GIR Section 4 - Rev01

8/3/2019 GIR Section 4 - Rev01

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CONTENTS

1. INTRODUCTION ........................................................................................ 1 2. SCOPE AND OBJECTIVES .......................................................................... 13. SITE LOCATION ........................................................................................ 24. SEISMIC CLASSIFICATION ....................................................................... 25. PROPOSED STRUCTURES .......................................................................... 26. METHODOLOGY ........................................................................................ 37. FIELD AND LABORATORY STUDIES ........................................................... 4

7.1 Ground Investigation ............................................................................ 47.2 Laboratory Test ................................................................................... 57.3 Information processing ......................................................................... 5

8. GEOLOGY .................................................................................................. 69. GROUND CONDITIONS ............................................................................. 610. SOIL AND ROCK PARAMETERS ..................................................................8

10.1 Mills, floatation tanks, floatation tanks and mills warehouse and substation 8 10.2 Slopes (mills and substation area) ......................................................... 9

11. GROUND WATER LEVEL .......................................................................... 1012. BEARING RESISTANCE ........................................................................... 10

12.1 Mills area (SAG and BALL)................................................................... 1012.2 Floatation Tanks and Warehouse (Mills and Floatation Tanks) .................. 1112.3 Substation ........................................................................................ 12

13. slope stability analysis ........................................................................... 13 13.1 Stability Analysis methodology ............................................................ 1313.2 Results ............................................................................................. 14

14. CONCLUSIONS AND RECOMMENDATIONS............................................... 1514.1 Conclusions ....................................................................................... 1514.2 Recommendations.............................................................................. 18

15. BIBLIOGRAPHY ...................................................................................... 19

TABLES


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Geological Geotechnical Report, Mirador Project

Mills, Flotation T. and Substation Area, Final Location

ii

Table 1 Structures loading information ..................................................................... 2Table 2 Equipment estimated weight ....................................................................... 3Table 3 Soil design parameters ............................................................................... 9Table 4 Soil design parameters for slope stability analysis ........................................ 10Table 5 Allowable Bearing Resistance ..................................................................... 13Table 6 Factor of safety for undrained conditions (short term) .................................. 14Table 7 Factor of safety for drained conditions (long term) ....................................... 14Table 8 Ground Water level .................................................................................. 17

Annexes:Annex 1: Project LocationAnnex 2: Borehole LocationAnnex 3: Borehole CoordinatesAnnex 4: Borehole LogsAnnex 5: StratigraphyAnnex 6: Bearing Capacity CalculationAnnex 7: Slope Stability AnalysisAnnex 8: Laboratory TestsAnnex 9: PhotosAnnex 10: Seismic Distribution of Ecuador NEC 2011


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1. INTRODUCTIONEcuacorriente S.A. (ECSA) has commissioned Laboratorio de Materiales de Construccin

(LMC), de la Pontificia Universidad Catlica del Ecuador (PUCE) to carry out the

Geological Geotechnical studies for the MiradorProject foundations.

Miradoris an open mine project for copper extraction. In order to facilitate the extraction

and processing of the material, a number of structures and facilities need to be constructed

such as:

y Open pit excavationy Primary crushery Processing plant which includes two production lines with an approximate capacity

of 30.000 tons a day

y Mine facilitiesy Water damy Access

2. SCOPE AND OBJECTIVESThe scope of this study is to identify the existing soil conditions and characterise the soil

strata. Soil parameters will be determined in order to provide with sufficient information to

estimate the bearing capacity of the existing strata on the locations where the Mills,

Floatation Tanks and Substation, will be placed, according to the latest location of the

structures.This study also includes the slope stability analysis of the cutting slopes that will be

generated in this area, which geometry has been proposed by ECSA.

This study has been based on the General Arrangement Drawing provided by ECSA, which

can be observed in the Annex No. 1.

This report has the following objectives:

y Describe the project geologyy Determine existing stratigraphyy Determine soil and rock parametersy Determine allowable bearing capacityy Recommend foundation type and depthy Determine the slope safety factors of the proposed geometry


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3. SITE LOCATIONThe mining concession of Mirador is located at the South West of Ecuador, in the Zamora

Chinchipe province, El Pangui borough in the locality known as Tundayme.

