Factors Affecting Unconfined Compressive Strength of Salt-Lime-Treated Clay

Transcription

1 17 anything approaching this rating beyond 3 or 4 years. CONCLUSIONS It appears that mch of the objectionable differentials in the Pierre shale that cased roadsrface roghness in the past have been alleviated. 1. It is possible to achieve relatively good density and moistre control by designating the nmber of roller passes and making freqent moistre tests. 2. The control of special nderctting and soil selection can be managed by the se of specially trained crews assigned to the work. 3. xtreme warping and heaving of the sbgrade over narrow falt lines appears to be redced by deep nderctting of expansive shale and replacement of it with soil having a lower liqid limit. 4. At this time, the ridability of the srfacing is extremely good and better than on similar highways constrcted throgh Pierre shale withot deep nderctting and rigid control of compaction efforts and moistre application. 5. The se of lime treatment in the pper.15 m (6 in) of the sbgrade and a limetreated base is effective in preserving the moistre content of the sbgrade over an extended period of time, which contribtes to improved ridability. 6. At the present time, the maintenance costs for the highways listed in this report are very low; however, longrange maintenance costs are time dependent. Althogh the methods discssed in this report will not be completely effective in correcting the differentials sally encontered in Pierre shale, the indications, after 5 to 8 years, are that the ridability will generally be mch better over a longer period of time at lower maintenance costs. RFRNCS 1. Mineral and Water Resorces of Soth Dakota. U.S. Geological Srvey, Committee Report to 88th Congress, 2nd Session, 1964, pp Treatment of xpansive Soils for 19 in Soth Dakota. WoodwardClydeShemond and Associates, Denver, May Review and Comments on WoodwardClyde Report. H. Allen, Bethesda, Md Jne Moistre and Density Control on I9 Projects I9 (34) to 19(55) ( ). R. Wold, Pierre, S.D Resm Repts Pblication of this paper sponsored by Compaction and Stabilization Section. Factors Affecting Unconfined Compressive Strength of SaltLimeTreated Clay Johnny M. Ozier,* Law ngineering Testing Company, Birmingham, Alabama Raymond K. Moore, Department of Civil ngineering, Abrn University Statistical procedres were sed to analyze the effects of salt content, lime content, cring time, cring temperatre, moldingwater content, and soil type on the nconfined compressive strength of compacted specimens. A modified centralcomposite, secondorder, rotatable experiment design and analysis of variance techniqes were sed to determine the significant main effects, crvilinear effects, and linear interactions at an alpha level of 1 percent. The following effects and interactions were significant at an alpha level of 1 percent: (a) main effectssalt content, lime content, cring temperatre, cring time, moldingwater content, and soil type and (b) interactionslime content and salt content, lime content and cring temperatre, lime content and moldingwater content, salt content and cring temperatre, cring temperatre and moldingwater content, cring temperatre and soil type, cring time and soil type, and lime content and salt content and cring temperatre. An engineering interpretation of each is given. A coded mltiple regression model was developed to the estimate nconfined compressive strength in terms of the statistically significant main effects and interactions. A combination stabilization strategythe se of salt in conjnction with the lime treatment of clay soilhas been stdied to determine whether small amonts of sodim chloride can be sed to accelerate the stabilization phase of the limesoil treatment process. Previos research by Mateos and Davidson (1) indicated that small amonts of sodim chloride are beneficial to the limefly ash treatment of Ottawa sand. The relationship between immersed compressive strength and sodim chloride content was parabolic, with maximm strengths at 7, 28, and 12 d cring times at a sodim chloride content of 1 percent. They also reported that 1 percent sodim chloride in conjnction with either calcitic hydrated lime or dolomitic monohydrate lime and fly ash prodced higher compressive strengths than those observed for limefly ashtreated dne sand and friable silt withot sodim chloride. A 6.1 C (43 F) cring temperatre was shown to be detrimental to limefly ashsodim chloride treatment of dne sand. Thornbrn and Mra (2), in a review of the literatre of salt stabilization, havesmmarized several stdies that sed varios inorganic salts with lime and limefly ash stabilization. This review did not note any specific reference to the effects of sodim chloride on the lime treatment of clay, althogh other componds, sch as sodim carbonate, have been sed sccessflly to in

