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CONSTRUCTING THE ROAD BED
Transcript of CONSTRUCTING THE ROAD BED
SOIL AS STRUCTURE
The roadway has three major structures, namely:
1. The subgrade or subbase
2. The base course
3. The pavement
The base course is classified into two types:
1. The granular base course or untreated soil mixture
2. The treated base course
The cross slope of untreated surface or gravel road must not be sufficient enough to drain water to prevent potholes and softening of the roadway, thus:
1. If the road materials are sufficiently stable and water tight, ¼ inch per foot slope is considered satisfactory although 3/8 to ½ inch per foot slope is preferred.
2. If the road is on steep grade, a substantial cross slope is needed to direct the water into the roadside.
is the earth beneath the road which is properly graded, compacted and stabilized.
is the materials laid on top of the subgrade which consist of crushed stone or gravel which may sometimes be mixed with asphalt binders.
is the materials laid over the base course. It may be asphalt or concrete. It is sometimes referred to as the wearing course.
The granular course is a road surface of untreated soil mixture described as gravel road.
1. The road must be stable. It must support the superimposed loads without detrimental deformation.
2. It must be resistant against various traffic activities and must withstand the abrasive action of traffic.
3. Water penetrating the subgrade might soften it and may cause loss of surface stability, thus, it must shed a large portion of rain that falls on the surface.
4. It must be free of large rocks or stones over one inch in diameter so that it could be regularly maintained by blading or dragging.
5. It must possess capillarity properties in amount that it sufficient enough to replace the moisture lost through surface evaporation.
6. In dry weather, the moisture film on the clay particles should bind the entire mass together, and in wet weather, the first rain that falls on the surface should expand the clay and close the pores to prevent water from entering and softening the materials.
7. Care should be exercised to prevent excessive amount of highly expansive clay because clay will swell and unseat the coarser materials when wetted and ultimately wil weaken the road structure.
8. It must be low cost.
9. Local materials must be stabilized.
If the surface road is to be maintained for several years without bituminous surface treatment or other impervious surfacing, the AASHTO standard specification requires a maximum liquid limit of 35 and plasticity index of from 4 to 9 and a maximum 8% passing the No. 200 sieve.
GRADING AND MAINTENANCE OF
The sequence of improvement could be as follows:
First: -It might be an earth road surface
Second: -Untreated Gravel Road
Third: -Application of Asphalt over the gravel
Fourth: -The use of stone type of pavement with gravel as part of the base course.
The maintenance of a gravel road surface is a routine case by maintaining the smoothness of the surface under the following manner:
1. By cutting off thin layer of the surface using a motor grader distributing the scraped layer uniformly over the roadway surfaces.
2. The cut should be deep enough to remove the corrugations of the road surface.
3. The blading sequence ranges from once or twice a year to monthly or weekly depending upon the finances, traffic and equipment availability.
4. The most effective routine maintenance is done immediately after a rain where the surface is soft for the sblade or drag.
5. After blading, compaction is necessary, but the cross section slope or the crown of the roadway should be maintained.
6. Losses of materials caused by grading and traffic wear generally ranges from ½ inch to one inch of the thickness per year although it varies depending upon the traffic volume, type, rainfall, wind intensity and frequency, maintenance practice or habit.
7. The compaction is better done with the use of pneumatic tired or wheeled rollers. Where surface is tight and non-variable sealing maybe omitted.
It is the base course stabilized by using either asphalt, lime, Portland cement or other materials as binders mixed with the soil aggregate base course.
Asphalt or bituminous treatment is employed to waterproof and bind the materials such as the granular soil to the sand and clay, thus, showing that the primary function of the bitumen in treated soils is waterproofing.
Asphalt also known as bitumen is a sticky, black and highly viscous liquid or semi-solid form of petroleum.
The types of asphalt binders for bitumen treated base course depend on several factors, such as:
1. The mixing procedure – either plant mixed or road mixed.
2. If the mixture is processed in the plant, the aggregate must be heated and the type of asphalt could be asphalt cement, cutback or emulsion.
3. The quantity of asphalt for the mixture is determined either for stabilizing or waterproofing purposes.
4. If the purpose is for stability, it is to be measured in the laboratory by the Marshall or Hveem stabilometer procedures. The weight percentage of asphalt would probably be in the range of 5% to 7%.
5. If the purpose is for waterproofing, 2% to 3% of the asphalt binder is added.
6. If the emulsion asphalt is used, enough water is included in the mixture to allow compaction at near optimum moisture content.
Sand and Asphalt Base Course
The sand-asphalt base course is composed either of loose beach sand, dune pit or river sand cemented with asphalt materials.
