Quarry Index:

About the Quarry

Meeting Agendas

Past Meeting Minutes

Definitions

Facts & Questions

Maps & Graphs

About the Reports

Links:
Austin Powder
Hanson Aggregates Servtex
USBM
USBM Criteria (“z” curve chart)
Vibra-Tech

QUARRY COMMISSION DEFINITIONS

These definitions only give an overview and are not designed to make you an expert. Links to informational sites are provided.

A - D

Aggregates – Engineering term for crushed rock.

Air Overpressure – Air overpressure is generally the most noticeable impact on structures. As this air wave (measured in decibels (dB)) contacts structures, it causes walls to vibrate. Up to 128 dB is the federal guidelines safe level. Glass may break between 150-170 dB and structural damage may occur at 180 dB.

Austin Powder – The current blasting contractor for Hanson.

Bench – The current bench cuts the face into two levels, each with a 50’ face. A blast on a 50’ face generally has less impact than one for a 100’ face.

Damage Threshold – Defined by the USBM as the loosening of paint, small plaster cracks at joints between construction elements or the lengthening of old plaster cracks.

Decking – Small charge or portion of a blast hole loaded with explosives, which is separated from other charges by stemming.

Delay – The time by which detonations are separated, measured in milliseconds.

F - I

Face – The wall of rock that is being blasted to produce rock for the crusher.

Frequency – Frequency refers to how many waves occur within a second, which is measured in hertz. High frequency waves occur so quickly that a structure does not have time to respond. Above 11 is better. At lower frequencies, the structure does have time to respond so that the impact is felt. Frequency is also impacted by distance and geology.

Hanson Berm – The mound of dirt that acts as a visual screen and helps to deflect noise. It is 30-40’ tall and up to several hundred feet wide. It serves as a buffer between the quarry and the Trophy Oaks property line.

Hertz – The term used to express the frequency of ground vibrations and air blast; one hertz is one cycle per second.

Inch/Second – The measure of distance and time used to record ground vibrations.

J - R

Max Pounds per Delay – The amount of explosives per detonation. Each blast is comprised of multiple separate detonations each of which are separated by milliseconds (delay). While these blasts are perceived as a single blast, they are actually a series on small blasts. Without these minute separations, a single blast would have an extremely high impact.

No Trigger – ground vibration resulting from the blast was less than the seismographs pre-set level of vibration, above which is necessary for the instrument to record an event.

Peak Particle Velocity (PPV) – This is the measurement of the vibrations that move through the ground and may be felt as they move below foundations. Federal guidelines indicate that damage can occur at 2.00. To err on the side of safety, federal guidelines have been set at 0.50 which may lengthen existing cracks in plaster and at 0.75 which may lengthen existing cracks in sheetrock. In reference to the latter, damage thresholds may be increased as frequency moves above 11 hertz (Hz).

Ramp – The sloping surface used to connect the floor of the quarry with the upper bench for transporting the rock from the blasts.

Rows – Line of blast holes to be loaded and detonated.

S - Z

Seismograph – An instrument that measures and may supply a permanent record of earth borne vibrations induced by earthquakes or blasting.

Set Back – The distance from the current property line to the quarry face.

South Texas Aggregate – Another aggregate producer located on Hanson property.

Stemming – Inert material, such as drill cuttings or gravel, used in the collar portion (or elsewhere) of a blast hole to confine the gaseous products of detonation.

USBM – United States Bureau of Mines

Vibra-Tech Engineers – Engineering firm selected by City of Garden Ridge that monitors each blast.

Whorley Property – A track of land purchased by Hanson, located between Trophy Oaks and the quarry face. A portion is being mined and the remainder, which includes the berm, serves as a buffer.