G.ADITHYAPGPCPM-06

5801713140129

ASSIGNMENT 2Earthworks and Foundations

Earth works

A. What would you consider important when setting out a construction site building?

When planning to construct any building, the most important factor to be considered is the location. Information about the subsurface and surface features is essential for the design of structure and planning.site investigation in one form or other is required for every project.Site investigation are generally done to obtain information for following purposes.

Determine the bearing capacity of the soil . Estimate the ground water level. Predict lateral earth pressure against retaining walls Probable differential settlements. Select suitable type and depth of foundation for a given structure. Select suitable construction techniques. Soil suitable as a construction material. knowledge about high flood level Good quality of water and availability of electric connection. checking whether your area comes in a Earth Quake prone zone.

B. Excavation/earthworks are often the cause of variations and extension of time claims. Explain why this is the case?

Parameters affecting delay of excavation can be classified into three general groups

Geological Mechanical and Operation

Geological and mechanical parameters usually define the net excavatin rates ,operational parameters define the overall performance of the system

Geological parameters

Rock mass properties Hydrogeology Physical and mechanical properties Physical and mechanical propertys Abrasivity and texture

Mechanical parameters

Machine type Cutting type Mechine dimensions Cuttinghead type

Operational parameters

Technical parameters Utility lines Ground treatment Labor availability

C. Your Construction site excavation project requires secant piles to be installed before excavation can begin. Describe the process in detail and what safety factors that you would consider when planning this process.

SECANT PILESSecant pile walls are formed by constructing a series of overlapping concrete-filled drill holes to form a continuous, relatively watertight wall

1)Position of bored pilesWooden pegs are used to mark center position of each bored pile. The gap between two bored piles will be between 100 to 200 mm.

2)Installation of CasingThe vibro-hammer drives casing into the ground, leaving 1m length of the casing projection from the ground

3)Augering of BoreholeThe auger removes the soil within the casing to form a borehole. The soil surrounding the borehole is supported by the casing. If the casing is not long enough to reach the required depth in the ground, bentonite slurry is used to support the soil below the casing.

4)Installation of Steel CageThe crane lifts up the steel cage and places it within the borehole.

5)Concreting of BoreholeConcrete is poured into the borehole to form the bored pile.

6)Extraction of CasingThe vibro-hammer extracts the casing from the ground

7)Repetition of ProcessSteps 2 - 6 are repeated till the entire length of the contiguous bored pile wall construction is completed.

CONSTRUCTION CHALLENGESVerticality.exact verticality should be maintained during whole drilling process

Water tightness excavation to greater depth, it is crucial to maintain specified level with as little leakage as possible. It is then essential to be able to build the permanent wall according to specification.

Wear and tearDue to the long drilling lengths tool wear may be high. Wear and tear result in impede progress.

D. The secant piles are now installed and you are to excavate to a depth of 10m. What challenges do you face and how will you complete the excavation process.

Installation of Retaining WallThe underground retaining wall is installed before excavation starts. The retaining wall can be a concrete diaphragm wall, a concrete bored pile wall or a steel sheet pile wall; depending on the site condition, soil type and the excavation depth.

Excavation & Installation of Steel StrutThe soil is excavated to the first strut level. The first level strut is installed before the excavation proceeds further.

Excavation & Installation of Steel StrutThe soil is excavated to the next strut level and the second level strut is installed.It continues till the excavation reaches the final depth or formation level.

Construction of Underground StructureAt formation level, the reinforced concrete base slab is constructed, followed by the removal of the lowest level strut and then side walls are constructed

Construction of Underground StructureThe next level of slab is constructed, followed by the removal of the strut near to that slab level. This process progresses upwards till the roof slab is constructed.

Backfilling & Reinstatementthe soil is backfilled to the first strut level before the first level strut is removed. If the retaining wall is a diaphragm wall or a bored pile wall, the top 2 metres of the wall will be removed. If it is a sheet pile wall the sheet piles will be extracted.

CONSTRUCTION CHALLENGESSeepageSeepage is the big problem it may also lead to delay of work.Piping The seepage of water through the body and foundation may lead to piping.

Geotechnical conditionsLoose, cohesionless soil below the groundwater table. The geological conditions of the catchment area should be such that percolation losses are minimum.

E. 5 metres down you have struck a large rock formation that was not identified in the contract documents. Explain the process you would use to remove the rock and why you have used that process.

ROCK EXCAVATION Rock excavation consists of excavation of igneous, sedimentary , and metamorphic rock . The material for this type of excavation is removed by blasting, by power shovel or by other equivalent powered equipment.

ROCK PRE-SPLITTING The rock is pre-split by the use of drilling and explosives. Pre split blasting requires small drill holes.The work is done in such a way that minimum breakage occurs outside the typical cross section. The holes for this operation are from 2 in. - 4 in. in diameter, spaced 3 ft apart, and drilled 2 ft below the predetermined bench elevation. The maximum depth of a pre-split lift is usually about 30 ft. If a cut section requires more than one lift, the holes are drilled in such a way that the specified offset for each succeeding lift is obtained. The pre-split face shall deviate no more than 6 in from the front line and 1 ft from the back line of holes. presplitting is most often used on slopes steeper than 1H:1V (45°)

ADVANTAGES Presplitting also allows for steeper and more stable cuts than any other blasting procedure.

