EVALUATION OF LIQUEFACTION RESISTANCE AND LIQUEFACTION INDUCED SETTLEMENT FOR RECLAIMED SOIL

Transcription

1 386 EVALUATION OF LIQUEFACTION RESISTANCE AND LIQUEFACTION INDUCED SETTLEMENT FOR RECLAIMED SOIL Lien-Kwei CHIEN 1, Yan-Nam OH 2 An Chih-Hsin CHANG 3 SUMMARY In this stuy, the fille material in Yun-Lin near shore in west Taiwan is aopte as testing samples. Using moist tamping metho, the specimens were prepare with ifferent relative ensities an fine contents. A series of triaxial liquefaction test was performe to evaluate the liquefaction resistance an liquefaction-inuce settlement of reclaime soil. Base on the propose evaluation metho an combine the one-imensional consoliation theory, the volumetric strain an settlement of reclamation lan woul be preict by ry ensity an fines content of reclaime soil. From the figures an results analysis, it can be a reference evaluation metho for liquefaction resistance an liquefaction-inuce settlement behavior of the reclaime soil. This result is very useful to preict the liquefaction potential analysis an settlement for planning, esign an relate research of reclamation engineering. Key Wors: Reclaime soil, Liquefaction resistance, Fines content, Settlement. INTRODUCTION Liquefaction is one of the most important, interesting, complex, an controversial topics in geotechnical earthquake engineering. Taiwan is locate at the center of west circumpacific earthquake zone, an between Philippine plate an Eurasia plate. When plates move with respect to each other. The relative eformation between plates occurs near their bounaries, an coul be inuce earthquakes. Therefore, Taiwan has 1 to 2 major earthquakes per year an woul cause severe amages. Earthquakes prouce spectacular examples of liquefaction-inuce amage for structures in lan reclamation area, incluing slope failures, brige an builing founation failures, an flotation of burie structures. The liquefaction of reclaime soil is influence by factors such as earthquake loaing, cyclic loaing, relative ensity an fines content. See an Iriss (1967) illustrate that relative ensity is the main factor affecting the liquefaction strength of soil. The major earthquakes of Niigata in 1964 have illustrate that soil below 5% of relative ensity woul liquefy. As for soil with 7% or higher relative ensity, the soil remains unchange. By using ynamic triaxial tests, See (1979) showe that, for soil with % to 7% of relative ensity, the shear stress ratio for initial liquefaction woul increase as the relative ensity increases. See et al. (1985) showe the influence of fines content on (N 1 ) 6 values an liquefaction strength of soil. The results showe that, the (N 1 ) 6 value ecreases as the fines content increases. Much of the early works relate to soil liquefaction inuce by earthquake are conucte in laboratory testing subjecte to cyclic triaxial test. Finn an Barsty (197) showe that, for soil uner cyclic loaing, the liquefaction strength of soil woul increase with.5% of initial strain. By using moist tamping metho with saturate specimen, Chien an Oh (1998) showe that, there is istinct influence of fines content on the ynamic properties of reclaime soil. Summarizing the above, for specimen uner pre-cyclic loaing, the soil aggregate woul become enser an woul increase the soil strength. In this stuy, the specimens are prepare with ifferent relative ensities (as 35%, 55% an 75%) an ifferent fines content (as 5%, 1%, 2% an 3%). The cyclic triaxial tests are Department of Harbor an River Engineering, National Taiwan Ocean University,Keelung, 22, Taiwan, R.O.C. Department of Harbor an River Engineering, National Taiwan Ocean University,Keelung, 22, Taiwan, R.O.C. Department of Harbor an River Engineering, National Taiwan Ocean University,Keelung, 22, Taiwan, R.O.C.

