Ethiopian Maritime Affairs Authority (EMAA) Beza Consulting Engineers Plc
Soil &Materials Investigation Report
Demand analysis, detail design preparation, supervision and July 2019 Contract admminstration of Modjo Green logistics Hub expansion project Page 1
Ethiopian Maritime Affairs Authority (EMAA) Beza Consulting Engineers Plc
Soil &Materials Investigation Report
Demand analysis, detail design preparation, supervision and July 2019 Contract admminstration of Modjo Green logistics Hub expansion project Page 2
Table of Contents CHAPTER–1........................................................................................................... 6 INTRODUCTION ..................................................................................................... 6 1.1. BACKGROUND ............................................................................................................................6 1.2. PROJECT LOCATION ..................................................................................................................7 1.3. METOROLOGICAL INFORMATION.........................................................................................8
1.4. GEOLOGY OF THE PROJECT AREA ........................................................................................8 1.5. SCOPE OF WORKS ......................................................................................................................9 CHAPTER–2......................................................................................................... 11 IN-SITU SUB GRADE MATERIAL INVESTIGATION ................................................ 11 2.1 FIELD SRUVEY ..........................................................................................................................11 2.1.1 SURFACE CONDITIONS .........................................................................................................11
2.1.2 SUBSURFACE CONDITIONS .................................................................................................12 2.1.3 TEST PIT AND SAMPLING .....................................................................................................18
2.1.4 DYNAMIC CONE PENETROMETER TEST (DCP TESTING) .............................................19
2.2 INTERPRETATION OF TEST RESULTS .................................................................................20 2.2.1 LABORATORY TEST RESULT ANALYSIS ..........................................................................20 2.2.2 FIELD DCP RESULT ANALYSIS............................................................................................27
2.2.3 PROBLEMATIC SUBGRADE SOIL AND TREATMENT MEASURES ...............................31 2.2.4 DETERMINATION OF DESIGN SUBGRADE STRENGTH .................................................33 CHAPTER–3......................................................................................................... 35 DEEP GEOTECHNCIAL INVESTIGATION .............................................................. 35 3.1 GENERAL ...................................................................................................................................35 3.1.1 SEISMICITY OF THE PROJECT AREA .................................................................................36
3.1.2 SITE GEOLOGY ........................................................................................................................36
3.2 FIELD INVESTIGATION ...........................................................................................................37 3.2.1 CORE DRILLING ......................................................................................................................37 3.2.2 DESCRIPTION OF GEOTECHNICAL LAYER ......................................................................40
3.2.2.1 Layer-I: Light to Dark Brown Clay (0.00 to 3.45 m) ........................................................40 3.2.2.2 Layer-II: Dark to Light Brown Silty CLAY Soil (3.45 to 6.45 m) ...................................40
3.2.2.3 Layer-III: Brown Silty CLAY (6.45 to 9.45m) .................................................................40 3.2.2.4 Layer IV: Light Brown Silty CLAY (9.45 to 13m) ...........................................................40
3.2.2.5 Layer IV: Silty Clay with Some Sand (13m to 20m) ........................................................41 3.2.3 STANDARD PENETRATION TEST (SPT) (ASTM D1586) ..................................................41 3.2.4 GROUND WATER LEVEL MEASUREMENT (ASTM D6000) ............................................45 3.3 LABORATORY TESTS ..............................................................................................................45
3.3.1 BULK UNIT WEIGHT () .........................................................................................................45
3.3.2 SPECIFIC GRAVITY (GS) (ASTM D854 – 14) .......................................................................45
3.3.3 WATER CONTENT DETERMINATION (%) (A5TM D 2974-87) ......................................45
3.3.4 SIEVE ANALYSIS (ASTM C136 / C136M – 14) .....................................................................46 3.3.5 CHEMICAL TEST OF SOIL .....................................................................................................46 3.3.6 ATTERBERG LIMIT TESTS (ASTM D4318 - 17E1) ..............................................................46
3.3.7 UNCONFINED COMPRESSION STRENGTH TEST (UCS TEST) (ASTM D2166 ..............46 3.3.8 DIRECT SHEAR STRENGTH TEST (DSST) (ASTM D3080 / D3080M – 11) ......................46 3.4 BEARING CAPACITY OF SOIL ...............................................................................................47
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3.4.1 BEARING CAPACITY OF SOILS BASED ON LABORATORY RESULT ..........................47 3.4.2 BEARING CAPACITY OF SOILS BASED ON FIELD SPT N- VALUES ............................50 3.4.3 SETTLEMENT ANALYSIS ......................................................................................................52 3.5 RETAINING STRUCTURES ......................................................................................................52 CHAPTER–4......................................................................................................... 53 LOCATION AND TESTING OF CONSTRUCTION MATERIALS ................................. 53 4.1 GENERAL ...................................................................................................................................53 4.2 GRAVEL BORROW SOURCE INVESTIGATION ...................................................................55 4.3 ROCK QUARRY SOURCES ......................................................................................................58
4.4 NATURAL SAND SOURCES ....................................................................................................61 4.5 WATER SOURCES FOR CONSTRUCTION ............................................................................64 CHAPTER–5......................................................................................................... 65 CONCLUSIONS AND RECOMMENDATIONS ........................................................... 65 5.1 CONCLUSION ............................................................................................................................65 5.2 RECOMMENDATIONS .............................................................................................................66
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LIST OF FIGURES
Figure 1.1: Satellite Image of dry port (Location of map)…………………….……6
Figure1.2: Geological map of the area ……………………………………………8
Figure-2.1: Partial view of hub expansion area………………………….………11
Figure -2.2: Erosion gullies within the expansion area…………………………….11
Figure 2.3: Test pit excavation……………………………………………………12
Figure 2.4: DCP Testing in Progress……………………………………………….18
Figure 2.5: Variation of Plasticity index (%) of the sub grade soils @1-2m depth.20
Figure 2.6: Plasticity index (%) of the sub grade soils at variable depth………....21
Figure 2.7: Variation of Plasticity index (%) of the subgrade soils 2-6m depth….22
Figure2.8: A-Line chart of the sub grade soils…………………………………….23
Figure2.9: Variation of Maximum Dry Density of soil at variable depth....……….24
Figure2.10: Variation of Optimum Moisture Content of soil at variable depth........24
Figure2.11: Variation of subgrade soil CBR at 95% MDD…………………….….25
Figure2.12: Variation of CBR-swell of subgrade soil……………………………...26
Figure 2.13: Laboratory test on progress @ BCE central Laboratory…………….26
Figure2.14: In-situ CBR values @ ground level……………………………………28
Figure2.15: In-situ CBR values @ 2m level…………………………………….….28
Figure2.16: In-situ CBR values @ 3m depth………………………………………29
Figure2.17: In-situ CBR values @ 4m depth……………………………………....29
Figure2.18: In-situ CBR values @ 5m depth………………………………………30
Figure 2.19: In-situ CBR values @ 5-6m depth……………………………………30
Figure2.20: In-situ CBR values @ 6-7m depth…………………………………….31
Figure 3.1: Location of the boreholes with respect to the site map……………….38
Figure 3.2: Core Drilling Process on the project Site………………………………39
Figure 3.3: Sample photos of Borehole boxes…………………………………….39
Figure 4.1: Natural gravel source at Melmele kebele…………………………….57
Figure 4.2: Rock quarry source within the compound (Q1)………………………..59
Figure 4.3: Rock quarry Source 11.8Km towards Debrezeit (Q2) …………...…...60
Figure 4.4: sieve analysis of natural sand sources …………………………….….63
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LIST OF TABLES
Table 1.1: Monthly Mean Maximum and Minimum Temperature of Modjo town…...7
Table 2.1: In situ material Description on trial test pits……………………………12
Table 2.2: Statistical summary of DCP- CBR’s value ……………………………...27
Table 2.3: Design Subgrade strength of Test Pits…………………………………33
Table 3.1: Bedrock Acceleration Ratio αo……………………………………...…36
Table 3.2: Summary of geological formation of the site………………………….36
Table 3.3: Location of boreholes………………………………………………….38
Table 3.4: Measured and adjusted SPT N-Values for the project………………...42
Table 3.5: Bearing Capacity of Selected depths………………………………….47
Table 3.6: Allowable bearing pressure (kPa) based on SPT at depth of 2.5m…...51
Table 4.1: Description of borrow source………………………………………….55
Table 4.2: The tests to be carried out on natural gravel source samples…………56
Table 4.3: Summary of test result of Natural gravel sources……………………...56
Table 4.4: Tests to be carried out on the rock sample…………………………….58
Table 4.5: Summary of Rock Quarry source ……………………………………...59
Table 4.6: Test result and requirements for rock aggregate……………………...61
Table 4.7: Test result and requirements for natural sand source …………………63
LIST OF ANNEXES
Annex – I Test Pit logs of subgrade soil
Annex – II DCP Test and analysis,
Annex – III Summary of Laboratory test Results of subgrade soil and
construction materials
Annex – IV Summary of Boreholes laboratory test Results and
Annex – V Boreholes logs
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CHAPTER–1
INTRODUCTION
1.1. BACKGROUND
The Government of the Federal Democratic Republic of Ethiopia, represented
by the Ethiopian Martime Affairs Authority(EMAA) has been allocated grant
funds from the World Bank towards consultancy services for demand
analysis, detail design preparation, supervision and contract administration
of Modjo green logistics Hub expansion project.
Ports are well known as playing an important role in multimodal transport
systems and international supply chains, apart from their traditional role as
clusters of economic activities. Ports engage in various activities:
loading/discharging cargo onto/from vessels; providing value- added
services such as labeling, packaging, cross-docking, and others; and acting as
warehouse and distribution centers (World Bank, 2007). Ports add more
value to shipments that are in the port area by further integrating themselves
into value chains. Many ports are increasingly being perceived as integrated
and inseparable nodes in their customers’ supply chains. Ports play a critical
role in the effective and efficient management of this industry.
