How is micropile capacity calculated?

Qa = (αb × qs × π × D × Lb) / FS, where αb is bond zone efficiency factor (0.8–1.0), qs is unit grout-ground bond strength (kPa), D is drill hole diameter (mm), Lb is bond length (m), and FS = 2.0 with load testing or 3.0 without. Per FHWA NHI-05-039 Table 4-5: qs = 70–190 kPa for sands, 35–70 kPa for clays, 300–1000 kPa for soft to hard rock, depending on grouting method (Type A gravity, B pressure, C/D post-grouted).

What diameter and reinforcement are typical for micropiles?

Micropiles range from 100–300 mm diameter and 3–30 m length. Central reinforcement (all-thread bar or casing) carries 50–70% of design load; the grout carries the remainder. Per AASHTO LRFD Section 10.9 and IBC, design must check steel bar tension/compression, grout-steel bond, grout-ground bond, and global geotechnical capacity. Load testing per ASTM D1143 (compression) or D3689 (tension) is required for high-capacity micropiles.

Micropile Skin Friction Calculator

Calculate micropile axial capacity using grout-to-ground bond strength for Type A, B, and C/D micropiles per FHWA NHI-05-039 (2005) design manual.

2D stress state at a point. All stresses in MPa.

σx — Normal Stress X (MPa)

σy — Normal Stress Y (MPa)

τxy — Shear Stress (MPa)

⚙ Mechanical Note: Results are based on standard textbook formulas and ISO/AASHTO references. Always verify critical designs with applicable codes (ISO 898, AASHTO 1993, AISC, Eurocode 3) and a qualified engineer.

How It Works

Calculate micropile axial capacity using grout-to-ground bond strength for Type A, B, and C/D micropiles per FHWA NHI-05-039 (2005) design manual

Each component has a specific meaning:

Grout-to-ground bond strength — The grout-to-ground bond strength recorded for the patient or scenario being assessed.

Note: Interpret the micropile skin friction result against the clinical thresholds and context described above.

How to Use

Enter the grout-to-ground bond strength for the patient or scenario you are assessing. Calculate micropile axial capacity using grout-to-ground bond strength for Type A, B, and C/D micropiles per FHWA NHI-05-039 (2005) design manual. Use the micropile skin friction result to inform your clinical assessment.

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Frequently Asked Questions

How is micropile capacity calculated?

What diameter and reinforcement are typical for micropiles?