may have to consider expansive soil conditions. The soil in a large number of geographic areas tends to swell in the presence of substantial moisture and carry the foundation up with it. Also in additional to compressive strength considerations, the foundation system must be safe against overturning, sliding, and any uplift (flotation). A general shear failure involves total rupture of the underlying soil. There is a continuous shear failure of the soil from below the footing to the ground surface (Fig 1). General shear failure ruptures and pushes up the soil on both sides of the footing.

(Fig 1)

For Strip Foundation: It is more economic to excavate and concrete the strip foundation that to work in a large number of individual pits. In fact, it is often though to be more economical to provide a strip foundation whenever the distance between the adjacent square pads is less than the dimension of the pads, and for ease in construction closed spaced pad foundation can be formed by inserting vertical joints in a continuous strip of concrete. This foundation won’t apply for low bearing capacity soil. The working procedure is too much such as digging, framing and other is the weakness.

For raft foundation: Advantages It may be more economical to excavate the site to a level formation, construct individual close spaced pad foundation and then refill them. The structure can protect the structure from failure if there is settlement or movement of the soil base because the raft base can hold the super structure. So it suitable for soil such as abandon mining site. Disadvantage A lot of concrete inquired for base at the low density capacity soil by adding the thickness of the base. The footing should construction on 150mm filled sand to avoid racking from horizontal raft footing should increase by construction side beam reinforcement increase the depth of raft was not give an efficient increase of foundation strength. For Pad foundation: The plan shape of a pad footing is usually square, but if the column is close to the site boundary it may be necessary to use a rectangular plan shape of equivalent area. The advantage was the space from the footings can provide more access for utility lines. Due to the water table and the materials under foundation was loose fill materials, subside or settle may occur, remodeling or extending the foundation may be easier. And jacked up to compensate was also easier. Also the excavation time was shorter than slab foundation. The disadvantages for this type of foundation were easier to subside or settle due to the high ground water table and loose fill materials. These types of foundation which is intended for sustaining concentrated loads from a single point load such as structural columns. But the slab foundation which extends over the entire loaded area so that loads from entire structure are spread over a large area leading to a reduction of the stress of foundation soils is reduced. (530 words) http://xa.yimg.com/kq/groups/2173108/1203322916/name/type+of+foundation.htm

Q.3 For the basic requirement in the design of a strutted excavation, we had three main concerns. First, the struts should have adequate factor of safety in resisting the lateral earth pressure arising from the retained soil. Second, the base of the excavation should have adequate factor of safety against heaving. The third one was the deformation of the temporary system should be limited. The lateral pressure distribution in a strutted excavation does not increase linearly with depth. In the case of a retaining wall, the active pressure is assumed to be mobilized by a rotation of the wall about its base. With a strutted excavation, the struts are inserted as the excavation proceeds. The amount of excavation before the first row of struts is placed is likely to be small and the original state of stress of the ground almost unchanged. As the excavation proceeds, the soil tends to yield progressively in a horizontal direction and the resulting deflected shape. The top strut will prevent the soil from stretching at the start of the sliding wedge and failure will occur as indicated. Thus the lateral pressure distribution will not increase linearly with depth. The solid slab raft foundation was another type of shallow foundation; the type of foundation was more stable and is considered less vulnerable to termite infestation because there are no hollow spaces or wood channels leading from the ground to the structure. The disadvantages are the lack of access from below for utility lines, and a very low elevation that expose the building to flood damage in even moderate rains. Remodeling or extending such a structure may also be more difficult. Over the long term, ground settling may be a problem due to loose fill materials and high ground water table, as slab foundation cannot be readily jacked up to compensate. And also the cost was more expensive due to more concrete and reinforcement. Reference: THE WIKIPEDIA FOUNDATION, INC. (n.d.). shollow foundaiton. United States of America: . 26th December 2013, (accessed 7th January 2014)

