1 INTRODUCTION
The Stress Control Method is a new quantitative method of designing underground mines with the aid of computers. The underlying concept of the Stress Control Method is to make the ground support itself naturally by regulating the geometry and timing of the excavation. This strategy requires working with, rather than fighting against, formidable earth stresses. Making use of the natural self-support is far more logical, more economical, and safer than the conventional strategy which relies upon artificial support, such as saturation roof bolting, wood cribbing, and arch building. The application of the Stress Control Method, for mine design, requires thorough understanding of the main characteristics of the ground media -- namely, in situ stress state (S), the material properties (P) of the mine ground, and the deformation response (D). A technique called SPDK has been developed in order to quantify the relationship among the above S, P, and D components, thus enabling us to design mine openings with greater safety and stability. The SPDK technique is the final outcome of our past 2 decades of studies aimed at quantifying geomechanics. The Stress Control Method, with the aid of the SPDK technique, is now being demonstrated successfully to benefit the coal mining industry. Such demonstrations have proven the superiority of the Stress Control Method in eliminating ground failure problems, which are inherent to the conventional methods of mining. The application of the SPDK method and its significant accomplishments in geomechanical work are discussed below.
2 PRINCIPLE OF SPDK METHOD
The SPDK method is based on the unique relationship that exists between the three components of ground behavior -- stress states (S), material properties (P), and ground deformation (D). The relationship of these three quantities at a point in a rock/soil mass can be locally represented using a constitutive model based on rheological concepts. This constitutive model is incorporated in a finite element program called KEM for global representation of the SPD from accurate in situ measurements of S, P, and D. Tile data obtained from field measurements are used for construction and calibration of the REM model. The mine model, thus calibrated, can be employed to explore optimum design parameters to suit the operational needs. The optimum mine design is field validated by comparing actual behavior with the computer projections, and, if discrepancies are found, the model is refined. The operating scheme of the SPDR method is illustrated in the flow diagram of Fig. 1.
3 COMPONENTS OF SPDR METHOD
The SPDR method encompasses the comprehensive use of four distinct proprietary tools: in situ stress measurements (S), In situ property measurements (P), deformation measuring system (D), and the KEM computer simulation program (R). These tools are briefly described below.
In Situ Stress Measurement System (S)
A new type of stress measuring probe (S-100) has been developed specially for application with the SPDR method. The probe is made of a highly expandable plastic tubing, capable of loading a borehole to induce a set of two mutually perpendicular fracture planes without allowing the loading liquid to contact the borehole boundary.
