01 thuyet minh excavationok (sua l1 27 5 16)

Môc lôc VRAMP – CONTRACT PACKAGE RAP/CP15 – MAINTENANCE OF NH6 FROM KM193÷KM233 IN SON LA EXCAVATION TABLE OF CONTENTS I COMMON EXCAVATION II ROCK EXCAVATION III EXISTING PAVEMENT EXCAVATION IV BACKFI[.]

EXCAVATION

TABLE OF CONTENTS

I COMMON EXCAVATION

II ROCK EXCAVATION

III EXISTING PAVEMENT EXCAVATION

IV BACKFILLING

V BORROW MATERIAL

I COMMON EXCAVATION

1 General

This work consists of excavation, hauling and utilization or disposal of all materials encountered within the limits of the work necessary for the construction of the roadway

Common Excavation shall include the removal, utilization or disposal of all excavated materials regardless of then nature or existing condition, and the shaping and preparation of the exposed surface of the excavation in accordance with these specifications to the lines, levels, grades, dimensions and cross-sections shown on the Drawings subject to approval by the Engineer

The Contractor shall prepare and submit his method statement for the earthworks which shall include an earthworks balance schedule or plan The earthworks balance schedule or plan shall include details of the use of suitable material, in particular the locations and volumes for excavation and placement of materials The plan shall be updated on a weekly basis, in accordance with the progress of the works, and submitted with the Contractor’s weekly work schedule until completion of the roadway excavation Where appropriate the Contractor shall use comparatively better materials in the upper levels of embankment construction

2 Preparation work

Prior to excavation all site clearing shall have been completed in accordance with the appropriate specification to the satisfaction of the Engineer

Before the start of any excavation the Contractor shall carry out a topographical survey of the area and prepare and submit the cross section and profile drawings to the Engineer for approval These drawings shall be used as a basis for the computation of the actual volume of excavated materials

3 Use of excavated material

All materials removed from the excavation shall be used in the formation of the conhensive slope material, capping layer, embankment, sub-grade, shoulders, slopes, bedding and backfill for structures, and for other purposes shown on the Drawings or

as approved by the Engineer

Any material surplus to these requirements, or any material declared in writing by the Engineer to be unsuitable, shall be disposed of by the Contractor outside the right-of-way or as directed by the Engineer in accordance with the provisions in the Specification

4 Removal of unsuitable material

No materials shall be classified as unsuitable and remove from site without quantification by the Contractor and approved by Engineer

Unsuitable material shall be removed and disposed to disposal areas provided by the Contractor and subject to the approval of the Engineer

The contractor shall comply with all environmental regulations when disposing of unsuitable material and shall include in Environmental Management Plan all relevant details for the hauling and disposal of unsuitable materials

5 Dimensional tolerances

Finished grades, lines and formations shall not vary from those specified by more than 25mm at any point with the exception of rock batters and excavations which shall not vary from those specified by more than 300mm at any point

Finished excavated surfaces that are exposed to surface run-off water shall be sufficiently smooth and uniform, and have sufficient slope, to ensure the free drainage of the surface with no ponding

II ROCK EXCAVATION

1 General

Material shall be classifiled as “Rock Excavation” in the following case:

- When the material is evidenced to the Engineer, prior to commencement of excavation, to consist of material that can not be excavated without blasting or the use of rippers (Single tine hydraulic ripper drawn by a tractor unit with a minimum weight of 40 tons and net horsepower rating of 285), including all boulder and detached stones have a vollume of 1m3 or more

- When the material is declared in writing by the Engineer to be Rock Excavation All Excavation not evidenced to be Rock Excavation and declared in writing by the Engineer to be Rock Excavation, shall be deemed Common Excavation

2 Preserving rock bellow subgrade

The contractor shall take care not to break down, lossen or damage the rock under the subgrade line Normally cuts will be made from the top; lift by lift, to protect the rock bench that will remain The Contractor shall be reponsible for methods use and for any damage caused to the roadbed, regardless of any previous approvals by the Engineer

