1、 GEOTECHNICAL SPECIAL PUBLICATION NO. 197 SLOPE STABILITY, RETAINING WALLS, AND FOUNDATIONS SELECTED PAPERS FROM THE 2009 GEOHUNAN INTERNATIONAL CONFERENCEAugust 36, 2009 Changsha, Hunan, China HOSTED BY Changsha University of Science and Technology, China CO-SPONSORED BY ASCE Geo-Institute, USA Asp
2、halt Institute, USA Central South University, China Chinese Society of Pavement Engineering, Taiwan Chongqing Jiaotong University, China Deep Foundation Institute, USA Federal Highway Administration, USA Hunan University, China International Society for Asphalt Pavements, USA Jiangsu Transportation
3、Research Institute, China Korea Institute of Construction Technology, Korea Korean Society of Road Engineers, Korea Texas Department of Transportation, USA Texas Transportation Institute, USA Transportation Research Board (TRB), USA EDITED BY Louis Ge, Ph.D. P.E. Jinyuan Liu, Ph.D. James C. Ni, Ph.D
4、. P.E. Zhao Yi He, Ph.D. Published by the American Society of Civil Engineers Library of Congress Cataloging-in-Publication Data Slope stability, retaining walls, and foundations : selected papers from the 2009 GeoHunan International Conference, August 3-6, 2009, Changsha, Hunan, China / hosted by C
5、hangsha University of Science and Technology, China ; co-sponsored by ASCE Geo-Institute, USA et al. ; edited by Louis Ge et al. p. cm. - (Geotechnical special publication ; no. 197) Includes bibliographical references and indexes. ISBN 978-0-7844-1049-3 1. Soil stabilization-Congresses. 2. Slopes (
6、Soil mechanics)-Stability-Congresses. 3. Retaining walls-Design and construction-Congresses. 4. Foundations-Design and construction-Congresses. I. Ge, Louis. II. Changsha li gong da xue. III. American Society of Civil Engineers. Geo-Institute. IV. GeoHunan International Conference on Challenges and
7、Recent Advances in Pavement Technologies and Transportation Geotechnics (2009 : Changsha, Hunan Sheng, China) TE210.4.S56 2009 624.151363-dc22 2009022667 American Society of Civil Engineers 1801 Alexander Bell Drive Reston, Virginia, 20191-4400 www.pubs.asce.org Any statements expressed in these mat
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13、 email: permissionsasce.org. A reprint order form can be found at http:/pubs.asce.org/support/reprints/. Copyright 2009 by the American Society of Civil Engineers. All Rights Reserved. ISBN 978-0-7844-1049-3 Manufactured in the United States of America. Geotechnical Special Publications 1 Terzaghi L
14、ectures 3 Landslide Dams: Processes, Risk, and Mitigation 7 Timber Bulkheads 9 Foundations 2Professor, Institute of Geotechnical Engineering, Southeast University, 2# Sipailou, Nanjing, China, 210096; 3Doctor, Institute of Geotechnical Engineering, Southeast University, 2# Sipailou, Nanjing, China
15、, 210096; 4Associate professor, Institute of Geotechnical Engineering, Southeast University, 2# Sipailou, Nanjing, China, 210096; ABSTRACT: Soil-cement deep mixing method is widely used in soft ground improvement for highway engineering application in China. However, there are some disadvantages o
16、f the conventional soil-cement deep mixing method in China, such as insufficient mixing, grouting spill and decrease of strength along column depth. In addition, small column spacing and cushion or geosynthestic reinforcement are often required, resulting in high cost. In order to conquer these disa
17、dvantages, a new deep mixing method named T-shaped deep mixing method is developed. The mechanism, construction issues, and pilot project monitoring results of T-shaped deep mixing column foundation are presented in the paper. The results indicate that the T-shaped deep mixing method makes the deep
18、mixing much more reliable and economical. INTRODUCTION Deep mixing method is a soil improvement technique that delivers reagent (cement or lime or a combination), either slurry or powder, into the ground and mixes it with in situ soils to form a hardened column (DM column). The deep mixing method wa
19、s introduced to China in the late 1970s (Han et al., 2002). The technology spreads rapidly throughout China in the 1990s, especially for highway engineering application. Many engineering practices of deep mixing method in China have demonstrated that it has many merits, such as easy and rapid instal
20、lation and relatively small vibration. More important, it can effectively reduce the settlement and increase the stability of soft ground (Liu and Hryciw, 2003; Chai et al., 2002). However, deep mixing method also encounters following problems in China: (1) Insufficient mixing, grouting spill, and d
21、ecrease of column strength along column depth. (2) Small column spacing and cushion or geosynthestic reinforced layer are 1GEOTECHNICAL SPECIAL PUBLICATION NO. 1972often required, which cause high cost. In order to conquer these disadvantages, a newdeep mixing method called T-shaped deep mixing meth
22、od and the relevant machineare developed (Liu et al., 2006). The mechanism, construction issues, and pilot projectmonitoring results of T-shaped deep mixing column composite foundation arepresented below.FUNDAMENTALS OF T-SHAPED DEEP MIXING MTHOLDIn highway or railway engineering, the differential s
23、ettlement between DMcolumns and the surrounding soil is induced by embankments which are usually treatedas flexible foundation, as a result of the different compressibility behavior betweenDM column and soil. The differential settlement is about 8%20% of the averagesettlement (Bergado et al., 2005).
