Hard Rock Tunneling Data Logger Analysis for Hard Rock TBMs
Most of Hard Rock TBMs are fitted with an automatic state-of-the art machine monitoring and recording system, which is called Programmable Logical Computer (PLC). All pertinent machine parameters, including propel thrust, motor amps and voltage, number of motors running, penetration rate, etc. are monitored and recorded by this on-board data acquisition system. The data is recorded in a digital form which are downloaded directly into a spreadsheet software package or any other database programs to manipulate the data. This made the data analysis effort much more straightforward than the analog systems which have been used in the past.
Description of PLC Data Logger
Total thrust is measured from the thrust cylinders that push the cutterhead against the cutting face (See Figure 1). The pressure transducer that measures the pressure in the thrust cylinders and this pressure value is multiplied by the area of the cylinders to calculate the load applied to the cutterhead during boring. The pressure transducer actually gives a voltage output based on the pressure in the thrust cylinders. Since, it is calibrated for voltage versus pressure, the applied force values are stored in the data file in pressure or load unit.
Figure 1. Components of a main beam TBM
The measurement of the amperage output of the electrical motors (cutterhead drive units) that rotates the cutterhead in a given thrust pressure is also done through a calibrated transducer. Knowing the number of cutterhead motors (column #14) in Figure 2) that engaged at the time, one can calculate the power of the cutterhead at given thrust pressure by using the motor curve.
As seen in the following figure (Figure 2), stroke data (column #4) is the position of the thrust cylinders at that time. In other words, it tells how much the thrust cylinders were opened in length. The difference between stoke values at the start and end of a stroke is the length of the tunnel excavated during one stroke. Since data is collected digitally at certain intervals, the number of data collected per stroke (i.e. every 60 seconds) is actually time elapsed to finish one stroke. Knowing the excavated tunnel length and time elapsed; one can calculate the rate of penetration (ROP) by dividing the excavated length with time elapsed (ft/hr or m/hr). In some cases, ROP values can also be stored in the raw data file for every data point within a stroke as shown in Figure 2.
The following figure illustrates an example raw data file form a PLC data acquisition system used on TBMs. These raw data files are used to calculate the actual machine thrust and power used during excavation at a certain penetration rate, and consequently, cutter loads at a given geology and rock conditions.
Figure 2. Example Raw Data File
Macro program to reduce TBM data logger
Earth Mechanics Institute (EMI) have been analyzing data from different TBM projects from all over the world. An Excel macro program is used to open the daily raw data files and retrieve the data from them according to the shift schedule and user defined reduction parameters. The following window is an example for format parameters to extract the raw data files in order to calculate the machine parameters at desired station numbers.
Figure 3. Data format for reduction
The following figure show typical reduction parameters, which are defined by the user according to the shift schedule and properties of the data logger on board of the machine.
Figure 4. User defined parameters for data reduction
A graphical output of the data can also be produced from the reduced data file as shown below. This plot can be used to check the data visually to see if there is any unusual behavior in the data that the program could not detect.
Figure 5. Strip chart for reduced daily data
After the program cleans up the data by using user defined parameters, it calculates the selected machine parameters. An example summary of this final calculation is given in the following tables.
Table 1. Summary on a stroke base for 04/01/99
Table 2. Summary on a shift base for 04/01/99
Table 3. Summary on a daily base for 04/01/99