Materials classified as rock shall be excavated to a minimum depth of 150mm and a maximum depth of 300mm below subgrade within the limits of the roadbed The excavation shall be backfilled and compacted with material designed in the Drawings and approved by the Engineer Rock excavation removed in excess of 300mm below subgrade will not be measured and paid for Backfill of the depth in excess of 300

mm below subgrade shall be at the Contractor’s expense

Undrained pockets shall not be left in the rock surface Depressions shall be drained The top of the rock slope pre-splitting line will be established by the Engineer Bore

holes shall be drilled along the slope line maintaining the drill holes at the angle designated on the plans and ensuring that all drill holes are in the sample plane The diameter, spacing and loading of pre-split holes shall be drilled for the full depth of the ledge

3 Scaling and dressing

To leave rock cuts in a safe, stable condition, the Contractor shall scale and dress the slope, removing all loose fragments and rocks not firmly fastened to the rock slope The contractor shall also remove any overhanging rock the Engineer sees as a hazard

to roadway users If the Engineer requires it, the Contractor shall also remve loose fragments and rocks lying outside the slope stakes

III EXISTING PAVEMENT EXCAVATION

Before excavating and repairing pavement, the Contractor shall submit the Engineer the proposed working schedule, list of equipment and the explanation of expected construction methods

The Contractor shall inform the Engineer to witness the measurement of defective area before excavating and.repaying any position Any change in geometric dimensions and types of damage in comparison with the approved design shall be recorded in the minutes and measured by the Conừactor and the Supervision Consultant in order to determine the geometric dimensions and types of damage in need of repaying which is the basis for acceptance and payment later Removed and excavated material amount before measurement and without the Supervision Consultant’s acceptance will not be paid

Excavation shall be implemented to the design level specified in the drawings, including cutting asphalt concrete, benching for each layer of material Excavation is not allowed to continue until the Engineer observes the pit and makes sure that at the excavated level, the structure is not defective and meets design requừements If the material layer at the excavation bottom of design level is not appropriate, the excavation shall be done to the full depth of defective material layer for treatment guided by the Engineer

Backfilling shall follow the drawings or Engineer’s instruction Backfilling material layers and the existing one shall be rolled to guarantee the density and adhesiveness

of the new and old materials

1 Skin patch

Skin Patches are employed to repaừ surface failures in the existing asphalt pavement Skin patches shall be provided as indicated on the Drawings at locations designated

in the field by the Consultant

- Surface Preparation: Saw cut down vertically to the full depth of the defective area of the pavement surface The saw cuts shall be made by transverse and

longitudinal cuts and form a neat rectangle The damage with the width < 1.3 m and the length < 5 m are removed manually The damage with the width > 1.3 m and the length > 5 m are removed by machine Excavate within the rectangle down to the bottom of the area and remove and dispose of unsuitable material that shows evidence of disừess, and remove and dispose of all excess asphalt material Clean sawdust in the asphalt concrete cut by brush and the foundation pit so as to clean and dry pit and no sawdust

- Surface Treatment: Apply a tack coat according to Specification section 05200 to all excavated, exposed surfaces, and place Asphalt Concrete Surface Courses according to the Specification

- Compact the patch mixture with a vibratory plate compactor weighing a minimum of 110 kilogram, or other suitable compactors approved by the Engineer

- Overlaying asphalt concrete mixture:

For the width < 2 m and the length < 5 m: are overlaid manually

For the width > 2 m and the length > 5 m are overlaid by machine

Overlaying asphalt concrete mixture follows the Specification

2 Base patch

Base Patches are employed to repair potholes or failed areas in the existing asphalt pavement and the base course of the road Base Patches shall generally be provided

as indicated on the Drawings at locations designated in the field by the Engineer

- Surface Preparation: Saw cut and remove the repaired area beyond the transverse and longitudinal limits of the pothole or failed area as designated and determined

by the Engineer The saw cuts shall be made by transverse and longitudinal cuts and form a neat rectangle Excavate within the rectangle down to the pavement base Remove and dispose of unsuitable asphalt and base material as determined

by the Consultant

- Surface Treatment: Compact the surface of the base course and apply prime coat according to the Specification Apply a tack coat according to the Specification

to the adjusted asphalt surfaces, and backfill the full depth of the hole with Asphalt Concrete Surface Courses according to the Specification

