Metehar Sugar.doc Improved Foundation Recommendation Final f

7/27/2019 Metehar Sugar.doc Improved Foundation Recommendation Final f

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CONSTRUCTION DESIGN SHARE COMPANY

1. INTRODUCTION

1.1 General

Following an agreement signed on 21st of April 2011 between

Matahara Sugar Factory and Construction Design Share Company

(CDSCo), Geotechnical works Business Unit of the Company has

performed geotechnical investigation works at Sabure, Afar for the

New Sugar Factory Project.

The investigation comprises of core drilling, pitting, insitu testing,

sampling and laboratory testing.

1.2 Location

The project site is located in Sabure, Afar Regional State, locally

known as Dankar, which is some 70km from Matahara town, which in

turn is at 200km from Addis Ababa along the road to Djibouti.

Location of the test points and layout plan of the project site is

attached.

2. METHODOLOGY OF INVESTIGATION

To get reliable and sufficient information about the surface and

subsurface geology and hydrogeology of the project area, the following

methodology was employed:

Planning of office and field work,

Rotary core drilling with in situ testing

Test pit excavation,

Sampling,

Logging, Conducting different laboratory tests and technical report writing.

2.1 Drilling and Pitting

The drilling operation was carried out using two mounted Koken

/Trailer rigs and a BR50 drilling machine.

New Sugar Factory at Kesem Geotechnical Investigation Report


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The methods applied in the investigation were in compliance with the

code, specification and standards of the American Society for Testing

Materials /ASTM/.

Plate. 1, 2 Trailer Mounted Koken Drilling Rigs



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A continuous rotary core drilling technique was used in order to obtain

high quality cores. During drilling, complete geological materials

reflecting the boreholes sections were collected as precisely as possible.

In loose and compacted soils, a dry drilling technique was used

starting with 116mm and reducing (when necessary) to 75mm

diameter with tungsten carbide bits fitted to a single core barrel.

As soon as soil or rock cores are removed from core barrels in each run,

they were placed in standard partitioned wooden core boxes and

described immediately on site. Finally, the boxes are properly labeled,

photographed and transported to the store.

For the purpose of visual inspection and completeness of data

numerous test pits were excavated distributed within the factorys

structures, inspected, logged and backfilled. Moreover, additional test

pits were excavated at the proposed road alignment of the factory and

samples were recovered for modified proctor density and tests.



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Plate 3, 4 Test Pits

2.2 Standard Penetration Test (SPT)

This test is performed to evaluate the degree of in site compactness

and/or consistency and strength of soils.

During drilling operation, at the bottom of the hole of required depth,

the split spoon sampler is lowered and driven in to the formation by a

drop of hammer of 63.5kg mass falling vertically through a height of

76cm. The method measures the resistance to penetration offered bythe formation. It is measured on the basis of the number of blows of

hammer required for a sampler tube penetration of 45cm. The number

of blows counted for the last two intervals, 15cm each, is added to

report as N-value of the test discarding the first 15cm penetration.

2.3 Sampling and Testing

Desired undisturbed soil samples were collected, where favorable

geological layers are encountered at depths shown on the log sheet of

each bore hole and sealed with wax in order to preserve the naturalmoisture content and transported to the main soil laboratory of

CDSCo. in order to perform the required tests.

3. GEOLOGY AND SEISMICITY



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3.1 Regional Geology

Since the area is located within the main Ethiopian Rift valley its

regional geology is highly affected by volcanism, tectonics, erosion, and

deposition.

3.2 Seismicity

The methods of assessing likely earthquake intensity and frequency at

a given site are complex, requiring reasonable judgment and collection

of geological and seismic data.

Due to this complexity for the structures with lesser magnitude, the

tendency is to rely upon seismic risk maps. The maps are often

published in national or state building codes, which recommend theengineering precaution to be taken in each rank of hazard in the map.

Ethiopia is divided into zones of approximately equal seismic risks

based on the known distribution of past earthquakes. By definition,

the hazard with in each zone can be assumed to be constant. (Refer

Table 1 below). From the seismic hazard map of Ethiopia, the project

site falls under zone 4 which corresponds to maximum hazard. This

map is based on the amplitudes to be expected during 100 years return

period.

