Updated Geotechnical Investigation

Transcription

1 Updated Geotechnical Investigation Proposed Residential Development Crichton Street, Ottawa, Ontario Prepared For: Mr. R.K. McConkey Cambridge Company 9 Coupal Street (Off River Rd) Vanier, ON K1L 6A2 Trow Associates Inc. 154 Colonnade Road South Ottawa, ON K2E 7J5 Tel: (613) Fax: (613) Project No: Report date: April 27, 2010

2 Table of Contents Summary 1 Introduction 4 Background Information 6 Procedure 7 Site and Soil Description 8 Foundation Considerations 10 Floor Slab and Drainage Requirements 11 Excavations 12 Backfilling Requirements and Suitability of On-Site Soils for Backfilling Purposes 14 Earth Pressure 15 Site Classification for Seismic Site Response 16 Subsurface Concrete Requirements 17 Access Roads and Parking Areas 18 General Closure 20 Drawings Drawing No. 1:... Site Plan Drawing Nos. 2 to 4:...Borehole Logs Drawing No. 5:... Drainage and Backfill Recommendations Drawing No. 6:...Suggested Exterior Drainage Construction Against Property Line Appendix Appendix A:... Shear-wave Velocity Sounding i

3 Summary A geotechnical investigation was undertaken at the site of the proposed residential development to be located at the civic address of Crichton Street in a residential area of the City of Ottawa, Ontario. This work was authorized by Mr. R.K McConkey of Cambridge Company Ltd. on February 1, The results of our findings were reported in the report titled Geotechnical Investigation, Proposed Residential Development, Crichton Street, City of Ottawa, Ontario under Project No. dated March 17, This report has now been updated to reflect changes in the proposed founding elevation and to comply to the Ontario Building Code 2006 requirements and supersedes the previous report. It is proposed to construct a five storey residential building with semi-basement and one level of below grade parking. The finished elevation of the lowest basement floor will be at Elevation 52.7 m approximately whereas the ground floor level will be set at Elevation m. The fieldwork for this investigation comprised the drilling of three boreholes (Borehole Nos. 1 to 3) at the site to depths varying between 4.3 m and 4.7 m. The boreholes revealed that the site is overlain by a thin deposit of fill overburden ranging in thickness between 0.5 and 1.7 m. The fill is underlain by highly weathered shale to very poor to fair quality shale bedrock of the Billings Formation. Additional data on the bedrock levels throughout the site was also obtained from a Phase II environmental site assessment report completed by our office at the subject site in October The Shale bedrock is prone to deterioration when exposed to the elements. It also heaves due to a complex mechanism caused in part by biooxidation of sulphides in the rock, which then react with calcite seams to form expanding gypsum. This occurs when oxygen is permitted to enter the rock, usually by lowering of the water table and is accelerated by the presence of heat. The groundwater table at the site was established at Elevation 54.0 m. It is subject to seasonal fluctuations and may be at a higher level during wet weather periods. The investigation has revealed that the predominant founding stratum at the site is shale bedrock of the Billings Formation. The proposed structure may be founded on spread and strip footings designed for factored geotechnical resistance at Ultimate Limit State of 960 kpa on shale bedrock. The factored geotechnical resistance at Ultimate Limit State (ULS) will govern the design since loads required to cause 25 mm settlement of the structure founded on bedrock will exceed the factored geotechnical resistance at ULS. The settlements of the structure are expected to be small i.e. less than 10 mm. Since the Shale bedrock is prone to deterioration when exposed to the elements, it is recommended that a skim coat of concrete should be placed on top of the bedrock surface following excavation and cleaning. Also, in this case, the concrete for the footings should be poured flush with the 1

