Download SECTION 2: INITIAL INVESTIGATION WORKS 2.1 SURVEY

SECTION 2: INITIAL INVESTIGATION WORKS
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2.1
SURVEY WORKS
Surveying works for Southern Makkah Landfill area were carried out by a surveyor
appointed by the Saudi Arabian counterpart. The objectives of surveying works were to
develop topographical maps and to capture the existing features of the landfill. The
topographical maps of the landfill were sent to USM via email. After validation was made
using maps from “Google Earth” and topography prints of Saudi Arabia, it was found that
the level used by the surveyor did not follow the ordinance datum. This discrepancy has
been corrected when USM team visited the site on 2nd March 2011. The team has met
the surveyor and has determined on site, the control points that were used in the survey.
Garmin was used to validate the elevations of control points. The elevations in related
contour maps have been rectified as well.
2.2
GEOLOGIC SETTING
Makkah, including the area of concern is located within the southern part of Hijaz region
on the west-central part of the Arabian Shield, which is dominated by different types of
igneous, metamorphic and sedimentary rocks of Precambrian and lower Palaeozoic era
(Greenwood et al. 1976, Abdulaziz Al Solami et al, 2006)). Generally, the area is covered
by Precambrian intrusive rocks. Intermediate rocks, ranging in composition from diorite
to Tonalite, predominate the Makkah batholiths and are assigned to the Kamil suite. The
dominant structural trends in the northeast to north-northeast direction and reflects three
major phases of Precambrian deformations and Tertiary faulting.
Geologic factors which are not always obvious without extensive study may hamper later
landfill performance. Therefore, the geological investigation for this project was mainly
carried out for identification, description, and classification with emphasis to provide
information on engineering geology and characteristics of the site. The resulting
information will be useful for the technical design and construction particularly for the
construction of slope and excavation of Advanced Cell 1 and Advanced Cell 2.
The new proposed site is an east-west oriented zone confined in a valley, the WadiUranah. The surrounding rocky terrain is predominated by complex intrusions of igneous
rock. They are mainly consisted of coarse grained, greenish-white, hornblende,
granodiorite, biotite monzogranite, and sills of various size and orientation, in various
places. The intrusions are normally by fine-grained dolerite and other ulramafic rocks
(gabbro), as well as by less than 10cm thick milky white quartz vein. Occasional and
isolated, grey, granitic schist is found exposed at the lowest part of the valley (BH-1).
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The site is considered as an upper part of the Wadi-Uranah-Aidiyah (SGS geological
map) system. The floor of this valley, at BH-1 and BH-2, indicates a thick sequence of
wadi alluvium, comprises of unconsolidated sand and gravel of about 20m thick,
underlying the centre part of the wadi. This alluvium generally consists of loose, subangular to subrounded, brownish grey, sand and rock fragments, originated from
surrounding hill, eroded and later transported by water during raining period. Very recent
form of erosions by water can also be seen through collapsed banks surrounding the
depression of partially excavated Advanced Cell 1.
2.2.1
Soil and rock properties
Table 2.1 gives the classification of typical soils around Makkah from geotechnical
investigations as compiled by Abdulaziz Al Solami et al (2006). The associated sources
have come from SGS of various locations and also supplied by construction companies
in Makkah (Abdulaziz Al Solami et al, 2006). About 50 percent of the samples fall under
Well graded (SW) category and the rest under poorly sorted (SP) category in accordance
with Unified Soil Classification System (USCS).
As observed in the field and from boreholes (BH-1 and BH-2), the unconsolidated wadi
alluvial of the site can be categorised as SW type – well graded sands, gravely sand,
little or no fine, and can be graded as loose to medium dense (SPTN-value of 4-10).
Table 2.1: Makkah soil classes according to USCS (Abdulaziz Al Solami et al, 2006).
Soil Class
Number of
Samples
Description
Symbol
1
Sandy silt
MS
10
Poorly graded sand
SP
9
Silty sand
SM
7
Poorly graded sand with silt
SP-SM
4
Well graded sand with silt
SW-SM
4
Silty sand with gravel
SM
1
Poorly graded sand with sand
GP
1
Poorly graded sand with gravel
SP
1
Well graded sand
SW
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2.2.2
Rock Mass properties
The rock mass quality of the site is variable with the types of rock, rate/degree of
weathering and alteration experienced by the outcrops, including distribution pattern of
joint sets, fractures, faults, bedding planes, and surface roughness.
There are many classifications that assign numerical values to properties of rocks.
Among them is the Rock Mass Rating (RMR) system proposed by Bieniaswski (1989)
which has been extensively applied in evaluating rock mass quality for different
engineering purposes.