The mineral processing plant, floatation tanks and substation, in accordance to the

provided information on the National Grid Reference, are located in the following

coordinates horizontal datum PSAD 56, zone 17S:

783 120 E; 9 605 976N

783 120 E; 9 605 765 N

783 415 E; 9 605 765 N

783 415 E; 9 605 976 N

A map showing this location is attached in Annex 1 of this document.

4. SEISMIC CLASSIFICATIONAccording to the Ecuadorian Construction Code, the project is located in a Seismic Zone III,

which represents a maximum effective acceleration value Z of 0.30 in bedrock. This zone is

considered as a high seismic hazard zone. Annex No. 10.

5. PROPOSED STRUCTURESAs part of the construction project, two mineral processing lines have been proposed to

build. In the Mills Area, two mills type SAG and two Ball Mills have been planned. In theFloatation Tanks area, material processing tanks will be located per each production line.

The study area also includes the substation warehouse.

Based on the provided information, the below table summarises the additional load of the

different structures to the ground.

Table 1 Structures loading information

Foundation of Building and Structures


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Building andStructures

Type ofStructure Total load (KN)

Main PlantBuilding

Steel bentframe

1750

SubstationReinforcedconcreteframe

200

Table 2 Equipment estimated weight

Main Equipment

EquipmentFoundation

TypeUnit load

Total load (KN)

SAG Mill

Reinforcedconcrete

40.000

Ball Mill 22.000

It is important to highlight that no information has been provided for the floatation tanks.

The design of these structures will be based on standard loads assumed adequate and

approved by the overseeing organization.

6. METHODOLOGYA walkover survey was carried out by Diego Aguirre Burneo and Jimmy Suing in August

2011 to familiarize the designers with the scheme, to examine the location of the

structures and to plan the borehole location.

Additionally, a Geological survey of the site was undertaken. This information has been

included in the Geological Report.

The design of the Site Investigation was designed based on the ECSA Tender Documents,

in accordance to the location of the structures and following the company representative

recommendations.

It is important to mention that the originally proposed number of boreholes and depths was

changed and reduced by ECSA.


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The borehole locations were referenced topographically on site.

Once the boreholes and in situ tests are completed, the samples were properly registered,

identified and packaged. The samples were sent to the Laboratory of Materials of the PUCE

in Quito to be tested.

Based on the type of structure, the specific conditions of each site and the allowable

bearing resistance, the most suitable foundation type will be recommended.

At the same time, in the office, selected slope models were produced based on the

geometry given by ECSA and the obtained soil and rock parameters. Slope stability

analyses were carried out on the agreed cross sections in order to obtain the minimum

factor of safety.

7. FIELD AND LABORATORY STUDIESIn order to comply with the proposed objectives the following activities were undertaken:

7.1 Ground InvestigationThe ground investigation carried out by PUCE and AOC Ingeniera on behalf of ECSA in

August 2011 has comprised a series of boreholes distributed along the site according to the

location of the structures. A brief description of the boreholes location and depth can be

found below.

A total of twelve boreholes with depths varying from 25 to 33 m have been located at the

mill area (three per mill).

For the warehouse of the mill area and floatation tanks, a total of eleven boreholes

have been carried out at the likely foundation location. The depth of the boreholes varies

between 20 and 41 m. In this area, six trial pits were carried out in order to get

undisturbed samples.

For the substation, a total of six boreholes have been carried out, with depths varying

between 15 to 27 m. In this area, five trial pits were carried out in order to obtain

undisturbed samples.

For the slopes of the mills area and substation, a total of eleven boreholes have been

located and also six trial pits were carried out to get disturbed and undisturbed samples.

The obtained information has been utilised for the slope stability analysis.

The boreholes have been carried out with a rotary drill, recovering samples of NQ and HWT

diameters. Additionally, SPT in situ test where undertaken were the conditions wereadequate in accordance to ASTM D-1586. At locations, due to special ground conditions a

Cone Penetration Test CPT (Dynamic Penetration Test) was carried out.

