Biện pháp được trình bày bằng tiếng anh, Mô tả chi tiết quy trình thi công hạng mục Embankment and Subgrade
PROJECT DESCRIPTION
Project Objective
The Cambodia Road Connectivity Improvement Project (RCIP) will support the improvement of climate resilient road accessibility in targeted provinces The Royal Government of Cambodia (RGC) has requested the World Bank (WB) provide an Investment Project Financing (IPF) Targeted provinces under the proposed investment include Kampong Cham, Kratie, and Tboung Khmum with a total population of over 2.3 million people The design of the proposed project builds on a network connectivity approach to improve road accessibility in rural areas, between rural areas and urban centers, and to the main network The project provinces were selected considering several criteria including density of rural population, agricultural potential, vulnerability to floods, condition of roads,and connectivity of provincial road networks to cover larger geographic area.
Road works will help to improve climate resilience and safety of road infrastructure The scope of works will include paving/sealing of the roads with climate adaptation and resilience measures and improving bridges and other road structure to climate-resilient standards The technical design will ensure that the identified climate-resilient measures reduce transportation costs and flooding risks and achieve the target of creating durable access to the main road network, markets, and services for the rural population.
INTRODUCTION
Reference Construction Specification
Other Standard Related
AASHTO M145 Classification of Soils and Soil-Aggregate Mixtures for Highway Construction
Purposes AASHTO T11 Materials Finer than 75-àm (No.200) Sieve in Mineral Aggregates by Washing AASHTO T27 Sieve Analysis of Fine and Coarse Aggregates
AASHTO T87 Dry Preparation of Disturbed Soil and Soil Aggregate Samples for Test
AASHTO T88 Particle Size Analysis of Soils
AASHTO T89 Determining the Liquid Limit of Soils
AASHTO T90 Determining the Plastic Limit and Plasticity Index of Soils
AASHTO T99 Moisture-Density Relations of Soil Using a 2.5kg Rammer 305mm Drop
AASHTO T146 Wet Preparation of Disturbed Soil Samples for Test
AASHTO T180 Moisture-Density Relations of Soil Using a 4.54kg Rammer 457mm Drop
AASHTO T191 Testing procedure on definition of compaction of road foundation and embankment by sand cone method AASHTO T205 Density of Soil In-Place by the Rubber-Balloon Method
AASHTO T224 Correction for Coarse Particles in the Soil Compaction Test
ASTM D1140 Amount of Material in Soils Finer Than the No 200 (75-àm) Sieve
AASHTO T100 Specific Gravity of Soil
Description
The embankment work shall consist of the construction of embankment and backfill not specified elsewhere by furnishing, placing, compacting and shaping suitable material of acceptable quality obtained from approved sources in accordance with General Specifications in clause 2.6, and to the lines, levels, grades, dimensions, and cross sections shown on the Drawings and as required by the condition of contract.
SCOPE OF WORK
Description
The Embankment Work shall be followed as:
1 Preparation Work (Manpower, Equipment, Materials, Traffic Safety Devices, Staking Out)
2 Embankment Works (Spreading Material, Compaction Work, Inspection and Acceptance)
3 Subgrade Works (Spreading Material, Compaction Work, Inspection and Acceptance)
Table List of Rural Roads under Project Scope
KRT-1 Thmor Krae – Chong Krang 11.1 Chetborei Dar
KRT-2 Sambok – Korsang 8.2 Chetborei Thmor Krae
KRT-3 Kbal Chour – Dei Sampateankakot 11.9 Chetborei
Kou Loab Dar KRT-6 Prek Brosob Ler - Sraengeat 14.2 Chetborei Sambok
KRT-20 Banteay - Koh dach 8.1 Chetborei Dar
Table 3: Table List of Rural Road under Project Scope
Work Quantities
The following tables are the estimated quantities of Embankment & Subgrade from the Bill Quantities of the main Contract intended for references only and not for measurement purposes.