- Compact the patch mixture with a vibratory plate compactor weighing a minimum of 110 kilogram, or other suitable compactor approved by the Consultant

- Patch preparation, placement and compaction shall be in accordance with the plans and specifications and shall follow the general procedures set forth in the

latest edition of: Asphalt in pavement maintenance - The asphalt institute manual series No 16 (MS-16)

3 Deep patch

Deep Patches are employed to repafr potholes in the existing asphalt that extend down through wearing, binder and base course Deep Patches shall generally be provided as indicated on the Drawings at locations designated in the field by the Consultant

- Surface Preparation: Saw cut down to 30 cm vertically through the existing pavement beyond the transverse and longitudinal limits of the pothole and/or the failed area as determined by the Consultant The saw cuts shall be made by transverse and longitudinal cuts and form a neat rectangle in the pavement Excavate asphalt, base and sub-base material within the rectangle down to the existing sub-grade Caution is to be taken during excavation Excavations shall be stepped/benched to prevent slides as directed by the Consultant Fill sub-base and base with Aggregate Base material in accordance with the Specification Fill Aggregate Base material to the level of the adjusted base course according to the Specification or as approved by the Consultant

- Prepare the Aggregate Base according to the Specification and provide and apply asphalt prime coat in accordance with the Specification

- Surface Treatment: Apply a tack coat to the adjusted asphalt surface, and place Asphalt Concrete Surface Course according to the Specification

- Compact the patch mixture with a vibratory plate compactor weighing a minimum of 110 kilogram, or other suitable compactor approved by the Consultant

IV BACKFILLING

1 Backfilling

On completion of the structure, excavated areas shall be back-filled with approved material to the level of the finished ground surface

2 Soil backfilling

Back-fill shall be placed in layers not exceeding 15 cm Initially and for any change

in soil type, the Maximum Dry Density (MDD) shall be established in accordance with AASHTO T99 from at least three soil samples Compaction, based on at least one test per backfill layer, shall be 95% of the MDD so established Compaction method and equipment shall be suitable for use with the backfill material

3 Granular backfilling

Granular backfilling required for specific structures or other locations detailed

in the drawings or as required by the Engineer shall be placed in layers not

exceeding 15 cm and compacted to 95% (for K95) or 98% (for K98) of the maximum dry density determined according to AASHTO T99, as indicated on the Drawings

The material shall be well-graded crushed or uncrushed gravel, stone, rock-fill or natural sand or a well-mixed combination of any of these Grading requirements for Granular Backfill shall be as follows:

- Maximum size 5 cm

- Passing 4.75 mm sieve 25% to 90%

- Passing 0.075 mm sieve0% to 10%

- Liquid limit TCVN4197-95 30% max

V BORROW MATERIAL

All suitable materials provided from borrow sources shall be used and placed to the grades, cross sections and other requirements indicated on the drawings subject to the approval of the Engineer

During the operation of the borrow pit the Contractor shall ensure the pit remains in a safe properly drained condition The drainage shall be kept functioning and in as good condition as practicable and the sides and ends of borrow pits shall be maintained at the slopes included in the Contractor’s submission

Where a borrow pit includes materials of distinctive types, excavation shall be carried out in a manner that ensures each type remains separate and that no mixing occurs Excavation shall also be carried out in such a way that excavated surfaces are free draining and that the as dug moisture content of borrow material remains unaffected

During excavation of the borrow pit temporary drainage shall be provided and maintained in order to prevent excessive surface run off and the erosion and possible sliding of materials onto adjacent properties or public roads Temporary drainage shall be directed into the existing local drainage system subject to suitable measures being taken to prevent silting or flooding from such existing drainage

All hauling trucks and other construction plant leaving the borrow area or the area of placement on the site shall have wheels, wheel arches and other dirty sections washed before entering onto public roads

Trucks used for hauling borrow materials shall not be overloaded

Trucks used for hauling borrow materials shall be covered with canvas to prevent materials from being blown or falling off the truck

The Contractor shall ensure that all operations related to the excavation and provision

of materials from borrow pits comply with his approved Health and Safety plan, his

approved Environmental Management plan and his approved Traffic Management plans

The Contractor shall not obtain borrow material from locations other than the borrow areas approved by the Engineer for the Project