Earthwork

• Earthwork


  The processes whereby the surface of the earth is excavated and transported to and compacted at another location
• Earthwork construction


  • Development of a wide range of earthwork plant (size, capacity and efficiency)
  • Ranges from small works (the excavation of ditches and trenches for drainage and pits and trenches for foundation) to the large earthworks (highways and dams)
• Completion of the earthworks within the scheduled time is often key to the completion on time of the whole construction project
• Success of earthwork construction


  • Adequate site investigation and preparing practical and satisfactory designs of the earthworks
  • Choice and efficient use of the correct types and size of plant to meet the particular requirements of the site
• Site consideration


  1. Nature of excavation

  2. Availability of work area

  3. Disposal of soil

  4. Existing services and structures
• Nature of excavation


  The situation of the excavation, whether for reduced levels, road works, trenches, basements or pits, have to consider the time available for excavation and the sequence of completed earthworks
• Availability of work area

  The total space available for the manipulation of plant and storage of materials
• Disposal of soil


  1. Storage in spoil heaps

  2. Immediate use as backfilling elsewhere on the site

  3. Immediate removal from site to other destination or dumping areas
• Existing services and structures

  • Care should be taken to establish the position of all pipes, cables and underground services, which should be clearly marked before, earth works commence
  • Existing structures adjacent to excavation areas will require support during excavations
• Existing structure support


  1. Cut off walling

  2. Strutting and shoring (sheet piles)

  3. Underpinning
• Ground conditions


  • Ground support required during excavation
  • Method of keeping the excavation free from water
  • Plant to be used
• Techniques of excavating


  1. Bulk excavation

  2. Rock excavation

  3. Trench excavation

  4. Support of excavations

  5. Embankments
• Bulk excavation


  Groundworks which remove large amounts of materials and reduce the general level down to near formation, made with large and efficient excavators
• Bulk excavation operations

  • Cuttings
  • Cut and fill areas
  • Basements and large pits
  • Hand excavations
• Bulk excavation plant


  • Bulldozers
  • Scrappers
  • Dragline
  • Combination of plant track mounted excavation
  • Face shovel
• Shallow cut and fill


  Shallow cut and fill operations occur in road works and airfield construction, where the formation level may be protected against water and the drying-out action of wind and sun, by some form of waterproof dressing
• Basement construction


  Deep pit excavation over 4.5m deep, with methods including open cut excavation, cut and cover techniques, top down techniques, and composite techniques
• Basement construction methods

  • Unshored excavations
  • Shored excavations
  • Dumpling method
  • Cut-off walling method
• Hand excavation

  Excavating deep basements and pits using pneumatic tools such as clay-spades and picks, occurring in excavations which are heavily supported, leaving little room for mechanical excavation
• Principal types of vertical cutoff walls

  • Sheet pile walls
  • Geomembrane walls
  • Slurry trench cutoff walls
• Vertical cutoff walls

  • Involve some form of support to the ground
  • Have an effect on the choice of plant to be used
• Unshored excavations


  There is an ample working space around the excavation to allow battering of the excavation
• Shored excavations

  The shoring can be made watertight by sealing the joints of sheet piling, thereby eliminating the free flow of water
• Hand Excavation


  1. Excavating deep basements and pits using pneumatic tools such as clay-spades and picks

  2. Occurs in excavations which are heavily supported, leaving little room for mechanical excavation

  3. Necessary in the vicinity of services which would be subject to damage by machine, or to the case of removing obstacles such as boulders, logs or other projecting objects

  4. Spoil from such excavations would be put into skips for periodic removal
• Methods of rock excavation

  • Breaking by hand (hammer & wedges)
  • Pneumatic breaker
  • Drilling with pneumatic machine : freezing liquid
  • Drilling with pneumatic machine : blasting
• Suitable rock excavation methods

  • The noise of blasting would cause annoyance
  • Adjacent buildings may be subject to damage
  • Blasting may cause inconvenience or stoppage of traffic
  • Landslides or rock falls might result
  • Accurate cutting is necessary and excessive 'over break' would be uneconomical

  
• Overbreak is defined as the unwanted removal of rock beyond a specified maximum excavation perimeter
• Modern methods of control allow very accurate vibration-controlled blasting in limited spaces
• One example


  • Excavation of a large basement in very hard rock, some of which was within 30 meters of an important computer installation
• Factors affecting choice of trench excavation method


  • The nature of the ground
  • Number of obstructions
  • The location of the trench
  • Purpose for which the trench is being excavated
  • Ground water conditions
  • The time scale of the work
• Methods of trench excavation

  • Full depth, full length excavation
  • Full depth, successive stages of excavation
  • Stage depth, successive stages of excavation
• Full depth, full length excavation

  Suitable for long narrow trenches of shallow depth in which the machine completes the trench non-stop ahead of any other operation. Suitable for pipelines and sewers
• Full depth, successive stages of excavation


  Suitable for deep trenches where several operations of work can proceed in sequence; this would prevent stretches of trench from being left open too long and thereby being subject to collapse
• Stage depth, successive stages of excavation


  Suitable for very deep trenches in confined areas or adjacent to existing property. Involves the support of the trench as the work proceeds and is most suited for operations such as deep foundations and underpinning
• Factors governing support of excavations

  • Type of soil
  • Ground water condition
  • Depth and width of excavation
• Soil types for discussion


  • Loose sand, gravel and silts
  • Compact sands and stiff clays
  • Rocks
• Support for loose sand, gravel and silts


  Requires some form of continuous support, which may consist of trench sheeting - lightweight pressed steel sheets or steel sheet piling
• Support for compact sand and stiff clays

  Can be achieved by using open timbering support. If the soil is subjected to drying out and crumbling, the spacing of the pooling boards can be reduced accordingly
• Support for rock excavation

  Depends to large extent on the type of rock and the slope of rock strata. In the case of unstable rock faces, open timbering should be used to prevent any slump/collapse. Where the depth of excavation is excessive, the rock face may be stabilized by rock bolting
• Rock bolting


  Consists of solid steel rods which are fixed in deep drill holes by means of wedges, sleeves or grouting process; light steel sections or steel plates are used to support the rock face through which the rods are threaded