4 rock faces. Alternatively, the sides of the excavations for the footings may be sprayed with gunnite or chemical sealer to prevent deterioration of the shale. The lowest level floor of the proposed structure may be constructed as a slab-on-grade provided that the floor slab is set on a bed of 19 mm clear stone at least 300 mm thick. Underfloor as well as perimeter drainage system should be provided for the structure with basement. However, the water table at the site should be maintained above the shale surface to prevent heaving of the shale. The invert of the drains should be set at least 150 mm above the shale bedrock surface. Also, the surface of the shale should be covered with a skim coat of concrete to prevent deterioration of the shale. Weep holes should be provided in the skim coat of concrete to facilitate drainage. Any localized pits should be constructed as water tight structures instead of locally depressing the water table around them which may result in dewatering of the shale. The general excavation at the site will extend to a depth of 4 m approximately below the existing ground surface whereas localized excavations for footing beds may be somewhat deeper. The excavations will extend through the shallow fill and will be predominantly in the shale bedrock. The excavation at the site may be undertaken as open cut. The overburden should be cut back at 45 degrees whereas the shale bedrock may be excavated with near vertical sides. However, any exposed shale face should be protected from deterioration by spraying gunnite or a suitable chemical sealer. In addition, stabilization of the rock face may be required using rock bolts or wire mesh. Excavation of the overburden containing foundation remnants, and upper weathered shale bedrock may be undertaken with large mechanical equipment. Excavation of the sound shale may require line drilling and blasting. Extreme care should be exercised during blasting to ensure that existing structures and services are not damaged. It is recommended that bedrock should not be blasted within 3 m of any existing structures or services which cannot be disturbed. Excavation in this area should be undertaken with hoe rams. The blasting should be undertaken under the direction and supervision of a blasting expert. Vibrations should be monitored at property boundaries and should not exceed 25 mm/sec. A condition survey of all the adjacent structures should be undertaken prior to commencement of excavation work. Alternatively, the shale may be excavated by hoe ramming although the progress is expected to be slow. Seepage of groundwater into the excavations should be anticipated. The groundwater should be collected in perimeter ditches and removed by pumping from sumps. It is possible that additional sumps may be required in areas where the seepage is extensive due to presence of fissures in the bedrock. The backfill against the subsurface walls should be free draining granular material preferably conforming to Ontario Provincial Standard Specifications for Granular B. It should be placed in 300 mm lifts and compacted to 95 percent of standard Proctor maximum dry density. The backfill in the service trenches below the shale level should consist of 2

5 compacted clay or concrete. Alternatively, the sides of the trench in the shale bedrock may be sprayed with shotcrete. Based on the proposed founding level and shear wave velocity measurements, the site has been classified as Class B for seismic site response in accordance with Table A of the Ontario Building Code, General Use Portland cement (GU) may be used in subsurface concrete at this site. The above and other related considerations are discussed in greater detail in the body of the report. 3

6 Introduction A geotechnical investigation was undertaken at the site of the proposed residential development to be located at Crichton Street in the City of Ottawa, Ontario. This work was authorized by Mr. R.K McConkey of Cambridge Company Ltd. on February 1, The results of the investigation were reported under our Project No. dated March 17, This report has now been updated to comply to Ontario Building Code 2006 requirement and supersedes the previous report. For this purpose, the additional testing undertaken comprised of measurement of shear wave velocity of the bedrock to 30 m depth. The proposed development would comprise of a five (5) storey residential structure with a semi-basement and one (1) level of below grade parking. The elevation of the lowest basement floor is anticipated to be at Elevation 52.7 m whereas the ground floor level will be set at Elevation m. The investigation was undertaken to discuss the following: (i) (ii) (iii) (iv) (v) (vi) (vii) Geotechnical and groundwater conditions encountered including soil and rock properties. Most suitable alternative type of foundation including foundings depths and allowable bearing capacity of founding stratum. Anticipated total and differential settlements. Excavation conditions anticipated including possible effects of groundwater during construction. Backfilling requirements and suitability of on-site materials for backfilling purposes. Lateral earth pressures on foundation walls. Subsurface drainage requirements around building foundations, beneath paved areas and behind retaining walls. (viii) Pavement structure thickness for access roads and parking areas. (ix) (x) Classify the site for seismic site classification as required by the Ontario Building Code, 2006; and, Subsurface concrete requirements. The comments and recommendations given in this report are based on the assumption that the above-described design concept will proceed into construction. If changes are made either in the design phase or during construction, this office must be retained to review these modifications. The result of this review may be a modification of our recommendations or it 4