2 conucte with pre-cyclic loaing to iscuss the influence of initial earthquake on soil strength an liquefaction inuce ynamic settlement of reclaime soil. In recent years, in orer to promote evelopment an utilization of marine resources an ocean space, the lan reclamation is important to solve the lack an evelopment of inustrial estate. In general, the basic properties of reclaime soil are low strength, low relative ensity an low SPT-N values with high water contents (Slaen an Hewitt (1989)). Therefore, the reclaime soil woul easily liquefie uner earthquake loaing an wave forces. Thus, in this paper, the ifferent relative ensities (as 35%, 55%, an 75%) an fines content (as 5%, 1%, 2%, an 3%) are consiere to evaluate the liquefaction resistance an liquefaction-inuce settlement. The results are very useful as reference for earthquake esigns an ensure the safety an stability reclamation engineering. Test Materials The reclamation soil use in this investigation was obtaine from Yun-Lin area. It is uniform, fine, black san an classifie as SP accoring to the Unifie Soil Classification System (USCS). Grain-size ata of the reclaime soil (as Fig. 1) inicate a mean iameter D 5 =.22 mm~.29mm, a coefficient of uniformity C u = 2.3~4.7, a coefficient of curvature C c =.6~1.42, an an efficient iameter D 1 =.6 mm~.15mm. The inex properties are shown in Table 1 respectively. From the in-situ exploration ata, the fines content istribution of reclaime soil ranges very large from small fines content is % ~1% to high fines content is 2%~4% below 2m soil layers. The average fines content is about 1%~2%. In this stuy, in orer to unerstan the influence of the fines content of reclaime soil, the ifferent fine contents were aopte as %, 5%, 1%, 2%, an 3% to evaluate liquefaction resistance an liquefaction-inuce settlement. Fines content was obtaine from the soil samples passing through the #2 sieve (<.75mm). The weight of specimen is provie as a component to control the fines content of the specimen (Chien (1994)). Test Proceure The specimens are prepare by moist tamping metho with ifferent relative ensities an fines content to iscuss the influence of soil fabric properties for the liquefaction resistance of the reclaime soil. In this stuy, the automatic triaxial test system is aopte to conuct the cyclic triaxial liquefaction test. The automatic triaxial test system was evelope by Mulils an Chan (1977) in University of California at Berkeley. The test system has great avantages in stress, strain an stress path control. After the specimen was prepare an consoliate, a series of liquefaction test is performe. In orer to unerstan the liquefaction-inuce settlement, the volume changes inuce by the issipation of pore water pressure of specimens after liquefaction-inuce consoliation is measure to evaluate the volumetric strain an settlement. Table 1 Physical properties of reclaime soil samples Properties Values Fines content Max. Dry Density (g/cm 3 ) Min. Dry Density (g/cm 3 ) Specific Gravity (G s) D 5(mm) D 1(mm) D 3(mm) D 6(mm) Coefficient of uniformity, C u Coefficient of curvature, C Dry Dr=35% (g/cm 3 ) Dry Dr=55% (g/cm 3 ) Dry Dr=75% (g/cm 3 ) Voi Ratio (Dr=35%) Voi Ratio (Dr=55%) Voi Ratio (Dr=75%)

3 Dr=76.9%~77.3% Dr=57.2%~59.3% Dr=39.8%~41.5% Dr=76.9%~77.3% Dr=57.2%~59.3% Dr=39.8%~41.5% Percentage Finer Than D (% ^ Number of Cycles,N Fig.2 Relation between number of cycle an cyclic stress ratio uner ifferent relative ensity (F.C.=%) 1 1 Grain Size ] mm) Fig. 1 Grain size istribution of reclaime soil samples..1.1 EXPERIMENT ANALYSIS AND RESULTS Influence of fines content on liquefaction resistance for reclaime soil Accoring to previous relate stuy about influence of relative ensity on liquefaction resistance for reclaime soil, the ense relative ensity of san has higher liquefaction strength than loose relative ensity of san. However, from in-situ ata analysis, ifferent relative ensities of sans also possible have same liquefaction strength. Fines content of reclaime soil is one of most influence factors. Therefore, in this stuy, in orer to unerstan the influence of fines content, a series of liquefaction test was