The borehole location drawing is shown in the Annex 2.


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Disturbed samples have been recovered in several locations. Due to soil characteristics

undisturbed samples were difficult to obtain, therefore only a few undisturbed sample thinwall type were recovered. This information alongside with soil description and NSPT values

have been included in the Boreholes Logs which are located in the Annex 4 of this report.

All samples have been identified and classified in situ by the Site Engineer in accordance to

Visual Manual Classification Method.

7.2 Laboratory TestIn order to complement the in situ information a characterisation of the soil has been

carried out based on the below laboratory tests. These tests have been undertaken in

accordance to the correspondent ASTM standard.

y Natural moisture content ASTM D-2216y Particle size distribution ASTM D-422y Atterberg limits ASTM D-4318y Uncofined compressive strength ASTM D-2166y UU Triaxial Test ASTM D-2850-95y Direct Shear Test ASTM D-3080-03y Consolidation Test ASTM D-2435-96

Based on the laboratory test results, the different soils have been classified following ASTM

D2487 Classification of Soils for Engineering Purposes (Unified Soil Classification System USCS). The laboratory test records and results have been attached in the Annex 8 of this

document.

Based on the laboratory test results of triaxial compression, direct shear, and unconfined

compressive strength, the mechanic parameters of soils and rocks (cohesion and friction

angle), while with the unidirectional consolidation results, the consolidation parameters

were defined.

The laboratory test records and results have been attached in the Annex 8 of this

document.

7.3 Information processingAll the information collected from site, during the in situ testing and from laboratory testing

have been processed, tabulated and interpreted by experienced engineers in order to build

the necessary knowledge of the site, to characterise the existing ground, to estimate the

bearing capacity and finally, based on the requirements, to recommend the most suitable

foundation.


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Slope stability analyses have been carried out on agreed cross sections in order to

determine the stability of the proposed geometry for the existing ground conditions.

8. GEOLOGYThe total study area comprises approximately 45 Ha located between 815 and 945

metres above sea level.

The area covered by native vegetation has proven difficult to identify any rock outcrop.

The morphology can be described as flat and could be the result of an early flooding

area. However, during site investigation works, anthropic slopes were created for the

drilling platforms showing the exiting ground material.

On the surface, boulders with diameters up to 5 m were found dispersed in the site. The

superficial geology comprises colluvium deposits including sub angular to roundedboulders mainly composed of quartz sandstones and lutitas within silty sand matrix with

low plasticity from the formation known as Holln. Occasionally, the colluvium has been

found overlying alluvial deposits composed of round clasts within sandy silt matrix. At

deeper depths, fractured granodiorites of Batolito de Zamora formation was

encountered.

The detailed information about the geology of the area can be found in the Geology

Report.

9. GROUND CONDITIONSMills and floatation tanks area including warehouse

In this areas twelve boreholes were undertaken (PL11-68 to PL11-90), with a maximum

depth of 41 mBGL. The borehole logs are in Annex 4.

The ground stratigraphy is consistent in this area and comprises a 20 to 27 m thick layer

of colluvium material which includes pebbles and round boulders of quartz sandstones

with diameters varying from 0.3 to 3 m. The material colour was described as reddish

yellow, yellowish white and oxidized material.

In this colluvium we also have found boulders of granodiorite and sub rounded porphyry

blocks, which are slightly weathered and alternating with sandstones blocks. The

diameters vary between a few centimetres to 3 to 4 m.

The colluvium matrix could be described as a mixture of very moist low plasticity silty

Sand, SM in accordance to USCS, and very moist low plasticity sandy Silt classified as

ML. The matrix is also includes some gravels and cobbles.

Within the colluvium, the quartz sandstone and the granodiorite boulders, represent

approximately, 35 to 50% of the material, while the matrix is 65% to 50%.


