Wedges and Feathers versus Piston Rock splitters

Traditional Stone Breaking versus Mass Rock Demolition

Wedge and Feathers photp from Wikipedia.org" plug and feather"

Traditional rock breaking tool has been used as seen on above photos.

Its principle is introduced as below picture.

             

Principles of  Plug and feathers rock breaking

The plug is pushed down which pushes the side feathers to set apart the rock( stone).

As a result the fracture is made between the split parts. This simple tool creates a very large force considering the "down" force (central arrow direction) and the 'splitting force" of the two directional forces. Usually this splitting force equals 10~15 times the 'down" force.

What we should remember is  that the continuous impact of this 'down' force may give much deep and large cracks to the rock. That is why a stone smith uses small but many shims along a line to break a large boulder.

Then we should regard the "splitting" force of  a bedrock different from that of a large boulder. The required splitting force for bedrock is not  same direction as insertion.  Instead, it has to shear along the bottom line of the hole . See below pictures.

Bed rock requires rectangular angled force against its inserting direction

Pisture 1 shows a wedge splitter acting on the wall of the rock through its holes.

Picture 2 shows a piston type splitter acting on the wall of the rock through its holes too.

A mechanical tool using hydraulic pressure includes a hydraulic wedge rock splitter (" darda" splitter) and a  hydraulic piston rock splitter .  ( See  " Hydraulic Rock Splitter" on Wikipedia.org)  The darda splitter is the first type of rock splitter using hydraulic pressure. The second type of rock splitter using hydraulic pressure is the Piston Rock Splitter shown as below.

                         

Piston type Rock Splitter  from Hrd-tech.com 

This Piston type rock splitting tool has evident differences  from the darda type rock splitters.

1. A Darda splitter is used mostly for concrete wall breaking or stone breaking.
  A piston splitter is used mostly for rock bed demolition.

 A Darda splitter has to keep close spacing between bore holes( spacing of 15~20cm ).  A  Piston type splitter's  spacing can be 40~60cm distance each other. 

2. The piston type rock splitter has higher stroke than a darda splitter and  can make fracture quickly.

3. The darda splitter requires greases and needs to replace worn feathers or shims continuously.

4. The darda splitter takes longer time in splitting. It splits very closely between holes.
 A small size darda needs spacing of 10cm~40cm depending on the rock mass.
 A piston splitter starts spacing from 35cm upto 60~70cm for the demolition of rock mass.

5. A darda splitter is vulnerable to breakage and easy to fail its operation.
 A piston splitter is durable for several months without any replacement.

6. A piston splitter requires holes of over 89mm upto 105mm usually for manual use.
 These bore holes need a crawler rock drill rigs to make holes .
  A darda splitter requires holes of small sizes upto 42~45mm. A darda splitter can be used in bore holes drilled by a manual rock drill.
 

Distinctive Features of darda splitter and piston splitter

As seen above, there are many different features between darda and piston splitters.
Both splitters show that  they are expanding in a hole with the hydraulic pressure from a power pack. Then  expanding force sets apart the hole( rock) first and then it cracks rock with "shearing force" making disconnection in the rock.
Let's see the following pictures (3. 4)

Wedge splitter acts on the rock's shearing strength,
 while Piston splitter acts on the rock's Tension strength.

Picture 3. shows a wedge splitter in a hole  The feather side acts on the rock wall as an expanding force . A small size splitter produces upto 400 tons . A large size splitter ,called a mechanized splitter,produces upto 1500~1800tons force. (A Yamamoto splitter has spltting pressure of 2,250tons and 3000tons.). This force cuts the rock mass with those enormous force. In the right direction, the rock bed is backed by a large bedrock. Only the left side can be broken. This left side is called " free face" side.

Usual spacing between the drilled rock holes is 20~40cm for a small size manual splitter. Mechanized  wedge splitter has spacing of 50cm~70cm . Manual size splitter has been used for concrete structure breaking. Only mechanized splitter has been used for rock splitting.

