岩石在单轴受荷条件下的超声波特性研究

1、岩石在单轴受荷条件下的超声波特性研究        【中文摘要】岩体介质超声波测试技术是近三十多年发展起来的一种新技术,它通过测定超声波穿透岩体后声波信号的声学参数的变化,间接地了解岩石或岩体的物理力学特性、结构构造特征及应力状态,已得到国内外岩土工程界的广泛重视。2003年,笔者的导师傅荣华和刘维国等在进行油气躲'岩石的力学性质实验时,观察超声波的横波速度值与岩石裂纹加速发展具有同步减小的现象,这种现象在超声波纵波中没有出现,在其他弹性波作用下,也不十分明显。于是提出了进行岩石扩容现象和超声波横波特性等参

2、数相互关系研究的新思路。因此,本文主要是利用岩石对超声波的横波十分敏感的这种特性,比较岩石变形过程中的超声波纵、横波参数的不同变化特征,从而对岩石的弹性极限以及应力应变特征的研究提供了更多的参考意义。本文主要通过对玄武岩、灰岩、石英砂岩以及砂岩等在单轴加载过程中进行超声波测试,研究几种岩石在单轴加载条件下超声波的传播特性,实验通过对岩石超声波参数以及实验产物的分析,研究几种岩石的弹性特征、非均质性、各向异性等性质。研究结果表明:第一,岩石的纵波速度随密度和压力增大均增大;横波速度在玄武岩、石英砂岩、砂岩中随密度增加而增大;在灰岩中出现例外:随压力的变化也与纵波不同,呈现先增后减的现象。这是由于

3、低压时纵横比小的孔隙易于闭合,当大量的孔隙闭合时,岩石表现出接近于岩石样品本身固有的弹性性质;随着压力增加,闭合的孔隙重新张开并扩展。这对超声横波的传播影响较大。第二,玄武岩、石英砂岩以及砂岩纵波和横波初至波的波峰、波谷随压力增大而增大;灰岩中纵横波的波峰是随压力的增加而增大,波谷随压力增加则呈现减小的趋势。这主要是由于,在受荷条件下,岩石的孔隙度降低,岩石内大部*纹闭合,并且矿物颗粒边界接触紧密,在裂纹表面和颗粒边界的能量损失减少;超声波通过灰岩出现不同于其他三种岩石的现象,这与灰岩在加压的过程中发生碎裂有关。第三,超声波在砂岩不同的层理面方向传播时,纵、横波的速度和衰减发生了不同的变化。垂

4、直砂岩层理面方向的速度小于平行砂岩层理面方向的速度;横波在垂直岩层层面方向的衰减大于平行岩层层面方向的衰减,纵波在垂直岩层层面方向的衰减小于平行岩层层面方向的衰减。横波速度小于纵波速度,横波衰减大于纵波衰减。这表明:即使是同一种岩石都可能存在明显的各向异性,说明岩石中的各向异性是普遍存在的。同时,衰减各向异性系数大于速度各向异性系数,说明衰减比速度对岩石的各向异性更为敏感。通过本文对岩石单轴加载条件下超声波的特性研究,为岩石或岩体的物理力学特性及结构特征的研究提供更多的依据。并为岩体扩容、岩体稳定性、岩体加固质量检测以及地震预告等方面提供了参考依据和实验基础。');【Abstract】

5、 Ultrasonic testing technique in rock mass medium is a new technique which has been developed during near thirty years.It realized physical and mechanics characters, structure and stress state of rock mass by testing the change of acoustics parameters of sound wave signal after penetrating rock mass

6、,which got recognition in domestic and overseas geotechnical engineering fields.In 2003,my tutor professor FuRonghua and LiuWeiguo Observed the ultrasonic S-wave velocity begins to decrease with the expansion of microcracks rupture in the test about Oil and Gas Reservoir rock mechanics properties. T

7、his phenomenon didn't appeared in ultrasonic P-wave,and it was weak in other elastic wave.So,they put forward new idea about study the relation of parameters with the dilatancy of rocks and the ultrasonic S-wave characteristics.Then, This * compared the parameters ultrasonic S-wave and P-wave in

8、 the process of rock deformation .which using the characteristic rocks are very Sensitive to ultrasonic S-wave.Thus providing more reference significance for studing about the elastic limit and Stress strain Features of rock.In this *,It studied the character about ultrasonic wave transimtion on bas

9、alt,limestone,quartz-sandstone and sandstone under the uniaxial compression.The experiment studied effects of elastic behavior, heterogeneous feature ,anisotropy and so on of these rocks by the analyse to ultrasonic parameter and teseted results of rocks. The study results demonstrate:First,The P-wa

10、ve velocity of rocks is larger and larger along with their densities and compression forces.The S-wave velocity is larger and larger along with their densities on basalt,quartz-sandstone and sandstone.It's exception on limestone.Which change is different from P-wave with compression force changi

11、ng.It's increase-before-reduce.Which is because that pore with low aspect ratio close easily under low compression.When large pores closed,rocks expressed approaching elastic behavior of theirselves.With compression force increased,closed pore reopen and extend.Which have important effecion to S

12、-wave.The second, The wave crest and through of first period of the P-waveform and S-waveform are larder and larger along with compression forces on basalt,quartz-sandstone and sandstone.On limestone,wave crest is larger and larger along with compression forces.But,wave through is opposite.Which is

13、because that porosity gets lower and most cracks close on rocks under compression forces.And the border of mineral grains contact closely. Whinch result that the lost energy of crack su*ce and grain border reduce. Ultrasonic transmiss differentliy from other rocks on limestone,this's because lim

14、estone disintegrated under compression forces.The third,when ultrasonic transmiss in different bed plane on sandstone,P-wave and S-wave velocity and attenuation have different change. The ultrasonic velocity wave velocity is bigger in vertical sandstone bedding than in the parallel. Ultrasonic S-wav

15、e attenuation is larger in the vertical than in the parallel. Ultrasonic P-wave attenuation is less in the vertical than in the parallel. Ultrasonic S-wave velocity is less than ultrasonic P-wave velocity.Ultrasonic S-wave attenuation is larger than ultrasonic P-wave attenuation. So,it is remarkable

16、 anisotropy on the same rock.Then, anisotropy is universal existence on underground rocks. The other,coefficient attenuation anisotropy is larger than coefficient velocity anisotropy.Which declare attenuation is more sensitive than velocity to rock anisotropy.It supplied important evidence for researching physical and mechanical property and structure feature of rocks or rock masses by resear