In Stockholm and in many other densely populated areas, Swedish contractors and explosives experts have brought the methods of controlling underground blasting to a fine art. The paper systematically lists the buildings and other objects that set limits for the level of disturbance that can be allowed. The nature of the ground vibration disturbances caused by different blasts at different distances is analyzed and-'methods for predicting and recording their magnitude are presented. Damage criteria for different types of buildings, structures, and other objects are discussed, as well as the separate subject of how to avoid disturbing the neighbors. Methods for optimal planning and implementation of the blasting operation from contract to completion are presented, with a survey of modern explosives systems, accessories and charging equipment.
The idea of having large scale underground structures in blast-excavated caverns right underneath a city is still a new one in many parts of the world. A person wanting to make reality of such an undertaking may well be faced with the question: How can you guarantee not to damage our fine city or irritate our citizens? In the Stockholm area alone, an average of about 300,000 m3 of rock was excavated underground each year in the decade from 1970 to 1980. This is perhaps the best proof that such guarantees can be obtained. The purpose of this paper is to present, in a reasonably simple form, the know-how developed in Sweden during many decades of underground construction work, and to show how blasting activities can indeed be controlled to prevent damage and disturbances.
In all rock blasting in a built up area, some measures of control have to be imposed to make sure no undesired side-effects occur. These controls include limitations in the planning and design stage as well as during the building & construction stage. From a town planning point of view, an obvious obligation is to check the desirability of having an underground installation at the proposed site. Perhaps a different location might leave better space for future installations or it might offer better prospects for long-term stability of the rock surrounding the excavation. Restrictions to the proposed blasting to avoid damage or disturbances should be clarified already at the planning stage, too. If this is done before bidding takes place and before contracts are settled, the contractor can include the necessary costs for the required level of controlled blasting in his bid. This excludes much unnecessary arguing later about who is going to pay for damages or for the cost of preventing them. The restrictions are conveniently divided into three kinds; of these two are external to the blasting site and one is internal. Restrictions are necessary to:
·Avoid damage to nearby buildings
·Avoid disturbing the neighbors
·Avoid damage to the own construction
The major factor to control in order to avoid these is the ground vibration caused by the blast, and the remainder of this paper will deal with this factor mainly.