Protects the final cut by producing a fracture plane along the final slope face that fractures from production blasts cannot pass.

Can produce steeper cuts with less maintenance issues.

Performs well in hard competent rock.

Foundations

A. When considering the formwork for foundation pads and beams, what factors would you consider important before ordering the material?

Formwork means the temporary structure used to support a permanent structure until the construction of the permanent structure has advanced to the stage that it attains self-supporting. Important aspects of the formwork operation are speed, safety, and quality. Speed. Speed of construction is defined as the rate in which concrete building is raised and can be expressed in terms of number of floors erected per week or months. Speed of construction can be also measured in terms of in or mm of concrete poured per hour. Formwork operations can control the pace of construction projects.Safety Formwork operations are risky, and workers are typically exposed to unsafe working conditions. Partial or total failure of concrete formwork is a major contributor to deaths, injuries, and property damages within the construction industry.Quality The quality of concrete is dictated by the quality of formwork materials and workmanship. some deformed concrete surfaces are due to deformed formwork systems caused by repetitive reuse and inadequate support of formwork.Choose a Formwork System. It also includes the process of selecting accessories, bracing, and a release agent for the selected formwork system. There are several forming systems used in the construction of reinforced concrete structures. For example, formwork systems for concrete slabs can be classified as hand-set or conventional systems and crane-set systems.Formwork materials Formwork range from traditional materials such as wood, steel, aluminum, and plywood to nontraditional materials such as fiberglass. Wood products are the most widely used material for formwork.

B. In India a large amount of reinforcing steel is cut, bent and fabricated on site. What are the advantages and disadvantages of installing reinforcing in this manner?

ADVATAGES Overall Savings in time. Labor related savings. High product quality. Overall efficiency is increased. Mass production is easier. Protected & controlled production environment. Potential for lower production costs. Independence of climatic conditions. Traffic disruption is avoided. High degree of Safety. Fabrication can be done according to the specifications.

DISADVATAGES Careful handling is required. Attention has to be paid to corrosion-resistance. Fabrication can be done according to the specifications. It requires large area for fabrication. Large prefabricated sections require heavy-duty cranes for handling and to

place in position.

C. Your foundation reinforcing is to be fabricated off site and delivered to site in pre-made cages. The foundations are 5 m deep. What factors would you need to consider before proceeding with this form of reinforcing installation?

There are different methods for fabricating PCS which include: punching or cutting out the openings using different methods such as laser cutting, plasma cutting, abrasive jet cutting, flame cutting, milling, electrochemical machining, and electrical discharge machining.Factors to be considered before proceeding with reinforcing installation.• Quantity of production • Variety of products

• Price of the machine • Initial setup price • Price of replacement parts • Maintenance costs • Lifetime of the machine • Production time • Possibility of mistake or errorQuantity of production:- Quantity of production is one of the most critical factors in deciding the method of production.For large volume production may be economical by methods such as punching, while small-scale production may be economical by other methods. Cutting methods such as milling, flame cutting, laser, and plasma cutting are good alternatives for small-scale production. Variety of products:- Variations in product specifications such as cage dimensions, plate thicknesses, opening dimensions and spacing are very important in choosing the production method. Production with wide variation in specifications may be too costly by some methods. Price of the machine:- Some methods, such as punching, require expensive punching machinery as a capital cost, whereas other methods, such as milling and flame cutting, donít require expensive machines. Initial setup price:- The initial setup cost for precise and accurate operation will vary for different methods. Some methods, such as laser cutting, abrasive jet cutting, ECM, and EDM, which are mainly controlled with a computer, require initial setup costs. Relatively high initial setup costs may be acceptable in large volume production.Production time:- Production speed is different in various methods. Some methods, such as flame cutting, milling, and ECM, take more time for cutting openings, while other methods, such as laser cutting and punching, are much faster.Possibility of mistake or error:-Some methods, such as flame cutting and milling, are more prone to mistakes and flaws, while some other methods, like laser cutting that are controlled by a computer, have much less chance for error.

D. Before pouring the concrete in the foundations you have to decide which method to use. Compare the use of a crane and skip with pumping in terms of efficiency and cost.

ADVANTAGES It has a continuous pour of concrete. Placing of concrete is much easier. It is more efficient when compared to cranes. Placing of conctere is continous It occupies less space. Less man power is required

E. You are required to organise the pouring of the concrete for the foundations. Explain what needs to happen for the concrete pour to be successful.

There are many causes of foundation failure, here are the six main ones. Soil type Poorly compacted fill material Slope failure Erosion Poor construction, & Transpiration

Foundation failure my be also due to some internal problems like insufficient compaction, interrupting the pour, nonporous backfill, rushing the cure.

Insufficient compacting. If the slab is poured over crushed stone that hasn't been firmly tamped, it will likely settle or crack.

Interrupting the pour. A concrete form should be filled in one go. If one stops the work and comes back the next day to finish work, there will be a "cold joint" between the fresh concrete and yesterday's work.

Nonporous backfill. Soils loaded with clay or organic matter hold water, increasing the risk of foundation cracks when the soil freezes and expands.

Rushing the cure. Concrete must cure slowly to reach proper strength (usually 3,000 psi). Keep it damp for at least three days by wrapping it in plastic, misting with water, and other techniques.