In the move to cater for an ever increasing volume of import-export goods in
a coordinated way, the government of Ethiopia has taken a strategic
measure by improve development of the dry port at several locations in the
country, Modjo dry port expansion being one of them.
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1.2. PROJECT LOCATION
Modjo dry port is located in the eastern Shewa zone at Lome woreda of the
oromia regional state , nearly 75 km East of Addis Ababa, it has a latitude
and longitude of N8°34'25.89880"E39°09'11.34467". Modjo town has long
been a commercial center of the Eastern Shewa zone .The proposed project
consists of demand analysis, detail design preparation, supervision and
contract administration of Modjo green logistics Hub expansion project.
Figure1.1 depicts the satellite imagery of Modjo dry port.
Figure1.1: Satellite Image of dry port (Location of map)
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1.3. METOROLOGICAL INFORMATION
The meteorological information of the area is collected from Meteorological
map of Ethiopia, 1979 edition. In addition to that, recent data were collected
from Modjo meteorological station. The data gathered include, climatic
classification of the area, Rainfall data, and temperature of the project area.
Climatically, the project area is classified as warm temperate climatic zones
and receives a mean annual rainfall of 875mm.
The monthly mean maximum temperature varies from 25.8 0c to 31.20c. the
higher usually recorded from March to April while lower temperature is
recorded from December to January.
Table1.1: Monthly Mean Maximum and Minimum Temperature of Modjo town
1.4. GEOLOGY OF THE PROJECT AREA
Parallel with the geotechnical investigation, the geological condition of the
site and regional geology of the site is always important to study. The project
area is characterized by different rock formations and soils emanating from
weathering of those rocks and transported from neighboring area. According
to the Geological Map of Ethiopia, Mengeshaet.al (1996) and field
observation, the area is covered by Tertiary and Quaternary volcanic,
lacustrine sediments and alluvium. In the main Ethiopian rift the quaternary
sediments are mostly of lacustrine origin. Lacustrine beds are inter-bedded
Temperature Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Maximum Mean.
28.6 29.6 30.2 30.5 31.2 28.7 26.3 25.8 27.6 28.4 28.4 27.8
Minimum Mean.
9.50 10.5 12.9 13.5 13.6 13.4 13.1 13.2 12.6 11.1 10.1 8.3
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with Plio-Pleistocencepyroclastics in the lake region and on the rift shoulders.
The lacustrine beds are mostly re-deposit volcanic sands, tuffs with calcareous
diatomite.
Figure1.2- Geological map of the area
1.5. SCOPE OF WORKS
In order to design heavy duty pavement structures, to locate suitable
construction materials for the pavement works and to assess geotechnical
hazards at green logistics hub expansion project, a full materials and
geotechnical investigation work were carried out within Modjo green logistics
hub expansion project.
Project area
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The scope of investigations included:
Subsurface soil Investigation: - this includes conducting borehole
investigation, Dynamic Cone penetration tests (DCPs) and
exploration of trial test pits.
Borrow sources Investigations: - this involves exploration of borrow
sources location, excavation of trial test pits and collect material
for laboratory.
Quarry sources Investigations: - this involves identification of rock
sources and hand pick rock samples from sources for laboratory
testing.
Sand and Water sources: - this involves identification sources and
collect sample from the sources.
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CHAPTER–2
IN-SITU SUB GRADE MATERIAL INVESTIGATION
2.1 FIELD SRUVEY
General site condition assessment was carried out visually, through datum
location, GPS recordings, test pit excavation, DCP surveys and basic soil
characteristic evaluation. The in-situ subgrade material investigations were
carried out in January 2019. The formation of subgrade material is
influenced by the geology of the area. A general description of the geology
is presented in section 1.4 of the report.
The following sub-sections provide a summary of the surface and subsurface
conditions encountered during the investigation.
2.1.1 SURFACE CONDITIONS
The ground surface at propose Modjo green logistics hub expansion area is
dominantly rolling and flat terrain with some mountainous terrain near to the
existing rail yard section. Erosion gullies up to 3m depth is observed at
several location within the proposed expansion area. The in-situ material
within the proposed expansion area is predominantly thick layer of clay to
silty clay soil soil formation but thickness of 3m depth rock out crop were
observed around the west north direction on existing rail yard. Vegetation
within surrounding is primarily limited to short grass, small bushes and
scattered trees grow.
There is huge amount of waste/spoiled material (from existing construction
works) on the proposed port development area, which needs to be removed
by the contractor during construction.
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2.1.2 SUBSURFACE CONDITIONS
The subsurface investigations on the expansion area are conducted by
exploration of trial test pits extended up to 4.5m and borehole investigation
extended up to 20m. As per the investigation , the in-situ material on the
project area is predominantly of Light to dark clay Soil, dark to light Brown
silty clay soil, Brown silty clay, Light Brown Silty clay soil and Silty clay with
some Sand. But limited thickness of weathered rock outcrops was observed at
near the existing rail yard. In all the trial pits and boreholes, no ground
water was encounter within the depths.
Total of 40 trial test pits and 14 boreholes were investigated within
expansion area from January to February 2019. The test pits were dug at
an average of 100m length interval. The locations are shown on table 2.1.
The soil profiles were logged and disturbed soil samples were collected for
Figure -2.2: Erosion gullies within the
expansion area
Figure-2.1: Partial view of hub
expansion area
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laboratory testing. Material description of each trial test pits are presented
in table 2.1.
Table2.1 In situ material Description on trial test pits
Test Pit
GPS (E,N) Depth (cm) Material Description
TP-1 0516605, 0948821
0-20 Light brown medium stiff clay soil
20-100 brown medium stiff clay silt soil
100-200 light brown medium stiff clay silt soil mixed with little gravel
TP-2 0516673, 0948916
0-30 light brown medium stiff silt clay soil
30-100 brown stiff sand silt clay soil
100-200 Reddish to brown stiff, medium dry sand silt clay soil mixed with gravel
TP-3 0516731, 0949012
0-20 brown sandy silt clay soil
20-40 dark brown clay silt soil
40-100 brown stiff silt clay soil
Figure 2.3: Test pit excavation
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100-200 light brown stiff, medium dry silty clay sand soil
TP-4 0516765 ,0948848
0-30 brown medium stiff clay silt soil
30-100 loose black brown moist clay silt soil
100-200 light brown silt clay sand soil
TP-5 0516847, 0948939
0-40 light brown to light gray medium stiff, dry silt clay sand soil
40-100 brown clay silt sandy soil
100-200 brown clay silt soil
TP-6 0517002, 0949011
0-260 gray medium stiff silt clay soil
260-360 light gray silt clay soil
360-460 loose light gray silt sand clay soil
TP-7 0517149, 0948993
0-50 light brown medium stiff ,medium dry silt clay sand soil
50-100 light gray silt clay sand soil with whitish sedmentary gravel material
100-200 whitish to light gray sand silt clay soil
TP-8 0517024, 0948812
0-30 light gray spoiled soil
30-100 natural soil ,black moist clay silt soil
100-200 light gray clay silt sand soil
TP-9 0516877, 0948838
0-80 dark brown medium stiff, medium dry clay silt soil
80-140 light gray medium stiff ,medium dry sandy silt clay soil with few gravel
140-200 light gray sand silt clay soil with few gravel material
TP-10 0516734, 0948748
0-20 light brown medium stiff clay silt soil
20-100 black medium stiff clay soil
100-200 light brown medium stiff moist clay silt soil
TP-11 0516467, 0948657
0-40 Light brown to gray clay silt soil
40-100 black clay soil
100-360 light brown medium stiff clay silt soil
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360-460 light gray medium stiff silt clay soil
TP-12 0516558, 0948618
0-20 light brown to brown clay soil
20-100 black clay soil
100-280 brown clay silt soil
280-380 light gray silt clay sand soil
380-480 light gray silt clay sand soil
TP-13 516618, 94875
0-30 dark brown clay silt soil
30-100 black clay silt sand soil
100-200 light brown clay silt soil mixed with few gravel
TP-14 516516, 948755
0-100 dark brown clay soil
100-150 light brown clay silt soil
150-200 light gray medium stiff, medium dry silt clay soil
TP-15 516731, 948670
0-100 dark brown stiff ,dry clay silt sand soil
100-200 light brown stiff, dry clay silt sand soil
TP-16 516875, 948750
0-100 dark brown clay silt soil
100-200 light brown clay silt soil
TP-17 516531, 948373
0-100 black clay soil
100-200 dark brown clay soil
TP-18 516648, 948576
0-20 light brown to brown clay soil
20-100 black clay silt soil
100-200 light brown clay soil
200-320 light gray clay soil
320-420 light yellowish gray clay silt soil
420-520 light yellowish gray medium stiff ,medium dry clay silt soil
TP-19 0516910 , 0948615
0-360 black clay soil
360-460 dark brown stiff clay silt soil
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TP-20 0517010, 0948572
0-10 black clay soil
10-100 light gray clay soil
100-200 light brown to light gray clay soil
TP-21 0517089, 0948488
0-100 Light brown clay soil
100-200 light gray clay silt soil mixed with few gravel material
TP-22 0516725, 0948829
0-20 light brown clay soil
20-100 black clay soil
100-200 light brown medium stiff clay sand silt soil
TP-23 516719, 948640
0-100 brown medium stiff clay silt soil
100-200 light brown very stiff, dry silt clay sand soil
TP-24 516796, 948582
0-30 brown clay soil
30-110 light brown silt clay sand soil
110-200 light yellowish to light gray very stiff ,dry silt sand clay soil
TP-25 516863, 948525
0-30 light brown clay soil
30-400 light gray clay silt sand soil
400-500 loose light gray ,moist silt clay sand soil
500-600 loose light gray moist clay silt sand soil
TP-26 0516743, 0948458
0-400 light brown clay silt soil
400-450 loose dark gray medium dry clay silt sand soil
450-500 light gray to light brown medium stiff, medium dry silt sand clay soil
500-600 light gray silt sand clay soil
TP-27 0516893, 0948411
0-50 black clay soil
50-250 light gray to light brown clay silt soil
250-400 light gray medium stiff, medium dry silt clay sand soil
TP-28 0516498, 0948245
0-240 brown medium stiff, medium dry clay silt sand soil
240-440 light brown moist clay silt soil
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TP-29 0516568, 0948109
0-50 brown stiff ,dry clay silt soil
50-110 light brown stiff, dry clay silt soil
110-200 brown stiff, dry clay silt soil mixed with few gravel material
TP-30 0516974, 0949078
0-90 light brown medium stiff, dry clay silt sand soil
90-150 light gray to whitish stiff ,dry clay silt sand soil mixed with gravel material
150-200 light brown clay silt soil
TP-31 0516952, 0948968
0-50 dark brown clay sand gravel material
50-120 light brown clay silt mixed with gravel material
120-200 light brown medium stiff, medium dry clay silt soil
TP-32 0516675, 0948504
0-20 light brown clay soil
20-110 black to brown clay soil
110-200 brown clay soil with few gravel material
TP-33 0516480, 0948022
0-30 light brown clay soil
30-120 brown clay soil
120-200 dark brown clay soil
TP-34 0516788, 0948704
0-90 dark brown medium stiff, medium dry clay soil
90-200 light brown silt clay soil
TP-35 0516849, 0949128
0-80 light red to light gray dry clay silt soil with few gravel material (can be as construction material)
80-200 light gray to light brown dry clay silt soil with gravel material (recommended as construction material)
TP-36 0516905, 0949061
0-100 light gray to light brown clay silt soil
100-200 light gray to light brown clay silt soil with gravel material
TP-37 0516399, 0948215
0-130 light brown gray silt clay soil
130-200 light gray sand silt clay soil
TP-38 0516326, 0948030
0-400 light gray sand silt clay soil
400-500 brown clay sand silt soil
TP-39 0516296, 0947971
0-100 black clay soil
100-250 Black clay silt soil
TP-40 0516382, 0947922
0-120 dark brown dry silt clay soil
120-200 light brown clay silt soil
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Based on field observations and laboratory test result analysis, it was
concluded that the in-situ subgrade layer cannot provide adequate bearing
strengths and less deformation resistance for design heavy load and
therefore, an improved subgrade layer is required.
