06 4 ok CW2C VCM

Applied vacuum depressurization shall be 65 kPa minimum measured atmid-depth of the PVD throughout the consolidation period and a minimum of 80 kPa prior to the installation of the fill.

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

SOFT SOIL IMPROVEMENT MEASURES

METHOD STATEMENT OF VACUUM

CONSOLIDATION METHOD (V.C.M)

Regarding requirements for construction using VCM, reference is made toMOT Decision 384/QD-BGTVT of 7 February 2013 Temporary regulations onvacuum treatment method using membrane method In principleconstruction using VCM should comply with the requirements of Decision

384, however the Contractor is permitted subject to the Engineer’s approval

to apply methods meeting alternative requirements based on the technicalrecommendation of their specialist VCM contractor, or if compliance withDecision 384 would lead to breach by the Contractor of another firm’spatents

Construction of other elements such as PVD installation, sand blanket,construction of embankment, and subgrade preparation shall be inaccordance with the relevant sections of this Specification

Applied vacuum depressurization shall be 65 kPa (minimum) measured atmid-depth of the PVD throughout the consolidation period and a minimum of

80 kPa prior to the installation of the fill The piezometric pressure reductionshall be measured by an electrical piezometer installed within a PVD at mid-depth along with a reference groundwater level measured by an observationwell in a non-improved area An adequate number of vacuum pumps shall beprovided to ensure that there is continuous application of vacuum throughoutthe consolidation period It should be emphasized that continuousdepressurization is essential in controlling the stability of the embankment.Vacuum pressure shall be maintained through the required period day andnight

Vacuum depressurization may and where necessary shall be applied prior

to placing of embankment and surcharge and may and where necessary shall

be applied simultaneously with the loading applied by the weight ofembankment and surcharge fill The height of the surcharge fill, duration ofvacuum application, and duration of surcharging are as shown on theDrawings Unless stated otherwise on the Drawings, or unless agreed

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

otherwise by the Engineer, the duration of vacuum application shall be thetotal duration of the “filling time” (embankment construction time) plus the

“waiting time” (consolidation time) as shown on the Drawings

VCM shall be implemented by zones VCM shall be terminated when thecriteria for acceptance are satisfied for the whole of the relevant zone TheContractor may propose the zoning system

The criteria for acceptance is that the specified piezometric pressurereduction together with the specified height of surcharge fill have beenachieved and maintained for the duration specified on the Drawings for thatzone

Surcharge fill as shown on the drawings shall be placed over the netimprovement area at an acceptable filling rate The side slope shall not begreater than 1 (V): 2 (H) If failure to maintain the required vacuum pressureleads to a requirement to increase the surcharge fill height or filling rate, theContractor is required to provide calculations on stability of the embankmentfor approval by the Engineer

At interfaces between VCM method and non-VCM sections, in principle theVCM treatment should be carried out first, in order that embankmentconstruction and surcharge filling may take place uniformly across thetransition

At the site of pipe or box culverts, the VCM treatment and any surchargingrequired shall be carried out first and settlement criteria achieved prior topipe or box culvert construction, in order that uniform ground improvementcan be achieved over the culvert and its approaches During implementation

of VCM, existing drainage shall be routed in temporary drainage pipesthrough the zone of VCM and fill, or diverted by pumping

1.1 WORK SCOPE

This method statement includes the following work scopes:

(i) PVDs Installation

(ii) Vacuum system installation and trial running

(iii) Placing Geo- membrane and Protecting geotextile

cross section drawings are attached to provide general view

2 RELEVANT SPECIFICATIONS, STANDARDS AND DOCUMENTS

RELEVANT SPECIFICATIONS AND STANDARDS

ASTM D 1621 Standard Test Method for Compressive Properties of Rigid Cellular Plastics

ASTM D3776 Standard Test Methods for Mass Per Unit Area (Weight)

of Fabric ASTM D3786 Standard Test Method for

Bursting Strength of Textile

Fabrics—Diaphragm Bursting Strength Tester Method

ASTM D 4491 Standard Test Method for Water Permeability of Geotextiles by the Permittivity method

ASTM D 4533 Test Method for Trapezoid Tearing Strength of

Geotextiles

ASTM D 4632 Test Method for Breaking Load and Elongation of

Geotextiles (Grab Method)

ASTM D 4716 Test Method for Determining the (In-plane) Flow Rate per Unit Width and Hydraulic Transmissivity of a Geosynthetic Using Constant Head