Asphalt binders with the grade of asphalt cement for hot plant mixing shall be of medium viscosity, rapid or medium curing asphalts, slow setting emulsified asphalt or tars grade RT-6 TO RT-10. The content of asphalt binder in percent by weight ranges from 4% to 10%.
Fine-Grained – Asphalt base
An asphalt stabilized base subgrade constructed with the fine grained has a controlled Plasticity Index of 6 and 10, respectively. Soil plasticity Index up to 30 are processed with lime. Soils with up to 50% passing the No. 200 sieve and Plasticity Index up to 18 can be stabilized even without pre-treatment.
Soil and Base Course Stabilized with Cement
The use of Portland cement in stabilizing soils and aggregates was initially practiced after world war in 1914, thus:
1. Cement stabilization in a mixture of natural materials and portland cement compacted an optimum moisture content and then cured to hydrate the cement.
2. It is a strong and stable base, less susceptible to deformation caused by moisture and temperature changes.
3. It is less rigid than portland cement concrete and its modulus of elasticity ranges from 100 000 for clay soils with little cement up to 1 000 000 for the strong mixture. Its compressive strength ranges from 300 psi to 600 psi with flexural strength about 2% of compressive value.
4. The modulus of elasticity for portland cement concrete ranges from 3 million to 6 million with compressive strength of about 3000 to 5000 psi.
5. The cement reaction with fine grained soil particles are classified into two ways:
a. By surface chemical action, it produces flocculation and reduces the moisture affinity of clays.
b. Slowly, it promotes cementation producing a semi-rigid soil framework.
6. A cement stabilized mixture is called “Soil Cement” produced with a native material subdivided into three:
a. Sandy and gravelly soils containing less than 25% silt and clay. AASHTO Classification A-1and A-2.
b. Sands with fewer amounts of fines such as beach sand, glacial and windblown sand AASHTO Classification A-3.
c. Silty and Clayey Soils, AASHTO Classification A-4 to A-7.
Materials having a plasticity index greater than 30 is rarely used, unless lime is added. Materials with high PH or sulfate content are not advisable for use. Sodium clays are difficult to stabilize unlike calcium clay.
7. The cement content for stabilized mixture ranges from 5% to 14% by volume of 3% to 16% by weight of dry aggregates. Sandy and gravelly soils requires less amount of cement unlike the silty and clayey soils which needs higher percentage of cement.
8. The dry densities for cement stabilized mixture compacted by the AASHTO Standard method range from 35 lb. per cubic foot for a well graded down to 85 lb. per cubic foot for silty or clayey soils. The recommended field density is about 95% of AASHTO Standards.
9. The quality of the soil-cement mixture is measured by its ability to resist abrasion and disintegration. Other methods of testing for stabilizing the cement content are unconfined and triaxial compression and flexural tests.
Lime-Stabilized Base and Subbases
Lime as a stabilizing agent was used in construction of the Appian Way and many other Roman roads. It was also employed for this purpose in ancient Greece, India and China.
UNTREATED BASE COURSE
The DPWH Standard Specifications on
Aggregate Sub-Base Course
classify the aggregate Subbase Course as Item -200 which consist of furnishing, placing and compacting an aggregate sub-base course on a prepared subgrade in accordance with the plans and Specifications.
1. The aggregate for subbase shall consist of hard, durable particles of fragments of crushed stone, crushed slag or crushed or natural gravel and filler or natural crushed sand or other firmly divided mineral matter. The composite material shall be free from vegetable matter and lumps or balls of clay and shall be such nature that it can be composed readily to form a firm stable base.
1. The fraction passing 0.075 mm (No. 200) sieve shall not be greater than 0.666 (two thirds) of the fraction passing the 0.425 mm (No. 4) sieve.
2. The fraction passing the 0.425 mm. (No. 40) sieve shall have a liquid limit not greater than 12 as determined by AASHTO T-89 and T-90 respectively.
3. The coarse portion retained on a 2.00 mm (No. 10) sieve shall have a mass percent of wear not exceeding 50 by the Los Angeles Abrasion Tests as determined by AASHTO T-193. The CBR value shall be obtained at the maximum dry density as determined by AASHTO to 180, method D.
California Bearing Ratio Method (CBR)
. This method, combines a load-deformation teat performed in the laboratory with an empirical design chart to determine the thickness of pavement, base, other layers.
1. The fraction passing the 0.075 mm (No. 200) sieve shall not be greater than 0.66 (two thirds) of the fraction passing the 0.425 mm (No. 40) sieve.
2. The fraction passing the 0.425 mm (No. 40) sieve shall have a liquid limit not greater than 25 and plasticity index not greater than 6.
