综合利用多道瞬态面波和微动探测分析斜坡内部结构

Analyses of internal structure of slopes using multi-channel transient surface wave exploration and microtremor survey

针对杭州部分地区残坡积层厚度薄、地形条件较差的特点,在余杭区鸬鸟镇典型斜坡段,开展了多道瞬态面波和微动探测工作,对这二项技术在斜坡内部结构调查中的适用性和有效性进行分析。分别基于频率—波数(F-K)和空间自相关(SPAC)法提取频散曲线,计算得到速度剖面,进而对表层含角砾粉质黏土、全风化凝灰岩、强风化凝灰岩及中—微风化凝灰岩之间的界面进行了划分。结果表明:面波勘探具有很好的分层性,能有效区分残坡积层覆盖斜坡内部结构;多道瞬态面波和微动探测计算得到的瑞利波相速度变化趋势一致,表层含角砾粉质黏土对应瑞利波相速度小于300 m/s,全风化凝灰岩对应瑞利波相速度为300~400 m/s,强风化凝灰岩对应瑞利波相速度为400~600 m/s,与钻孔资料基本吻合。数据分析还表明,频率小于15 Hz时,微动探测空间自相关函数与第一类零阶贝塞尔函数具有很好的拟合关系,高于15 Hz时,拟合精度有所降低。

According to the characteristics of thin eluvium and poor topographic conditions in research area,this paper analyzes the suitability and effectiveness of multi-channel transient surface wave and microtremor survey technology in investigating slope internal structure of the typical slope in Luniao Town,Yuhang District,Hangzhou Ctity.The dispersion curve is extracted using frequency-wave number(F-K)and spatial autocorrelation method(SPAC).Based the velocity profile,the surface silty clay with breccia,completely weathered tuff,strongly weathered tuff and medium-slightly weathered tuff is interpreted.The results show that the surface wave exploration can effectively distinguish the internal structure of slope covered by thin eluvium.Both multi-channel transient surface wave and microtremor survey have a high accuracy in depth interpretation of the interface between strongly weathered and medium-slightly weathered tuff,which is well consistent with the borehole data,and there is a little bit of error in depth interpretation of the interface between surface silty clay with breccia and completely weathered tuff.The data analysis also shows that the fitting relationship between spatial autocorrelation function and Bessel function J 0 is good when frequency less than 15 Hz,and the accuracy lose when it is higher than 15 Hz.Furthermore,the microtremor survey velocity is generally lower than the multi-channel transient surface waves exploration velocity.