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2017 International Conference on Transportation Infrastructure and Materials (ICTIM 2017) ISBN: 978-1-60595-442-4
Study on Light Dynamic Penetration to Test Coarse Sand
Relative Density in Bridge Culvert Back Sand Filling
J.B. Lv, Y.M. Yin, Z.T. Yu, Z.C. Xu, G. F. Chen, F. Yang
Guangdong University of Technology, Guangdong Guangzhou, China, 510006
With the rapid development of highway construction in China, vehicle
bouncing at bridge approach has become a very important influencing factor
and has been paid much attention in domestic and overseas transportation study.
Strict quality control in bridge-culvert back sand filling and construction
process is of vital importance to prevent the differential settlement of bridge
approach. However, the objective and effective test of sand relative density in
bridge-culvert backfilling has been a hot yet difficult problem. In this study,
based on model and on-site test under a scientific research program of the
Guangdong Transportation Group - Sand Relative Density Test on
Bridge-Culvert Backfilling (2008-13), the mechanism and the feasibility of light
penetration test have been systematically studied. Through model and field test,
the feasibility of light penetration to test relative density of coarse sand in
bridge-culvert back-wall filling is testified. And through static penetration test
contrast, the reliability of this test is further confirmed. Based on the above, the
empirical relationship between the light penetration blow-counts N10 and the
relative density Dr is established after simple calculation. Thus the light
penetration method is proposed to test the relative density of medium and
coarse sand in bridge-culvert back-wall filling. This study lays a foundation for
the spread-use of the light dynamic penetration to count the technical
index—the relative density of sand in bridge-culvert back-wall filling.
Keywords: highway bridge-culvert back-wall filling; light penetration,
blow-counts, relative density, test method
1. Introduction
Light dynamic penetrating test is a kind of commonly used in-situ soil test
method. The method utilizes hammer force to hit the drill into soil and judges
the soil nature according to the strength of penetrating force, which reflexes the
different nature of soil mechanism. The light dynamic penetrating test apparatus
is light, portable and convenient for control, and many countries have launched
researches in this field and reached great achievements ever since the 1950s. At
the same time, the application of the light dynamic penetrating test method in
the sand soil has been improved. However, due to the light hammer and the
weak hitting force and the possible elastic bending of the pile, this method was
considered applicable only in dividing the soil mechanism layers and in
evaluating the equi-distribution degree of soil layers in fine sand soil. However,
construction practice manifests that light penetration is also applicable to test
the relative density of medium, coarse and gravelly sand in bridge-culvert
back-wall filling.
In bridge-culvert back-wall filling, sand soil and material of good
permeability are suitable. The medium coarse sand is widely used in highway
bridge-culvert backfilling for its good permeability, availability, convenience
and low price. However, the appropriate evaluating method is still unavailable
to measure the technical index—the “relative density” of backfill sand, which
causes a problem for quality control of bridge-culvert back-fill that is widely
and dispersedly used in highway construction. Based on the model test and field
test, the study systematically analyzed the feasibility, the test and evaluation of
light penetration to test the sand relative density in bridge-culvert back-wall fill.
The symbols and notation used in the paper analysis are defined in table l.
Table 1. Symbols and notation.
Cu coefficient of uniformity, uniformity coefficient
Cc coefficient of curvature
Dr sand relative density
emax maximum void ratio
emin minimum void ratio
F coefficient of compressibility
Gs specific gravity
h drill penetrating depth
hcr critical depth
Mx Fineness modulus
N10 the light penetration 30cm blow-counts above
critical depth
N10L blow-counts right at the critical depth
N10' revised light penetration blow-counts above critical
depth
N10L' revised light penetration blow-counts right at
critical depth
ρ the Correlation Coefficient
Qc the static penetration cone point resistance
2. Model test
2.1 Brief introduction of model test
Figure 1. The testing model tank.
φ45
40
φ25
drill
drill pole
hammer base
heavy hammer
Leading bar
Figure 2. The light dynamic penetrating apparatus.
16
φ40
60°
34.64
8
φ25
Figure 3. Size of the driller (unit mm).
In this study, sand of four sizes are chosen in bridge and culvert backfill,
and the model test is proceeded in a model tank (2m×2m×2m). 23 effective tests
are accomplished and 72 groups of data are collected. The model sink is shown
in figure 1, the light dynamic penetrating equipment and its index is shown in
table 2. The drawing of the light dynamic penetrating equipment is shown in
figure 2, the driller structure in figure 3, the constituents of test sand in table 3
and the substantial index of sand in table 4.
Table 2. The dynamic penetrating equipment and its index in model test.
The hitting hammer The driller Diameter of
the
penetrating
pile
(mm)
Penetrating
index
(Blow/30cm)
Weight of
the hammer
(kg)
Hitting
distance
(cm)
Diameter
(mm)
Cone-shaped
angle
(°)
10±0.2 50±2 40 60 25 N10
Table 3. Constituents of test sand(%).
Sand Sieve grain diameter(mm)
10 5 2 1 0.5 0.25 0.074
No.1 97.2 86.8 32.9 14.8 6.3 0.0 0.0
No.2 100.0 99.8 92.6 66.8 42.6 17.5 4.0
No.3 100.0 94.1 73.4 57.5 41.2 13.9 2.9
No.4 100 95.3 66.8 38.1 20.8 3.2 1.2
Table 4. Substantial index of the test sand.