3. The coarse portion retained on a 2.00 mm (No. 10) sieve shall have a mass percent of wear not exceeding 50 by LAA Test AASHTO T-96.
4. The material passing the 19 mm (3/4’’) sieve shall have a soaked CBR value of not less than 80% AASHTO T-193.
1. The portion passing the 0.075 mm (No. 200) sieve shall not be greater than 0.66 or two thirds of the portion passing the 0.425 mm. (No. 40) sieve.
2. The portion passing the 0.425 mm (No. 40) sieve shall have a liquid limit of not more than 25 and plasticity index of not more than 6.
3. The coarse aggregate retained on 2.00 mm (No. 10) sieve shall have a mass percent of wear not exceeding 45 by LA Abrasion Test and not less than 50 mass percent shall have at least one (1) fractured face.
4. The material passing the 19 mm (3/4’’) sieve shall have a minimum soaked CBR value of 80% tested by AASHTO T-193.
Item – 203 Lime Stabilized Road Mix Base Course
This item consist of a foundation for a surface course composed of soil aggregate, lime and water in proper proportion mixed on site and constructed on a prepared sub-grade or sub-base.
1. Soil aggregate refers to the combination of gravel, sand, silt and clay or other approved combination of materials free from vegetable or other objectionable matter.
2. It might be material encountered in the construction site or obtained from other approved sources.
3. The intent of the specification is to utilize soils exiting on the roadbed if the quality is satisfactory and at the same instance minimizing cost.
4. If the quality of the material is poor or deficient, the soil aggregate must be obtained wholly or partially from an approved outside sources.
1. The plasticity Index should not be less than 4 nor more than 10.
2. The aggregate mass percent of water should not exceed 50 (AASHTO T-96 requirements).
3. Salvage soil aggregate to be used for stabilized road mix base course must consist of materials meeting the requirements of soil aggregate.
4. Hydrated lime shall conform to the requirement of construction lime Item 701. The amount of ,ime to be added to the soil aggregate shall be from 3 to 12 mass percent of the dry soil.
5. Lime shall not be applied during windy, rainy or impending bad weather.
6. The equipment to be used shall include scarifying, pulverizing, mixing, spreading, hauling, watering, finishing and compacting equipment including a slurry liMe distributor equipment.
Pulverizing is an innovative and cost-effective method of reconstructing failed asphalt.
7. Distributor equipment must include pressure gauge, accurate volume measuring devices or a calibrated tank. It shall be equipped with a power unit for the pump and full circulation spray bars adjustable laterally and vertically and also agitator to prevent setting of solid lime.
Preparation of Soil Aggregate
Case I – For New Soil Aggregate
1. The existing roadbed shall be scarified lightly, and bladed to uniform grade as shown on the cross section of the plans then rolled or watered and rolled.
2. Depressions on the surface shall be filled, and the weak portion of the road bed shall be strengthened with new soil aggregates.
3. Allow one day for measuring, sampling and testing of the sample for approval of the quality and gradation before the windrow is spread for application of the hydrated lime.
4. If soil aggregate moisture exceed 2 mass percent of the dry aggregate, apply aeration by harrowing the soil aggregate until the moisture content is reduced to 2% or less.
5. Finally, spread the aggregate smoothly and uniformly over half the road or other convenient width of the surface ready for the application of hydrated lime.
Case II – Salvage Soil Aggregate
1. When the materials in the site are to be used for mixing, the surface shall be scarified lightly and bladed to uniform grade conforming to the cross section as shown on plans.
2. The reshaped surface is then scarified again to a depth required, leaving a foundation of undistributed material parallel both in profile and in cross section.
3. The loosened materials are bladed aside into a windrow at the side of the road. The undistributed materials are then rolled, or watered and rolled as directed.
The mixing procedures are as follows:
1. After the last lime application and partial mixing, the entire mass of the mixture is withdrawn on the road surface and then mixed by blading mixture from side to side of the road, or by manipulation producing equivalent results until the whole mass has a uniform color. The mixture shall be free from fat or lean spots or balls of unmixed particles.
2. Should the mixture show an excess of deficiency or uneven distribution of lime, the condition must be corrected by adding soil aggregate or lime as required, then remixed.
3. If the mixture contains excessive amount of water or volatile matter, as maybe encountered in slurry operation, it should be bladed, aerated or manipulated until the moisture and volatile content becomes satisfactory.
4. Whether mixing is completed or not, all loosed materials are bladed into a windrow at the end of each day’s work and retained as such until operations resumes.
Spreading Compacting and Finishing
The methods of spreading, compacting and finishing are as follows:
1. The materials are spread by self-propelled pneumatic tired blade grader or mechanical spreader of approved type. Cutting into the underlying course must be avoided.
