Transitional behaviors in well-graded coarse granular soils. Associate professor, State Key Laboratory of Coal Mine Disaster Dynamics and Control,

Transcription

1 1 2 Tranitional behavior in well-graded coare granular oil 3 4 Yang Xiao, S.M.ASCE 1, M. R. Coop 2, Hong Liu 3, Hanlong Liu 4 and Jinghan Jiang Yang Xiao, S.M.ASCE Aociate profeor, State Key Laboratory of Coal Mine Diater Dynamic and Control, Chongqing Univerity, Chongqing 43, China; Reearcher, China Key Laboratory of New Technology for Contruction of Citie in Mountain Area (Chongqing Univerity), Minitry of Education, Chongqing, 445, China; Aociate profeor, School of Civil Engineering, Chongqing Univerity, Chongqing, hhuxyanon@163.com 2. M. R. Coop Chair Profeor, City Univerity of Hong Kong, Hong Kong. mrcoop@cityu.edu.hk 3. Hong Liu Ph.D. School of Civil Engineering, Chongqing Univerity, Chongqing, 445, China. liu61523@163.com 4. Hanlong Liu Profeor and Chair, College of Civil Engineering, Chongqing Univerity, Chongqing, 445, China. cehliu@hhu.edu.cn 5. Jinghan Jiang Lecturer, School of Civil Engineering, Nanjing Intitute of Technology, Nanjing, , China. jinghanjiang@yahoo.com

2 Abtract: Drained triaxial compreion tet were carried out for a well-graded coare granular oil (CGS) to invetigate the effect of the initial pecific volume on the location of the critical tate line (CSL). A family of parallel CSL in the v ~ log p plane wa oberved for the well-graded CGS, indicating that it exhibited tranitional behavior. The degree of tranitional behavior wa quantified from the relationhip between the intercept of the CSL and the initial pecific volume, giving a value of.59, which indicated a ubtantially tranitional behavior. The obervation of the CSL pattern in the CGS illutrated that tranitional behavior could be extended to large-ized granular oil, beyond the uual tranitional oil that have been oberved o far, which generally have grading between thoe of clean and and platic clay Keyword: coare granular oil; tre-train relationhip; critical tate line; pecific volume; tranitional behavior 2

3 Introduction Clean and can be decribed within a framework of critical tate imilar to that for clay (Been and Jefferie 1985). Their normal compreion line (NCL) and critical tate line (CSL) are unique. However, more recent reearch ha identified that many oil exhibit a tranitional mode of behavior, which cannot be decribed within a imple critical tate framework. Thee tranitional oil, uch a gap-graded oil (Martin et al. 21; Ferreira and Bica 26), well-graded ilty clay (Nocilla et al. 26) and well-graded and (Altuhafi et al. 21; Altuhafi and Coop 211), have gradation and mode of behavior between that of clean and and platic clay. The ditinct feature of tranitional behavior i that unique NCL and CSL cannot be identified (Martin et al. 21; Ferreira and Bica 26; Nocilla et al. 26). Martin et al. (21) found that the compreion curve in oedometer tet of the gap-graded Botucatu reidual andtone did not converge to a unique NCL even though the tre wa up to 6 MPa. Ferreira and Bica (26) then confirmed that convergence to a unique NCL could till not be oberved even if the compreion wa taken to 24MPa, and alo that recontituted ample of the oil did not define a unique CSL. Nocilla et al. (26) pointed out that tranitional behavior wa not confined to gap-graded oil a they oberved that their well-graded clayey ilt alo howed tranitional behavior with non-unique NCL and CSL. For well-graded glacial ediment, Altuhafi et al. (21) identified that the compreion path did not converge to a unique NCL, but that a unique CSL wa oberved, uggeting that whatever fabric of the oil that caued the non-convergence during compreion could be detroyed during hearing. Shipton and Coop (212) oberved that non-convergent 3

4 compreion behavior tended to exit in oil of mixed grading and mineralogy, while Shipton and Coop (215) found that the ample preparation method, overconolidation, tre level and fine platicity did not affect the tranitional mode of a and with fine, although the fine platicity could influence the degree of thi tranitional behavior. Ponzoni et al. (214) propoed two parameter to quantify the degree of non-uniquene of the NCL and CSL. Thee oil exhibiting the tranitional behavior have gradation between thoe of clean and and platic clay. Whether or not thi tranitional behavior could be extended to other larger-ized granular oil ha not previouly been tudied. The main objective of the current tudy wa therefore to invetigate the tranitional behavior of a well-graded coare granular oil (CGS) through a erie of drained triaxial tet, invetigating in particular the CSL pattern and in addition quantifying the degree of the tranitional behavior through the parameter P defined by Ponzoni et al. (214). The poible reaon for thi tranitional behavior are alo dicued Triaxial compreion tet Triaxial compreion tet were conducted on a well-graded CGS from the wetern region of China. The CGS i widely ued in rockfill-dam, railway and pavement engineering in China. The main mineralogy of the CGS i andtone. Fig. 1 how the grain ize ditribution (GSD) with a maximum ize of 6 mm. The grain hape of the CGS i characterized by the percentage of the flat, elongated and flat-elongated particle according to ASTM (21), which wa found to be 9.5%. The uniformity and curvature coefficient are calculated a 5.53 and Conequently, the CGS with a fine content of 1.8% i categorized a a well-graded 4

