Rock Breaking

Introduction

The number of civil engineering projects requiring rockbreaking or rockfracturing is increasing. It is important for a client to be able to choose the most economical and environmentally acceptable solution for a particular project.

The IHC Hydrohammer, developed as a piling hammer or pile driver, can be applied for rock breaking jobs in combination with a chisel- rockbreak package. This offers an opportunity to use it as an alternative to other conventional methods.

The Hydrohammer unique and proven qualities, such as high efficiency (also at underwater operation) and precision, as well as its pollution free operation, have demonstrated their values in this type of projects on land or in water.

If cutter dredging is no longer possible because the rock is too hard (average compressive strength greater than 40 MPa), or dredging is economically not justified in case of relatively small volumes, a rockbreaker can be an excellent solution.

Where removal of hard rock by means of explosives is not permitted for safety or ecology reasons, the utilisation of an IHC rockbreaker may be the ONLY solution.

Working principle

The Hydrohammer can be used as a rockbreaker both on land and underwater. For that purpose, the standard S-35, S-70  or even more powerful S-280 Hydrohammers are equipped with a special sleeve with an internal anvil (seated on a spring cushioning) and a chisel which slides in the special sleeve. After being driven in the rock, the hammer and chissel are then lifted and moved to the next spot. In this way holes can be punched in a certain pattern, leaving the fractured rock for removal by other equipment such as an excavator or clamshell. An important advantage of the Hydrohammers is the ability to deliver upwards blows. Doing so while at the same time lifting the hammer, highly facilitates the retraction of jammed chisels.

Operating principles

In order to withstand the heavy resistance forces exposed to the hammer and chissel (rockbreaker) it needs to have  proper guidance in a leader guide profile of sufficient stiffness. This operating criteria secures the center alignment of chisel and hammer for optimal energy transfer between ram/anvil and chisel. During breaking (making one hole) and extracting the position of this leader profile should be fixed.

Different types of handling equipment can be used to lift and position the Rockbreaker including leader profile such as :

1.      Fundex piling rig

2.      excavator or back-hoe

Other more specialized methods are:

3.      cutter dredger

4.      special frame

Choice depends on waterdepht and (mostly) equipment available for/on the project. Naturally the handling equipment needs sufficient lifting capacity to position hammer and chisel and sufficient traction power to retract a jammed chisel.

Extracting takes place with use of an extracting cat placed on the leader profile in between the pulling line. This will create a continuous pulling force on the rockbreaker and prevent damage to the rockbreaker and/or hammer.

1. rockbreaker on an piling rig

One of the most proven methods to break rock under water is the use of a piling rig whereby the leader can be lowered down in the water. In this way the leader is part of the rig. With a standard IHC F12SE FUNDEX piling rig the leader can be lowered down about 15m underwater. With a special long leader and some other modifications a water depth of about 45m can be reached

2. rockbreaker on an excavator

The operation of the rockbreaker with an excavator has been successfully carried out on several projects. In these cases a custom-built short leader of about 10m length is fitted on the stick of the excavator.  Water depth which can be reached depends on the excavator and varies between 8 and13m. Extracting of the chissel takes place with two hydraulic cylinders mounted on the leader.

The combination with an excavator provides the most versatile operation: breaking is possible at any angle and the hammer with chisel can be moved rapidly and independently from the pontoon. The Hydrohammer can be used for precise breaking operations, such as close to works of art and ancient foundations, both on land and under water. The only limitation is the water depth (a maximum of approx. 13 m).

3. rockbreaker on a cutter dredger

The Hydrohammer also offers a good solution for large dredging operations where relatively small amounts of hard rock needs to be removed.

Rock Breakability

Which rocks can be broken or fractured with the Hydrohammer depends on a number of factors:

• Rock hardness
• Its stratification and homogeneity
• Thickness and surface profile
• Methods used, which in itself depends on the  water depth and available equipment.

Rock hardness

So far, rocks with a hardness up to 80 MPa (compressive strength) have been successfully broken with an S-70 Hydrohammer to punch vertical holes in a relatively level surface. If the fractured rock can disperse from the breaking zone, it will undoubtedly be possible to break even harder soils. The average compressive strength that a normal cutter dredger can handle is 40 MPa. Bigger hammers such as the S-200 or S-500 are able to break harder rocks.


Stratification and homogeneity

If the rock has horizontal layers, good results can be obtained by positioning the rock breaker at an angle.
Adapt the breaking pattern to obtain penetration in harder spots in the soil.


Thickness and surfuce profile

A relatively thin layer will be easy to crack. If layers are thicker than say 1 m, it may be necessary to break layer by layer. Needless to say that irregular surfaces are easier to break since the broken material normally crumbles away.


Refusal

For efficient operation and to prevent damage to the hammer, it is essential that the chisel penetrates the rock. The maximum number of strokes of the hammer is limited to 200 strokes per 25 cm penetration. If more strokes are required to break the rock, a more powerful hammer can be selected.

One can choose from a wide variety of Hydrohammers. So far, the S-35, S-70, S-90, S-280 and S-500 have been used during rockbreaking operations.