2.1.3 TEST PIT AND SAMPLING
To determine the engineering properties and to assess the suitability of the in
situ material within the expansion area ,representative disturbed samples
were collected by digging test pits from each layer of variable soil profiles
hence, more than one samples were taken from each test pit where the soil
profiles exhibit variability. Test pits of approx 1.5 m x 1.5 m size were
excavated to depth up to 4.5m below the actual ground surface.Upon
completion of the pit excavation and sampling, the vertical soil profile of
each test pit was recorded and the test holes then carefully
backfilled,compacted and leveled off to their original level. The collected
samples from test pits were tested at Beza consulting engineer Central
laboratory.The test pit logs are summarized and presented in Annex–I of
report.
The following tests were performed:
Particle Size Analysis (AASHTO T88-90)
Atterberg Limits, LL , PL and LS(AASHTO T89-90 and T90-87)
Moisture-Density Relationship (AASHTO 180-90, Method D)
Four days soaked 3-Point CBR (AASHTO T193)
CBR-swell and
Linear shrinkage limit test
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2.1.4 DYNAMIC CONE PENETROMETER TEST (DCP TESTING)
A Dynamic Cone Penetration Survey (DCP testing) was carried out within
propose dry port expansion area at 40 test pits location .The DCP test is a
rapid but continuous assessment of in situ strength of the foundation material.
The in-situ DCP tests were performed during the dry season hence the in-situ
CBR values derived from the DCP testing were greater than laboratory CBR
values . Detailed analysis of DCP field data and interpretation of results are
given in Annex II.
The underlying principle of the DCP test is that the rate of penetration of a
60o steel cone driven by a standard (8kg) hammer freely falling through a
controlled (575mm) drop is inversely related to the strength of the material
as measured by, for example the low rate of DCP penetration resistance is
associated with high strengths material while high rate of penetration is
encountered in weak layers. While conducting the test, in majority of sections
of the road were found appropriate to take reading at increment of with 3
to 10 consecutive blows. DCP testing was carried out using the equipment,
test procedure and data interpretation method as recommended by TRRL
Manual (Road Note 31).
Figure 2.4: DCP Testing in Progress
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The DCP penetration rate (mm/blow) has been converted to CBR value using
the standard TRL correlation formula Log10(CBR)=2.48–1.057 x
log10(mm/blow). The UK DCP version 3.1 software which was developed
by TRRL has been used for analysis and delineates the boundaries of various
subsurface strata and computes field DCP data in to layer wise in-situ -CBR
values.
2.2 INTERPRETATION OF TEST RESULTS
2.2.1 LABORATORY TEST RESULT ANALYSIS
In order to design heavy duty pavement structures of Modjo Green Logistics
Hub expansion , the in-situ sub grade material lies within of 3000 mm depth
below finished design sub grade level were properly analyzed since it is
critical to pavement structure to perform satisfactorily.
In general, the subgrade layer is required to resist repeated stressing by
heavy duty traffic and to be stable to the stresses imposed by varying
climatic and moisture influence. For the pavement design purpose, the in-situ
sub grade material within the infulence depth has been analyzed in
accordance with the procedures given in different design manuals. As
recommended in the design manuals the roadbed formation will be re-
compacted to 95% of BS Heavy compaction density in order to ensure that a
high level of subgrade support is obtained.
As a matter of interest the subgrade material were also classified in
accordance with the average in-situ-CBR values derived from the DCP tests
at full depth. This will give an alternative indication of uniformity and in-situ
strength of the layer. Apart from the uniform ground level; deteroration of
ground(erosion gully) were encountered in any of the test pits which were
samples were collected from a depth of approximately more than 4m.
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As per the test result, the in-situ material is predominantly fine grained soils
but few sections had coarse grained soils. The fine grained soils of silty clay
and clay soil had high plasticity with Liquid Limit values ranging from 0% to
98% and Plasticity index values ranging from 0% to 46%.The variation of
Plasticity of subgrade soil is presented in figure 2.5 below.
Figure 2.5: Variation of Plasticity index (%) of the sub grade soils @1-2m depth
0
10
20
30
40
50
60
70
80
90
100
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
Pla
stic
ity
Val
ue
s (%
)
TP-No.
Varation of Plasticity of Sub grade soil
LL
PI
UL LL
UL PI
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0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
LL @1-2m
PI @1-2m
LL @2-3m
PI @2-3m
LL @3-4m
PI @3-4m
LL @4-5m
PI @4-5m
LL @5-6m
PI @5-6m
LL @6m
PI @6m
UL LL
UL PI
TP-No.
0
10
20
30
40
50
60
70
80
90
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
Pla
stic
ity
Val
ue
s (%
)
Station TP-No.
Plasticity of subgrade soil
LL
PI
UL LL
UL PI
Figure 2.6: Plasticity index (%) of the sub grade soils at variable depth
Figure 2.7: Variation of Plasticity index (%) of the subgrade soils 2-6m depth
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0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90 100 110
Pla
stic
ity
Ind
ex
(%)
Liquid Limit
A-Line Chart for Sub grade soil
A-line
The plasticity chart helps to classify the type of soils based on their plasticity
characteristics (i.e. Atterberg Limits and Indices of soils). Generally, materials
falling above the A-Line are classified as clays and below the A-Line are
classified as silts or gravel. A-line plot shown in Figure below indicates that
the predominate samples from expansion area have been found above the
A-line plotting which again confirmed that the material has high plastic fine
grain soil.
Figure2.8: A-Line chart of the sub grade soils
Soil samples collected from trial pits have been compacted in the laboratory
at various moisture contents to derive a dry density versus moisture content
relationship.The Maximum Dry Density (MDD) and optimum moisture content
(OMC) of subgrade soil samples on Modjo green hub project graphically
presented in Figure 2.9 below: As per the test result, the MDD and OMC
values of sub grade material over variable depth ranged from 1.36 to
1.86g/cm3 and 12% to 36% respectively but in majority section the MDD
value >1.42g/cm3 and OMC value > 14.0%.
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1.30
1.40
1.50
1.60
1.70
1.80
1.90
0 5 10 15 20 25 30 35 40
MDD (g/cm3)1mMDD (g/cm3)2-3mMDD (g/cm3)3-4mMDD (g/cm3)4-5m
MDD of Subgrade soil at variable depth
Test pit
MD
D (
g/c
m3)
Figure2.9: Variation of Maximum Dry Density of soil at variable depth (T180
Compaction)
Figure2.10: Variation of Optimum Moisture Content of soil at variable depth
(T180)
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0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
CBR at95%MDD
Min CBR
Variation subgrade soil CBR @95%MDD
Test pit no.
Four days soaked three point CBR test in accordance with AASHTO T-193
was carried out on disturbed soil samples recovered from test pits to
determine the strength of the sub grade material. CBR-swell test also
conducted to evaluate potential expansiveness of the material.
