Micropile Design Example

MICROPILE STRUCTURAL DESIGN

Pt −all = 0.55 ( Fy −bar Abar + FY −ca sin g Aca sin g )

PC −all = 0.4 f C′−grout Agrout + 0.47 (0.55 ( Fy −bar Abar + FY −ca sin g Aca sin g ) )

Fy − ca sin g = 2.4e5 Aca sin g = π (

kN

m2

2 OD 2 ID 2 0.076 2 0.068 2 − ) =π( − ) = 9.04e − 4 m 4 4 4 4

Micropile Type I(L=20 m) USE φ32 AIII

FY −bar = 4.0e5

φ76 / 68; St 240 / 370

kN

m2

Abar = 8.04 e − 4 m f c′−grout = 5.3e4

kN

2

m2

2 0.068 2 0.032 2 − ) = 2.82 e − 3 m 4 4 = 0.4(5.3e4 × 2.82 e − 3) + 0.47 ( 4.0e5 ×8.04 e − 4 + 2.4e5 ×9.04 e − 4)

Agrout = π ( Pc −all

= 312 .9 kN > 300 kN Pt −all = 0.55 ( 4.0e5 ×8.04 e − 4 + 2.4e5 ×9.04 e − 4) = 305 kN > 300 kN

MICROPILE GEOTECHNICAL DESIGN Micropile Axial Capacity Soil category (according to soil test result attached to tender documents): Soil description: Loose Sand According to technical specification and considering silt and clay, for primary grout placed under gravity head (Table 5-2 ,attached): α

bond nominal strength

PG-allowable =

αbond

= 120

nominal strength

F .S .

kN/m2 * 3.14 * DIA bond * bond length

F.S = 2.5 DIA bond = 0.10 m PG20 – allowable =

120 2.5

* 3.14 * 0.10 * 20.00 = 301 kN > 300 kN