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Haramain High Speed Rail

Geotechnical Design Report

Rail Bridge at Station 447+044

Doc.: HHR-RW-TN-C-OOO-20516-AA

February 2012 2 SCEC-K&A

1. INTRODUCTION .................................................................................................................. 32. GEOLOGY ........................................................................................................................... 33. GEOTECHNICAL SUBSURFACE INVESTIGATION .......................................................... 44. WATER TABLE LEVEL ....................................................................................................... 55. SEISMICITY ......................................................................................................................... 56. SOIL PARAMETERS DETERMINATION ............................................................................ 57. FOUNDATION DESIGN ....................................................................................................... 8

7.1 BEARING CAPACITY............................................................................................................ 97.2 SETTLEMENT.................................................................................................................... 127.3 LATERAL RESISTANCE ...................................................................................................... 14

8. RECOMMENDATIONS ...................................................................................................... 16

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1. Introduction

This design report presents the geotechnical conditions encountered at the Rail Bridge located

at Station 447+044. The report includes also calculations for bearing capacity and settlement of

the foundations and concludes with relevant recommendations to be taken into account during

the construction phase. The footings dimensions and stresses are provided based on the

abutment and piers structural calculations.

2. Geology

The geological maps developed in the area indicate that the main formations encountered at the

Rail Bridge location consist of basaltic rock as shown in Figure 1 below.

Figure 1: Geological Map

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A detailed geological survey was specifically carried out for the whole Project alignment. The

detailed survey indicates one main geological unit of moderately weathered flows in the studiedarea:

UNIT (Qtb): This unit consists mainly of alkaline-olivine flood basalt flows. These basalts are

pale to dark-grey, generally massive at the base and becomes porous, vesicular, scoviaceous

and much darker toward the top; and occur in the form of undulating flat gently sloping plateau

surface; and are characterized by columnar joining and fracturing resulting various sized rock

fragments. Lacustrine marls and clay deposits are interstrafied between basaltic flows.

The distribution and legend of this unit along the alignment route are shown in Figure 2 below:

Figure 2: Soil/Rock units as per the geological survey

3. Geotechnical Subsurface Investigation

The geotechnical investigation at the Rail Bridge location consisted of drilling Seven (7)

boreholes down to a maximum depth of 30m. The in situ testing campaign included carrying out

Standard Penetration Tests (SPT). Samples have also been retrieved from boreholes in order to

carry out lab tests to determine the mechanical, physical and chemical properties of the soil/rock

(sieve analysis, Atterberg limits, direct shear, and unconfined compression test).

The borehole logs and laboratory test results are summarized in Appendices A and B.

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4. Water Table Level

Ground water table was not encountered during the soil investigation at the executed boreholes

in this area.

5. Seismicity

According to the zonation map developed for the kingdom based on the peak ground

acceleration, PGA, values calculated for 50 years service lifetime with 10% probability of

exceedance, this quadrangle lies in zone 1 implying a peak ground acceleration of 0.1g.

However, this value was checked in view of the project specific geological and seismographic

context and a site specific peak ground acceleration was adopted based on the results of theseismic hazard assessment study. Accordingly, the peak ground acceleration considered for this

bridge is 0.13g.

6. Soil Parameters Determination

The soil profile detailing the encountered subsurface material is provided in Appendix C.

SPT, RQD and unconfined compressive strength results drawn with depth are shown in Figures

3, 4 and 5 below. The graph indicates loose to very dense fill material/silty Sand with presence

of boulders and cobbles at the top 0.5 to 4.5 meters, followed by highly to slightly fractured

Basalt to the termination depth of the boreholes.

Figure 3: SPT versus depth

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Figure 4: RQD versus depth

Figure 5: Unconfined compressive strength versus depth

Rock is encountered at the following depths along the bridge:

A1: basalt is encountered at 4.5m below NGL

P1: basalt is encountered at 1.5m below NGL


P3: basalt is encountered at 1m below NGL


P5: basalt is encountered at 3m below NGL

A2: basalt is encountered at 1.5m below NGL

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The expected soil stratigraphy is summarized in the idealized soil profile in Figure 6 below.