2 18 crease the 28d strength of limetreated clay (3). More iecent investigations by Marks and HaTibUl'ton (4, 5) and by Drake and Halibrton (6) have been spectficay designed to stdy the effects of sodim chloride on the lime treatment of clay soil and have indicated that there is an optimm percentage of salt beyond which frther addition decreases the They also reported that small amonts of salt accelerate formation of the stabilization componds associated with lime treatment. This acceleration of the formation of the pozzolanic componds wold redce the relatively long time periods reqired for the development of the cred strength, which is especially significant in areas with short constrction seasons and a limited nmber of months having sfficiently high soilcring temperatres. The object of this stdy was to develop additional information abot the effects of mixtre design, constrction, and environmental variables, and their interactions on the nconfined compressive strength of sodim chloridelimetreated clay soil. MATRIALS AND SOILS The sodim chloride sed was common, noniodized table sall. The lime sed was a commercial grade, hydrated, highcalcitn lillle, processed to have a maximm particle size of.37 mm (no. 4 sieve). Permian red clay (PRC) is a medim plastic, cohesive soil of marine origin fond in central Oklahoma with a distinctive red color prodced by iron oxide. The PRC sed in this experiment was taken from a depth of approximately 3 m (1 ft) below the grond srface on the Oklahoma State University camps in Stillwater, airdried, and crshed to finer than.42 mm (no. 4 sieve). The mineralogical composition indicated that 5 to 75 percent of the PRC is chlorite, 1 percent is mica, and the remainder is illite and smectite. The Black Belt soils of Alabama are located in a narrow strip rnning east to west throgh the soth central portion of the state and are characterized by a high volmechange potential. The Hoston clay (HC) sed in this experiment was sampled at a depth of 38 to 76 cm (15 to 3 111) in a pastre near Downs, Alabama, airdried, and crshed finer than.42 mm (no. 4 sieve). Hoston clay was created by the decomposition of Selma chalk and marine deposits of the Cretaceos age (7) and is visally identified by its greyyellow color interspaced with modles of calcareos materials and its high plasticity (8). Smectite constittes abot 65 percent of the clay in t1ie Alabama Hoston soils and 3 to 45 percent of the whole soil in the Hoston profile. Kaollite is the second most abndant cla.y mineral, constittng abot 25 perc;ent of the clay fraction. Other clay minerals present are mica, vermiclite, small amonts of qartz, and trace qantities of intergrade chlorite (7), The physical properties of the clays sed are given be: low l.74 and.2 mm =no. 2 and no. 1 sieves respectively). Property PRC HC Specific gravity Liqid limit,% Plastic limit,% Plasticity index, % Percent finer than.74 mm 9 9 Percent finer than.2 mm XPRIMNT DSIGN A modified fivefactor, centralcomposite, rotatable experiment design was sed for both soil types (9). A fll factorial was selected withln th.is experlmenf design so that all main effects, linear interactions, and qadratic effects cold be analyzed. This type of experiment design has been sccessflly sed previosly (1). The factors and levels sed in the experiment are given below (the lime, salt, and moldingwater contents are measred as airdried weight of soil; C = ( F 32)/1.8). Level Factor Lime content Sa It content Moldingwater content Cring ti me, d Cring temperatre, C Before completion of the analysis of variance, the estimates of experimental error obtained from the center points were compared for each soil type to determine whether the variances within the two poplations were homogeneos. The two estimates of experimental error indicated homogeneity and, therefore, the analysis of variance was pooled. Ths, soil type was treated as a sixth variable, and its main effect and all linear interactions involving it as a qantitative variable were analyzed. SPCIMN PRPARATION AND TSTING Lime, salt, and soil were weighed ot in separate containers at predetermined levels to minimize the time reqired for specimen preparation. The compacted specimens were prepared by measring the proper amont of distilled water; selecting the proper preweighed qantities of salt, lime, and soil and dry mixing them; adding the water; and blending by hand ntil