7 may require additional field or laboratory work to check whether the changes are acceptable from a geotechnical viewpoint. 5

8 Background Information A Phase III Environmental Site Assessment (ESA) completed by our office at the subject site in October 2003 under Report No. MP14929A was reviewed. Nineteen boreholes drilled throughout the site revealed the subsurface conditions to comprise of a shallow deposit of sand and silt underlain by bedrock, which was encountered at a depth ranging from 1.0 m to 1.5 m. Groundwater was not encountered in any of the boreholes drilled at the site. 6

9 Procedure The fieldwork at the site was undertaken with a truck mounted CME-55 drill rig equipped with continuous flight augers and rock coring equipment. The fieldwork was undertaken on February 19, 2004 and was supervised on a full time basis by an engineer from Trow Associates Inc. The fieldwork comprised the drilling of three (3) boreholes to depths varying between 4.3 to 4.7 metres. The locations of the boreholes are shown on Site Plan, Drawing No. 1. All the boreholes were initially advanced by continuous flight hollow stem auger equipment to refusal encountered at a depth of 1.5 m to 2.7 m. Standard penetration tests were performed in the overburden in these boreholes at 0.75 m to 1.5 m depth intervals and soil samples retrieved by split barrel sampler. The bedrock was then core drilled using NQ size core barrel to termination at a depth of 4.3 to 4.7 metres (Elevation 51.7 m to 52.2 m). All the soil and rock samples were visually examined in the field, logged and identified. On completion of the fieldwork, all the soil samples and rock cores were transported to the Trow laboratory in the City of Ottawa where they were examined by a geotechnical engineer and borehole logs prepared. Laboratory testing comprised of performing moisture content, on all the soil samples and unconfined compressive strength tests and ph and sulphate on selected rock core samples. 13 mm slotted standpipes were installed in all the boreholes for long term monitoring of the groundwater table at the site. The locations of the boreholes were established in the field by a representative of Trow Associates Inc. Their elevations referenced to a geodetic datum were estimated from spot elevation provided on a grading plan prepared by our office as Drawing No. 1 reference Project MP14929B. In addition, shear wave velocity measurements were undertaken at the site to 30 m depth on March 2, 2010 by Geophysics GPR International Inc. The geophysical investigation utilized the Multi-channel Analysis of Surface Waves (MASW) and the Spatial Autocorrelation (SPAC) methods to generate a shear-wave velocity depth profile. 7

10 Site and Soil Description The site of the proposed development is located on the north side of Crichton Street and registered by the street address of Crichton Street in the City of Ottawa, Ontario. It is bounded by residential development on the east, west and north sides and by Crichton Street to the south. Two 2 ½ storey residential dwellings currently situated on the property will be demolished as part of the proposed development. The ground surface at the site is relatively flat with elevations varying from Elevation 56.3 m to Elevation 56.7 m. A detailed description of the geotechnical conditions encountered in the three (3) boreholes (Boreholes 1 to 3) drilled at the site are given on Borehole Logs, Drawings Nos. 2 to 4 inclusive. The borehole logs and related information depict subsurface conditions only at the specific locations and times indicated. Subsurface conditions and water levels at other locations may differ from conditions at the locations where sampling was conducted. The passage of time also may result in changes in the conditions interpreted to exist at the locations where sampling was conducted. Boreholes were drilled to provide representation of subsurface conditions as part of a geotechnical exploration program and are not intended to provide evidence of potential environmental conditions. A review of these drawings indicates that the below 25 mm to 30 mm of asphaltic concrete, shallow deposit of fill material, 0.5 m to 1.7 thick, comprising of sand and gravel to reworked till was encountered. The moisture content of the fill ranged between 8 to 10 percent. The fill in Borehole No. 3 is likely part of the backfill material around the existing structures. Beneath the fill, weathered shale bedrock was encountered and extends to the maximum auger depth of 1.5 m to 2.7 m i.e. Elevation 54.6 m to 55.0 m. A review of the geological maps indicated that the bedrock in the general area of the site varies from dark black limestone of the Eastview Formation to black shale of the Billings Formation. Examination of the recovered cores revealed that the bedrock at the site is shale of the Billings Formation. A Total Core Recovery (TCR) ranging between 85 and 100 percent was obtained during drilling. Rock Quality Designation (RQD) of the cores recovered was established to range between 0 and 71 percent. On this basis, the bedrock within the depth ranges investigated may be classified as very poor to fair quality. Unconfined compressive strength of rock samples tested from Borehole Nos. 1, 2 and 3 was established to vary from 39 to 69 MPa indicating a medium strong to strong bedrock. The unit weight of the bedrock samples tested ranged between 2545 and 2559 kg/m 3. The Shale bedrock is prone to deterioration when exposed to the elements. It also heaves due to a complex mechanism caused in part by bio-oxidation of sulphides in the rock, which 8

