【作者】 兰凯；

【导师】 鄢泰宁；

【作者基本信息】 中国地质大学 ， 地质工程， 2008， 博士

【摘要】 随着我国经济高速发展,各类楼房、桥梁、港口码头等大型建筑物(构筑物)越来越多。钻孔灌注桩以其独特的技术经济优越性,成为建筑物(构筑物)的主要基础形式之一。钻孔桩成桩多采用水下现浇混凝土的工艺,为保证桩顶质量,经常要求混凝土超灌出设计标高一定高度,在基坑开挖后再凿除超灌部分。由于灌注过程中孔内充满泥浆,导致桩顶混凝土上存在浮浆层,所以很难准确知道砼灌注面究竟到了什么位置。目前,现场主要靠人工用测绳测量超灌高度,费时、费力、误差大,过量超灌的现象屡见不鲜,造成大量混凝土材料浪费,工程成本增加。我国是世界上施工钻孔灌注桩最多的国家,据不完全统计每年完工4000～5000万根钻孔灌注桩,如果计算全国灌注桩工地因超灌引起的混凝土浪费,将是天文数字。因此,开发便携式砼灌注面高程测量仪具有重要的经济意义和极高的实用价值。为响应建设节约型社会的号召,满足国内工程界的需求,在充分对比现有各种遥测方法的基础上,借鉴空气中超声波测距思想和水声传播理论,在中国地质大学(武汉)鄢泰宁教授的主持下,我们与江西省地质工程(集团)公司共同承担了江西省地质矿产勘查开发局科技项目“钻孔灌注桩超声波测砼灌面高程系统的研究及开发”(简称“高程仪”,下同)。论文以此项目为背景,围绕钻孔灌注桩砼灌面超声波测量的若干关键技术展开研究,弄清作用机理,以指导仪器的开发。关键技术问题一:超声波在粘土泥浆中的传播特性桩基工程使用两相水基粘土泥浆。由于粘土颗粒的存在,使超声波在其中的传播衰减过程与纯水中有较大区别。目前,关于超声波在钻井泥浆中传播规律的国内外文献很少。为弄清楚超声波在泥浆中的传播衰减规律,本文展开了以下研究。(1)学习研究超声波基础理论,分析与之相关的粘土泥浆特性,提炼在水基粘土泥浆中影响超声波声速的因素,将主要影响水基粘土泥浆中超声波声衰减的因素归结为声束扩散、声波散射和介质吸收三种。(2)在吸收前人关于悬浮液介质中超声波传播理论的基础上,首次引入ECAH理论,建立超声波在水基粘土泥浆中传播衰减模型;对ECAH理论的求解进行了适当简化,并在此基础上给出了ECAH理论模型的McClements显式简化解;根据导出的公式,采用数值模拟方法分析了颗粒粒径、泥浆密度(泥浆中固相体积分数)、超声频率与超声声速、声衰减之间的关系。采用唐应吾理论模型及实测数据,对理论模型的准确性进行了对比分析。(3)按照实验设计,安排了若干组超声波在粘土泥浆中传播特性的室内试验,探讨超声波在泥浆中的传播规律,研究超声波频率、功率与泥浆的密度、粘度、温度及深度的相互关系,以及超声波在粘土泥浆中的衰减系数和声速;通过室内试验,获取了大量的超声波传播波形原始图像,应用小波分析方法对原始波形进行数据处理,寻找回波信号的突变奇异点;得到了200kHz超声波在不同密度泥浆中的声速与声衰减系数;在掌握200kHz超声波在小口径管中传播特性的基础上,查明了在小口径管中存在着超声波传播的聚能效应,从而拓宽了超声波高程仪在不同孔径中的适用范围;实测数据与理论数据的对比表明ECAH理论可以准确描述超声波在水基粘土泥浆中声速值和声衰减系数。这个关键技术的突破,为优选高程仪的工作频率、功率及后续数据处理工作奠定了基础。关键技术问题二:浮浆层对超声波的传播影响在大多数建筑桩孔施工(尤其是正循环施工)现场,普遍存在泥浆比重明显超过规范要求的现象。致使桩孔壁上泥皮厚且松散,在灌注混凝土成桩的过程中,砼灌面以上会形成较厚的浮浆层。用超声波检测时,超声波并不能首先达到未固结的砼灌面,而是先到达浮浆层,一部分能量被反射,另一部分能量进入浮浆层到达砼灌面后再反射回孔口探头。论文从浮浆层的成因和特性出发,就超声波在浮浆层中的声反射系数、声衰减系数与浮浆层参数的关系等问题展开了理论分析。(1)将浮浆层视为一个覆盖在均匀孔隙弹性半空间固体上的液性介质层,借鉴水声学研究海底沉积物的理论模型,建立了浮浆层中声反射系数的理论计算模型,采用数值方法模拟了频率和入射角与浮浆层声反射系数之间的关系。结果表明,声反射系数与频率关系不明显,但与沉积物本身的形状密切相关,当入射角大于π/3后,反射系数有较大梯度的提高。(2)引入沉积物中声衰减数学模型来分析浮浆层中超声的衰减问题。数值模拟结果表明:对于可视为松散泥质沉积物的浮浆层,粘滞摩擦不是引起超声衰减的主要原因;但在20kHz到约150kHz范围内,粘滞摩擦的声衰减系数将大于内耗引起的声衰减系数;对给定的浮浆层,因内耗引起的声衰减系数只与频率密切相关,且两者呈线性关系。