a niform appearance was attained. Next, the soil was compacted by sing a Harvard miniatre compaction mold and a scaled model of the ASTM D698 compaction hammer. The specimens were extrded from the compaction mold, weighed, wrapped to minimize moistre loss, identified, and stored at the desired cring temperatre ntil the test day. Immediately before testing, the specimens were removed from their temperatre chambers and weighed. The nconfined compression testing procedre sed a strain rate of 1 percent/ min. The remains of the entire sample were sed to determine its moistre content for the determination of its dry nit weight. STATISTICAL INFRNCS The analysis of variance reslts are given in Table 1. No qadratic effects were fond to be significant at an alpha level of 1 percent. ach significant effect will be individally discssed in the following sections. A mltiple regression eqation to predict the nconfined compression strength in terms of the mixtre, constrction, and environmental variables stdied is presented. Main ffects Salt Content Figre 1 shows that increasing the salt content from 1 to 3 percent decreases the nconfined compxessive strength. Previos research (5) had lnclicated thal an optimm salt content below 3 percent maximizes the nconfined compressive strength obtained in saltlime treatment, and the data in Figre 1 indicate a similar trend. Thornbrn and Mra (2) have reported that ii creasing the salt content of a soil Increases tj1e dry nit weight, and this experiment indicated a simila1 trend. Therefore,

3 19 an increase in dry nit weight cannot be the reason why an increased salt content cased a decreased strength. A more plasible explanation for the lower strengths associated with higher salt contents is that the excess qantity of salt recrystallizes in the cementitios gels, which may disrpt the crystalline strctre of the pozzolanic prodcts and redce the nconfined compressive strength. Lime Content Figre 2 shows that increasing the lime content from 2 to 6 percent increases the nconfined compressive strength. The 2 percent level of lime provides an adeqate qantity of calcim to modify the soil, bt leaves very little for the formation of pozzolanic componds. The 6 percent level provides adeqate calcim for both modification and the formation of strengthprodcing cementitios componds. Cring Temperatre As is shown in Figre 3, increasing the cring temperatre from 4.4 to 43.3 C (4 to ll F) cases a large increase in the nconfined Increased temperatres accelerate the rate of the strengthprodcing chemical reactions between the lime and the soil. The hightemperatre c1 ing prodces large increases in strength (however, the specimens were wrapped and sealed to minimize moistre loss). Cring Time Figre 4 shows that as the cring time is increased from 1 to 3 d, the nconfined compressive strength increases, which illstrates the beneficial effect of longer cring periods. However, sbstantial strengths were developed by the end of 1 d. MoldingWater Content Figre 5 shows that increasing the moldingwater content from 12.5 to 17.5 percent increases the nconfined Becase the specimens were sealed, significant amonts of moistre were not lost dring cring. The lower level of moistre does not provide an adeqate qantity of water for the stabilization reactions; however, the 17.5 percent level of moistre provides the additional water needed for the formation of pozzolanic componds. Soil Type As is shown in Figre 6, the two types of soil sed in this research have significantly different mean nconfined compressive strengths. Becase of differences in clay mineralogy, HC has a mch higher cation exchange capacity and a larger specificsrface area than does PRC. This creates several differences in the lime, salt, and moistre reqirements of the two soils. First, the qantity of lime reqired to modify and stabilize HC is greater than that necessary for the modification and stabilization of PRC. Second, becase of the differences in the specificsrface areas of the two clays and the different water reqirements reqired to develop the diffsed doble water layers, it wold be expected that HC wold reqire more molding water than does PRC, which has a lower specificsrface area. Therefore, at identical moistre contents, more free water will be available in PRC to participate in the stabilization reactions than will be available in HC. The confonding effect of the dry nit weight is also present in these data. The mean dry nit weight of the PRC specimens was 1514 kg/ m 3 (94.6 lb/ft 3 ) as compared to 1322 kg/ m 3 (82.6 lb/ ft 3 ) for the HC specimens. The difference in dry nit weights will contribte