Description Items No Unit Quantities
ORGANIZATION CHART
Organization Chart is as follow:
MANPOWER AND EQUIPMENT
Equipment
Table of Equipment serving for the construction:
No Equipment Capacity Unit Qty Remarks
1 Bulldozer 140CV each 2 For spreading the embankment materials
2 Excavation 0.8m 3 each 1 For excavation works
3 Motor Grader 108CV each 1 For Spreading the subgrade materials
4 Tandem Roller 12 tons each 2 For compaction works
5 Vibrator Roller 25 tons each 2 For compaction works
6 Dump truck 15 tons each 8 For transporting materials
7 Water supply truck 10m3 each 2 For watering the embankment, Control dust
8 Pump each 2 Use during necessary work
9 Survey Instruments set 1 Serving survey works
* Note: This equipment will be increased according to the site requirements
Manpower
Manpower to be mobilized for construction work as below:
8 Safety Worker Person 2 Depend on site condition
* Notes: This manpower will be increased according to the site requirements
MATERIALS REQUIREMENT
Definition of Unsuitable Material
Unsuitable Material shall be defined such as:
Material containing quantities of organic materials such as grass, roots, sewerage, peat and muck Soils with liquid limit > 80% or Plastic Index > 55%
Soil with natural water content > 100%
Soil with very low density ≤ 800 kg/m3
Soil that cannot be properly compacted as determined by Engineer
Embankment Material
Description Test Designation Item Ref Spec Limit Design Requirement
CBR Value at 90% AASHTO T-193 2.6.2 CBR ≥ 4% CBR > 4%
Refer Sub-Clause 2.6.2 of II-C: “Particular Specifications”
Selected Subgrade Material
Description Test Designation Item Ref Spec Limit Design Requirement
CBR Value at 95% AASHTO T-193 2.6.2 CBR ≥ 10% CBR > 10%
Refer Sub-Clause 2.6.2 of II-C: “Particular Specifications”
Sand Embankment (If any)
Description Test Designation Item Ref Spec Limit
Material Gradation AASHTO M-45 2.6.2 Max Particle size: 10mm
Plasticity Index AASHTO T-90 2.6.2 Non-plastic and free from clay lumps
CBR Value at 95% AASHTO T-193 2.6.2 CBR ≥ 10%
Refer Sub-Clause 2.6.2 of “General Specifications”
TESTING AND SAMPLING
Lab
The contractor will submit to the consultant a qualified testing unit The profile will be submitted separately by the contractor The experimental unit will serve the project with the approval of the consultant.
Testing Standards
Unless otherwise specified, all tests shall be performed in accordance with the methods used by AASHTO/ASTM and shall be made by the Engineer or his designated representative Refer
“Table 2: Standard Related” of Sub-Clause 2.2 of This Method Statement.
Sampling and Testing Frequency
No Stage/ Activity Inspection required Reference
1.1 Approval of Materials Sampling & testing AASHTO Method
Table 1.1 (Sub-Clause.1.11.7) of General Specification
Moisture Density (Lab) AASHTO T-99 1 per 2,000 m Relative Density D-7049 (ASTM) 1 per 1,000 m
Field Density AASHTO T-191 5 per 2,000 Sq.m
2.1 Length, width & height of work Line & level As per the drawings Per area
2.2 Formation level Finish level As per the drawings Per area
3.1 Remove unnecessary parts Free from roots, garbage etc Visual inspection Per area
3.2 Compaction Density 90% AASHTO T-191 5 per 2,000 Sq.m
4.1 Placing of Embankment Evenness 150mm thick Visual inspection Per area
4.2 Embankment Compaction Density 90% AASHTO T-191 5 per 2,000 Sq.m
4.3 Placing of Subgrade Evenness 150mm thick Visual inspection Per area
4.4 Subgrade Compaction Density 95% AASHTO T-191 5 per 2,000 Sq.m
Experimental Work
- Contractor will provide full test certificates, origin of all supplier's materials.