Q.4 Columns are vertical members which carry the loads transferred from the beams to the foundation. In a concrete beam, the upper portion of the beam is in compression, and the lower part is in tension. The line where the internal stresses of the beam section change from compression to tension is Called the neutral axis. The forces must balance on each side of the neutral axis. A plain concrete beam, being so much stronger in compression than in tension, will have its neutral axis located very low. Beams are traditionally descriptions of building or civil engineering structural elements, but smaller structures such as truck or automobile frames, machine frames, and other mechanical or structural systems contain beam structures that are designed and analyzed in a similar fashion. (1) Steel is so much stronger in tension than concrete that a very small steel rod or bar placed in the bottom of a concrete beam will raise the neutral axis and balance the compressive forces exerted above. 183 Plain concrete, when used in the form of pillars and posts, is capable of carrying heavy direct loads through its great compressive strength. But when it is subjected to a direct pull hat is, to tensile strains t is weak. For example, if a plain concrete beam is subjected to a load, it will break apart at the bottom just as a piece of chalk would under like conditions, being unable to resist the tension in the lower portion of the beam. In order to overcome this, reinforcing steel is used to give proper tensile strength and elasticity. The concrete in the top of the beam takes care of the compression. A properly reinforced concrete beam, therefore, has the strength of stone in resisting compression, united with the tension-resisting power of steel. When a beam is loaded and supported at the two ends, it will have a tendency to deflect or bend. To illustrate, assume that a beam is made up of a series of flat plates, in other words, like a pad of paper or a book he difference being that in the pad of paper the leaves are not in any way connected to one another, whereas in a beam the adhesion or sticking together of the various particles of the material ties the imaginary

plates together. Now, when the sup posed beam starts to deflect, one of two things will happen: either the various plates separate, as when a book or pad of paper is bent, and, in separating, slide by one another; or, if the plates are held together and sliding is prevented, the particles in the upper plates compress, and those in the lower plates elongate or stretch out. It is thus seen that in addition to the compression and tensile stresses in the top and bottom of the beam, there are internal stresses of equal importance, against which the concrete must also be properly reinforced. These may be tensile or they may be shearing forces.

Fig. 39 shows a plain concrete beam, sup ported freely at the ends, which has failed upon the application of a small load applied near its center.

Fig. 40 shows a similar beam having horizontal reinforcing rods located near the bottom surface of the beam. The method of failure under a medium load, in this case, was said to be due to the ends of the reinforcing rods slipping in the concrete. The diagonal or slanting cracks are partially due to horizontal shear set up by the bending of the beam. These are sometimes spoken of as due to diagonal tension. A means of fortifying against horizontal shear is by the use of stirrups. Bands or rods of steel or iron are bent in the shape of a U, and either placed loosely around, fastened rigidly to, or made as a part of the reinforcing rods. Fig. 41 shows the method of failure of the same type of beam as previously shown, but having loose stirrups surrounding the horizontal reinforcement bars and embedded vertically in the concrete. This beam failed when tested to destruction, by the slipping of the horizontal rods. The figure shows the shearing of the concrete along the horizontal plane above the

rods, but no diagonal cracks. The stirrups evidently prevented the shearing action above the rods. As a means of preventing such a method of failure, some companies have either rigidly fixed the stirrups to their reinforcing bars or formed them as a part of same. The result of such a construction seems to throw the greater part of the body stresses of the beam onto the horizontal bars for support. Some authorities consider this a weakness in the construction.

Reference: Radford’s Cyclopedia of Construction (1909). Cement Construction Reinforced Concrete. United States of America: . 26th December 2013, (accessed 7th January 2014)

Shearing force may be resisted by bent up bars at 45_ to the horizontal and positioned to cut the anticipated shear failure plane at right angles. These are in fact main bars from the bottom of the beam which are no longer required to resist tension and can be bent up and carried to the support.

More often, stirrups or binder are provided in close centres about the position at which shear is likely to occur to replace the bent up bars. Several stirrups may cut the

shear plane and therefore the total area of steel crossing the shear plane is increased to offer the tensile resistance to the shearing force.

A column is a vertical member carrying the beam and floor loadings to the foundation and is a compression member. Since Concrete is strong in compression it may be concluded that provided the compressive strength of the concrete is not exceeded no reinforcement will be required. However, rebar is often added in columns to increase its compressive strength and to resist bending because bending may be induced in columns in the following conditions: 1. Load coupled with the slenderness of the column; a column is considered to be slender if the ratio of effective height to thickness exceeds 12. 2. Reaction to beams upon the column, as the beam deflects it tends to pull the column towards itself thus inducing tension in the far face of the column. 3. Wind loadings.

The load of a particular level is transferred to the foundation by the columns which require the columns to have a high compression capacity yet the tension capacity is also important as the loads due to lateral load like wind load may also be borne by these. First the vertical bars positioned according to the column size and drawings. The first vertical bars fixed at the ground level. After that the stirrups are inserted from the top of the reinforcement cage and are bound at the specified spacing. The starter bars have to be kept for the column at next level with at least one lap length. Where the column size is reduced at a particular level docking has to be done, A column is a slender, vertical member that carries a superimposed load. When the structure’s height is less than three times its least lateral dimension, this structure is known as a pier or pedestal . Concrete columns must always have steel reinforcement because they are subject to bending.

