Experimental investigation to the settling and consolidation of dredged glacial till

Experimental investigation to the settling and consolidation of dredged glacial till

Van Dijk, N.N.

Jommi, C. (mentor)

Civil Engineering and Geosciences

Section Geo-Engineering

2016-02-11

In this research we studied the behaviour of dredged glacial till in the creation of a landfill. An experimental approach is used where we primarily focussed on the settling and consolidation characteristics. Till is in general a well graded, non sorted material and segregation during dredging and transportation can be expected. The aims of this research were to classify the fine-grained till slurry, to determine the consolidation related soil parameters and to validate the parameters, approach and assumptions made by the client who previously performed research on the same material. The researched also focussed on the expected segregation within the fine-grained slurry and on the environmental conditions (sea-salt environment). Additionally, multiple landfill scenarios are discussed. The dredging process is simulated by immersion and wet sieving and the fine grained slurry (<0.063mm) forms the base of all tests. In this slurry, all particles are disintegrated. A segregation is made within the fine slurry, at a level of about 0.0085mm, to investigate the different fractions. The grain size distribution of the bulk shows a well graded material containing 50% fines. The atterberg limits are relative low, the plastic and liquid limits are in the range of 10.6% to 18.8% and 19.8% to 38.5% respectively with the lowest values for the samples with the highest grain sizes. The column settling test showed that the void ratios after one week of free settling in a sea-salt environment vary between 1.7 and 5.9 with the highest value for the finest grain size. However, the result of the latter test result shows that settling has not yet finished at the termination of the test (after 7 days). The executed one-dimensional compression tests (oedometer tests) show that the coefficients of consolidation cv vary between 10E-9 and 10E-6 m2/s with the lowest values for the fines material. We see a gradual increase in cv value with increasing stress. The compression ratio CR shows a decrease with increasing stress and is 0.25-0.14 for the finer material and 0.12-0.06 for the coarser material. The coefficient of secondary compression Calpha also decreases with increasing stress and is for all samples in the range of 0.009-0.001 with the lowest values for the coarser material. The amount of disintegration and segregation of the particles determines which grain size dominates and controls the consolidation of the soil. In case the particles do not disintegrate during dredging, a scenario with coarser material should be investigated. In this scenario, the data from the client is very conservative. A scenario with full disintegration and segregation during dredging and transportation leads to a combination of coarser and finer material in which the most fine material controls the consolidation. In this scenario, the data from the client is progressive in terms of the expected consolidation period and gives a good estimation of the total settlement. Modelling the compression parameters in a simplified geometry in D-Settlement led to a shorter consolidation period and less settlement for the coarser particles compared to all other fractions. The most fine grained material, led to a considerable longer consolidation period and more primary and secondary settlement. However, the most settlement can be expected at very low stress levels because the oedometer results show that at a stress level of 0.3kPa, the void ratio has already decreased to 1.5 in case of the most fine material and to 0.8 for the coarser material. The 'immediate' settlement in the lower stress regime is not modelled in the described model and does not obey the compression parameters mentioned above.

till
self-weight consolidation
landfill
reclamation
segregation
dredging

http://resolver.tudelft.nl/uuid:1c0060de-8f6a-4e24-beae-9cca2bf73e42

2021-02-01

Student theses

master thesis

(c) 2016 Van Dijk, N.N.