2. After spreading, the surface is leveled to the road centerline, then at the outer edges of the road overlapping the shoulders, and finally, toward the center. T=rolling of super elevated curves shall progress from the lower to the upper edge.
3. Each pass shall terminate at least .90 m. advance or to the rear of the end of the preceding pass.
4. During compaction, the surface is dragged or bladed as necessary to fill and remove incipient corrugation or other surface irregularities.
5. Rolling must continue until the surface is of uniform texture and satisfactory compaction is obtained.
6. Rolling must be stopped whenever there is excessive pulverizing of the aggregate or displacement of the mixture.
Protection Curing and Maintenanc
After the lime-stabilized base course has been finished, it shall be protected against rapid drying for a period of at least 5 days by either of the following curing methods:
1. Thorough and continuous moist condition must be maintained by sprinkling water.
2. The surface must be covered with a 50 mm layer of earth of sand and maintained in moist condition.
3. The surface must be applied with asphalt membrane of the type and quantity approved by the highway agency.
Item – 204 Portland Cement Stabilized Road Mix Base Course
Consist of a foundation for surface course composed of soil aggregate, portland cement, and water in proper proportions of road-mixed and constructed on a prepared subgrade or subbase.
1. The amount of cement added to the soil aggregate shall be 6 to 10 mass percent of the dry soil.
2. Construction requirement and procedures shall be the same as that of Item 203. In all cases, the word “Lime” shall be replaced with portland cement.
Item – 205 Asphalt Stabilized Road Mixed Base Course
Materials: -Asphaltic materials shall be anionic or cationic emulsion asphalt of the slow setting type.
Mixture Proportions: -The amount of asphaltic material to be added to the soil aggregate shall be from 4 to 7 mass percent of the dry soil aggregate.
Item -206 Portland Cement Treated Plant Mix Base Course
This Item shall consist of a foundation for surface course composed of aggregate, Portland Cement and water in proper proportions, mixed by a travel plant or in a central plant and spread and compacted on a prepared subgrade/subbase in one or more layers.
Travel Plant Method
: The salvaged or new soil aggregate are pulverized until at least 80 mass percent of all materials other than stone or gravel will pass a 4.75 mm (No. 4) sieve. Any material retained on a 50 mm A. Travel Plant Method: The salvaged or new soil aggregate are pulverized until at least 80 mass percent of all materials other than stone or gravel will pass a 4.75 mm (No. 4) sieve. Any material retained on a 50 mm (2 inches) sieve and other unsuitable materials must be removed.(2 inches) sieve and other unsuitable materials must be removed.
Procedures for the travel plant method:
1. The soil aggregate to be treated are placed in a uniform windrow spread to a uniform thickness to the required depth.
2. Portland cement of proper quantity is applied uniformly in a trench on top of the windrows or spread uniformly over the soil aggregates.
3. Mixing is done by machine so that the cement and soil aggregate is thoroughly blended.
4. When this method is used, a maximum time of 2 hours is allowed for wet mixing, lay down and finishing.
Central Plant Method
: The plant must be equipped with feeding and metering devices which will introduce the cement soil aggregate and water into the mixer in the quantities specified. Mixing should continue until uniform mixture has been obtained.
Spreading, Compacting and Finishing
Effect of Compaction Method on the Strength of Soils
1. Not more than 60 minutes should elapse between the start of mixing and the time of starting compaction of the spread mixture.
2. After spreading, the mixture is compacted and finished in accordance with the procedure as enumerated for lime stabilized road mix base course item 203.
- is the process in which the concrete is protected from loss of moisture and kept within a reasonable temperature range.
CLEARING AND GRUBBING
Clearing and grubbing
is classified under item 100 of the DPWH Standard Specification. It consists of clearing, grubbing, removing and disposing of all vegetable matter and debris except those objects that are designated to remain in place or are to be removed in consonance with other provisions of the specifications. It also includes the preservation from injury or defacement of all objects designated to remain.
The Specifications provides:
1. “All surface objects and all trees, stumps, roots and other protruding obstructions, not designated to remain shall be cleared and/or grubbed including mowing as required as provided below:
a. Removal of undisturbed stumps and roots and non-perishable solid objects with a minimum of .90 m. below sub-grade or slope of embankments will not be required.
b. Outside the grading limits of cut and embankment areas, stumps and non-perishable solid objects shall be cut off not more than .15 m. above the ground line or below water level.
c. Grubbing of pits, channel changes and ditches will be required only to the depth necessary by the proposed excavation within such areas.
Method of Measurement
– By hectare and fractions thereof acceptably cleared and grubbed.
