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OTHERS SOFT ROCK METHOD

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Method of Tunneling in Soft Rock

 LINER PLATE METHOD

Standard sized pressed steel plates ,plain or corrugated are used to support the soil,and work is carried in short length corresponding to the length of these plates.The plates are made with flanges of angle shape on all four sides.All the flanges carry holes through which they are connected together by bolts and nuts longitudinally and transversely  It is presented steel plates, plain or corrugated are used to support the soil during excavation.

Liner plate method in Method of Tunneling in Soft Rock
Liner Plate

Liner plates are generally made 16" by 36" with a 2" flange on all four sides. The latter dimension along the circumference of tunnel section. The advantage of this size is that the number of plates required is equal to the diameter of the tunnel in feet 
  1. The size of the plates is 0.9 * 0.4 with a flange of 0.05metre
  2. This method used in subaqueos strata
  3. Trench braces may be used if support needed
  4. To exert soil pressure
  5. Top drift extended upto full length to 48"

Stiffening Ribs:

When the diameter of the tunnel is 10 feet or more stiffening of the liner plate becomes necessary to withstand pressure. These stiffeners consist of RS Beam bulkheads to the web of which the liner plate flanges are bolted. The depth of the beam is usually 1" to 1.5" per every 3' dia of the tunnel . The ribs are generally spliced near the crown and on the flanges as the web connects the liner flange . All bolts and nuts for splicing stiffeners or connecting liner plates and stiffeners should be made of same size. 
For 6' to 7' diameter tunnel 1/8" thick and used without stiffeners.For 8' to 10' diameter tunnel 1/4" thick and used without stiffeners. For 10' diameter and above 1/8" thick with RS Beam at 16" centers as a stiffener.

Use of liner plates without ribs:

  1. A hole 16" in depth is cut out at crown action and crown liner plate is inserted
  2. Excavation is gradually widened from crown sideways and adjacent liner plates are set. Trench braces may be used if need be for supporting case soil exert pressure  
  3. Top drift is excavated for the total length of three liner plate of 48" and widened sideways as before
  4. Excavation is continued sideways to the springing line 
  5. Now wall plates are carefully introduced with tightening wedges under the liner plates which are spiked to wall plates 
  6. The trench braces if used are now removed leaving the liner plate arch to support the roof
  7. After joining the bottom and top half metal plates the braces are removed
Liner plate with stiffners in Method of Tunneling in Soft Rock



Liner plate without stiffners in Method of Tunneling in Soft Rock


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SHIELD METHOD

  1. It is used for driving a tunnel through water bearing strata
  2. To prevent caving danger shield tunnel is used
  3. Diameter of tunnel vary from 10 ̍ to 30 ̍
  4. It is an equipment which act as a bridge with roof for worker.

Definations:

  1. Hood – Forward extension of ring at top and affords protection to miners
  2. Tail – Rear section which project a little distance over complete lining
  3. Cutting edges – Provided with proper stiffner from forward circular edge of shield
  4. Propelling jacks – Push shield forward cutting soil
  5. Port holes – To permit muck flow into section
Shield for tunneling in Method of Tunneling in Soft Rock
Shield for tunneling

• Shield Tunneling Factors

1)Length of Shield:
It depend on
i. Storage reqd in shield
ii. Problem of changing direction

2)Shape of Shield:
Resistance of motion:
 Contact area of the shape-∏DL
 Cross section area / unit perimeter for circular and square=d/4

Resistance to pressure caused by Surrounding soil :
 Circular is best

Terms used with shield:
1) Shove – forward movement of shield in alignment
2) Length of shove – movement of shove in single alignment=length of overlap of primary lining before shove –
length of overlap of primary lining after shove
= 1.5 length of ring - 0.5 length of ring = 1 ring length
3) Open Shove – When shield moves in incompressible soil shield get open
4) Partially Blind Shove - When shield moves in compressible soil shield get open
5) Blind Shove – When shield is driven in quick sand


Plenum or Compressed Air Method

• Use of compressed air to forced water
• Suited for soft or water bearing strata
• Adopted for pressure upto 1 kg/cm2

EQUIPMENT REQUIRED

1) Air Lock
2) Bulk head
3) Blow line
4) Air compressor

Duration of work in Compressed Air method
a. For pressure upto 18 lb/sq working period is of 8 hr with at least 1⁄2 an hour in air
b. For pressure from 20 lb/sq tp 20 lb/sq working period is reduced to 4 hr with at
least 2 hr in free air


Volume of Air Method

Volume of air reqd depend on quality of soil. As 6 m3 to 14 m3 free air per minute
per m2 of face area is provided. Air compressor with capacity of 1100 m3 free air per
minute at maximum pressure of 3.5 kg/cm2 is adopted for 30 minutes.


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