5 gravel. Fig. 1 how that the grading deviate greatly from thoe of the typical ilty oil (Nocilla et al. 26; Ponzoni et al. 214) which exhibited tranitional behavior. The tet were conducted through a large-ize conventional triaxial apparatu. The height and cylinder diameter of the pecimen were 6 mm and 3 mm, repectively. The value of the initial pecific volume v ued in the tet were mainly divided into four group, i.e., 1.187~1.193, 1.242~1.245, 1.283~1.286 and 1.315~ The required initial dry denitie 87 = G v, where d could be obtained from d w 3 w =1 1 kg/m3, and the pecific 88 gravity G of the CGS i 2.69, giving average value of d for the four group of 2.26, , 2.1 and 2.4 kg/m 3. The required amount of material determined for the deired denity wa divided into five part for compaction, each layer being compacted uing an automatic vibrator with a 7 Hz frequency, but uing different compaction time to obtain different initial pecific volume. The pecimen were aturated, obtaining B-value over.96. A wide range of confining preure (.2~1.6 MPa) wa ued for each group, and after applying the confining preure the pecimen were heared under drained condition with an axial-diplacement rate of 1 mm / min. The volume change of the pecimen wa meaured from the volume of the expelled water. The tet were ceaed at an axial train of 15%, which wa the maximum in thi large-ize apparatu, at which the ample howed a light-bulging failure mode without any obviou hear band Extenion of tre-dilatancy curve The critical tate line (CSL) in the q ~ p plane wa found to be unique (a hown in Fig. 2), 12 with a critical tate tre ratio M c equal to It wa oberved in Fig. 3 that the tre 5

6 ratio ( q p) and dilatancy d ( d v d ) at the end of tet tate (i.e., Point A) were very cloe to the critical tate (i.e., the zero-dilatancy line d =). But a mall extrapolation to the critical tate a uggeted by Carrera et al. (211) wa neceary. And Point B in Fig. 3 give the critical tate tre ratio of Critical tate line The CSL of the CGS in the v ~ log p plane are hown in Fig. 4. During hearing, the pecific volume of the CGS decreaed a little then increaed for maller confining preure (e.g., p =.2 MPa) while it decreaed monotonically under larger preure (e.g., p =1.6 MPa). The comparion of the curve in Fig. 4 how that the critical tate point (CSP) of the CGS at the ame confining preure varied ignificantly with the initial pecific volume. Thee difference are too large to be explained by any inaccuracy in the mall extrapolation to critical tate. Group of drained tet at the ame confining preure p have been elected in Fig.5. If a unique CSL exited in the v ~ln p plane, drained tet at the ame p but different v hould converge to a unique v at the critical tate. However, Fig. 5 how that although there are ome reduction in the difference of pecific volume, the tet path tend to become parallel at the critical tate for each group of tet, indicating that the CSL of the CGS wa dependent on the initial pecific volume. In Fig.5 mall extrapolation are made from the end of tet tate to contant volume, but it i clear that incomplete teting could not be reponible for the lack of convergence. For non-platic oil, e.g., the Toyoura and (Verdugo and Ihihara 1996) or Stava ilty 6

