3 APROACHING AND METHODOLOGY
1.2 METHODOLOGY
3.2.2 Field Data Collection/Primary Surveys 1.1.1.3 Preliminary Survey
1.1.1.5 Soil Investigation
The consultant will conduct an investigation of all existing materials and also conduct a soil investigation at the location of the toll road route directly in the field or in the laboratory.
a. Surface Geology 1) General
The surface geological map shows all the geological conditions in the project area, namely at the planned location of the dam/dam shaft, other buildings located at the project site and inundation areas and the location of the source of embankment material. In addition, the map must also show the name of the rock, the overburden and their distribution, geological features, such as joints, fault areas, movements and slopes of the layers.
Investigations with new test trenches and wells were carried out to determine changes in soil formation, which were very useful to help determine the type of rock distribution, the degree of weathering and the properties of the overburden.
2) Base map
Both topographic maps and large aerial photographic maps can be used for mapping surface geology. The final geological report is based on the results of field investigations, and uses the following maps as references:
i. Regional map with a scale of 1: 50,000 at least 1: 100,000 ii. Semi-detailed map with a scale of 1: 25,000 at least 1:
50,000
iii. Detailed map with a scale of 1: 500
3) Procedures
Mapping of surface geology for toll road plans is primarily intended for engineering geology purposes, including discussion of:
i. Geomorphological state
ii. The distribution of rock units (lithology), which includes rock and soil, must be clearly distinguished, for example bedrock, soil cover, weathering level, etc., physical properties, texture,
iii. Cementation and rock types.
iv. Rock hardness must be described based on the degree of rock hardness qualitatively for civil engineering purposes.
v. For cohesive soils, the symbol OH (overburden hardness) is used, while for rock hardness, the symbol RH (rock hardness) is used.
vi. Gikuchi and Saito classification of violence
vii. For the degree of rock weathering, the Gikuchi and Saito classifications are used
viii. Soil classification should be used based on the Unified Soil Classification.
ix. Geological structure: stance, layering slope, joint, fault.
x. Stratigraphy: the vertical order of rock units based on their formation, according to their geological history.
xi. Other symptoms: landslides, earthquakes, groundwater and others.
b. Deep Booring / Drilling
Deep Booring / Drilling required for engineering geological investigations is drilling by means of rotary core drilling. This drilling is carried out by turning the drill handlebar along with the sampling tube with the engine as the driving force.
1) Determination of the number of Drilling points
i. The purpose of this drilling is to obtain data from the condition of rock/soil under the dam or other buildings, as well as to determine the carrying capacity and the value of water seepage under the building.
ii. Drilling locations are generally carried out around:
2) Drilling Diameter
The drill that will be used is the “NMLC” size drill based on DCDMA (Diamond Corce Drilling Manufactures Association) with:
i. core diameter 52 mm ii. core diameter 75.7 mm
3) Core Barrel
For the core tube, it is required to use a single tube core barrel or a double tube core barrel or for special cases, a triple tube core barrel can be used. All types of core were used depending on field conditions.
4) Feed Boron
The drill bit is used depending on the state of the rock, but generally a tungsten drill bit or a diamond drill bit will be used. For weathering soil and rock conditions, a tungsten drill bit is used, while for compact and hard rock a diamond drill bit is used. Core recovery must be obtained at least 90%.
5) Other Equipment
i. One unit drilling machine capable of exceeding the maximum borehole depth
ii. Drill handlebars that match the borehole depth and casing iii. Three pots
iv. Water pumps, hoses for water lines, water meters and pressure meters and rubber packers, for water testing equipment.
v. Oil, grease, diesel, meter, stationery etc
6) Drilling
i. After the drilling location is approved by the Board of Directors, the next step is to mobilize tools and personnel to the work location.
ii. Clean the drilling location area from plants, roots and if the drilling location is on a slope / cliff area, or in the middle of a river, then preparation for making andang is required.
iii. Finding a location for water extraction which will be very necessary for the wet drilling process and for water testing.
iv. After the drilling machine and three pots and water pumps have been installed, work can begin immediately.
v. Drilling is carried out using tungsten bits for soil and soft rock conditions and dry drilling. For hard rock conditions, the method is wet drilling and using diamond bits. Pay attention to changes in the color of the rinse water and record it in the drilling diary. The drilling method is by rotary drill, not by percussion drilling (mashing).
vi. Install the casing (shield pipe) in a location that is prone to collapse.
vii. After each drilling, the coring is put into the core box and placed in accordance with the initial order of depth. Mark the limit for coring.
viii. After 5 m of work progress, the core box is covered with boards. Annotate on the cover board with Project Name, No.
