Hydraulic Impact Hammer (hoe ram)

How do you determine feasibility and performance in rock?

How do impact hammers work?

Let us take a look……………..

Hydraulic Impact Hammer Operation

A Little Tutorial

To make some important distinctions

How impact hammers break rock

What rock properties affect performance

Principles of Impact Hammers

Impact hammers work on two principles in breaking rock, namely

Primary breakage and

Secondary breakage

What is primary breakage?

Primary breakage is when the impact hammer breaks an intact material, such as:

A slab of concrete (with limited thickness) or

An intact rock mass (devoid of discontinuities)

Primary Breakage

What is secondary breakage?

Secondary breakage is when the impact hammer reduces the size of existing blocks of: concrete or

rock

into smaller pieces, such as joint blocks of rock as illustrated in the next slide.

Secondary Breakage In Jointed Blocky Rock

Secondary Breakage of Rock Blocks

Rock Properties Control!

What rock properties control the breakage of rock by impact hammer?

Primary breakage depends on the rock intact properties

Secondary breakage depends on the rock mass properties

Rock Properties

What are rock …

Intact and Mass

properties?

Engineering Properties of Rock Rock Intact & Mass Properties

Rock Intact Properties

Rock intact properties are determined by testing of intact samples in terms of:

Unconfined compressive strength Tensile strengthTotal HardnessSonic VelocityEtc

Rock Mass Properties

Rock discontinuities and their properties: SpacingNature Orientation

Seismic velocity (similar to use in Caterpillar Ripping Chart)

RQD (Rock Quality Designation)

Using RQD (relative to depth)Minimum, Average, and Maximum b

Using RQD(top of rock to 15 ft)

Impact Hammer Excavation Greens - efficient Grays - difficult/slow Reds - tedious

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Using RQD (bottom of excavation)

Impact Hammer Excavation Greens - efficient Grays - difficult/slow Reds - tedious

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Using Fracture SpacingAverage and Maximum

Using Seismic Velocity

Would provide the best indication of rock mass amenability to excavation by impact hammer

Needs to be developed further If you seek more specific answers, contact

us …….