Rigid Pavement Design for Ports in Chile

Transcription

1 TRANSPORTATION RESEARCH RECORD Rigid Pavement Design for Ports in Chile ]AoB GREENSTEIN AND CHAIM]. PoRAN A ase study of rigid pavement design for two ports loated in the entral zone of Chile, whih is an area of high seismi risk, is presented. Speial onsiderations were required to address the problem of liquefiable sub grade soils that were the ause of severe damage to existing pavements during the large earthquake of Marh 3, Rational design harts were developed for rigid pavements on the basis of tensile stresses indued by ritial edge loads. Slab stresses were evaluated by using two omputer odes, and tensile stress-slab thikness relationships were developed for various values of omposite modulus of subgrade reation and for several modes of port pavement loads, inluding ontainer staks and loading equipment, suh as front lift truk and straddle arrier. Results indiated that ontainer staking on the slab edge is the ritial load and would require substantial strengthening of existing pavements and large investments in new ones. To overome this problem it was deided to restrit ontainer staking to a minimum distane of 38 m (15 in.) from the edge. Consequently, new pavements were designed on the basis of the loads of the ontainer-handling equipment, and existing pavements were strengthened to meet the same riteria. A design hart was developed to assess the risk of liquefation of loose sandy subgrade soils during future large earthquakes. The hart is based on expeted ground motion levels and standard penetration test N values. Finally, remedial measures were reommended to improve density and the liquefiable deposits in new pavement areas. A ase study of rigid pavement design is presented for the ports of Valparaiso and San Antonio loated in the entral region of Chile, as shown in Figure 1. A large earthquake ourred in the Paifi oast area near the ports on Marh 3, 1985, as reported by Poran et al. (1,2). The earthquake had a surfae wave magnitude of Ms = 7.8 on the Rihter sale and its intensity was rated as VII and VIII (on the modified Meralli sale) at the Valparaiso and San Antonio ports, respetively. Both ports suffered severe damage from the earthquake. The rehabilitation plan for these ports inludes the ddition of substantial ontainer-handling failities as deribed in the report on development program of ports of the ifth Region (3). The existing pavements in the ports are rigid. everal alternatives for new pavements were onsidered in a reliminary life yle ost analysis on the basis of design rieria (4-6). Results of the study indiated that new rigid avements are most eonomial primarily beause of the oprational onstraints in the ports where the new failities are lso designated for general argo. Evaluation of existing pavements in the ports indiated that he solid and unraked slabs are 3 m (12 in.) thik with a. Greenstein, Interamerian Development Bank, 13 New York ve., N.W., Washington, D.C C. J. Poran, Department of ivil Engineering, University of North Carolina at Charlotte, Chartte, N.C modulus of elastiity of over 34 5 MPa (5 million psi) and have a flexural strength of over 462 kpa (67 psi). The onrete slabs are supported by ement-stabilized granular base plaed on high-quality ompated subbase overlying hydrauli fill that varies in thikness between 3 and 12 m (1 and 4 ft). Large-sale liquefation was indued by the 1985 earthquake in the areas in whih the hydrauli fill onsisted of loose sandy soils. As a result, many existing rigid pavement areas suffered severe damage and were rendered inoperable (2). Performane observations of rigid highway pavements and numerial methods (7) have shown that edge stresses are more ritial than orner or interior stresses in pavement slabs. Experiene with rigid airport pavements is similar, as reported by FAA (8). A omputer ode H51 that was developed for FAA on the basis of the work by Kreger (9) was used for this analysis. The program permits aurate omputation of tensile stresses at the edge of a onrete slab under any loal onfiguration. This program was used to develop the