The parameter o, the ratio of the bedrock acceleration to the

acceleration of gravity depends on the seismic zone (see the table

below)

Table1. Bedrock acceleration ratio o


Zone 4 3 2 1

o 0.10 0.07 0.05 0.03


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Figure 2: Seismic hazard map of Ethiopia

Project location



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3. 3 Topography, Local Geology

3.3.1 Topography

The area and its surroundings have flat topography. Currently it is further

modified and leveled as preparation for construction. No hills are observed in

close range to the site. A river called Kebena is located near the site.

3.1.2 Local Geology

Surfacially the area is covered uniformly by grayish color silty soil. In order

to establish subsurface geology and groundwater condition of the site 38

boreholes and 18 test pits (distributed within the different structures or

blocks of the factory) were proposed by the client. Progressive observation

and characterization was made in the course of drilling and it was agreedthat since the site is constituted by uniform formations some boreholes were

omitted. The formations were characterized according to samples recovered

by drilling and visual inspection of the test pits. Detailed outcome of the

drilling is presented on the log sheets while summary of the encountered

units is presented below.

A. Grayish Silty SAND

This unit is encountered in all the boreholes. It covers the surface of the site

as well as the top 5.50 to 7.0m. It is medium dense to dense, grayish, siltySAND/ sandy silt with occasional gravels. Standard Penetration Test

conducted on this layer gave an N-value in the range of 11 to 24. This unit

appears loose when observed from core recovered by drilling but when

observed in the test pits the walls are intact and not easy to excavate using

pick axe and shovel. This is further supported by the high N values.

Occasionally this unit comprises high percentage of gravels and rock

fragments, as can be observed in boreholes K33, K32, and K34.

The following averaged design engineering parameters are considered to

represent the layer:-

Bulk Unit Weight = 14.4KN/m3

Specific Gravity = 2.49

Moisture Content = 10.3%

Cohesion Value = 18.8KN/m2

Angle of internal friction = 25.70

New Sugar Factory Geotechnical Investigation Report


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Free Swell = 10%

Plasticity Index = 11.5%

B. River GRAVELS and SANDS

This unit is encountered underlying the top sandy silt/ silty sand soil. It is a

granular material composed of rounded, smooth river gravels and pebbles

mixed with sand. Occasionally pure river sand becomes dominant. Sometimes

this unit is intercalated by thin layer of silty formation. Standard Penetration

Test conducted on this layer gave varying N values in the range 23 to

refusals.

C. Sandy SILT

This unit occupies the bottom part of all of the boreholes. It underlies eitherthe top silty sand soil or the river sand and gravels. It is firm, brownish (wet)

and grey (dry) sandy SILT with some clay. Occasionally this unit is

intercalated by lamina of sand dominated formation. Groundwater is

encountered on this formation; as a result part of this formation which lies

below the water level is more cohesive than the part which lies above.

Standard Penetration Test conducted on this layer gave an N value in the

range of 11 to 43 with the most part being in the range of 14 to 19.

The following averaged design engineering parameters are considered to

represent the layer:-

Bulk Unit Weight = 15.7KN/m3

Specific Gravity = 2.5

Moisture Content = 9.1%

Cohesion Value = 8.4KN/m2

Angle of internal friction = 27.40

Free Swell = 12.3%

Plasticity Index = 6.3%

3.3.3 Ground Water Condition

Groundwater was encountered during drilling at depths in the range of 13.50

to 14.50m.

The following averaged engineering parameters are considered to represent

the water:-



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Chloride Content = 116.5mg/c

Sulphate Content = 77.7mg/c

PH-Value = 6.9

4. FOUNDATION RECOMMENDATION

4.1General

The geology of the site is uniform and it is composed of loose to medium dense

silty sand with occasional gravels followed by a relatively thin layer of

rounded gravels and pebbles and firm moist sandy silt soil is encountered to

the end of the drilling.

In some borehole log sheet the rounded gravel sand pepples will disappear

and pure, loose to medium dense sand will be found below the top soil layer.

In general the country has been divided in accordance with figure 2 (from the

geological report) and table 1 in to seismic zones, depending on the local

hazard .The site is located at the highly seismic area and seismic hazard

shall be taken in to consideration in the design of the structures.

4.2 Bearing Capacity Calculation

Bearing capacity computation is made using different calculation methods

giving stress to field tests. Site inspection results with engineering

considerations are taken to give the foundation recommendations.

Meyerhof approach is used for computing the allowable bearing capacity.

This approach is calculated for 25-mm settlement using SPTvalues

(Standard Penetration Test values) as can be seen below.