The shear strength of a material is closely related to the material
classification. The CBR results therefore follow the trend of the material
classifications. For fine grained of clay and silt clay soil have low CBR values
and have high CBR swell. Isolated higher CBR values are encountered at few
test pits as shown in Figure 2.11 below. As per the test result, about 85% of
the total sub grade samples of expansion area have CBR strengths value less
than 5% and these can be classified as unsuitable soil hence it needs
replaced with selected suitable material.
Figure2.11: Variation of subgrade soil CBR at 95% MDD
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0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
CBR-swell of subgrade soil.
Av. swell(%)
SwellLimit
Test pit
The amount of CBR-swell also determined on disturbed samples of soil
recovered from test pits to evaluate potential to heave of the material. As
per the test result predominate sub grade soil samples have CBR-swell value
of greater than 3% .These soil could be potentially expansive and have low
bearing strength. The CBR-swell values of subgrade soil samples graphically
presented in Figure below. The summary of the subgrade soil test result is
given in Annex-III of the report.
Figure2.12: – Variation of CBR-swell of subgrade soil
Figure 2.13: Laboratory test on progress @ BCE central Laboratory
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2.2.2 FIELD DCP RESULT ANALYSIS
DCP testing was carried out using the equipment, test procedure and data
interpretation method as recommended by TRRL Manual (Road Note 31). The
UK DCP version 3.1 software which was developed by TRRL has been used
for analysis and delineates the boundaries of subsurface strata and computes
field DCP data in to layer wise in-situ-CBR values.
The DCP tests were carried out to obtain the in-situ strength of the subgrade
soil within the expansion area. The DCP-CBR’s are usually higher than the
laboratory CBR results .The statistical in-situ CBR values derived from the DCP
testing are summerized in the table 2.2 below.
Table2.2: Statistical summary of DCP- CBR’s value
Parameters
DCP – CBR values over the influence depth.
Ground Level
1-2m Depth
2-3m Depth
3-4m Depth
4-5m Depth
5-6m Depth
6-7m Depth
Average Value 12.2 17.7 18.5 11.9 13.6 9.3 13.5 Maximum Value 27 37 40 21 45 19 19 Minimum Value 1 3 2 1 2 3 8 90th Percentile 22.1 29 27.6 19.6 25.8 16.6 17.9
Median 10.5 19 19 12.5 7 7.5 13.5
The summary of DCP test result is given in Annex-II of the report
The distribution DCP-CBR Value at variable depth are presented through
Figure 14 to Figure 20
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0
5
10
15
20
25
30
0 5 10 15 20 25 30 35 40
Insitu CBR Value @ Ground Level
DCP-CBR%
DC
P-C
BR
%
Test Pit No.
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40
Insitu CBR value @ 1-2m Depth
DCP-CBR
DC
P-C
BR
%
Test Pit No.
Figure2.14: In-situ CBR values @ ground level
Figure2.15: In-situ CBR values @ 2m level
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0
5
10
15
20
25
30
35
40
45
0 5 10 15 20 25 30 35 40
Insitu CBR value @ 2-3m Depth
DCP-CBR
DC
P-C
BR
%
Test Pit No.
0
5
10
15
20
25
0 5 10 15 20 25 30 35 40
Insitu CBR value @ 3-4m Depth
DCP-CBR%
DC
P-C
BR
%
Test Pit No.
Figure2.16: In-situ CBR values @ 3m depth
Figure2.17: In-situ CBR values @ 4m depth
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0
5
10
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30 35 40
Insitu CBR value @ 4-5m Depth
DCP-CBR%
DC
P-C
BR
%
Test Pit No.
Figure2.18: In-situ CBR values @ 5m depth
Figure 2.19: In-situ CBR values @ 5-6m depth
0
2
4
6
8
10
12
14
16
18
20
0 5 10 15 20 25 30 35 40
Insitu CBR value @ 5-6m Depth
DCP-CBR%
DC
P-C
BR
%
Test Pit No.
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Figure2.20: In-situ CBR values @ 6-7m depth
2.2.3 PROBLEMATIC SUBGRADE SOIL AND TREATMENT MEASURES
By virtue of their unfavorable properties, sub-grade materials fall into the
category of “Problem Soils” and, when encountered, will normally require
special treatment before acceptance as a pavement foundation. Thick
formation of clay and clayey silty soil have been predominately found on
the project area. The test result indicate that,these soil are potentially
expansive and have low bearing strength( i.e, which is characterized by
LL>60 or PI>30 or CBR <5% or CBR-swell>2%).
As per the analysis , about 85% of subgrade soil on the port expansion
section is unsuitable material and hence it needs to excavate the unsuitable
subgrade material within the infulence depth and replaced with selected
material (specified in borrow source section). The depth of replacment for
capping layer depends on CBR value (for CBR 1%, 2%, 3%, 4% replacment
depths are 900mm,600mm,400mm and 250mm respectively).
While carrying out the replacement activity, the excavated bed shall be
exposed to sun and wind causing loss of moisture. This would initiate volume
0
2
4
6
8
10
12
14
16
18
20
0 5 10 15 20 25 30 35 40
Insitu CBR value @ 6-7m Depth
DCP-CBR%
DC
P-C
BR
%
Test Pit No.
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reduction in the surrounding soil, which becomes prone to attract suction
generated moisture during wet season. Such rise in the moisture would
aggravate the differential swelling along the profile. Scarify or loosen about
250 mm from the new roadbed level reached after excavation for
replacement, and recompact the loosened soil on wetter side of the OMC
(Optimum Moisture Content established from the density – moisture relation on
the bed soil). It is proposed to recompact the roadbed below replacement
level not more than OMC +2% moisture in accordance with the requirements
of AASHTO T-180 (heavy compaction). This partly compensates the loss of
moisture on excavation and also helps achieve a reasonable level of moisture
in the roadbed precluding excessive ingress of moisture later during the wet
season. The capping or fill material shall not contain particles more than two-
third of the specified layer thickness, any compacted layer shall be not be less
than 100mm or more than 200mm. Each layer shall be compacted to
minimum of 97% of maximum dry density in accordance with the requirements
of AASHTO T-180 (heavy compaction), however the scarified layer shall be
compacted to minimum of 100%MDD (light compaction).
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2.2.4 DETERMINATION OF DESIGN SUBGRADE STRENGTH
As per the analysis of test results discussed in the above sections, the
predominant sub grade soil class of modjo logistics green hub is weak
subgrade soil ( i.e about 85% of the test pit have CBR values below 5%).
For pavement design purposes it is important to consider that the strength of
the subgrade is not seriously underestimated for large areas of pavement or
overestimated to such an extent that there is a risk of local failures.
Therefore, the best compromise for design purposes is to use the lower CBR
value of within each design depth or the lower depth CBR value. But if the
lower depth of CBR is much greater than the upper depth it was taken as
average of them to be safe. The laboratory CBR values of each test pit
interms of depth and the recommended CBR values are presented in the
shown table.
Table2.3: Design Subgrade strength of Test Pits
TP No.
Depth (m)
CBR value (%)
Recommended design CBR of
pits (%)
TP No.
Depth (m)
CBR value (%)
Recommended Design CBR of
pits (%)
1 1 4.7
2 21 1 1.6
3 2 2 2 2.6
2 1 1.3
1 22 1 0.3
1 2 1.2 2 0.4
3 1 3
2 23 1 1.9
2 2 1.5 2 1.5
4 1 1.7
2 24 1 0.3
5 2 1.7 2 9.4
5 1 0.4
1 25 5 1
2 2 1.1 6 2
6 4 23
12 26 5 3
3 5 9 6 3
7 1 2.3 15 27 3.5 2.9 5
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2 28 5 5
8 1 0.7
2 28 3.5 2
1 2 2.3 5 1
9 1 1.8
1 29 1 3.8
5 2 0.3 2 5
10 1 0.5
2 30 1 2.8
4 2 2.2 2 3.6
11
1 2.8
1
4 0.7 31
1 7.2 4
5 1 2 4
12
1 0.3
1 32
1 2.7 2
4 1.1 2 2.4
5 1 33
1 1.9 10
13 1 0.5
1 2 19.5
2 3 34
1 0.3 1
14 1 0.2
1 2 1
2 0.4 35
1 18.5 18
15 1 1.5
3 2 18.5
2 2.7 36
1 2.3 7
16 1 0.8
1 2 7
2 1.2 37
1 2.3 3
17 1 14
1 2 3.5
2 1.2 38
6
3
3
18 5 1
1 6 4
39 1 0.4
2 19 5 2 2 2 2.5
20 1 2.2
2 40 1 2
1 2 1.8 2 1
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CHAPTER–3
DEEP GEOTECHNCIAL INVESTIGATION
3.1 GENERAL
A deep geotechnical investigation was carried out to determine geological
conditions of Modjo Green logistics Hub expansion project and foundation
conditions at the buildings and ware house area. A detailed investigation
with core drilling in 14 Boreholes were done on the project site. Most of the
boreholes were done up to an average depth of 18m, where the minimum
depth of 15m and the maximum is 20m. Both disturbed and undisturbed
samples were collected for laboratory tests. Ranges of laboratory test have
hence interpreted. The geotechnical investigation work was carried out in
very close cooperation with the materials investigation. Geotechnical
investigation (borehole drilling) was not carried out at the cut sections (north
side of the project) and location of accumulated material (from existing
construction), thus it is recommended to investigate during construction phase.
The purpose of deep site investigation is to determine the existing soil
profiles and engineering characteristics of the subsurface conditions at the
expansion site and to provide :
• Subsurface profile (type and thickness/extent) of layers;
• Ground water location (if encountered with the vicinity of the
recommended drilling depth)
• Geotechnical design parameters such as the soil bearing capacity,
expected foundation settlement, side slope stability, hydrological
conditions which will be required for a safe , economic design and
excavation of the engineering works, at the site and other special
recommendation.
