15-070 Micropile Design Calculation Rev 2-26-10 2015

DESIGN AND CONSTRUCTION OF MICRO PILE FOR CLINKER SILO FOUNDATION OF ARABIAN CEMENT COMPANY-RABIGH-EXPANSION

PROJECT -7, RABIGH, KINGDOM OF SAUDI ARABIA

DESIGN OF MICRO PILE

(R-15-070)

CLINKER SILO FOUNDATION ACCREP 7, RABIGH

Prepared for:

China National Building Material Company LimitedRiyadh, Kingdom of Saudi Arabia

Client File # R-15-070 26th October, 2015

Document #R-15-070Revision #2Page #1



1. PROJECT & DESIGN INTRODUCTION

CNBM entrusted Omar Jazzar Consulting Engineers for the design and installation of Micropile for

Clinker Silo Foundation of Arabian Cement Company – Rabigh – Expansion Project – 7. In view of

this, the following design assumptions/facts are used herein.

a. Geotechnical Investigation Report # R-14-156– Rev - 3

b. Reference Boreholes - BH 88 - 90 (annexed with this design)

c. Depth of the clinker silo foundation as per the approved drawings is 4.5 m below the FFL

d. Reference Design Document – “Micropile Design & Construction by U.S. Department of

Transportation – Federal Highway Administration – Publication # FHWA-NHI-05-039-

December 2005”

2. STRUCTURAL DESIGN OF MICROPILE

a. The allowable compression load of a Micropile is given by the following empirical equation

Pc-allowable = 0.4 f’c-concrete x Aconcrete + 0.47 Fy-steel x Abar

Where

Pc-allowable = allowable compression load;

f’c-concrete = unconfined compressive strength of concrete (typically a 28-day strength) = 20 MPa. This

is considered for the design only but has been revised to 35 MPa as per the construction drawings.

Aconcrete = area of concrete in Micropile cross section = 16867.211 mm2

Fy-steel = yield strength of steel rebar = 420 MPa

Abar = cross sectional area of steel rebar = 804.247 mm2

Hence Pc-allowable = 0.4 x 20 x 16867.211 + 0.47 x 420 x 804.247 = 293696.046 N = 293. 7 kN

However the design compression load on the micropile shall be limited to 200 kN

b. The allowable Tension load shall be calculated by the following empirical relation

Pt-allowable = 0.55x Fy-steel x Abar

And Pt-allowable = 0.55 x 420 x 804.247 = 185781.057 N = 185.8 kN; Limit to 150 kN for tension

load. However there is no uplift load on the micropile. The above design features the internal

capacity of micropile and the external design capacity shall be verified by a load test on site. The

load factors applied as per the design document reference.




3. EVALUATE GEOTECHNICAL CAPACITY OF MICROPILE

The subsurface stratum is “Coralline Limestone Rock” and the type of grouting shall be gravity

grouting, as per the design reference “Type A” Grout-to-Ground Bond Ultimate Strength shall be

used. Considering the existing subsurface strata as very dense gravel due to the inconsistent rock

quality below the founding level we have

Grout-to-Ground Bond Ultimate Strength bond = 250 kPa= 0.25 MPa

The bond length is given by

Lb = PG-allowable x FS/ bond x x Db

Where

Lb = Bond Length

PG-allowable = Allowable geotechnical bond capacity which is the maximum compression or tension

load for design = 200 kN

FS = Factor of Safety = 2.5

bond = Grout-to-Ground Bond Ultimate Strength = 250 kPa = 0.25 MPa

Db= Diameter of the drill hole = 150 mm

We have Lb = 200 x 2.5 / 250 x x 0.150 = 4.25 m;

Hence adopt 5.0 m bond length for micropile.

4. TESTING OF MICROPILE

The test arrangement is generally by a hydraulic jack and reaction load. The actual micro pile

capacity and external design capacity shall be validated by a load test. A minimum of 10 test shall be

done and can be increased depending upon the consistency of test results. Ultimate and or

verification shall be done before and during the installation of micropiles. Proof test shall be done

during the installation program of micropiles.

5. ALLOWANCE FOR CORROSION

The 32 mm rebar shall used with epoxy coating for the central reinforcement of the micropile since

we have high aggressive substratum (rock and ground water) is existence.
































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15-070 Micropile Design Calculation Rev 2-26-10 2015