Thoughts about Development Trends of Minerals Surveying

Karoly Wisnovszky M. Sc (Forestry cum Geol.eng)

Adviser ALUTERV-FKI Mining Dept.

Budapest, Hungary

 

According the different topics investigated in them our colleague Mr. Istvan KLEMENCSICS compiled a statistical evaluation of the papers presented on ISM Congresses. The percentage of the lectures submitted on three earlier international meetings are as follows

                                                               1972               1979          1982

1) Minerals Surveying                                  13         11          6

2) Mineral Deposits                                    15         22          15

3) Instrumentation and Techniques               41         33          33*

4) Ground Movement                                     31         30          42

5) Minerals Exploitation                              ╛            4           4

 

* Included 12 % of computer technique

We have to suppose, that the above mentioned ratio has been deformed but not more than 10 percent by papers submitted by delegates who were not belonging to the mine-surveying branch. The inclining tendency of group 4 (Ground Movement) is quite clear. This interesting area of activities covers mainly observations of surface subsidence. The picture is different country by country, but its essential feature can be found in the fact, that mainly mine surveyors are those who are producing data and documentation for register of mining rights, designing of constructions, hydraulic-works and transportation on the surface, environmental protection and so on; namely for the use not only of mining organizations, but other for authorities as well.

The mine surveying is classified as industrial geodesy mainly by belonging the above mentioned activities to the sphere of the civil engineering. In the same time these tasks take away a lot of efforts would be necessary in the mine itself. By this statement I should like to emphasize that a part of rock movements which are connected directly to the underground exploitation but being at the same time somewhat marginal between mine surveying and rock-mechanics are a little bit neglected. The past 30 years have given excellent technical instruments into the hands of mine surveyors. The formerly very troublesome longimetry became quick and exact by introducing electro-optical range-finders and electronic distance meters in the everyday practice. The danger of angle-torsion has been eliminated by gyrotheo-dolites. In the mining a huge quantity of information can be registered simultaneously and repeatedly with the application of photogrammetry. Along with the use of lasers the computer became or becoming (i.e. computer graphic) the working tool of the mine surveyors.

In the same time the requirements have been raised rapidly against this profession:

- the claims to the direction of drifts multiplicated because of the accelerated exploiting works

- much more and exact data are required for mounting of machinery

- the preparatory works and direction of a long-wall stopping require more exact knowledge of the seem and their irregularities.

This enumeration might be continued, but principally the basis activity is the definition of geometrical elements. Those elements are partly motionless, partly moving. The ratio is changing for the good of the later. Originally the aim of the miner was to keep motionless the shafts, drifts and other spaces mine. The mine surveyors tried to avoid the moving areas too, especially with the marked points.

This stationary system was the key of the exactness of the whole mining geometry.

The velocity and accuracy of the new instruments created the possibility for measuring much more points than earlier, including the momentary position of the moving ones.

 

 

 

Determination of Optimal Size of Water Barrier When Mining Under Water Bodies in Different Hydrogeological Conditions

 

Eheng Shiyan Engineer, Central Coal Mining Research Institute, Beijing, China

 

      China is vastand well known for its abundant coal resource. Coal hes underground in almost every province from Tibet in the west to the Taiwan island in the east. Millions of tons of coal which lay close to surface were extracted by our ansector in the early ages. However, not all coal could be exploited safely so far as we know. One of the factors that jeopardize coal mining is the danger of water bodies. Based on scientific experiments and practice for many years, the research engineers in China associated with coal mining under water bodies experience in coping with water hazard of mine, from the coal field under different structure units and of Paleozoic, Mesozoic, Cainozoic Ears. First the water bodies which affect mining activity can be divided into two types in accordance with their flow states: running water and permeable water.