performe with ifferent fine contents (as FC = % to 3%) an ifferent relative ensities (as Dr 35%, 55%, an 75%). The typical test results between cyclic stress ratio an number of cycles are shown in Fig. 2. From the figures shows that the liquefaction resistance of ense relative ensity soil has greater than the loose relative ensity soil uner the same fines content. In orer to evaluate the increment of cyclic stress amplitue with ifferent fine contents, by use of the 1,15, 2 number of cycles correspon to cyclic stress ratio is conucte. Base on the cyclic stress ratio of loose soil, the percent increment of cyclic stress ratio is efine, an shown in Table 2. The cyclic stress ratio has ecreasing as fines content increasing tenency. The percent increment of cyclic stress ratio is not significant with number of cycles. For meia ensity, the percent increment of cyclic stress ratio ranges from 1.25 (as FC is %) to 1.12 (as FC is 3%). In aition, for ense ensity, the percent increment of cyclic stress ratio ranges about from 1.75 (as FC is %) to 1.55 (as FC is 3%). In higher fines content, the percent increment of cyclic stress ratio has significant ecreasing. Relative Density Table 2 of relative ensity uner ifferent fines content inuce by cyclic stress ratio. Fines Content=% Fines Content =1% (SR) 1 (SR) 15 (SR) 2 Relative Density (SR) 1 (SR) 15 (SR) Relative Density Fines Content =2% Fines Content =3% (SR) 1 (SR) 15 (SR) 2 Relative Density (SR) 1 (SR) 15 (SR) When the relative ensity keeps constant (as initial relative ensity is 35%) an changes the fines content (as % to 3%), the relationship between number of cycles an cyclic stress ratio is presente in Fig. 5. From the figures 3 386

4 shows that the liquefaction resistance of reclaime soil has ecrease as the fines content increases tenency uner constant relative ensity. The fines content ranges from % to 1%, the liquefaction curve is not istinctive for initial relative ensity 35% an 55%. The variable range values are very closely. When the fines content is greater than 1%, the influence of liquefaction curve has significant reucing. For 75% of initial relative ensity, the liquefaction resistance uniform ecreases as the fine content increases. When Nc = 1, 15, an 2, for specimen with ifferent fine contents, the cyclic stress ratio can be obtaine. As shown in Fig. 6, the ratio of cyclic stress ratio with clean reclaime soil without fines content for 38.4% to 42.9% after consoliate relative ensity relate with Nc uner ifferent fine contents. From the figures shows that the linear relationship is well. In general, the ratio values are small than 1., an ifference of ratio value increases as the Nc increases. The Dr = 56.5% ~6.7% also has similar behavior. For ense relative ensity (as Dr = 76.% ~77.9%), the ratio of liquefaction resistance curve has small increasing uner fines content is 5%. Other curves are steay ecreasing with fines content increasing Dr=41.5% Dr=41.5% Dr=39.8%~41.5% Dr=42.4% Dr=39.9% Dr=39.7%~4.2% Dr=4.7% Dr=38.4%~4.% Dr=42.7% Dr=39.7% Dr=39.9% Dr=4.8% Dr=41.3%~42.4% Dr=41.3% Dr=39.9% Dr=39.7% Dr=41% Dr=41.8%~42.9% Dr=42.4% Dr=39.7% Dr=4.4% Dr=38.4% Dr=38.4% Dr=4.8% Dr=41.5% Dr=4% Dr=42.9% Dr=39.2% Dr=41.7% Dr=4.2% Dr=42.5% Dr=41.8% (Cyclic stress ratio with fines content) (Cyclic stress ratio of clean san ^ Number of Cycles,N Number of Cycles ]N ^ Fig.3 Relation between number of cycles an cyclic stress ratio uner ifferent fines content. (Initial Dr=35%) Fig.4 Comparison curve for specimen with fines content an clean san (Dr=38.4%42.9%). The liquefaction resistance of the reclaime soil As shown in Fig. 5, the relationship between the cyclic stress ratio an voi ratio of reclaime soil with ifferent fine contents is presente. Uner number of cycles (Nc) is 1, consiering the voi ratio of the reclaime soil cyclic stress ratio of liquefaction, the linear relationship of liquefaction resistance curves is well. It very clear can be compare with ifferent fine contents. When consiering the fines content ae the increment of fines content woul be equal to the ecrement of large grain material of specimen. Therefore, for high ensity with low fines