to the increased nconfined compressive strengths observed in the PRC as compared to the HC. Linear Interactions Lime Content and Salt Content Figre 7 illstrates one of the most important interactions investigated in this research: A 2 percent lime content and a 3 percent salt content prodces slightly higher nconfined compressive strengths than does a 2 percent lime content and a 1 percent salt content; however, a 6 percent lime content and a 1 percent salt content prodces a mch higher nconfined compressive strength than does a 6 percent lime content and a 3 percent salt content. There are several possible explanations for this alparent contradiction. The lower level of lime (2 percent) is very nea1 the qantity reqired for modification of the soils; therefore, very little if any, calcim will be available for the prodction of pozzolanic componds. This sggests that the qantity of salt added wold far exceed the qantity of lime available for stabilization of the soil. This excess salt cold then only fill the voids, adding strength throgh increased density, bt not throgh chemical reactions with the soil itself. Also, if the lime content is low, the salt is present in mch too great a qantity to act solely as a catalyst in the formation of pozzolanic componds. At a 6 percent lime content, the decrease in strength of the soil with a corresponding increase in the level of salt strongly sggests that not only is there an optimm qantity of salt, bt also that excessive salt can be detrimental to the development of nconfined Lime Content and Cring Temperatre At a lime content of 2 percent, an increase in cring temperatre cases an increase in strength (Figre 8), and at a lime content of 6 percent, a change in the temperatre from 4.4 to 43.3 C (4 to 11 F) cases a larger increase in the strength of the specimens becase the chemical reactions involved in the formation of the pozzolanic componds are greatly accelerated at the higher temperatre. The lime content of 2 percent spplies very little calcim for the formation of these componds after the modification reactions have taken place. A lime content of 6 percent spplies a srpls of calcim after modification that is available for the chemical reactions that increase the nconfined Lime Content and MoldingWater Content At a 2 percent lime content, an increase in moldingwater content from 12.5 to 17.5 percent increases the nconfined compressive strength (Figre 9). At a 6 percent lime content, the increase in strength as the moldingwater content is increased is larger than that at a 2 percent lime content. This interaction shows the positive effect of increased molding water and lime contents on the nconfined compressive strength. The percent moldingwater content provides more of the water for the reqired development of pozzolanic componds when sfficient calcim is present.

4 2 Salt Content and Cring Temperatre Figre 1 shows that increasing the salt content from 1 to 3 percent at a cring temperatre of 4.4 C (4 F) prodces little change in the nconfined compressive strength. The same increase in salt content at 43.3 C Table 1. Analysis of variance for nconfined (11 F) prodces a decrease in the nconfined compressive strength. The nconfined compressive strengths for each salt content were higher at a 43.3 C (11 F) cring temperatre than at a 4.4 C (4 F) cring temperatre, again becase the chemical reactions are accelerated at a higher temperatre. The decrease in the nconfined compressive strength when the salt content is increased frther illstrates the detrimental effect of excessive salt. Sorce of Variation Degree of Freedom Mean Sqares F Vale' Significance Level() Cring Temperatre and Cring Time Total 63 Salt content 1 Lime content I Cring temperatre 1 Cring time 1 Moldingwater content l Soll type l Lime content and salt content Lime content and cring temperatre Lime content and moldingwater content l Salt content and cring temperatre Cring temperatre and cring time Cring temperatre and moldingwater content Cring temperatre and soil type Cring time and soil type Lime content and salt content and cring temperatre 1 Residal 48 Center points As shown in Figre 11, at a cring temperatre of 4.4 C (4 F), there is little change in the nconfined compressive strength as the cring time is increased from 1 to 3 d, bt at a cring temperatre of 43.3 C (11 F), an Figre 3. ffect of cring temperatre on nconfined c:..; 5 :: 25 Note: 1 kpa =.145 lbf/in; C = ( F 32)/1.8. 'Critical Fvale: Fil, 11,.1) = Figre 1. ffect of salt content on nconfined Cring Temperatre, c 75 Note: 1kPa=.145 lbf/in. f 5 :.c:. f 25 g ::: l. 3. Salt Content, % Figre 2. ffect of lime content on nconfined 1 Figre 4. ffect of cring time on nconfined 75 Note: 1 kpa =. 145 lbf/jn2; C = ( F 321/1.B. <o.. 5 U.c:. f 25 :: 1 3 Cring Time, Days Figre 5. ffect of moldingwater content on nconfined 75 f o,, 15.c: r '. 5 C:V 8 25 c: :: Note: 1 kpa =.145 lbf/in f ff.c: c 5 C:.::; f.. V c: :: Note: 1 kpa =. 145 lbf/in Molding Water Content, %