Lump Sum Basis
– No measurement of area will be made for such an items.
Individual unit Basis
– The diameter of trees will be measured at a height of 1.4 m. above the ground. Trees less than .15 m. (6”) in diameter will not be measured for payment.
The unit basis will be designated and measured in accordance with the following schedule of sizes:
Diameter at height 1.4 m. - pay item Designated
Over 150 mm to 900 mm - small
Over 900 mm - large
Excavation is the process of loosening and removing earth or rock from its original position in a cut and transporting it to a fill or to a waste deposit.
1. The removal of earth, usually to allow the construction of a foundation or basement.
2. The hole resulting from such removal.
Roadway excavation are classified into
1. Unclassified excavation
2. Rock excavation
3. Common excavation
4. Muck excavation
5. Borrow excavation
is the excavation and disposal of all materials regardless of its nature, or not classified and included in the Bill of quantities under other pay items.
are those not included in the Bill of Quotations under “rock excavation” or other pay items.
consist of the excavation and utilization of approved materials required for the construction of embankment or for other portions of the work and shall be obtained from approved sources in accordance with the following:
1. Borrow Case 1 consists of materials obtained for sources designated on the plans or in the special provisions.
2. Borrow Case 2 consists of materials obtained for sources provided by the contractor.
shall be excavated and finally dressed to blend with the existing topography and sloped to prevent ponding and to provide drainage.
1. When there is evidence of discrepancies on the actual elevations and that shown on the plans, a pre-construction survey with reference to the datum plane used in the approved plan shall be undertaken by the contractor or agency to serve as basis for the computation of the actual volume of the excavated materials
2. All excavations must be finished to reasonably smooth and uniform surface. As much as possible, no materials shall be wasted. Materials outside of the limits of slope should not be distributed by the excavation operations. Excavations are done only after the clearing and grubbing in the area.
3. Topsoil encountered in excavation and on areas where embankment is to be placed must be removed to the depth as the Engineer may determine and shall be transported and deposited in storage pile designated area prior to the start of regular excavation or embankment work in the area and shall be kept separate from other excavated materials for later use.
4. The use of Excavated Materials
All suitable materials that were removed from the excavation are used in the formation of:
f. Backfill for structure
Prewatering and Presplitting
a. Excavation areas and borrow pits maybe prewatered before excavating the material. When prewatering is adopted, the areas to be excavated has to be moistened to the full depth from the surface to the bottom of the excavation.
b. The water must be controlled so that excavated materials will contain the proper moisture content to permit compaction to the desired density.
c. Prewatering has to be supplemented where necessary by truck watering unit to assure that the embankment materials contains the proper moisture at the time of compaction.
is a drilling and blasting procedure that maybe employed or specified to control overbreak and give a uniform face to the backslope or rock cuts. Presplitting is performed by:
1. Drilling holes at uniform intervals along the slope line.
2. Loading and stemming the holes with appropriate explosives and stemming materials.
3. Detonating the holes simultaneously.
If presplitting is under contract, prior to drilling operations for presplitting the contractor shall:
1. Furnish the engineer a plan outlining the position of all drill holes, depth of drilling type and explosive to be used, loading pattern and sequence of firing.
2. The drilling and blasting plan is for record purposes only and will not absolve the contractor of his responsibility for using proper drilling and blasting procedures.
3. Controlled blasting must begin with a short test section of a length to be approved by the Engineer.
4. The test section shall be presplit, production drilled and blasted and sufficient material excavated for the Engineer to determine if the contractor’s methods are satisfactory.
5. The Engineer may order discontinuance of the presplitting when he determines that the materials encountered have become unsuitable for presplitting.
6. The holes shall be charged with explosive of the size, kind and strength and the spacing suitable for the formation being pre splitted and with stemming materials which passes a 9.5mm (3”) standard sieve and which has the qualities for proper confinement of the explosive.
7. The finished presplit slope must be reasonably uniform and free of loose rock. Variance from the true plane of the excavated back slope shall not exceed .30 m. However, localized irregularities or surface variations that do not constitute a safety hazard or impairment to drainage courses or facilities will be permitted.
8. A maximum offset of .60 m. will be permitted for a construction working bench at the bottom of each lifts for use in drilling the next lower presplitting pattern.
distance is the specified distance that an excavated material will be hauled without additional compensation. The free haul distance is 60C meters unless otherwise specified in the contract. The overhaul consist of authorized hauling in excess of the free haul distance. Example, if the hauling distance of materials is 800 meters, considering that the free haul is 600 meters, then the excess 200 meters is considered overhaul.
Free Haul: The distance within a given limit, set by the specifications, that material is hauled in construction work.