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• Methods of construction, site seismicity characters, groundwater
conditions and quality control requirements.
3.1.1 SEISMICITY OF THE PROJECT AREA
Different areas do have different seismicity zoning according to their vicinity
to seismic effects. In Ethiopia we have 4 common seismic zones. Accordingly,
the project area which is located in Modjo is classified as Zone 4. This hence
needs consideration of seismic effects like from earth quake while designing
different structures in and around this area. It is recommended to follow the
EBCS-8 provisions while working any design in this zone. In this code there
are also Bedrock acceleration factors that we need to stick to.
Table 3.1: Bedrock Acceleration Ratio αo
Zone 4 3 2 1
αo 0.1 0.07 0.05 0.03
3.1.2 SITE GEOLOGY
The geological formation of the specific site can be seen from the results of
the 14 boreholes .In these boreholes the underground profiles of each is
clearly defined to the respective depth. In most of these test location the
geological formation can be summarized as per the following table.
Table 3.2: Summary of geological formation of the site
Depth (m) Geological Formation Remark
0-3.45 Light to Dark Brown Clay Soil
3.45-6.45 Dark to Light Brown Silty CLAY soil
6.45-9.45 Brown Silty CLAY
9.45-13.00 Light Brown Silty CLAY soil
13.00 to 20.0 Silty CLAY with some Sand
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The summary in Table 3.2 is a very average classification of the ground and
may not represent to some of the core logs. The exact profiling of each of
the boreholes Logs are attached annex-V of this report.
3.2 FIELD INVESTIGATION
A detailed investigation with rotary core drilling at 14 Boreholes were done on
the project site. Most of the boreholes were done up to an average depth of
18m, where the minimum depth of 15m and the maximum is 20m. Both disturbed
and undisturbed samples were collected for laboratory tests. During the field
investigation, the following activities were facilitated.
Core drilling and collection of all the cored samples;
Collection of undisturbed sample ;
Taking the SPT reading at different intervals;
Checking/ Recording the depth of ground water table (if/ when exists)
3.2.1 CORE DRILLING
A detailed investigation with rotary core drilling at 14 boreholes were done
on the Modjo Green logistics Hub project. The drilling work has been started
on February 4, 2019 and ended on February 25, 2019. The GPS locations
of the BHs where the UTM Adindan Datum was considered are listed in the
following table.
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Table 3.3: Location of boreholes
Bore Hole ID
Northing (m)
Easting (m)
Elevation (m), Original Ground Level
Excavated depth (meter)
BH-1 948961 516745 1822 15
BH-2 949052 516383 1840.6 18
BH-3 948883 517026 1815.2 17
BH-4 948823 516662 1819 17
BH-5 948685 516486 1813.8 18
BH-6 948937 517207 1807.4 17
BH-7 948614 516635 1813.1 17
BH-8 948929 516472 1839.2 20
BH-9 948628 516886 1814 16
BH-10 948331 516588 1812 19
BH-11 948328 516895 1812.1 15
BH-12 948470 516702 1811.6 17
BH-13 949018 516094 1825.8 20
BH-15 949059 516906 1817 20
Figure 3.1: Location of the boreholes with respect to the site map
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Figure 3.2 Core Drilling Process on the project Site
Figure 3.3: Sample photos of Borehole boxes
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3.2.2 DESCRIPTION OF GEOTECHNICAL LAYER
Fourteenboreholes were drilled to investigate study the subsurface condition
of the project. Visual inspection, in-situ tests ,laboratory tests and
interpretations were done to describe the ground condition. The core logs of
all the fourteen boreholes are detailed and given in the annex-V of this
report.
3.2.2.1 Layer-I: Light to Dark Brown Clay (0.00 to 3.45 m)
The top layer of the ground as indicated in all boreholes and test pits
indicate there is almost uniformly clay layer. This top layer which may be
normally excavated during the site clearing of the project has weak bearing
capacity.
3.2.2.2 Layer-II: Dark to Light Brown Silty CLAY Soil (3.45 to 6.45 m)
The clay layer has continued deep to the ground with a change on the color
and obviously on the density and the bearing capacity following
consolidation due to the over burden pressure. In this range a silty soil
behavior has encountered.
3.2.2.3 Layer-III: Brown Silty CLAY (6.45 to 9.45m)
There is still a silty clay layer in this deep depth. Checking starting from the
top most layer up to this depth, one can see that the ground is still a clay
layer with a limited variation between pure clay and silty clay. Furthermore,
such a pronounced variation in bearing capacity is not anticipated.
3.2.2.4 Layer IV: Light Brown Silty CLAY (9.45 to 13m)
In this range with a similar fashion there is no any change except the color of
the soil, it is still a silty clay soil. Regardless of the bearing capacity increase
due to overburden pressure (depth dependent), the bearing capacity is
expected to have more or less similar to the previous layers.
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3.2.2.5 Layer IV: Silty Clay with Some Sand (13m to 20m)
The end of the test pits has some fluctuations ranging between 15m to 20m,
where most of them are greater than 15m. In this range, there was a change
of the soil property to have some behavior of sand. Moreover, the bearing
capacity here is relatively higher than the one above, not only due to over
pressure but also due to the change of the soil type to silty sand.
3.2.3 STANDARD PENETRATION TEST (SPT) (ASTM D1586)
Standard penetration tests were being done during the process of core
drilling. The Standard Penetration Test (SPT) was carried out using a
standard split-barrel sampler in accordance with BS1377:Part9:1990. The
test was conducted to determine the design N-values that were used to
determine the allowable bearing capacity using the empirical relationships
evolved by Terzaghi & Peck (1948) and Meyerhof (1956). The test was also
used to provide an indication of the density and consistency of the subsurface
soils . By means of the split spoon sampler and a hammer, Standard
Penetration Tests were conducted at intervals of 2.0m depth in the borehole
where possible and at points where a change in the soil profile was
realized.SPT test results are considered refusal when more than 51 blows are
required to penetrate 15cm. SPT blows were done at various depths in all
the fourteen boreholes. In each case the standard 63.5kg hammer is dropped
from 76cm to penetrate the ground at certain number of blows. The average
numbers of blows from the Standard Penetration Tests (SPT) conducted in the
borehole are as shown in the tables below. Furthermore, the results of the SPT
result are used in the computation of the bearing capacity at the borehole
locations.
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Table 3.4: Measured and adjusted SPT N-Values for the project
BH No Depth (m) SPT N-Value for 300mm penetration
Adjusted N Values
Design Value
BH-01
2.15-2.45 33 31.07
30.78
4.15-4.45 50 39.58
6.15-6.45 32 23.39
8.15-8.45 50 31.93
10.15-10.45 46 27.94
BH-02
7.15-7.45 10 6.84
22.27
7.65-7.95 18 11.91
9.15-9.45 49 29.78
10.65-10.95 48 28.38
12.15-12.45 50 27.94
16.65-16.95 50 23.89
15.15-15.45 50 24.7
16.65-16.95 50 23.89
18-18.15 50 23.08
BH-03
3.15-3.45 46 36.6
30.24
5.15-5.45 50 35.8
7.00-7.30 50 34.62
9.00-9.30 50 30.39
11.00-11.30 50 29.16
13.00-13.30 50 26.73
15.00-15.15 50 25.11
17.15-17.45 50 23.49
BH-04
1.65-1.95 34 35.93
24.41
3.15-3.45 34 27.05
4.65-4.95 14 10.5
15.15-15.45 50 24.7
16.65-16.95 50 23.89
BH-05
1.65-1.95 41 43.33
29.23
3.15-3.45 34 27.05
4.65-4.95 27 20.26
6.15-6.45 50 36.55
7.65-7.95 47 31.1
9.15-9.45 50 30.39
10.65-10.80 50 29.97
12.15-12.45 50 27.94
13.65-13.95 50 26.32
15.15-15.45 50 24.7
16.65-16.95 50 23.89
BH-06 2.15-2.45 36 33.89
23.02 3.15-3.45 42
33.42
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5.15-5.45 22 15.75
6.15-6.45 20 14.62
8.15-8.45 40 25.54
9.15-9.45 40 24.31
10.15-10.45 26 15.79
12.15-12.45 36 20.12
15.15-15.45 50 24.7
17.15-17.45 50 23.49
18.15-18.45 50 22.68
20.00 50 21.87
BH-07
2.15-2.45 25.33 23.85
27.21
3.45-3.75 29.33 22.27
5.15-5.45 42.66 30.54
7.15-7.45 50 34.24
9.15-9.45 50 30.39
11.15-11.45 50 29.16
12.45-12.75 50 27.54
14.15-14.45 50 25.92
15.45-15.75 50 24.7
17.15-17.45 50 23.49
BH-08
3.45-3.75 38 28.85
29.59
4.65-4.95 48 36.02
6.15-6.45 50 36.55
8.15-8.45 42 26.82
9.15-9.45 50 30.39
11.15-11.45 50 29.16
12.15-12.45 50 27.94
14.15-14.45 50 25.92
15.15-15.45 50 24.7
BH-09
2.15-2.45 24.66 23.22
25.41 3.45-3.75 28.66 21.76
5.15-5.45 44.66 31.97
15.45-15.75 50 24.7
BH-10
2.15-2.45 4 3.76
3.45-3.75 15.33 11.64
5.45-5.75 27 18.77
7.15-7.45 50 34.24
9.15-9.45 50 30.39
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11.45-11.75 50 28.75
22.72 13.45-11.75 50 28.75
15.15-15.45 50 24.7
17.15-17.45 50 23.49
BH-11
1.65-1.95 21 22.19
27.85
3.15-3.45 24 19.09
4.65-4.95 34 25.51
6.15-6.45 50 36.55
7.65-7.95 50 33.08
9.15-9.45 50 30.39
10.65-10.95 50 29.56
12.15-12.45 50 27.94
13.65-13.95 50 26.32
BH-12
1.65-1.95 30 31.71
30.46
3.15-3.45 50 39.79
4.65-4.95 41 30.76
6.15-6.45 50 36.55
7.65-7.95 50 33.08
9.00-9.15 50 30.78
10.65-10.95 50 29.56
12.15-12.45 50 27.94
13.65-13.95 50 26.32
15.15-15.45 50 24.7
16.65-16.95 50 23.89
BH-13
3.45-3.75 38 28.85
22.00
5.15-5.45 25.33 18.13
6.45-6.75 24.66 17.64
8.15-8.45 50 31.93
9.45-9.75 48 28.81
11.15-11.45 30.66 17.88
12.45-12.75 20.66 11.37
14.15-14.45 42 21.77
15.45-15.75 40.66 20.09
17.15-17.45 50 23.49
BH-15
2.15-2.45 50 47.08
29.58
11.15-11.45 50 29.16
12.15-12.45 50 27.94
14.15-14.45 50 25.92
15.15-15.45 50 24.7
18.15-18.45 50 22.68
Refusal Values (SPT N> 50)
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3.2.4 GROUND WATER LEVEL MEASUREMENT (ASTM D6000)
The ground water level measurement is done parallel or during the core
drilling process. In all the fourteen boreholes no ground water was encounter
within the coring depths. However, we have checked in a glance that there is
under ground water being used in the compound for different activities.