design harts and personal omputer programs for most standard airraft, inluding the largest 747s and DC-lOs (8). Comprehensive design harts for port pavements were published by the British Port Assoiation (6). However, these harts were not appliable for the evaluation beause the existing pavement struture in Chilean ports is not inluded. The omputer program CORNER, whih is based on Westergaard's orner equations published by Ioannides et al. (1), was used to ompute stresses in the slab orner. Speial onsideration was given to improvement and densifiation of sandy subgrade soils for new pavement in hydrauli fill areas on the basis of a liquefation risk evaluation proedure outlined by Seed et al. (11,12). The riteria are based on standard penetration test (SPT) N-values and expeted peak ground aeleration (PGA) at the ports during a future large earthquake in the entral region of Chile. The results of these ase studies are outlined as follows. EXISTING PAVEMENT SYSTEMS Design Speifiations Available design reports indiate that the existing rigid pavements at the Chilean ports of Valparaiso and San Antonio were designed to speifiations similar to those for a pavement struture that onsists of the following layers: Conrete slabs Thikness, 3 m (12 in.); -Minimum ompressive strength, 36.2 MPa (5,25 psi);

2 12 TRANSPORTATION RESEARCH RECORD I I ) SCALE (km) /\>. PCIFIC 1 km =.62 mile/ OCEAN l. ARGENTINA. FIGURE l Port loations. CHILE ) \. u u. \ J: ) u ' 4 -, -Minimum flexural strength, 459 kpa (665 psi); -Minimum modulus of elastiity, MPa ( 4 x 1 6 psi); -Estimated Poisson's ratio,.15. Cement-stabilized base: The thikness of the ex1stmg ement-stabilized base (CSB).y aries in different port areas between 25 and 38 m (1 and 15 in.). The CSB was stabilized with 6, perent portland ement by weight and was required to have a minimum elasti modulus of 69 MPa (1, psi). Subbase: Under the CSB there is a high-quality subbase material 41to61 m (16 to 24 in.) thik. The subbase material was required to have a minimum California bearing ratio (CBR) of 4 perent.. o- Fill: The sub base overlies areas of. Hydrauli or loal fill with thikness of 3 to 12 m (1 to 4 ft) above the natural dense granular_ soil deposit and bedrok (in several loations at the port of Valp.araiso). Mean sea level is generally 2.8 m (9 ft) below the top of the fill. Evaluation of Existing Pavement Systems Nondestrutive testing (NDT) based on defletion measurements an be effetive in the evaluation of existing onditions of both rigid and flexible pavements, as disussed by Greenstein (13) and numerous other authors. Although NDT was initially onsidered for these ports' pavements, no suh tests were onduted beause of budgetary onstraints. However, available plate load test results onduted on a subbase layer of a similar pavement indiated that the minimum omposite subgrade reation of subbase and fill was 2 lbf/in. 3 These results were used for orrelations (3). On the basis of boring logs and test results from the ports' pavements, it was onluded that the atual properties of the existing pavements were as follows: Conrete slabs -Thikness, 3 m (12 in.); -Minimum flexural strength, 462 kpa (67 psi); -Minimum modulus of elastiity, 34,5 MPa (5 x 1 6 psi). Cement-stabilized base: The minimum elasti modulus was estimated to be 13 MPa (15, psi). Figure 2 (14) was used to evaluate the omposite modulus of subgrade reation for the CSB, subbase, and fill material. Using a minimum subgrade reation modulus of 54 MN/m 3 (2 lb/in. 3 ) on the sub base, the estimated result on the CSB is 136 MN/ m 3 (5 lb/in. 3 ). Subbase: Soil testing data indiated that the AST D-2487 lassifiation of the subbase is SP-GP or SM-GM wit a CBR of more than 4 per.ent. Test results indiated tha the omposite elasti modulus of the sub base and fill material varies between 145 and 386 MPa (21, and 56, psi) an the omposite modulus of subgrade reation (k) is in the rang of 54 to 95 MN/m 3 (2 to 35 lb/in. 3 ). Fill: Many SPT N-value profiles were ompiled for th fill material and were used in the liquefation risk evaluatio as subsequently desribed in this paper.