11 then react with calcite seams to form expanding gypsum. This occurs when oxygen is permitted to enter the rock, usually by lowering of the water table and is accelerated by the presence of heat. Water level observations were made in the boreholes during the fieldwork and in standpipes installed in some of the boreholes subsequent to completion of the fieldwork. The observations indicate that the groundwater table is at a depth of 2.3 m below the existing ground surface i.e. Elevation 54.0 m. Water level observations were made in the exploratory boreholes at the times and under the conditions stated in the scope of services. These data were reviewed and Trow s interpretation of them discussed in the text of the report. Note that fluctuations in the level of the groundwater may occur due to seasonal variation such as precipitation, snowmelt, rainfall activities, and other factors not evident at the time of measurement and therefore may be at a higher level during wet weather periods. 9

12 Foundation Considerations The investigation has revealed that the geotechnical conditions at the site are suitable for the construction of the proposed five (5) storey residential development on spread and strip footings. The lowest level floor slab will be at Elevation 52.7 m approximately whereas the ground floor will be set at Elevation m. The footings of the proposed structure are expected to be founded at a depth of 0.5 m to 1.0 m below the floor slab level i.e. Elevation 51.7 m to Elevation 52.2 m. The founding stratum at this level is expected to be sound shale bedrock of the Billings Formation. The factored geotechnical resistance at Ultimate Limit State (ULS) for footings founded on the shale bedrock may be taken as 960 kpa. It is noted that the loads required to cause 25 mm settlement of the bedrock will be much higher than the geotechnical resistance at Ultimate Limit State. Therefore, Ultimate Limit State will govern the design. All the footing beds should be visually inspected to ensure that they have been prepared properly. The coefficient of friction between the footing concrete and the sound shale bedrock may be taken as Settlements of the footings founded on the shale bedrock and designed to the recommended factored geotechnical resistance at Ultimate Limit State are expected to be very small i.e. less than 10 mm. As indicated in the previous section, the Billings Shale is prone to swelling under certain conditions of heat and humidity. It is also prone to rapid deterioration especially from below the water table when exposed to the elements. Therefore, the bedrock exposed in the footing beds should be cleaned of any soil or deleterious materials and covered with a skim coat of concrete within hours of its first exposure. Alternatively, the shale surface may be kept wet at all times. For reasons given previously, the concrete for the footings should be poured flush with rock surface. Alternatively, the shale exposed in the sides of footing trenches may be sealed by spraying gunnite. A third alterative would be to backfill the footing trenches with well compacted cohesive soils of low permeability. All the footing beds should be thoroughly examined by a geotechnical engineer to ensure that the shale bedrock is capable of supporting the design bearing capacity and to locate and map any minor fault zones, which may contain fractured bedrock and require special foundation treatment. Where fractured rock is encountered in a fault zone, sub-excavation may be undertaken to the underlying more competent bedrock. Alternatively, the footings may be redesigned to a reduced allowable bearing pressure. 10

