Missouri University of Science and Technology Scholars' Mine International Conference on Case Histories in (1993) - Third International Conference on Case Geotechnical Engineering Histories in Geotechnical Engineering 03 Jun 1993, 10:30 am - 12:30 pm Behavior of a Braced Sheet Pile Wall in Soft Clay T. Edstam Leif Jendeby Follow this and additional works at: https://scholarsmine.mst.edu/icchge Part of the Geotechnical Engineering Commons Recommended Citation Edstam, T. and Jendeby, Leif, "Behavior of a Braced Sheet Pile Wall in Soft Clay" (1993). International Conference on Case Histories in Geotechnical Engineering. 4. https://scholarsmine.mst.edu/icchge/3icchge/3icchge-session05/4 This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License. This Article - Conference proceedings is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in International Conference on Case Histories in Geotechnical Engineering by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. Proceedings: Third International Conference on Case Histories in Geotechnical Engineering, St. Louis, Missouri, !!!! June 1-4, 1993, Paper No. 5.14 ~.,:..~ . Behavior of a Braced Sheet Pile Wall in Soft Clay T. Edstam l. Jendeby Chalmers University of Technology, Gotherburg, Sweden Chalmers University of Technology/NCC, Nordic Construction Company, Gothenburg, Sweden SYNOPSIS The earth pressure distribution against, and the displacement of, a braced sheet pile wall in soft clay have been examined. In connection with the construction of a fly-over, on the west cost of Sweden, two sections of a braced sheet pile wall were instrumented. The instrumentation consisted of earth pressure cells and inclinometer pipes mounted on three sheet piles. The sheet pile wall was also analyzed by means of the FLAC code in which the interaction between the sheet pile wall, the struts and the soil was studied. The movements and the calculations are compared with a conven­ tional design method according to Peck. The results indicate that the earth pressure distribution and the ~eflection of the wall is strongly dependent on the construction procedure. The FLAC code was found to be a useful tool for parameter studies, but can hardly be used for design. INTRODUCTION In areas with deep deposits of soft soil, deep excavations often require expensive construc­ tions, e.g. braced sheet pile walls. The design of such a construction is often decisive for the economy of the project as a whole. Further, the :c design of the construction is a question of saf­ ety for the personel working down in the excava­ tion. I~ N"umerous computer programs are today available for the design of retaining structures. However, :=.ut='lf=rflf:Zifl:r- -·-·-!1"--·-·-1-.~ almost exclusively the main effort is devoted to I the design of the wall itself and the strutt­ J f3qgHJ .... ' ings, while the load acting on the construction, i.e. the earth pressure, is determined in a very KA= 1- m4T,u_ simplified way. This is, for example, often done qgH 0,2<8<0,4 according to Rankine's theory, despite that one ~nows that the pressure acting on the wall has a 0,4< ffi< 1,0 iifferent distribution. rhe knowledge within this very central geotech- Fig. 1 Maximum envelope for earth pressure to 1ical domain is, however, still limited. In be used for design of supports L972, Bj errum et al stated that "The number of neetings on the subject seems at least somewhat a) soft clay, N ~ 4 to 6 )Ut of proportion with the progress being made b) stiff clay, N < 4 Ln the field", [1]. N = pgH/r:ru ~he lack of analytical models describing the (After Peck, 1969) Jroblem is explained by the extreme complexity Jf the problem. Except that the problem is :hree-dimensional and requires information con­ :erning the properties of the soil as well as :he structure, it is also influenced by time and Extensive work by Peck [ 2] during the forties JY the construction procedure at the site. The resulted in principal earth pressure distribu­ lifficulty of predicting the actual stress dis­ tions for strut design, see fig. 1. This is not, :ribution is also increasing when the construc­ however, an attempt to describe the actual :ion is statically undetermined, which is the stress distribution, but instead an envelope of :ase for walls with more than two bracing le­ the maximum pressure that can occur at any time ·els. during the whole excavation process. Third International Conference on Case Histories in Geotechnical Engineering 717 Missouri University of Science and Technology http://ICCHGE1984-2013.mst.edu Numerous field studies in Oslo, about 30 