Water Table Necessitates Construction Procedures

Soil Type

Discuss About The Water Table Necessitates Construction Procedures?

Structure locale: the shopping centre structure will be located in 87 Northlakes Drive in Cameron Park, New South Wales putting its streetscape between Northlakes Drive, Elanet Avenue and will border the IGA Cameron Park to the west. Only the basement will be below ground and the building will extend to two floors above ground.Entry: the entry location of the shipping centre will be on the Northlakes Drive which is shown in site plan. This is because Northlakes Drive is at a relatively lower risk of traffic congestion compared to Elanet Avenue which has 2 intersections at a distance of less than 100m from each other. Also, it is easier to access with the presence of a roundabout nearby from which vehicles can use to access the site.Exit: the preferable exit location will be on Elanet Avenue which is shown in the site plan. This is because the avenue leads to the nearby roundabout from which clients can disperse to their various directions.Location of Basement: it will utilize the whole plot area so that parking spaces are maximized; the site will have a perimeter with a 2m offset distance inwards in order to ensure utilization of the pathway during and after construction.Soil typeMechanical operations: there will be a combination of natural ground types: soft sandy top soil with some organic matter, medium dense, firm ground fine to coarse sand with fine gravel, medium dense becoming dense grey fine to coarse angular to sub rounded flint gravel with cobbles, and a trace of sand.Strength properties: the larger portion of the ground is closely dense, necessitating a reinforced foundation. A shallow foundation best suits this type of profile.Water tableThe water table, initially 4m deep, rose to 2.5m in a relatively short time of 50 minutes during boring. The reduced level is +28.5m from sea level. This necessitates careful attention to the pumping and drainage of the ground water and water proofing Clear siteVegetation clearing: 10 trees, 11 trees below 0.5m, 7 trees 0.5 – 1m.Tree removal: for trees less than or equal to 0.5m is $162 each; for trees 0.5-1m, $162 each. Therefore, the cumulative cost of tree removal is $2916.

Mechanical Plants (Fixed Plants):

2. Backacter excavator: The depth capacity of this excavator ranges from 6 to 7m with a possible load haul rate of 40 cycles per hour making the giving it a possible excavated volume per hour of between 4-72m². It operates by picking soil from above it, reaching soil below it, at the same level and in a backward direction. Its cost is $510 per day.
3. Front shovel excavator: The volumetric capacity of this excavator ranges from 0.3 to 6m³ with a possible load haul rate of 80 cycles per hour making the giving it a possible excavated volume per hour of between 24-480m². It operates by picking soil from below it, reaching soil below it, soil at the same level and in a forward direction. Pricing information is not available in the Rawlinson’s Australian construction handbook 2010.
4. Bucket wheel excavator: The this excavator consists of up to 20 buckets per wheel, each of which could have up to 15m³ capacity with a possible load haul rate of 100-12,500m³ per hour. They have varying boom lengths ranging from 6-80m. This makes them fairly capable of excavating material up to 240,000m². It operating by picking soil from ground above it, picking soil from below ground (from above), soil at the same level and soil in a backward or forwards direction. Pricing information is not available in the Rawlinson’s Australian construction handbook 2010.

Summary: A Front shovel excavator would be most practical because of its capacity and haul rate and also because of the relative ease of excavation in a directional manner which would suit this particular site.

4. Tracked shovel loader: this plant is capable of a variety of tasks including excavation, moving and loading although not specialized for any of them. It can excavate to a depth of 1m below it and can lift up to a height of 4.5m. Pricing information is not available in the Rawlinson’s Australian construction handbook 2010.
5. Bulldozer: this plant is capable of a variety of tasks including excavation up to 300mm, clearing trees and vegetation, moving and loading rubble. This makes them perfect for site stripping, levelling the site and earthmoving. Its bucket has a capacity of 3.7-5.6m³. Pricing information for this specific type of excavator is $804 per day.
6. Scrapper: These have a carrying capacity of between 6-50m³. It is useful for site levelling and stripping with an excavation depth of up to 300mm. It is perfect for discharging materials after collecting and moving it. Pricing information is not available in the Rawlinson’s Australian construction handbook 2010.

Methodological Analysis

Summary: we conclude that a scrapper may not be suitable for the site due to the size of the site. A bulldozer on the other hand may be disqualified due to the fact that it is limited to moving and loading. This makes the tracked loader the most suitable mechanical plant for the job.

