DESIGN AND CONSTRUCTION OF SLAB FOR WATER RESERVOIR

CHAPTER ONE

1. INTRODUCTION

It is a conventional practice to rest the foundations of major bridges anchored firmly into sound rock. Streams where fundable strata is not available at a reasonable depth, always pose a problem to select appropriate type of foundations. The bridge engineers generally do not like to deviate from guide lines given in the IRC codes1,2,3,4 which are general in nature covering various conditions all over the country. The bridge engineer, however, has to exercise his insight to adopt unique solution, to suit a particular site conditions. Such decisions a build up confidence level, if they are supported by sound performance record of precedents.

Over the years, Maharashtra state has developed raft foundations as available alternative for deep foundations such as wells and piles in locations where hard foundable strata are deep seated and dry weather flow is such that construction of cut off walls with manual open excavation is feasible. Recognizing the indisputable merits of raft foundation, design and construction, engineers of the department have been constantly innovating to achieve economy and furtherance of constructional ease. Construction of cut off walls upto desired depth is possible by excavating an open trench in case of cohesive soils which can be vertically cut. Dewatering is one of the major difficulties faced in the construction of raft foundations6 especially in case of sandy soils and structures near irrigated areas because recharging of the ground makes dewatering difficult. Various innovative methods7 have been devised and put into practice in the field to overcome such difficulties.

1.1            Statement of the Problems

The bed material predominantly consists of pure sand with almost no silt/clay content & could not stand a vertical cut necessary to allow excavation of an open trench. The work was, however, commenced with a conventional method of excavating a wide open trench. A block of 28.0 m x 10.0 m was excavated in the sandy bed. The pit could hardly be excavated to a depth of 1.50 m below the bed level & it was observed that further digging is not possibly due to following impediments:

(a) Collapse of sides due to heavy sand blows during excavation

& dewatering, inspite of shoring & strutting.

(b) The water level remained constant even after employing 200 HP water pumps for dewatering.

Further work was hampered due to occurrence of non–seasonal floods & the excavated pit got filled up to the original bed level. It was therefore considered necessary to explore the possibility of casting the cut off walls at bed level & thereafter lowering it down to the desired level below the bed, instead of conventional method of casting in situ in open trench.

1.3 Objectives of the Study

The broad objectives of the Detail Project Report (DPR) are to determine a technically and economically viable water supply project for a phased implementation to meet the requirements of the year 2021. Following are the specific objectives:

1. Assessment of the existing supply situation

2. Population and water demand projections

3. Planning for Projects identified for JnNURM

4. Project scheduling & cost estimates

5. Projects phasing

6. To prepare operational plan

7. To assess environmental and social impact

1.4 Scope & Limitations of the study

1. The study is limited to Rajkot city admeasuring area app.104.86 sq.kms.

2. The study is limited to Water supply projects for Rajkot city which are identified and outlined in City Development Plan ( 2005-2012)

3. Projects which are identified in CDP for RUDA area are excluded.

1.5     Specifications the following abbreviations are used :

IS : Indian Standard ANSI : American National Standards Institute

API : American Petroleum Institute

ASME : American Society of Mechanical Engineers

ASTM : American Society of Testing and Materials

AWS : American Welding Society

AWWA : American Water Works Association

ISO : International Organisation for Standaridisation

DIN : Deutsches Institute fur Normung

BS : British Standard

IEC : International Electrotechnical Commission

IEE : Institution of Electrical Engineers

IEEE : Institute of Electrical and Electronic Engineers

NEMA : National Electrical Manufacturers Association

AGMA : American Gear Manufacturer’s Association

Order the full materials for this project from chapter one to References.

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