years decrease due to the wall deflection. B ago, led to further understanding of the pro­ arching the stresses then will increas blem. Especially the influence of the stability above level I, and below level II. of the excavation as a whole was examined, and thereby the true strength properties of the soil ii) since the excavation of the soil will de became important parameters, ( 1] • A model that crease the vertical stresses below the bas accounts for anisotropy as well as time effects of the excavation, the horizontal stresse was presented, see fig. 2. between levels II and III will also de crease. This, in turn, leads to a movemen of the soil below level II to the left. Th )1.,. earth pressure on the active side wil active passive therefore be redistributed by means of arch soft clay ing, and in this case it will be transferre partly to the lowest strut, partly to th 1,5 0,5 lp <0,5 stiffer strata at level III. lp<0,5 1,5 0,8-1,0 as~--~--~--~~ 0 (§) @ · o.2 o;. o.s o.s 1,o p 11 p p plasticity index, lp --~ I 1- Fig. 2 Correction of undrained shear strength -·-·_j_ - I due to rate of loading and anisotropy I t I v I 'r 1: Dr I fu JJ.A JJ.R fu -~ 'r undrained shear strength from fu field vane test JJ.R correction factor for rate of Fig. 3 Arching effects due to excavation loading a cross section JJ.A correction factor for anisotro- py b schematic change of earth pressur due to the disapperance of eart (After Bjerrum et al, 1972) pressure between I and II on th excavation side. c schematic change of earth pressur due to decrease in vertical stresse Except the properties of the soil, there is two on the excavation side. factors governing the magnitude and the distri­ (After Bjerrum et al, 1972) bution of the earth pressure acting on the wall, namely the deflection of the wall, and the geo­ metry of the excavation (which influences the overall stability). In order to study those effects, and to get a overall understanding of the load-displacemen A sheet pile wall driven into soft clay will relations for braced sheet pile walls in sof rather soon after installation be exposed to clay, three instrumented full scale sheet pile earth pressures close to the at-rest conditions, were manufactured. The instrumentation made i which corresponds to a K -value of about 2/3. As 0 possible to measure earth pressure against th the excavation then progresses, the wall will "active side" of the piles, and the deflectic move towards the excavation leading to decreased of the piles above as well as below the dredg earth pressure against the backside of the wall, level. which in turn means that the shear stresses within the soil increase. If the deflections get The results of these measurements are presente large enough, the shear stresses will reach the in the following, and the problem is also ana shear strength,and the earth pressure will then lyzed by means of the FLAC code (3]. jecrease to its minimum value, which is normally =alled the active earth pressure (Rankine) . How­ \Ver, due to a limited deflection, variations in FIELD STUDY 1oil or construction stiffnesses, or limited 1tability, the earth pressure distribution will The three instrumented sheet piles were drive liffer from the Rankine distribution. such in a soft clay deposit where a six meter deep .Jhenomena are shown in fig. 3. 19 m wide, and more than 40 m long excavatio was to be carried out. A cross section of th When excavation is carried out from level I to excavation is shown in fig. 4. level II, the earth pressures will be changed due to two principal effects; Since the instrumented sheet ·piles were place close to the center of the wall, two-dimensiona i) the earth pressure on the "passive side" conditions can be assumed. The subsoil consist caused by the soil between levels I and II of soft marine clay overlying a thin layer o is removed, bringing the wall to deflect frictional material, which in turn rests o towards the excavation. The pressure on the rock. The thickness of the clay layer is ap "active side" at the same level will then proximately 15 m. The properties of the clay i shown.in fig. 5. Third International Conference on Case Histories in Geotechnical Engineering Missouri University of Science and Technology http://ICCHGE1984-2013.mst.edu 718 RESULTS OF FIELD MEASUREMENTS SYI< FILL SOX PILE C Sm Readings of the earth pressure were taken at totally 3 3 occasions 1 before, during and after the excavation work. The displacements of the sheet pile wall were measured at 15 occasions. The observations continued for a period of 107 HEB 360 BOX PILE C 4,5 m days.