3.3 LABORATORY TESTS
Both disturbed and undisturbedsamples were collected from each of the
boreholes and the following different laboratory tests were conducted.
3.3.1 BULK UNIT WEIGHT ()
The bulk unit of all the test pits was done in the laboratory. As per the test
result, the bulk unit weight of underlain soil at the selected points ranged
from 1650 to 1970 Kg/m3.The summary of bulk unit weight of soil is
attached in the annex-IVof this report.
3.3.2 SPECIFIC GRAVITY (GS) (ASTM D854 – 14)
The specific gravity of the soil sample taken from all boreholes were
conducted in the laboratory .As per the test result, the specific gravity of
underlain soil at the selected points ranged from 2.47 to 2.72 and summary
of results are attached in the annex IV of this report.
3.3.3 WATER CONTENT DETERMINATION (%) (A5TM D 2974-87)
The percentage of water within the soil sample was determined in all the
boreholes . Summary of Test results are attached in the annex-IV of this
report.
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3.3.4 SIEVE ANALYSIS (ASTM C136 / C136M – 14)
Sieve analysis test were conducted for all the samples taken from boreholes.
The test result inducate that most of the samples are fine grained soils.
Summary of Test results is attached at the annex-IV of this report.
3.3.5 CHEMICAL TEST OF SOIL
Chemical test of soil (chloride content, sulphate content, organic contents and
PH value) for every boreholes were conducted. The test result inducate that
the proposed expansion project area is free and clear of any chemical
contaminations. Summary of Test results is attached at the annex-IV of this
report.
3.3.6 ATTERBERG LIMIT TESTS (ASTM D4318 - 17E1)
The atterberg limit tests were conducted samples taken from boreholes. The
fine grained soils of silty clay and clay soil within this section had Liquid Limit
values ranging from 46.3% to 70.3% and Plasticity index values ranging
from 13.9% to 27.3%. Summary of Test results is attached at the annex-IV
of this report.
3.3.7 UNCONFINED COMPRESSION STRENGTH TEST (UCS TEST) (ASTM D2166
The UCS test is commonly used for the shear strength determination of fine
grained and cohesive soils where it’s mandatory to set up an undisturbed soil
sample. The test result indicate that the UCS of underlain soil at the selected
points ranged from 165.25 to 349.6 KN/m2and summary of results is
attached at the annex-IV of this report.
3.3.8 DIRECT SHEAR STRENGTH TEST (DSST) (ASTM D3080 / D3080M – 11)
Direct shear strength test is recommended for granular soils (none-cohesive
soils). From the sieve analysis and the atterberg tests it was also seen that
there were limited samples where they are convenient for direct shear
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strength test. As per the test result, the Cohesion (KN/m2) and Angle of
Internal friction (Degrees) values of underlain soil at the selected points
ranged from 13 to 28(KN/m2) and 5.5 to 25 (Degrees) respectively .
Summary of Test results is attached at the annex-IV of this report.
3.4 BEARING CAPACITY OF SOIL
3.4.1 BEARING CAPACITY OF SOILS BASED ON LABORATORY RESULT
The bearing capacity of soil at the selected points in each borehole is
computed as per Terzaghi formulation. The table 3.5 below indicate
summary of bearing capacities soil at different depths. Since most of the BHs
has bearing capacities at different two points hence one can get a clear
image of the bearing capacity at a preferred depth. Since the laboratory
parametres are deterimned exact width can be determined by the designer.
The width figures (Df=B) used to determine the bearing capacity presented
below are allowable bearing capacity at specified depths.
Furthermore effective depth of each borehole is determined considering the
difference of original ground level (OGL) and design (finished) surface level
of the port at each borehole location. It is due to the fact that, there is high
cut and fill, some borehole locations are excavated even upto 20m and fill
more than 5m.
From the table below; majority of the boreholes indicates that the bearing
capacity is above 300Kpa at about 3m depth (shallow foundation) which is
economical. As depth increase the higher bearing capacity, however
construction cost also increases. Therefore based on the soil property and soil
type of the project maximam of 3.5m is recommended economic depth,
however based on the superstructure load the designer can decide the depth.
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Table 3.5: Bearing Capacity of Selected depths
BH
Dep
th (
m)
fro
m
OG
L(s
am
ple
taken
)
To
tal exc
avate
d
Dep
th (
m)
Eff
ecti
ve
exca
vate
d d
ep
th
(fro
m f
inis
hed
level)
(m
)
Dep
th (
m)
aft
er
fin
ish
ed
lev
el
(sam
ple
ta
ke
n)
Reco
mm
en
ded
Desig
n d
ep
th (
m)
C ϕ γsat Df =B Nc Nq Ny σall
[ID]
KP
a
Deg
ree
KN
/m3
[m] [-] [-] [-] KPa
1 8-845 15 5.3
above 26 20 18.46 above 14.83 6.40 4.66
1 10-10.45 0.3-0.75
3 23 20 18.34 3.00 14.83 6.40 4.66 299.4
2 5.5-5.85 18
tested BH depth
totally removed
above
19 21 18.81 15.81 7.07 5.43
investi
gate
du
rin
g
co
nstr
ucti
on
2 10.5-10.95
above 21 21 18.71 --- 15.81 7.07 5.43
3 11-11.30 17 12.6
6.6-6.9 3 23 21 18.34 3.00 15.81 7.07 5.43 327.1
3 12-12.45 7.6-8.05 22 21 18.74 15.81 7.07 5.43
4 6-6.45
17 10.3
above 25 20 18.33 14.83 6.40 4.66
4 8.10-8.45 1.4-1.85
2.5 27 21 18.31 2.50 15.81 7.07 5.43 326.0
4 12-12.45 5.3-5.75 28 20 18.29 14.83 6.40 4.66
5 7.50-8.00
18 15.80
5.3-5.8 3.00 143 0 18.64 3.00 5.14 1.00 0.00 336.0
5 10.50-10.95
8.3-8.75
21 18 18.81 13.10 5.26 3.42
5 15.00-15.45
12.8-13.25
24 19 18.67 13.93 5.80 3.99
6
8.00-
8.30
17 22.40
5.40 3.50 20 12 18.8 3.50 9.28 2.97 1.26 156.8
6
11.70-
12.00
17.1-
17.4 19 15 19.7
10.98 3.94 2.11
6
15.70-
16.00
21.1-
21.4 20 12 18.9
9.28 2.97 1.26
7 9.00-9.45
17 15.50
7.5-7.95
3 27 19 18.71 3.00 13.93 5.80 3.99 301.4
7 10.50-10.95
9-9.45 25 19 18.36 13.93 5.80 3.99
7 13.50-13.95
12.0-12.45
22 22 18.73 16.88 7.82 6.32
8
11.35-
11.65 20
tested BH depth
totally removed
above
13 8
18.50 7.53 2.06 0.58
investi
gate
du
rin
g
co
nstr
ucti
on
8 12.45-12.80
above 15 5.5 16.50 --- 6.65 1.64 0.32
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9 7-7.45 16 14
5-5.45 3.5 16 20 18.36 3.50 14.83 6.40 4.66 279.8
9 15-15.45 13-
13.45 21 19 18.47 13.93 5.80 3.99
10 6.45-6.75
19 16.00
3.45-3.75
3 149 0 17.92 3.00 5.40 1.00 0.00 367.3
10 10.50-10.95
7.5-7.95
26 22 18.10 16.88 7.82 6.32
10 17.25-17.55
14.25-14.55
24 22 17.98 16.88 7.82 6.32
11 7-7.15
15 11.85
3.85-4 3 23 21 17.98 3.00 15.81 7.07 5.43 323.8
11 12-12.30 8.85-9.15
26 20 18.24 14.83 6.40 4.66
11 13.50-13.95
10.35-10.80
24 23 18.21 18.05 8.66 7.35
12 7.50-7.95
17 17
7.50-7.95
3.5 20 19 18.55 3.50 13.93 5.80 3.99 280.8
12 10.50-10.95
10.50-10.95
27 19 18.69 13.93 5.80 3.99
12 13.50-13.80
13.50-13.80
28 21 18.70 15.81 7.07 5.43
13 12.70-13.00
20 15.2
7.9-8.2 3 21 21 18.23 3.00 15.81 7.07 5.43 312.4
13 15-15.45 10.2-10.65
10 23 21 18.47 15.81 7.07 5.43
15
1.50-
1.95
20 16.20
above 83 0 18.30 5.41 1.00 0.00
15
6.00-
6.30 2.2-2.5 2.50 28 23
18.80 2.50 18.05 8.66 7.35 400.8
15
12.00-
12.45
8.2-
8.65 25 25
18.80 20.72 10.66 9.94
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3.4.2 BEARING CAPACITY OF SOILS BASED ON FIELD SPT N- VALUES
Foundation recommendation refers to fixing the bearing layer and depth
from the OGL, allowable pressure on the bearing layer and type of
foundation to be adopted safely and economically. The main factors to be
considered while selecting a foundation are the load to be transmitted to the
foundation and the subsurface condition of the soil.