Figure 6: Idealized soi l profile

The results of the site investigation are used to determine the soil and rock properties that could

be adopted for the foundations calculations. As foundations will be socketed into rock, we are

interested in rock parameters, in particular the unconfined compressive strength. The minimumreported unconfined compression strength 25.0 MPa and the 90 th percentile value is 38.0 MPa.

We have adopted 25.0 MPa as a characteristic strength parameter of rock for bearing capacity

calculations. The in situ and lab test data are also complemented by correlations available in the

technical literature in addition the AASHTO 2002 for comparable soil conditions (References:

Pile Design and Construction Practice 4th edition by Tomlinson and Foundation Analysis and

Design 5th edition by Bowles).

The design is done according to Design Approach 3 which applies partial factors to actions and

to material properties, while resistances are left unfactored. Design Approach 3 employs factors

from Sets A1 or A2, M2, and R3. The factors in Set R3 are all 1.0 and hence resistance is

mostly unfactored. For rock material the partial coefficient on the unconfined compressive

strength is equal to 1.4.

The adopted soil parameters can be summarized as follows:

Table 1: Adopted rock parameters

Material DesignParameters References

Basalt

quc,d 18MPa CharacteristicvaluedividedbypartialsafetyfactorE 1000MPa AsafeestimatefromTomlinsonPileDesignand

ConstructionPractice (

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7. Foundation Design

The foundation design is carried out in accordance with the Eurocode 7 recommendations. To

check the resistance of the ground and foundations (GEO), Approach 3 is adopted as per the

Project Specifications. The structural loads are summarized in the Table below:

Table 2: Structural Loads and foot ing dimensions

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Based on the structural loads and in view of the nature of the subsurface material encountered,

it is recommended to adopt a shallow foundation system. Footings shall be socketed within the

basaltic rock to minimize settlements and to provide a proper lateral resistance againsthorizontal loads. It is recommended that the footings be partially socketed into rock (1m for

abutment and 0.5 m for piers) in view of the high lateral loads and in order not exceed the

allowable lateral deformations and to avoid any potential differential lateral behaviour should the

footing be embedded in both soil and rock formations.

7.1 Bearing Capacity

Using Eurocode approach which includes partial safety factor on the unconfined compression

strength of rock, the ultimate bearing capacity is high on rock.

Ultimate bearing capacity can be estimated using the US Corps of Engineers approach for

jointed rock with spacing s less than foundation width B.

Figure 7: Bearing capacity general shear failure by US Corps of Engineer

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In the case where the shear failure is likely to develop along planes of discontinuity, cohesioncannot be relied upon to provide resistance to failure. In such cases the ultimate bearing

capacity can be estimated from the following equation: 0.5BN+DNq

This Bearing capacity equation is applicable to long continuous foundations with length to width

ratios (L/B) greater than ten. The table below provides correction factors for circular and square

foundations, as well as rectangular foundations with L/B ratios less than ten. The ultimate

bearing capacity is estimated from the appropriate equation by multiplying the correction factor

by the value of the corresponding bearing capacity factor.

Table 3: Corrections factors

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Table 4: Estimated bearing capacity for Piers and Abutments using US Corps of

Engineers Approach

Also, the allowable bearing capacity can be estimated based on numerous methods proposed in

the technical literature. In view of the good quality of rock, the allowable contact stress for

footings supported on level surfaces in competent rock may be determined using Peck et al.

approach (also used in AASHTO 2002) as shown in Figure 8.

Figure 8: Allowable bearing capacity for footing on Rock (Peck et al. (1974)).

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The RQD used in this figure shall be the average RQD for rock within a depth of B below the

base of the footing, where the RQD values are relatively uniform within that interval. If rockwithin a depth of 0.5B below the base of the footing is of poorer quality, the RQD of the poorer

rock shall be used to determine the allowable bearing capacity. The results are summarized in

Table 5 below:

Table 5: Estimated bearing capacity beneath Piers and Abutments

Abutment

A1

PierP1 PierP2 PierP3 PierP4 PierP5 Abutment

A2

RQDValue 0% 15% 8% 35% 0% 0% 0%AllowableBearingCapacity(KPa) 950 1915 1430 3830 950 950 950

Ultimate and allowable bearing capacities are very high and settlements should be checked.

