DOI

10.5703/1288284314216

Abstract

Peats and organic soils in general pose significant problems to geotechnical engineers due to their low strength, high compressibility and elevated creep. The research performed addressed one soil improving technique, deep soil mixing, that has been widely used for treating soft clays, but that especially in the US has found limited use in presence of organic soils. The work performed made use primarily of one soil sampled on Lindberg Road (LR) in West Lafayette, IN characterized by LOI= 45-52%, LL= 327%, PL= 162%, LLoven dried/LLnon-dried = 0.31, Gs = 2.05-2.12, fiber content ~2.29%, clay fraction = 40.6%. In addition, a limited number of tests were performed making use of soils with LOI of 10-20%, manufactured in the lab from LR soil and an illitic clay.

A procedure was developed for preparing samples of reconstituted LR soil both untreated and mixed with a binder and which included a “curing” stage under a surcharge to simulate treatment at depth. Specimens obtained from these samples were used for the engineering tests which included constant rate of strain (CRS) consolidation tests, end-of-primary incremental loading (EOP-IL) consolidation tests with one long term creep stage, and unconfined compression tests. A battery of characterization tests and an in depth review of the literature complemented this work.

Unconfined compression tests provided a preliminary evaluation of the effects of treatment on the strength of the soil; highlighted the effects of curing under a surcharge; and allowed to identify in Portland cement (PC) the most promising binder, which was subsequently used for all other engineering tests, at dosages ranging from 8% (~25 kg/m3) to 100% (~320 kg/m3)by dry mass of the soil. The results of the consolidation tests highlighted how the accurate characterization of the primary consolidation behavior of soils characterized by high tendency to creep must rely on either CRS or EOP-IL loading tests and demonstrated the effects of treatment with cement on the stiffness, the hydraulic conductivity, the rate of consolidation and the rate of creep of the soil. Specifically, the tests showed how the addition of cement is associated with the development of a preconsolidation pressure and the shift of the compression curve towards higher effective stresses. Once this yield stress is exceeded the compressibility in the virgin compression range is found not to vary significantly with cement content. Also associated with the addition of cement is an increase in the hydraulic conductivity, an increase in the coefficient of consolidation, and a reduction in the creep coefficient at any given stress level. Moreover, the Cα/Cc ratio decreases markedly with cement addition indicating a decreased susceptibility of the soil to creep. All these effects are more marked with increasing cement content and the treatment appear especially effective once the PC% exceeds 50% (~160 kg/m3).concrete, pavement, life-cycle cost, specifications

Report Number

FHWA/IN/JTRP-2004/38

Keywords

organic soils, LOI, compressibility, consolidation, constant-rate-of-strain (CRS), secondary compression, strength, ground improvement, cement, SPR-2460

SPR Number

2460

Project Number

C-36-50U

File Number

6-19-20

Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, IN

Date of this Version

9-2005

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