- The material criteria shall conform to the requirements in Sub-Clause 6 “Materials Requirement” of this Method Statement and the requirements of Project General Specification.
- All tests shall be conducted in a manner approved by the engineer and shall be conducted in the contractor's laboratory.
CONSTRUCTION REQUIREMENT
Preparation of Foundation for Embankment
Natural ground (including slopes of existing road) situated less than 1.5 meters below the design surface of the road or side slopes shall, after proper clearing and grubbing or scarifying of existing road surface, be compacted to a depth of 150 mm, measured from original ground as shown on the cross-section sheet, to not less than 90% of the maximum dry density of the material as determined by AASHTO test method T180 Compression of existing soil which may result from this compaction will not be measured and backfilling of the corresponding volume of earth fill is considered incidental to other items of work and will not be separately paid for.
If unsuitable materials occur in some areas under the embankment or in existing embankments, such materials shall be removed to levels as directed in writing by the Engineer, the bottom of the excavation shall be compacted, as described above, and the areas backfilled and compacted layer by layer with suitable material Fill material replacing unsuitable materials being excavated on the written instruction of the Engineer will be measured and paid for under Item No.2.6 (1), Embankment (General Specification)
All compaction shall conform to the requirements in Sub-Clause 2.6.3.3 of General Specification”. Where an existing surface of a road is situated at subgrade level or lower, the surface shall be scarified, except where otherwise shown on the Drawings, to a depth of 150mm or as instructed by the Engineer., graded, spread and compacted, to the density prescribed for layers at the depth concerned below subgrade, in the full width of the new embankment No materials shall be removed from these areas unless ordered in writing by the Engineer.
Works of compaction for preparation of foundation for embankment and preparation of subgrade in cut areas will not be measured or paid for but will be considered incidental to the works of constructing embankment Widening of existing embankments shall be accomplished as shown on the Drawings.
Placing Embankment
Embankment shall be placed in accordance with the following requirements:
(a) General : Except as otherwise required all embankments shall be constructed in layers approximately parallel to the finished grade of the road bed During construction of embankment, a smooth grade having an adequate crown or super-elevation shall be maintained to provide drainage Embankments shall be constructed to the required grade, and completed embankment shall correspond to the shape of the typical sections shown on the Drawings and to the tolerances specified in Clause 1.11.8 of General Specification.
(b) Common Embankment : Common embankments shall be defined as those principally of material other than rock, and shall be constructed of approved material from designated or other approved sources.
Except as specified for embankment in swamps, common embankments shall be constructed in successive layers, for the full width of the cross section and in such lengths as are suited to the compaction and watering methods used Prior to compaction the layers shall not exceed
200 mm in depth unless permission is granted by the Engineer.
(c) Placing over swamp ground : Embankment in or over swamps or in water shall be placed as indicated on the Drawings and as specified in the Special Provisions, and as required by the Engineer.
(d) Adjacent to culverts and bridges : Embankment within 2 meters measured horizontally, or 0.5 meters measured vertically of a structure, bridge or culvert shall be compacted in the manner prescribed for backfill in Section 2.5 Structural Excavation and Backfill (General Specification) This clearance distance may be varied for individual structures, as indicated on the drawings or at the discretion of the Engineer.
Embankments placed around spill-through type abutments shall be compacted in 150 mm layers (measured before compaction) of uniform suitable material placed in such a manner as to maintain approximately the same elevation on each side of the abutment and each layer of material shall be mixed, wetted and compacted as specified herein.
Material placed adjacent to any portion of any structure shall be material free of any appreciable amount of gravel or stone particles more than 100 mm in greatest dimension and of such gradation as to permit thorough compaction.
(e) Preparation of subgrade : The surface of the finished subgrade shall be neat and workmanlike and shall have the required form, super-elevation, levels, grades, and cross section The surface shall be constructed to sufficient accuracy to permit the construction of subsequent layers of material to the thickness, surface tolerance, and compaction specified.