3 Greenstein and Poran 13 Slab Edge=i T x p 5.8 MPa {ontat pressure)...j V> La.. V> 3,... :::>..,, o E ::::E z... 3 I- v; a.. ::::E u 25 t t i----; NOTE= t-T-"1,..._...-t t-1 MN/m 3 = 3.68 pi 1 MPa = 145 psi <::- 1 m =.394 in 75 t ;--->i:-1-'<-, --r---;---;--- <v,1,,--...-'<---/(; 1 I NOTE: 1 MPa = 145 pi 1 m2= 1,55 in FIGURE 3 Layout of ontainer stak astings near the slab edge. 15 '-----' FIGURE 2 Nomogram to determine the omposite subgrade reation modulus for stabilized base overlying subgrade. a) DESIGN LOADS Design load alulations for the ontainer stak loads and handling equipment (inluding dynami fators) generally were based on the proedures outlined (6). The following representative loads were onsidered for these port pavements: Container stak loads: The most ommonly used ontainers in Chilean ports are 12.2 m (4 ft) long. On the basis of Chilean statistis, a maximum weight of 214 kn (24 tons) was onsidered for a single ontainer. Aording to the Chiean speifiations, the design loads were based on staking n three levels, one on top of the other. Therefore, the total oad was 642 kn (72 tons) and the design load was redued y 2 perent aording to the design reommendations ( 6) eause it is unlikely that all three ontainers in the stak will e fully laden. These loads are transferred to the rigid paveents through four orner supports (astings). Eah support as a ontat area of 289 m 2 (44.8 in. 2 ). Therefore, the design ontat pressure for eah support is equal to 58 kpa (737 si). Figure 3 shows the ritial ontainer load onfiguration n the slab edge. Obviously, the distane from the slab edge X) signifiantly affets the tensile stresses in the slab. These tresses reah their maximum value for X =. Front lift truk: The front lift truk is a ommon type of ontainer-handling equipment in multipurpose port failities. b) We 2b a b 59.9 m 4.6 m 24.4 m NOTE: 1 m =.394 in FIGURE 4 Front lift truk: a, dimensions and weights; b, ritial edge loading layout.

4 14 A front lift truk is shown in Figure 4a. It has two dual wheels, as shown in the assembly onfiguration of Figure 4b. The ritial front end design load (W 1 ) is distributed on two wheels; the load on eah wheel is 246 kn (55, lb), with a ontat pressure of 783 kpa (113.6 psi) and a ontat area of.31 m 2 (484.4 in. 2 ). Straddle arrier: The straddle arrier, also ontainerhandling equipment, is shown in Figure 5. Under ritial operating onditions the design loads were onsidered for a sin- gle wheel parallel to the slab edge (the adjaent wheel has a negligible effet on these stresses) and all wheel loads are onsidered equal. Two different types of straddle arriers were speified with wheel loads of 195 and 342 kn ( 44, and 77, lb) and ontat pressures of 177 and 783 kpa (156.2 and psi), respetively. EVALUATION OF PAVEMENT STRESSES The effets of various load onfigurations and slab thiknesses on tensile stresses in the slab were investigated for both edge and orner loading. Edge loading stresses were omputed with the H51 omputer ode, and stresses at the slab orner were omputed with the CORNER omputer program, as follows. Stresses Caused by Container Stak Loads Figure 6 shows the relationship between the tensile stress at the slab bottom and the slab thikness for ontainer stak loads. Lines la and lb represent free edge loading for om- TRANSPORTATION RESEARCH RECORD 1388 We D FIGURE 5 Layout of a straddle arrier and ating loads. posite subgrade reation modulus of 136 and 95 MN/m 3 (5 and 35 lb/in. 3 ). It is well established that adequately onstruted joints transfer loads between the jointed slabs. Aording to Chilean experiene this load transfer is at least 25 perent (i.e., 25 perent of the edge load is transferred to the jointed slab). Therefore