| With the development of Chinese economy, all kinds of high-rising structures, such as buildings, bridges and harbors become more and more. Bored pile is a main foundation type used in these infrastructure construction projects for its special economic and technical advatages. To ensure the quality of the shaft, concrete are always casting to the level higher than the cut-level, and then the surpass parts are cut off. Usually the pile head is beneath the ground, it is difficult to know the exact level of the surface of concrete because of the existence of a layer of mud deposit caused by the drilling fluid spreading the whole drilled hole during the casting process using underwater concrete casting technique. Nowadays, the commom equipment to measure concrete casting level is measuring rope. That method is time-consuming and laborious, and 'Casting too much concrete problem' occurs sometimes which make the cost including concrete and the other related wastes increase conspicuously. Take all the bored pile foundation projects into consideration, the cost induced by 'Casting too much concrete problem' would be astronomical for China is the country installed the most number of bored pile as much as 40-50 million. In this condition, develop a portable and precise ultrasonic device to measure the concrete casting level is of vital importance and economic value.To fulfill vocation of 'construct a economical society', our group, which is led by Prof. Yan Taining of CUG, take the project 'Development of a ultrasonic concrete casting level measurement equipment for bored pile' granted by The Bureau of Exploration & Development of Geology & Mineral Resources of Jiangxi Province together with Jiangxi Geo-engineering (group) corporation. The thesis presents some achievements on this project, which mainly analyses some key techniques on ultilizing ultrasound to measure concrete casting level.Key problem 1: Ultrasonic propagation in water-based bentonite slurryThe drilling fluid used in pile foundation is the two-phase water-based bentonite slurry. The existance of clay particles makes the ultrasonic propagation and attenuation in drilling fluid much different from pure water. Until now, there are few literatures to describe the ultrasonic propagation in the drilling fluids. So ultrasonic propagation and attenuation in water-based bentonite slurry is the first key problem should be solved. To understand the relationship between ultrasonic frequency and slurry density, viscosity, depth and temperature, the dissertation finished the following taskes.(1) After the introduction of the basic knowledge about ultrasound and bentonite slurry, the paper deduced the factors related to ultrasonic velocity and concluded that the reasons for ultrasonic attenuation are sound diffusion, dispersion and absorption.(2) Based on the ultrasonic propagation theory in suspensions, the paper introduced ECAH theory to explain the ultrasonic propagation in water-based bentonite slurry, which is the first time in this field. Considering the difficulty in solving coefficients from ECAH formulae, the dissertation analysed the feasibility to predigest the ECAH formulae. Then a McClements obvious simplified solution was gained. Based on the theory, numerical simulation had been done to analyse the relation among particle diameter, slurry density and ultrasonic frequency, velocity and attenuation. Tang Yingwu model and other laboratory data were used to corroborate the adopted theory.(3) In order to know the relation among ultrasound frequency, slurry density, viscosity, temperature, depth, velocity and attenuation coefficient, a series of laboratory experiments about ultrasound propagation in water-based bentonite slurry were finished. Wavelet method was adopted to process the gained original graphs of ultrasonic propagation in slurry, so we knew the velocity and attenuation coefficient of 200 kHz ultrsound propagated in different drilling fluids with different density. The laboratory data also shows the ultrasonic propagation property in pipe with samll diameter which illustrated that the small diameter can help ultrasound to propagate long ranges for the energy can be focused in small diameter pipe. It seems that the developed equipment can be used in small-diameter-borehole, which broke the customary assumption. These measured data corroborated the velocity and attenuation coeffocient calculated from ECAH theory.Figuring out this key problem makes a rigid base for the development of the equipment and post-process of the measured data.Key problem 2: The effect of mud deposit layer on ultrasonic propagationIn the borehole constructed by the positive circulation technology, the density of drilling fluid is high and difficult to regulate for the restriction in site. This made the quality of the mudcake weak enough to form the mud deposit layer on pile top. In this case, during the concrete casting level measurement, the ultrasound would be refelcted by the mud deposit before it reaches the concrete layer. This gives birth to the second key problem, which is the effect of mud deposit on ultrasonic propagation in borebole. After introduction of the formation and properties of mud deposit, the relationship between ultrasonic reflection coefficient and attenuation coefficient and parameters of mud deposit were theoretically analyzed.(1) Assume that the mud deposit is a liqiud layer over a porous elastic solid half-space referring to the underwater acoustic theory for sea bottom, a theoretical model to calculate the reflection coefficient of mud deposit was established. Use that model, the relatioship between ultrasonic frequency and reflection coefficient was numerically simulated. The calculated results shows that reflection coefficient was little correlative to frequency but pertinent to the intrinsic properties of mud deposit. When incidence angle is greater than 60°, the reflection coefficient is largely increased.