湿陷性黄土的强夯震动观测

OBSERVATION ON VIBRATION FROM POWERFUL RAMMER IN SOAKING SETTLING LOESS

摘要:

利用5-40吨的重锤从10-40米高空自由下落的冲力,对软弱地基进行强夯处理以达到加固的作用,是国外在六十年代末期开始采用的方法。这种方法的优点在于简便易行,成本低,效率高,效果好。我国在这方面也取得了一定的经验,但在处理湿陷性黄土方面,尚缺乏经验。尤其像兰州这样地处西北黄土高原、位于黄河谷地的老城,在城中使用强夯法时对附近的各种建筑物是否可能造成直接破坏或影响、其破坏与影响的程度和范围有多大、有无预防措施等,都需要从实验中摸索。这就是本文所述强夯震动观测的目的。

Abstract:

Strengthening the foundation soil with the powerful rammer has been developed for the last 20 years.This method has gradually been emplo-yed in China since the 1970s,and during this period some results of experiment were informed but there is still not enough experience now for strengthening the soaking setting loess and for the restruction of the old urban area in cities.This is just the object for which this pa-per is written.
Two construction sites in Lanzhon were chosen for obstruction on the Vibration effects from the powerful rammer.Observation was carried out along several sections.Among them some sections are across shocking protective ditches with different width and depth.
The results of abservation are as follows:
1.Both displacement and acceleration on soaking settling loess from the powerful rammer increase with the subseqttence of driving rammer and rapidly reduce with the distance.and the attenuation of displace-ment in radial direction is faster than that of acceleration.The chara-cteristics of attenuation of displacement and acceleration on the ident-ical point are different from each other.
2.when the depth of the shocking protective ditch is greater than 2 m and its length is 5 meters more than the dimension of structures,its pretecting effects from shocking are obvious,especially for horizontal vibration in radial direction the effects of the protective are not dep-endent on its width.
3.It is effective to strengthen the soaking settling loess by employing the powerful rammer.The experiment shows that the effective depth of strengthening is 3-5m,whereas the influenced depth may reach 4-9m below the ground surface.