ASTM D4751 Standard Test Method for Determining Apparent OpeningSize of a Geotextile

ASTM D 4833 Test Method for Index Puncture Resistance of

Geotextiles, Geomembranes, and Related Products

ASTM D 5101 Measuring the Soil-Geotextile System Clogging Potential(By the Gradient Ratio)

ASTM D 5321 Standard Test Method for Determining the Coefficient of Soil and Geosynthetic or Geosynthetic and Geosynthetic Friction by the Direct Shear Method

 ASTM D 5567 Hydraulic Conductivity Ratio (HCR) Testing of

Soil/Geotextile Systems

 MOT Decision 384/QD-BGTVT of 7 February 2013 Temporary

regulations on vacuum treatment method using membrane method

Environment & Safety Engineer

Project Manager

Construction Manager Site Engineer

QC Manager

Team for VCM work

Team for PVD work

Construction preparation

Set up filtration and main pipeLaying geotextile (first layer) and geo-membrane (2 layers)

Set monitoring equipment

Drainage ditch constructionInstall PVD

Set outerway of vacuum and bury geo-membrane

Laying the second geotextile layer

Marking of PVD

Trial penetration of PVD

Mass construction of PVD installation

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

separated by tags or signs

- Miscellaneous materials such as hardware and welding supplies shall

be stored in the warehouses and managed by a material staff

- Machine, equipment and material should be ensured in good qualityand supply on time

(2) Installation of Prefabricated Vertical Drains (PVDs)

The construction flow of PVD is shown as below:

Prefabricated vertical drains (PVDs) shall be installedthroughout the soft soil layers; Table 4.1 shows the main properties of PVDmaterial to be used

Table 4.1 Required characteritics of PVD matterial according to

“Technical specification for soil

improvement-Technical design documents”

Properties Test

Designati

on

Requireme nts

Less than 75 Less than 75

Grab Tensile Strength, kN

Catalogue of PVD material shall be submitted for approval beforepurchasing and supplying for installation in soil improvement areas withspacing and penetration depth according to the Technical Design

 Technical requirements for PVD installation

 PVD material shall be stored in the warehouses to protect from rains,sunshine and ruins PVDs with any defects are strictly not allowed to use

 Extension of PVD shall be implemented by opening the filter cover andoverlapping (≥300 mm) the core, then wrap and staple to ends

 Tags shall be used to locate the installation points

 PVD installation is presented as below:

- Use ruler or marked line to measure the spacing and points with deviation

of ±100 mm

- PVDs shall be installed by static pressing or vibration method

- After completion, self-confirmation shall be executed Once confirmed, thework is reported to the Supervisors

 Marking of Vertical Drain

After coordination survey work, the all vertical drain points will bedemarcated using bamboo chopsticks and any other materials to mark thepoints Tolerance shall be within 100 mm at this moment The horizontal andvertical tolerance is 5%; the depth tolerance is 1%

 Trial Penetration of Vertical Drain: Calibrate monitoring unit

Mobilize Vertical Drain Rig to the marking location Then, set

up the Plastic Band Drain to the Rig

Then, Vertical Drain will bepulling out from the casing pipe and marking each one (1) meter for checkingthe monitoring unit

After the marking, band drain will be re rolled for their installation

Then, trial penetration work will be done slowly to check and adjustmonitoring unit and actual penetration depth (calibration)

After the calibration of monitoring unit, we will continue trial penetration

to check the treatment thickness

Then, the vertical drain length will be recorded and submitted forapproval

Besides, trial PVD installation will be carried out at outside of treatmentarea for inspection by the Engineer

 Vertical Drain Arrangement

All vertical drain shall be recorded to designated record formatand submit these record with summary

 Mandrel : A mandrel (dimensions: 140x70x10mm), which is pushed

downwards into the weak subsoil

 Set Anchor Plate : Set anchor plate (140x85mm) to band drain and

reinsert to the casing pipe

 Splicing

Splicing of the PVD shall be done by stapling with proper workmanshipensuring the structural and hydraulic continuity of the drain At the splice thejacket of the upper part of the drain shall be external to the lower portion Amaximum of one splice per drain will be permitted without specific permissionfrom the Engineer

The jacket and core shall be overlapped a minimum of 300 mm at any splice

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

 Cut and Record

When casing pipe will be set back to original position, the plastic banddrain shall be cut by knife Vertical Drain shall be remained at least 300 mmfrom the platform

