400 QUARRYING Engineering Geology in Design and Operation of Quarries Quarry development and operation has become a recognized field of practice requiring engineering geologists As with many industries, quarry technology entered the machine age post-World War II, when excavation equipment became universally available to the family enterprises that owned most quarrying operations Small operations are now rapidly disappearing and multinational companies control most of the stone that is mined today In some instances, this equates to huge scales of magnitude (the ‘superquarry’) Such are the economies of scale and the relatively low cost of bulk ocean transport that stone is imported over considerable distances, especially from quarries located close to coastal shipping Geological Factors Affecting Quarried Stone Building stone is the traditional building material of mankind and still remains a critical construction material today, primarily as the aggregate, or bulking agent, for Portland cement and asphaltic concrete Both cement and asphalt have been known to humans for several thousand years, yet their modern counterparts and their uses stem strictly from the industrial age Desirable Physical Properties of Quarried Stone Quarried stone must have certain physical properties to serve as an effective building material It must have strength, mainly compressional, to resist the load forces applied in engineered works; it must be durable and resistant to surface wear, especially when the use is for pavement; and it must be resistant to dynamic and chemical attacks, particularly from marine (saline) waters when the use is for port, harbor, and seacoast protective structures Mined stone for building purposes must also be resistant to ‘weathering’ due to chemical attack by water and incident urban rainfall and must have consistency, be of uniform quality, and contain no deleterious minerals (e.g., pyrite, which causes staining of facing stone, and chert nodules, which cause eruptive pitting in concrete) tectonic stress may be a cost factor related to uneven responses to blasting patterns and explosive loading, due to release (relaxation) in strain-displacement relief (‘pop-ups’) of floor rock The compressive strength of the quarry product, independent of geological structure, serves as a measure of the explosive force that will be needed (and thus the cost of explosives) to break the rock to requisite handling size Other Characteristics of Quarried Stone Every stone quarry starts with an outcrop of durable stone or an excavated pit made in the overburden of surficial soils, often glacially deposited, so as to expose an artificial outcrop (working face) of stone Once exposed, the stone must be subjected to efforts to dislodge it from the rock deposit In most cases, the rock deposits selected for quarrying are cut by natural geological structural and depositional discontinuities such as bedding planes, foliation planes, and joints Figure depicts a rock face in which the supporting rock mass has three dominant joint ‘sets’, each representing a distinct array of joints, all of which will control the overall character and planar outline of a quarry developed in the rock mass Rock masses are virtually without strength in tension, and thus mechanical efforts to remove rock from a working face employ excavation machines to pull (‘rip’) discontinuity-bounded rock blocks from the quarry face (Table 1) Where the rock cannot be ripped, it is pulled from the working face by the judicial (planned) use of explosives set in geometrically arrayed and nominally vertical, drilled ‘shot holes’ Discontinuities have value to the final product of the quarry only when the rock is destined to be recovered and sold as dimension stone, building stone, ornamental stone, or rip-rap Rip-rap, used in shore protection works, is of great value when its quarry blocks are without further discontinuities, because the pieces can resist the constant pounding and surging action of ocean waves Many quarries also contain crystalline igneous and metamorphic rocks and the harder varieties of igneous and volcanic intrusive rocks The many types of geological formations worldwide and their importance in quarrying operations are shown in Table Types of Rock Quarries Desirable Mass Characteristics of Quarried Stone Recovery cost for quarried stone is governed by several invariant cost factors inherent in the quarry site geology The nature, pervasiveness, and orientation of discontinuities control the ease of extraction and the resultant stability of highwalls and benches Stored Quarries are established on the simple theme of locating and supplying a needed stone product at a competitive price in the free-enterprise system There are some interesting relationships of quarry rock type and location worldwide (Table 2) Stone is intrinsically nearly valueless, and when obtained on a royalty