CN106353357B - The monitoring device and method that sandy soil medium microscopical structure changes under a kind of seepage effect - Google Patents
The monitoring device and method that sandy soil medium microscopical structure changes under a kind of seepage effect Download PDFInfo
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- 238000012360 testing method Methods 0.000 claims abstract description 44
- 238000005481 NMR spectroscopy Methods 0.000 claims abstract description 28
- 239000004576 sand Substances 0.000 claims abstract description 25
- 238000012544 monitoring process Methods 0.000 claims abstract description 20
- 238000004458 analytical method Methods 0.000 claims abstract description 14
- 238000003384 imaging method Methods 0.000 claims abstract description 13
- 238000000685 Carr-Purcell-Meiboom-Gill pulse sequence Methods 0.000 claims abstract description 10
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Abstract
本发明公开了一种渗流作用下砂土介质细观结构变化的监测装置，包括核磁共振分析与成像系统和渗流系统，渗流系统包括水箱、试验固定装置、试样填充装置、测压管以及量筒；试样填充装置固定于核磁共振分析与成像系统内，一端连接水箱，一端连接收集装置；水箱固定于高处，试样填充装置两端设置有测压管。还公开了监测方法：逐渐改变水箱高度，对试样施加CPMG信号，根据核磁共振分析系统可得到试样T2谱，根据T2谱计算试样初始的物理性质；利用核磁共振成像系统扫描试样内部截面，得到砂土介质内部初始截面照片。该监测装置在渗流和监测过程中试样不发生任何移动，不需要反复拆卸装置，可完全实现无损实时检测，具有方便、可靠的优势。
The invention discloses a monitoring device for the mesoscopic structure change of sand medium under the action of seepage, which includes a nuclear magnetic resonance analysis and imaging system and a seepage system. The seepage system includes a water tank, a test fixture, a sample filling device, a piezometric tube and a measuring cylinder The sample filling device is fixed in the nuclear magnetic resonance analysis and imaging system, one end is connected to the water tank, and the other end is connected to the collection device; the water tank is fixed at a high place, and pressure measuring tubes are arranged at both ends of the sample filling device. The monitoring method is also disclosed: gradually change the height of the water tank, apply CPMG signals to the sample, obtain the T2 spectrum of the sample according to the nuclear magnetic resonance analysis system, and calculate the initial physical properties of the sample according to the T2 spectrum; use the nuclear magnetic resonance imaging system to scan the test sample The internal cross-section of the sample was obtained to obtain the initial cross-sectional photos of the sandy soil medium. The monitoring device does not have any movement of the sample during the seepage and monitoring process, does not need to repeatedly disassemble the device, can completely realize non-destructive real-time detection, and has the advantages of convenience and reliability.
Description
技术领域technical field
本发明属于岩土工程、水利工程技术领域，具体涉及一种渗流作用下砂土介质细观结构变化的监测装置，还涉及了其监测方法。The invention belongs to the technical fields of geotechnical engineering and water conservancy engineering, and in particular relates to a monitoring device for the change of the mesoscopic structure of sand medium under the action of seepage, and also relates to a monitoring method thereof.
背景技术Background technique
砂土介质材料广泛分布在自然界，且被大量运用为岩土工程材料，如地基基础材料、大坝坝壳料和边坡材料。研究表明由砂土介质材料组成的岩土结构经常发生渗透破坏(流土、管涌和颗粒水力侵蚀等)，从而发生地基失稳、边坡滑移等地质灾害。为预防此类地质灾害的发生，需了解砂土介质材料在渗流作用下结构的变化情况，从而提出相应预防措施。Sand medium materials are widely distributed in nature and are widely used as geotechnical engineering materials, such as foundation materials, dam shell materials and slope materials. Studies have shown that the rock-soil structure composed of sandy-soil medium materials often suffers seepage damage (flowing soil, piping, and granular hydraulic erosion, etc.), resulting in geological disasters such as foundation instability and slope slippage. In order to prevent the occurrence of such geological disasters, it is necessary to understand the structural changes of sandy soil media materials under the action of seepage, so as to put forward corresponding preventive measures.
