基于动力触探的砾性土液化判别方法通用性研究
Reliability of Chinese dynamic penetration test for liquefaction evaluation of gravelly soils
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摘要: 动力触探是针对砾性土力学性能评价的一种原位测试技术,具有设备简单、操作方便等优势。分别在成都平原和美国Utah地区选取典型砾性土场地,进行中美联合动力触探和有效锤击能量的测试与标定,结果表明:①在成都平原3个砾性土场地获取了中国超重型动力触探1321个重锤锤击能量记录,锤击能量传递系数的平均值约为90%,标准差为7.7%,锤击数离散性受设备操作方法的影响较大;②在美国钻机上安装中国超重型动力触探标准探头,可以有效穿透选取的试验深度为20 m的砾性土场地,并进行分层、力学性能评价;③在美国Echo dam下游坝基上2个砾性土场地获取了美国动力触探1438个重锤锤击记录,锤击能量传递系数约为74%,标准差为8.7%,锤击数离散性受拉绳、钻杆摩擦力的影响较大;④对锤击数进行能量修正之后,以2008年汶川地震砾性土液化为背景、以动力触探锤击数为基本指标的砾性土液化判别方法,具有国际通用的可行性。Abstract: Chinese Dynamic penetration test (DPT) is an in-situ testing with the advantages of simple apparatus, economical test, and continuous data acquisition, especially for measuring bearing capacity, relative density and classification of gravelly soils. The typical gravelly soils sites are selected from the Chengdu Plain in China and the river bed of Echo dam downstream in the U.S., and China-US dynamic penetration testing and hammer energy measurements are conducted. The results show that: (1) The average of energy transfer ratios is 90% and the standard deviation is 7.7%, derived from 1321 energy time-history records, tested at 3 gravelly soils sites in the Chengdu Plain. The deviation is greatly affected by operation procedure. (2) The DPT test depth, using US drill rig assembling with Chinese DPT cone, can reach as much as 20 meters for assessing soil properties. (3) The average of energy transfer ratios is around 74% and the standard deviation is 8.7%, derived from 1438 energy time-history records, tested at 2 gravelly soils sites on the river bed of Echo dam downstream. The deviation is greatly affected by friction of drill rod and rope. (4) The DPT blows should be corrected according to different hammer energies. The proposed evaluation method for gravelly soils liquefaction, developed from the DPT database of gravelly soils liquefied during 2008 Wenchuan Earthquake, can be applicable for worldwide use.