5 21 increased nconfined compressive strength is observed when the cring time is increased from 1 to 3 d. This indicates that little chemical activity takes place at 4.4 C (4 F) for the two ci ing times sed and that both increased cring time and increased cring temperatre increase the nconfined Figre 6. ffect of soil 1 type on nconfined compressive strength. 75 <1J a. 5.c +. <1J O t 25 Vl ::: Note: 1 kpa =.145 lbf/in2. HC Soil Type PRC Cring Temperatre and MoldingWater Content As shown in Figre 12, at 4.4 C (4 F), there is a small increase in the nconfined compressive strength with increased moistre content. However, the nconfined coml?ressive strength s bstantially increas es at a 43.3 C (11 F ) cw ing t emperatre when the moldingwater content is increased from 12.5 to percent. As p1 evios ly discssed, at 4.4 C (4 F), the for mation of cementitios componds is slower than at 43.3 C (11 F). A combination of high levels of moldingwater content and temperatre prodces increased nconfined compressive strength, which illstrates the need for water in the prodction of the pozzolanic prodcts. Cring Temperatre and Soil Type Figre 13 shows that at 4.4 C (4 F), PRC has a slightly greater nconfined compressive strength than does HC; however, at 43.3 C (11 F), the difference is large. The difference in the nconfined compressive strengths of the two soils can be partially explained by the differ Figre 7. ffect of interaction between lime content and salt content on nconfined comoressive strength. Figre 9. ffect of interaction between lime content and moldingwater content on nconfined a..<.c +. O <1J 1 Vl 75 ;;::: ::: 5 25 Note: 1kPa=.145 lbf/in a..< 1 O +. Vl <1J 75 c. <1J ;;::: ::: 5 25 Note: 1 kpa =.145 lbf/in Figre 8. ffect of interaction between lime content and cring temperatre on nconfined Figre 1. ffect of interaction between salt content and cring temperatre on nconfined Note : 1kPa =.145 lbl/in'. ; Note: 1 kpa =. 145 lbf/in'; 1 C = ( F 32)/1.8. en Vl 75 c :::. oi..; ; 1 +. O Vl <1J 75 5 <1J ;;::: 25 ::: l.o Sa l t Content, %..; 3.

6 22 ence in their dry nit weights. That difference shold explain the difference in their nconfined compressive strengths at low temperatres, even when chemicals have been added, becase vh tally no strengthprodcing stabilization i eactios take place at 4.4 C (4 F). At 43.3 C (11 F), the difference between the strengths of the two soils can no longer be explained withot considering their mineralogical properties. Becase HC cold very well have a specificsrface area for to five times larger than that of PRC, one wold expect that it wold reqire mch more chemical to treat HC than is reqired for PRC. Hence, the PRC wold have a larger increase in the nconfined compressive strength at the higher cring tempe1 atre for the levels of lime content, moistre content, and salt content sed. Cring Time and Soil Type As is illstrated in Figre 14 for a cring time of 1 d, PRC develops a higher nconfined compressive strength than does HC. This is also tre for a cring time of 3 d, and the difference in strength of the two clays is mch greater. This interaction strengthens the postlat e that the qantity of lime reqired to stabilize HC is greater than that reqired to stabilize PRC and that soil type is confonded with dry nit weight. Lime Content, Salt Content, and Cring Temperatre At a cring temperatre of 4.4 C (4 F), the average nconfined compressive strength increases as the rne content is inc1' eased from 2 to 6 percent and as the salt content is decreased from 3 to 1 percent (Figre 15). These increases are very small, bt tl\ere is a mch larger average strength increase at 43.3 C (11 F) as the lime content is increased from 2 to 6 percent and the salt content is decreased from 3 to 1 percent. This interaction illstrates a response srface among several of the sggested hypotheses. First, lower temperatres retard and higher temperatres accelerate the formation of strengthprodcing componds. Second, excessive qantities of salt appear to be detrimental to the stabilization process. The espos e srface created by the 43.3 C (11 F) cring temperatre slopes toward higher percentages of lime and lower percentages of salt for the development of higher nconfined compressive strengths. The major inference from this effect is Figre 11. ffect of interaction between cring temperatre and cring time on nconfined m g,. V) 125 = 1 75 c. 5 O 1! 