13 Floor Slab and Drainage Requirements The lowest level floor of the proposed building may be constructed as a slab-on-grade provided it is set on a bed of well compacted 19 mm clear stone at least 300 mm thick. The clear stone would prevent the capillary rise of moisture to the floor slab. Adequate saw cuts should be provided in the floor slab to control cracking. It is recommended that perimeter as well as underfloor drains should be provided for the proposed structure. The underfloor drainage system may consist of 100 mm diameter perforated pipe or equivalent placed in parallel rows at 5 m to 6 m centres and at least 300 mm below the underside of the floor slab. The drain should be set on 100 mm of pea-gravel and covered on top and sides with 150 mm of pea-gravel and 300 mm of CSA Fine Concrete Aggregate (Drawing No. 5). The perimeter drains may also consist of 100 mm diameter perforated pipe set on the footings and surrounded with 150 mm of pea-gravel and 300 mm of CSA Concrete Aggregate. If normal perimeter drains cannot be installed due to space restrictions, the drainage arrangement shown on Drawing 6 may be utilized. The perimeter and underfloor drains should be connected to separate sumps so that at least one system would be operational should the other fail. The Shale Bedrock is known to heave due to a complex mechanism caused in part by the biooxidation of sulphides in the rock which then react with the calcite seams to form expanding gypsum. This occurs when oxygen is permitted to enter the rock, usually by lowering the water table. Cracking of the floor slab due to heaving of the shale has occurred in some structures in Ottawa. It is therefore recommended that the water table at the site should be maintained above the shale surface. The invert of the drains should be set at least 150 mm above the shale bedrock surface. In addition, a mud coat of concrete at least 75 mm (3 inches) thick should be placed on the surface of the shale as a seal prior to placement of the granular fill. Weep holes should be provided in the skim concrete layer to facilitate drainage. Any granular fill to be placed under the floor slab should be compacted to at least 98 percent of the Standard Proctor Maximum dry density. Any elevator pits and sumps should be constructed as water tight structures instead of trying to locally depress the groundwater table around them which may result in dewatering of the shale. The finished exterior grade should be sloped away from the building to prevent surface ponding close to the exterior walls. 11

14 Excavations The general excavation at the site will extend to within 2.5 m to 3.5 m of the property boundary on all sides. General excavation at the site will be undertaken to Elevation 52.5 m approximately. The general excavation will therefore extend to a depth of 4 m approximately below the existing ground surface although the localized excavations for footing beds may be somewhat deeper. The general excavation will extend through the shallow fill and will be predominantly in shale bedrock. It will be up to 1.7 m below the groundwater table. A thicker overburden comprising of fill material should be anticipated close to the existing structure on site. Excavation at the site may be undertaken as open cut. The sides of the excavation in the overburden should be cut back at 45 degrees whereas the bedrock may be excavated with near vertical sides. Exposed faces of the shale bedrock (weathered and sound) should be protected from deterioration by spraying gunnite or a chemical sealer. In addition, stabilization of the excavated rock face may be required by bolts and wire mesh. The spacing of rock bolts will depend on the block sizes in the rock mass. Based on the borehole information, a rock bolt spacing of 1 ½ to 2 m center to center, in the vertical direction and 1 ½ m in the horizontal direction is suggested subject to modification based on field inspections. Rock bolts must extend into the rock at least 2 m. In some weathered areas, closer spacing, longer bolts, and surface treatment will be required to stabilize the rock mass. Spacing and locations must be verified by visual review of the excavated face, by representative of Trow Associates Inc. Excavation of the overburden soils may be undertaken by conventional large mechanical shovel. It should be possible to excavate the remnants of the old foundations and the upper levels of the shale bedrock with hoe rams. The excavation of the bedrock at the site may be undertaken by hoe ramming although the progress is expected to be slow. Excavation of the sound shale bedrock may require the use of line drilling and blasting. Blasting of the bedrock should not be undertaken closer than 3 m of existing structures and/or services which cannot be disturbed. Excavation of the bedrock in this area should be undertaken with hoe rams. In order to prevent any damage to the surrounding structures, the blasting operations would have to be carefully planned and closely monitored. It is recommended that the blasting contractor should retain the services of a blast specialist to provide him with a blasting plan. Exposed faces of the shale bedrock should be protected from deterioration by spraying gunnite. In addition, stabilization of the excavated rock face may be required by bolts and wire mesh. The contractor should have a licensed blaster on site at all times during the blasting and a vibrations engineer on retainer. Prior to commencement of the blasting operations, the contractor s proposed plan should be reviewed by this office. 12

