水平成层场地动力特性研究

為了探究地震波作用下水平成層場地的動力響應特徵，設計並開展了水平成層場地的大型振動台模型試驗，並基於希爾伯特-黃變換對水平成層場地在時域和頻域的響應進行了研究．研究結果表明：地震波在水平成層場地內自下而上傳播過程中被放大，場地表層碎石土層對地震波的放大效應強於下覆軟岩層和硬岩層，碎石土層加速度放大係數達到5.94；地震波從硬岩層傳入軟岩層時，高頻成分（27~40Hz）被吸收，低頻成分（0~22Hz）被放大，地震波從軟岩層傳入碎石土層時，7~27Hz頻段進一步被放大，同時，碎石土層內的地震波表現出雙卓越週期特性；反應譜峰值隨著輸入地震波幅值的增大而增大；軟岩地層在反應譜週期T≤0.3s部分錶現出衰減效應，在周期T>0.3s 部分，自下而上3個地層的反應譜表現出放大效應；碎石土層／軟岩層分界面對地震波能量具有一定的聚集和放大作用；軟岩層／硬岩層分界面對地震波的能量僅僅表現為聚集作用；在碎石土層內，地震波的能量被放大，Hilbert能量譜由單峰發展為三峰，峰值在時間軸上向坐標軸正方向發散，在頻率軸上由低頻向高頻移動. A large scale shaking table test of horizontal layered site was conducted, and based on which the seismic response of horizontal layered site was researched in this paper. The research results show that: the seismic wave is amplified when propagating from bottom to top of test model, the amplification effect in gravel soil layer is stronger than that in soft rock layer and hard rock layer, and the acceleration amplification factor in the gravel soil layer reaches 5.94. In the propagation process of seismic wave from hard rock layer to soft rock layer, the high-frequency components with 27-40 Hz are absorbed and the frequency components with 0-22 Hz are amplified, in the propagation process of seismic wave from soft rock layer to gravel soil layer, the frequency components with 7-27 Hz are amplified further. Meanwhile, the seismic wave in the gravel soil layer presents two predominant periods. The peak values of the response spectra increase with the input seismic wave amplitude. At the same time, the seismic wave in gravel soil layer has two predominant periods. The peak values of response spectra increase with increasing the input seismic wave amplitude. The soft rock layer presents attenuation effect at the period T≤0.3 s of response spectrum, while at the period T>0.3 s, the response spectrum presents amplification effect from hard rock layer to gravel soil layer. The interface between gravel soil layer and hard rock layer will gather and amplify the energy of earthquake wave, while the interface between soft rock layer and hard rock layer will just gather the energy of seismic wave. In the gravel soil layer, the energy of earthquake wave is amplified and the Hilbert energy spectrum develops to have three peaks, the peaks of Hilbert energy spectra divulge to the forward direction of time axis, and move to high frequency part from low frequency part in frequency axis. © 2016, Editorial Department of Journal of Southwest Jiaotong University. All right reserved

藏北高原高寒草甸地上生物量与气候因子的关系

采用收获法测量了藏北不同海拔高度(4300~4700m)2010年(6~8月)嵩草草甸群落地上总生物量,通过相关分析和多重回归分析法探讨了地上生物量与土壤温度、土壤含水量、空气温度、相对湿度、饱和水汽压亏缺以及比湿的关系。结果表明:总体而言,随着海拔高度的升高地上生物量逐渐增加,地上生物量与相对湿度、比湿以及土壤含水量分别呈极显著的正相关关系,与饱和水汽压亏缺呈极显著的负相关关系,而与土壤温度、空气温度呈不显著的负相关关系;相对湿度和饱和水汽压亏缺共同解释了地上生物量94%的变异,其中相对湿度的贡献较大。相对湿度是决定高寒嵩草草甸沿海拔分布的主导因子