1.0 PURPOSE / TUJUAN
To provide guidance for operator to perform vibrocoring method safely
and efficiently / untuk menyediakan panduan untuk operator dalam melakukan
vibracor dengan aman dan efektif.
2.0 RESPONSIBILITY / TANGGUNG JAWAB
2.1
Supervisor / Pengawas
2.2
Operator / Operator
2.3
Project Manager / Manajer Proyek
2.4
Operational Manager / Manajer Operasional
3.0 DEFINITIONS / DEFINISI-DEFINISI
Vibrocorers are used
wherever soil conditions are unsuited to gravity corers or where greater
penetration of the seabed is necessary / Vibrocorer digunakan pada tanah dalam segala kondisi yang
tidak sesuai dengan coring gravitasi atau jika penetrasi dasar laut diperlukan.
4.0 PROCEDURES / PROSEDUR
4.1 Describe
Sampling
with a vibratory corer is divided into four steps: intrusion, extraction, core sampling,
and packaging. The following
procedure describes the use of a VibraCore to collect subsurface sediments /
Sampling dengan core vibrator dibagi dalam 4 step : Intrusi, pencabutan,
sampling core dan pengepakan. Mengikuti prosedur dideskripsi penggunaan
vibracore untuk mengumpulkan sedimen bawah permukaan.
·
Intrusion step
is the vibrator head should be attached near the top of the unsharpened end of
the core barrel prior to initiating the coring procedure. After a coring
location has been determined, the core pipe will be vertically positioned. The
core barrel will initially sink into the sediment by its own weight, giving the
barrel stability. Once the vibrator head engine is started, the pipe will
rapidly penetrate into the sediment. Tying a teather line (rope) to the core
barrel and pulling down by adding weight will aid in getting the pipe through
resistant subsurfaces / Tahap Intrusi yaitu kepala vibrator harus terpasang di
dekat bagian atas akhir yang tumpul dari core barel sebelum memulai prosedur
coring. Setelah lokasi coring ditentukan, pipa core diposisikan vertical. Core
barel dipermulaan akan turun ke dalam sedimen oleh bebannya sendiri, lakukan
stabilitas pada barel. Jika vibrasi bagian kepala mesin dimulai, pipa akan
menekan ke lapisan sedimen. Ikat core barel menggunakan tali dan turunkan
dengan menambahkan beban dan akan terbantu oleh pipa melalui bagian bawah
permukaan yang resistan.
·
Extraction, after removing the vibrator head,
the remaining pipe is cut off with a hacksaw approximately 2 feet above the
ground surface. The distance to the sediment surface inside and outside of the
pipe is measured to determine the amount of compaction. The pipe is then filled
with water and a gas-main sealer plug is inserted and tightened to prevent loss
of sediment from the core pipe when it is removed / Pencabutan, setelah membuka
kepala vibrator, pipa sisa yang dipotong menggunakan gergaji besi kira kira 2
feet di atas permukaan. Jarak ke permukaan sedimen dalam dan luar dari pipa
diukur untuk menentukan jumlah kompaksi. Pipa kemudian diisi dengan air dan
gas-sealer utama dipasang dan dikencankan untuk mencegah sedimen jatuh dari
pipa core saat dibuka.
A tripod is assembled and
placed over the intruded pipe. Two come-alongs are fastened to the eyeballs on
the tripod head and to a rope securely fastened to the core pipe. The core is
guided through the core pipe slot in the tripod head and then rested against
the tripod head to prevent falling over during extraction. When the core is
completely out of the sediment, the come-alongs are removed and the core pipe
slot is opened by pulling on the cord that moves the spring-loaded slot gate.
The core barrel is gently placed horizontally, to prevent disturbance of the
core, and examined.
·
Core Sampling
Sediment
samples can be removed from the core either by splitting the core lengthwise
and removing the sample or by drilling holes in the core liner. Splitting the
core lengthwise is preferred since it allows direct observation of the sediment
structure, bedding, lithologies and other features. Samples can be collected
from one half of the core and the other half can be preserved for future
studies or sampling. Alternatively, a power drill fitted with a 1.5- to 2-inch
saw can be used to make holes in the liner. Samples can then be removed with a
spoon and the hole closed by replacing the cutout disk and sealing with duct or
plastic electrical tape. Spacing of approximately 1 foot is recommended to
ensure that the samples are representative of the lithologies in the cores
4.2
Standard
Operational Procedure
The following two sampling procedures apply to the submersible (S) and
pole (P) vibrocoring systems. First:
-
Locate
the sampling station with an appropriate field positioning system that provides
suitable accuracy (± 3 to 5 m).