The steel reinforcement in columns is designed primarily to sustain compressive stress to reinforce the compressive strength of concrete, but also to reinforce the poor tensile strength of concrete against tensile stress due to bending from fixed end beams, eccentric loading and wind pressure. Reference: CONSTRUCTIONFIELD (n.d.). column reinforcement. United States of America: . 14th February 2011 (accessed 7th January 2014)

The minimum number of the main bars in a column should not be less than four for rectangular columns and six for circular columns. To prevent the slender main bars from buckling due to compression and hence causing spalling of the concrete, links or binders are used as a restraint. All bars in compression should be tied by a link passing around the bar in such a way that it tends to move the bar towards the centre of the column.

Falsework Falsework is a temporary structure used to support formwork and/or permanent structures until the wet concrete hardened or the permanent structures are self-supporting. Many manufacturers produce pre-fabricated falsework frame sets with accessories. They are easily assembled and disassembled. During erection, the manufacturer’s recommendation must be strictly followed. Adequate diagonal bracings must be provided to prevent swaying of the falsework.

Formwork Concrete when first mixed is a fluid. Formwork is the temporary moulds for casting concrete members where the wet concrete can be placed to retain its shape, size and position as it sets. A lot of materials can be used as formwork materials, such as timber, steel, aluminium, glass reinforced plastic, etc. The advantage for timber formwork: 1. Timber formworks can be constructed at a lower initial cost than steel due to higher availability and cheaper production costs. The cost of timber varies depending on the quality and treatment of the wood. 2. People new to building formworks typically choose timber because it requires no special tools nor a high level of construction experience. It is also easier to handle due to its light weight. 3. An aesthetically pleasing architectural effect can often be achieved using a timber formwork. Painted timber formwork not only adds color and a finished look, but oil or epoxy treatments can double the number of times the formwork may be reused.

The disadvantage for timber formwork: 1. Constructing timber formwork is a labour intensive work; it is uneconomical in large scale projects. 2. Mechanization usually cannot be employed. 3. The reusability of timber formwork is low, only two to five times. 4. Considerable amount of timber waste produced which increase the cost to treatthe solid waste. 5. Considerable amount of hardwood consumed which destroys our rain forest.

Concreting Advantage for precast concrete: 1. Control of the quality of concrete. 2. Smoother surfaces, and plastering is not necessary.

3. Less storage space is needed. 4. Concrete member can be cast under all weather conditions. 5. Better protection for curing. 6. Weather conditions do not affect erection. Faster erection time.

Advantage for site mixing concrete:
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SAVING THE CUSTOMER MONEY - we offer a smaller minimum load and are able to measure the exact amount of concrete that was used for the job. Ordering additional concrete to be sure there is enough is never necessary. KEEPING A FLEXIBLE SCHEDULE - available after hours and Saturdays. USING A REMOTE DRIVE - Dave is able to control the truck and the chute from the remote at the back of the truck. An extra person to control the flow of concrete is not necessary. FRIENDLY SERVICE & ASSISTANCE - Dave keeps a wheel barrel and some concrete tools in the truck in case the customer needs additional help on the job. He is willing and able to assist in the pour if needed. HEATED MATERIALS - Materials are stored on heated slabs to ensure quality concrete even in cold months. Hot water is also used. PRODUCING FRESH CONCRETE - mixing begins at the job site which offers more time for the customer to work the concrete. This can allow for a smaller crew to complete the job. It is also ideal for remote jobs where the concrete would be too “hot” to work with from a ready-mix plant.

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Reference: ADVANTAGE SITE MIXED CONCRETE, INC. (n.d.). How is Advantage Site Mixed Concrete different than Ready-Mixed Concrete?. South of Sandpoint: . (accessed 7th January 2014)

Concrete curing method: Methods of curing concrete fall broadly into the following categories: 1. Those that minimise moisture loss from the concrete, for example by covering it with a relatively impermeable membrane. 2. Those that prevent moisture loss by continuously wetting the exposed surface of the concrete. 3. Those that keep the surface moist and, at the same time, raise the temperature of the concrete, thereby increasing the rate of strength gain. This method is typically used for precast concrete products and is outside the scope of this data sheet. Impermeable-membrane Curing