总之,对于絮凝状泥质浮浆层,其总的声衰减系数随着频率的升高而增加,但不是一一对应的线性增加关系,而是分段线性的趋势。关键技术问题三:超声波在充液桩孔中的数值模拟实际桩孔为充满泥浆、孔径有限、孔壁分层、孔内存在浮浆层的无限厚壁筒,目前国内外鲜有文章论及超声波在桩孔中的传播问题。笔者用数值模拟方法研究不同孔径和泥浆条件下超声波的传播特性,力求揭示桩孔中声场分布及其波形的规律。(1)用DPSM法对半空间各向同性液态介质中超声场的数值模拟结果表明,超声频率越高,其指向性越强;频率为200kHz时,在离探头较近的区域内(0.2m范围内)声压曲线波动很大,这可能是由于探头与液体之间的粘附作用放大了探头的振动效应,故探头有一定的检测盲区;频率50kHz的声压波动作用不明显,声压在近场达到峰值后迅速减小;在远场超声波的声压降低明显,在一定的距离之外,声压值很小且变化不大,说明信号在远场较微弱。(2)用DPSM法对分层各向同性液态介质中超声场的数值模拟结果表明,由于桩孔中的泥浆密度和声速分布呈连续模式,其液-液界面的存在不会改变声场分布趋势,故分析桩孔内超声场分布时可忽略液-液界面的存在;当密度和声速存在较大跳变时,其液-液界面的作用不能忽略,要计算其对超声场分布的影响;即使浮浆层密度较接近底部泥浆,也应该计算其对超声场的影响。(3)用DPSM法对固体边界内各向同性液态介质中超声场的数值模拟结果表明,泥浆底部固态介质的参数对超声场分布影响较大,底部固态介质密度越大,超声波在固液界面上的反射系数就越大,发射信号对声场的贡献也越大;随着传播距离增加,超声波能量衰减明显,声场中信号显著减弱,固液界面上的声压值降低。(4)采用模态分析法对超声波在均匀充液硬壁无底管中的传播声场进行了分析,导出了用模态法求声场幅值分布的方法。(5)借助射线声学理论,编制了分析桩孔中超声传播特性的模拟软件。模拟结果表明,由于孔壁的影响,声场出现混响叠加现象,与半无限空间衰减趋势不同的是,总体上强度随深度增加而减弱,但局部可能出现强化现象;孔径越小,声波传播时的聚能现象越显著;探头位置越靠近孔壁,折射效应越显著,声场分布呈衰减的正弦模态分布;频率越高,其声场指向性越强;声线追踪结果表明,超声接收信号很微弱,为实现砼灌面测量必须提高超声探头功率,并增加信号接收电路的放大倍数(万倍级);笔者采用波形预测方法与小波分析的结果比较吻合,说明其有一定的实用价值。以上述三个关键技术问题的研究成果为基础,项目组开发了高程仪样机。文中在简介高程仪总体方案和发射频率、功率等参数的基础上,详细阐述了电压转换电路、信号调理电路、模数转换电路、DSP控制处理电路及液晶显示接口电路等关键模块的研发内容,给出了相关程序。为检验高程仪的可靠性,笔者设计并实施了一系列室内外试验。论文用一章的篇幅分析了高程仪的试验效果,讨论了高程仪存在的不足,为今后进一步改进设计积累了经验。纵观全文,论文的主要创新点在于:1、以ECAH理论为基础,建立了超声波在水基粘土泥浆中传播特性的数值计算理论模型,并采用McClements简化方法数值模拟研究了粘土颗粒粒径、泥浆密度(泥浆中固相体积分数)、超声频率与超声声速、声衰减之间的关系;与唐应吾理论模型结果和部分实测数据的对比验证了所采用理论方法的可信性。2、在国内首次进行了超声波在粘土泥浆中传播特性的室内试验,得到一些有价值的实测数据。采用小波方法找出了回波信号突变点,求得了声速和声衰减值。3、引入水声学中研究海底沉积物的方法,首次建立了桩孔浮浆层影响超声波反射和衰减的理论模型。4、借助射线声学理论,采用数值模拟方法,首次研究了超声波在桩孔中的传播特性及接收信号的特点。笔者展望,泥浆是桩基工程、地质钻探及油气钻井中最常用的循环介质,研究超声波在泥浆介质中的传播不仅对开发测砼灌面高程仪有现实意义,而且对研究其它以泥浆为信号载体的仪器也具有理论意义和借鉴价值。随着我国城市建设步伐的加快,灌注桩的应用数量巨大,控制砼灌面标高是响应“建设节约型社会”的具体行动。我们相信,在各界同仁的共同努力和支持下,随着项目组的持续攻关,商用“钻孔桩砼灌面超声波高程仪”必将很快走向市场,应用于桩基工程施工。更多还原

【Abstract】 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.更多还原