基于Mastersizer 2000的不同前处理方式对滑坡堰塞湖沉积物粒度特征的影响

EFFECTS OF DIFFERENT PRETREATMENT METHODS ON GRAIN SIZE CHARACTERISTICS OF SEDIMENTS FROM A LANDSLIDE-DAMMED LAKE BASED ON MASTERSIZER 2000

滑坡堵江形成的堰塞湖沉积物是很好的地质记录体,是古气候和古环境很好的“见证者和记录者”,而沉积物的粒度特征是普遍、常用且重要的解析指标,对其进行精确测量就显得格外重要。本研究以云南省永胜县下院滑坡堰塞湖沉积物10.5 m厚的剖面为研究对象,从顶至底共取得15层样品,对样品采用5种不同的前处理方法以后用Mastersizer 2000粒度仪对其粒度进行测量,对75个样品测试结果从粒度频率、平均粒径、分选系数、偏度、峰度分析等参数来分析不同前处理对粒度特征的影响。结果表明:粒度频率分布曲线随前处理方法不同而不同,但均呈单峰形态,沉积物颗粒物质来源单一,非多物源沉积;加分散剂会使部分样品分选系数小幅增大,但对平均粒径、偏度、峰度均没有明显影响,表明采用超声波振荡也可以有好的分散效果;在本研究低有机质含量的堰塞湖沉积物中采用过氧化氢(H_(2)O_(2))对有机质进行去除不会对平均粒径、分选系数、偏度和峰度产生显著影响;盐酸对粒度特征影响最为明显,特别是对于细粒沉积物,会使粒度整体变粗,20~50μm粒组颗粒含量大幅增加,使所有粘土质粉砂皆转为粉砂;添加盐酸会使分选系数减小,分选性变好;对低偏度的沉积物使其偏度增加,对高偏度沉积物则使其偏度减小;对低峰度沉积物使其峰度增加。结合矿物分析结果和其他粒度参数分析可知,受不同前处理方法的影响不同类型不同成土条件形成的土样颗粒特征不同,需选择适宜的方法对不同沉积物样品进行前处理,本研究中建议采用C方法对滑坡堰塞湖沉积物进行前处理。

Xiayuan ancient landslide-dammed lake,located in the southeastern of Qinghai-Tibetan Plateau and the northwest of Yunnan Province,is a good geological record and a good"witness and recorder"of paleoclimate and paleoenvironment.As we all know,the grain size characteristics of sediments are common,commonly used as the analytical indicators,so it's necessary to measure them accurately.In this paper,we taken Xiayuan landslide-dammed lake(26.12°N,100.55°E)in Yongsheng County,Yunnan Province as the research object and we aimed to find the most suitable pretreatment method for grain size of ancient landslide-dammed lake.We obtained a typical section of Xiayuan paleolandslide-dammed lake,the profile height is about 10.5 m,and divided it into 15 layers and taken samples.After five different pretreatment methods are adopted for the samples,the grain size is measured with Mastersizer 2000.The test results of 75 samples are analyzed from the parameters such as particle size frequency,average particle size,sorting coefficient,skewness and kurtosis analysis to analyze the influence of different pretreatment on particle size characteristics.The results show that the particle size frequency distribution curves vary with different pretreatment methods,but they all show a single peak shape.The source of sediment particulate matter is single and non multi-source deposition;The addition of dispersant will slightly increase the sorting coefficient of some samples,but it has no obvious effect on the average particle size,skewness and kurtosis,indicating that ultrasonic oscillation can also have a good dispersion effect;In the landslide-dammed lake sediments with low organic matter content,the removal of organic matter by H_(2)O_(2) will not have a significant impact on the average particle size,sorting coefficient,skewness and kurtosis;Hydrochloric acid has the most obvious effect on particle size characteristics,especially for fine-grained sediments,which will coarsen the particle size as a whole,20~50μm.The particle content of particle group increases greatly,which turns all clayey silt into silt;Adding hydrochloric acid will reduce the separation coefficient and improve the separation performance;For low skewness sediments,the skewness increases,while for high skewness sediments,the skewness decreases;For low kurtosis sediments,the kurtosis increased Combined with the mineral analysis and sem-scan results,we think hydrochloric acid dissolve fine particles and excesssive hydrochloric acid will cause condensation;On the other hand,it will change the microscopic morphology and structure of particles,so adding hydrochloric acid is not necessary for grain size pretreatment of ancient landslide-dammed lake.It can be seen that affected by different pretreatment methods,the particle characteristics of soil samples formed by different types and different soil forming conditions are different,so it is necessary to select appropriate methods for pretreatment of different sediment samples.In this paper,method C is suggested to be used for pretreatment of the sediments of landslide dammed lake.