content of specimen, the voi ratio is possible lower than low ensity with high fines content of specimen, as shown in Fig.6. From the figures without consiering the fines content, uner after consoliate the average relative ensity is 4.59%, 58.51%, an 76.94%, the relationship between voi ratio of reclaime soil an the cyclic stress ratio can be obtaine. When number of cycles from 1 increases to 2 with ifferent relative ensities, cyclic shear stress require to cause liquefaction has ecreasing tenency. For example, consiering voi ratio.8, an Nc = 1, for FC = %, the cyclic shear stress ratio require liquefaction (SR) 1 is.59. For FC = 3%, (SR) 1 is.24. When number of cycles increases to 2, for FC =1%, the cyclic shear stress ratio require liquefaction (SR) 2 is.53. For FC = 3%, (SR) 2 is.22. The liquefaction resistance has small ecreasing tenency. Summarizing the above, uner ifferent fine contents, the liquefaction strength of reclaime soil ecreasing with the voi ratio increasing. On the other han, combine the above results, uner same number of cycles, the Fig.7 an Fig.8 can be obtaine. Accoring to initial liquefaction curve correspon to Nc = 2 an ouble axial amplitue strain (DA) reach to 5%, the liquefaction strength (SR) 2 is aopte to evaluate the properties of liquefaction strength. Between voi ratio, ry ensity an liquefaction strength is presente in Fig.9 an Fig.1. In practice engineering, by use of fines content an ry ensity of soil layer, the liquefaction strength an relative ensity can be evaluate. From the regression analysis, the ry ensity relate to liquefaction strength (SR) 2 with ifferent fine contents can etermine as follows: 4 386

5 For FC = %, (SR) 2 =.59 x( γ ) 5.31 R 2 =.994 (1) For FC = 5%, (SR) 2 =.46 x( γ ) 5.3 R 2 =1. (2) For FC = 1%, (SR) 2 =.53 x( γ ) 4.5 R 2 =.995 (3) For FC = 2%, (SR) 2 =.27 x( γ ) 5.4 R 2 =.987 (4) For FC = 3%, (SR) 2 =.38 x( γ ) 4.13 R 2 =.924 (5) Combine above equation (Eq.(1) to Eq. (5)) an regression analysis, it can be obtaine the ry ensity( γ ) relate with (SR) 2 uner ifferent fine contents as follows: (SR) 2 = a 1 x ( γ ) b1 Where, a 1 an b 1 are function of fine content, a 1 = FC +.15 FC 2, an b 1 = FC FC 2. From the above test results analysis, consiering the relative ensity an fine content to evaluate the liquefaction strength, it can be obtaine goo agreement. The results are very useful to provie the reference of liquefaction strength evaluation of the lan reclamation engineering. (6) (Dr)av=76.94% (Dr)av=76.94% (Dr)av=58.51% (Dr)av=4.89%.2.2 (Dr)av=58.51% (Dr)av=4.89% Voi Ratio, e Voi Ratio, e Fig.5 Relation between voi ratio an cyclic stress ratio uner ifferent fines content (No. of cycle=1) Dr=76.%~77.9% Dr=56.5%~6.7% Dr=38.4%~42.9% Fig.6 Relation between voi ratio an cyclic stress ratio uner ifferent relative ensities (No. of cycle=1) Dr=56.5%~6.7% Dr=38.4%~42.9% Dr=76.%~77.9% Voi Ratio, e Dry Unit Weight (g/cm 3 ) Fig.7 Relation between voi ratio an cyclic stress ratio uner ifferent fines content an relative ensities (No. of cycle=1). Fig.8 Relation between ry unit weight an cyclic stress ratio uner ifferent fines content an relative ensities (No. of cycle=1). Liquefaction-inuce settlement in reclaime soil In this stuy, in orer to unerstan the liquefaction inuce settlement on reclaime soil, a series of liquefaction test was performe an the volume change after liquefaction-inuce consoliation was measure. Base on one-imensional consoliation theory, the ynamic settlement of reclaime soil can be evaluate an is iscusse as follow: 5 386

