(Also. Suggested for Subdivision and Other Road Systems) Highway. Virginia. Highway Research Council. Charlottesville, Virginia

Transcription

1 METHOD FOR SECONDARY ROAD FLEXIBLE PAVEMENTS IN VIRGINL-, DESIGN Suggested fr Subdivisin and Other Rad Systems) (Als K. Vaswani N. Research Engineer Highway Highway Research Cuncil Virginia Cperative Organizatin Spnsred Jintly by the Virginia (A Virginia January Department f Highways and the University.f Virginia) Charlttesville, VHRC 71-R18

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3 DESIGN METHOD FOR SECONDARY ROAD FLEXIBLE PAVEMENTS IN VIRGINIA K Vaswani N. Research Engineer Highway design methd fr secndary rads is based n AASHO Rad Test Results Virginia's design experience It is divided int tw parts. (1) the evaluatin and the sil supprt value f the subgrade, the thickness equivalencies f the paving f and the traffic in terms f vehicles per day; and (2) design cnsideratins materials, as the determinatin f the required thickness index f the pavement and the such f the materials and layer thicknesses t meet the design thickness index. selectin Sil Supprt Value (SSV) Design CBR* " x resiliency factr. Virginia Methd f Determining CBR Values" (VTM-8) is t be used fr evaluating Test design CBR. In unusual circumstances where actual CBR data cannt be the predicted design values as given in Appendix I (page A-l) may be used. btained, these predicted values are used, the SSV f the subgrade can be btained If predicted reginal resiliency factrs are given in Figure 2 (page 3) Appendix I. se factrs are valid when the misture cntent f the and sil is at r belw the plastic limit. Fr sils with misture cntents subgrade t their liquid limits, the resiliency factrs are much lwer and the. clse Thickness Equivalencies f Paving Materials are given in Tab[e 1, page,4. materials and cnstructin specificatins shuld be in accrdance with current Virginia Department f Highways Rad and Bridge Specificat.ns r the supplemental specificatins. apprpriate by INTRODUCTION THE EVALUATION OF VARIABLES frm Figure 1 (page 2) r Appendix I (page A-l). $SV shuld be a maximum f 2. Traffic in Terms f Vehicles per Day (vpd) is available frm district engineers. Fr tw-lane facilities prvide fr the tta traffic. Fr traffic fur-lane use 8 percent f the ttal traffic. * Califrnia Bearing Rati

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6 EQU.IVAI::ENCY VALUES FOR MATERIALS THICKNESS IN SECONDARY AND SUBDIVISION ROADS USED Lcatin Ntatin a 1 a 1 a 1 a 2 a 2 a 2 a 2 a 2 a 2 a 3 a 3 a 3 a 3 a 3 a 3 a 3 Cncrete (S-5) Asphaltic and dubl.e seal* Prime Prime and singie seal * Cne fete (B-3 r B- 1) Asphaltic Aggregate Untreated Material Ntatin Agg. CTA Agg. CTA.84*.42* TABLE 1 Lcatin Materia! Equiv. Thick. Value Surface 1.67 A.C. Base a Cement treated Aggregate 1.67 Sel. Mat..84 Sel. Mat, Type I & III 1. Sil Cement Cem. Tr. Sel. Mat., Type II Sel. Mat. C 1.17 Sel. Br. C Cem. Tr. Sel. Brrw I. O Subbase Aggregate Untreated treated Aggregate Cement Sel. Mat. Sel. Mat., Type I & III Sil Cement S. L Sil Lime Cem. tr. Sel. Mat,,, II Type tr. Sel Brrw Cem Sel. Mat. C Sel. Br. C i. Use this value fr alh 1 as shwn in examples 1, 2," and 3 given n pages 7, 8, and