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The colluvium overlies a stratum composed of saprolite and residual soil, as result of the

completely weathering of the granodiorite rock. This layer has a thickness that variesfrom 0 to 6 m. In some boreholes no saprolite material has been found. Residual soil can

be described as very moist, medium plasticity sandy silt, ML in accordance to USCS.

Finally, a third layer composed of an intrusive granodiorite rock was found. The rock is

described between fracture and very fracture and slightly weathered. In this rock there

are epidote, chlorite, and oxides filling the fractures.

All this information can be found in the Borehole Logs in Annex No.4 and in the

geological and geotechnical cross sections in the Annex No 5 Stratigraphy.

Substation area

In this area eleven boreholes were undertaken, where most of the boreholes reached amaximum depth of 20 mBGL. The borehole logs are included in Annex 4 of this report.

The ground description in these 20 m is described as colluvium material which includes

boulders, cobbles and gravel of quartz sandstones and Granodiorite, with diameters

varying from 0.3 to 3 m. The material colour was described as reddish yellow, yellowish

white and oxidized material. These boulders in some cases are slightly weathered to

moderately weathered.

The sandstones boulders present sericite and argillite alterations and the Granodiorite

boulders and cobbles present quartz sericite, argillite and propylitic alterations.

The colluvium matrix is mainly described as sandy silt, with low to medium plasticity and

very moist, ML according to a USCS. The percentage of matrix in the total colluviummay vary from 60% to 90 %. In the matrix there are also pebbles and gravel in some

areas.

In this area, there is no borehole entering the bedrock.

All this information can be found in the borehole logs Annex No.4 and in the geological

and geotechnical cross section in the Annex No 5 Stratigraphy.

Slopes Area

In this area eleven boreholes were undertaken, where maximum depths between 19 and30,5 mBGL. The borehole logs are included in Annex 4 of this report.

The ground stratigraphy in this area is mainly formed of colluvium layer with cobbles,pebbles and gravel. The matrix vary between a sandy silt , medium to low plasticity,

very moist, ML according to USCS and a silty sand, low plasticity, very moist, SM

according to USCS.

In this area no large boulders were found and the percentage of matrix in this colluvium

is much higher varying between 70% and 90%.


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All these information are in the borehole logs Annex No.4 and in the geological and

geotechnical cross sections in the Annex No 5 Stratigraphy.

10. SOIL AND ROCK PARAMETERSSoil and rock parameters have been estimated based on the results obtained from in situ

and laboratory testing as well as the description given by the site engineer.

The stratigraphy is consistent in the area studied. Mainly, three different layers have been

found: the colluvium, the residual soil (saprolite) and the granodiorite rock. According to

the ground utilisation, given loads and anticipated type of foundation; the soilcharacterisation has been divided in facilities area and slopes.

10.1 Mills, floatation tanks, floatation tanks and mills warehouse andsubstation

In the mills area, according to the percentage of matrix material (between 50% and

65%) the behaviour of the layer is going to be more like the matrix than the combination

of boulders, cobbles and gravel.

The parameters for the colluvium have been estimated based on the percentage of the

matrix, triaxial tests results, SPT N values, and using the oedometer consolidation test,

while the parameters of the rock have been estimated using the unconfinedcompressive strength test, and the RQD parameter.

Mechanical properties for rock has been derived mainly from unconfined compressive

strength test (UCS) and cohesion based on Mohr Coulomb criteria.

For design purposes, the rock angle of friction has been assumed as 45 based on

similar values used for this type of material (Bowles).

Based on the Mohr-Coulomb criteria, it has been assumed the worst case scenario where

the failure surface is 45+J/2, the lateral support is neglected W1 = Wm = UCS and W3 =

0. The lineal criteria of Mohr-Coulomb have been adopted following these two

recommendations:

y To assume a cohesion value close to a 10% of the UCS valuey To adopt a friction angle in accordance to the working confined stress

of the rock

Table 3 summarizes the estimated soil and rock parameters to be used for bearing

resistance calculations.