6 Cyclic Shear Stress Ratio Dr=76.%~77.9% Dr=56.5%~6.7% Dr=38.4%~42.9% Nc=2 DA=5% Cyclic Shear Stress Ratio Dr=38.4%~42.9% Dr=56.5%~6.7% Dr=76.%~77.9% Nc=2 DA=5% Voi Ratio, e Dry Unit Weight ]g/cm3 ^ Fig.9 Relation between voi ratio an cyclic stress ratio uner ifferent fines content an relative ensities (No. of cycle=2, DA=5%). Fig.1 Relation between ry unit weight an cyclic stress ratio uner ifferent fines content an relative ensities (No. of cycle=2, DA=5%). (1) The relationship between relative ensity an settlement of reclaime soil The relations between relative ensity an consoliate volumetric strain after liquefaction are shown in Fig.11. When the relative ensity increases, the volumetric strain of reclaime soil ecreases. For sake of convenience the settlement inuce by liquefaction, the concept of one-imensional consoliation is aopte. Assume the cross section area of tests specimen kept constant after liquefaction inuce consoliation, the vertical axial settlement (as the settlement inuce by liquefaction of reclaime soil) coul be calculate from the volume changes, an can be expresse as follows: V ΔH = Where, AΔV is the volume changes inuce by liquefaction rainage, A is the section area of tests specimen, an ΔH is the settlement changes of specimen base on the concept of one-imensional consoliation. (7) By use of original volume changes an settlement changes are ivie by the consoliate volume an specimen height, the percent of volumetric(ε v ) an settlement ratio (S r ) are efine. The typical results are shown in Fig.11. The percent of volumetric ranges about from 3.5% to 9.5% an the settlement ratio ranges about from.35% to.95%. When relative ensity is 4%, the average settlement ratio is.78. For the soil with relative ensity 6% an 75%, the average settlement ratio are.58 an.42, respectively. These results inicate that the settlement ratio of reclaime soil has increase as the relative ensity ecreases. Thus, also shows the enser san is not easy to inuce the settlement. Accoring to regression analysis, the relationship between percent of volumetric, settlement ratio, an relative ensity can be etermine as follows: ε v = -.1 Dr , R 2 =.88 (8) S r = -.1 Dr +1.17, R 2 =.89 (9) The typical results between percent of volumetric, settlement ratio, an fines content presente in Fig.12. It is clearly show that the influences of ifferent fine contents on variable change values is not istinctive for ifferent relative ensities. But, consiering the same fines content, an taking the average value of istribution ranges, coul be foun from F c =% to F c =5% has ecreasing tenency. When fines content is greater than 5% has increasing tenency. But when fines content is greater than 1% has ecreasing tenency. In general, the average percent of volumetric strain ranges from 4% to 8%, an the settlement ratio ranges from.4% to.8%. Therefore, the istribution ranges of percent of volumetric strain an the settlement ratio are always influence by relative ensity. When the high relative ensity was aopte, it coul be obtaine lower values tenency. If the low relative ensity was aopte in testing, it coul be obtaine great values. Hence, the istribution ranges of percent of volumetric strain an the settlement ratio can be increase. (2) Influence of fines content on settlement Consiering the ifferent fines contents such as %, 5%, 1%, 2%, 3%, the effects of fines content was consiere. The typical test results were presente in Fig.13. As shown in the figure, the linear relationship is 6 386

7 well uner ifferent ry ensity of reclaime soil. It very clear can be compare with ifferent fine contents an the curve with ifferent fine contents right-han sie moving with fine content increasing. This is expresse the settlement ratio of reclaime soil ecreases as the ry ensity increases. For the settlement ratio, the istribution ranges about from.4% to.8%. The settlement ratio increases as the fines content increasing. Uner the same ry ensity of reclaime soil, the more fine content easy to inuce settlement tenency. In orer to unerstan the effect of fines content, the case of γ = 1.5 g/cm 3 is iscusse. From the Fig.13 shown that, when the fines content from % increases to 3%, the settlement ratio of reclaime soil from.39% increases to.8%. Base on regression analysis, the reclaime soil of ry ensity(γ ) relate with settlement ratio(s r ) can be expresse uner ifferent fines content(f c ) as follows: FC = %, S r % = -2.56γ , R 2 =.86 (1) FC = 5%, S r % = -2.14γ , R 2 =.96 (11) FC =1%, S r % = -2.26γ + 4.4, R 2 =.83 (12) FC =2%, S r % = -2.2γ + 4.5, R 2 =.92 (13) FC =3%, S r % = -2.21γ , R 2 =.99 (14) Combine above equations (Eq.(1) to Eq.