对监测砂土介质材料结构变化的研究多为宏观试验和数值模拟试验。宏观试验多为砂土材料直剪试验和基础渗流试验等，监测粘滞系数、渗透系数等宏观参数的变化。并通过这些宏观参数反映砂土介质材料在渗流作用下的结构的变化情况。然而宏观试验大多不能做到实时、无损监测砂土介质的结构变化，并且细观结构参数(孔隙大小分布、自由水与束缚水的比例关系 、孔隙连通性等)相比宏观结构参数能更好反映砂土介质材料渗流作用下的结构变化情况。数值模拟试验虽能很好模拟砂土介质结构的变化情况，然而有些结构变化情况并不符合实际试验变化。因此有必要存在一种能实时、无损监测砂土介质细观变化的方法，预测渗流作用下砂土介质渗流破坏程度。Most of the studies on monitoring the structural changes of sandy media materials are macroscopic experiments and numerical simulation experiments. Most of the macro tests are direct shear tests of sandy soil materials and foundation seepage tests, etc., to monitor the changes of macro parameters such as viscosity coefficient and permeability coefficient. And through these macroscopic parameters reflect the change of the structure of the sand medium material under the action of seepage. However, most of the macroscopic tests cannot achieve real-time and non-destructive monitoring of the structural changes of the sand medium, and the mesoscopic structural parameters (pore size distribution, the ratio of free water to irreducible water , pore connectivity, etc.) can better reflect the structure of sand media materials under the action of seepage than macroscopic structural parameters. Changes. Although the numerical simulation test can simulate the change of the structure of the sandy soil medium well, some structural changes do not conform to the actual test changes. Therefore, it is necessary to have a real-time and non-destructive monitoring method for the mesoscopic changes of sandy soil media, so as to predict the seepage damage degree of sandy soil media under the action of seepage.
发明内容Contents of the invention
本发明的目的是提供一种渗流作用下砂土介质细观结构变化的监测装置。The purpose of the invention is to provide a monitoring device for the change of the mesoscopic structure of the sand medium under the action of seepage.
本发明的另一目的是提供采用上述装置的监测方法，解决了现有监测方法不能进行实时、无损监测砂土介质细观结构变化的问题。Another object of the present invention is to provide a monitoring method using the above-mentioned device, which solves the problem that the existing monitoring method cannot perform real-time and non-destructive monitoring of changes in the mesoscopic structure of the sand medium.
本发明所采用的技术方案是，一种渗流作用下砂土介质细观结构变化的监测装置，包括核磁共振分析与成像系统和渗流系统，渗流系统包括水箱、试验固定装置、试样填充装置、测压管以及量筒；试样填充装置固定于核磁共振分析与成像系统的信号采集系统内，一端与外部的水箱连接，另一端与外部的收集装置连接；水箱通过试验固定装置固定于高处，试样填充装置两端设置有测压管。The technical solution adopted in the present invention is a monitoring device for the change of the mesoscopic structure of the sand medium under the action of seepage, including a nuclear magnetic resonance analysis and imaging system and a seepage system. The seepage system includes a water tank, a test fixture, a sample filling device, Pressure measuring tube and measuring cylinder; the sample filling device is fixed in the signal acquisition system of the nuclear magnetic resonance analysis and imaging system, one end is connected to the external water tank, and the other end is connected to the external collection device; the water tank is fixed at a high place through the test fixture, Pressure measuring tubes are arranged at both ends of the sample filling device.
本发明的特点还在于：The present invention is also characterized in that:
试验固定装置具有可调节水箱高度的结构。The test fixture has a structure that can adjust the height of the water tank.
水箱内部设置隔板。A partition is arranged inside the water tank.
试样填充装置的进水口和出水口设有过滤纱网。The water inlet and outlet of the sample filling device are provided with filter gauze.
核磁共振分析与成像系统内设置有用于固定试样填充装置的固定板夹。The nuclear magnetic resonance analysis and imaging system is provided with a fixing plate clamp for fixing the sample filling device.