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Table 3 Soil design parameters

AreaMaterial

descriptionLevelmasl

J()

c(MPa)

Knat(kN/m3)

Cc

Mills (SAG andBall)

Colluvium 885 - - -

Mills (SAG andBall)

GranodioriteRock

865 45 4 26 -

Floatation Tanks,warehouse (millsand tanks)

Colluvium 885 880 10 60 17 0,15

Substation Colluvium 883 12 55 17 0,20

10.2 Slopes (mills and substation area)In the slopes area, we have also found the same colluvium, but with a higher percentage

of matrix material (between 70% and 90%) therefore the behaviour is definitely similarto the matrix soil.

The parameters for the colluvium have been estimated based on the percentage of the

matrix, triaxial tests results, SPT N values, and using the oedometer consolidation test,

while the parameters of the rock have been estimated using the unconfined

compressive strength test, and the RQD parameter.

Additional to the information obtained from the laboratory tests, some correlations have

been used to estimate soil parameters, using SPT N values and plasticity index.


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Table 4 Soil design parameters for slope stability analysis

Material

descriptioncu

(KPa)J()

c(KN/m2)

UCS(kPa)

Knat(kN/m3)

Colluvium 60 30 6 - 18

Saprolite 70 0 70 - 18

Granodiorite rock - - - 27000 26

11. GROUND WATER LEVELGround water level has been recorded in the majority of boreholes and summarised

below.

y Mills area, 893 masl averagey Flotation tanks, 883 masl averagey Substation, 885 masly Slopes vary between, 877 masl and 885 masl

12. BEARING RESISTANCEBearing resistance has been calculated in accordance to the existing ground conditions per

each structure location and the given loads.

For bearing capacity analysis of shallow foundations two different methodologies have

been used, the first methodology is based on the adjusted Meyerhof equation

considering the corrected N SPT value obtaining the allowable bearing capacity for a

maximum settlement of 25 mm (Bowles, 1996); and, the second methodology is based

on the Terzaghi equation for strip foundations that utilises the shear strength parameters

to determine the bearing capacity (Das, 1999).

12.1 Mills area (SAG and BALL)


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For both mills, SAG and BALL, deep foundations are recommended, this is due to the

nature of these structures, which transmit large loads to the ground and are sensitive todifferential settlements; and, because of the existing ground conditions.

The deep foundations are defined as rock socket piles, comprising a bored pile embedded in

the rock head at least three diameters.

For the pile bearing resistance, only base capacity has been considered, which has been

estimated based on the lowest value of the following methodology proposed by Bowles

(1996).

The first calculation is based on the shear strength of the rock and the square value of RQD

(see equation below).

qult = qult (RQD)2

The second value has been estimated based on the unconfined compressive strength test

UCS carried out in 14 samples of rock. The values obtained vary from 28 to 129 MPa. The

allowable rock bearing pressure is the range from 1/3 to 1/10 of the unconfined

compression strength obtained from intact rock samples. For bigger RQD, 1/3 and for

smaller RQD, 1/10 of the UCS test.

Taking the above in consideration and applying an overall recommended factor of safety of

6, the proposed bored pile diameter could be in the range of 500 mm, 600 mm, 700mm,

800mm (depending on the geometry of the pile cap), and the allowable bearing capacity of

10 MPa at 865 masl elevation.

The bearing capacity analysis for the mills area, can be found in the Annex No. 6.1

12.2 Floatation Tanks and Warehouse (Mills and Floatation Tanks)According to the type of structures of this area and the soil mechanic behaviour, a

shallow foundation will be needed.

Bearing Capacity from SPT

The recorded information for NSPT (70) values, varies from 2 to 25. Higher values have

been ignored since those could be produced due to cobbles and boulders presence.

After correcting N field value to get a NSPT (70), the bearing capacity analysis has been

made for B= 1 m and a Df=1 m, for each borehole at the depth, where we have SPT

information. Taking into account the available information and based on the bearing

capacity calculated following modified Meyerhof equation (Bowles); it has been

estimated that the soil allowable bearing resistance is 1265 kN/m2.


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Additionally, the subgrade modulus k has been calculated based on the equation

recommended by Scott. A value K30 = 35 MN/m3 has been estimated. This value shall beconfirmed on site with a plate load test for detailed design stage.