3. Dump Trucks: These can be tractors or trailers that have different discharge options which include sideways, front tipping and elevated dumping. They also have different carrying capacities ranging from 5-30m³. They transport materials on and off-site and can cover a distance of 0.8-10km. They are the largest material transport equipment on road. No pricing information is contained in the Rawlinson’s Australian construction handbook 2010.
4. Industrial trucks: These are trucks not licensed to use the public network of roads. Their carrying capacities range from 3-68m³. They transport materials on site where other transporting options are impractical but disposal is within the site or does not require use of public roads. They can cover a distance of 0.8-10km. No pricing information for this specific type of loader is contained in the Rawlinson’s Australian construction handbook 2010.
5. Railway: These have varying carrying capacities depending on the length of the carriages and their total number. They transport materials off site where the distance is long other transporting options are uneconomic. The disposal location is usually relatively far away from the site. They carry the most amount of material at a go. Pricing information is not available in the Rawlinson’s Australian construction handbook 2010.

Summary: it is difficult to give an accurate judgement as the disposal location and its distance from the site is unknown. The dump truck would be the best option for a nearby disposal location but it is far, it could be combined with the railway system.

3. Sheet piles: these are steel sheet piles specifically fabricated offsite to link together forming a continuous wall. Can be permanent or temporary (reusable) with the advantage of being light weight and strong tensile strength. Their disadvantages include noise pollution, cost, water seepage and obstruction by hard material in the ground. Their cost $652 per m³.
4. Bored piles: these are concrete piles specifically fabricated offsite to link together forming a continuous wall. Can also consist of primary piles with secondary linking piles between them. Their advantage is low noise and vibrations, minimal excavation needed and they perfect for small sites. Their disadvantages include slow boring process, relatively weaker vertical joints and lower tensile strength. Their cost is up to $318 per m³.
5. Diaphragm: these are concrete walls made of trenches that are first filled with slurry for support then reinforcement lowered and concrete placed once depth is achieved to displace the slurry. Their advantage is low noise and vibrations, impermeability for water tightness, and can serve as footings. Their disadvantage is their high cost. Their cost $350 per m³.

Summary: a diaphragm is the best option due to its impermeability as the water table may rise in the site, durability and structural strength.

74. Sump pumping: this method includes the utilization of a shaft or sump pump to collect the water and pump it into a different part of the site or containment system. Their advantages are that the capacities of the pumps can vary depending on the amount of work. It is also an inexpensive method of dewatering. It is however time consuming and can be affected by seepage. Their price varies from $74.17-$254 per day.
75. Well point systems: this system consists of a collecting intake strainers in the ground connected to a suction pipe which are then connected to a header pipe. A filter media is introduced all around the pipe and strainer. The water pumped out by a Well point pump connected to the header pipe. They are economically sound, cost effective and can be used either on a temporary or long-term basis. Pumping is however noisy causing noise pollution. Pricing information is not available in the Rawlinson’s Australian construction handbook 2010.

Summary: a Well point pump is expedient as it is both cost effective and practical for a large construction site with large volumes of water.

1. Open cut: This method of construction is suitable for very large sites that are open and unobstructed. They require minimal lateral protection and have minimal special provisions too. They however require large and heavy machinery and material is removed by use of a ramp.
2. Bottom-up: This method of construction is suitable for small open sites and is adaptable to a vast range of environments. They require small to medium sized machinery and material is removed by use of a bucket system or staged platform. They require minimal special provisions too. They however require extensive lateral protection
3. Top-down: This method of construction is suitable for large sites and is adaptable to a vast range of environments. They require small to medium sized machinery and material is removed by use of a bucket system or staged platform. They require minimal lateral protection where shoring is only implemented when the need arises. However, this approach necessitates extensive vertical support on a temporary basis.

Summary: we disqualify the open cut method due to the obstructions in form of diaphragm wall and the top-down method too as the site is small. Bottom-up method will be used.

Pad footing: is a remote footing limited to just one column. It is cheap, consumes less material and good for hard ground. It his however not applicable in cohesionless soils. Their cost is $204 without reinforcement and $292 per m³ with reinforcement.

Raft footing: is a slab-like footing covering a wide area and contains more than one column. It is good for medium to hard soils and the footing can act both as a slab and foundation. It is also lightweight. It is however time consuming and not good for cohesionless soils. Their cost is $204 without reinforcement and $261 per m³ with reinforcement.

Strip footing: this is a foundation that is continuous along the load path and goes around the structures perimeter. It is relatively stronger than pad and raft footing and good for both medium and hard soils. They are however the most complicated foundation types. Their cost is $270 without reinforcement and $273 per m³ with reinforcement.

Summary: strip footing is advisable due to its durability and strength over pad and raft footing. It is also economic in comparison to the other methods. Reinforcement will be used.

This is not necessary as the soil in the site is stable and cohesive.