it is neessary to look at 25 perent stress redution at jointed slab edges. Line 2 represents the stress-thikness relationship for ajointed edge and k-value of 136 MN/m 3 (5 lb/in. 3 ). Line 3 represents the stress-thikness reltionship at the orner of the slab. On the basis of operational foreasts (3), 1, load repetitions were onsidered for ontainer staking during the design life of these pavements. On the basis of the literature (1,15), the allowable stress/strength ratio (SSR) for 1, load repetitions is.64. Therefore, the allowable tensile stress in the slabs is 2965 kpa (43 psi, omputed as.64 x 67 psi). Finally, Line 2 in Figure 6 was used to determine the ll. ::::& fl) fl) Cl) L v;..! ;; Cl) Legend p = 5.8 MPa (ontat pressure) Area = 2.89m 2 Edge Stresses 1A) k 136 MN/m 3 } free Ed 9,...,...,.,,------, B) k = 95 MN/m3 g 2) k = 136 MN/m 3 - Jointed Edge Corner Stresses C 753 of <D) >o, >o-,,_--<- 3) k = 136 MN/m Slab Thikness (m) NOTE: MN/m 3 = 3.68 pi MPa = 145 psi m.394 in m 2 = 155 in 2 FIGURE 6 Tensile stress versus slab thikness relationship for ontainer stak load (X = ).

5 Greenstein and Poran 15 required slab thikness to support ontainer staks at the edge. For allowable stress of 2965 kpa ( 43 psi) the required slab thikness is 48 m (19 in.). This also implied that an additional overlay onrete slab with a minimum thikness of 18 m (7 in.) will be needed to support 1, repetitions of these loads provided that there is a monolithi bond between the overlay and the existing slab and that the joints overlap. In many areas of the ports the existing slabs are raked and shattered. Based on FAA (8), these areas will require onrete overlays of up to 33 m (13 in.). This requirement was rendered eonomially infeasible, as subsequently disussed. Stresses Caused by Container-Handling Equipment Figures 7 and 8 show stress-thikness relationships for frontlift truk and straddle arrier, respetively. These relationships were omputed with the H51 and CORNER omputer programs for edge and orner stresses, respetively. Figure 7 learly shows that edge stresses are muh higher than orner stresses and therefore are onsidered ritial. Based on operational foreasts (3), 1, load repetitions were onsidered for the front lift truk during the design life of these pavements. In this ase an SSR =.56 was used, and therefore the allowable stress was redued to 2586 kpa (375 psi). Finally, Line 4 was used for thikness design under front lift truk loads. This line represents 25 perent of the load transfer of the jointed slab and a omposite modulus of subgrade reation of 136 MN/m 3 (5 lb/in. 3 ). Figure 7 indiates that the required slab thikness for front lift truk operations is 45 m (17.5 in.). Figure 8 shows a stress-thikness relationship aused by straddle arrier operations. Again, slab edge stresses are higher than orner stresses (whih were not plotted on this figure). The graph is based on the required 1, load repetitions for this type of equipment during the design life of the pavement (3). Lines 4 and 5 are used for design with the 342- and 195-kN (77,- and 44,-lb) wheel loads, respetively. For an allowable stress of 2965 kpa ( 43 psi), these lines indiate that the required slab thiknesses are 35 and 3 m (14 and 12 in.), respetive I y. DESIGN RECOMMEND A TIO NS On the basis of the evaluation mentioned earlier, the design reommendations were as follows. Container Stak Loads The evaluation indiated that a 48-m (19-in.) slab is needed to support the ontainer staks. This was previously determined for the worst ase, in whih the ontainer astings are plaed on the slab edge (X = ). If the staking is restrited to a ertain short distane from the edge (X > ), these stresses are signifiantly redued. The Chilean Port Authority requested an evaluation of the alternative to restriting the Q.. :I 6 C/) C/) CD iii 5.! 4 CD I- Legend 1) k= 5-4 MN/m 1 } ' ) k= 95 MN/m 1 FREE EDGE 3) k= 136 MN/m 1-4) k= 136 MN/m 1 -JOINTED EDGE 5) k= 5-4 MN/m 1 6) k= 95 MN/m 1 CORNER 7) k= 136 MN/ NOTE: Slab Thikness {m) FIGURE 7 Tensile stress versus pavement thikness for front lift truk. MN/m3 = 3.68 pi MPa = 145 psi m =.394 in