本发明所采用的另一个技术方案是，一种渗流作用下砂土介质细观结构变化的监测方法，使用上述检测装置，包括以下步骤：Another technical solution adopted in the present invention is a monitoring method for the change of the mesoscopic structure of the sand medium under the action of seepage, using the above-mentioned detection device, comprising the following steps:
步骤1，测试准备Step 1, Test Preparation
将砂土介质按土工试验填入试样填充装置，试样填充装置连接水箱、量筒和测压管，通水排气后将试样填充装置放入核磁共振信号采集系统中；对试样施加水力坡降至试样处于完全饱和状态；Fill the sand medium into the sample filling device according to the geotechnical test. The sample filling device is connected to the water tank, measuring cylinder and piezometric tube. After passing water and exhaust, put the sample filling device into the nuclear magnetic resonance signal acquisition system; Hydraulic ramp down The sample is fully saturated ;
步骤2，测试砂土介质初始结构特性Step 2, testing the initial structural properties of sandy soil media
对试样施加CPMG(可排除磁场均匀性干扰的脉冲序列)信号，根据核磁共振分析系统可得到试样T2谱(自旋弛豫时间)，根据T2谱计算试样初始的物理性质；利用核磁共振成像系统扫描试样内部各截面，得到砂土介质内部初始截面图像；Apply CPMG (pulse sequence that can eliminate the interference of magnetic field uniformity) signal to the sample, according to the nuclear magnetic resonance analysis system, the T2 spectrum (spin relaxation time) of the sample can be obtained, and the initial physical properties of the sample can be calculated according to the T2 spectrum; Use the nuclear magnetic resonance imaging system to scan the internal sections of the sample to obtain the initial cross-sectional image of the sandy soil medium;
步骤3，测试砂土介质不同水力坡降下的结构特性Step 3, testing the structural properties of sandy soil media under different hydraulic gradients
按一定梯度依次提高水箱高度，以获得逐渐增大的水力坡降，并在施加水力坡降相同时间后，对试样再一次施加CPMG信号和扫描试样内部各截面，从而得到不同水力坡降下砂土介质的结构特性；Increase the height of the water tank sequentially according to a certain gradient to obtain a gradually increasing hydraulic gradient, and after applying the hydraulic gradient for the same time, apply the CPMG signal to the sample again and scan the internal sections of the sample to obtain different hydraulic gradients. Structural properties of sandy soil media;
步骤4，测试砂土介质最大水力坡降的结构特性Step 4, Test the structural characteristics of the maximum hydraulic gradient of the sandy soil medium
在最大水力坡降下，在不同的时间下，对试样施加CPMG信号和核磁共振成像系统扫描试样内部截面，得到该水力坡降下不同时间段砂土介质的结构特性；Under the maximum hydraulic gradient, at different times, the CPMG signal is applied to the sample and the nuclear magnetic resonance imaging system scans the internal section of the sample to obtain the structural characteristics of the sandy soil medium in different time periods under the hydraulic gradient;
步骤5，分析步骤2-4得到的试验数据，获得砂土介质不同水力坡降下细观结构的变化情况。Step 5, analyze the test data obtained in steps 2-4, and obtain the change of the mesoscopic structure of the sandy soil medium under different hydraulic gradients.
本发明的有益效果是，本发明的监测装置借助了核磁共振的优势，能快速、无损监测多孔介质孔隙信息，并且从细观角度出发，得到砂土介质孔隙分布、连通性、内部界面孔隙分布等细观参数，相比宏观角度更合理揭示砂土介质的渗流过程。该监测装置使渗流装置融合在监测装置内部，渗流和监测过程中试样不发生任何移动，不需要反复拆卸装置，可完全实现无损实时检测。在不同工况下连续测量试样的信息，具有方便、可靠的优势。The beneficial effect of the present invention is that the monitoring device of the present invention can quickly and non-destructively monitor the pore information of porous media by virtue of the advantages of nuclear magnetic resonance, and obtain the pore distribution, connectivity, and internal interface pore distribution of sandy soil medium from a microscopic point of view. Compared with the macroscopic perspective, it is more reasonable to reveal the seepage process of sandy soil media. The monitoring device integrates the seepage device inside the monitoring device, and the sample does not move during the seepage and monitoring process, and does not need to repeatedly disassemble the device, which can completely realize non-destructive real-time detection. Continuous measurement of sample information under different working conditions has the advantages of convenience and reliability.
