[Note to Engineer: Choose one below. Confirm with your geotech if you need further compaction.]

Transcription

1 2-06 SUBGRADE PREPARATION (******) Cnstructin Requirements 2-6.3(1) Subgrade fr Surfacing This sectin is supplemented with the fllwing: The subgrade must be suitable, as determined by the Engineer, prir t placement f getextile fabric (Nte t Engineer: if required include, if nt delete) r permeable ballast base curse. All csts fr prtecting the subgrade frm siltatin r ver-cmpactin, including replacing all material that becmes unsuitable while the subgrade is expsed, shall be cnsidered incidental t the Wrk and shall nt be measured fr separate payment. While the subgrade is expsed it shall be graded t drain t ensure that water des nt pnd. Preparatin and cmpactin f the subgrade, bth fr permeable and dense pavement, shall be cnsidered as essential t the cnstructin and all csts theref shall be incidental t the Wrk. Preparatin, cmpactin, maintenance, and all ther wrk related t subgrade shall nt be measured fr payment. The subgrade shall be shaped and maintained t drain at all times during cnstructin, including temprary ditches and mdificatins t drainage structures necessary t eliminate standing water n the subgrade. Add the fllwing new sectin: (3) Subgrade fr Permeable Pavement [Nte t Engineer: Chse ne belw. Cnfirm with yur getech if yu need further cmpactin.] a) Subgrade shall be cmpacted t 90-92% f maximum dry density accrding t standard prctr (ASTM D698) and shall be firm and unyielding prir t placing pavement sectin material. Subgrade preparatin density tests shall be cnducted at a rate f 2 tests per 5000 square feet, and 4 tests per 200 lineal feet f radway. Density tests shall als be cmpleted at and near each infiltratin test lcatin (sectin (4)). Density tests at infiltratin test lcatins shall be cmpleted at distances f 5, 10, and 15 feet frm the infiltratin test, parallel and perpendicular t and within the prject alignment. The test results shuld then be averaged t represent the density at the infiltratin test lcatin, t which ther subgrade density tests may be cmpared. Engineer shall review test results and lcatins fr acceptance. The subgrade preparatin density tests results shall be within + 2 percent f the average density recrded at the nearest infiltratin test lcatin. If exceeded scarify the subgrade and cmpact. Density tests shall be crrelated t tests taken in the Subgrade Infiltratin Test sectin (4). Percent cmpactin shall be within + 2 percent f the average density recrded at the infiltratin test lcatins. b) Subgrade shall be in a firm and unyielding cnditin prir t placing pavement sectin material.

2 Cntractr shall prtect the subgrade as necessary t maintain precnstructin infiltratin rates. A ptential prcedure t prevent excessive subgrade cmpactin is as fllws: Excavatin t final subgrade elevatin shall ccur immediately prir t placing pavement sectin materials and paving. If necessary, Cntractr may excavate t an intermediate subgrade elevatin established at 12-inches abve the final subgrade elevatin. Grading t final subgrade elevatin shall be cmpleted by machinery perating n the intermediate subgrade level r the adjacent nn-pervius pavement subgrade. T prevent excessive cmpactin f subgrade during placement f pavement sectin material the fllwing steps shuld be fllwed: Excavate t subgrade elevatin using methd by which equipment, including trucks, are nt perated n the final subgrade elevatin. Scarify subgrade during excavatin as stated belw. Cmpact subgrade t density specified herein r as directed by the Engineer. Install getextile fabric (Nte t Engineer: if required include, if nt delete)). Back dump the material nt the subgrade frm the edge f the installatin and push it ut nt the subgrade using lw grund pressure equipment. Trucks then back dump subsequent lads n tp f the previusly dumped/pushed material as the installatin prgresses. Avid subgrade preparatin during wet cnditins. Cntractr shall phase the wrk s as t nt cmprmise r verly cmpact the subgrade. Shuld it be necessary fr machinery r trucks t access the final subgrade in certain areas, Cntractr shall prtect said areas frm ver-cmpactin by placing steel sheets n the areas access t diffuse pint lading. Areas determined t be verly cmpacted, in the sle pinin f the Engineer, shall be scarified by the Cntractr t a depth specified by the Engineer and re-cmpacted, and all csts theref shall nt be measured fr separate payment. [Nte t Engineer: Chse ne belw. Cnfirm with yur getech if yu need cmpact.] a) Prir t installatin f the getextile fabric ((Nte t Engineer: if required include, if nt delete)) and permeable ballast, the cntractr shall cmplete subgrade infiltratin tests in cnfrmance with sectin (4). If testing indicates that the infiltratin rate is in cnfrmance with the design lng term infiltratin rate and the remaining subgrade areas are similarly prepared scarificatin will be at the Engineers discretin. b) Prir t installatin f the getextile fabric ((Nte t Engineer: if required include, if nt delete)) and permeable ballast, the cntractr shall scarify the subgrade t a minimum depth f 4-inches t ensure that subgrade is nt sealed, cmpact the subgrade t 90-92% maximum dry density cnditin, and prf-rll by the Cntractr and/r prbe by the Engineer t check fr areas nt in a firm, unyielding cnditin. c) Prir t installatin f the getextile fabric ((Nte t Engineer: if required include, if nt delete)) and permeable ballast, the cntractr shall scarify the subgrade t a minimum depth f 4 inches t ensure that subgrade is nt sealed, cmpact the subgrade t a unifrm firm and unyielding cnditin, and prf-rll by a fully laded dump truck the Cntractr and/r prbe by the Engineer t check fr areas nt in a firm, unyielding cnditin. Lse r disturbed areas identified during prf-rlling shall be ver-excavated t firm bearing and replaced with Gravel Brrw. The Cntractr shall ntify the Engineer a minimum f 2 wrking days prir t scarifying the surface t schedule an inspectin.