-
Triple
anchor the boat (if any) to insure keeping it on station.
-
Measure
the water depth using appropriate means, such as a sounding line, marked pole
or fathometer.
4.2.1 Collecting the Core
Submersible (S) Vibrocorer System:
S-1) Check for secure
attachment of the vibro-head to the winch cable and the aluminum core tube/CAB liner assembly.
S-2) Using the winch
and draw works, suspend and lower the vibrocorer slowly until the core tube
contacts the bottom. A measuring tape attached to the top shackle of the
vibrohead is used to calculate this when
water depth and length of the core tube is known.
S-3) Begin vibration
and continue penetration until the core tube is fully buried or refusal occurs.
Be careful to maintain a taught cable to keep the core tube vertical. Turn off
the vibration when penetration is completed.
S-4) Withdraw the core
tube slowly by winch, using vibration only if extraction is difficult (as from
clay). Raise the core tube until the lower end is accessible from on deck.
Thereafter, keep the tube in a near vertical position to preserve core
integrity.
S-5) Cap and tape the
lower end. If a lined aluminum tube is used, remove the nose piece rivets,
slide the liner out (downward) until the sediment/water interface is visible
through the liner wall. Drill a small hole just above the interface to drain
off all water above the sediment core. Carefully cut off (hacksaw) the liner at
this hole, capping and taping it to seal the tube at both ends.
S-6) Label the upper end of the core
with date, time and a unique station number.
Transfer the core
ashore as soon as possible to the processing location, protecting the core from
sunlight, heat and physical disturbance as much as possible.
Pole (P) Vibrocorer System:
P-1) Check for secure
attachment of the retrieval lines to the core tube mounting clamp.
P-2) Insert a 6.5 ft.
length of 2" diameter CAB core tube (core catcher end down) into the mounting
clamp and tighten the four wing nuts securely by hand. Make sure clamp is
tightened evenly.
P-3) Choose an
extension pole of appropriate length (water depth or longer) and insert it into
the mounting plate socket; secure it using a 1/4" bolt and locknut.
P-4) Slip the flared
lower end of the extension tube over the check-valve end of the core tube
adapter, and hold it on by applying upward tension on the retrieval lines.
Lower the system vertically (CAB tubing first). into the water to the bottom.
Press and vibrate tube into the sediment until it is inserted 6 ft., or until
refusal occurs. Note insertion length by markings on extension pole.
P-5) Disengage the
extension pole and stow on board sampling vessel.
P-6) Retrieve the core
tube containing the sample by pulling on the two retrieval lines, either
manually or by using a davit-mounted hand winch.
P-7) With tube and
barrel held vertically in the boat, drill hole in tube just above the top of the
sediment column to drain off water.
P-8) Cut off the tube
just above the sediment surface and cap both ends.
P-9) Label the tube
lengths with sample station ID codes with a permanent marker; make sure the
upper ends are marked as such.
P-10) Stow core within
a cooler or enclosed box with bag ice. Transport ashore for
processing as soon as
possible.
4.2.2 Processing the Core
The sediment core is
usually processed in a nearby field facility in order to describe its structure
and create subsamples for chemical analysis. This is important to document the
core content and to maintain sample quality.
Both the 2" pole
vibrocores and the 4" submersible vibrocores, contained and transported ashore
in CAB plastic tubes after sampling, are processed in the same way. First, cut
off cap and tape the cores in sections of 40" (about 1 meter) in length.
This length fits onto a stainless steel tray on the core processing table, and
can be photographed conveniently in only three frames of film. Alternatively,
the entire core length may be photographed in 18" steps using a moveable camera
box with a built-in light source. Make any cross cuts with either a hacksaw or
the vibrating cutter tool described below. When sub-sampling the core later on,
take care not to
include any sediment
from this cut surface, or any plastic chips from the saw cut.
Next, cut the CAB core
liner (filled with sediment) lengthwise along opposite sides of the 40" or
longer section. Usually this is done with a vibrating saw, router, or with a
hooked cutting blade. Note: cut through the liner wall without cutting
significantly into the sediment core itself. Disturbed sediment adjacent to the
liner wall should not be sampled anyway, but it is important not to contaminate
the undisturbed interior of the core with plastic chips or other debris from
the cutting process. If, before coring, the outer wall of the Lexan liner
(1/8" thick) is scored or precut halfway through with with a circular saw
or other tool, then the final cut during processing can be made with a hooked
blade. However, Lexan plastic is very tough, and cutting with a razor knife can
be dangerous and difficult to control without cutting into the core. The best
hand tool available for cutting hard plastic liners is an electrical vibrating
or "reciprocating" saw of the type used in industry to cut sheet
metal, or in medical practice to cut off plaster casts. (one such saw is made
by Fein.) When used with a blade guide, the cut depth can be controlled so as
to barely cut through the liner wall. The cuttings tend to form ribbons rather
than chips, which helps in avoiding contamination of the sediment inside. Also,
the vibrating blade is much safer to use than a conventional saw blade, since
it does not readily cut soft material such as skin.