Formwork Leaving formwork in place is often an efficient and cost-effective method of curing concrete, particularly during its early stages. In very hot dry weather, it may be desirable to moisten timber formwork, to prevent it drying out during the curing period, thereby increasing he length of time for which it remains effective. It is desirable that any exposed surfaces of the concrete (eg the tops of beams) be covered with plastic sheeting or kept moist by other means. It should be noted that, when vertical formwork is eased from a surface (eg from a wall surface) its effectiveness as a curing system is significantly reduced. Membrane-forming curing compounds Curing compounds are liquids which are usually sprayed directly onto concrete surfaces and which then dry to form a relatively impermeable membrane that retards the loss of moisture from the concrete. Their properties and use are described in AS 3799 Liquid Membrane-forming Curing Compounds for Concrete. When used to cure fresh concrete, the timing of the application of the curing compounds is critical for maximum effectiveness. They should be applied to the surface of the concrete after it has been finished, as soon as the free water on the surface has evaporated and there is no water sheen visible. Too early an application dilutes the membrane; too late results in it being absorbed into the concrete, with a consequent failure of the membrane to form. They may also be used to reduce moisture loss from concrete after initial moist curing or the removal of formwork. In both cases, the surface of the concrete should be thoroughly moistened before the application of the compound to prevent its absorption into the concrete. The use of curing compounds will not prevent formation of early age thermal cracking. Curing compounds can be applied by hand spray, power spray, brush or roller. The type or grade of curing compound should be matched to the type of equipment available and the manufacturer’s directions followed. The rate of application should be uniform, with coverage normally in the range 0.20 to 0.25 litres/m2. Where feasible, two applications at right angles to each other will help ensure complete coverage. Water Curing General Water curing is carried out by supplying water to the surface of concrete in a way that ensures that it is kept continuously moist. The water used for this purpose should not be more than about 5°C cooler than the concrete surface. Spraying warm concrete with cold water may give rise to ‘thermal shock’ that may cause or contribute to cracking. Alternate wetting and drying of the concrete must also be avoided as this causes volume changes that may also contribute to surface crazing and

cracking. Wet coverings Fabrics such as hessian, or materials such as sand, can be used like a ‘mulch’to maintain water on the surface of the concrete. On flat areas, fabrics may need to be weighed down. Also, it is important to see that the whole area is covered. Wet coverings should be placed as soon as the concrete has hardened sufficiently to prevent surface damage. They should not be allowed to dry out as they can act as a wick and effectively draw water out of the concrete. Fabrics may be particularly useful on vertical surfaces since they help distribute water evenly over the surface and even where not in contact with it, will reduce the rate of surface evaporation. Care should be taken however, that the surface of the concrete is not stained, perhaps by impurities in the water, or by the covering material. New fabrics can leach fabric stains, pre‑washing should be essential. Prior to placement of any fabric – pre moisten to avoid wicking of moisture from the concrete that can result in the fabric texture negatively absorbed into the concrete surface. Reference: CEMENT CONCRETE & AGGREGATES AUSTRALIA, (n.d.). Curing of concrete. [electronic resource]. Australia: Available at: (accessed 7th January 2014)

Q.6 Retaining walls are structures designed to restrain soil to unnatural slopes. They are used to bound soils between two different elevations often in areas of terrain possessing undesirable slopes or in areas where the landscape needs to be shaped severely and engineered for more specific purposes like hillside farming or roadway overpasses. Definition A retaining wall is a structure designed and constructed to resist the lateral pressure of soil when there is a desired change in ground elevation that exceeds the angle of repose of the soil.[1] A basement wall is thus one kind of retaining wall. But the term usually refers to a cantilever retaining wall, which is a freestanding structure without lateral support at its top.[2] These are cantilevered from a footing and rise above the grade on one side to retain a higher level grade on the opposite side. The walls must resist the lateral pressures generated by loose soils or, in some cases, water pressures.[3]

Every retaining wall supports a “wedge” of soil. The wedge is defined as the soil which extends beyond the failure plane of the soil type present at the wall site, and can be calculated once the soil friction angle is known. As the setback of the wall increases, the size of the sliding wedge is reduced. This reduction lowers the pressure on the retaining wall. [4] The most important consideration in proper design and installation of retaining walls is to recognize and counteract the tendency of the retained material to move downslope due to gravity. This creates lateral earth pressure behind the wall which depends on the angle of internal friction (phi) and the cohesive strength (c) of the

retained material, as well as the direction and magnitude of movement the retaining structure undergoes. Lateral earth pressures are zero at the top of the wall and - in homogenous ground increase proportionally to a maximum value at the lowest depth. Earth pressures will push the wall forward or overturn it if not properly addressed. Also, any groundwater behind the wall that is not dissipated by a drainage system causes hydrostatic pressure on the wall. The total pressure or thrust may be assumed to act at one-third from the lowest depth for lengthwise stretches of uniform height. [5] Unless the wall is designed to retain water, It is important to have proper drainage behind the wall in order to limit the pressure to the wall's design value. Drainage materials will reduce or eliminate the hydrostatic pressure and improve the stability of the material behind the wall. Drystone retaining walls are normally self-draining. As an example, the International Building Code requires retaining walls to be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift; and that they be designed for a safety factor of 1.5 against lateral sliding and overturning.[6] Type of retaining wall:

Various types of retaining walls Gravity walls depend on their mass (stone, concrete or other heavy material) to resist pressure from behind and may have a 'batter' setback to improve stability by leaning back toward the retained soil. For short landscaping walls, they are often made from mortarless stone or segmental concrete units (masonry units).[7] Dry-stacked gravity walls are somewhat flexible and do not require a rigid footing in frost areas. Home

owners who build larger gravity walls that do require a rigid concrete footing can make use of the services of a professional excavator, which will make digging a trench for the base of the gravity wall much easier. Earlier in the 20th century, taller retaining walls were often gravity walls made from large masses of concrete or stone. Today, taller retaining walls are increasingly built as composite gravity walls such as: geosynthetics such as Geoweb cellular confinement earth retention or with precast facing; gabions (stacked steel wire baskets filled with rocks); crib walls (cells built up log cabin style from precast concrete or timber and filled with soil); or soil-nailed walls (soil reinforced in place with steel and concrete rods).[8] Cantilevered retaining walls are made from an internal stem of steel-reinforced, cast-in-place concrete or mortared masonry (often in the shape of an inverted T). These walls cantilever loads (like a beam) to a large, structural footing, converting horizontal pressures from behind the wall to vertical pressures on the ground below. Sometimes cantilevered walls are buttressed on the front, or include a counterfort on the back, to improve their strength resisting high loads. Buttresses are short wing walls at right angles to the main trend of the wall. These walls require rigid concrete footings below seasonal frost depth. This type of wall uses much less material than a traditional gravity wall

Sheet pile retaining walls are usually used in soft soils and tight spaces. Sheet pile walls are made out of steel, vinyl or wood planks which are driven into the ground. For a quick estimate the material is usually driven 1/3 above ground, 2/3 below ground, but this may be altered depending on the environment. Taller sheet pile walls will need a tie-back anchor, or "dead-man" placed in the soil a distance behind the face of the wall, that is tied to the wall, usually by a cable or a rod. Anchors are then placed behind the potential failure plane in the soil. Reference: THE WIKIPEDIA FOUNDATION, INC. (n.d.). retaining wall. United States of America: . 4th December 2013 (accessed 7th January 2014)

Q.8 Entry time is the inlet time required for a raindrop to flow form the most remote part of the catchment area to reach the most upstream point of a drainage system. It varie with the nature of surface cover, surface gradient, spacing of inlets, method of collecting and discharging roof drainage, and the rainfall intensity. Generally, inlet time of 3 to 10 minutes may be used for well developed urban areas, the lower figure being applicable to areas where water flows quickly to stormwater drains through closely spaced inlets and the upper figure applicable to areas which are relatively flat with widely spaced inlets.

The time of flow is the time required for the water to flow from the most remote inlet of urban drainage system to the design section in that system. It may be estimated closely form the hydraulic properties of the stormwater drain usually based on full-bore velocity, i.e. the pipe is running full of water.

Rate of surface runoff is the difference between the amount of rainfall during the time of concentration and the losses due to infiltration, evaporation, transpiration, interception and storage. Major factors governing amount of runoff are as follows: (1) Type and condition of the soil with respect to infiltration - rainwater will infiltrate into granular soil until the soil is saturated before the runoff flows on the surface. (2) Kind and extent of cultivation and/or vegetation. (3) Length and steepness of slopes. (4) Number, arrangement, slope and condition of the natural and manmade drainage channels in the catchment area. (5) Irregularity of ground surface. (6) Size and shape of catchment. (7) Temperature of air and water. (8) Changes in land use. The rate of surface runoff can be calculated by the Rational method, also known as the Lloyd-Davies method. It is the most common method used. The equation is:-

where : Q= maximum runoff (litre/sec)

i = design mean intensity of rainfall (mm/hr) A= area of catchment (m2) K = runoff coefficient Runoff Coefficient (K) is the ratio of surface flow to the amount of rainfall and is mainly dependent on the impermeability of the surface. In general, the value of K may be taken as 1.0 i.e. fully impermeable, for developed urban areas. In less developed areas, unpaved surfaces may be given a K value less than 1.0, but consideration should be given to possible future development and the possible saturation of soil with water before a rainstorm both of which will increase the impermeability of the surface. In Hong Kong, the values of K with respect to types of surface commonly encountered are:-

The above coefficients are applicable for the more frequent storms (say 10-year and below). Less frequent storms of higher intensity may require the use of different coefficients.