06 5 ok CW2C SAND PILE

GENERAL The objective of this method statement is to describe the construction methodology and procedure and required site management controls for construction of Sand Drain works for th

METHOD STATEMENT OF SAND PILE

TABLE OF CONTENTS

I INTRODUCTION

II CONSTRUCTION REQUIREMENT

III RESOURCES TO BE USED

IV QUALITY CONTROL

V OCCUPATIONAL HEALTH AND SAFETY CONTROL

VI ENVIRONMENTAL CONTROL

I INTRODUCTION

1 GENERAL

The objective of this method statement is to describe the construction methodology and procedure and required site management controls for construction of Sand Drain works for the project

Sand drain work is carried out to:

- To improve the soft soil

- To shorten consolidation period

2 WORKING DRAWING

Prior to commence the work, Working Drawings will be submitted for Engineer’s approval Designated areas for the works will be shown in Working Drawings with Work Quantity

3 RELEVANT SPECIFICATIONS, STANDARDS AND DOCUMENTS

Technical specification: 03500 Soft soil improvement Measures

Contractor shall furnish all necessary labor, equipment and materials, and perform all operations necessary for the installation of Vertical Sand Drains (VSDs) in accordance with the details shown on the Drawings and with the requirements of this Specification Section

Contractor shall first satisfy the requirements for submittals of the VSD sequence and method of installation for the Engineer’s approval,

VSDs shall be staked as shown on the Drawings and installed after construction

of the “Coarse Sand Blanket” and prior to embankment construction VSDs shall

be installed from the top of the “Coarse Sand Blanket” by use of a mandrel or other approved method

Sand drains will be installed by driving a pipe with a closed valve at its lower end, using pile-driving equipment When it has penetrated to the required depth, the inside of the pipe is filled with dry coarse sand and the valve at the bottom of the pipe opened The upper end of the pipe is closed, and compressed air applied inside of the pipe to raise the pipe out of the ground, simultaneously expelling the sand out of the bottom of the pipe

The use of water to flush sand into the drain shall not be permitted

The Contractor shall propose the detailed construction method of filling sand into the drain to ensure adequate density of the sand placed, to avoid filling sand into holes with high porosity which will cause great settlement

Filling operation shall be suspended during rain Sand shall be protected from rain, and any sand that becomes damp shall be spread out and left to dry before use

VSDs shall be installed vertically from the working surface to the required

elevation and in a sequence that will not require equipment to travel over previously installed drains Contractor shall provide the Engineer with a suitable means for determining the depth of the drain at any time The equipment shall not have deviations more than 1 horizontal in 100 from vertical All VSDs shall be located within 100 mm of the plan positions shown on the approved drain layouts

Where obstructions are encountered which cannot be penetrated, Contractor shall abandon the hole A maximum of two attempts shall be made to install a new drain within 0.5 meter of the obstructed hole Drains that otherwise deviate from the plan location by more than 150 mm, or that are damaged or improperly installed, will be rejected

Installation of the drains should consider and be coordinated with the geotechnical instrumentation shown on the drawings Special care shall be taken when installing drains near instruments already in place Replacement of instruments damaged by Contractor will be the responsibility of the Contractor Contractor shall demonstrate that the equipment, method, and materials can produce a satisfactory installation in accordance with these Specifications For this purpose, the Contractor shall install trial drains at different locations within the work area

Contractor shall first satisfy the requirements for submittal of the detailed and dimensioned layouts of vertical drain locations for the Engineer’s approval,

Approval by the Engineer shall not relieve Contractor of the responsibility to install VSDs in accordance with the Drawings, and this Specification If at any time, the Engineer determines that the method of installation does not produce a satisfactory drain, the Contractor shall alter the method and equipment as necessary

Contractor shall keep daily records of the vertical drains placed Copies of these shall be submitted to the Engineer within two days following the placement The records shall show:

a) date, b) grid and area reference of each drain, c) depth of placement of each drain below the working surface, d) in the case of sand drains, the quantity of sand placed in each drain, obstructions and delays,

e) number and type of tests carried out, f) readings of installed instruments, g) Any unforeseen conditions encountered shall be noted briefly

in the records

1 WORK PROCEDURE:

The procedure for construction of sand drain is as follows:

Step 1

A closed casing (steel tubular pipe) with 40 centimetres in diameter is penetrated into the ground at pile location by vibration hammer The penetration will stop when the casing has been reached the designed level If soil around bottom of casing enter into inside and the casing cannot achieve the required depth, it will pull up and penetrate again During penetration, the vertical direction of casing will be checked by plumb bob with two directions The air compaction system operates continuously during penetration of casing

Step 2

The sand for sand drain will be supplied to besides installation points When the casing has been penetrated to required depth, using worker or excavator fills sand into the casing through a hopper that was fastened to the casing top During sand filling process, vibration hammer will be used for compaction until required sand volume is confirmed The air compaction system does not operate

in this step

200

430

430

Hopper

H.E (Hopper elevation)

(Sand mat elevation) S.M.E

Steel pipe Stopper

Steel pipe

Hopper

Hopper

T.P.E

S.M.E (Top pipe elevation)

(Sand mat elevation)

(Hopper elevation) H.E 430

Stopper

cable rope

to shut up stopper

Hopper for pouring sand

Step 3

After finish the operation of pouring sand, the casing will be pulled up from the ground by vibration In this time, there operates the air compaction system to compact the sand drain At this moment under the weight of sand, the valve at the lower end of casing is opened, sand drain will be constructed Normally, when the casing is pulled up completely, the top of sand drain will be sunk down and covered by ground soil Thus, this may be impossible to keep continuity of sand drain

In order to solve this problem, when the length of casing was pulled from ground about 2m or 3m, the pulling up stops and pour sand by excavator again, after that restart doing Furthermore the top level of sand drain will be checked after

finished the pulling up In case that we can see the top of sand drain, installation work will be finished In case that we cannot see the top of sand drain, sand will

be poured into the hole up to designed level

Step 4

After installation of sand drain at place, the casing is moved to next pile location and executed Step1 The above sequence from Step1 to Step4 is repeated

Structure of steel tubular pipe

Flow-chart of installation work

If the top of sand drain sink down

Start

Penetration of steel pipe (by vibration hammer and air compaction)

Pulling up of steel pile

Fill sand into the steel pile (sand for sand drain)

Confirm the top level of sand drain

Confirm designed length

Not ok

ok

Confirm required sand volume

Pulling up of steel pipe (with vibration and air compaction)

2m or 3m in length of pulling up

Completion

Stop the pulling up and fill sand into steel pile

(without air compaction)

Fill sand into hole up

to designed level ok

Next pile Continue to pull up the steel pipe (with vibration and air compaction)

Step 2

Step 1

Step 4

Step 3

Vibration, without air compaction

During inserting steel tubular pipe into soil, if any soft soil comes out, the soil shall be removed manually The ground surface shall have gradient and small ditch shall be constructed at the boundary to drain rainwater and water come out from piles If the ground has not enough bearing capacity, steel plate will be provided in order for movement of machine and equipment

The detail of steel tubular pipe and installation are as follows:

Equipments for sand drain works per group are listed below

7 Air compactionmachine system 2

With regard to the quality control, all the works shall be carried out the following established Project Quality Control Plan

With regard to the quality control, all the works shall be carried out the following established Project Occupational Health and Safety Control Plan

With regard to the quality control, all the works shall be carried out the following established Project Environmental Control Plan