The RMR system was the most suitable rock mass classification systems for engineering
purpose in the arid environments such as of Saudi Arabia (Al-Harthi, 1993). RMR is a
composite property of rock taking into account several other properties such as:
(a) Strength of intact rock mineral represented by Uniaxial Compressive Strength (UCS)
and Point Load strength index,
(b) Rock Quality Designation (RQD),
(c) Spacing of discontinuities,
(d) Condition of discontinuities or degree of weathering and
(e) Groundwater (Bieniaswaki 1989) – dry
The rock mass (RMR) is then defined as very good rock (100-81), good rock (80-61), fair
rock (60-41), poor rock (40-21) and very poor rock (<20) respectively as shown in Table
2.2. The rocks listed in the table can be found in the project area thus the values indicate
certain properties of the materials.
2.2.3
Rock excavate-ability
The excavate-ability of rock depends on the geotechnical properties of the material,
method of working, and type and size of excavation equipment used. It is generally
accepted that discontinuity spacing and the strength of intact rock as particularly
important rock properties. The aperture, infilling and the wall strength of the
discontinuities are also important factors. The main excavation methods are blasting,
ripping and digging. Table 2.3 summarizes the classes of excavate-ability of various rock
types. Thus excavate-ability of rock in Makkah area is a function of RQD, UCS and
discontinuity spacing. Table 2.3 combines these three parameters and divides rock types
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into five classes I, II, III, IV and V, and four excavation methods (i) Blast to fracture (ii)
Blast to loosen (iii) Rip and (iv) Dig
Table 2.2: Rock types and RMR classification
Rock Type
Number of Stations
RMR
Very Good
Good
Fair
Diorite
1
13
4
Quartz-Diorite
5
47
15
Tonalite
Poor
Very poor
1
1
Granodiorite
1
Amphibolite
1
11
4
Gabbro
4
Meta Basalt
1
2
Chlorite
2
1
Phyllite
1
Table 2.3: Excavate-ability classes of various rock types
2.2.4
Rock Type
Class
Diorite
III-II
Quartz-Diorite
III-II-I
Tonalite
II-I
Granodiorite
II-I
Amphibolite
IV-III-II
Gabbro
III-II
Meta Basalt
II-II
Chlorite
II-I
Phyllite
V
Conclusion
The rock mass categories in the proposed landfill generally fall into Class II to Class V on
the excavate-ability rating. This classification is mainly based on the density of joints set
(blocky). The rocks of the area are easy to excavated or ripped as indicated in Table 2.2.
The valley/wadi floor are overlain by thick sequence of silty sand to gravely sand which
can easily be removed by scraping machine (bulldozer). The underlying bedrock at the
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centre of wadi seemed undulating in places. They seemed to be underlain by
granodiorite/quart diorite and of schist such as at BH-2.
2.3
2-D RESISTIVITY SURVEYS
The purpose of the surveys was to map the resistivity of the subsurface of the landfill
area mainly for leachate detection and estimates of depths to the bedrock.
The
resistivity measurements were made along two 2-D electrical imaging survey lines
(Figure 2.1).
Figure 2.1: Map showing location of survey lines
2.3.1
Field procedures
Electrical Imaging System is now mainly carried out with a multi-electrode resistivity
meter system (Figure 2.2). Such surveys use a number (usually 25 to 100) of electrodes
laid out in a straight line with a constant spacing. A computer-controlled system is then
used to automatically select the active electrodes for each measure. Throughout the
survey conducted in the proposed site, the Pole-dipole array was used with the ABEM
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SAS4000 system. The data collected in the survey is then processed using RES2DINV
software. The survey carried out in Southern Makkah has generally followed the given
procedures.
Station 3
C1
P1
3a
P2
3a
Laptop
computer
C2
3a
Resistivity meter
Station 2
C1
P1
2a
P2
2a
C2
2a
Station 1
Data
level
n=1
n=2
n=3
n=4
n=5
Electrodes
C1 P1 P2 C2
a a a
1
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2
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3
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4
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5
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n=6
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6
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Figure 2.2: The arrangement of electrodes for a 2-D electrical survey and the sequence
of measurement used to build up a pseudo section
The resistivity method basically measures the resistivity distribution of the subsurface
materials. Table 2.4 shows the resistivity and conductivity values of some of the typical
rocks and soil materials that are normally associated with landfills.
Table 2.4: Resistivity of some common rocks, soil minerals, and chemicals in the area
Material
Resistivity
(ohm-m)
Leachate (plume)
0 to 5
Saturated fractured zone with leachate
Groundwater (fresh)
Unsaturated fractured zone
Bedrock Granite
< 10
10 to 100
200
> 4000
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2.3.2
Results and discussion
A total of 2 survey lines were conducted at the site. Line L1 traversed along N-S direction
while Line L2 traversed along E-W direction. The locations of the survey lines are shown
in Figures 2.3 and 2.4. A spacing of 5 meters using the pole-dipole array of ABEM LUND
SYSTEM was used on the survey. The maximum depth of investigations for the surveys
varies from 70 to 80 meters. The total length of the survey lines was 200 m. Generally,
the subsurface is made up of low resistivity zones of below 10 ohm-m which appear to
be zones fully saturated with leachate. Bedrock can be divided into unsaturated fractured
zones with resistivity of more than 200 ohm-m and granites of more than 800 ohm-m.
