As a Construction Management Consultant of I-Consult Ltd appointed by I- Build Sdn Bhd, I am required to suggest different types of retaining wall system available. My proposal focuses on the site probe, importance of retaining wall, building methods, design constructs and preventative steps to extenuate functional failures. I am required to suggest an appropriate choice of the most suited retaining wall system used to the Board of Directors, in which the undertaking is located at hilly country which consists of 20 units of luxury cottages.
In this proposal, I am traveling to discourse:
the importance of site probe,
the importance of retaining wall,
the construct of retaining wall,
types of retaining wall
the most suited retaining wall for this hilly undertaking.
The Importance of Site probe
Every semisynthetic civil technology construction is found on, in or with land. The construction we put on the land is semisynthetic. We can command to plan every point that goes into our construction, such as concrete, support, bricks and even the last wall stopper. However, the land below on which this construction will stand is non semisynthetic. We normally have less cognition about it and we doubtless can non plan or command its behaviour. The land below will find the economic systems of how tall, how heavy, how safe the concluding construction is traveling to be and non the other manner unit of ammunition. In short, the safety and economic sciences of every civil technology construction is influenced by the belongingss of the land on which this construction will stand. These belongingss of the land below or sub-soil belongingss are obtained via Site Investigation.
In any site probe work, the inquiries which should be resolved in finding the probe plan are:
What type of probe is needed,
Why they are needed,
Where the existent field plants should be performed,
How the work is to be done.
Whether the probe is sufficient or excessively much.
Site probe is usually important and carried out prior to the beginning of design of a building undertaking. Site probe has been defined as probe of the physical features of the site and includes documental surveies, site studies and land probe. It is besides refers to the existent surface or subsurface probe, including on site and research lab trials. In wide sense, survey of the site history and environment, reading and analyses of all available informations, and doing recommendations on the favorable/unfavorable locations, economic and safe design, and anticipation of possible hazards should besides be included in site probes.
First and first, a desk survey to uncover informations which may already be refering the site, its geology and history, together with a site reconnaissance, is priceless and can be done before purchase at minimum cost. This may be followed by test roughness, examining or tiring as appropriate to the conditions revealed by predating surveies and in the visible radiation of the development proposals. It is besides a safeguard to minimise harm that could be caused by these dirts could besides be communicated at this phase. At least place inhabitants would be alerted to possible jobs ( and the associated costs ) from the beginning, therefore enabling them to do informed determinations sing the most appropriate foundation system for their places.
Site probe is designed to place the features of dirts or fill stuffs which lie beneath the site, the groundwater conditions and the being and extent of other physical characteristics or contaminations which may be present. This information influences the choice and design of an appropriate structural signifier for the proposed edifice. It is a procedure which should go on on an iterative footing throughout the design and building stages. Post-construction monitoring can besides be of importance in many cases as portion of a proof procedure.
The combined edifice tonss indicated in figure 1 must be safely supported by the undersoil and besides guarantee that unreasonable motions of the edifice do non happen. If the back uping dirt is sufficient resistant and its features under burden are likely to stay satisfactory, the jobs of support and motion will be easy resolved. However, few soils other than stone can defy these concentrated tonss and it is normally necessary to roll up the single-minded tonss at their lowest point and reassign them to adequate bearing dirt known to be available on a peculiar site ( figure 2 ) .
Figure 1: Combined edifice tonss
Figure 2: Method of reassigning combined edifice tonss to back uping dirt.
The general distribution of dirt types in the United Kingdom is indicated in figure 3 ; the dirts include peat, clay, slit, sand and crushed rock. Matching safe bearing force per unit areas are besides given.
Figure 3: simplified distribution of assorted types of back uping dirts
Last, site probe should be undertaken by professional specializers, such as surveyors, geotechnical applied scientist and land probe contractor, and in a phased mode. The land probe contractor is responsible for supplying dependable factual information. The geotechnical adviser should responsible for the planning & A ; executing of the probe plan, reading and analyses of consequences, and doing appropriate design recommendations to avoid over design every bit good as insecure design.