7 tailing (Carrera et al. 211), the CSL in the v ~ log p plane i generally found to be nonlinear. The tet data in Fig. 6 alo how a omewhat nonlinear trend epecially at lower pecific volume. Li and Wang (1998) propoed a nonlinear CSL for thee granular oil, which could be expreed a.7 v p p (1) a 13 where and are fitting parameter (Li et al. 1999). The material contant and (a hown in Fig. 7) can be directly determined from the linear fitting of the tet data on v veru.7 p p (Li et al. 1999). The value of i.11 for the CGS. a The nonlinear CSL of the CGS move downward with a decreae in the initial pecific volume. Therefore, the intercept of thee CSL i dependent on the initial pecific volume. Thee CSL remain parallel, indicating that the CGS ha a tranitional behavior a ha previouly been oberved in oil with maller particle (Ferreira and Bica 26; Nocilla et al. 26; Altuhafi et al. 21; Altuhafi and Coop 211; Ponzoni et al. 214; Shipton and Coop 215) Quantification of tranitional behavior Ponzoni et al. (214) defined a parameter P to quantify the degree of the CSL non-convergence and to quantify tranitional behavior, which i the gradient of the relationhip between the linear CSL intercept and v. And the definition will be extended for the nonlinear CSL. The parameter P ha a limiting value of 1 for perfectly tranitional behavior in which CSL have the ame offet of pecific volume a the initial value, while P = when there i a unique CSL no matter what the initial pecific volume i (Ponzoni et al. 7

8 ). To obtain the P value of the CGS, a eparate value of wa calculated for every 148 tet by projecting back it critical tate in the v ~ log p plane uing of.11. The relationhip between and v for every ample (a hown in Fig. 8) can be decribed a + Pv (1) 151 where i the intercept of the line. The value of and P are.6 and.59, repectively. The P of.59 for the CGS i cloe to the P of.58 for the clayey ilt ediment from Lido in the Venice Lagoon with a clay fraction of 1-2% (Ponzoni et al. 214), which illutrate that a tranitional behavior can exit not only in well-graded ilty oil but alo in well-graded coare granular oil. Conequently, the tranitional mode of behavior may be more common than previouly realized Dicuion Ponzoni et al. (214) pointed out that difference in pecific volume at imilar tre tate can only be upported by difference in the oil fabric. However, different ample preparation have not been found to lead to any ignificant difference in the tranitional behavior of oil (Nocilla et al. 26; Shipton and Coop 212, 215). Shipton and Coop (215) alo howed that the tranitional behavior of the clayey and wa not linked to aniotropy. A true critical tate hould be defined where a unique fabric and pecific volume are reached. Neverthele, tranitional behavior (i.e., the family of parallel CSL) can be very robut and not eaily broken down by imple tre path like triaxial compreion (Ferreira and Bica 26; Shipton and Coop 215). 8

9 Unlike previouly oberved tranitional oil with ignificant fine (Martin et al. 21; Ferreira and Bica 26; Nocilla et al. 26; Altuhafi et al. 21; Shipton and Coop 212; Ponzoni et al. 214; Shipton and Coop 215), the CGS poee a very mall fine content (1.8% by weight) and a large amount of large-ized grain (95% larger than 1 mm in Fig. 1). Thu, the CGS doe not have a grading between that of clean and and platic clay, which i the uual range for tranitional oil. Neverthele, it did exhibit the tranitional mode of behavior. The grain hape of the CGS were angular (or ubangular) for grain ize maller than 1 mm, while the grain hape were rounded (or ubrounded) for grain ize larger than 1 mm. The maller-ized angular grain could provide a cuhion for the larger-ized rounded grain, and the oil fabric reponible for the tranitional behavior may be related to thi relationhip between the different grain ize and grain hape. While no ditinct fabric could be oberved, the effect could hardly be detroyed under hearing even though the confining preure wa up to 1.6 MPa (a hown in Fig. 5). It eem that the angular (or ubangular) grain ranging from to 1 mm (18%) in the well-graded CGS played a imilar role to that of platic or non-platic fine in other tranitional oil (Nocilla et al. 26; Ventoura and Coop 29; Ponzoni et al. 214; Shipton and Coop 215). In other word, a well-graded CGS can alo exhibit tranitional behavior. However, further reearch i neceary to explain how the tranitional behavior of the CGS relate to it fabric. The current tudy identified that the CSL of the well-graded CGS in the v ~ log p plane wa dependent on the initial pecific volume, indicating the correct ultimate volume change could not be predicted auming a unique CSL. The parallel non-unique CSL hould be ued for the precie determination of the ultimate deformation of the earth tructure uing thee 9

10 191 material Concluion A erie of drained triaxial compreion tet were conducted to invetigate the critical tate behavior of the well-graded CGS. It wa oberved from the tet that the CSL in the v ~ log p plane were not unique but dependent on the initial pecific volume. A decreae in the initial pecific volume led to a downward movement of the CSL. The parameter P for evaluating the degree of tranitional behavior wa quantified a.59, indicating that the well-graded CGS exhibited a clear tranitional behavior. Thi how that the tranitional mode could exit not only in oil with the grading between thoe of clean and and platic clay but alo in large-ized granular oil beyond the boundary of clean and Acknowledgment The author would like to acknowledge the financial upport from the National Natural Science Foundation of China (Grant No ) and the Fundamental Reearch Fund for the Central Univeritie (Grant No CDJXY28) Notation The following ymbol are ued in thi paper: G =Specific gravity; d =Dry denity; p = Mean effective tre (kpa); 1