Figure 2.3: Resistivity sections of Line L1 and L2 showing leachate and depth of
bedrock
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Figure 2.4: Map showing locations and results of resistivity survey lines and estimated
flow of leachate
2.4
SUB-SURFACE DESCRIPTION IN SOUTHERN MAKKAH LANDFILL
2.4.1
Site Investigation Results
The aim of doing site investigation in Southern Makkah Landfill was to aid in the design
of cells particularly in determining maximum depths of cell excavation. BH1, drilled and
completed on March 2nd, 2011, is located within the area of future Cell 2, and not very far
from the existing dump. BH2 drilled and completed on March 3rd, 2011, is located within
the area of future Cell 1, and further away from the existing dump as compared to the
location of BH1. Figure 2.5 shows the borehole locations. Figures 2.6 and 2.7 show the
interpreted profiles for BH1 and BH2 respectively. Figure 2.8 – BH1 and BH2 put
together in a subsurface profile across Southern Makkah Landfill.
BH1 was drilled on original ground while BH2 was drilled inside an excavated depression
of about 7 m lower than surrounding area. Both boreholes are 1 foot in diameter and
were cased down to about 3 m from surface. Water samples taken from boreholes
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indicate that the level of contamination at BH1 is more severe than at BH2, as evidenced
by relative darkness of the samples. The water sample from BH2 was clean and
appeared to have not been affected by the leachate of the dump.
2.4.2
Excavation Limits
For BH1, the water level was recorded as 63 feet (19.2 m) below ground surface. In this
location, the plan to prepare for Cell 2 was to excavate the area 20 m deep. However,
since water level was found at 19.2 m, in order to avoid reaching ground water, the
deepest possible excavation would be only to a depth of about 18 m.
For BH2, the water level was recorded as 33 feet (10 m) below ground surface. Note that
since BH2 is located inside a depression, the ground surface is already 7 m below
surrounding area. In this location, the plan to prepare for Cell 1 was to excavate the area
a further 13 m so that the total depth would be 20 m. However, since water level was
found at 10 m, in order to avoid reaching ground water, the deepest possible excavation
would be to a depth of about 8 m, making total depth to about 15 m instead of the
planned 20 m.
Figure 2.8 also shows the limits of excavation for BH1 (Cell 1) and BH2 (Cell 2) put
together in a cross sectional profile.
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BH2
BH1
Existing
Dump
Note: BH1, drilled and completed on March 2 nd, 2011, is located within the area of future Cell 2,
and not very far from the existing dump. BH2 drilled and completed on March 3 rd, 2011, is located
within the area of future Advanced Cell 1, and further away from the existing dump as compared
to the location of BH1. BH1 was drilled on original ground while BH2 was drilled inside an
excavated depression of about 7 m lower than surrounding area. Both boreholes are 1 foot in
diameter and were cased down to about 3 m from surface. Water samples taken from boreholes
indicate that the level of contamination at BH1 is more severe than at BH2, as evidenced by
relative darkness of the samples. The water sample from BH2 was clean and probably has not
been affected by the leachate of the existing dump.
Figure 2.5: Locations of BH1 and BH2 in Southern Makkah landfill
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Note: BH1, drilled and completed on March 2 nd, 2011, is located within the area of proposed
Advanced Cell 2. The water level was recorded as 63 feet (19.2 m) below ground surface. Water
sample collected from this borehole has indicated contamination by leachate. In this location, the
plan to prepare for Advanced Cell 2 was to excavate the area 20 m deep. However, since water
level was found at 19.2 m, in order to avoid reaching ground water, the deepest possible
excavation would be only to a depth of about 18 m.
Figure 2.6: Interpreted profile at BH1, Southern Makkah landfill
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Note: BH2, drilled and completed on March 3rd, 2011, is located within the area of proposed
Advanced Cell 1. The water level was recorded as 33 feet (10 m) below ground surface. Water
sample collected from this borehole had indicated that it might still be free of leachate. In this
location, the plan to prepare for Advanced Cell 1 was to excavate the area a further 13 m so that
the total depth would be 20 m. However, since water level was found at 10 m, in order to avoid
reaching ground water, the deepest possible excavation would be to a depth of about 9 m,
making total depth to about 16 m instead of the planned 20 m.
Figure 2.7: Interpreted profile at BH2, Southern Makkah, inside existing depression
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BH1
BH2
Limits of excavation
Figure 2.8: BH1 and BH2 put together in subsurface profile of Southern Makkah landfill
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