Failure of Site Investigation
Due to miss of or insufficiency of guide/code demand sing the extent every bit good as quality of site probe work, geotechnical failures frequently occurred. These failures sometime led to catastrophic catastrophe and imposed serious menace to public safety.
For the Highland Incident in Kuala Lumpur in 1993, the Architect appointed qualified civil applied scientist to be the confer withing applied scientist for Highland Towers. Initially, civil applied scientist ‘s range of plants was restricted to the structural facet of the three blocks. But later, the civil applied scientist was engaged by the developer to subject proposals over the drainage of the country. His drainage program was approved. He was besides retained by the developer to plan and oversee the building of two retaining walls on the Highland Towers site. The Plaintiffs claimed that the civil applied scientist was negligent for the undermentioned grounds:
( I ) Planing unsuitable foundations ;
( two ) Lack of attention and concern of the hill and incline ;
( three ) Publishing a notice to the governments corroborating the drainage plant was completed when merely a fraction of it was done.
By the above Acts of the Apostless of preparing, planing and oversing the building of Highland Towers and the drainage system of the Highland Towers site, he was negligent and had caused nuisance to them. The civil applied scientist had used rail hemorrhoids welded together as foundation to back up the three flat blocks. This type of hemorrhoids, which was considered inferior to concrete hemorrhoids, was accepted in the technology and edifice industry to back up high-rise edifices at the material clip. Therefore, no mistake can be attributed to the civil applied scientist in utilizing the rail hemorrhoids as he was merely adhering to the recognized professional pattern at that clip. However, there was deficiency of consideration by the civil applied scientist to the hill and the incline straight behind the three blocks. The tribunal ruled that the civil applied scientist should hold moderately anticipate the danger of a landslide bring forthing a sidelong burden against the foundation of the edifice. For this, he should hold exercised attention to either design or concept a foundation to suit the sidelong burden or guarantee that the incline was moderately stable. Failure to make so is a breach of his responsibility of attention he owes to the Plaintiffs since his responsibility was to guarantee the safety of the edifices he designed and built. The civil applied scientist ‘s effort to deny liability on the land that he relied on the developer to guarantee that other retaining walls were constructed decently was unsuccessful. The justice found that it was incumbent upon the civil applied scientist to ask and determine whether the work was that of a qualified professional and what its impact might be on the safety of his ain edifice.
Figure 4: Highland Incident in Kuala Lumpur in 1993
What is Retaining Wall?
A retaining wall is a stabilising construction designed and constructed to retain dirt at a incline that is greater than it would of course presume, normally at a perpendicular or near-vertical place. Besides, the retaining wall used to forestall the eroding and the motion of dirt. The map of retaining wall is to defy the sidelong force per unit area of dirt when there is a coveted alteration in land lift that exceeds the natural incline taken by the dirt which is called the angle of rest of the dirt. The retaining wall is the cuneus of dirt resting on this upper plane of the angle of rest that a retaining wall has to back up.
It is besides designed with weep holes which allow gathered H2O to get away. This releases the extra force per unit area created by a accrued H2O and helps in stabilising the retaining wall.
The walls are designed to offer the necessary opposition by utilizing their ain mass to defy the push or trusting upon the rules of purchase. The nomenclature used in retaining wall building is shown on figure 5:
Figure 5: Terminology of Retaining Wall
Constructing a retaining wall, several types of stuffs can be used. Stone and concrete are the most common stuffs used in building a retaining wall. Besides, there are besides particular retaining wall blocks crafted from aggregative stuffs and light concrete which are designed for this intent. Because each block fits firmly with the following, some manners interconnect, doing edifice simpler, less dearly-won and clip required. These blocks do non necessitate the add-on of howitzer due to the tantrum of these blocks is secure.