Bearing Capacity from Shear Strength

For floatation tanks and warehouse area, according to the loads and type of foundation

material, the bearing capacity for local shear case, has been carried out using undrained

unconsolidated parameters of the soil from the triaxial tests. The parameters used for

this calculation are in Table No. 3 Soils Design Parameters.

Applying a FS= 3, the allowable shear bearing, for the floatation tanks and warehouse

area is 124 kN/m2.

The bearing capacity analysis for the floatation tanks and warehouse area are located in

the Annex No. 6.2

12.3 SubstationAccording to the type of structures of this area and the soil mechanic behavior, a shallow

foundation will be needed.

Bearing Capacity from SPT

The recorded information for NSPT (70) values, varies from 3 to 32. Higher values have

been ignored since those could be produced due to cobbles and boulders presence.

After correcting N field value to get a NSPT (70), the bearing capacity analysis has been

made for B= 1 m and a Df= 1 m, for each borehole at the depth, where we have SPT

information. Taking into account the available information and based on the bearing

capacity calculated following modified Meyerhof equation (Bowles) it has been estimated

that the soil allowable bearing resistance is

1200 kN/m2.

Additionally, the subgrade modulus k has been calculated based on the equation

recommended by Scott (1981). A value K30 = 35 MN/m3 has been estimated. This value

shall be confirmed on site with a plate load test for detailed design stage.

Bearing Capacity from Shear Strength

For substation area, according to the loads and type of foundation material, the bearing

capacity for local shear case, has been carried out using undrained unconsolidated

parameters of the soil from the triaxial tests. The parameters used for this calculation

are in Table No. 3 Soils Design Parameters.


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Applying a FS= 3, the allowable shear bearing, for the substation area is

125 kN/m2.

Table 5 Allowable Bearing Resistance

AreaMaterial

descriptionLevelmasl

Qu(KN/m2)

Qa(KN/m2)

Floatation Tanks andwarehouse (mills and

Floatation Tanks)Coluvium 885 880 372 124

Substation Coluvium 883 376 125

The bearing capacity analysis and calculations for the substation area are located in

Annex No. 6.3

13. SLOPE STABILITY ANALYSISBased on the general arrangement and the topography provided by ECSA, nine cross

sections have been produced. The cross sections are considered the most representative

of the proposed geometry and have been attached in the Annex No. 7.

The proposed geometry of the cutting slopes comprises a 45 degree gradient with a

maximum height of 10 m. These 10 m slopes are separated for a 2 m bench. Themaximum expected height for the cutting slope is 50 m, however, at some locations, the

cutting slope alignment will follow the existing slope gradient forming greater high slopes

(see cross section 3-3 and 7-7, Annex No. 5).

13.1 Stability Analysis methodologyA ground model has been created for each of the proposed cross section based on the

ground investigation carried out by PUCE. Additionally, historical ground information (GI,

2006 by Higgeco and others) has been analysed in order to complete the model needed

for the stability analysis.

The slope stability has been analysed for cross sections 1, 2, 3, 7 and 8 which have beenconsidered the worst case. The chosen cross sections have been analysed using

specialised software based on the limit equilibrium and applying Bishop methodology.

A minimum Factor of Safety and the location of the expected slip surface of the analysed

cross sections have been found considering the two different conditions described below.


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Undrained Conditions (short term)

Due to the natural apparent cohesion of the soil, it is expected that the material will

have very low permeability, therefore the dissipation of pore water pressures would be

retarded by the size of the particles. This special feature could maintain its micro

particles together due to suction forces for a short period of time, allowing steep cutting

slopes to remain stable in the short term.

The short term analysis can be applied to predict the behaviour of the temporary cutting

slope that will be carried out during the construction period. The undrained analysis is

based on the undrained shear strength cu of the soil obtained from the available triaxial

test data.