(f) Where new embankment is to be compacted against existing embankments or in natural ground having a side slope of greater than 1 on 5 or where embankment is built in half- widths, the slopes of the existing ground and old and new embankment shall, after removal of topsoil, be benched in accordance with the Drawings or as instructed by the Engineer The material which is excavated to form benches shall either be taken to waste or if suitable used as fill.
(g) Clods or hard lumps of earth over 150 mm in greatest dimension shall be broken up before compacting the material in embankment.
(h) All settlement occurring in embankment construction shall be corrected by the contractor by providing additional layers of embankment or selected material at no additional cost to theEmployer except where preloading and/or waiting period are designated on the Drawings, in which case measurement and payment will be performed as described on the Drawings and in the Special Specification The Contractor shall be fully responsible for the stability and integrity of the embankment during the Contract and Defects Liability periods.
(i) If a soil failure either occurs or becomes imminent during the construction of the embankment, the Engineer shall have the authority to suspend all embankment construction in the affected area until corrective measures can be determined and implemented Any delay in the embankment construction schedule and any other effects caused by implementation of the above clause shall not constitute grounds on the part of the Contractor for a claim for extension of the Contract and/or financial compensation.
Compaction of Embankments
Embankment (other than rock) shall be compacted in accordance with the following requirements:
(a) Before full scale embankment construction is started, the Contractor shall construct trial sections for compaction as directed by the Engineer and its result shall be accepted by the Engineer The purpose of the trials is to check suitability of the materials and the efficiency of the equipment construction method, which are proposed to be used by the Contractor. Therefore, the Contractor shall use the same material, equipment and procedures that he proposes to use for the main works If the basic conditions regarding the type of material or procedure change during the execution of the work, new trial sections shall be constructed.
No separate payment will be made for this work, which will be regarded as a subsidiary obligation of the Contractor covered under other Clauses of these Specifications.”
Before compaction, each layer shall be processed as required to bring the moisture content uniformly throughout the layer to within plus 1 and minus 2 percent of optimum moisture content as determined in AASHTO T180 or such other moisture content as shall be agreed with the Engineer as a result of compaction trials The material shall be so worked as to have uniform moisture content throughout the layer Full compensation for any additional work involved in wetting or drying embankment material to the required moisture content shall be considered as included in the contract price paid for embankment and no additional compensation will be allowed.
(b) Each layer of material shall be compacted uniformly by use of adequate and appropriate compaction equipment The compaction shall be done in a longitudinal direction along the embankment and shall generally begin at the outer edges and progress toward the center in such a manner that each section receives equal effort Hauling equipment shall be operated over the full width of each layer in so far as practicable
(c) Embankment compaction shall be carried out as follows: Embankments shall be constructed in layers of uniform thickness not to exceed 150 mm in thickness after compaction and compacted to the requirements of this section Each layer of the embankment shall be compacted to a dry density equal to at least 90% of the maximum dry density of the material as determined by AASHTO test method T180 In place density determinations shall be carried out for embankments in accordance with AASHTO T 191 or other method approved by theEngineer at a rate of one test for every 75 linear meters of complete embankment in every layer or part thereof Density test results shall be submitted to the Engineer within 24 hours after the measurement.
(d) Embankments shall be maintained to the grade and cross section shown on the Drawings throughout the contract period.
(e) The Contractor shall protect the prepared subgrade from both his own and public traffic The Contractor shall maintain the subgrade by blading, watering and rolling as frequently as necessary to preserve the subgrade in a completely satisfactory condition as specified above.
