A series of tests are carried out to study the dynamic compaction parameters and their effects on the deep collapsible loess foundation under super-high fill in Lishi region. Analyses are made on the average settlement of each test area before and after dynamic compaction and on the regularity of the main physical and mechanical indexes of soil. The main parameters are gained

such as the centre distance of dynamic compaction points

the best impact number

the standard of cutting out

and the effective reinforcement depth under the energy levels of 2 000 kN•m

3 000 kN•m or 6 000 kN•m; hence

the empirical formula of the effective reinforcement depth of dynamic compaction is given. The results of the tests show that the deep collapsible loess foundation in Lishi region can be effectively reinforced by dynamic compaction and that the loess collapse in the reinforced range is removed. Moreover

the results show that after dynamic compaction above the energy level of 2000 kN•m

the eigenvalue of the bearing capacity of collapsible loess foundations in Lishi or similar regions can reach over 300 kPa

the foundation soil deformation modulus is more than 25 MPa

and the effective reinforcement depth can be computed by the modified formula Menard

in which the modified coefficient is 0.35-0.37. Furthermore

the results indicate that under the energy levels of 2 000 kN•m

3 000 kN•m or 6 000 kN•m

the best impact numbers of dynamic compaction are 11

10 and 10 respectively; the effective reinforcement depths are 5 m

6 m and 9 m respectively; the optimum centre distances of dynamic compaction points are 4m

4m and 5m respectively; and the average settlements of the last two impacts

which are not more than 5 cm

5 cm and 10 cm respectively

can be used as the optimum standards of cutting out. Therefore

the results of the tests can provide a reference for the design and construction of engineering projects of the same kind.