Picture 4. shows a different feature of the piston rock splitter from a wedge splitter.  
 We have observed several different breaking cases with the piston splitters.
 With the most soft rocks, we hear the sounds of cracking from the top piston( P1) first and the next one( P2) and so on to the bottom piston(P5).
 With some hard rocks, we hear similar sound as the soft rock . But occasionally, we hear that only one or two pistons break the rock ( may be P2,  P4, and P5).
In some cases we hear only one fracture by the deepest piston(P5) Among 5 pistons, 4 pistons do not crack the rock. Only the bottom piston makes cracks. Other 4 pistons push together against the rock wall until the bottom piston making cracks. The bottom piston hits the rock's surface , which fractures the rock bottom  making a small crack ,which initiates the total fracturing of the bottom line of the piston.
The cracking continues while the stroke ( usually very short distance of 15~20mm only) is  exhausted.  The stroke of a piston splitter is between 20mm and 25mm only. That means that a piston strikes on the wall 10~15mm deep into the rock side. This 10~15mm stroke makes "hammering" impact on the rock with the help of the similar high expanding forces from other pistons.

Each piston has pushing( expanding) force of 19~25 tons only. This hammering stress to the rock surface  is  acting as  a strong hammer as long as piston's top part is hitting on the rock surface,  This piston's impact takes advantage of tension-breaking. 

The piston splitter looks like " pushing force" only. But when we analyse it carefully, we  find that "hammering force' of the piston from the bottom piston is working as a real "wedge cutter". The shape is not so important. The round top part of the piston or a sharp top works as a "hammering wedge"!

The darda splitter looks like "wedge" cutter, but actually it acts like a compressing compactor toward the rock wall.  It presses the rock wall with its whole side surface( The side of the feather is a  continuous wall .)

This difference between darda splitter and piston splitter is shown in their different performance. A darda with 400tons pressure splits little rock,while the piston splitter with 180tons pressure splits more rock .  Isn't this amazing?  The difference in performance is visible in  difference of hole spacing. A wedge has to be used with closer distance than a piston splitter.

A darda splitter has large splitting force of 400 or 1500 tons. It can break the rocks with closer distance only.

A piston splitter has usually 100~250tons ( manual splitter) and can break the rocks with the spacing of 30~70cm. 

The blogger has been living with piston splitters for more than 20 years. 

The discovery of these conceptual and experiential features such as  shearing strength,and tensile strength gives us lots of  insights in designing a drilling pattern for a different tool.

For the readers' further information, following thesis is recommended :
"Engineering geological evaluation of the applicability of Drill & Split tunnels at the Follo line project" by Jens Anders Volden, june,2015

Following picture is used:

It remains regretful that Piston rock splitter was not mechanized at the time of above project. They reviewed our piston splitter but was not convinced because  the piston splitter was not mechanized  at time of use and had to be handled by worker's handle.!!!!

Now piston splitter is mechanized and can be used very efficiently by using simple 

toolings.

The author, Jens Anders  Volden summarized two splitting methods as follows;( PP 28-29) in his thesis.

<Wedge type splitter>

1. Advantages

 (1) can be mounted to excavators that are common among contractors.

 (2) relatively cheap investment( assuming the contractor owns suitable excavators)

 (3) intuitive system to use,needs little time to learn how to operate efficiently.

 (4) can be operated from a safe distance inside excavator.

2. Disadvantages

 (1) maintenance, greasing every 5-10 hole

 (2) tip may break off if borehole is insufficiently deep.

 (3) counter wedges may break if borehole is not straight.

 (4) only one splitter per excavator limits productivity (this can be overcome if cross section is large enough for two excavators side by side)

< Piston type splitter>

1. Advantages

 (1) individual piston gives les rigid system, with less chance of damageing equipment

 (2) less downtime due to maintenance( greasing)

 (3) possible to exert splitting force closer to the bottom of the hole.

2. Disadvantages

 (1) this configuration is little established and less intuitive to use than wedge systems.

 (2) their handheld nature may present challenges in creating a safe working environment while operated on vertical faces.

 (3) they are also a reasonably new type of equipment, which suggests that contractors are not likely to be experienced with their use.( hwacheon Engineering Co.Ltd,2014)

The blogger has agreed with the author. The blogger has mentioned about the mechanized system of piston splitter  by using lifting system such as winch( balancer) or  attachment or gripper for mechanizing it. Already those are available on the market. Unfortunately this system was not introduced to the author at that time in 2014.