6 16 TRANSPORTATION RESEARCH RECORD Legend WHEEL LOAD = 342 kn 1) k= 54 MN/rn' 9 2) k= 95 MN/rn' } FREE EDGE 3) k= 136 MN/m 1 ""'"' 8 4) k= 136 MN/m 1 - JOINTED EDGE a. WHEEL LOAD = 196 kn 5) k= 136 MN/m JOINTED EDGE 7 en en G> L.. iii 6 iii G> NOTE: Slab Thikness (m) MN/m3 = 3.68 pi MPa = 145 psi m =.394 in kn = lb FIGURE 8 Tensile stress versus pavement thikness for straddle arrier. ontainer staking at slab edges. This required that the appropriate distane (X) be determined to ensure that the edge stresses would not exeed 2965 kpa (43 psi). The H51 program was used for this evaluation, and the results are shown in Figure 9. For example, Line 3 represents the stress-thikness relationship that ours when the ontainer spport is loated 4.6 m (16 in.) from the edge. This line yields edge tensile stresses of 27 and 283 kpa (3 and 41 psi) for slab thiknesses of 41 and 3 m (16 and 12 in.), respetively. Line 1 represents the worst ase (X = ), in whih these tensile stresses reah their maximum value. Aording to Figure 9, with the existing slab thikness of 3 m (12 in.) the stresses will be equal to the allowable stress of 2965 kpa ( 43 psi) when the ontainer stak is loated 38 m (15 in.) from the slab edge. The poliy of ontrolling the ontainer stak loation was found more eonomial and pratial than strengthening the existing pavement struture with a minimum onrete overlay of 18 m (7 in.). Front Lift Truk As previously evaluated, the required slab thikness for the front lift truk is 45 m (17.5 in.). Beause this handling equipment is going to be used only in defined and hannelized lanes, only a limited area needs to be strengthened (3). The reommendations speified that in these areas a monolithi onrete overlay of 15 m (6 in.) be onstruted on solid and unraked existing slabs only and that the raked and shattered slabs be replaed with new slabs 45 m (17.5 in.) thik. Straddle Carrier No strengthening was reommended for the areas in whih the lighter equipment is used [195 kn (44, lb) per wheel load]; the unraked slabs 3 m (12 in.) thik were judged adequate. On the other hand, it will be neessary to onstrut an 8-m (3-in.) monolithi onrete overlay for the straddle arrier with a load of 342 kn (77, lb) per wheel (based on a minimum overlay thikness) and onstrut slabs 35 m (14 in.) thik for the new pavement. EARTHQUAKE CONSIDERATIONS The massive earthquake that took plae on Marh 3, 1985, in the entral region of Chile had a surfae wave magnitude of Ms = 7.8 on the Rihter sale. Its epienter was loated in the Paifi Oean approximately 39 km (24 mi) from the port of San Antonio. The earthquake intensity was rated as VII and VIII on the modified Meralli sale at the ports of Valparaiso and San Antonio, respetively. The damage to the port failities was extensive (3). Large settlements ourred in bakfill and pavement areas where loose sandy deposits liquefied and some existing pavement areas were destroyed. Liquefation risk analysis was onduted on the basis of the proedure desribed previously (11,12), and the results are presented in Figure 1. The ritial envelope shown is a onvenient method for evaluating liquefation potential based on SPT N-values for a large number of soil borings performed in the sandy hydrauli fill deposits before and after the earth

