Secondary settlement estimation in surcharge preload subject to time effect of secondary consolidation coefficient

Abstract

In order to eliminate the settlement underestimation in surcharge preload engineering, a study based on Bjerrum’s creep diagram and the tangent slope definition of secondary consolidation coefficient was carried out to analyze the time effect of secondary consolidation coefficient of over consolidated soil, and a time–growth model for it was formulated. As Bjerrum’s creep diagram is an idealized model, oedometer tests were performed to improve the above time–growth model of secondary consolidation coefficient for the purpose of achieving a better agreement with the actual ground situations. It is found that secondary consolidation coefficient of over consolidated soil not only decreases with the ratio of historical maximum to current effective stress of soil (OCR), but also increases with the development time of secondary consolidation. No matter how large OCR is, the long-term time effect of secondary consolidation coefficient of over consolidated soil is all significant. Based on the above results, a model for settlement estimation was formulated and a case study to estimate it indicates that the settlement estimated by our method is 2–5 times larger than that estimated by the previous method. Moreover, the larger the OCR is as well as the longer the service life is, the larger the difference between our method and the previous method is. Thus, the post-construction secondary settlement in surcharge preload engineering will be underestimated when neglecting the time effect of secondary consolidation coefficient in over consolidated state.

Keywords

post-construction secondary settlement / time effect / tangent slope / secondary consolidation coefficient

References

[1] GongX-nanFoundation treatment manual [M], 2008BeijingChina Architecture & Building Press70-97

[2] AlonsoE, GensA, LloretA. Precompression design for secondary settlement reduction [J]. Geotechnique, 2000, 50(6): 645-656

[3] LiuH-l, HuS-x, HassanA. Test study on creep characteristics of soft clayey soils under consolidation by vacuumsurcharge combined preloading method [J]. Rock and Soil Mechanics, 2008, 29(1): 6-12

[4] GuoL, CaiY-q, GuC, WangJun. Resilient and permanent strain behavior of soft clay under cyclic loading [J]. Journal of Zhejiang University (Engineering Science), 2013, 47(12): 2111-2117

[5] BjerrumL. Engineering geology of normally consolidation marine clays as related to settlements of buildings [J]. Geotechnique, 1967, 17(2): 81-118

[6] YinJ H, GrahamJ. Visco-elastic-plastic modeling of one-dimensional time-dependent behavior of clays [J]. Canadian Geotechnical Journal, 1989, 26(2): 199-209

[7] YinJ H, JamesG. Equivalent times and one-dimensional elastic visco-plastic modeling time-dependent stress-strain behavior of clays [J]. Canadian Geotechnical Journal, 1994, 31: 42-52

[8] HuY-yuan. Application of plastic-like visco-elastic model to clay [J]. Chinese Journal of Geotechnical Engineering, 2003, 31(3): 353-360

[9] YinZ-z, ZhangH-b, ZhuJ-g, LiG-wei. Secondary consolidation of soft soils [J]. Chinese Journal of Geotechnical Engineering, 2003, 25(5): 521-526

[10] NashD F T, RydeS J. Modelling consolidation accelerated by vertical drains in soils subject to creep [J]. Geotechnique, 2001, 51(3): 257-273

[11] DegagoS A, GrimstadG, JostadH P, NordalS, OlssonM. Use and misuse of the isotache concept with respect to creep hypotheses A and B [J]. Geotechnique, 2011, 61(10): 897-908

[12] MeiG-x, YinJ-hua. Coupled model of consolidation and creep for consolidation test [J]. Journal of Central South University, 2008, 15(1): 357-361

[13] ZhouQ-j, ChenX-ping. Experimental study on creep characteristics of soft soils [J]. Chinese Journal of Geotechnical Engineering, 2006, 28(5): 626-630

[14] LiG-w, ShengW-g, JiangH-z, YinZ-ze. Secondary compression characteristics and settlement calculation of soft clay under over-loading-unloading and reloading [J]. Chinese Journal of Geotechnical Engineering, 2009, 31(1): 118-123

[15] YinJ H. Non-linear creep of soils in oedometer tests [J]. Geotechnique, 1999, 49(5): 699-707

[16] ZengL-l, HongZ-s, LiuS-y, ZhangD-j, DuY-jun. A method for predicting deformation caused by secondary consolidation for naturally sedimentary structural clays [J]. Rock and Soil Mechanics, 2011, 32(10): 3136-3142

[17] MesriG, StarkT D, AjlouniM A, ChenC S. Secondary compression of peat with or without surcharging [J]. Geotechnical Engineering, 1997, 123(5): 411-421

[18] NashD F T. Precompression design for secondary settlement reduction: discussion [J]. Geotechnique, 2001, 51(9): 822-823

[19] HuY-yuan. Discussion on “Secondary compression characteristics and settlement calculation of soft clay under overloading-unloading and reloading” [J]. Chinese Journal of Geotechnical Engineering, 2009, 12: 1963-1965

[20] BuismanK. Result of long duration settlement tests [C]// Proceeding of 1st International Conference on Soil Mechanics and Foundation Engineering. Delft Geotechnics, Delft, the Netherlands, 1936103-112

[21] HuY-yuan. A practical evaluation of the surcharge preload period in staged construction subject to creep [J]. Computers and Geotechnics, 2011, 42: 171-179

[22] HuY-yuan. Approximately determining preloading duration considering creep [J]. Journal of Zhejiang University (Engineering Science), 2009, 46(2): 250-256

[23] SchmertmannJ H. The mechanical aging of soils [J]. Journal of Geotechnical Engineering, 1991, 117(9): 1288-1330

[24] CrawfordC B. Interpretation of consolidation tests [J]. Soil Mech Found Div, ASCE, 1964, 90(5): 87-102

[25] YuX-j, YinZ-z, DongW-jun. Influence of load on secondary consolidation deformation of soft soils [J]. Chinese Journal of Geotechnical Engineering, 2007, 29(6): 913-916

[26] ZengL-l, ZengJ, ChenF-quan. Mechanism of surcharge preloading on deformation of soft natural clay affected by soil structure [J]. Journal of Fuzhou University (Natural Science Edition), 2013, 41(2): 235-241