In situ concrete: this is a concrete element that is cast progressively in place over timber formwork or metal moulds. It is usually 150mm thick but the thickness can vary depending on the nature of work and the strength required. Its strength and setting time can also be varied by using a variety of admixtures. Their cost is $209 per m³ without reinforcement and $292 per m³ with reinforcement.

Mechanical Plants (Fixed Plants)

Precast concrete: this is a concrete element that cast away from the site in moulds. It is usually 150mm thick but the thickness can vary depending on the nature of work and the strength required. Its strength and setting time can also be varied by using a variety of admixtures. Their cost is $120 for waffle slab and $300 per m³ for solid filled block inclusive of moulds, reinforcement and fixing.

Summary: in situ concrete is favourable as a chemical bond is desired with the diaphragm to maximize on its strength providing a strong retaining wall.

Tanking: this is a method of installing an impermeable layer either on the internal or external side of a basement or foundation. When applied internally, water getting in is directed to a discharge point. When applied externally, a geomembrane is usually added as a drain with water being collected into a sump for pumping out or discharge. It can accommodate high water table levels with the drawback of noisy pumping. Their cost ranges from $12-38 per m² as in the Rawlinson’s Australian construction handbook 2010.

Cavity drainage: this is where a waterproof layer is installed consisting of membrane with gaps for water collection and direction into a sump. It also has an insulating layer and a dry soft board. It is quick to install while providing an unnoticeable and adaptable front face. It is however unsuitable where water table is high or where floors and walls are not impermeable. Pricing information is not available in the Rawlinson’s Australian construction handbook 2010.

Exterior foundation drain: this utilises a porous soil or rock layer adjacent to the external walls of a basement and waterproofing membrane layer on the underside of the foundation. It drains water relatively fast but is not applicable where the water table is high. Pricing information is not available in the Rawlinson’s Australian construction handbook 2010.

Summary: we can conclude that external tanking best suits this foundation as the water table may rise above the foundation level.

Polymer Membrane: this is a solid but flexible impermeable material that can be used for complex structural environments and under the slab. Its drawback is the relatively longer installation time. Its cost is $26.32 per m² for solid filled block inclusive of moulds, reinforcement and fixing.

Styrofoam Membrane: this is a solid but flexible impermeable material that can be used under the slab. Its drawback is that it cannot be used for complex structural environments and the relatively longer installation time. Pricing information is not available in the Rawlinson’s Australian construction handbook 2010.

Mechanical Plants (Moving Plants)

Bituminous paint: this is an impermeable liquid paint that is applicable in complex structural environments but not under the slab. Its cost is $10.77 per m² for solid filled block inclusive of moulds, reinforcement and fixing.

Summary: a polymer membrane should be used as it is applicable under the slab and also because the site will be a complex environment.

Reinforced concrete: could be in situ or precast and their strength varies with the type of cement and admixtures used. They are also durable with their main challenge being the cost. Their price ranges from $201-$273 per m³ (inclusive of reinforcement) in the Rawlinson’s Australian construction handbook 2010.

Steel: These are cold worked steel bars usually 150mm by 150mm. They are moulded offsite and have medium strength. Their drawback is the relatively lower compressive strength and higher rate of corrosion. Their price is $247 per m².

Timber: can be wooden cylindrical poles or square with sides 100mm by 100mm. They are generally weak and prone to corrosion. Their price is $38 per m².

Brick/Block: these are made of interlocking bricks or ordinary masonry bricks and can be circular or rectangular. They are generally strong and durable but consume a lot of time. Their price is $60 per m².

Summary: In situ cast reinforced concrete columns will be used to ensure strong chemical joints with the base plate and because of their durability.

In situ concrete: this is a concrete element that cast progressively in place over timber formwork or metal moulds. Their cost is $209 per m³ without reinforcement and $221 per m³ with reinforcement.

Precast concrete: this is a concrete element that cast away from the site in moulds. Their cost is $185 for waffle slab and $300 per m³ for solid filled block inclusive of moulds, reinforcement and fixing.

Summary: precast waffle slab is favourable as due to the cost effectiveness, light weight, less installation time and ease of installation.

Conclusion

Construction will utilize a diaphragm wall because of its strength, impermeability and durability over the other methods. Strip footing foundation is to be used because of its relatively higher strength and ease of use in a large site. During and after excavation, a well point system of drainage will be used to lower the ground water level due to its time and cost saving attribute. It will be used in combination with a polymer membrane to waterproof the building due to its applicability in complex structural environments. The ground slab will be cast in situ while the suspended slab precast and these will be held up by reinforced concrete columns cast in situ to maximize on strength through better chemical bonds.

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