15 A condition survey of all the existing structures in the vicinity of the site should be undertaken prior to commencement of construction. Vibration monitoring should be carried out in the adjacent structures during blasting operations. The blast charge should be such that the peak particle velocity should not exceed 25 mm per second at the property lines. Water inflow into the excavation should be expected. However, it should be possible to handle this inflow by collecting the water in perimeter ditches and pumping from properly filtered sumps. It is possible that additional localized sumps may be required in areas where the seepage is more extensive from fissures in the bedrock face. It is noted that permit to take water would be required from Ontario Ministry of the Environment if the quantity of water to be pumped from the site exceeds 50,000 litres per day. This process may take up to 4 months. Although this investigation has estimated the groundwater levels, at the time of the fieldwork, and commented on dewatering and general construction problems, conditions may be present which are difficult to establish from standard boring techniques and which may affect the type and nature of dewatering procedures used by the contractor in practice. These conditions include local and seasonal fluctuations in the groundwater table, erratic changes in the soil profile, thin layers of soil with large or small permeabilities compared with the rock mass etc. Only carefully controlled tests using pumped wells and observation wells will yield the quantitative data on groundwater volumes and pressures that are necessary to adequately engineer construction dewatering systems. As indicated previously, the shale bedrock, if dewatered, and exposed to the elements is susceptible to deterioration. It is therefore recommended that the shale bedrock at the founding level should be cleaned of any soil or deleterious materials and covered with a mud slab of lean concrete within hours of its first exposure. Alternatively, the shale surface may be kept wet at all times until concrete for the footing is poured. The concrete for the footings should be poured flush with excavations in the bedrock. If this is not possible, the sides of the excavations in the shale bedrock may be sealed with gunnite. 13

16 Backfilling Requirements and Suitability of On-Site Soils for Backfilling Purposes Conventional backfill against the subsurface walls should be free draining granular material preferably conforming to the Ontario Provincial Standard Specifications (OPSS) for Granular B. It should be placed in layers not exceeding 150 mm in thickness and compacted to 95 percent of standard Proctor maximum dry density. Where basement walls would be poured against the bedrock or temporary shoring, vertical drainage channels must be installed on the face of the excavation wall or lagging to provide the necessary drainage. Vertical drains such as Alidrain or Geodrain may be used for this purpose (Drawing 6). At least one vertical drain should be installed every 2.5 m. Depending on the groundwater inflow after excavation, additional drains may be necessary locally. Where the upper portion of the wall is backfilled with granular material, the vertical drains should extend into this backfill to provide drainage of the backfill. As indicated previously, the drainage of the shale bedrock is to be prevented. Consequently, special attention would be required when backfilling any of the services located in the shale bedrock. The portions of the excavation in the shale bedrock may be backfilled with clay, concrete or the sides of the excavations in shale bedrock may be sealed with gunnite. 14

17 Earth Pressure The subsurface walls of the proposed structure will be subjected to lateral static earth pressure as well as lateral dynamic earth pressure during a seismic event. The lateral static thrust that the subsurface walls would be subjected to may be computed from the following equation: P A = ½ K a γ H 2 + K a q H where P A = lateral active force kn K a = active earth pressure coefficient = 0.4 γ = unit weight of backfill = 22 kn/m 3 H = height of wall, (m) q = Surcharge acting close to the subsurface wall at ground surface, kpa The lateral force due to seismic loading may be computed from the equation given below: ΔP E = 0.1 γ H 2 where ΔP E = resultant force due to seismic activity; acts at 0.6 H from the footing base γ = unit weight of backfill = 22 m 3 H = height of wall, (m) The resistance to sliding of the building footings will be provided by friction between the footing concrete and the shale bedrock. The resistance to sliding of the foundations may be computed using unfactored Ultimate Limit State friction angle of 25 degrees between the footing and the underlying shale bedrock. The resulting coefficient of friction is