Drilling Point, Drilling Location, Drilling Depth, No Core Box.
Close the core box with a padlock.
ix. Materials such as slime, cuttings and other materials that are not part of the drilling results cannot be put into the core box.
x. The drill technician must record every drilling job execution, work time, work process, groundwater level, water test testing work, soil bearing capacity testing with SPT, undisturbed soil sampling and others into the field book.
xi. The surveyor must provide data on the coordinates (x and y) and elevation of the borehole and submit the data to the driller. Reference for measurements at this drilling site is taken from the Benchmark and the coordinates and elevation will be indicated by the Engineer.
7) Sample Storage
Core samples are placed in wooden box and arranged according to the order of drilling progress. For examples of cores that are not taken at all, the storage crate can be replaced with bamboo or wood which is painted red and placed according to its depth.
The size of the sample box:
i. length = 1.00 m ii. width = 0.50 m
Each sample chest to store 5 meters of drilling progress, consists of 5 paths. Each path is 1 meter long. On the left and right walls of the sample crate, the drilling depth is written from top to bottom. At each extraction with a core barrel, the drilling results are placed in a storage box by placing a mark on the bulkhead of the sample crate.
On the lid and the front of the sample storage case, the following data must be clearly stated:
i. The project name ii. Location name iii. Drill point number
iv. Initials and the last depth where the core sample was taken
All crates and their cores must be stored in a safe place (avoid from heat, rain, etc.) for further use in the design and construction phase.
Figure 15. Arrange of soil sample
8) Description
The consultant geologist examined all the cores that had been obtained, made a description of the lithological properties of the sample as well as all information during drilling, and made it into the drill log.
9) Log drill
A description of the drilled rock samples must be entered into a specific column (drill log) and include the project name, project location, drill hole number, date, elevation, drill point coordinates, groundwater level, drilling response, daily drilling depth, formation rock/soil, rock/soil name, rock weathering, rock hardness, core shape, core recovery, description, rock unit, RQD, permeability/lugeon coefficient, SPT, rinse water, core barrel type and protective pipe.
The description is carried out by a geologist and the naming of rock units and symbols must follow the standards/classifications that have been determined as follows:
- Land : unified soil classification
- Rock : texture, mineral composition, rock name - Weathering : degree of weathering gikuchi and saito - Gikuchi and saito rock violence scale
10) Groundwater Measurement Notes
Groundwater encountered should be measured and recorded as follows:
i. If groundwater is encountered for the first time, the depth is measured. Drilling is postponed for at least 20 minutes to allow time for the free static water to develop.
ii. The depth of the water must be recorded every 2 minutes within 20 minutes. If 20 minutes have elapsed and the water level is still rising, the Contractor must decide something before drilling resumes.
iii. If groundwater is found in a deeper layer after the previously encountered groundwater has been sealed with a protective pipe, a similar record must be made. The exception is if the groundwater flow is only a small seepage into the borehole. In this case, the seepage point should be noted and drilling continued.
iv. The water level should be recorded at the beginning and end of each shift of working hours. When groundwater is encountered, the depth of the borehole, the length of the section of the protection pipe that enters the borehole, and the time must be recorded.
v. The water level was recorded 24 hours after drilling was completed and during that time the borehole was left open.
vi. The method of recording the water level as described above applies to all boreholes.
c. Standart Penetration Test (SPT)
Standard penetration tests are carried out to obtain a “value – N” and a representative subsoil sample. Value – N is used to estimate the condition of the subsoil in relation to the bearing capacity for the calculation of the foundation design. Execution of tests based on ASTM D-420 and 1586-84.