7.2 Settlement

The footing dimensions are as follows: real dimensions P1, P2, P3, P4 and P5 (13mX13m),

Abutment A1 (13mX15.4m) and Abutment A2 (16.5mX19.4m).

The geotechnical investigation indicates that the subsurface material over which footings are

placed is rock. Settlements of the foundations are therefore essentially of immediate/short terms

nature. The settlement can be estimated using the following equation (AASHTO 2002):

Where B and L are the effective width and length of the footing respectively; is the Poissons

ratio assumed to be equal to 0.25; is the elastic modulus of the rock layer beneath the

foundation level. is a factor to account for footing shape and rigidity, table 6 shows the elasticand shape and rigidity used. q0 is the effective stress at the level of the bottom of the foundation.

Table 6: Elastic shape and rigidity factors EPRI (1983)

L/B z,Flexible z,Rigid

Circular 1.04 1.131 1.06 1.082 1.09 1.103 1.13 1.155 1.22 1.2410 1.41 1.41

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The settlements are divided into two parts: during construction phase (i.e. earth pressure, dead

load) and during service (deck, superimposed loads, live loads, etc.). They are calculated basedon the stresses applied during construction and during service conditions using the effective

foundation dimensions (B and L to take eccentricities into account).

The data used and the corresponding estimated settlements are listed in Tables 7, 8 and 9

below.

Table 7: Subsurface materials for Piers and Abutments

Type Foundationembedmentconditions Foundationmaterial

PierP1 Foundationsshallbesocketedatleast0.5mintogoodrock.Thesoilcoverabovefootingsisaround0.5m. BasalticRock

PierP2 Foundationsshallbesocketedatleast0.5mintogoodrock.Thesoilcoverabovefootingsisaround5m. BasalticRock



PierP5 Foundationsshallbesocketedatleast0.5mintogoodrock.Thesoilcoverabovefootingsisaround1m. BasalticRock

AbutmentA1 Foundationsshallbesocketedatleast1mintogoodrock.Thesoilcoverabovefootingsisaround3m. BasalticRockAbutmentA2 Foundationsshallbesocketedatleast1mintogoodrock. BasalticRock

Table 8: Estimated settlements beneath Piers and Abutments during construction

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Table 9: Estimated settlements beneath Piers and Abutments during service

*Twosettlementvaluesarecomputed:duringconstructionandduringserviceasperTables8and9above.Thenetsettlementisthedifferencebetweenthesetwovalues.

Based on the above, most of the settlements will occur during construction and settlements

during service conditions are within tolerable limits.

7.3 Lateral Resistance

The footings are partially socketed into rock to provide proper resistance against lateral loads.

The lateral loads are particularly high for Abutment where the ultimate lateral loads can reach

50,364 KN. The contribution of the soil above footings is conservatively ignored. Different modes

of failures can occur:

a. Failure along interface between footing and rock. In this case the resistance is ensured

by the sliding resistance at the foundation bottom in addition to the rock wedge in front of

the footing. The failure path can also occur along discontinuities. However in view of the

massive nature of the rock encountered as confirmed by the high RQD values reported,

this mode of failure is not likely to occur as the longer the failure paths are, the higher is

the resistance against lateral loads.

b. Failure is initiated by buckling of the upper layer of rock under lateral loads. This failure

mode can be disregarded in view of the high compressive strength of the rock.

c. Rock can be simulated to a c- soil. In view of the relatively high c and values that can

be adopted for the rock mass and the large footing dimensions (thickness, width andlength), resistance is ensured via the passive pressure.

d. Failure by bearing capacity would not happen in view of the large footing dimensions

(thickness, width and length). The lateral pressure would not exceed 400 kPa.

An example of evaluation of lateral resistance for Abutment A2 is provided in Appendix D.

