Embankments constructed on Embankments constructed on soft foundation soilssoft foundation soils

TECHNICAL UNIVERSITY OF CIVIL TECHNICAL UNIVERSITY OF CIVIL ENGINEERING BUCHARESTENGINEERING BUCHAREST

FACULTY OF CIVIL ENGINEERING IN FOREIGN LANGUAGES FACULTY OF CIVIL ENGINEERING IN FOREIGN LANGUAGES

StudentsStudentsŞŞtefantefan MihaiMihai

PaiuPaiu AlexandruAlexandru

TutorTutorSefSef. . LucrariLucrari IngIng. Andrei . Andrei ConstantinConstantin OlteanuOlteanu

Location of the area of interestat national and county level

Two road sectors of 10 km respectively

5 km in length

Stratification of Stratification of subgradesubgrade soilsoil

• 12m thick soft clay layer resting on sand

• moisture contentw=23.60%

• oedometer modulus M2-3=2000÷3000kPa

•consolidation coefficientcv=0.057mm2/s

The diagram clearly shows the presence of high differential settlement

Settlement of the road structure before ground improvement

Ground investigationGround investigation

Diagram of sampling operations

Undisturbed Soil Sampling

Schematic drawing of an open-tube sampler

Improvement techniquesImprovement techniquesVIBROVIBRO--COMPACTION : COMPACTION : VibroVibro--compaction cannot be employed compaction cannot be employed effectively where the fines content (silt and clay) exceeds aboueffectively where the fines content (silt and clay) exceeds about 20 t 20 percent.percent.

DYNAMIC COMPACTIONDYNAMIC COMPACTION: : Dynamic compaction is not effective in soft Dynamic compaction is not effective in soft alluvial or marine clays alluvial or marine clays

TOTAL DISPLACEMENTTOTAL DISPLACEMENT: : This solution, tough usable, was rejected as This solution, tough usable, was rejected as being totally unpractical from cost and duration considerationsbeing totally unpractical from cost and duration considerations

VERTICAL DRAINS: VERTICAL DRAINS: This solution was taken into considerationThis solution was taken into consideration

LIME COLUMNS (SWEDISH METHOD): LIME COLUMNS (SWEDISH METHOD): This method was examined to This method was examined to understand case history experience of lime usage in soft soil imunderstand case history experience of lime usage in soft soil improvementprovement

We chose the solution microWe chose the solution micro--piles made of piles made of

compacted dry quicklimecompacted dry quicklime

Settlement diagram of improved soilSettlement diagram of improved soil

After ground improvementthe settlement values areroughly reduced by half

Reduced scale modelReduced scale model

Natural soil sampleReduced scale model of the soil

enforced with micro-piles made of lime- The natural soil sample was taken

from the site and it was placed in a 10x10x10 box.

- An identical natural soil sample was enforced with micro-piles made of compressed quicklime powder.

- Same material was used as in the case of the real solution.

- The model is a reduced scale representation of a section on the entire width of the subgrade soil (12m real = 10cm model).

- The dimensions and positioning of the micro-piles were computed based on the above considerations.

Theoretical supportTheoretical support

Numerical solutionNumerical solution

Depth-time grid

)2()(

1,,1,122

2

jijiji uuuzt

u−+

Δ=

∂∂

+−

)2()( ,,1,12,1, jijiji

vjiji uuu

ztc

uu −+ΔΔ

+= +−+

Vertical drainsVertical drains

Cylindrical blocks

Trch t⋅

4R2time factor for consolidation due to radial drainage only

Tvcv t⋅

d2time factor for consolidation due to vertical drainage only

c.v

Solution for radial consolidationSolution for radial consolidation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

15 9 7.8 6.6 5.976 5.4288 5.04288 4.71226 4.44768 4.21886 4.02436 3.85332 3.70303 3.56872 3.44823 3.33908 3.23973 3.14873 3.06502 2.98765

15 15 12.6 11.64 10.584 9.8928 9.2592 8.76307 8.32332 7.95148 7.62112 7.33092 7.07029 6.83622 6.62358 6.42979 6.25196 6.08817 5.93661 5.79571