Then, Anchor plate shall be arranged again

At the same time, the length of each vertical drain shall be recorded tothe monitoring format Total vertical drain length will be calculated each day,cumulated and presented every day as a daily progress report

(3) Setup Horizontal Drain

 Placement of horizontal drain

- One main pipe will be placed along the centre line of road Other subpipes will be placed overlap the row of PVD with spacing as shown inworking drawing The distance between boundary of treatment and the end

of pipe that is 10 – 15cm

- Position of the filter pipes Use shovels to excavate ditches The ditchescan be rectangular cross-section (15-20 cm wide and 15 cm deep) ortriangular cross-section (15 opening and 20 cm deep)

- Install pipes into the ditches, which are connected by four-way joint tofilter pipes Recheck the performance of the pipes before the placement,e.g., the ruins of the filter, the broken of the pipes

- The connection joints shall be wrapped and wired by geotextiles toprevent from the intrusion of sand particles

- PVD will be rolled around the filter pipe and then belted by plastic belt

- Fill sand into the ditches after completion of placement pipes

- The main pipe are connected to the UPVC pipe without holes by three –way joint and connected to the pump, placing along the road

 Attention

- The excavation depth of the ditches shall be guaranteed

- Check the appearance and ruin of the filter membrane and pipe body

- The joints shall be firmly connected to the filters and wrapped bygeotextiles.

Transported geomembrane to siteLaying the first geotextile layer

Laying first layer of geomembraneCheck and patch first layer of geomembraneLaying second layer of geomembraneCheck and patch second layer of geomembrane

Bury geomembraneLaying the second geotextile layerInstallation vacuum system

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

(4) Placement of Geomembrance

 The installation of Geo-membrane must meet the following

requirements

Geo-membrane is keyed into anchor trenches which are filled with clay groutfor air tightness Geo-membrane should be sustainable, flexible and anti-punch airtight materials

Prior to the placement of the geo-membranes, the jobsite shall be leveled andcleared Rigid and sharp materials (e.g., gravels and chunks) shall be cleared.Meanwhile, a protection layer of non-fabric geotextile shall be placed below thegeo-membranes

The size of the geo-membranes shall be pre-determined in accordance with thetreatment scope by manufacturer The size shall also account for theembedment into the cut-off wall An overlapping between 02 sheets ofgeomembrane is joined by glue, it shall not be less than 20 cm During the test

of the vacuum preloading, the overlapping shall be carefully inspected

The geo-membranes strips shall be firstly mobilized by excavators to the center

of the jobsite and unpacked two-ways During mobilization, the geo-membranesshall not be ruined by the excavators

The placement of the geo-membranes shall proceed daytime with less thanforce 5 wind power

Two geo-membranes are placed independently Each placement will be followed

by careful checks and repairs of ruins After installation of geomembrane, sandbags shall be put on geomembrane

In the course of geo-membranes placement, the persons shall wear soft shoes.Each placement will be followed by careful checks and repairs of ruins oropenings

In the course of geo-membranes placement, the geo-membranes shall not bepulled excessively A length of geo-membrane shall be reserved at the sides ofeach treatment unit

An opening can be repaired using a small size geo-membrane Firstly, clear thesurface of the opening and the geo-membrane Then, daub the binder aroundthe opening When the binder is felt non-cohesive, place the small geo-membrane onto the opening, without leaving air bubbles between the contactsurfaces

When position the settlement measurements on the geo-membranes,geotextiles, soft mats or geo-membranes shall be placed beneath themeasurements Weight shall also be placed on the base

Check the geo-membranes very carefully prior to the vacuum operation Assessthe leaking potentials based on the vacuum meter, vision and hearing Any

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

opening or ruin shall be repaired immediately

Geo-membranes shall be backed up on-site for at least operations of two units.When ruins or vacuum leaking is identified after surcharge is loaded, it is hard

to correctly identify the points of ruins

- Gloves shall be worn to prevent from ruins

- Geo-membranes binding works shall be completed by skilled persons

- Geo-membranes shall be embedded into the impervious soil for at least

50 cm

- Miscellaneous materials shall be immediately cleared from the ditches

 Edge Treatment

After the Airtight sheet arrangement, Edge Treatment shall be executed

by Excavator for excavation and backfilling work

Airtight sheet shall be embedded into the cohesive material at least 50

cm to prevent air leak