Drained Conditions (long term)

For cutting slopes, effective stress (drained or long term conditions) is normally morecritical than total stress conditions (undrained). This condition is reached when the pore

water pressure has been dissipated and the suction forces (cohesion) no longer keep its

particles together, making the soil behave as granular material where effective

parameters will be used for analysis. A list of the drained shear strength parameters

were summarised in Table 4.

13.2 ResultsFive different cross sections have been analysed 1, 2, 3, 7 and 8. These cross sections

are considered as the worst case due to the height of the slope, soil configuration or

difficult geometry. The obtained results were summarised in the below table of factor of

safety.

Table 6 Factor of safety for undrained conditions (short term)

Cross section Seismic Load FOS

1-1 ---- 0.56

2-2 ---- 0.42

3-3 ---- 0.61

7-7 ---- 0.58

8-8 ---- 0.78

Table 7Factor of safety for drained conditions (long term)

Cross section Seismic Load FOS

1-1 ---- 0.71

2-2 ---- 0.42


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3-3 ---- 0.87

7-7 ---- 0.78

8-8 ---- 0.80

At this stage no seismic analysis has been considered since the preliminary results show

potential slope instability.

14. CONCLUSIONS AND RECOMMENDATIONS14.1 Conclusions

1. Generally, the ground description is consistent through the site comprisingcolluvium occasionally overlying alluvial deposits. The colluvium is overlying theBatolito de Zamora formation, composed of Granodiorita. Before the intact rock a

layer of highly weathered rock has been identified.

2. The proposed borehole grid, location and depth have been decided based on thepreliminary site walkover, structures location and importance. This proposed Ground

Investigation was submitted to ECSA for approval. Some boreholes were eliminated

and some exploration depths were reduced by ECSA. The final proposed borehole

location is included in Annex No. 2 Borehole Location.

3. A total of forty boreholes (40) have been undertaken with depths varying from 15mGBL to 41,30 mGBL. Information of six (6) boreholes of earlier investigation of

PUCE, and seven (7) boreholes of other companies have also been used. Annex 2and Annex 4.

4. A total of sixteen (16) trial pits have been undertaken with an excavator, withdepths varying from 2 and 2,50 m. The trial pit logs are located in the Annex No. 2.

Information of two (2) trial pits from earlier investigations of other companies has

also been used (see Annex 2 and Annex 4).

5. Thirty one (31) geotechnical cross sections showing the stratigraphy have beenproduced based on the information compiled during this site investigation and

previous investigations. These profiles have been attached in Annex 5.

6. For better understanding the ground configuration the soil description has beendivided in two sections below; one describing the ground conditions at thestructures area, and another description for the cutting slopes.


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a. MILLS, FLOATATION TANKS, SUBSTATION STRATIGRAPHYThe ground stratigraphy has been consistent in this area and comprises a 20 to

27 m thick layer of colluvium which includes pebbles and round boulders of quartz

sandstones and Granodiorita, with diameters varying from 0.03 to 3 m. The

material colour was described as reddish yellow, yellowish white and oxidized

material. The matrix is a mixture of very moist low plasticity silty Sand, SM in

accordance to USCS, and very moist low plasticity sandy Silt classified as ML. The

matrix also includes gravels and cobbles. The matrix is approximately the 60% of

the colluvium. Underlying the colluvium a residual material has been identified, thismaterial can be described as saprolite which is the Granodiorite rock weathering

process result. The thickness of this stratum varies from 0 to 6 m. Finally a third

layer was founded, composed of an intrusive rock Granodiorite that is described

as fracture and very fracture. In this rock it has been identified epidote, chlorite,

and oxides filling the fractures.

The borehole logs on which this ground model has been based are located in the

Annex No. 4 and 5.

b. SLOPES AREA STRATIGRAPHYIn this area eleven boreholes were undertaken, with depths varying between 19mBGL and 30,5 mBGL. The borehole logs are located in Annex No. 4 of thisreport.

The ground stratigraphy in this area comprises colluvium in the first layer, with

cobbles, pebbles and gravel. The matrix varies between a sandy silt , medium to

low plasticity, very moist, ML according to USCS and a silty sand, low plasticity,

very moist, SM according to USCS.