25 g = Note: 1 kpa =. 145 lbf/in2; 'C = ( F 32)/1.8..; 1 Cring Ti me, Days.; 3 Figre 13. ffect of interaction between soil type and cring temperatre on nconfined.,:. en. V c. e 'O 5 c ;;: = 25 Note: 1 kpa =.145 lbf/in2; C = lf 32) /1.8. HC. Soil Type.; PRC Figre 12. ffect of interaction between cring temperatre and molding water content on nconfined Figre 14. ffect of interaction between soil type and cring time on nconfined m..,_ 125 = 1 V) 75,_ c_ O 1! 5 25 g = Note: 1 kpa =. 145 lbf/in2; C = ( F 32)/1.8. '?,, M.; Molding Water Content, %.; M =. Q).,_ IZ5 1 V) Q),_ c_ e 75 O 5 1! ;;: = 25 Note: 1 kpa =. 145 lbf/in'. ::c l 1 Cring Time, Oays ::c 3

7 23 Figre 15. ffect of interactions among I ime content, salt content, and cring temperatre on nconfined c i 1 O 75 c 5 :5 25 Note: 1 kpa.145 lbf/in'; C = ( F 32)/ ; that there is an optimm salt content that maximizes nconfined compressive strengths in limetreated clays and that this is probably less than 3 percent if sfficient lime is present for the development of pozzolanic componds. Prediction qations A mltiple linear regression was sed to generate a coded prediction eqation that inclded all of the main effects, twofactor interactions, and threefactor interactions fond to be significant at an alpha level of 1 percent. S = A B l 8C + I F 11. IOAB 8.3AC BC IB + 8.2CD C CF+7.12DF7.84ABC where S = nconfined compressive strength, A = salt content, B = lime content, C = cring temperatre, D = cring period, = molding water content, and F = soil type. The coded levels given in Table 1 are sed. The standard error of estimate of the eqation is kpa (24.9 lbf/in 2 ), and R 2 is The eqation has a lack of fit at an alpha level of 2. 5 percent and is valid only for predictive prposes within the factor space stdied, which is a fnction of the factors and levels stdied. Any attempt to extrapolate beyond the factor space with regression eqations may introdce conditions that were not investigated and reslt in erroneos predictions. CONCLUSIONS All six factors stdied in this research were fond to be significant as main effects at an alpha level of 1 percent with respect to the nconfined No qadratic effects were fond to be significant; however, eight twofactor linear interactions and one threefactor linear interaction were significant at an alpha level of 1 percent. Those main effects and interactions were 1. Main effects: salt content, lime content, cring temperatre, cring time, moldingwater content, and soil type and (I) 2. Interactions: lime content and salt content, lime content and cring temperatre, lime content and moldingwater content, salt content and cring temperatre, cring temperatre and cring time, cring temperatre and moldingwater content, cring temperatre and soil type, cring time and soil type, and lime content, salt content, and cring temperatre. ach of the effects and interactions had a positive regression coefficient except salt content, lime content and salt content, and salt content and cring temperatre. A positive coefficient implies that the dependent variablenconfined compressive strengthis increased as the qantity of the independent variable is increased. For the range of the variables sed in this research, the nconfined compressive strength was increased by 1. Increased lime content, 2. Decreased salt content, 3. Increased cring temperatre, 4. Increased cring time, 5. Increased moldingwater content, and 6. Using PRC rather than HC. The reslts of this experiment are indicative of the complexity involved in combination stabilization processes. RFRNCS 1. M. Mateos and D. T. Davidson. Frther valation of Promising Chemical Additives for Accelerating Hardening of SoilLimeFly Ash Mixtres. HRB, Blletin 34, 1961, pp T. H. Thornbrn and R. Mra. Stabilization of Soils With Inorganic Salts and Bases: A Review of the Literatre. HRB, Highway Research Record 294, 1969, pp C. C. Ladd, Z. C. Moh, and T. W. Lambe. Recent SoilLime Research at the Massachsetts Institte of Technology. HRB, Blletin 262, 196, pp B. D. Marks and T. A. Halibrton. A SaltLime Soil Stabilization Feasibility Stdy. School of Civil ngineering, Oklahoma State Univ.; Oklahoma Research Program Project Agreement No. 6, Final Rept B. D. Marks and T. A. Halibrton. Acceleration of LimeClay Reactions With Salt. Jornal of the Soil Mechanics and Fondations Division, Proc ASC, Vol. 98, No. SM4, April 1972, pp J. A. Drake and T. A. Halibrton. Accelerated Cring of SaltTreated and LimeTreated Cohesive Soils. HRB, Highway Research Record 381, 1972, pp. 119.