(14)) an regression analysis, it can be obtaine the relationship between ry ensity(γ ) an settlement ratio(s c ) as follows: S c = aγ + b (15) Where, a an b are function of fines content, a= FC.3 FC 2, an b= FC +.4 FC ã3% ]D ^av=7.cm ]H ^av=14.95cm ]V ^av=575.34cm Dr=35% ã75% ]D ^av=7.cm ]H ^ av=14.95cm Volumetric Strain Volumetric Strain Relative Density Fig.11 Percentage of volumetric strain inuce by liquefaction uner ifferent relative ensity Fines Content Fig.12 Percentage of volumetric strain inuce by liquefaction uner ifferent fines content. Summarizing the above analysis, it coul be foun that only consiering the relative ensity to evaluate the settlement of after liquefaction for reclaime soil, is not completely response the effects of the fine content. On basis of the soil ry ensity an fines content, a new propose metho is establishe to evaluate the liquefaction inuce settlement of reclaime soil, an goo agreements are obtaine. 1.8 ã3% ]D ^av =7.cm ]H ^av =14.95cm ]V ^av =575.34cm 3 Settlement Ratio ]% ^ Dry Unit Weight ]g/cm3 ^ 7 386

8 Fig.13 Settlement ratio inuce by liquefaction uner ifferent fines content an ry unit weight. CONCLUSIONS In this stuy, consiering ifferent relative ensities an fine contents for reclaime soil in Yun-Lin nearshore area in west Taiwan. A series of liquefaction test was performe to evaluate the liquefaction strength an liquefaction inuce settlement. Base on the results of laboratory tests, the following conclusions can be rawn. 1. Uner the same fines content, the liquefaction strength of reclaime soil increases as the relative ensity increases tenency. In aition, uner the constant relative ensity, the liquefaction strength ecreases as the fines content increases. 2. The relationship between ry ensity, voi ratio, an liquefaction strength of reclaime soil is establishe, an the linear relationship is well. 3. For the liquefaction inuce settlement analysis, the settlement ratio of reclaime soil increases as the relative ensity increases. Uner the same ry ensity, the settlement ratio increases as the fines content increases. 4. On the basis of the reclaime soil ry ensity an fines content, a new propose metho is establishe to evaluate the liquefaction resistance an liquefaction inuce settlement. 5. For the liquefaction inuce settlement analysis, the results inicate that, the settlement ratio of reclaime soil increases as the relative ensity increases. Uner the same ry ensity, the settlement ratio increases as the fines content increases. Base on the reclaime soil ry ensity an fines content, a new propose metho is establishe to evaluate the liquefaction inuce settlement. The results in the paper are useful for liquefaction resistance an settlement analysis. The results presente can be as a reference for planning, esign an relate research in lan reclamation engineering. ACKNOWLEDGMENT This research was supporte by National Science Council of R.O.C. uner Grant No. NSC P19-2, an was greatly appreciate. REFFERENCES Chien, L.K., A Stuy on the Dynamic Properties of Reclaime Soil in West Taiwan, National Science Council Report NO. NSC P-19-1B (1994) (in Chinese). Chien, L.K. an Y.N. Oh, "Influences On The Shear Moulus An Damping Ratio Of Hyraulic Reclaime Soil In West Taiwan", International Journal Of Offshore an Polar Engineering, Vol.8, No.3, pp (1998). Finn, W. D. an Barsty, D. T.,Effect of Strain History on Liquefaction of San,JSMFD, ASCE, June, pp ,(197). H.Bolton See,Soil Liquefaction an Cyclic Mobility Evaluation for Level Groun During Earthquakes, Journal of the Geotechnical Engineering Division, ASCE, Vol.15, No.GT2, Feb., pp (1979). H.Bolton See, K.Tokimatsu, L.F.Harer, an Riley M.Chung, Influence of SPT Proceures in Soil Liquefaction Resistance Evaluations,J. Geotech. Eng., ASCE, Vol.111, No.12, Dec, pp (1985). Mulilis, J. P., See, H. B., Chan, C. K.,Resistance to Liquefaction ue to Sustaine Pressure,Journal of Geotechnical Engineering Division, ASCE, Vol.13, No.GT7, July, pp , (1977). See, H. Bolton an Iriss, I.M., Analysis of Soil Liquefaction :Niigata Earthquake, JSMFD, ASCE, Vol. 93, No. SM3, pp , (1967). Slaen, J.A. an K. J. Hewitt, "Influence of Placement Metho on the In Site Density of Hyraulic San Fills," Canaian Geotechnical Journal, Vol. 26, No. 3, pp (1989)