      As far as running waters such as rivers, laces, sear, water in reservoirs and in karts cavities, and hidden underground rivers are concerned, once they come into mines, the results are often et critical with the rapid inrush of large amount of water along with silt once in a while. The danger from that kind of water can be prevented by leaving sufficient water barrier so as to realize safe mining under the water. The thickness of so called sufficient water barrier is not necessarily the 40 or even 100 times of mining height. The criterion to determine the size depends on the protection of the impermeable layers between the body of running water and the seam extracted from being fractured by mining effect.

      Apart from the above principle, the depth of factures induced by mining on rockhead or soil adjacent to the water should also be taken into consideration. The height of permeable fractured zone used by mining can be estimated either based on observations of experience in situ, or by making the comparison among different mine areas of having similar hydrogeological condition. In facilitate users, a complete set of formulae which can be used in predict heights of caving or fractured zone when mining under water bodies in China is suggested in the books listed later.

      As for permeable water such as porous water insand layers and conglomerate, or in alluvial layers, as well as flow net water all of them observe the Darcy law of permeability during their current while they take times to permeate into mines, we can use pace to drain them out.

      Along with smaller size of water barrier under permeable water bodies having moderate or small amount of water can be proceeded safely with the help of water draining. The thickness of smaller water barrier (we call sand proof barrier) is usually not more than the height of fractured zone, but more than that of caving zone induced by mining, while the thickness of the smallest water barrier is even equal to the later one.

      The water draining could be arranged before mining when developing or drilling are underway. Draining during mining is also an alternative to do the work such as in some coal mines in China. The working condition of coal face be greatly improved when the overlying strta are dominated by dilatant siltstone which might further expand after absorbing water seeping from the fractured zone, while highly impermeable layers can be formed in the way. As the coal face continues to move, the overlying strata behind the face are gradually stabilized, resulting in the reduction of the amount of water that is pouring or seeping. The water will gradually diminish and may eventually disappear as mining towards end.

      Water inruch likely occurres due to initial roof pressure as a new face is opened. Afterwards, regular gushing would follow as roof layers are broken periodically. Under the above circumstances, using the technique of water draining while mining, there will be neither extra draining projects added, nor general amount of water inruch increased due to the expension of area of mining panel. In the meantime, underground water resource would not be destroyed due to the mining. Naturally, if the water resources affected by mining are neither rich nor in need of protection, water draining should be reasonable from the economical point of view. Using the method of water draining while mining, the maximum amount of coal can be extracted by leaving very small size of waber barrier under the water body.

      Coal mining under the filled Karst cavities possesses almost the same style as which under loose aquifers because of, in a sense, that the flow state of water in the cavities belongs to permeable flow which also observes the law of Darcy permeability.

      Secondly it is important to asses the water content and the impermeability of loose layers and strata, Based on the information, the design of water barrier could be more reasonable.

      As for impermeability of bedrock, it is preferable to test its absorptivity and plastic coefficient in both dry and saturated states by hydrophysical experiment along with the analysis of rock as well as mineral as a standard of the quantitative evaluation. The measures have been proved simple and effective, which revealed the mechanism of impermeable roof formed, in turn, assist us to predict correctly the amount of water inrush.

      As for the richness of the aquifers, it is depend on the ability of water draining in mines which should be compatible with the amount of water gushing. For instance, we have succeeded in mining while draining under the aquifer which has the permeability factor of 100-200m2/day. It is evident that sticky particles are the main composition that constructs impermeable layers.

      The impermeability of high quality could be reached when the percentage of the particles is up to 20-30. It is discovered by research and practice that the powdery particles, main composition of loess in China, can greatly lower the permeability of water as long as it possesses a certain ration in loose layers, as well as its plastic coefficient is in the neighborhood of 10.

      The information in situ indicates that in the formation of alluvium, corse particles mix with fine particles, giving rise to the reduction of richness of the would-be richly waterd gravel layers. For example, using the method of gydrolic stowing, the coal seam of 4m height under a river and a gravel aquifer of alluvium was successfully extracted with water barrier of sand-shale stone only 6m in stick ness. The amount of water gushing in the mine kept 6m3/min. in dry season, and reached 12m3/min.