Shear and compression behaviour of crushed mudrocks in Malaysia
Mudrocks is a type of rock that tends to deteriorate upon exposure to water. Studies have found mudrocks to be in low to medium durability in which its shear strength and compressibility were easily influenced by its resistance towards wetting and drying. However, in Malaysia, it is difficult to...
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| Format: | Thesis |
| Language: | English |
| Published: |
2019
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/84267/1/FK%202019%20106%20-%20ir.pdf |
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| Summary: | Mudrocks is a type of rock that tends to deteriorate upon exposure to water.
Studies have found mudrocks to be in low to medium durability in which its
shear strength and compressibility were easily influenced by its resistance
towards wetting and drying. However, in Malaysia, it is difficult to avoid
mudrocks from exposure to water due to the tropical climate. When mudrocks
were encountered on construction sites, they were often been excavated
however, it is not a sustainable solution. Thus research on shear and
compression behaviour of crushed mudrocks with detailed explanations on
morphological changes that relate with mineralogical and chemical
composition is required before suitable stabilisation or any advance solutions
on working out crushed mudrocks as geotechnical material could be carried
out. Hence this research implied direct shear tests, XRD, XRF and VPSEM to
evaluate the shear and compression behaviour of crushed mudrocks in
Malaysia. This study was conducted onto mudrocks in Malaysia from
Putrajaya, Semanggol (Perak) and Durian Tunggal (Melaka). The materials
were named as CM1, CM2, and CM3 respectively. These crushed mudrocks
predominantly contained of swelling clays where CM1 contained 38.2%, CM2
contained 35.1% and CM3 contained 58% of swelling clays respectively.
Three types of slaking tests were carried out; jar slake test, slake durability
test, and slaking immersion test. Based on the results, CM2 was the most
durable, followed by CM1 and lastly CM3. This pattern of sequence agrees
with swelling clay minerals contents but went inversely with total mica contents
in which CM2 has the highest with 34.7%, followed by CM1 with 29.4% and
lastly CM3 with 25%. Shear and compression behaviour of crushed mudrocks
were investigated at various compaction degree, various initial moisture
content, and various terms of immersion in which the tests were accompanied
with staged-loading process using direct shear box test. Higher compaction
degrees caused crushed mudrocks to exhibit highest peak shear strength in which decrease of subsequent 5% compaction degrees had caused 11% to
12% peak shear strength reduction and 2% compression to take place. Due to
increment of initial moisture content from natural to optimum, peak shear
strength of crushed mudrocks increased by 4.4% to 6.9% with reduced
brittleness and about 0.6% to 1.2% compression took place since early
loading stage. Upon immersions, direct shear tests revealed that all crushed
mudrocks failed in brittle deformation when without immersion. Short term
immersion had intensified crushed mudrocks brittle behaviour with peak shear
strength reduction of 15% for CM1 and CM2, and 42% for CM3. Long term
immersion, on the other hand had caused only 3% strength reduction with fully
plastic straining behaviour after failure. In addition, short term immersion
caused immediate compression of about 3% to crushed mudrocks while long
term immersion caused CM1 and CM2 to show progressively reduced
compression, and CM3 to show progressive compression along stagedloading
process.VPSEM images shown that vigorous micro activities that took
place during short term immersion had led to strength reduction and high
compressibility of mudrocks while long term immersion had enabled prolonged
micro-activities hence resulted into higher peak shear strength than that of
recorded by short term immersion. As a result, micro flaws; micro holes, micro
fracture and micro cracks were seen from VPSEM images of mudrocks after
short term immersion. The micro flaws had caused mudrocks to experience
strength reduction and high compression. However the micro flaws were seen
resealed after long term immersion as prolonged micro activities had
promoted healing to the flaws. Interestingly, these micro activities were able to
occur due to presence of swelling clay minerals which seem to have increased
aggregate’s ability to absorb water and to weave with each other. This study
hence found that mudrocks are not only sensitive to moisture changes but to
sudden moisture changes as pictured through short term immersion while prewetting
effect through long term immersion had reduced mudrocks sensitivity
towards moisture changes throughout staged-loading. |
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