附图说明Description of drawings
图1是本发明监测装置的结构示意图；Fig. 1 is the structural representation of monitoring device of the present invention;
图2是本发明监测方法的流程图；Fig. 2 is the flowchart of monitoring method of the present invention;
图3是实施例砂土混合体不同水力坡降下孔隙分布；Fig. 3 is the pore distribution under the different hydraulic gradients of the sand-soil mixture of the embodiment;
图4是实施例砂土混合体同一水力坡降下孔隙分布；Fig. 4 is the pore distribution under the same hydraulic gradient of the embodiment sand-soil mixture;
图5是实施例砂土混合体在最大水力坡降下不同时间段砂土混合体孔隙分布；Fig. 5 is the pore distribution of the sand-soil mixture of the embodiment in different time periods under the maximum hydraulic gradient;
图6是实施例砂土混合体总孔隙、自由水孔隙与渗透率的关系；Fig. 6 is the relation of embodiment sand-soil mixture total porosity, free water porosity and permeability;
图7是实施例砂土混合体总孔隙和自由水孔隙随时间变化关系。Fig. 7 is the relationship between total pores and free water pores of the sand-soil mixture as a function of time.
图中，1.水箱，2.信号发射装置，3.梯度装置，4.温控装置，5.水管，6.测压管，7.核磁共振分析与成像系统，8.核磁共振信号采集系统，9.试样填充装置，10.量筒。In the figure, 1. Water tank, 2. Signal transmitting device, 3. Gradient device, 4. Temperature control device, 5. Water pipe, 6. Pressure measuring tube, 7. Nuclear magnetic resonance analysis and imaging system, 8. Nuclear magnetic resonance signal acquisition system , 9. Sample filling device, 10. Graduated cylinder.
具体实施方式Detailed ways
下面结合附图和具体实施方式对本发明作进一步的详细说明，但本发明并不限于这些实施方式。The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited to these embodiments.
本发明的监测装置如图1所示，包括核磁共振分析与成像系统和渗流系统，核磁共振分析与成像系统7包括核磁共振信号采集系统8、梯度装置3、温控装置4以及信号发射装置2，渗流系统包括水箱1、试验固定装置、试样填充装置9、测压管6以及量筒10。试样填充装置9位于核磁共振信号采集系统8内，且核磁共振信号采集系统内有固定装置保证试样填充装置不发生移动，一端通过软管5与位于核磁共振系统外的水箱1连接，另一端通过软管与位于核磁共振系统外的量筒10连接。水箱1通过试验固定装置固定于高处，水流从试样填充装置9一端流入，从试样填充装置另一端流出的水流进入量筒。测压管6设置于试样填充装置两端，用于检测进出水管压力变化。试验固定装置可根据水力坡降要求自由调节高度，使得水箱提供符合要求的水量。水箱内部隔板能保证水箱相对水位恒定。试样填充装置9固定在本装置中实施在线无损监测，需注意渗漏、试验前期排气及试样填充装置移动等问题。本装置进出水口和填充区采用螺纹和特殊橡皮垫(防渗性能较好)连接，防止试样填充装置漏水，且螺纹连接有利于试验填充。本装置把测压管作为试验前期排气，解决试验前期排气问题。为保证试样填充装置再监测过程不发生移动，在试样填充装置前后设有用于固定填充装置的固定装置，固定装置为2个机玻璃材质的固定夹板，利用固定夹板夹住核磁共振信号采集系统，利用前后夹板抵住填充装置，使其固定。为保证试验过程中，砂土因冲刷淤堵在试样填充装置的进出水口和软管，进出水口设有过滤纱网。As shown in Figure 1, the monitoring device of the present invention includes a nuclear magnetic resonance analysis and imaging system and a percolation system, and the nuclear magnetic resonance analysis and imaging system 7 includes a nuclear magnetic resonance signal acquisition system 8, a gradient device 3, a temperature control device 4 and a signal transmitting device 2 , The seepage system includes a water tank 1 , a test fixture, a sample filling device 9 , a piezometric tube 6 and a measuring cylinder 10 . The sample filling device 9 is located in the nuclear magnetic resonance signal acquisition system 8, and there is a fixed device in the nuclear magnetic resonance signal acquisition system to ensure that the sample filling device does not move. One end is connected to the water tank 1 located outside the nuclear magnetic resonance system through a hose 5, and the other is One end is connected with the graduated cylinder 10 located outside the nuclear magnetic resonance system through a flexible pipe. The water tank 1 is fixed on a high place by the test fixture, the water flows in from one end of the sample filling device 9, and the water flowing out from the other end of the sample filling device enters the measuring cylinder. Pressure measuring tubes 6 are arranged at both ends of the sample filling device, and are used to detect pressure changes in the water inlet and outlet pipes. The test fixture can freely adjust the height according to the hydraulic gradient requirements, so that the water tank can provide the required water volume. The internal partition of the water tank can ensure that the relative water level of the water tank is constant. The sample filling device 9 is fixed in this device for online non-destructive monitoring, and attention should be paid to problems such as leakage, exhaust in the early stage of the test, and movement of the sample filling device. The water inlet and outlet of the device and the filling area are connected by threads and special rubber pads (good anti-seepage performance) to prevent water leakage from the sample filling device, and the threaded connection is conducive to test filling. This device uses the pressure measuring tube as the exhaust in the early stage of the test to solve the problem of exhaust in the early stage of the test. In order to ensure that the sample filling device does not move during the re-monitoring process, a fixing device for fixing the filling device is provided before and after the sample filling device. The fixing device is two machine glass fixed splints, and the NMR signal acquisition is clamped by the fixed splints. system, using the front and rear splints against the filling device to hold it in place. In order to ensure that during the test, the sandy soil is blocked by the water inlet and outlet of the sample filling device and the hose due to scouring, and the water inlet and outlet are provided with filter gauze.