15 15 15 14.04 13.464 12.7728 12.2352 11.7145 11.2694 10.8582 10.4924 10.1569 9.85237 9.57211 9.31446 9.07593 8.85472 8.64872 8.45595 8.275

15 15 15 15 14.616 14.3088 13.9094 13.5531 13.1875 12.8503 12.525 12.2215 11.9338 11.6639 11.409 11.1691 10.9425 10.7273 10.5229 10.328

15 15 15 15 15 14.8464 14.6928 14.4778 14.2627 14.0292 13.7989 13.5668 13.3404 13.1185 12.9037 12.6957 12.4924 12.2949 12.1026 11.9155

15 15 15 15 15 15 14.9386 14.8648 14.7542 14.6323 14.4926 14.346 14.1922 14.0361 13.8784 13.714 13.5486 13.3817 13.2146 13.0476

15 15 15 15 15 15 15 14.9754 14.941 14.886 14.8199 14.7407 14.6537 14.5596 14.4421 14.3188 14.1875 14.0508 13.9092 13.7636

15 15 15 15 15 15 15 15 14.9902 14.9744 14.9493 14.9178 14.8798 14.7894 14.6975 14.5953 14.4847 14.3658 14.2398 14.1075

15 15 15 15 15 15 15 15 15 14.9961 14.989 14.9769 14.9606 14.9399 14.8963 14.8464 14.784 14.7125 14.6314 14.5418

15 15 15 15 15 15 15 15 15 15 14.9984 14.9953 14.9896 14.9814 14.9704 14.9414 14.9045 14.8564 14.7991 14.732

15 15 15 15 15 15 15 15 15 15 15 14.9994 14.998 14.9953 14.972 14.9442 14.9048 14.857 14.7991 14.7321

15 15 15 15 15 15 15 15 15 15 15 15 14.9997 14.9511 14.9041 14.8486 14.7855 14.7129 14.6317 14.5419

15 15 15 15 15 15 15 15 15 15 15 15 14.8798 14.7894 14.6975 14.5953 14.4847 14.3658 14.2398 14.1075

360 348 0 340.8 0 334.56 0 329.28 0 324.499 0 320.156 0 316.122 0 312.352 0 308.794 0 305.422 0 302.211 0 299.147 0 296.024 0 292.919 0 289.836 0 286.762 0 283.69 0 280.616 0 277.537

A Uvt Tv(kPa) (-) (-) Tr Uvt

180 0 0 0.27 0.66795180 0 0.00625174 0.03333 0.0125

170.4 0.05333 0.01875167.28 0.07067 0.02499164.64 0.08533 0.03124162.25 0.09861 0.03749

160.078 0.11068 0.04374158.061 0.12188 0.04999156.176 0.13236 0.05624154.397 0.14224 0.06248152.711 0.15161 0.06873151.106 0.16052 0.07498149.574 0.16904 0.08123148.012 0.17771 0.08748146.46 0.18633 0.09373

144.918 0.1949 0.09997143.381 0.20344 0.10622141.845 0.21197 0.11247140.308 0.22051 0.11872138.769 0.22906 0.12497

Computation of soil improvement solution

ConclusionsConclusions

The solution that was chose was that of quicklime microThe solution that was chose was that of quicklime micro--piles piles bored beneath the road embankment.bored beneath the road embankment.The calculus provided the following dimensions for the chosen The calculus provided the following dimensions for the chosen solutionsolution::

Compacted dry quicklimeCompacted dry quicklime injected into boreholes will be used for the injected into boreholes will be used for the micromicro--pilots;pilots;The microThe micro--pilots will have the following geometry: pilots will have the following geometry: 15 cm diameter and 12 m depth15 cm diameter and 12 m depth (the bottom of the clay layer)(the bottom of the clay layer)The positioning is of successive intercalary rows of pilesThe positioning is of successive intercalary rows of pilesThe spacing between piles is equal to the spacing between piles The spacing between piles is equal to the spacing between piles on a on a row, row, 1 m.1 m.

For this geometry, placing and composition of the ground For this geometry, placing and composition of the ground improvement solution, improvement solution, complete consolidation complete consolidation of the soil (of the soil (80%80%) ) should take place within approximately should take place within approximately 3 months3 months..