7 N. 1 fr sandy and sandy clay sils f the castal plain and where the Example 15; 3, and 8 vpd DESIGN PROCEDURE design prcedure is as fllws: design nmgraph is given in Figure 3 6). Frm the nmgraph with a given SSV and vpd in bth directins the thick- (page ness index (D) can be determined as shwn by the example. nmgraph specifies a minimum D f 6 4 and a maximum D f 2. D value culd be reduced fr service rads nly If the D value btained minimum the nmgraph is greater than 2, stage cnstructin with D 2 in the first frm may be prvided stage the value f D is btained, the material in each layer f the pavement and After thickness f each layer can be determined by the fllwing equatin: the D =alh l+a2h 2 +a3h 3 (see Figure 4, page i). is shwn by three examples, given n pages 7, 8, and 9 This belw. using the data given N. 2 fr micaceus sils r micaceus clay silts and where the vpd 35, Example and 4,. 9, N. 3 fr clayey sils with n mica cntent and where vpd 2; 5, Example 3,. and -5-

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12 flexible pa-ements f secndary rads in Virginia usually cnsist f tw three layers f different materials f varying depth ver the subgrade, as shwn r in Figure 4 belw, Surface $h 1 Thick. Equiv. a 1 Base ;h.2 T!ick Equiv. =a 2 Subbase Sh 3 Tnick Equiv a 3 Base :l..h 2 Thick Equiv a 2 Figure 4. Secndary rad flexible pavement sectins average CBR value f the prject is the average f the CBR test values rejecting the very lw and very high values, after design CBR value f the prject is tw-thirds f the average CBR value the prject factr f tw-thirds is adpted as a safety factr t cmpensate f the nnunifrmtty f the sil encuntered n the prjects, and als t cmpensate fr the very lw bearing CBR samples which are nt cnsidered when cmputing the fr CBR values f the sils encuntered n the prject. Further, fur days f average as specified in the test methd des nt necessarily give the minimum saking- strength f sme sils Thus the tw-thirds factr wuld cmpensate fr CBR variatins such classificatins based n their resiliency prperties. resiliency factrs are five in Table 2 belw. Please nte that the higher the resiliency, the lwer the given DISCUSSION OF THE DESIGN METHOD Surface J,h 1 Thick Equiv al. Subgrade Subgrade (a) Three-layer System (b) Tw-layer System CBR Values each prject sufficient CBR tests shuld be run t determine the true Fr value f the varius sils in the subgrade. supprt Resilienc, Factr (RF) subgrade sils fr secndary and subdivisin rads have been divided int 1-

13 ,factr de:gree f resiliency f a sil culd be btained if its sil resi!ieney is knwn as shw in Appendix ii.: page A=. classificatin Very lw resilient sils design nmgraph (Figure 3, page 6) has a vpd curve which shws the traffic in bth. directins, since this is nrmally the way the ttal traffic vlume ttal btained n secndary rads,, If the data available are fr traffic in ne directin is g,,, n a ne-,way street), this value shuld be dubled fr use f this.nmgraph, (e. it shuld be nted that the thickness index (D) curve is calculated Hwever, n ne directin traffic nly, and hence gives the thickness index f the pavement based nmgraph assumes truck traffic (2 axles and six tires r heavier) nt than 5 percent, Fr truck traffic greater than 5 percent the thickness index greater the pavement shuld be increased as fllws: Fr every 5 trucks (2 axles and f tires r heavier) ver the,5 pe:rcent level the thickness index (D) as btained frm 6 Thic kn_e. s E qu iv ale n_c thickness equivalency (a) f a given material is the index f strength the cntributes t the pavement,, Its value depends n the type f the material material TABLE 2 RESILIENCY FACTORS FOR SOILS Degree f Resiliency RF resilient sils Hi.gtfly Medium resilient sils 15 Medium lw resilient sils 2 Lw resilient sils Traffic in each traffic lane the nmgraph shuld be increased by 1 and its lcatin in the pavement 11-