N-Value is defined as the number of hits with a hammer weighing 63.5 kg that falls freely from a height of 75 cm, to insert the sampler 50 cm deep into the ground.
This test is generally carried out at 2 meter depth intervals and/or at each replacement of the material in the soil layer.
1) Equipment
i. Drive Hammer Assembly
Hammer weighing 63.5 kg.
Guide pipe, of sufficient length to allow the hammer to fall freely from a height of 75 cm.
Knocking head.
ii. Bor
Diameter: 40,5 mm or 42 mm.
iii. Split Spoon Sample Tool
Outer diameter: 2” and inner diameter 1 3/8”. 50 cm long, iv. Others
Airtight transparent sample cover tools (plastic bags), data sheets and others.
2) Method
i. After the drilling reaches the planned depth, the borehole must be cleaned to the bottom by washing from the debris of the drilled material to ensure that the tested soil is not disturbed.
ii. The sampling device (clean and lightly lubricated) is mounted on the drill rod. All joints must be strong so that they will not come loose during the test. The sampler is lowered to the bottom of the hole. The protective cap, guide pipe is fixed on the top of the drill rod. Drill rods are marked using a marker around the drill rods at 15 cm intervals from bottom to top.
iii. Then the hammer is dropped on the protective cap until the sampler is 15 cm deep into the ground as a seat drive. The first 15 cm (0.0 cm - 15.0 cm) are mentioned as N1. Each hammer drop is counted to a depth of 15 cm. If N1, the
stroke has exceeded 50 times then the execution is considered complete. The total N is more than 50 and it is recorded how many cm of drill rods enter the soil.
iv. If the initial 15 m of N1 has not reached 50 strokes, then proceed to the next 15 m. Like the N1 at the start, the number of strokes counts to a depth of 15 cm. At a depth of 15 cm – 30 cm it is called N2. If N2 exceeds 50 strokes, then the execution is considered complete. If it has not reached 50 strokes, then the number of strokes entered at this depth is recorded. (N2=...hit)
v. If N2 has not reached 50 strokes, then it is continued at a depth of 30.0 cm - 45.0 cm, it is called N3. Then count the number of hits that come in.
vi. N total is the number of hits in N2+N3. Meanwhile, if N1 is less than 50 strokes, it is not included in the calculation because it is considered N1 which is at a depth of the first 15.0 cm as remaining / not original soil.
vii. "Free fall" from a height of 75 cm, must be done with care.
The drill rod above the borehole must be held in a vertical position to prevent energy transfer due to bending and so on.
viii. After the test is complete, the sampler shall be removed from the borehole and opened. Then the samples taken must be put in plastic and marked with the values N1, N2 and N3 on the outside of the plastic. Both ends of the plastic must be tied. Then this plastic is put into the sample crate. On the chest is written a label containing the values N1, N2 and N3. To get the price of soil bearing capacity (qu) from the value of N:
Peck's formula is only used for clay soil as follows:
qu = (0.4 + (N/20)) kg/cm)
To get the value of Ø (internal shear angle) for sandy soil, Peck's formula is used as follows:
Ø = 0.3 N + 27
Test results and samples must be submitted to the Engineer.
The results must be submitted in the format as shown on the attached data sheet, or in another format with the approval of the Engineer.
d. Soil Samples
The consultant takes soil samples from soil samples to determine the characteristics of the soil layer, both for foundations and for structure materials.
There are 3 types of soil samples that must be collected : undisturbed (native) soil samples, litle disturbed soil samples and disturbed samples. The location and depth at which samples are to be taken will be determined by the Employer.
1) Sample of undisturbed soil
So that the data on parameters and soil properties can still be used, soil sampling must be carried out carefully.
The collection, transportation and storage of these soil samples must meet certain requirements, so that:
i. The soil structure is not too disturbed or changed, so it is close to the same condition as the field condition.
ii. The original water content can still be considered in accordance with field conditions.
iii. Taking samples from the drilling operation. ASTM D-420, D- 1587 and D-3550
Using a tube with a length of 50 cm
Tubes are inserted according to the depth of undisturbed soil sampling, namely from very soft soil, soft and medium hardness
The tube is pressed using pressure from a drilling machine
After the collection is complete, both ends of the tube are closed with paraffin
On the tube wall is marked: Project name, drill point location, drill point number, depth, tube number
Stored in a safe place, protected from hot sun, vibration
Immediately the tube is brought / sent to the laboratory for testing.