Qall= N x Kd BF4 F1

Qall = N (B+F3)2 Kd B>F4

F2 B2

Where: - Kd = 1 +.33(D/B) 1.33

N = Adjusted SPT blow count

B = Width of foundation



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D = Depth of foundation

So = Allowable settlement

For So=25mm

N70

F1 0.04

F2 0.06

F3 0.3F4 1.2

Adjusted N- Value calculation

Adjusted N value = N-count x Cn x 1x 2 x 3x 4

Where: - Cn = Adjustment for effective overburden pressure

1 = Adjustment for hammer energy

2 = Adjustment for rod length

3 = Adjustment for liner 4 = Adjustment for borehole diameter

In these equations N is the statistical average value for the footing influence

zone of about 0.5B above footing base to at least 2B below.

Note:-In these equations, footing width is a significant parameter. Obviously

if the influence depth is on the order of 2B a larger footing width will affect

the soil to a greater depth and strains integrated over a greater depth will

produce a larger settlement.

Considering the allowable settlement to be 25mm at the recommended

foundation depth the following allowable bearing capacity is calculated for

the following structures.

No. Type of Structure Foundation Type Foundation Depth

from N!

"earin#

Capacity



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1 Cane Handling Isolated Footing 3.0m 220Kpa

2 Boiler House

2.1.For the Building Isolated Footing 3.0m 200Kpa

2.2.For the Tanks Mat oundation 3.0m 2!0Kpa

3 Po"er #u$%#tation Mat oundation 2.&m 3&0Kpa

' Milling House Mat oundation 2.&m 3&0Kpa& Centriugal House Isolated Footing 3.0m 220Kpa

( #ugar #tore Isolated Footing 3.&m 1)0Kpa

* +orkshop Isolated Footing 2.&m 200Kpa

! Pro,ess House Mat oundation 2.&m 300Kpa

) Pump House Mat oundation 3.0m 300Kpa

10 -iuser Isolated Footing 2.0m 1)0Kpa

Additional Consideration

PH, Chloride and Sulphate content of soil was determined according to BS

1377, and all values are with in the permissible requirement (BS 3148).Therefore Ordinary Portland Cement can be used for the structures.

4.3 DESIGN CONSIDERATION FOR THE ROAD

Engineering characteristics of sub grade soil, i.e. its CBR strength is used to

design foundation of heavy duty pavements. It is clear that heavy trucks are

expected to move around the service area within the premises of the factory

for loading and unloading purposes. Considering this fact sub grade soil

investigation has been conducted using test pits along with sampling andsubsequent libratory testing.

The entire site is composed of uniform geology as revealed by borings and pit

excavation. For this particular case associated with road base, test pits

TP19, 20, 21 and 22 have been dug to a maximum depth of 4m. The test pits

were properly logged and representative samples were taken for laboratory

testing form layers that are likely to be affected by traffic load.

The laboratory tests conducted on the sub grade soil samples are

CBR test

Classification test (Atterberg limits and grading)

Natural moisture content.

The summary of the soil test results are appended in the report.



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4.3.1. LABORATORY TEST RESULTS AND ANALYSIS

The test pit logs depict that there exist two layers which are sandy silt soils.

The most problematic in sub grades are expansive soils which does not exist

at this site makes the situation very favorable for the desired purpose.

4.3.1.1. Laboratory CBR

Laboratory CBR indirectly measures the shearing resistance of a soil under

controlled moisture and density conditions. Therefore, Laboratory CBR tests

were under taken on the sub grade soil samples to measure its strength. The

CBR values are reasonably high enough which falls in the range of 9% -18%

with one exceptional result of 3%.

4.3.1.2. Plastic Index

The Plasticity of a soil gives very good indication of its expansion potential.

Therefore, Atterberg limit tests were undertaken to asses its expansion

potential and the results reveal that the soil is low plastic. Besides the swell

test result also depicts that it is very far below the permissible limit which is

4%.

4.3.1.3. AASHTO Soil Classification

After conducting Atterbergs limit and gradation tests it is possible to classify

sub grade soil as per AASHTO soil classification. In general, using AASHTO

soil classification a material can be rated as excellent to poor as road sub

grade material. Accordingly, the sub grade soil of the site in consideration

falls dominantly in A-5 class and rated as fair to good as per AASHTO road

sub grade rating.


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Metehar Sugar.doc Improved Foundation Recommendation Final f