24、 The differential settlement at the surface of groundcan transfer to the embankment, and even harm pavement if the differential settlementis large enough. As a result, small spacing (typically l.lmtol.Smin China) isadapted in DM column composite foundation in highway engineering. And cushion orgeosy
25、nthestic reinforced layer is often set above columns to reduce the differentialsettlement, which cause high cost. The additional stress in upside of DM columncomposite foundation is larger than in underside. So a DM column with large upsidecolumn diameter and small underside column diameter can impr
26、ove the soft groundbetter than conventional shaped column.FIG. 2. Construction process of T-shaped deep mixing methodFIG. 1. Blades sketch of T-shaped deep mixing machineThe blades of T-shaped deep mixing machine can spread outward and shrink inward at any position when they work underground (as sho
27、wn in FIG. 1), and a column with two column diameters can be installed by this new deep mixing machine. So a deep mixing column which has large diameter upside and small diameter underside can be installed by this new deep mixing machine (as shown in FIG. 2). The shape of this new deep mixing column
28、 is similar to the shape of T, so it is called T-shaped deep mixing column (TDM column). Before the usage of this new method, almost all of the soil-cement deep mixing columns in China are installed with single mixing method that the mixing blades run in one direction (Yi and Liu, 2008). The single
29、mixing method results in insufficient mixing of soil-cement, grouting spill, and decrease in column strength along column depth. From this point of view, double mixing method (Shen et al., 2003, 2008; Chai et al., 2005; Liu et al., 2008) is adopted in TDM column installation to improve mixing effici
30、ency and column uniformity(Yi and Liu, 2008). The construction process of T-shaped deep mixing method is shown in FIG. 2. FIELD TESTS Test Site and Column Composite Foundation Design The pilot project was set in the construction field of Husuzhe highway. The test site was divided into four sections,
31、 and two sections were presented in this paper. One section was improved by TDM columns, and the other was improved by conventional DM columns. CPTU testing results indicated the engineering geological conditions in the two sections are similar (Yi and Liu, 2008). Laboratory tests were also conducte
32、d, and the main index properties of each layer are presented in Table 1. Table 1. Index properties of soil layers in test site Soil layers Depth (m) (kNm-3)W (%)e0WL (%) Wp(%)c (kPa)3 () Es1-2 (MPa)Clay 02 19 35 0.94 41.9 23.6 31.2 25 8.8 Mucky clay 214 17 50.9 1.43 53.6 24.1 12.6 16.3 1.9 Silty cla
33、y 1416 20.3 23.9 0.67 46.7 21.7 40.3 23.5 7.5 Clay 16 20.5 24.1 0.65 35.8 14.8 37.9 29.7 25.1 The arrangements of columns were quincunx in both sections. The cement content was 255 kg/m3, and water cement ratio of was 0.55. The design parameters of TDM and conventional DM column composite foundation
34、 are shown in FIG. 3. It can be easily calculated with the design parameters in FIG. 3 that the replacement ratio of the upside TDM column composite foundation is 0.227, of the underside TDM column composite foundation is 0.057, and of conventional DM column composite foundation is 0.116. On one han
35、d, the upside replacement ratio of TDM column composite foundation is almost twice that of conventional DM column composite foundation, which can reduced differential settlement between column and surrounding soil. On GEOTECHNICAL SPECIAL PUBLICATION NO. 197 3GEOTECHNICAL SPECIAL PUBLICATION NO. 197
36、4the other hand, the underside replacement of TDM column composite foundation isnearly half that of conventional DM column composite foundation, which can savemuch cement. The cement cost is 535 kg/m in TDM column composite foundation,and 632 kg/m in conventional DM column composite foundation, whic
