Basement Construction

Table of Content

It discusses general background information on topography, geology and rounder aspects of the site. It describes the factors which have influenced the design and construction of the proposed commercial retail development at Lot 4 Coronation Park. HELM Consultants undertook the assessment at the request of Dreamboats Furniture Group Pity Ltd. The report compares and contrasts the advantages and disadvantages of a variety of methods and technologies for constructing basements. A basement, for the basis of this report, is part of a building partly or wholly extends below ground level.

It is essential basements are well planned, designed ND constructed to ensure that for the life of the building it functions effectively and efficiently. A common concern of basement construction is the effects of groundwater. These issues are considered and the areas where these issues could potentially occur are identified. Additional cumulative effects of basements have also been considered. Finally the report sets out recommendations on the appropriate approach to the design and construction of the basement and details the steps which should be taken in the construction of the chosen design and construction.

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Page | 3 1. 0 | INTRODUCTION In general, basements provide an effective internal space within a building without compromising the site area. Basements commonly are used as utility space for building including but not limited to car parking, plant equipment, amenities and storage. The project brief provides that the commercial building is intended to be a precedent development which reflects “a successful professional company’. The project involves the construction of a new commercial retail structure.

The structure will effectively comprise of no more than two commercial retail levels above ground with basement car parking, plant and storage areas. The structure is to be constructed of materials which are durable and low maintenance with access to be established via Main Road to the basement car parking level. The main purpose of this report is to address the above criteria and provide a thorough discussion and analysis on the various excavation lateral support systems, foundation and basement methods for the construction, in addition addressing excavation, ground water control and waterproofing methods.

Fundamentally, through comparison and contrast of the basement construction methods, including cost analysis, the appropriate method will be determined and n illustrated construction sequence provided detailing the tasks and activities involved in the construction. 2. 0 | SITE INVESTIGATION / CONSTRAINTS A site investigation is essential for each site and is one of the first steps into designing a building. It is the process of acquiring information by a geological and categorical assessment and analysis of the ground conditions.

Such information is required as it may affect the construction or performance of a building. An inadequate understanding of the site conditions may result in construction delays, increase or a faulty building. The process of a site inspection commonly involves; Site inspection objectives Desk study Site reconnaissance Page | 4 Ground investigation Reporting The objectives of a site inspection includes; Suitability Design Construction Materials Effects of changes Identify alternatives Desk study involves gathering information from available records, such as geological maps and aerial photographs.

The desk study will indicate any potential ground and groundwater conditions and any issues that may arise. Then a site reconnaissance is undertaken in the form of a walk over survey and visual assessment of the site. Following is a ground investigation. A ground investigation involves intrusive work such as trial pits and boreholes. Trial pits are trenches or shallow excavations, either by hand or mechanically. Boreholes enable a greater depths to be achieved as well as provide more detailed profiles of soils and rock, and has less ground disturbance in companions.

Finally, a report is provided detailing the results of the site investigation. A categorical investigation was undertaken with three boreholes to a depth of mm. See figure 1. The investigation revealed that the site consists of very stiff clay between 1 1. M (83) and 13. Mm (BE) from ground level. According to engineer details, differential settlement shall be reduced when foundations are erected on even bearing materials, in accordance with Australian Standard 2870-2011 (AS, 2011). Clay is a cohesive, relatively impermeable material that can exhibit high strength.

When exposed, clay expands and contracts as the equilibrium between the intracellular soil particles become unbalanced (Methane, Scarborough & Remarries, 2013). Accordingly, the soil is deemed to a classification ‘M’ (moderately reactive clay), in accordance with ASSESS-2011 Table 2. . Due to the shear failure and excessive movement of the foundation material, the footings will need to be designed to accommodate such aspects. Page | 5 Figure 1: Existing Site Plan and Elevations The water table is identified to vary between 2. Mm (Bal ) and 5. Mm (BE) from ground level. It is known that there is a pond located within mm of the site.

As a result of the identified groundwater depths, dewatering methods may be necessary during excavation and construction works, given the changes in groundwater elevation height and strain on the intracellular bearing materials (Keels, 2004). Initially clay is considered exhibits an almost-vertical angle of repose, however when combined with groundwater it may slump (Bowels, 1977) (Allan & llano, 2004). Any excavations would be required to be certified by a professional structural engineer and have consideration of any potential impacts on adjacent structures, for example compromising zones of influence.

Statutory Provisions: page | 6 Basement construction must meet the provisions of the National Construction Code Series, Volume One, Building Code of Australia, Class 2 to 9 buildings(ABACA, 2013) and the provisions of relevant Australian Standards. In addition consultation with the chief executive officer of the rail authority would be required for developments located within mm of a rail corridor, in accordance with Division 15 of the State Environmental Planning Policy(launderettes)2007. 4. | BASEMENT CONSTRUCTION The following is a discussion on the advantages and disadvantages of the various basement construction methods 4. 1 | Earthmoving In general, earthmoving is the process of loosening and removing soil material, leaving space above or below ground. Earthmoving in most situations is commonly done mechanically. For the Basement construction significant earthmoving is necessary. This significant earthmoving will involve excavation, transportation, placement, compaction and finishing of excavated soil material.