In this area no large boulders have been found and the percentage of matrix in

this colluvium is much higher varying between 70% and 90%.


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7. Ground water levels registered during the site investigation are shown in thefollowing Table.

Table 8 Ground Water level

Area of studyMinimum GWT

(masl)Maximum GWT

(masl)

Mills 890 897

Floatation tanks and

warehouse (mills, tanks)875 898

Substation 877 885

Slopes 883 904

8. The bearing capacity has been checked for elastic settlements from SPT values (seeAnnex No.6)

9. The bearing capacity based on the shear strength has been calculated consideringthe UU triaxial results.

10.Warehouse and floatation tanks can be founded on shallow foundations, whereasSAG and BALL mills should be founded using bored piles.

11.Based on the general arrangement and the topography provided by ECSA, ninecross sections have been produced in the slopes area. The cross sections areconsidered the most representative of the geometry proposed by ECSA, and have

been attached in the Annex No. 7.

12. The geometry of the cutting slopes comprises a 45 degree gradient, and amaximum height of 50 m.

13.The slope stability has been analysed for cross sections 1, 2, 3, 7 and 8 whichhave been considered the worst case. The chosen cross sections have been

analysed using specialised software based on the limit equilibrium and applying

Bishop methodology.

14.A minimum Factor of Safety of the slopes has been found considering the twodifferent conditions: Undrained conditions for short term analysis and drainedconditions for long term analysis.

15. The Factor of Safety for all cross sections analysed are less than one, withoutconsidering the seismic load. Therefore it can be said that the proposed slope

geometry is unstable.


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14.2 Recommendations

1. The foundation recommended for mills area (SAG and BALL mills) should followthe below recommendations:

2. The foundation recommended for floatation tanks and warehouse (mills andfloatation tanks) has been summarized below:

3. The foundation recommended for substation has been summarized below:

Type of foundation:Deep Foundation

(Rock socket bored pile)

Pile diameter: 600 mm

Foundation level: 865 masl (at least 3 diam into rock

head)

Bearing resistance: 10 MPa

Type of foundation:Shallow foundation (Continuous spread

footing)

Foundation level:Variable (at least 1m below platform

level)

Soil replacement: 0,50m of sub-base class 3

Bearing resistance: 120 KPa

Subgrade reaction modulus K30: 35 MN/m3


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4. It is recommended to carry out plate load test in order to confirm the estimatedsubgrade reaction modulus.

5.

It is recommended to carry out a pile load test on at least 2% of the proposedpiles in order to confirm the estimated pile capacity.

6. Any soft spots should be removed and replaced with granular material sub basetype class III, according to MTOP -001 F Standards.

7. For shallow foundations, a 500 mm thickness layer of compacted granularmaterial type Base III, according to MTOP-001 F Standards, shall be placed

underneath the foundation. This layer should have 300 mm more of the

proposed width of the foundation (B).

8. Prior foundation and platform construction, ground water level shall be loweredto at least two times the foundation width from the proposed formation level.

9. Due to the instability of the proposed cutting slopes, during detailed designstage, stability measures should be taken such as change in the proposedgeometry, retaining walls, soil nails, etc.

10.It is recommended the presence of a Geotechnical Engineer during excavationworks and foundation construction in order to ensure that expected soil

conditions are confirmed.

15. BIBLIOGRAPHY

y Bowles, Joseph. 2001. Foundation Analysis And Design 5th Edition

Type of foundation: Shallow foundation (Continuous spreadfooting)

Foundation level: 882 masl

Soil replacement: 0,50m of sub-base class 3

Bearing resistance: 120 KPa

Subgrade reaction modulus K30: 35 MN/m3


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y Gonzales de Vallejo, Luis et al. 2004 Ingeniera Geolgicay Barnes, Graham. 2005 Soil Mechanics 2nd Editiony Das, Braja M. 1999. Principles of Foundation Engineering 4 th Editiony Blockley, David. 2005. New Dictionary of Civil Engineering

GIR Section 4 - Rev01

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Transcript of GIR Section 4 - Rev01