SPT tests are the dominant methods to determine the allowable bearing
capacities of the foundations since it is easy to compute the bearing capacity
of the ground at different depths. However, in this investigation sample was
collect and put it in to Direct Shear Strength Test (DSST) at only selected
depth on each borehole hence it is difficult to compute the bearing capacity
of the ground at different depths using results of laboratory tests.
SPT values will therefore be used to compute the bearing capacity of the soil
layers below the foundation as an alternative to the values computed using
the laboratory tests. Allowable bearing capacity for the selected layer is
based on correlation of the relative compaction of the in-situ ground as
indicated from SPT and after all the necessary adjustments are made to
determine the actual SPT values
In order to determine the bearing capacity soil ,it is necessary to know the
load from the super structure. The maximum pressures the soils are capable
of resisting were estimated from the field SPT N-values using empirical
relations. For purposes of computing the soil’s bearing Capacity, the
maximum allowable settlement in cohesive soils is 25mm;
After adjusting the N-Values, design N-values are chosen from consecutive
depths where the test is performed. The design N-Values are taken as the
average of adjusted N-values which are found in between ½ B above and
2B below the proposed footing depths where B is the width of the
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foundation. The data record from all boreholes was used to compute the
allowable bearing capacity of the geotechnical layer.
The bearing capacity for an footing can be calculated from the SPT N-values
using Meyerhof’s equation as follows (Bowles, 1997):
qall=N/F2*(1+F3/B)2*1/Kd………………………B>F4
Where
qall= Allowable bearing capacity for settlement limited to 25 mm.
The following allowable bearing pressures are computed for isolated
footings placed at a depth of 2.5m below the natural ground level. However,
the SPT tests are done at various depth deeper than 2.5m.However; the
ground condition in most boreholes starting from 0.00m to the end is quite
similar and the SPT reading at 6.45m to 8m with obvious understanding of
the effect of the depth can be considered for that of 2.5m. Foundation widths
are varied from 2.0m to 4.5m. A maximum settlement limit of 25mm is taken
in to account for the allowable bearing capacity computation.
Table 3.6: Allowable bearing pressure (kPa) based on SPT at depth of 2.5m
Footing Width (m) 2 2.5 3 3.5 4 4.5
Design N-Value (Minimum is considered here)
22 22 22 22 22 22
Kd-calculated 1.41 1.33 1.27 1.23 1.2 1.18
Kd-designed 1.33 1.33 1.27 1.23 1.2 1.18
Allowable bearing pressure
343.91 345.82 349.34 351.39 353.1 353.54
From the above analysis, it is revealed that the allowable bearing pressure
computed using bearing capacity equations from SPT test results at a depth
of 2.5m and width ranging from 2 to 4.5mvaries from 343.91kPa to
353.54kPa. The bearing capacity equation is calculated considering 25mm
settlement as the maximum threshold.
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3.4.3 SETTLEMENT ANALYSIS
Settlement is another criterion for evaluating the performance of structure
because excessive settlements will result in poor performance of the structure.
Various codes set the limiting settlement for the type of structure and
foundation. The proposed foundation should hence meet this limit. Though
different types of settlement are there, the major ones are immediate and
consolidation settlements.
These two settlements depend on a number of parameters as well as type of
soils.
As discussed in different portions of this project, the sub surface condition at
the depth of each of the test pits is week ground where it is dominated with
clay soils. In this project, the consolidation settlements are anticipated to
happen, if the conditions of the soil is not given a due attention during design
and construction.
3.5 RETAINING STRUCTURES
In sections where there are high cut and high fill, which are more expected
as there is a varies topography on the project area, retaining structures of
different types which mostly are dependent on the height and behavior of
the ground to be retained are anticipated to be used.
The following retaining walls are among the common ones that are
recommended for this specific project considering the behavior of the ground
form both the laboratory and field tests summarized in this report.
Masonry Retaining wall (if the height to be retained is preferable less
than 4.5m)
Cantilever retaining walls (if the height to be retained is more than 4.5m)
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CHAPTER–4
LOCATION AND TESTING OF CONSTRUCTION MATERIALS
4.1 GENERAL
Basic objective of construction material investigations is to identify the
potential sources of construction materials along the project vicinity, to yield
adequate quantity of materials which are suitable for various pavement
layers viz. embankment, sub grade, sub base, base, concerte ,etc.
Suitable material sources have been identified along the project vicinity by
local enquiry. Besides ,consultant has carried out tests on selected material
sources to find their suitability for use. Sufficient material sources have been
identified to verify availability of materials within economical leads.
The information on the materials sources were summarized with the following
objectives:
Identification of source locations indicating places and the status of
sources whether in operation or new sources.
Identification of requirements for pavements, embankment works, cross
drainage and other works.
Testing and evaluation of materials for use in works
Material specification and characteristics.
The Consultants has identified rock quarries for various pavement layers such
for crushed subbase,stablized base course ,concrete pavement works and
borrow sources for earth work , embankment or capping layer. Large quantity
of borrow source is available near to modjo green logistics Hub. The samples
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were tested in the laboratory to evaluate their suitability for construction.
Location of various quarries and borrow sources are given in table below.
Potential sources of construction materials were investigated through the
following activities:
A Desktop study: The information that was studied includes
geological maps, geological reports and topographical maps.
Discussion with Contractor on the going project of the port:
communication with the contractor represntative of the on going
project port was enquired about the existence of potential
sources of construction material.
Enquired local people: Local people on the vicinity of the
project were enquired about the existence of potential sources
of construction material.
Field investigation: All potential sources were investigated,
inspected and evaluated.
Laboratory tests: labortory tests were conducted on the
identified construction material source to assess the suitablity of
material quality and to compare with the specifications
requirement.
In general prior to locating construction material sources the following factors
were considered:
Performance of the material to be used for construction;
Accessibility;
Quantity and Quality;
Type and thickness of overburden materials;
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Availability of ample space for erecting crusher and stockpiling
;and
Environmental and social aspects
Taking into account these factors the following potential sources of
construction material were identified.
4.2 GRAVEL BORROW SOURCE INVESTIGATION
The investigation of borrow materials which can be used for the construction
of earth work , embankment or capping layer is conducted in the project
vicincity. Normally natural granular materials have shown inconsistency
proprties even in the single source which as a result of frequent change in
weathering and extreme variability of geological and tectonic processes that
are responsible for their present state of occurrences.
The natural gravel sources investigations was carried out from January to
February 2019. Overburden thickness, suitability of extraction, sufficiency
and the impacts to local settlement were considered during selection of
potential borrow source. As per the investigation,only one(1) large quantity
of borrow source was identified around Modjo green logistics hub ,which is
located 1.5km far from the main gate at melmel village and the source is
sufficent for the construction works . Pit excavated and samples were
recovered from sources for laboratory testing. The locations and description
of the borrow source is indicated in the table 4.1 below.
Table 4.1: Description of borrow source
SN GPS Location Offset/
Distance
Estimated
quantity
(m3)
Type of Material and
status
BP1 0514801,
0946849
Melmele
kebele
1.5 from
the main
gate
≈1,300,000 Slightily weatherd
gravel material
Existing source
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The recovered sample from source was delivered to the laboratory for
testing. Tests are being carried out on these samples to determine the
physical and mechanical properties of the soil which can be used to classify it
as suitable for earth work ,embankment and cappinglayer. The sample is
tested in accordance with several appropriate standards shown in table 4.2
below.
Table 4.2: The tests to be carried out on natural gravel source samples
Test No. Name of Test Standard Test
Method
Sample Status
1 Liquid Limit AASHTO T-89 Disturbed
2 Plastic Limit AASHTO T-90 Disturbed
3 Linear shrinkage BS 1377: Part 2:
1990
Disturbed
4 Sieve analysis AASHTO T-27 Disturbed
5 Maximum Dry Density
(MDD)
AASHTO T-180 Disturbed
6 California Bearing Ratio (CBR) and CBR-swell
AASHTO T-193 Disturbed
In order to assess the suitability of the materials tested as selected fill and as
embankment fill, the test results obtained were compared with the
requirements of specifications as given in table 4.3 below.
Table 4.3: Summary of test result of Natural gravel sources
Station (location) CBR value (%)
LL (%)
PI (%) LS (%) CBR-Swell (%)
Melmele(1.5km far from the main gate)
25 NP NP NP 0.1
Material Requirement for
capping layer or fill
≥15 <45 <12 6.0 <1.5
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As per test results ,the identified borrow source is granular material and
suitable for selected capping layer and embankment fill. Besides ,it may
require proper verification on borrow site during construction time to check it
consistency and satisfy project specification.
Figure4.1: Natural gravel source at Melmele kebele
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4.3 ROCK QUARRY SOURCES
Investigation of quarry sources that will use for crushed subbase,stablized
base course and concrete pavement works have been undertaken in the
Modjo logistics green hub project.
