Effect of cyclic soaking and drying on the behavior of gypsum

Dissertant

Salim, Bushra Mikhail

University

University of Technology

Faculty

-

Department

Department of Building and Construction Engineering

University Country

Iraq

Degree

Ph.D.

Degree Date

2006

English Abstract

This thesis presents an experimental study into the effect of cyclic soaking and drying on the behavior of gypsum sand sub-grade soil brought from Al-Gama village in Al-Anbar governorate, north-west of Baghdad.

The tested soil is poorly graded sand with gravel (SP) according to Unified Soil Classification System and A-l-b according to AASHTO Soil Classification System.

The soil contains total soluble salts (TSS) of 42.58 % and a gypsum content of 38.75 %.

For studying the effect of cyclic soaking and drying on the strength., stiffness and deformation characteristics of the soil tested, five different cycle lengths were adopted namely 8.

14.

28.

60 and 180 days.

For each cycle length the study eared six cycles.

Hash cycle consists of two phases of equal length namely a soaking phase followed Bv a driving phase.

CBR soil samples were prepared at 95 % relative modeled AASHTO compaction and subjected to a surcharge load of 45 lb (200.3N) representing a flexible pavement structure of about 57cm total thickness.

At the end of each phase of each cycle, and for every evil length.

CBR load-penetration test was carried out to arrive at the variation of soil strength and stiffness during cyclic soaking and drying.

For cycle lengths of 14 and 60 days, use was made of the wave propagation technique for determining the resilient modulus of the soil at the end of each phase of each cycle of the selected cycle length.

The results reveals that the CBR decreases during the soaking phase and increases during the drying phase of each cycle of the cyclic soaking and drying and that the equilibrium condition is rather achieved at the end of the fifth cycle independent of the cycle length.

The results reveals also that there is strong correlation between the resilient modulus results obtained from the CBR full load-penetration curves with those obtained from the wave propagation technique.

The distributions of moisture content and gypsum content along CBR soil samples were determined after each soaking phase and after each drying phase for all cycles and all cycle lengths.

Vertical displacement measurements were carried out for each cycle length to arrive at the soil behavior of swelling / settlement with time.

Regarding the deformation it was found that continuous soaking underestimates generally the final deformation of gypsiferous soils as compared with cyclic soaking and drying.

Regarding the gypsum content, it was found that a non-uniform distribution takes place along the CBR samples.

Gypsum concentrates at the lower layers for short cycle lengths.

However for long excel lengths the migration of gypsum to upper lavers encourages the dissolving in soaking phases, hence a greater less in gypsum content was pronounced for long cycle lengths.

Main Subjects

Civil Engineering

Topics

• Soil mechanics
• Iraq
• Anbar
• Calcareous soils

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305927