A retaining wall can be grades or a series of “ stairss ” , which allow more efficient eroding control every bit good as a more sophisticated design. Different types of plantings, flowers or stuffs in each grade can be included in the design to convey more colour, texture and involvement to the country. By interrupting down the sum of dirt and force per unit area, a tiered design besides give a better eroding control held by each division of the retaining wall alternatively of adding the aesthetic value.
Today, there are several manners and types of retaining wall blocks, and most people choose preformed blocks. Unlike today, big rocks and railway ties were frequently used to build a tiered retaining wall in the yesteryear. Performed blocks are low-cost and user- friendly, doing other methods out of day of the month at all, except the expression of unsmooth rock or wood is preferred.
The Concept of Retaining Wall
DESIGN PRINCIPLES
The design of any retaining wall is fundamentally concerned with the sidelong force per unit areas of the maintained dirt and any subsoil H2O. The intents to build a retaining wall are shown as below:
It is hard to exactly place the belongingss of any dirt because they are inconsistent stuffs. The computation of force per unit area exerted at any point on the wall is a undertaking for the expert, who must take into history the undermentioned factors:
Nature and type of dirt ;
Height of H2O tabular array ;
Subsoil H2O motions ;
Type of wall ;
Materials used in the building of the wall.
Design computations related to the attendant push of retained stuff behind a 1m length of wall. There are two well-established methods can be used to find the attendant push:
Rankine ‘s expression ;
Coulomb ‘s graphical representation or cuneus theory.
Earth PRESSURES
The interior decorator is chiefly concerned with the consequence of two signifiers of earth force per unit area:
ACTIVE EARTH PRESSURE are those that tend to travel or turn over the retaining wall, and are composed of the Earth cuneus being retained together with any hydrostatic force per unit area caused by the presence of groundwater. The latter can be reduced by the usage of undersoil drainage behind the wall, or by infixing drainage gaps called weep holes through the thickness of the root, enabling the H2O to run out off.
PASSIVE EARTH RESISTANCES are reactionist force per unit areas that will respond in the signifier of a opposition to motion of the wall. If the wall tends to travel frontward, the Earth in forepart of the toe to antagonize the forward motion. This force per unit area can be increased by enlarging the deepness of the toe or by organizing a rib on the bottom of the base.
Active Earth force per unit areas must be to passive Earth oppositions in order to avoid overturning and round faux pas. Typical illustrations of these force per unit areas are shown in figure 6 and figure 7.
Figure 6: Active and Passive Earth Pressures act on Mass Retaining Wall
Figure 7: Active and Passive Earth Pressures act on Cantilever Retaining Wall
Stability
The overall stableness of a retaining wall is governed by the consequence of the action and reaction of a figure of tonss:
Consequence OF WATER
The design and stableness can be affected by land H2O behind a retaining wall whether inactive or leaching through undersoil. The force per unit area on the dorsum of the wall will be increased. By cut downing the dirt shear strength, the bearing capacity of the dirt can be reduced ; it can cut down the frictional opposition between the base and the dirt and cut down possible inactive force per unit area in forepart of the wall. As a consequence, the issue of drainage of the H2O behind the retaining wall is the extreme of import in the design.
SLIP CIRCLE FAILURE
Slip circle failure ( shown in figure 8 ) is sometimes encountered with retaining wall in clay dirts, peculiarly where there is a heavy surcharge of retained stuff. It takes the signifier of a rotational motion of the dirt and wall along a round discharge. The discharge commences behind the wall and base on ballss under the base, ensuing in a tilting and forward motion of the wall. Further motion can be prevented by driving sheet hemorrhoids into land in forepart of the toe, to a deepness that will cut the faux pas circles arc.
Moment due to weight of maintained Earth and wall above faux pas circle arc about O is greater than reconstructing minute RM.