2) Sample of disturbed soil
i. An example of disturbed soil :
A sample of approximately 30 kg of soil must be taken from the test trench.
If each layer of soil is thick enough, then samples must be taken from each layer by vertical sampling.
If the layers are thin (<0.5 meters) then the whole soil sample is taken by vertical sampling.
Soil samples are put into sacks and the ends of the plastic sacks are tightly tied. On the outside of the sacks are marked with the name of the project, location of collection, depth, number of soil samples.
ii. Litle disturbed sample
A sample of 1 kg of soil must be taken from a certain depth from each test trench or borehole to be tested for moisture content and classification.
These samples must be stored in plastic bags or other suitable bags.
iii. Handling soil samples
All samples must be labeled indicating the name and location of the project, sample number, drill hole number or test well, depth and description of the soil. The information must be clearly written on the note and included in the sample container.
e. Test Pit / Borrow Pit 1) Description
The work of the test pit or test pit is to determine the type and thickness of the layer below the soil surface more clearly, both for building foundations and for embankment materials in the
drill area. Thus, a clearer picture of the type of layer and its thickness will be obtained, and the volume of available excavated material can be calculated.
2) Procedures
i. The Contractor must dig a test pit to determine the division of the soil layer and take samples for testing.
ii. Test well size.
iii. The cross section of a test pit must be large enough to allow excavation work to be carried out, which is about 1.5 x 1.5 m with a depth of 3 to 5 meters.
iv. The contractor must be able to interpret the location of the borrow area well, for example the type of backfill material for the dam core, sand and rock. So that the manufacture of test wells is more efficient.
v. The material removed from the excavation must be collected around the test pit to identify other materials at a certain depth.
vi. In order for soil sampling and classification to be carried out properly, the bottom of the test pit must be horizontal.
vii. For undisturbed soil sampling, it can be carried out in different soil layers or at a certain depth that has obtained approval from the board of directors.
viii. The method of taking undisturbed soil samples can be done with materials made of wood and in the form of a cube, where one area of the cube is still open. The inside of the cube is coated with paraffin. The size of the cube is 30 x 30 x 30 cm. At a predetermined depth for undisturbed soil sampling, the soil is shaped like a cube with a size smaller than the size of the cube. After that the cube is inserted into the soil that has been formed earlier. When the soil has completely entered into the cube, then the bottom of the cube is cut. One part of the cube that is open is then covered with wood which has been coated with paraffin and then nailed that part.
ix. The outside of the cube is marked: Project name, test pit number, soil sampling depth and time of collection and stored in a safe place.
x. As for taking disturbed soil samples, it can be taken from the walls of the test pit. Soil samples can be taken from each different soil layer of at least 30 kg. Then the soil sample can be put into a plastic bag and tied at the end. On the outside of the plastic there is a symbol of the project name, the location of the soil sampling, the depth of the soil sampling and the time of collection.
xi. For examples of heap materials in the form of sand and stone, put in a plastic sack of at least 30 kg and mark as above.
xii. After each well is completed, the geotechnical expert from the Contracting Party must make a note of the findings, describe the test pit, take color photos, and submit it to the Employer. All descriptions of the project name, soil sampling location, soil sampling depth, hole description, etc. must be presented by the Contractor in one test pit log where the log format has been approved by the Employer.
xiii. At the time of making the test pit, a weight-volume test must be carried out in the field at every 2.0 m depth using the sand-volume weight method or the water-volume method according to JIS A 121 H/1971 or ASTM D 2937 – 71, SNI 03-6872-2002
3) Special condition
The making of this test well is stopped when:
i. A hard layer has been found and is estimated to be really hard around the test wellbore.
ii. Simple digging tools such as crowbars, hoes, shovels or pickaxes can no longer penetrate them.
iii. If groundwater seepage is found which is large enough that it is difficult to overcome it with simple pumping equipment in the field.