采用上述装置监测渗流作用下砂土介质细观结构变化的方法如图2所示：The method of using the above-mentioned device to monitor the change of the mesostructure of the sand medium under the action of seepage is shown in Figure 2:
步骤1，测试准备Step 1, Test Preparation
采用70％砂子、30％黏土的砂土混合体作为试样，将试样按土工试验填入试样填充装置，试样填充装置上连接水箱、量筒和测压管，通水排气后将试样填充装置放入核磁共振信号采集系统中。对试样施加0-1.5的水力坡降，通水4h以上让试样处于完全饱和状态(小水力坡降不至于改变砂土介质性质)。A sand-soil mixture of 70% sand and 30% clay is used as the sample, and the sample is filled into the sample filling device according to the geotechnical test. The sample filling device is connected with a water tank, a measuring cylinder and a pressure measuring tube. The sample filling device is put into the nuclear magnetic resonance signal acquisition system. Apply a hydraulic gradient of 0-1.5 to the sample, and pass the water for more than 4 hours to make the sample in a fully saturated state (a small hydraulic gradient will not change the properties of the sand medium).
步骤2，测试砂土介质初始结构特性Step 2, testing the initial structural properties of sandy soil media
然后对试样施加CPMG信号，根据MesoMR23-060H-I中尺寸核磁共振分析系统可得到试样T2谱，试样T2谱类似于试样孔隙分布，且T2值与孔隙直径有如下关系：Then the CPMG signal is applied to the sample, and the sample T2 spectrum can be obtained according to the MesoMR23-060H-I medium-sized nuclear magnetic resonance analysis system. The sample T2 spectrum is similar to the sample pore distribution, and the T2 value has the following relationship with the pore diameter:
r＝cT2 r=cT 2
其中r为孔隙直径；c为变换系数(um/ms)，可通过恒速压汞试验测得。Where r is the pore diameter; c is the conversion coefficient (um/ms), which can be measured by constant-speed mercury porosimetry.
再根据T2谱计算试样的其他物理性质，孔隙率、NMR渗透率以及自由水含量等信息。Then other physical properties of the sample, such as porosity, NMR permeability and free water content, were calculated according to the T2 spectrum.
再利用MesoMR23-060H-I中尺寸核磁共振成像系统扫描试样内部截面，得到砂土介质内部截面成像。以此得到初始时刻砂土介质的结构特性。Then use the MesoMR23-060H-I medium-sized nuclear magnetic resonance imaging system to scan the internal cross-section of the sample to obtain the internal cross-sectional imaging of the sandy soil medium. In this way, the structural characteristics of the sandy soil medium at the initial moment can be obtained.
步骤3，测试砂土介质不同水力坡降下的结构特性Step 3, testing the structural properties of sandy soil media under different hydraulic gradients
按一定梯度依次提高水箱高度，以获得逐渐增大的水力坡降，并在施加水力坡降相同时间后，对试样再一次施加CPMG信号和扫描试样内部截面，从而得到不同水力坡降下砂土介质的结构特性。Increase the height of the water tank sequentially according to a certain gradient to obtain a gradually increasing hydraulic gradient, and after applying the hydraulic gradient for the same time, apply the CPMG signal to the sample again and scan the internal cross-section of the sample, so as to obtain different hydraulic gradients. Structural properties of soil media.