3 Cntractr shall submit a Subgrade Preparatin Plan t the Engineer fr review and apprval prir t beginning excavatin wrk. The Subgrade Preparatin Plan shall include methd(s) by which the Cntractr plans n treating ver-cmpacted subgrade areas and methds by which access t private driveways will be maintained. [Nte t Engineer: Add SPP t the ROM. Delete private driveways if nt applicable. If applicable WARN the residents that there will be a steep ramp built and that cars with lw clearance may have issues] Add the fllwing new sectin: (4) Subgrade Infiltratin Tests Cntractr shall cnduct infiltratin tests immediately fllwing final subgrade preparatin t verify that the subgrade is nt ver-cmpacted. Infiltratin tests shall be cnducted at a rate f 1 test per 5000 square feet, and 1 test per 200 lineal feet f radway. One test per lt fr residential sites, fr a minimum f 5 and a maximum f 10. Subgrade infiltratin tests shall be cnducted at the discretin f the Engineer. Engineer shall chse the lcatins f the infiltratin tests. The tests shall be cnducted using the: [Nte t Engineer: Select preferred test methd] Small scale Pilt Infiltratin Test ring The small-scale and large-scale PITs shall be cmpleted at the planned subgrade elevatin as fllws: Excavate t and prepare the subgrade in accrdance with the specificatins. Excavate a shallw test pit t minimum dimensins f 2 feet wide by 6 feet in length. Depth f the trench shuld be at r within 6 inches f the planned subgrade elevatin. The side slpes may be laid back sufficiently t avid caving and ersin during the test. Hwever, the side slpes fr the depth f pnding during the test (6-12 ) shuld be vertical. The hrizntal surface area f the bttm f the test pit shuld be 12 t 32 square feet. The pit may be circular r rectangular, but accurately dcument the size and gemetry f the test pit. Install a vertical measuring rd adequate t measure the water depth and it in half-inch r centimeter increments and install in the center f the pit bttm. Alternatively, a self-lgging pressure sensr may als be used t determine water depth and drain-dwn. Use a rigid pipe with a splash plate n the bttm t cnvey water t the pit and reduce side-wall ersin r excessive disturbance f the expsed subgrade. Pre-sak perid: add water t the pit s there is standing water fr at least 6 hurs. Maintain the pre-sak water level at least 6 inches abve the bttm f the pit. At the end f the pre-sak perid, add water t the pit at a rate that will maintain a minimum 6-inch and maximum 12-inch water level abve the bttm f the pit ver a full hur. The specific depth shuld be the abut the same as the maximum designed pnding depth.

4 Every 15 minutes, recrd the cumulative vlume and instantaneus flw rate in gallns per minute necessary t maintain the water level at the same pint n the measuring rd. After ne hur, turn ff the water and recrd the rate f infiltratin in inches per hur frm the measuring rd data until the pit is empty. Fill and repeat the drain dwn prtin f the test. Prvide the test results t the Engineer fr review and acceptance. Large Ring Infiltratin Test The large ring infiltratin test shall be cmpleted at the planned subgrade elevatin as fllws: Excavate t and prepare the subgrade in accrdance with the specificatins. Install a large (steel, cncrete, r plastic ring) with a minimum internal diameter f 3-feet and a minimum height f 12-inches. Press the ring int the sil t firmly seat it and backfill arund it with native excavatin spils. Install a vertical measuring rd adequate t measure the full pnded water depth and marked in half-inch r centimeter increments in the center f the pit bttm. Alternatively. a self-lgging pressure sensr may als be used t determine water depth and drain-dwn. Use a rigid pipe with a splash plate n the bttm t cnvey ver the expsed subgrade t reduce ersin r excessive disturbance f the subgrade. Pre-sak perid: add water inside the ring s there is standing water fr at least 6 hurs. Maintain the pre-sak water level at least 6 inches abve the bttm f the pit. At the end f the pre-sak perid, add water inside the ring at a rate that will maintain a minimum 6-inch and maximum 12-inch water level abve the subgrade. The specific depth shuld be the abut the same as the maximum designed pnding depth. Every 15 minutes, recrd the cumulative vlume and instantaneus flw rate in gallns per minute necessary t maintain the water level at the same pint n the measuring rd. After ne hur, turn ff the water and recrd the rate f infiltratin in inches per hur frm the measuring rd data until the water has infiltrated Fill and repeat the drain dwn prtin f the test. Prvide the test results t the Engineer fr review and acceptance. [Nte t Engineer: Amend the testing t fit yur prject and prvide directin n what t d with the infiltratin test results (such as Cnvert it t a lng term rate and cmpare it t the design lng term rate). Prvide a remedy if the lng term infiltratin rate determined frm the subgrade infiltratin rate is less than the design lng term infiltratin rate. Identify an allwable tlerance between the cnstructin measured rate and the rate the design lng term infiltratin rate. (why is it different scarificatin. Prvide fr design engineer t review testing and results fr cnfrmance with the design.]

5 Add the fllwing new sectin Measurement Preparing, maintaining, testing, and restring (as necessary) subgrade shall nt be measured fr payment. END OF SECTION