(f) The compaction of subgrade and that of areas of existing road, where surface layers have been removed, shall extend to a minimum depth of 450mm and 150 mm respectively, or such greater depth as shall be instructed by the Engineer” Subgrade shall be constructed in layers of uniform thickness not to exceed 150mm in thickness after compaction The compaction of subgrade shall attain not less than 95% of the maximum dry density determined by AASHTO test method T180 In place density determinations shall be carried out for the subgrade in accordance with AASHTO T 191 or other method approved by the Engineer at a rate of one test for every 75 linear meters of complete embankment or part thereof, for each 150mm layer of subgrade Density test results shall be submitted to the Engineer within 24 hours after the measurement Acceptance criteria for subgrade densities shall be as above.
Preparation of Subgrade Surface
The subgrade shall be shaped to correct line and level and the Contractor shall at all times ensure that the subgrade is well drained and protected against damage from public as well as construction traffic The subgrade shall be constructed to the tolerances specified in Clause 1.11.8 of GeneralSpecifications The surface shall be maintained in this state, with a regular light sprinkling of water to prevent a dusty condition until the pavement layers are spread.
Compaction and Trimming of Slopes
Attention is drawn to the fact that the general compaction requirements shall at any level apply to the full width of the embankment Slopes to be covered with topsoil and grassing shall have a firm surface before topsoil is placed.
In practice it is assumed that the embankment will be constructed slightly wider that the design cross section to enable the slopes to be trimmed on completion to conform to the design cross section, thus ensuring adequate compaction of the slope faces Where embankments are not constructed to the full width required these shall be benched and reconstructed in accordance with the provisions of Sub-Clause 2.3.3.3 of General Specification.
Under no circumstances shall additional embankment material be tipped over the slopes and spread to make up a shortfall in width of embankment.
If in the opinion of the Engineer the embankment slopes do not appear to be suitably compacted, additional compaction shall be provided to the slopes as directed by the Engineer.
The slopes of cuttings and embankments shall be trimmed by hand or by approved mechanical means to uniform batters as shown on the Drawings or as instructed by the Engineer prior to top soiling and grassing where specified or instructed.
Proof rolling
All subgrade and embankment layers, cuttings, benches and original ground shall be proof rolled with a loaded scraper or truck with a minimum axle load of 8 tonnes Proof rolling shall be satisfactorily completed before the layer is submitted to the Engineer for approval and shall be carried out in the presence of the Engineer.
CONSTRUCTION PROCEDURE
Preparation before Working
- Submitting construction method documents to consultants;
- Mobilizing machinery and equipment for construction;
- Testing and Inspection of materials supplied for Embankment, Subgrade works
- Arrange traffic safety control devices at the working area
- Setting out bamboo for elevation and toe of Embankment as Figure 3
(Figure 3: Traffic Control Arrangement for Embankment Works)
Preparation of Foundation for Embankment
- By using the excavator to clear and remove top soil, tree, garbage, old concrete, fence etc. Location in the right of working Approx.15m from the road center line No top soil shall be removed from the areas outside the limits of the earthworks.
- By using bulldozer to clear and remove top soil more than 15cm (15cm-30cm).
- Material to be used for top soil will be transport by dump truck and locate at stock yard Stock yard will be outside the limits of the earthworks and inside of ROW.
- Collected spoiled material and spoiled soil and transport those materials by dump truck to the disposal area Please refer to figure 4 bellow.
- Clearing and remove top soil, tree, garbage, old concrete, fence etc by backhoe.
- Clearing and remove top soil more than 15cm by bulldozer or excavator.
- Transport spoiled material and spoiled soil to the dumping by dump truck.
Figure 4: Plan and Cross Section of Clearing and Grubbing
- Natural ground (including slopes of existing road) situated less than 1.5 meters below the design surface of the road or side slopes shall, after proper clearing and grubbing or scarifying of existing road surface by bulldozer and Excavator, we will compact by Sheep roller and Vibration roller.
- Base on the result of the DCP test approved by the engineer, we will scarify and use natural ground and access road of local house's entrance for the embankment In case CBR > 10, use Subgrade layer Incase CBR >4, use embankment layer In case CBR