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a. Failure along interface and discontinui ties

b. Failure by buckl ing c. Failure by bearing capacity

d. Rock simulated to a c- soilFigure 9: Potential failure surfaces under lateral loads

It should be noted that failure by sliding is not expected in view of the high vertical loads applied

on the foundation which restrain it from sliding.

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8. Recommendations

The following is recommended for the construction of foundations of the Rail Bridge:

1- The allowable bearing capacity is 400 kPa.

2- The expected subsurface material over which foundations are laid consists of moderately

fractured to massive Basalt.

3- Foundation embedment (from Ground surface to bottom of R.C. foundation) shall be:

Abutment A1: 5.5 m depth below the natural ground level, foundation shall be

socketed at least 1m into good rock;

Piers P1: at 3.0 m depth below natural ground level, foundation shall be socketed at

least 0.5m into good rock.

Piers P2: at 8 m depth below natural ground level, foundation shall be socketed at








Abutment A2: at 2.75 m depth below natural ground level, foundation shall be

socketed at least 1m into good rock.

4- Should in situ material encountered on Site be different from those expected then foundation

recommendations shall be revised accordingly.

5- A cautious method of excavation shall be performed so as not to disturb rock around and

under the footings. An even and uniform excavation surface shall be obtained. Proper

preparation of the areas to receive foundations shall be done as per Project Specifications.

6- No ground water is reported so cold paint water proofing should be applied.

7- Existing Utilities are present and all measures for supporting/protecting them should be

provided by the Contractor and properly installed, maintained and monitored and shall be

submitted to the Engineer for approval.

8- Cement type I should be used as chemical tests indicates non aggressive environment.

9- Probing and filling of cavities shall be done as per the approved Method Statement for cavityprobing and filling.

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APPENDIX A

(BOREHOLE LOGS)

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656.64

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655.51

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E=570910.531N=2704853.443

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E=570910.531N=2704853.443

655.14

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E=570910.531N=2704853.443

655.14

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E=570910.531N=2704853.443 655.14

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E=570910.531N=2704853.443 655.14

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E=570910.531N=2704853.443 655.14

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APPENDIX B

LAB TEST RESULTS

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APPENDIX C

(SUMMARY OF LABORATORY TESTS AND GEOLOGICAL PROFILE)

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2704853.4

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APPENDIX D

(EXAMPLE OF LATERAL RESISTANCE FOR ABUTMENT A2)

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Sliding: For Abutment A1 which carried the largest lateral load (ultimate load = 50,364

kN), the footing dimensions are 16.5m length, 19.4m width and 2.75m thickness. Takinginto account the cohesion and friction angle adopted, sliding along the interface rock-

footing would not occur (1000 kPa X length X width = 1000 kPa X 19.4m X 16.5m =

320,100 KN).

Failure plane: Consider that failure would happen along a failure plane that has an angle

of 60 from the vertical (around /4+/2). The horizontal resistance from the triangular

wedge of rock would be:

cohesion X length of wedge X cos(30) X length of footing =

1000kPaX5.5mXcos(30)X16.5m=78,591 KN.

Rockwedgecontributiontoresistance

FoundationLateralload L=13m

2.3m cohesion

4.6m

Bearing capacity: Consider a discontinuity with weak infilling material having a low

cohesion of 100 kPa along which failure/sliding will occur. In this case the resistance

provided by this layer against sliding would be equal to the footing dimensions X

cohesion = 19.4mX16.5mX100kPa = 32,010 KN. The remaining pressure caused by the

lateral load of 50,364 KN on the sides of the footing is (50,364KN-32,010)/(thickness X

length) = 18,354/(2.75m X 16.5m) = 405 KPa which is equal to the allowable capacity of

rock.

2.75m

5.5m

L=16.5 m

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FoundationLateralload L=13m

1.4m

Failurezonealongaweakinfillingzonewithlowcohesion

Resistingrockatthesidesofexcavation

Rock simulated to a c soil: in this case the friction and cohesion of the equivalent soil

will contribute in resisting the loads. Kp can be conservatively taken equal to 1.

Foundation

LateralloadL=13m

2.3m

2.75 m

2.75 m

L=16.5 m

L=16.5 m

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