Excavation and leveling of the basement building envelope is recommended to be done with a fixed position backhoe, With a dump truck transporting the soil material to a location on-site or off-site. A static roller is to compact the excavated areas in preparation for footings and slabs to be constructed, ensuring relative compaction is achieved. 4. 2 Excavation Lateral Support (ELLS) Excavation Lateral Support (ELLS) systems are earth retaining structures designed to stabilize an excavation over mm in depth. The following are some commonly used ELLS system: the sheet pile wall, the bored pile wall, the diaphragm wall and soil nailing.

Sheet Pile Wall Sheet piles consists of structural sections that vertically interlock and are embedded into foundation material to create a continuous wall. Typically sheet piles have a U profile or a Z profile. Steel sheet piling is the most commonly used ELLS system due to several advantages over other materials: Provides high resistance to driving stress Light weight Easily stored Page | 7 Long service life above or below water with modest protection Pile length is easy extended by welding or bolting Joints are less apt to deform during driving (Tang.

P, 2014) However, sheet piles are a costly imported product and require specialized and experienced contractors for installation. They also are rarely used as part of the permanent structure, not suitable for soils with boulders or hard obstructions, created significant noise and vibrations during installation and may cause settlement disturbance on adjacent properties due to vibrations. Figure 4: U profile sheet pile section (http://www. Mathematicians. Com/l_l-profile-sheet-pile. HTML, retrieved April 2014) Figure 5: Sheet pile wall in excavation (http://deconstructs. Rig/categorical/sheet-pillages/7131/, retrieved April 2014) Figure 6: Z profile sheet pile section (http://www. Mathematicians. Com/Straightness’s. HTML, retrieved April 2014) Page | 8 Bored Pile Wall (Secant Concrete Piles) Secant bored piles consist of interlocking piles which form a continuous wall. The piles are constructed so that one pile intersects with the other. They are tallied to transfer loads through weak soil to a suitable bearing foundation. The construction involves two stages. Stage 1: the primary piles are constructed with concrete.

Stage 2: the secondary piles are constructed in between and overlapping the primary piles with placement of reinforcement cages and concrete. Refer to figure 7 Secant pile walls are commonly utilized to increase construction alignment flexibility to fit complex sites maximizing land use; the system has increased wall stiffness compared to sheet piles, reduce ground movement on adjacent land, appropriate for difficult ground consisting of boulders or hard obstructions and effective in high water table conditions without excessive dewatering.

However, secant pile walls limitations include: Vertically tolerances may be hard to achieved for deep piles Total waterproofing is difficult to obtain at joints Increased cost compared to sheet pile Figure 7: Secant Concrete Piles (http://www. Sentential. Com/sites/secant tipples/technocracies. Asps, retrieved April 2014) Page | 9 Figure 8: Secant Concrete Piles in excavation tipples/actualities. Asps, retrieved April Diaphragm Wall Diaphragm walls are a series of narrow rectangular trenches filled with reinforcement and concrete to form a continuous wall.

Using a guide wall, trenches are excavated in discontinuous sections or panels using a hydrofoils drill. The excavations are temporarily supported by slurry, followed by lowering steel reinforcement cage into the centre of each section or panel and placement of concrete using a termite concrete. Diaphragm walls are commonly used in top-down construction methods, in crowded areas including in close proximity to other structures, with minimal impacts on support to foundations and in unstable soil material below the water table where continuous support and watertight conditions are required (Tang. P, 2014).

Key advantages of diaphragm walls also include: Can be installed to considerable depths Easily incorporated into permanent work, delivering a smooth finished surface for walls Impermeable Minimal noise and vibration during construction. While diaphragm walls have many advantages the method has some distinct limitations. These limitations are summarized below: High cost, requiring specialized plant equipment Large plant equipment requiring large site area and headroom Page | 10 Disposal or storage of contaminated slurry Figure 9: Diaphragm wall construction process (http://fundamentalism’s. Wordless. Mom/2012/08/15/advantages -and-disadvantages-slurry-hallucinations/, retrieved April Figure 10: Diaphragm wall (http://www. Menarche. Com. AU/diaphragm_walls. PH, retrieved April 2014) page | 11 Soil nailing is a technique used to stabilize slopes or excavations. The technique can be designed for temporary or permanent support. The walls are generally a top-down construction method using grouted misrepresenting steel elements (nails) installed closely spaced to increase the shear strength of unsupported soil material, followed by applying reinforced shoetree facing or precept facing panels.

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