Abstract: A new formation technology of post-grouting jacked steel pipe micropiles is presented, including mixture grout (tailing sands and cement mixed in water) ratio test and construction technology. Ratio tests are conducted to analyze the compression strength under influence of water-cement ratios and tailing sand mass-cement mass ratios. The compression tests on 7 short piles and 6 large piles are carried out at the field site; the relationships between mixture grout types, grouting methodology, mixture grout volume and ultimate compression bearing capacity are studied; and then the test results are also compared with the calculated results of standards in operation and miniature pile construction manuals and instruction of federal highway administration(FHWA). Research results show that the mixture grout early hardening is faster than neat cement grout and no significant difference of 28d strength; the strength and grouting technology can be met with w/c = 0.6 and s/c = 0.5; the ultimate compression bearing capacity of post-grouting micropiles increase by 75%-150%; the test results are 1.33 times that of the calculated values, and similar with that of the FHWA calculated values.

Key words: micropile, jacked pile, pressure grouting, compression bearing capacity, water-cement ratios