Once the liner wall is
cut through along opposite sides (top and bottom of the horizontal core), use a
series of flat, thin blades of rectangular shape (and pre-cleaned) to cut the
sediment core lengthwise into two half-cylinders, using a series of vertical
cuts along the core's radial axis. Use a clean blade for each cut. Vertical
cutting in discrete steps, rather than "dragging" the blade through
the core) insures that the layered structure of the core is not obscured, and
that contaminants are not spread across layers. Between each vertical cut, wash
and scrub all adhering
sediment off of the
blade in a bucket of clean tap water. Note: it is usually not practical to decontaminate
the blade fully after each cut, but any chance of contaminant carryover between
zones can be minimized by cutting through the less oily parts of the core
first. Alternatively, several clean blades can be used -- one for each
increment of length. It helps if the blade is wet when cutting through oily
silt or stiff clay sediments, which tend to adhere. A cleanly cut surface is
best for documenting core structure.
Arrange the two half-cylinders
of the core section side-by-side, with the cut surfaces
facing up. Extend a
tape measure along beside them, starting at the original top end of the core. Photograph
the core in color with a track-mounted 35 mm camera. With 160 watts (4, 4' bulbs)
of fluorescent light, 200 speed film is suitable for good results. Insure that
the wet surface of the core does not reflect light directly into the camera
lens. A polarizing filter helps to reduce reflectance off the wet core surface.
Photograph the core section in overlapping frames; place a small label with
core field ID number so that it appears in each frame. Advance the tape measure
appropriately for any additional sections of the same core.
If a moveable light box
is used, the tape measure is first positioned along the full length of the
core. Overlap the fields of view at least one inch. While the core section is
still intact, record a general description of the core structure, noting zones
of different color, texture, sediment type (silt, sand, clay, gravel, etc.),
and apparent
oiliness.
Collect each core
interval, as pre-determined in the study plan, from the undisturbed core interior
with a clean, stainless steel spoon or spatula. Place the sediment from an
individual core interval into a clean stainless steel mixing bowl of
appropriate size (bowls and spoons are precleaned according to OEPA protocols).
Mix the sediment with a clean stainless steel spoon thoroughly or until
visually homogeneous. During this operation, remove any obviously "nonsediment"
objects from the sample; bottle caps, broken glass, sticks, large rocks, etc. Place
approximately 150 mL of sediment collected from each core interval into a
labeled
250 mL wide-mouth glass
jar (pre-cleaned according to EPA protocols), leaving space at the top of the
bottle for later mixing (unless the samples are for volatile organics analysis,
in which case the jar should be completely filled). Label each jar with a
unique station identification number, with a suffix indicating the layer (X cm
- Y cm) of the sample. Record a description of the layers in each core on Core
Observation Log Sheets. Store the sample bottles on ice or in a refrigerator until
transfer shipment to the analytical laboratories.
4.2.3 Sample Storage
Freeze all sample jars at
-5 to -10 °C until analysis.
3.0 Health and Safety and Environmental Compliance
1)
Field
crew personnel should always wear appropriate personal protection clothing and equipment,
which at a minimum includes:
- Safety glasses or
face shields
- Poly-coated Tyvek or
Saranex jump suits
- Double gloves (Latex
inner gloves and Nitrile outer gloves)
- Steel-toed rubber
boots
- Life jacket, under
jump suit (to avoid contaminating it)
The intention of this
clothing is to minimize personal exposure to the possibly hazardous sediments.
2)
Field
crew personnel should make a point of consuming liquids (cool water recommended)
on a regular basis, to minimize heat stress, and take periodic rest breaks to minimize
fatigue.
3) Excess sample will
usually be disposed of by the client firm or agency.
4) The sediment
processing crew at the field facility should wear protective clothing to include
safety glasses or goggles, a Tyvek (or Saranex) jump suit, latex gloves and
rubber boots. Personnel involved in the decontamination work should also wear
nitrile outer gloves.