(2) Introduce the model used for analyzing acoustic attenuation in sea bottom sediment to study the ultrasonic attenuation in mud deposit. The numerical simulation results showed that viscous friction is not the main reason to induce attenuation in loose muddy deposit. In the range from 20 kHz to 150 kHz, attenuation coefficient caused by viscous friction is larger than inner friction. For the given mud deposit, attenuation caused by inner friction is closely and linearly linked to ultrasonic frequency. In general, the total attenuation coefficient is segmentally linearly increased with frequencies for floccutional muddy deposit.Key problem 3: Numerical simulation of ultrasonic propagation in borehole with slurryThe real borehole is an infinite-thick-walled tube, which has finite diameter, is full of drilling fluid, the walls can be divied into finite soil layers and has mud deposit in the bottom. Ultil now there are few literatures referring ultrasound propagating in boreholes. That gave birth to the third key problem, which is the numerical simulation of ultrasound propagating in boreholes full of drilling fluids. For this aim, the following tasks had been finished.(1) DPSM method was used to simulate ultrasund propagating in half-space with isotropy fluid medium. The results indicate that the higher the frequency, the stronger the directivity. For 200 kHz ultrasound, sound pressure in the near region of ultrasonic probe fluctuates drastically. This phenomenon is not conspicuously for 50 kHz ultrasound. Sound pressure decrease drastically with range.(2) DPSM method was used to simulate ultrasund propagating in half-space with layered isotropy fluid medium. The results indicate that for the drilling fluid with linear varing desity in borehole, the fluid-fluid interface would not change the tendacy of sound field, so the interface between drilling fluid filled in the hole can be ignored. But if the density or velocity of sound changes suddenly, the effect of interface should be concluded. The bottom interface between drilling fluid and mud deposit has important effect on sound field.(3) DPSM method was used to simulate ultrasund propagating in half-space with isotropy fluid medium and a bottom. The results indicate that properties of bottom medium have vital importance to the sound field in drilling fluid. The larger the density of bottom medium is, the greater of the reflection coefficient. With the increase of the propagating range, the ultrasound energy decreases sharply and the pressure on the solid-fluid interface weaken.(4) Propagating modes method was used to calculate amplitude when ultrasound propagated in a no-end, hard wall pipe filled with isotropic fluid.(5) Based on ray theory, a softwave to simulate ultrasound propagating in a simplified two dimensional borehole was composed. The results indicate that because of the existance of walls surrounding borehole, reverbration was found, so sound pressure was strengthened in some regions far from source. With the decrease of borehole diameter, the focus of sound pressure becomes more conspicuous. If we place the source towards to the wall, reflection on wall becomes much more notable. The higher the ultrasonic frequency is, the greater of the directivity of sound field. The results of the ray tracing procedure show that the received signal is very weak. So we should increase the power of the source and also we should enhance the magnification factor of siganl receiving circuit to realize the casting level measurement in borehole by ultrasound. The given wave forcasting method can get results similar to the wavelet analysis on the original signal, which indicates the adopted method is useful.The above three key problems can clarify the theoretical base to measure concrete casting level in borehole by ultrasound. Guided by the theoretical analysis, our group developed the experimental prototype equipment. The frequency, power, sketch, relative program were introduced. And the voltage conversion circuit, signal process circuit, A/D conversion circuit, DSP control circuit and LCD display interface circuit were depicted. Then the prototype equipment was shown.To validate the reliability and usability of the developed equipment, a series of laboratory and insitu experiments were conducted. In the dissertation, the experiments were depicted in detail. A lot of graphs were used to corroborate the usability of the equipment. Some shortages were also concluded that needed to be solve in the next phase research.To sum up, the creative ideas in this dissertation are followings:(1) A model to analyze ultrasonic propagation in water-based bentonite drilling fluid is established based on ECAH theory. The McClements simplified solution is presented to analyze the relation among clay particle diameter, slurry density, ultrasonic frequency, and velocity and attenuation coefficient. Compared with Tang Yingwu's Theory and some meausred data, the model is creditability.(2) It is the first time to report the laboratory results on ultrasonic propagation in water-based bentonite slurry. Wavelet method was used to find out the time of receiving echo signals, based on this information, velocity and attenuation coefficient of ultrasound were calculated.(3) It is the first time to estabilish a model to analyze reflection and attenuation in mud deposit in borehole, which is based on the theory on seabed sediment in underwater acoustics.(4) It is the first time to analyze the ultrasonic propagation in bore hole and the properties of received signal by numerical method based on ray tracing method.Drilling fluid is a commom flushing medium used in pile foundation, geological drilling and petroleum drilling. Study on the ultrasonic propagation properties in drilling fluid is of vital importance. With the urbanization of Chinese cities, the amount of piles is tremendous. So clearly know the concrete casting level can help save cost and is according to the requirements of constructing an economical society. With the continous effort by our group on this project and collaboration with other colleagues, we optimistically believe that the commercial Ultrasonic Concrete Casting Level Measurement Instrument for Bored Pile will appear in market to make benefit for pile foundation construction.
|
PDF Full Text Request