FREE HAUL – OVERHAUL
Methods of Measurement:
The overhaul distance for material obtained and placed within the roadway limits will be measured along the centerline of the roadway. No allowance will be made for transverse or lateral movement to or from the centerline except materials moved to or from designated areas outside the roadway limits, such as case I, borrow pits disposal area, etc. In such a way, measurement is along the shortest route determined by the Engineer to be feasible and satisfactory.
If the contractor chooses to haul materials over some other route, and such other route is longer, the computation for payment will be based on the overhaul distance, measured along the route designated by the Engineer.
The number of cubic meter-kilometer of overhaul to be paid is the number of cubic meters of overhaul materials multiplied by the overhaul distance in kilometers. The unit cubic meter kilometer is the amount of hauling required to move one cubic meter a distance of one kilometer beyond the free haul distance.
Los Angeles Abrasion Test Apparatus
consists of igneous, sedimentary and metamorphic rocks which cannot excavated without lasting or the use of rippers and all boulders or other detached stones each having a volume of 1 cubic meter or more as determined by physical measurement or visually by the Engineer.
consists of the removal and disposal of deposits of saturated or unsaturated mixtures of soils and organic matter not suitable for foundation materials regardless of moisture content.
d. In areas covered by cogon/talahib, wild grass and other vegetations, top soil shall be cut to a maximum depth of 150 mm below the original ground surface or as designated by the Engineer, and disposed outside the clearing and grubbing limits
2. Burning should be under the constant care of competent watchman that the surrounding vegetation, adjacent property, or anything designated to remain on the right of way will not be jeopardized.
FILLS AND EMBANKMENT
A superior and stable embankment is attained by spreading the materials into a thin layer then compacted at moisture content closer to optimum. These layered processes of compaction produce uniformity and higher density of the material and moisture content. On the other hand, filling materials which are just dumped in thick layers even if compacted will have a varying density and moisture contents from one spot to another. This will result to differential settlement or swell between the adjacent areas of the embankment.
The AASHTO-ARBA Joint Committee on Compaction of Earthwork proposed the following amendment to the original AASHTO density requirements to with:
1. Granular aggregates or those with only slight degree of plasticity should be compacted to 95%-100%.
2. Fine grained aggregate possessing a low degree of plasticity is compacted to approximately 100% at moisture content near laboratory optimum.
3. Densities for aggregate possessing moderate to high plasticity should not be so high as to lead to subsequent swelling. Compacting procedures should not exceed the aggregate shear strength.
4. Clay soil should not be over compacted beyond about 90% to avoid post construction swelling.
Basically, there are two procedures employed to assure specified embankment density.
1. To specify the expected value to the minimum acceptable amount of relative compaction and to ascertain from the fill density tests that the specified value is obtained.
2. To specify the manner and methods of constructing the embankment particularly the layer thickness, moisture control and the number of passes by a roller of specified type and weight. Field control is a matter of ascertaining and defining the specific procedures to be done. What is important is the manner and method that will give the result as expected.
Field control is a matter of ascertaining and defining the specific procedure to be done. What is important is the manner and methods that will yield the expected result.
Source: AASHTO M-57-64
* Compaction at 95% of T-99 optimum content.
** Use of these materials requires special design and construction.
+ AASHTO Desig. M-145 basement soil compacted soil.
The problems encountered in the control of embankment construction are:
1. Difficulties in maintain uniform moisture content. This is due to:
a. Variable wetness of the soil.
b. Problems in evenly distributing and mixing in water.
c. Evaporation or rainfall during compaction.
2. Some soil may not easily assimilate water unless wetting agent is employed. Sometimes soil type cannot be segregated during construction unless brought to laboratory.
3. Materials are hauled from different sources and segregation of the same type is difficult in the actual work.
Construction Requirements and Equipment
1. Density test requirements
Effect of Density on the behavior of Soils
As a particular soil becomes denser, it will contain a greater number of particles, and the (pore) volume remaining for air and water will be decreased.
2. Moisture control
3. Compaction equipment like:
a. Tampering Roller
b. Grid Rollers
c. Pneumatic Tire Roller
d. Smooth Tired Roller
e. Vibratory Compactor
f. Hauling and Spreading equipment.
varies from light unit test weight 6, 000 to 10,000 lbs. for an 8 ft. width. For giant fully loaded roller, 75,000 lbs. for a 10 ft. width.
are effective in breaking down clods and soft rock.
Pneumatic Tire Roller
with rubber tires, weighing 8 tons or more. 200 tons for airport.
Smooth Tired Roller
of two or three-wheeled type used to compact bases and bituminous surface.
is effective in compacting stones of Macadam road.