RM=permissible shear emphasis x length of arc ABC x arc radius OC
Consequence: mass above ABC rotates about O. Wall tilts frontward and earth broken winds in forepart.
Figure 8: Retaining wall failure due to rotational motion.
The Importance of a Retaining Wall
A retaining wall might be built on belongings for assorted grounds. Some degree of soil and dirt will be held off from place, garden, pool or play country by constructing a retaining wall.
The sheer aesthetics might besides be added on it. A more useable land will be provided if there have a batch of turn overing and spilling pace.
The importance of retaining wall is stated as below:
Retaining Walls Hold Back the Earth
Buildings might be built on a hill or in a vale between several hills. Retaining wall will keep back the Earth one time the hillside has been dug out to build edifices. Soil does back in from the sides of the wall with each shovel full. The more you shovel, the soil begins to fall back in. the sides are loose and weak, so they will crumple at the slightest aggravation.
The soil which remains has to dispatch when the side of a hill is dug out. If left entirely, it will finally comes toppling down. The soil will be held back and the safety will be ensured.
Retaining Walls Provide More Useable Land
A walk-out cellar, terrace, resort area, garden, tennis tribunal or swimming pool might be installed into proposed development. If the land is turn overing or hilly, work can non be begun until the land is leveled off.
A kind of drop, where a portion of the proposed land which is non dug out is higher than the lower level land, will so be left out. Adding a retaining wall will hold more useable land every bit good as will add construction and beauty to your new country. Retaining wall can be used as stairss into the pool where pool equipments to be held.
Retaining Walls Avoid the Ground from Washing Away
If the country gets a batch of rainfall or close H2O such as lake, a retaining wall will maintain the H2O from gnawing the dirt of your landscape gardening and around your foundation. This could be a safety step to forestall landslides and river of soil from drifting towards the edifices.
Types of Wall
Mass retaining walls
Mass retaining walls besides known as gravitation walls. They rely upon their ain mass together with the clash on the bottom of the base to get the better of the inclination to skid or turn over. They are by and large economic merely up to a tallness of 1.800m. Mass walls can be constructed of semi-engineering quality bricks bedded in a 1:3 cement howitzer or of aggregate concrete. Mass concrete could hold some light fabric support to command surface checking. Natural rock is suited for little walls up to 1.000m high, but by and large it is used as a facing stuff for walls up to 1.000m high, but by and large it is used as a facing stuff for wall over 1.000m.
Typical illustrations of mass retaining walls are shown in figure 9 and 10:
Figure 9: Brick Mass Retaining Walls
Figure 10: Mass Concrete Retaining Wall with Stone Facings
Cantilever walls
Cantilever walls are normally of strengthened concrete, and work on the rules of purchase. Two basic signifiers can be considered: a base with a big heel so that the mass of the wall with a big toe ( figure 10 ) . The figure shows typical subdivisions and forms of support encountered with these basic signifiers of cantilever retaining wall. The chief steel occurs on the tenseness face of the wall, and nominal steel ( 0.15 % of the cross-sectional country of the wall ) is really frequently included in the opposite face to command the shrinking snap that occurs in unmoved concrete work. Reinforcement demands, bending, manufacturing and puting are dealt with in item in the subdivision on the strengthened concrete.
Reinforced cantilever walls have an economic tallness scope of 1.200-6.000m. Walls in surplus of this tallness have been economically constructed utilizing prestressing techniques. Any lasting facing stuff may be applied to the surface to better the visual aspect of the wall, but it must be remembered that such coatings are cosmetic and add nil to the structural strength of the wall.
Figure 10: Reinforced Concrete Cantilever Retaining Walls
Counterfort Retaining Walls
These walls can be constructed of strengthened or prestressed concrete, and are considered suited if the tallness is over 4.500m. The counterforts are triangular beams placed at suited Centres behind the root and above the base to enable the root and base to move as slabs crossing horizontally over or under the counterforts. Figure 11 and figure 12 show a typical subdivision and form of support for a counterofrt retaining wall.