11 p =Initial confining preure (kpa); p a =Atmopheric preure (kpa); q =Deviatoric tre (kpa); =Stre ratio; a =Axial train (%); v =Volumetric train (%); v =Specific volume; v =Initial pecific volume; =Intercept of the nonlinear CSL; =Slope of the nonlinear CSL; P =Degree of the CSL convergence in the depiction of tranitional behavior. 11

12 Reference Altuhafi, F., Baudet, B. a., and Sammond, P. (21). "The mechanic of ubglacial ediment : an example of new tranitional behaviour." Can. Geotech. J., 47(7), Altuhafi, F. N., and Coop, M. R. (211). "Change to particle characteritic aociated with the compreion of and." Geotechnique, 61(6), ASTM (21). "Standard tet method for flat particle, elongated particle, or flat and elongated particle in coare aggregate." D4791-1, Wet Conhohocken, PA. Been, K., and Jefferie, M. G. (1985). "A tate parameter for and." Geotechnique, 35(2), Carrera, A., Coop, M., and Lancellotta, R. (211). "Influence of grading on the mechanical behaviour of Stava tailing." Geotechnique, 61(11), Ferreira, P. M. V., and Bica, a. V. D. (26). "Problem in identifying the effect of tructure and critical tate in a oil with a tranitional behaviour." Geotechnique, 56(7), Li, X. S., Dafalia, Y. F., and Wang, Z. L. (1999). "State-dependent dilatancy in critical-tate contitutive modelling of and." Can. Geotech. J., 36(1999), Li, X. S., and Wang, Y. (1998). "Linear repreentation of teady-tate line for and." J. Geotech. Geoenviron. Eng., 124(12), Martin, F. B., Breani, L. A., Coop, M. R., and Bica, A. V. D. (21). "Some apect of the compreibility behaviour of a clayey and." Can. Geotech. J., 38(6), Nocilla, A., Coop, M. R., and Colleelli, F. (26). "The mechanic of an Italian ilt: an example of 'tranitional'behaviour." Geotechnique, 56(4),

13 Ponzoni, E., Nocilla, A., Coop, M., and Colleelli, F. (214). "Identification and quantification of tranitional mode of behaviour in ediment of Venice lagoon." Geotechnique, 64(9), Shipton, B., and Coop, M. R. (212). "On the compreion behaviour of recontituted oil." Soil Found, 52(4), Shipton, B., and Coop, M. R. (215). "Tranitional behaviour in and with platic and non-platic fine." Soil Found, 55(1), Ventoura, K., and Coop, M. R. (29). "On the behaviour of Thanet Sand: an example of an uncemented natural and." Geotechnique, 59(9), Verdugo, R., and Ihihara, K. (1996). "The teady tate of andy oil." Soil Found, 36(2),

14 Figure Caption Lit: Fig. 1. Initial gradation of ilt and coare granular oil Fig. 2. CSL of CGS in q ~ p plane Fig. 3. Extenion of tre ratio-dilatancy curve Fig. 4. Variation of pecific volume at different initial denitie and preure: (a) v =1.187~1.193; (b) v =1.242~1.245; (c) v =1.283~1.286; (d) v =1.315~1.319 Fig. 5. Variation of pecific volume with axial train: (a) p =.2 MPa; (b) p =.4 MPa; (c) p =.8 MPa; (d) p =1.6 MPa Fig. 6. Nonlinear CSL of CGS in v ~ log p plane p / p plane Fig. 7. Determination of material contant for CSL in e ~.7 Fig. 8. Quantification of tranitional behavior for CGS with nonlinear CSL a

15 Fig. 1. Initial gradation of ilt and coare granular oil

16 Fig. 2. CSL of CGS in q ~ p plane

17 Fig. 3. Extenion of tre ratio-dilatancy curve

18 Fig. 4. Variation of pecific volume at different initial denitie and preure: (a) v =1.187 ~1.193; (b) v =1.242~1.245; (c) v =1.283~1.286; (d) v =1.315~1.319

19 Fig. 5. Variation of pecific volume with axial train: (a) p =.2 MPa; (b) p =.4 MPa; (c) p =.8 MPa; (d) p =1.6 MPa

20 Fig. 6. Nonlinear CSL of CGS in v ~ log p plane

21 p / p plane Fig. 7. Determination of material contant for CSL in e ~.7 a

22 Fig. 8. Quantification of tranitional behavior for CGS with nonlinear CSL