37、h means theformer is 15.3 % less than the latter. The photos of T-shaped cement-soil deep mixingcolumn are shown in FIG. 4.FIG. 4. Photo of T-shaped cement-soil deep mixing columnFIG. 5. Cross-section view of instrumentation (not to scale, unit: m)Monitoring Results While Embankment FillingBefore em
38、bankment was filled, monitoring instruments, including settlement platesand inclinometers were installed in both section, and the cross-section view ofinstrumentation was shown in FIG. 5. The settlements plates were installed on top ofFIG. 3. Parameters of column composite foundation (not to scale,
39、unit: m)the soil between the columns along the embankment centerline. The inclinometers were installed at the embankment toes to measure the lateral displacement of soil under embankment loads. Staged construction and surcharge techniques were used for the embankment filling. The measured settlement
40、s with time are presented in FIG. 6. It is shown that the measured settlement increased with the embankment height. The embankment height in TDM column composite foundation is 0.6 m larger than in conventional DM column composite foundation, while the total settlement in the former is only 50% of th
41、at in the latter. FIG. 6. Variation of ground settlement during embankment filling The lateral displacement of the soil at the embankment toe was measured by an inclinometer (shown in FIG. 5). The measured results are shown in FIG. 7 (one of the inclinometer tubes was destroyed 3 months after instal
42、led). It was found that the embankment heights were similar in two sections, but the maximal lateral displacement in TDM column composite foundation is 20.84 mm while in conventional DM column composite foundation is 55.57 mm. CONCLUSION The filed tests indicate that when the embankment heights were
43、 almost the same, the ground surface settlement and maximal lateral displacement in TDM composite foundation are much less than in conventional DM column composite foundation while cost less cement. This means that the T-shaped deep mixing method makes the deep mixing much more reliable and economic
44、al than conventional deep mixing method. GEOTECHNICAL SPECIAL PUBLICATION NO. 197 5(a) TDM column composite foundation (b) Conventional DM column composite foundation FIG. 7. Variation of lateral displacement during embankment filling GEOTECHNICAL SPECIAL PUBLICATION NO. 1976ACKNOWLEDGMENTS The auth
45、ors are very grateful to Mr. Peisheng, Xi, Mr. Bafang, Zhang and Mr. Zhihua, Zhu in the research group. This work is supported by National Natural Science Foundation of China (Grant No. 50879011) and Scientific Research Innovation Program for Graduate Students in Jiangsu Province (Grant No. CX08B_10
46、1Z). REFERENCES Bergado, D.T., Noppadol, P. and Lorenzo, G.A. (2005). “Bearing and Compression Mechanism of DMM Pile Supporting Rein-forced Bridge Approach Embankment on Soft and Subsiding Ground”. 16th International Conference on Soil Mechanics and Geotechnical Engineering, Osaka, Japan: 1149-1153.
47、 Chai, J.C., Liu, S.Y. and Du, Y.J. (2002). “Field Properties and Settlement Calculation of Soil Cement Improved Soft Ground-A Case Study”. Lowland Technology International, Vol.4(2): 51-58. Chai, J. C., Miura, N. and Koga, H. (2005). Lateral displacement of ground caused by soilcement column instal
48、lation. Journal of Geotechnical and Geoenvironmental Engineering. Vol.131(5): 623-632. Han, J., Zhou, H. T. and Ye, F. (2002). State of practice review of deep soil mixing techniques in China. Journal of the Transportation Research Board. No.1808:49-57. Liu, S.Y. and Hryciw, R.D. (2003). “Evaluation
49、 and Quality Control of Dry-Jet-Mixed Clay Soil-Cement Columns by Standard Penetration Test”. Journal of The Transportation Research Board, No.1849: 47-52. Liu, S. Y., Gong N. H., Feng, J. L. and Xi, P. S. (2007). Installation method of T-shaped soil-cement deep mixing column. Chinese Patent: ZL 2004 10065862.9. (in Chinese) Liu, S.Y., Yi, Y. L. and Zhu, Z. D. (2008). Comparison tests on field bid