7 Greenstein and Poran ::::E... Cl) Cl) G> L.. ;;.!! ;; G> t ""' "" legend 1) X= 2) X= 3.5 m... 3) X= 4.6 m ""' 4) X= 5.8 m I Note: k= 135 MN/rrfS for all o- f'... "" """' I -... <D r "'--- --r-- ---t r-(j) r-- -1;v , Thikness of onrete slab (m) NOTE: MN/m3 = MPo = 145 psi 1 m =.394 in pi FIGURE 9 Stress-thikness relationship of a jointed edge for ontainer stak load. quake. The limits indiated are based on the range of PGA values reorded at the port of San Antonio during the Marh 3, 1985, earthquake (1,2). The earthquake design onsidered for the ports is expeted to result in PGA values within this ritial range. The range shown on the left side of Figure 1 is the lower limit. It orresponds to sandy soils in whih liquefation is likely to our. The range loated between the two limits is defined as the ritial range or the zone of unertainty. This ritial range orresponds to PGA values of.67 and.43 g for the upper and lower limits, respetively. The upper limit may be applied to sandy soils with D 5 larger than.25 mm (.1 in.), and the lower limit may be better suited for silty sands with 15 perent fines. The upper limit in Figure 1 was reommended as the design urve for the minimum required density of the fill material under water level. In the Chilean ports the water' level is approximately 3.95 m (13 ft) from the ground surfae. For example, at a depth of 4.5 and 9 m (15 and 3 ft) from ground surfae, the SPT N-value should be a minimum of 3 and 4, respetively, to resist liquefation during an earthquake similar to the one in These riteria are reommended for hydrauli fill deposits under water level in new rigid pavement areas and in areas in whih existing pavements were badly damaged from liquefation indued by the 1985 earthquake. The damaged pavements will be reonstruted to the new speifiations. Dynami ompation, sand piles, or vibroflotation were reommended as effetive soil improvement methods for these loose sandy deposits (3) to mitigate the risk of liquefation. Reorded SPT N-Value Legend: Crltlal Range SPT Results Before the Marh 3, 1985 earthquake:. Berth 1 After the Marh 3, - Q) 't: :I ti) :I e (!) E.!:.. 1i. Q) 1985 earthquake: Berth 1 Berth 2 Berth 3 NOTE: 1 m = ft FIGURE 1 Critial liquefation range for sandy soils in the Port of San Antonio.

8 18 In addition, it was shown (2) that loose sandy fill above the water level may also undergo onsiderable settlement during strong earthquakes. Therefore, it was reommended that the fill material above water level be ompated to a minimum of 95 perent of AASHTO-T SUMMARY AND CONCLUSIONS 1. A rational methodology for rigid pavement design was developed for the Chilean Port Authority. Tensile stressthikness relationships were omputed at slab edge and orner for various levels of omposite modulus of subgrade reation and representative loads assoiated with ontainer operations. Two omputer programs were used for this evaluation. Generally, it was onluded that edge loading governs pavement thikness. 2. The representative design loads used in this analysis were ontainer stak astings, front lift truk, and straddle arrier. The loads were omputed on the basis of Chilean speifiations with the proedures outlined (6). A total load of 514 kn (58 tons) was used for a stak of three ontainers with ontat pressure of 58 kpa (737 psi) and a ontat area of 289 m 2 (44.8 in. 2 ). The front lift truk was onsidered with two dual wheel assemblies, a wheel load of 246 kn (55, lb), and ontat pressure of 783 kpa (113.6 psi). Two types of straddle arriers were onsidered with wheel loads of 195 and 342 kn ( 44, and 77, lb) and ontat pressure of 177 and 783 kpa (156.2 and psi), respetively. 