14 strength equivalencies f the paving materials are given in Table i. As m.at.erials are intrduced, their thickness equivaiencies have t be evaluated. new full depth asphaltic cncrete (cnsisthg f an S-5 surface and the remainder Fr base) placed directly n the subgrade,,a.,.,e tentative recmmendatins are that it B-3 have a minimum thickness f 7 incb.es arid a thickness equivalency f 1.5. shuld thickness equivalency f the same material,,.:hen placed in the base is higher than placed in the subbase. Thus unt.reated s,..e has a 1. in the base curse and when.6 in the subbase curse. Cement treated aggregate and select materials types a have shm that tt,.e strength f the cement treated native sil r Investigatins materials (e. g., select mate^al type H and select brrw) varies depending brrwed thickness index (D) is the strength " the pavement based n its resistance a deflectin caused by a wheel lad. It is btained by the equatin t D =alh 1 +a2h 2 a3h 3 al, and a 3 are the thickness equivalencies f the materials in the surface, when a2, subbase layers, and h base, h2, and h are and the thickness in inches f the 3 1, the required thickness index f the pavement has been determined, the After f material and the thickness f the layer are determined by the pavement designer. chice decisins are usually based n dllar value, structural adequacy, and pavement se Based n design and cnstructin experience, the fllwing are serviceability. Fr a pr subgrade with lw sil supprt values, stabilize the subgrade r 1) material with lime r cement t prvide a rigid fundatin. subbase I and III are similarly cnsidered. their physical and chemical prperties. Fr this reasn, the thickness upn f such materials is kept the same whether they are placed in the base equivalenctes r in the subbase. Thickness Index surface, base, and subbase layers, respectively. Smetimes a subbase may nt be prvided, and in this case h 3. SOME DESIGN RECOMMENDATIONS recmmended: -

15 rigid fundatin is a gd invest.ment where the traffic is likeiy t A cnsiderably, Fr example, a rigid fundatin (e.g., 6" sil increase r sil lime) with 3 t 4" f untreated aggregate is capable f carrying cement very high traffic vlume. a subgrades (particularly thse stabilized with cement) shuld be Stabilized cyered with unl:reaed aggregate t eliminate r reduce misture immediately thermal cracking r der, eriratin with a resultant lwer strength r the and material. This culd nrmall.y be handled by a firm specificatin stabilized the subgtade strength is still cnsidered t be weak in prprtin t the If amunt f traffic, cement stabilized material may be prvided ver expected type designs shuld be set up where practical t prvide reasnable Alternate This practice might attract mre bids with resultant ecnmies cmpetitin. 2) n requirement. 3) Cement stabilizatin shuld be cmpleted befre cld weather (say 4 F) sets in. 4) sils, r sandy sils with high subgrade misture cntent, r subgrades Marshy water springs r A-3 type sils shu],d be stabilized with a suitable agent. with the stabilized subgrade. 5) in cnstructin cst. -13-

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17 i t acknwledge the great help f J. B. Bassett and K. H McGhee, This tk pains t verify and carefally evaluate each statement made in this reprt. wh study was cnducted under the general supervisin i Jack H Dillard, state research engineer, and wa financed frm state research funds. highway AC KN W LEDG EME NTS 15--

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19 Cunty r E f Rte. 29 Albemarlef Rte 29 W. Alleghany Amelia Appmattx Augusta a bulge in the Bteturt-- rck, eastern way up t half Rck. Eagle Campbell W. f Rte. 2 Carline i 1 Sil Supprt (SSV) Value 25 3 APPE q31x I CLASSIFICATION BASED ON RESILIENCY AND CBR VALUES OF SOILS Twn Cde Factrx Resiliency. Design Factr (Res CBRValues C BR) W, f Rte, 95 Arlingtn f Rte 95 E Accmack ,5 5 8 Amherst Bath Bedfrd 1 Bland 11 Remainder f cunty, 11 Brunswick 13 Buchanan 14 Buckingham E. frte. 2 Carrll Charles City II