Hauling and Spreading equipment
4. Thickness of soil layers – maximum layer thickness before compaction ranges from 15 cm. and 30 cm. with 20 cm. most prevalent.
5. Compaction of original ground – compacted layers from 10 to 30 cm. with 15 cm. most common, before the overlaying materials are placed.
Embankment on Swampy Areas
Conventional construction of roadways in swampy area is not advisable because record shows that muck and plate provide unstable support for fills causing failure of highways and railroads. Construction of roadway through swampy area requires either of the following methods:
1. Removal and replacement of unsuitable materials.
2. Displacement under the following methods:
a. Surcharging method
b. Vertical sand drain
c. Fabric reinforcement
d. Weight reduction
Removal and Replacement Method
is applicable where the unstable material is shallow or thin. Unstable materials are removed to the level of the underlying materials before filling.
Imported Materials are carefully placed along the advancing slope allowed to flow under the dense muck to displace it.
is applied on low fill over shallow muck up to 30 or 40 centimeters depth. Where top of the muck is soft, displacement through careful filling is done.
Fabric Reinforcement Method
is covering the muck with permeable fabrics.
Weight Reduction Method
is installing a block of Styrofoam over the muck to reduce the weight of the fill.
DPWH Specification on Embankment classified under Item 104 –
Embankment shall be constructed of suitable materials defined as follows:
1. Suitable materials are materials which are acceptable in accordance with the contract and which can be compacted in the manner specified in this item. It can be common materials or rock.
Selected borrow for topping
– Soil of such gradation that all particles will pass a sieve with 75 mm (3 in) square opening and not more than 15 mass percent will pass the 0.075 mm (No. 200) sieve (AASHTO T-11). The material must have a plasticity index of not more than 6 and a liquid limit of not more than 30 as determined by AASHTO T-90 and T-89 respectively.
2. Unsuitable Materials are materials other than suitable materials such as:
a. Materials containing detrimental quantities of organic materials, such as grass, roots and sewage.
b. Highly organic soils such as peat and muck.
c. Soils with liquid limit exceeding 80 and or plasticity index exceeding 55.
d. Soils with natural water content exceeding 100%.
e. Soils with very low natural density, 800 kg/m3 or lower.
f. Soils that cannot be properly compacted as determined by the engineer.
Method of Construction
1. Where embankment lower than 120 centimeters below the sub-grade is to be made, all sods and vegetables matters are removed from the surface.
2. Roadway embankment on earthy materials are placed in horizontal layers not exceeding 20 centimeters loose volume than compacted as specified before the next layer is placed.
3. When excavated materials contains more than 25 mass percent of rock larger than 15 centimeters in greatest diameter and cannot be placed in layers of the thickness prescribed without crushing, pulverizing or further breaking down into pieces.
4. Lifts of materials containing more than 25 mass percent of rock larger than 15 centimeters in greatest dimension should not be constructed above an elevation of 30 centimeters below the finished sub-grade.
5. Hauling and leveling equipment should be routed and distributed over each layer of the fill to make use of compaction efforts affording and to minimize rutting and uneven compaction.
The compactor shall carry out full-scale compaction trials on areas not less than 10 meters wide and 50 meters long. Compaction trials with the main types of fill materials to be used in the work should be completed before any work with the corresponding materials is allowed to start.
Rounding and Warping Slope
Rounding. Expect solid rocks, the top and bottom of all slopes including the slopes of drainage, ditches, are rounded as planned.
Warping. Adjustment in slopes are made to avoid injury to standing trees or marring of weather head rock or to harmonize with existing landscape features adjusting to the gradual slope.
This item consists of the preparation of the subgrade for the support of overlying structural layers. It shall extend to the full width of the roadway.
1. Except when the subgrade is in rock cut, all materials below subgrade level to a depth 0.15m or to such greater depth as specified shall meet the requirements of selected borrow for topping.
2. Prior to the start of subgrade preparation, all culverts, cross drains, duets and the like including their fully compacted backfill, ditches, drains, and drainage outlets shall be compacted. Any work on the preparation of the subgrade shall not be started unless prior work, herein described shall have been approved by the Engineer.
Subgrade Level Tolerances
The finished compacted surface of the subgrade shall conform to the allowable tolerances as specified hereunder.
1. Permitted variance from design +20mm
Level of Service -30mm
2. Permitted surface irregularity
measured by 3m. Straight Edge +/- 30mm
3. Permitted Variance from Design
Crossfall or Camber 0.5%
4. Permitted Variance from Design
Longitudinal Grade over 25m length +/- 0.1%
Subgrade in Common Excavation
1. All materials below subgrade level in earth cuts to a depth of 0.15m or other depth shown on plans shall be excavated.