3. Design harts of required slab thikness that are based on load repetitions during the design life are presented. It was onluded that a slab 3 m (12 in.) thik is adequate if the ontainer staking areas are arranged in suh a way that the astings are restrited to a minimum distane of 38 m (15 in.) from the edges of the slabs. This arrangement will result in substantial savings in the new pavement areas and will not require overlays on the existing ones. A rigid pavement 45 m (17.5 in.) thik will be required in the hannelized areas of front lift truk operations. The straddle arrier with a 195-kN (44,-lb) wheel load will require slabs 3 m (12 in.) thik. However, the heavier straddle arrier with 342-kN (77,-lb) wheel load will require a minimum overlay of 8 m (3 in.) on existing slabs, for a total of 38 m (15 in.), and a thikness of 35 m (14 in.) for new pavements. 4. Deep soil improvement and densifiation were reommended to minimize liquefation settlements and pavement failures. The liquefation risk evaluation proedure is based on SPT N-values. For the pavement areas, a minimum N value is speified for any given depth of the sandy fill material below water level. Dynami ompation, vibroflotation, or TRANSPORTATION RESEARCH RECORD 1388 sand piles were reommended for deep soil improvement. Conventional ompation was also reommended to minimize subgrade settlement of loose sandy soils above water level. REFERENCES 1. C. J. Poran, J. Greenstein, and L. Berger. Geotehnial Problems in Port Design in Chile. In ASCE Speialty Conferene Pro., Ports '89, Boston, May 1989, pp C. J. Poran, J. Greenstein, and L. Berger. Earthquake Indued Settlements in Port Failities in Chile. Pro., 12th International Conferene on Soil Mehanis and Foundation Engineering, Rio de Janeiro, Brazil, Vol. 3, Aug. 1989, pp Louis Berger Intemational-lneon. Development Program of Ports of the 5th Region and Feasibility, 1st Stage. Ministry of Transportation and Teleommuniation of Chile and the World Bank, M. Meletiou and J. Knapton. Container Terminal Pavement Management. UNCT AD Monographs on Port Management: Monograph 5, Report UNCT AD/SHIP/494(5) GE /6982E, M. Meletiou. The Task of Container Terminal Pavement Seletion. In ASCE Speialty Conferene Pro., Ports '89, Boston, May 1989, pp The Strutural Design of Heavy Duty Pavements for Ports and Other Industries. British Port Assoiation, London, England, M. T. Darter. WESTY V4.-Computerized Version of the Westergaard Equations for Interior, Edge, and Corner Stresses and Defletions. ERES Consultants, In., Champaign, Ill., May Airport Pavement Design and Evaluation. Advisory Cirular AC 15/532-6C. FAA, U.S. Department of Transportation, De W. C. Kreger. Computerized Airraft Ground Floatation Analysis Edge Loaded Rigid Pavements. Researh Report ERR-FW-572. General Dynamis, Jan A. M. loannides, M. R. Thompson, and E. J. Barenberg. The Westergaard Solutions Reonsidered. Presented at 64th Annual Meeting of the Transportation Researh Board, Washington, D. C., Jan H. B. Seed, I. M. Idriss, and I. Arango. Evaluation of Liquefation Potential Using Field Performane Data. Journal of the Geotehnial Engineering Division, ASCE, Vol. 19, No. 3, Marh 1983, pp H. B. Seed, K. Tokimatsu, L. F. Harder, and R. M. Chung. The Influene of SPT Proedures in Soil Liquefation Resistane Evaluation. Report UBC/EERC-84/15. National Siene Foundation, Washington, D.C., J. Greenstein. Using Nondestrutive Testing in the Semi-Arid Zone of Peru. In Transportation Researh Reord 1137, TRB, National Researh Counil, Washington, D.C., Rigid Pavements for Airfields Other than Army. Report T.M and Report AFM 88-6, Chapter 3, U.S. Army, U.S. Air Fore, Aug R. G. Pakard. Design of Conrete Airport Pavement. Portland Cement Assoiation, Publiation of this paper sponsored by Committee on Rigid Pavement Design.