If the counterforts are placed on the face of the root they are termed buttresses, and the whole agreement is called a buttress-retaining wall. The design and building rules are similar in the two formats.
Figure 11: Reinforced Concrete Counterfort Retaining Wall
Figure 12: Reinforced Concrete Counterfort Retaining Wall
Reinforced masonry retaining walls
Steel support may be used in brick retaining walls to defy tensile forces and to forestall the effects of shear. A brick bonding agreement known as Quetta bond is used to make a unvarying distribution of perpendicular nothingnesss. Vertical steel support is tied to the foundation support and spaced to co-occur with purpose-built nothingnesss. The nothingnesss are filled with concrete to bring forth a series of strengthened concrete mini-columns within the wall when the brickwork is completed.
Where visual aspect is non of import, or the wall is to have a surface intervention, support and unmoved concrete within hollow concrete block work provide for economical and functional building. Figure 13 shows the application of standard-profile, hollow, heavy concrete blocks lay in stretcher bond as lasting formwork to uninterrupted perpendicular columns.
Figure 13: Reinforced Concrete Block Retaining Wall
The height potency and slenderness ratio ( effectual tallness to width ) for reinforced masonry walls can be enhanced by post-tensioning the construction. For intents of brick walls there are a figure of building options, including:
Quetta bond with steel bars concrete in the nothingnesss ;
Stretcher-bonded broad pit with strengthened steel bars coated for corrosion protection ;
Solid wall of pierced bricks with uninterrupted nothingnesss incorporating grouted steel support bars.
Some illustrations are shown in figure 14:
Figure 14: Post-tensioned Brick Retaining Walls
Decision
Based on treatment shown on above, I would wish to choose Cantilever retaining wall as the most suited retaining wall for the undertaking where is located at hilly country which consists of 20 units of luxury cottages.
Equally shown as above, a cantilever retaining wall is a signifier of masonry installing that holds a big sum of Earth in topographic point. The cantilever design is merely one of several fluctuations on a retaining wall design, utilizing assorted rules to pull off earth tonss. Cantilever retaining wall has an economic tallness scope of 1.200-6.000m. This type of retaining wall is suited for cottages because the tallness is sufficient to back up the cottages.
A concrete cantilever retaining wall uses a comparatively thin root of steel-reinforced, cast-in-place, concrete or mortared masonry. In a cantilever retaining wall design, an Earth force per unit area vector acts horizontally against the side of the wall. The bottom portion of the wall presents a gravitation vector downward. That gravitation vector produces an opposite force upward. The ensuing vector counters the Earth force per unit area vector, and pushes back against the Earth burden. This type of retaining wall is more stable compared to the other three types which stated on above in order to construct 20 units of luxury cottages because the tonss are distributed every bit.
Retaining wall design is evaluated to chair the effects of a landslide. Retaining walls can be helpful in protecting dirt against the sorts of motion associated with these natural catastrophes. Looking at landslide hazard and the hazard of liquefaction, the H2O impregnation of Earth, is portion of measuring how a retaining wall plants. Cantilever retaining wall is one that consists of a unvarying thickness wall which is tied to a terms. It located at the cellar of cottages. Therefore, cantilever retaining wall will keep back the Earth. Soil eroding, landslides and environment catastrophes are less likely to be occurred. In other words, checking and prostration of 20 units of luxury cottages are avoided.
Weep holes are designed in the cantilever retaining wall to let go of the extra force per unit area created by a accrued H2O and helps in stabilising the retaining wall. This ensures the edifice will non fall in due to the fast flow of H2O on the hill.
In decision, a suited retaining wall is able to stabilise the dirt and avoid overturning and sliding of edifice. Beside, a suited retaining wall can besides assist in salvaging the building cost. Therefore, cantilever retaining wall is the most suited retaining wall for 20 units of luxury cottages which are located on the hilly country.