步骤4，测试砂土介质最大水力坡降的结构特性Step 4, Test the structural characteristics of the maximum hydraulic gradient of the sandy soil medium
在最大水力坡降下，在不同的时间下对试样施加CPMG信号和核磁共振成像系统扫描试样内部截面，得到该水力坡降下不同时间段砂土介质的结构特性。Under the maximum hydraulic gradient, the CPMG signal is applied to the sample at different times and the MRI system scans the internal section of the sample to obtain the structural characteristics of the sandy soil medium at different time periods under the hydraulic gradient.
步骤5，分析步骤2-4得到的试验数据，获得砂土介质不同水力坡降下细观结构的变化情况。Step 5, analyze the test data obtained in steps 2-4, and obtain the change of the mesoscopic structure of the sandy soil medium under different hydraulic gradients.
本装置主要优势体现在，不需要反复拆卸装置，可使渗流装置与监测装置融合成一个装置，渗流和监测过程中试样不发生任何移动，可完全实现无损实时检测。The main advantage of this device is that it does not need to repeatedly disassemble the device, and the seepage device and the monitoring device can be integrated into one device. The sample does not move during the seepage and monitoring process, and non-destructive real-time detection can be completely realized.
为了说明本发明的装置和方法能够实现实时无损监测，进行以下实验。In order to illustrate that the device and method of the present invention can realize real-time non-destructive monitoring, the following experiments were carried out.
选取自然界常见的砂土混合体，按照土工击实试验，制备重塑试样。为保证重塑试样的性质接近原状砂土混合体性质，制作的试样时不可以改变砂石的含量比、级配等其他性质，制作之后养护28天，以提高重塑土中自由水转化为结合水的概率，让重塑砂土的强度接近原状砂土。其中砂子与黏土重量比例为7:3，黏土直径范围为0-2.25mm，砂子直径范围为1-2.5mm。试样高度为55mm，直径45mm，试样数量为6个。对6个试样进行平行试验，对比6组试验结果，选取最具有代表性一组试验数据进行分析。Select the common sand-soil mixture in nature, and prepare remodeling samples according to the geotechnical compaction test. In order to ensure that the properties of the remolded sample are close to those of the original sand-soil mixture, the content ratio, gradation and other properties of the sand and gravel cannot be changed when making the sample. The probability of converting into bound water makes the strength of the remolded sand close to the original sand. The weight ratio of sand to clay is 7:3, the diameter range of clay is 0-2.25mm, and the diameter range of sand is 1-2.5mm. The height of the sample is 55mm, the diameter is 45mm, and the number of samples is 6. Parallel tests were carried out on 6 samples, the test results of 6 groups were compared, and the most representative group of test data was selected for analysis.
MesoMR23-060H-I中尺寸核磁共振分析与成像系统参数为：TE(90脉冲中心到回波中心的时间间隔)＝0.6ms,TW(重复采样等待时间)＝4s，echo numbers(180度射频脉冲个数)＝8000，scanning numbers(扫描次数)＝64，仪器内部系统温度稳定32℃。成像slieswidth(选层层厚)＝3mm。MesoMR23-060H-I medium size NMR analysis and imaging system parameters are: TE (time interval from 90 pulse center to echo center) = 0.6ms, TW (re-sampling waiting time) = 4s, echo numbers (180 degree radio frequency pulse Number) = 8000, scanning numbers (scanning times) = 64, the internal system temperature of the instrument is stable at 32°C. Imaging slieswidth (thickness of selected layers) = 3mm.