18 Site Classification for Seismic Site Response The subsoil and groundwater information at this site has been examined in relation to Section of the OBC The subsoil in the area of the proposed building generally consisted of, fill and reworked shale and weathered to sound shale bedrock. Shear wave velocity of the upper 30 m of the overburden and bedrock was measured by Geophysics GPR International Inc. using the Multi-channel Analysis and Surface Waves and the Microtremors Array Method. The results are included in Appendix A. The average shear velocity in the upper 30 m of the soil/bedrock below the founding level of the structure was established as 836 m/s. It is noted that the proposed building would be founded on shale bedrock. Based on the average shear wave velocity value and the founding conditions, the site has been classified as Class B for seismic site response in accordance with Table A of OBC,

19 Subsurface Concrete Requirements Chemical tests limited to ph and sulphate content were undertaken on three selected rock samples. The test results are given in Table I below; Table No.: I Chemical Test Results Borehole No. Depth (m) PH Sulphate (%) BH 1 Rock 3.0 m BH 2 Rock 3.2 m BH 3 Rock 4.2 m The test results indicate a shale bedrock with a sulphate content of less than 0.1 percent. This concentration of sulphates in the rock would have a negligible potential of sulphate attack on subsurface concrete. In such cases, National Standards of Canada, CAN/CSA - A permits the use of General Use Portland cement (GU) in the concrete. The concrete should, however, be dense, well compacted and cured. 17

20 Access Roads and Parking Areas Pavement structure thicknesses required for the access roads and parking areas to be used by light automobile traffic and heavy traffic were computed. The pavement structures are shown on Table No. II. The thicknesses are based upon an estimate of the subgrade soil properties determined from visual examination and textural classification of the soil samples and functional design life of eight to ten years. The proposed functional design life represents the number of years to the first rehabilitation, assuming regular maintenance is carried out. Table No. II Recommended Pavement Structure Thicknesses Pavement Layer Compaction Requirements Light Duty Roads and Parking Areas Access Roads Asphaltic Concrete 97% Marshall Density 65 mm HL3 90 mm (PG 58-34) OPSS Granular "A" 100% SPMDD* 150 mm 150 mm Base (crushed limestone) OPSS Granular "B" Sub-Base, Type II 100% SPMDD* 300 mm 400 mm * Denotes standard Proctor maximum dry density, ASTM-D698. Any subgrade fill must be compacted to 98% SPMDD for at least the upper 300 mm. Construction procedures for the pavement structure are discussed below. After all the underground services have been installed, backfilled and satisfactorily compacted, the entire road should be excavated to the subgrade level. The subgrade should be crowned with a centre edge to edge slope of at least 2 percent. It should then be proof rolled with a heavy roller. Any soft areas which become evident should be sub-excavated and replaced with approved native fill or free draining granular material. All subgrade fill should be placed in maximum 300 mm lifts and compacted to 98 percent of standard Proctor maximum dry density. In-place density tests should be performed at regular intervals to ensure that the specified degree of compaction is being achieved. It is stressed that the overall satisfactory performance of the recommended pavement structure is contingent upon the provisions of good drainage. It is therefore recommended that subsurface drains should be provided on both sides of the pavement. The drains should be located with their invert approximately 300 mm below the subgrade level. Drainage facilities may consist of 150 mm diameter perforated pipe set on 100 mm of 19 mm clear stone and covered top and sides with 150 mm of 19 mm stone. The stone should be 18

21 surrounded with a suitable filter cloth, such as Terrafix 270 R or equivalent. The remainder of the trench should be backfilled with well compacted, free draining granular material. The granular materials used for pavement construction should conform to Ontario Provincial Standard Specifications (OPSS) for Granular "A" and Granular B and should be compacted to 100 percent of the standard Proctor maximum dry density. The asphaltic concrete used and its placement should meet OPSS requirements. It should be compacted to 97 percent of the Marshall Density. 19

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