"5 12"汶川地震震后龙门山山前地表塌陷成因探讨

应用NND有限差分格式求解轴对称可压缩N-S方程，研究了不同驻室与 环境压力比条件下欠膨胀超声速射流近场的失稳特性. 计算结果表明欠膨胀超声速射流的失 稳机制根据射流激波结构的特征可分为3种失稳模式：具有规则反射激波结构和单一剪切层 特征的射流不稳定性；带有马赫反射激波结构和双剪切层特征的射流不稳定性；具有弯曲马 赫杆和高度欠膨胀射流的不稳定性. 对于欠膨胀超声速射流，沿射流方向重复出现拟周期性 的射流激波结构是射流稳定发展的特征，这种射流激波结构的消失是射流开始失稳的标志.

DISCUSSIONS ON POSSIBLE CAUSES OF THE FORMATION OF MORE THAN FIFTY GROUND COLLAPSE PITS IN ANXIAN COUNTY IN FRONT OF LONGMENSHAN AFTER THE 5. 12WENCHUAN EARTHQUAKE

Mo re than fifty ground co llapse pits w ere formed in succession about 20 days after the " 5. 12" Wen chuan Great E arthquake. They w ere in Lijiayuanzh i v illage at the southeastern o fAnchang town, Anx ian county in front o f Longmen Shan. This paper ana lyzes the possib le reasons o f the p it fo rmation using the propert ies o f strata, rock, g roundw ater, erosion and topso i.l Primarily, it w as the pre- cond ition that the ca lcareous cemented sandy cong lom erate of Jurassic period presented below the g round surface. The rock co llapse and excess porew ater pres sure caused by serious seism ic groundmo tion w ere the start- up factors. A ftershocks resu lted in the emergence and deve lopment of so il holes. Furthermore, groundw ater change acce lerated th is process. Las,t the soil eng ineering properties determ ined the shape o f the pits. A t the same t ime, this paper a lso pays attent ion to other possible rea sons inc lud ing buried fault activ ity and soil particle loss due to groundw ater flow. The paper presents the relavant background evidences. It is desirab le that th is paperwould bring some innovative ideas to find out the real reasons of the p it format ion.