本实验中，试样填充装置的进水口和出水口直径为4mm，试样填充区高50mm、直径45mm。试验固定装置的固定结构主体呈棱台形状，高2.9m、上长0.6m、下长2.1m、宽1.5m，左侧有一扶梯用于检修，固定结构主体顶部固定有用于调节水箱高度的滑轮，滑轮沉重上限为1.5t。水箱尺寸为300×300×300mm，水箱的进水口位于水箱右侧面底部，出水口位于水箱底面中间部位，用于给试样提供水力坡降的稳定水位出水口位于水箱左侧面距底面203mm，进水口和出水口直径12mm。水箱可调节高度为0.9m-2.6m。In this experiment, the diameter of the water inlet and water outlet of the sample filling device is 4mm, the height of the sample filling area is 50mm, and the diameter is 45mm. The main body of the fixed structure of the test fixture is in the shape of a prism, with a height of 2.9m, an upper length of 0.6m, a lower length of 2.1m, and a width of 1.5m. There is an escalator on the left side for maintenance, and a pulley for adjusting the height of the water tank is fixed on the top of the fixed structure main body. , The upper limit of pulley weight is 1.5t. The size of the water tank is 300×300×300mm. The water inlet of the water tank is located at the bottom of the right side of the water tank, and the water outlet is located in the middle of the bottom of the water tank. It is used to provide a stable water level for the sample to provide a hydraulic gradient. The outlet is located on the left side of the water tank and is 203mm from the bottom. , The diameter of the water inlet and outlet is 12mm. The adjustable height of the water tank is 0.9m-2.6m.
按本发明试验步骤，对样品施加10、15、18、20和23水力坡降，测量不同水力坡降下砂土介质材料细观结构。在水力坡降为23下，测量15min、60min、90min、150min和180min下砂土介质材料细观结构。According to the test procedure of the present invention, 10, 15, 18, 20 and 23 hydraulic gradients are applied to the sample, and the mesoscopic structure of the sand medium material under different hydraulic gradients is measured. Under the hydraulic gradient of 23, the mesoscopic structure of the sand medium material was measured for 15min, 60min, 90min, 150min and 180min.
实验结果如下。The experimental results are as follows.
图3是砂土混合体不同水力坡降下孔隙分布，由图3可知砂土混合体T2谱存在三峰，左锋代表微小孔隙，中锋代表中等孔隙，右锋代表大孔隙和裂隙。可知砂土介质孔隙发育良好，存在大量微小孔隙和中等孔隙，且孔隙连通性较好。随着水力坡降增加，峰面积增大，峰向右推。可知各孔隙类型体积都有一定程度增加，孔隙直径变大和连通性变好，且砂土介质颗粒粘聚力下降。Figure 3 shows the pore distribution of the sand-soil mixture under different hydraulic gradients. It can be seen from Figure 3 that there are three peaks in the T2 spectrum of the sand-soil mixture. The left front represents small pores, the center represents medium pores, and the right front represents large pores and cracks. It can be seen that the pores of the sand medium are well developed, there are a large number of micro pores and medium pores, and the connectivity of the pores is good. As the hydraulic gradient increases, the peak area increases and the peak is pushed to the right. It can be seen that the volume of each pore type increases to a certain extent, the pore diameter becomes larger and the connectivity becomes better, and the cohesion of the sand medium particles decreases.
图4是砂土混合体在水力坡降等于23的情况下，不同时间段砂土混合体孔隙分布。由图4知孔隙体积和孔隙数量随着时间增加而增加，且时间越长越明显，大孔隙明显变多，且孔隙直径变大(T2值右移)。Figure 4 shows the pore distribution of the sand-soil mixture in different time periods when the hydraulic gradient is equal to 23. It can be known from Figure 4 that the pore volume and pore number increase with time, and the longer the time, the more obvious the large pores are, and the pore diameter becomes larger (T 2 value shifts to the right) .
在渗流过程中，水压力扩张孔隙，使孔隙数量变多和孔隙体积变大，导致孔隙连通性变好以及介质颗粒粘聚力变小。在较大水力坡降下，时间越长，砂土介质出现裂隙，小颗粒冲刷出孔隙等现象。During the seepage process, the water pressure expands the pores, increasing the number of pores and increasing the pore volume, resulting in better pore connectivity and smaller cohesion of media particles. Under a larger hydraulic gradient, the longer the time, the sand medium will have cracks, and the small particles will wash out the pores.
表1砂土混合体渗流过程细观变化情况Table 1 Mesoscopic changes in the seepage process of sand-soil mixture
表1为砂土混合体渗流过程中总孔隙、自由水孔隙与渗透率变化情况。由表可知总孔隙、自由水孔隙与渗透率都有一定增长。Table 1 shows the changes of total pores, free water pores and permeability during the seepage process of sand-soil mixture. It can be seen from the table that the total pores, free water pores and permeability all have a certain increase.
