honours thesis poster - rolling dynamic compaction
TRANSCRIPT
Rolling Dynamic CompactionSHUZHUANG CHEN, ZHONGYAN YUDAVID, AIERYSchool of Civil EngineeringFACULTY OF ENGINEERING & INFORMATION TECHNOLOGIES
IntroductionBackground Rolling Dynamic CompactionRolling Dynamic Compaction (RDC) is a widely used ground improvement technique which has been particularly cost-efficient in large construction areas. Despite its popularity, there is a general lack of understanding on its working mechanism.
Objective of ResearchA 1:15 physical impact roller model was employed to examine the effectiveness RDC as well as the feasibility of testing this technique in a laboratory environment.MethodologyBasic Configuration River sand and River sand mixed with 20% fines were tested at three different RDC running speed. In total 9 sets of tests were conducted for this project in a 1.4x0.5x0.28m tank.
Measuring DeviceThe settlement of subgrade soil due to RDC was measured by buried displacement plates connected to LVDT at the tank base. Additionally, CPT was performed as an alternative method to evaluate soil densification.
Results and DiscussionQualitative Observation The videos and photos taken by high speed camera during the test shows the roller was compacting the soil downward as well as pushing the soil out of its way at the same time.
THIS RESEARCH IS SP
THIS RESEARCH IS SPONSORED BY
CPT Results The comparison of CPT results before and after RDC in some group of tests shows a significant improvement of cone tip resistance.
Calibration of sand with different densities was performed to investigate the correlation between normalized and relative densities for a more in-depth dimensionless analysis.
The correlation was found to be. River Sand : Mixture Sand:The relative density vs depths profile produced by dimensionless analysis does not show a clear densification caused by RDC.
Nevertheless, student-T test results suggested that some CPT results may be subjected to severe disturbance from soil surface and should be not relied upon as the lone source of evidence, because of the exceptionally low probabilities values for pre-RDC data.
Settlement Results Subgrade soil settlement provides a solid evidence of soil densification up to 80 mm underneath the surface.
Applying 1-D elastic theory on the settlement results, relative densities before and after RDC can be estimated by the following calculation.
Id(%) = For this research project, the density was shown to experience a 20%-30% increase.
Scale-up of Results The empirical formula for influence depth estimate produced by Maneard and Borise (1975) suggests the following relationship
The laboratory results returns n values ranging from 0.24 to 0.69 It is consistent with the research result conducted by Rollins and Rogers (1994) which approximated the n value to be 0.4-0.6. Conclusion 1. Loosening and densification were both
observed near soil surface at RDC.2. Soil densification (up to 20-30%increase)
occurred under the surface 3. The influence depth of RDC model has a
minimum value of 80 mm. 4. CPT result can be used as a more reliable
evaluating tool at tests with larger scale. 5. The use of empirical methods for influence
depth estimate has worked reasonably successfully.
Insert SPONSOR LOGO
0 0.1 0.2 0.3 0.4 0.5 0.60
5
10
15
20
25
30
v = 0.72m/s , Mixture Sand
before compaction
after com-pactionqc (MPa)
Dep
th (c
m)
20 21 22 23 24 25 26 27 28 29 30
-25
-20
-15
-10
-5
0
Loose sand relative density vs Depth
Initial 0.42 m/s0.72 m/s1 m/s
Relative Density (%)
Dep
th(c
m)
5.0% 10.0%15.0%20.0%25.0%30.0%35.0%40.0%45.0%
-90-80-70-60-50-40-30-20-10
0
Relative Density of Loose River Sand
0.42m/s
1.0m/s
0.72m/s
Before RDC
Relative Density(%)
Dep
th (m
m)
0 0.2 0.4 0.6 0.8 1 1.2 1.40
102030405060708090
Settlement vs Depth at Speed = 0.72m/s
loose river sand
mixturesettlement (mm)
Dep
th (m
m)
0 1 2 3 4 5 6 7 8 905
101520253035
Calibration Results with Different Densities
17kN/m^3
18kN/m^3
19kN/m^3
16.2kN/m^3
18.3kN/m^3
Cone Resitance qc (MPa)
Dep
th (m
)
020
040
060
080
010
0012
0014
0016
0018
0020
000
102030405060708090
100
Relative Density(%) vs Normalised qc (MPa)
Normalised Qc
Rel
ativ
e D
ensi
ty(%
)
1 2 3 4 5 60%
10%20%30%40%50%60%70%80%90%
Student T-Test Results 1m/s
0.72m/s
0.42m/s