This paper presents a new method to accurately determine the strata while drilling. We developed an original prototype of instrumented drilling system, with it the measurement was performed on a hydraulic servo drilling rig. The drilling parameters (i.e., thrust or weight of drill strings, rotational speed, bit shift, torque as well as vibration of drilling rig) were recorded. According to the harmonious principle, a coding method for identification of sub-penetrating processes is established through the determination of parameter status. A slope coefficient searching identification algorithm is proposed for the penetrating data with the features of multiple pulses, noisy, huge data and nonlinear. Field drilling tests were carried out in three different sites. The results show that the approach well agrees with that of conventional drilling investigation, which provides a new method for in-situ intelligent survey in geological and geotechnical engineering.
In geological and geotechnical engineering investigation, the primary methods to obtain strata structure are drilling and related in-situ test techniques. For example, geophysical detecting techniques (GD), resistivity, magnetics, electromagnetic, seismic wave, seismic CT, gravity, sonic and ultrasonic methods have been extensively applied to the identification of strata interfaces at initial stage of geologic prospecting (1). In terms of technology, borehole penetrating test and coring are the most authentic and reliable for geotechnical investigation and geological survey. Unfortunately, the job of borehole logging, sampling, in-situ testing and indoor physical mechanical parameters testing is overloaded, time-consuming and expensive. According to incomplete survey, in drilling exploration of foundation, the time consuming ratio of net penetrating in the whole drilling is less than 30%, the costs of drilling exploration are generally accounted for 8%-28% of a project cost, this ratio will possibly increase with the increase of investigation depth.
In geological drilling, the borehole depth generally reaches thousands of meters. At present, the maximum depth has reached over 4500 m in metal mining; for nearly 1/3 underground metal mines, the mined depth has exceeded 1000 m in China; in coal mines, the numbers of well over 1000 m in depth have made a substantial growth in recent 10 years; the constructed depth of tunnel has rose up to near 3000 m. In earth science drilling, this figure has exceeded 10 000 m, and among the earth science boreholes, there are dozens of boreholes over 4000 m in depth worldwide. Obviously, with the growth of drilling depth, the complexity of geological conditions will increase, processing time will greatly grow in non-drilling such as sampling, lifting and lowering of drill strings and in-situ testing. For example, the depth of core drilling in the earth drilling-CCSD-1 reached 5158 m, totally spent 16.6189 million Chinese Yuan, core length of 4400 m with a cored rate 85.30%, for nearly 4 years. On the other hand, the geophysical approaches have good prospect for application in field investigation, but can be easily interfered with external factors and the interpretation accuracy is not very high when a single method is applied. Due to uncertainty, multiplicity of interpretation, it needs a combination of various methods to recognize formations. Besides, it is hard to give all the required basic data for geotechnical and geological engineering, and is difficult for rock mass classification.