20 Chesterfield S.W. Msiey 2 Clnial and Heights f cunty Remainder f Rtes. 229 W. 15S and Fairfax- E. f Rte f Rte 95 W. Fauquier N. f Rte f Rte. 211 S. Greensville E. Rte Rte. 95 W. Pd,.ted.Resiliency Design Sil Supprt (SSV) Value Factr x 21 4 APPENDIX I (cntinued) C de Cunty r Twn Factr (Res. C BR) C BR Values i9' Charltte 131 Chesapeake Clarke Craig 2: E. f Rtes. 229 Culpeper- 15S and Cumberland 25 Dickensn Dinwiddie Essex Flyd Fluvanna Franklin 33 Frederick Giles Glucester W. Rte. 522 Gchland- Rte. 522 E ii 18 Graysn 38 Greene

21 Resiiiency Design Factr x CBR) Halifax 41 E. Rte. 95 Hanver- Rte. 95 and W. Rte. 715 E. Rte. 715 W. W. Rte. 95 Henric-- Rte. 95 E. Highland f Wight Isle Mntgmery Nansemnd APPENDIX I (cntinued) Si iprt (SSV) Value Cde (Res. C BR Values Cunty r Twn Factr 114 Hamptn 27 i Henry James City King Gerge 3 1 3O 49 King and Queen 1 3O 5O King William 1 3O 51 Lancaster I 3O 52 Lee W Rte. 15 Ludun- Rte. 15 E Luisa Lunenberg 55 Madisn Mathews 1 3O Mecklenburg Middlesex 1 3O 6O Nelsn New Kent 27 1 Newprt News 27.9-

22 Resiliency Orange N. f Rte. 2 and Rte. 522 E, f Rte. 2 and 1. N. Rte. 522 W. f Rte. 2 and 1.5 S. Rte. 522 E, f Rte. 2 and 1.5 S. Rte,, 522 W. Page W. Alma Alma 1. E. Pwhatan W. Rte 522 and Rte. Rte. 522 and E. 69 Rte. Prince William- W, Rte Rte E. Rappahannck N. Flint Hill Flint Hill i. S. Rckbridge W. James, Maury, Suth Rivers and James, Maury, 1.5 E., Suth Rivers and Design Sil Supprt (SSV) -- Value 4 21 Factr x (cntinued) Cde Cu.nty r Twn (Res. C.BR Values C BR) ] 22 N rf.[k 3., Nrthamptn 3. 3O 66 Nrtbumber land 3,: i 6 7 Nttway Patrick Pittsylvania Prince Edward Prince Gerge Pulaski Richmnd 3O Ranke 2. 1

23 Cunty r Twn Smyth Suthamptn Rte 95 Sussex--W. Rte 95 E Washingtn Westmreland Wythe Yrk, 6 6 i.factr x i' Supprt (SSV) Valu.e (cntinued) APPENDIX I R.esi]iency Design Cde Factr CBR Values (Res CBR) W Rte 81 Rckingham Rte 81 E Ru, ssell 84 Sctt 85 Shenandah W Rte 95 Sptsylvania- Rte 95 E i 9 25 W Rte 95 Staffrd Rte. 95 E i O 27 Surry Tazewell Beach- N. Rte 44 Virginia Rte. 44 S Warren O 96 Wise

24 resi.!iet.t sils (a) A,a (with G, I f 5 Highly up) ha.,ing iarge percentage passing #2 but and lw mica cntent. (b} Sandy sil. wth high with cntent. Gelgically they are high and mica clay, Mstly they are silts withut mica entent lw resi.lient sils Clays- A-4-2, A 6 Medium r A-8 (n mica entent) A-7-6, resilient sils Cmbinatin f sand, silt Lw clays (n mica cntent). and lw resilient sils --Sands. A-l, A-2, A-3, Very A-4 (with G. I,. less than 5). Gelgically they r Valley & part f Nrthern District Richmnd Resiliency Factr APPEhI Ii EVALUATION OF SOIL RESILIENCY FACTORS Sil. Type Zne Piedmnt lw quartz granittds. Mediumly resilient sils A-7-,5 r micaceus Piedmnt Ridge 2 Castal plains are castal plain sediments (n mlca cntent)