8 24 7. Chemical, Mineralogical, and ngineering Properties of Alabama and Mississippi Black Belt Soils. Alabama and Mississippi Agricltral xperiment Stations and Soil Conservation Service; Sothern Cooperative Series No. 13, Abrn Univ Abrn, Ala Feb Soil Srvey of Macon Conty, Alabama. U.S. Department of Agricltre and Alabama Department of Agricltre and Indstries, Series 1937, No. 11, W. B. Cochran and G. M. Cox. Some Methods for the Stdy of Response Srfaces. xperimental Designs, Wiley, New York, 2nd d R. K. Moore, T. W. Kennedy, and J. A. Kozh. Tensile Properties for the Design of LimeTreated Mixtres. HRB, Highway Research Record 351, 1971, pp Pblication of this paper sponsored by Committee on Chloride Stabilization. *Mr. Ozier was at the Department of Civil ngineering, Abrn University, when this research was performed. Laboratory Stdy of the ffectiveness of Cement and of Lime Stabilization for rosion Control George Machan,* L. R. Sqier, Inc Lake Grove (Portland), Oregon Sidney Diamond, School of Civil ngineering, Prde University dmond Leo,* Geo Testing, Inc San Rafael, California Soils ranging in textre from sand to heavy clay can be rendered effectively resistant to the soil erosion cased by raindrop impact by treatment with as little as 1 percent portland cement or hydrated lime. ro sion resistance was evalated in a standard rainstorm seqence in which 8.2 cm (3.25 in) of rain was applied for 1 h on each of two sccessive days. Compacted bt otherwise nstabilized soils lost 1 to 2.5 g/cm 2 (.14 to.35 lb/in 2 ) of exposed srface. eqivalent to 45 to 11 tons/acre, in!his standard test. Incorporation of stabilizer and appro priate cring before exposre decreased this.erosion loss to abot.11 g/cm 2 (.16 lb/in 2 l. eqivalent to 6 tons/acre, for flly compacted specimens. Cementtreated soils tested after only modest compaction maintained their erosion resistance, bt limetreated soils were adversely affected by redced levels of compaction. These laboratory test reslts do not necessarily predict practical field performance, becase the et fects of rnning water erosion, of the incomplete mixing characteristic of field incorporation of stabilizers, and of cycles of temperatre change, wetting and drying, and freezing and thawing have not been tested. Accelerated soil erosion at constrction sites is a serios envirornental problem in many parts of the United States. The present methods of erosion control are not niformly effective. For many years, soils have been stabilized for se as highway or airfield sbgrade materials by treatment with portland cement or hydrated lime. The present work is based on the idea that treatment of soils exposed on constrction sites with small amonts of cement Ol' lime might be sefl in p1 eventing erosion. The se of these stabilizers wold be relatively expensive in terms of the sal costs of erosion control, bt it might provide effective erosion resistance and be a sefl alten1ative to conventional methods, particlarly where erosion may lead to especially harmfl or serios conseqences. VALUATION MTHODS Characterizing the erosion resistance of a particlar soil or treated soil is, in the final analysis, a fieldscale problem. Neve1 theless, laboratory assessment based on measrement of the soil lost in controlled artificialrainstorm tests shold be helpfl in screening the effectiveness of varios kinds of erosioncontrol treatments on varios soils. The present paper reports the reslts of tests on a range of Indiana soils treated with small amonts of hydrated lime or portland cement, compacted, and cred to varios degrees before exposre to a standardized laboratory rainstorm seqence and discsses the extent to which sch laboratory reslts might reflect field effectiveness. The apparats sed measred the resistance of 1.2 cm (4in) diameter test specimens exposed to a standard rainstorm seqence of app1 oximately 7.6 cm (3 in) of rain delivered in 1 h, followed by a 23h i est period, and then by another r ain cycle of the same kind. qipment qirks prevented the delivery ot exactly 7.6 cm (3 inj of rainfall in 1 h, and 8.2 cm (3.25 inhvas standardized on. The rainfall device delivered droplets of niform size and spatial distribtion that had a kinetic energy approximating that of the average drop in natral storms of the same intensity. In the tests, the sw faces of the specimens were maintained a a 5 angle to lhe horizontal to prevent ponding. Three replicate specimens were exposed simltaneosly, and the actal amont of rainfall delivered was monitored by rain gages between the specimens. The soil removed from each specimen was collected and dried and weighed for the qantitatlve assessment of the atnont of e1 osion. rosion was expressed in terms of weight loss per nit area of exposed specimen srface. The apparats and test procedres have been described previosly(_!_). SOILS AND STABILIZRS USD For natral Indiana soils were chosen to provide examples of a fll range of textral classes from a heavy, montmorillonitebearing clay soil to a predominantly sandy soil with only abot 3 percent clay. They are described in Table 1.