Design of micropiles to increase earth slopes stability

Abstract

A methodology was proposed for the design of micropiles to increase earth slopes stability. An analytic model based on beam-column equation and an existing P-y curve method was set up and used to find the shear capacity of the micropile. Then, a step-by-step design procedure for stabilization of earth slope with micropiles was introduced, involving six main steps: 1) Choosing a location for the micropiles within the existing slope; 2) Selecting micropile cross section; 3) Estimating length of micropile; 4) Evaluating shear capacity of micropiles; 5) Calculating spacing required to provide force to stabilize the slope; 6) Designing the concrete cap beam. The application of the method to an embankment landslide in Qinghai Province was described in detail. In the final design, three rows of micropiles were adopted as a group and a total of 126 micropiles with 0.23 m in diameter were used. The micropile length ranged between 15 and 18 m, with the spacing 1.5 m at in-row direction. The monitoring data indicate that slope movement has been effectively controlled as a result of the slope stabilization measure, which verifies the reasonability of the design method.

Keywords

micropiles / earth slope stabilization / lateral response analysis / design method / P-y curve

References

[1] BruceD A, JuranI. Drilled and grouted micropiles: State-of-practice review [R]. US Federal Highway Administration, Washington, D C: Aluminum Company, 1997

[2] LizziF. Reticulated root piles to correct landslides [C]. ASCE Convention and Exposition, 1978ChicagoASCE3370

[3] CantonR, CollottaT, GhionnaV. A design method for reticulated micropiles structure in sliding slopes [J]. Ground Engineering, 1989, 22(4): 41-47

[4] PearmanS L, CampbellB D, WithiamJ L. Slope stabilization using in-situ earth reinforcement [C]. ASCE Specially Conference on Stability and Performance of Slopes and Embankments, 1992BerkeleyASCE59-71

[5] JuranI, BenslimaneA, BruceD A. Slope stabilization by micropile reinforcement [J]. Landslides, 1996, 5: 1718-1726

[6] LoehrJ E, BowdersJ J, OwenJ W. Slope stabilization with recycled plastic pins [J]. Journal of Transportation Research Record, 2000, 1714: 1-8

[7] SunS-w, ZhuB-z, MaH-min. Model tests on anti-sliding mechanism of micropile groups and anti-sliding piles [J]. Chinese Journal of Geotechnical Engineering, 2009, 31(10): 1564-1570

[8] LizziF. The pali radice (root piles) [C]. Symposium on Soil and Rock Improvement Techniques including Geotextiles, Reinforced Earth and Modern Piling Methods, Bangkok, 1992, 3: 155-164

[9] PlumelleC. Improvement of the bearing capacity of soil by inserts of group and reticulated micro piles [C]. International Symposium on In-situ Reinforcement of Soils and Rocks, 1984ParisENPC Press83-89

[10] PalmertonJ BStability of moving land masses by cast-in-place piles [R], 1984Washington D CFederal Highway Administration

[11] PearlmanS L, WolosickJ R. Pin piles for bridge foundations [C]. Proceedings 9th Annual International Bridge Conference, 1992PittsburghPennsylvania69-77

[12] ReeseL C, WangS T, IsenhowerW M. Use of drilled shafts in stabilizing a slope [J]. Stability and Performance of Slopes and Embankments, 1992, 2(31): 1318-1332

[13] HognestadEA Study of combined bending and axial load in reinforced concrete members [M], 1951UrbanaUniversity of Illinois Engineering Experiment Station37-52

[14] RuschH. Researches toward a general flexural theory for structural concrete [J]. Journal Proceedings, 1960, 57(7): 1-28

[15] MatlockH. Correlations for design of laterally loaded piles in soft clay [C]. Proc Annual Offshore Technology Conference. Houston, Texas, 1970387-392

[16] ReeseL C, WelchR C. Lateral loading of deep foundations in stiff clay [J]. Journal of the Geotechnical Engineering Division, 1975, 101(7): 633-649

[17] SunS-w, ZhuB-z, ZhengJing. Design method of micropile group for soil slope stabilization based ultimate resistance of micropile [J]. Chinese Journal of Geotechnical Engineering, 2010, 32(11): 1671-1677

[18] PoulosH G. Design of reinforcing piles to increase slope stability [J]. Canadian Geotechnical Journal, 1995, 32: 808-818

[19] PoulosH G, DavisE HPile foundation analysis and design [M], 1980New YorkJohn Wiley & Sons351-368

[20] LinH, CaoP, GongF-q, LiJ-t, GuiY-lin. Directly searching method for slip plane and its influential factors based on critical state of slope [J]. Journal of Central South University, 2009, 16(1): 131-135

[21] HollowayD M, MoriwakiY, StevensJ B. Response of a pile group to combined axial and lateral loading [C]. Proceedings of 10th International Conference on Soil Mechanics and Foundation Engineering, 1981387-392

[22] BrownD A, MorrisonC, ReeseL C. Lateral load behavior of pile group in sand [J]. Journal of Geotechnical Engineering, 1988, 114(11): 1261-1276

[23] ItoT, MatsuiT. Methods to estimate lateral force acting on stabilizing piles [J]. Soils and Foundations, 1975, 15(4): 45-59

[24] China National Standards GB50010—2002. Code for design of concrete structures [S]. (in Chinese)

[25] China National Standards GB/T50123—1999. Standard for soil test method [S]. (in Chinese)