2. The material, if suitable shall be set aside for future use or, if unsuitable, shall be disposed of in accordance with the requirement of sub. Sec. 102.2-9. DPWH Standard Specifications.
3. Where material has been removed from below subgrade level, the resulting surface shall be compacted to a depth of 0.15m.
4. The full width of the subgrade on embankment after completion shall be conditioned by removing any soft or other unstable material that will not compact properly. The resulting areas and all other low sections, holes or depressions shall be brought to grade with suitable materials. The entire roadbed shall then be shaped and compacted.
Subgrade in Rock Excavation
Surface irregularities under the subgrade level remaining after trimming of the rock excavation shall be leveled by placing specified material and compacted.
Subgrade on Embankment
After the embankment has been completed, the full width shall be conditioned by removing any soft or other unstable material that will not compacted properly. The resulting areas and all other low sections, holes, or depressions shall be brought to grade with suitable material. The entire roadbed shall be shaped and compacted. Scarifying, blading, dragging, rolling, or other methods of work shall be performed or used as necessary to provide a thoroughly compacted roadbed shaped to the cross-sections shown on the Plans.
Subgrade on Existing Pavement
Where the new pavement is to be constructed immediately over an existing Portland Cement concrete pavement and if so specified in the Contract the slab be broken into pieces with greatest dimension of not more than 500 mm and the existing pavement material compacted, as directed by the Engineer. The resulting subgrade level, as part pavement construction shall be shaped to conform to the allowable tolerances by placing and compacting where necessary a leveling course comprising the material of the pavement course to be placed immediately above.
ITEM 106 Compaction Equipment and Density Control Strips
Compaction Equipment shall be capable or obtaining compaction requirements without detrimentally affecting the compacted materials. The compacting units may be of any type, provided they are capable of compaction each lift of material as specified and meet the minimum requirements as contained herein.
The minimum requirements for rollers are as follows:
Sheep’s foot Rollers
, tamping as grid roller shall be capable of exerting a force of 45 Newton per millimeter (250 lb./in) of length of roller drum.
Steel Wheel Rollers
, other than vibratory shall be capable of exerting a force of not less than 45 Newton per millimeter of width of the compression roll or rolls.
Vibratory Steel Wheel Rollers
shall have a minimum mass of 6 tons. The compactor shall be equipped with amplitude and frequency controls and specifically designed to compact the material on which it is used.
Pneumatic Tire Rollers
must have smooth thread tires of equal size that will provide a uniform compacting pressure for the dull of the roller and capable of exerting a ground pressure of at least 550 kN (80 psi).
units may be required to achieve the specified density of the embankments.
SINGLE STEEL VIBRATORY
SHEEP FOOT ROLLER
THREE STEEL WHEEL
THREE STEEL WHEEL
CHINA PNEUMATIC TIRE ROLLER
COMPACTION AND STABILIZATION
Whether the oil is used as foundation material to support vertical structures, roads or other structures, it is important to know that the in-place materials should possess the following properties:
1. The soil must have adequate strength.
2. The soil must be relatively incompressible so that future settlement in insignificant.
3. The soil must be stable against volume change as water content or other factors vary.
4. The soil must be durable and safe against deterioration.
5. The soil must possess proper permeability.
These desirable features could be achieved with a compacted fill by:
1. Proper selection of the soil type
2. Proper placement of the materials
Other Subgrade Preparation Practices
1. Ensure the compacted subgrade is able to support construction traffic. If the subgrade ruts excessively under construction traffic it should be repaired before being paved over. Left unrepaired, subgrade ruts may reflectively cause premature pavement rutting.
2. Remove all debris, large rocks, vegetation and topsoil from the area to be paved. These items either do not compact well or cause non-uniform compaction and mat thickness.
3. Treat the subgrade under the area to be paved with an approved herbicide. This will prevent or at least retard future vegetation growth, which could affect subgrade support or lead directly to pavement failure.
The types of equipment commonly used for compaction are:
1. Pneumatic or rubber tire rollers. Can be used effectively on all types of soils.
Light Rollers of 20 tons type can compact 6 inches thick layer with few passes.
2. The drum type rollers that have projecting feet or logs such as the sheep’s foot roller. It is limited to cohesive soils. Its pressure varies from 700 kN/m^2 to 4,200 kN/m^2.
3. Vibratory compactors. Is the most effective compactor on non-cohesive soils available as:
a. Vibrating drum type.
b. Vibrating pneumatic tire.
c. Vibrating plate equipment.
d. Steel wheel rollers. Other than vibratory should be capable of exerting a force not less than 45 Newton per millimeter of width of the compression roll or rolls.
4. Smooth drum rollers.