During the mine shafts construction the designers, engineers and operational staff have to deal with huge information flows of various technical and spatial data. Special user-friendly tools which provide an effective access to these data as well as the evaluation and forecast of different situations which may appear during various stages of shaft sinking provide the owner of such tools with substantial benefits.
The solution offered by our company significantly increases the efficiency of the entire construction process and helps reduce the risks during the design, construction and sinking stages. These solutions are based on special software and experts’ assessment in turn making it more reliable and justified.
The set of modules dedicated to resolving the problems during the shaft sinking is called Shaft Builder. Shaft Builder can be effectively used in combination with other solutions offered by our company. In particular the most effective is the combination with our solutions for mining and geology which provides analytical and visual tools for processing of geological, geotechnical and geophysical data in the areas designated for shaft sinking.
Shaft Builder incorporates the unique instruments for making competent decisions at the most important stages of construction of a mine shaft:
- during the preparation of rock mass for shaft sinking by means of ground freezing;
- during the lashing and the installations of rock support and shaft lining;
- during the ground thawing and rock grouting;
- during the shaft equipping phase.
The delivery of various Shaft Builder components may vary and is dependant on the requirements of a particular shaft sinking project.
Shaft Builder includes the following basic features:
Modelling of freezing and thawing of rock mass around the designed shaft
Ground freezing (along with rock cementation and grouting) is a very necessary part of practically any shaft sinking project. Ground freezing and/or rock grouting are used to prevent shaft flooding during the sinking stage.
The dynamics of the ground freezing process is critically important for general project success. Properly executed freezing significantly influences the effectiveness of the following sinking phase whereas “under-frozen” or “over-frozen” rock mass creates substantial problems for the sinking contractors during the next phases of shaft construction.
Natural desire to freeze the rock mass around a shaft as soon as possible (with the purpose to start rock hoisting earlier) may lead to the incomplete establishment of an ice wall with the required thickness at certain depth intervals and therefore cause substantial water leakages during the sinking. Another extreme is the excessive freezing which leads to the unreasonable power consumption and to the technical difficulties of sinking in the completely frozen rock, this may delay the start date of full capacity operations. Therefore it is highly recommended to effectively control the process of an ice wall formation in order to obtain a significant financial gain.
Technically the freezing process is carried out by permanent circulation of special cooling agents (brines) in freezing boreholes which are usually arranged in a circle pattern and are located beyond the boundaries of a sinking zone.
The speed of freezing generally depends on mineralogical composition of the rock formations, and especially on their moisture content and salinity. Typically the aquifers take longer to freeze than the less water saturated horizons since the water has much higher heat capacity in comparison to the solid rocks.
Prior to the start of freezing the engineers usually make approximate and empirical prediction of process dynamics which looks like an expert assessment rather than proper engineering calculations. The felicity or failure of prediction can be checked by the periodical monitoring of temperature at different depths in specifically drilled boreholes.
The technology offered as a module in Shaft Builder solution enables mining engineers involved in design and / or sinking of the mine shaft to obtain very accurate and reliable estimates of the dynamics of ice wall formation. The model is based on the resolution of the crystallization process – so-called Stephan problem – and allows us to calculate the ice wall status (and thickness) at any required date for each geological layer. The design engineer gets an opportunity not only to play with “what-if” scenarios by changing the parameters of the freezing process (cooling agents temperature, location of freezing bore holes, turning off and on of particular boreholes) but also to calibrate the model (to refine the geotechnical parameters) using actual measurements in the monitoring boreholes.
Therefore the freezing process becomes well-planned and well-controlled.
Ground thawing is the process inverse to ground freezing. Thawing operations start immediately after completion of sinking through the deepest aquifer and reaching the reliable impermeable rocks . Thawing can be natural or induced when a warm solution is poured into “freezing” boreholes. Shaft Builder includes special module for thawing process simulation with additional optimisation tool for geotechnical parameters.
Instrumental support of underground surveying during shaft sinking and construction
The traditional way of shaft sinking normally assumes drilling and blasting operations at the shaft bottom followed by cleaning of loose material. The problem is that after blasting any shaft has some amount of overbreak (over-blast). The typical contractual allowance is 15 cm in any radial direction but if the surrounding rock is weak or fractured then an extra overbreak in inevitable. It results in extra ground to be hoisted (time and money) and extra concrete to be poured (time and money again). Very often the amount of extra muck and extra concrete is a contentious point between a sinking contractor and a client as the latter has to pay extra for both.
The set of tools offered by Shaft Builder provides highly efficient and very accurate methods to assess any additional mucking and concrete works required and is based on processing the data from a static 3D laser scanner installed at the shaft bottom. The scanning (for the section of the shaft up to 20 metres in height and 6-12 m in diameter) is normally done before pouring the concrete lining or tubbing installation and takes only about 3-5 minutes to complete. Thereafter the sinking operations can be resumed.
By integrating the processed scans with information contained in the mine shaft data base (rock support, lining design, surrounding geology and face mapping, engineering drawings etc.) Shaft Builder provides fast and accurate calculation of mined volumes and required amount of concrete. It also helps to visualise, print and organise surveying documentation required by various regulating authorities.
Installation of permanent lining and some elements for mine shaft equipping.
The majority of works related to the installation of permanent concrete lining and some elements required for subsequent shaft equipping are carried out from the sinking stage. In case of using cast-iron tubbings as a permanent lining the installation of tubbing rings is carried out from the shaft bottom face after completion of cleaning works. 3D static laser scanning of mine shaft walls is done from the top deck of the sinking stage or from the shaft bottom and it offers the effective method of controlling the quality of lining installation. The processing of the captured scanning data and its analysis by a special module which is part of the Shaft Builder solution allows to find explicit defects in concrete or tubbing lining (cracks, scaling, gaps between segments), it also checks the geometric shape of lining (deviation from a proper cylinder or any other designed layout) and actual position of nut-boxes, mounting brackets, rock-bolts etc. It is supposed that during this stage of scanning the main elements of shaft equipping e.g. buntons and guides are still not installed.
Mine shaft equipping
The last stage of mine shaft surveying is capturing of its internal infrastructure after the installation of the main constructive elements (buntons and guides) and other engineering services (pipelines, electrical cables, ventilation ducts etc.). This scan not only provides quality control of the installed construction elements but also serves as an etalon (template) for the following shaft inspections and monitoring during the operations.
Scanning should be carried out is such a manner as to avoid any blind spots. This way one can build a complete 3D model of the actual constructed mine shaft.
Shaft Builder includes a special module for point cloud integration and processing. Processing takes place in the surveyor’s office at the surface and the results can be kept in the integrated mine shaft database.