图5是砂土混合体总孔隙、自由水孔隙与渗透率的关系。由表1和图5可知：孔隙和介质渗透率存在指数关系，在低孔隙阶段渗透率增长较慢，随着孔隙增多渗透率增长速率加大。且自由水孔隙对渗透率的影响比结合水大。图6是砂土混合体总孔隙和自由水孔隙随时间变化关系。在渗流作用180min下，总孔隙和自由水孔隙增长不大，但渗透率增长明显。Figure 5 shows the relationship between total pores, free water pores and permeability of sand-soil mixture. It can be seen from Table 1 and Figure 5 that there is an exponential relationship between the pores and the permeability of the medium, and the permeability increases slowly at the stage of low porosity, and the growth rate of the permeability increases with the increase of pores. And the influence of free water pores on permeability is greater than that of bound water. Figure 6 shows the relationship between the total pores and free water pores of the sand-soil mixture over time. After seepage for 180 minutes, the total pores and free water pores did not increase much, but the permeability increased significantly.
由上可知，砂土混合体在渗流作用下孔隙数量增多，且孔隙直径和体积变大，导致混合体孔隙连通性变好，渗流通道变多以及混合体颗粒间粘聚力变小，从而渗透率上升以及颗粒被拖拽，加速了混合体的渗透破坏。同时得到混合体的孔隙-渗透率的关系以及随时间变化情况，以此可以通过细观结构变化预测砂土混合体的破坏程度等信息。It can be seen from the above that the number of pores in the sand-soil mixture increases under the action of seepage, and the diameter and volume of the pores become larger, resulting in better connectivity of the pores of the mixture, more seepage channels, and smaller cohesion between the particles of the mixture, thereby infiltrating The rate rises and the particles are dragged, accelerating the osmotic destruction of the mixture. At the same time, the relationship between the pore-permeability of the mixture and the change with time can be obtained, so that information such as the degree of damage of the sand-soil mixture can be predicted through the change of the mesostructure.
图7是水力坡降等于23的情况下，不同时间段砂土混合体内部界面孔隙分布图。其中黑色为幕布、白色代表孔隙。白色范围越多且越亮代表孔隙越大且连通性越好。由图可知孔隙体积和孔隙数量随着时间增加而增加且时间越长越明显，孔隙连通性显著提高，且孔隙分布变大。Fig. 7 is a diagram of the internal interface pore distribution of the sand-soil mixture at different time periods when the hydraulic gradient is equal to 23. The black is the curtain, and the white is the pore. More and brighter white ranges represent larger pores and better connectivity. It can be seen from the figure that the pore volume and pore number increase with time, and the longer the time, the more obvious, the pore connectivity is significantly improved, and the pore distribution becomes larger.
由以上实验可看出，本发明装置做到了实时在线监测，可在不同时间段对试样进行无损检测，且渗流过程不被打断(反复中断渗流过程，不符合天然砂土介质渗流规律)；在测量精度上，本发明在渗流和监测过程中试样不发生任何移动，可以监测试样不同工况同一断面的孔隙变化，且试样始终饱和状态，测量的细观结构参数更精确。本发明装置操作简单，拥有实时无损监测优势。It can be seen from the above experiments that the device of the present invention has achieved real-time online monitoring, and can perform non-destructive testing on samples at different time periods, and the seepage process will not be interrupted (repeatedly interrupting the seepage process does not conform to the seepage law of natural sandy soil media) In terms of measurement accuracy, the present invention does not move the sample during the seepage and monitoring process, and can monitor the pore changes of the same section of the sample under different working conditions, and the sample is always in a saturated state, and the measured mesostructure parameters are more accurate. The device of the invention is simple to operate and has the advantage of real-time non-destructive monitoring.
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| CN104034745B (en) * | 2014-06-30 | 2016-09-07 | 中国科学院武汉岩土力学研究所 | A high-pressure nuclear magnetic resonance CO2 geological storage model test system |
| CN105891248A (en) * | 2015-04-17 | 2016-08-24 | 北京大学 | On-line testing device for high temperature and high pressure rock physical property and percolation mechanism nuclear magnetic resonance |
| CN205280545U (en) * | 2015-12-07 | 2016-06-01 | 西安理工大学 | Seepage tests sand post or earth pillar suitable for nuclear magnetic resonance analysis and imaging system |
| CN105973781A (en) * | 2016-04-27 | 2016-09-28 | 重庆大学 | Stress-chemical coupling visualization testing system for laminated salt rock |
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