Potential quarry sources for aggregate to use in construction of crushed
subbase,stablized base course , concrete pavement works and other
structures are available only at two places, in the nearby vicinities of the
project area within reasonable haulages and samples were collected for
laboratory testing. Overburden thickness, suitability of extraction, sufficiency
and the impacts to local settlement were considered during selection of the
quarry.
The recovered samples were delivered to the laboratory for testing. Tests
are being carried out on these samples to determine the physical and
mechanical properties of the rock which can be used to classify it as suitable
for intended pourpose. The samples were being tested in accordance with
several appropriate standards shown in table 4.4 below.
Table 4.4 Tests to be carried out on the rock sample
Test No. Name of the test Standard test method
1 Aggregate Crushing Value (ACV) test BS 812, Part 110: 1990
2 10% Fines Value (TFV) test BS 812, Part 111: 1990
3 Aggregate Impact Value BS 812, Part 110: 1990
4 Sodium sulphate soundness AASHTO T104
5 Water absorption ASTM D6473
6 Los Angeles Abrasion Value ASTM C131-89
Summary description of potential rock quarry source is presented table
below.
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Table 4.5: Summary of Rock Quarry source
SN Station GPS Estimated quantity(m3)
Type of material
Remarks
Q1 Within the project compound
516383, 949052
160,000.0 granite/ Ignimbrite rock
Existing quarry soucre and acceptable for crushed aggregate
Q2 11.8 Km towards Debrezeit
0643652, 102494
1,000,000.0
Basaltic rock
Existing quarry soucre and acceptable for crushed aggregate
Figure4.2: Rock quarry source within the compound (Q1)
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Figure 4.3: Rock quarry Source 11.8Km towards Debrezeit (Q2)
Aggregate Crushing Value (ACV), Aggregate Impact Value , 10% Fines
Value (TFV) test ,Sodium sulphate soundness, Water absorption and Los
Angeles Abrasion Value tests were conducted on the samples to assess their
suitability. The test results on rock sample are compiled in the table 4.6
below. The rock samples test result were compared with corresponding
requirements for crushed aggregates in table 4.6 below.
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Table 4.6: Test result and requirements for rock aggregate
Parameters Specification
Test result
Quarry (Q1) Quarry (Q2)
Aggregate Crushing Value Max 29% 26 13.0
Aggregate Impact Value Max 25% 19 12.82
Los Angeles Abrasion (LAA) Max 30% 21 18.00
Sodium Sulphate Soundness Min 10% 1.29 2.38
Water absorption 5.99 1.10
Bulk specifc gravity 2.16 2.38
Appernt specifc gravity 2.48 2.44
Four days soakedCBR CBR>80% 83% 95%
As per the test results, the both rock quarry sources are comply the
requirment for crushed subbase, stablized base course and for concrete
pavement works in accordance with specification however, high water
absorption result at quarry source one(Q1) needs to be recheck during
construction stage.
4.4 NATURAL SAND SOURCES
Investigation of natural sand sources for concrete pavement works has been
undertaken in the Modjo logistics green hub vicincity. Potential sand sources
to use in construction of concrete pavement works and other structures are
available only at two places, the first source is located 150km far from
modjo town towards Hawassa (around langano) area called seva and the
second source is located 15km far from the project area on the way to
zeway. The samples from both sources were collected for laboratory testing
to assess its suitability for use as fine aggregate for concrete.
The quality test such as Clay lumps & friable particles, gradation, organic
impurity, specific gravity, water absorption, Soundness, mortar strength and
sand equivalent were conducted on the collected samples .The quality of the
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sand sample was assessed with respect to AASHTO M6 specifications for fine
aggregates for use in concrete.
The natural sand from Sand (S1) offset 150km fromModjo, has organic colour
No 02, the soundness loss of 9%, the clay content is 1.26%, sand equivalent
92% and water absorption 2.15%. The gradation is with the allowable limit
enveolpe. From the test results, the sand has fulfilled the requirement and thus
it is suitable for construction of concrete works. However tarnsportation
(haulage) cost makes it uneconomical.
The natural sand from Sand (S2) offset 15km from Modjo has organic colour
No 02, the soundness loss of 12%, the clay content is 13.9%, sand equivalent
74% and water absorption 4.4% and the gradation is finer than the
allowable limit . From the test results, the sand has not fulfill most of the
requirement thus it is not suitable for construction concrete works. Therefore it
require thoroughly washed to minimized clay content but this may not be
economical due to high clay content.
Generally for concrete pavement works and other structures works, significant
amount of sand will be required however the identified natural sand source
may be deficient to satisfy the actual project demand for all concrete
pavement works and other structures works. In view of this prevailing
conditions, it is recommended that use of crusher run sand (material passing
the 4.75mm sieve from the crusher site) shall be the most likely solution to
avoid facing such problems for all concrete works. Since the parent rocks
satisfy all quality requirements, the crusher run sand as its by-product will
surely satisfy the required quality requirements.
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0
20
40
60
80
100
120
0.1 1 10
% o
f p
assi
ng
Sieve Size mm
sieve analysis of natural sand
Min
Max
S1
S2
Figure 4.4: sieve analysis of natural sand sources
Table 4.7: Test result and requirements for natural sand source
Parameters Specification
Test result
Sand (S1) (offset
150km fromModjo)
Sand (S2) (offset
15km fromModjo)
Organic impurity Max No 3 2.0 2.0
Sodium sulphate soundness (%) Max 10% 9.0 12.0
Clay lumps & friable particles Max 3% 1.26 13.9
Water Absorption Max 2% 2.15 4.4
Sand Equivalent Min 75 92.0 74.0
Bulk specifc gravity 1.89 1.78
Appernt specifc gravity 1.97 1.80
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4.5 WATER SOURCES FOR CONSTRUCTION
Water is required for compaction, concrete and mortar works, therefore, trial
was made to locate all perennial and seasonal rivers that drain to the project
vicincity. As per the investigation it has observed a scarcity of natural water
sources in the project area thus to overcome water shortage especially for
the compaction works and it is recommended to produced water from under
ground within the compound .Besides , we have checked in a glance that
there is under ground water being used in the compound for different
activities.
Althogh the ground water is drinkable and need of testing; however for the
purpose of the report, sample was collected from the ground water, and
laboratory quality test was conducted. Based on the test result this groud
water is clear and qualified for the intended purpose. The testresult is
attached in the annex.
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CHAPTER–5
CONCLUSIONS AND RECOMMENDATIONS
5.1 CONCLUSION
Test pit excavations and sampling, dynamic cone penetration tests, borehole
drilling and sampling, assessment of construction materials and sampling were
conducting during field investigation stage. Samples from test pit, borehole
and construction materials were also collected and delivered to laboratory
for further laboratory tests. Laboratory test result were analysised
conclusions and recommendations were aslo drawn based on field and
laboratory test result analysis.
Due to the coverage of accumulated of waste/spoiled material on the
expansion project (waste material from existing construction) and due to high
cut section mainly on north side of the project; test pit excavation and DCP
test wasn’t carried out during design stage.
Based on the test pit (sub grade laboratory test) and DCP test results, above
85% of the project area is unsuitable for pavement foundation.
The project area is located in active seismic zone are (Zone-4) and it is also
in the vicinity of the Rift valley. This area hence needs attention in case there
is a plan for the construction of high raised building and other important
cases like machine foundations where the draw serious attention during the
foundation design.
The bearing capacity results attached in this report are just at different
depths where our foundation may not be placed there. Therefore, the
bearing capacity at different depths (where the designer needs) can be
computed using the SPT results attached in the Logs.
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The sub surface condition at the depth of each of the test pits is week ground
where it is dominated with clay soils. In this project, the consolidation
settlements are anticipated to happen, if the conditions of the soil is not given
a due attention during design and construction.
The subsurface formation of the test pit log and the 14 boreholes
investigation dominately indicates that the area is covered with thick
formation of clay to silty clay soil.
Enough amount of borrow and quarry sources were identified at the vicnity
of the project area, which can satisfy the needed amount and quality of the
project area.
Two sand sources were identified; however one of them is qualified but
150km far which is uneconomical to use it due to haulage distance; the other
source is 15km far but very fine and unqualified for the intended purpose.
5.2 RECOMMENDATIONS
From the above conclusion, one can recommend the following main points
regarding of the soil and material investigation.
Due to the coverage of accumulated of waste/spoiled material on the
expansion project (waste material from existing construction) and due to
high cut section mainly on north side of the project; test pit excavation
and DCP test wasn’t carried out during design stage, thus it is
recommended to conduct the test during construction after clearing the
waste material and excavation of the cut section.
For unsuitable soil locations, the best recommended option of mitigation
of problems is excavation and replacement options. The depth and
extent of this replacement method is as indicated in chapter 2. The
removed material should be replaced by a suitable, non-expansive and
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impermeable material, the material requiremant for eath work and
capping layer is indicated in chapter four.
From the discusions and conclusion given above, it can be seen that the
ground almost uniformly CLAY and Silty CLAY. For the actual project site, the
following general recommendations of geotechnical based are important.
In case shallow foundations are selected as foundation option,
provided that there are only light structures, the construction need to
be facilitated in the dry season to avoid the effect of the volume
change of the CLAY soils.
Shallow foundations (Isolated and Mat Foundations) for light structures
and Pile foundation for heavy structures (if any) are recommended on
this site
Retaining structures (where their type depends on the actual height of
the section to be retained) are recommended in sections of high fill and
high cut.
Considering the significance amount of needed for the project and the
economic haulage distance of natural sand, it is recommended that use of
crusher run sand (material passing the 4.75mm sieve from the crusher site)
shall be the most likely solution to avoid facing such problems for all concrete
and masonry works