Sand
Fineness
modulus
Mx
Gs emax emin F d50
/mm Soil
No.1 4.17 2.65 0.9410 0.3862 1.4358 1.285 Super-coarse sand
No.2 2.47 2.63 1.0293 0.4611 1.2323 0.565 Fine sand
No.3 2.66 2.65 0.7980 0.4096 0.9478 0.600 Medium sand
No.4 3.36 2.66 0.9710 0.4409 1.2014 1.450 Coarse sand
Note 1: Mx is counted out after sieving analysis, compressibility factor
F=(emax-emin)/emin;
Note 2: The test sand is called quartz sand because of its quartz
component.
2.2 Model Test Work
0
30
60
90
120
150
180
210
0 20 40 60 80100120140160
enetrating depth h(cm)
blow counts N10(blow/30cm)
Dr=
0.5
4Dr=
0.7
0
0
30
60
90
120
150
180
210
0 20 40 60 80100120140160
enetrating depth h(cm)
blow counts N10(blow/30cm)
D
r
=
0…
Figure 4. Sand No.1 result. Figure 5. Sand No.2 result.
0
30
60
90
120
150
180
210
0 20 40 60 80 100 120 140
enetrating depth h(cm)
blow counts N10(blow/30cm)
Dr=0.49
Dr=0.59
Dr=0.74
Dr=0.90
0
30
60
90
120
150
180
210
0 20 40 60 80 100 120 140 160 180
enetrating depth h(cm)
blow counts N10(blow/30cm)
Dr=0.49Dr=0.62Dr=0.7
6
Figure 6. Sand No.3 result. Figure 7. Sand No.4 result.
Based on the features of material commonly-used in highway
bridge-culvert backfill, four different sizes of medium and coarse sand are
chosen for model test in the model tank (2m×2m×2m) and Figure 4~7 is a
curve graph that shows the relation between Dr and N10 and h. as shown in the
figures, from the very beginning of the driller penetrating into the earth surface,
N10 increases gradually with the reaching of penetrating depth; when certain
depth is reached, N10 reaches its utmost and increases little downward. The
certain depth is called critical depth and marked as hcr.
2.2.1 Analysis of model test results
1. Critical depth hcr
When the light penetration is applied to test the sand relative density in
bridge-culvert backfill, the sand surface is also a part of vital importance.
However, because of the influence from the surface effect and sand self-weight
stress, the light penetration blow-counts N10 increases with the reach of
penetrating depth. In order to figure out change rule of the blow-counts in such
a depth range so as to control the construction quality of bridge-culvert backfill
and to effectively measure the backfill-sand relative density, it is necessary to
make sure of the critical depth in light penetration and make the critical depth as
a boundary. When the drill is above the critical depth, right at it or under it, the
rules of blow-counts change with the depth are studied separately.
Through analysis of the model test results, hcr~Dr relation (shown in
Figure 8) of the four sand types is revealed. And as shown in Figure 8, hcr in
light penetration test really exists and increases with Dr.
2. Light penetration blow-counts N10
From model test results, N10 increases with penetrating depth h and sand
relative density Dr. when above critical depth; when critical depth is reached and
downward, N10 keeps stable. Test results shows that Dr is the most sensitive
factor to influence the blow-counts right at critical depth N10L, which is well
related to the sand relative density Figure 9). From Figure 9, N10L evidently
increases with Dr.
0
30
60
90
120
150
180
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
relative density Dr
critical depth h
cr(cm)
sand No.1 Mx=4.17 sand No.2 Mx=2.47
sand No.3 Mx=2.66 sand No4 Mx=3.36
Figure 8. hcr-Dr relation in model.
In addition, N10L also has relation with the sand fineness modulus Mx. from
Figure 9, when Dr<0.80 and N10L is stable, the bigger the Mx, the greater the
relative density. The size order of Dr is: fine sand<medium sand<coarse sand
<super coarse sand.
0
30
60
90
120
150
180
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
blow counts N10L
relative density Dr
sand No.1 Mx=4.17sand No.2 Mx=2.47sand No.3 Mx=2.66
Figure 9. N10L-Dr relation in model test.
3. Contrastive analysis of light penetration to test sand relative density in
bridge-culvert back-wall fill
There have already been a great deal of static penetration study and its
theory and test study are relatively mature. Therefore, the static penetration is
accepted and testified in the engineering field. In order to test the feasibility of
light penetration to test the sand relative density in bridge-culvert back-wall fill,
the contrastive analysis between light penetration and static penetration occurs
at the same time. After comprehensive study on the test results from static
penetration and light penetration, close linear relationship are found existing in
the two penetration methods to test coarse sand relative density, as shown in
Table 5.
Table 5. Relationship between light penetration blow-count above critical
depth N10 and the static penetration cone point resistance Qc.
Sand Formula concerned ρ
No.1 N10=5.6916Qc+3.1361 0.9852
No.2 N10=4.5820Qc+7.4610 0.9800
No.3 N10=4.4725Qc+7.3006 0.9881
No.4 N10=4.0083Qc+2.3670 0.9791
In the above table, N10 in the formula refer to 30cm blow-counts, Qc is the
weighted average of cone point resistances at the correspondent 30cm depth.
2.2.2 Dr~N10 empirical formula regression of the model test
According to the features of light penetration test curve-line and the analysis on
the Dr~N10 relation, application of critical depth as the boundary leads into two
cases:
When above the critical depth, statistical analysis and linear regression of
test data of the four sands show multi-linear relation between Dr and Mx and h
and N10 (blow-counts/30cm). Non-linear regression analysis results in formula
(1).
When at critical depth and below, based on the non-linear regression
analysis, the N10L ~ Dr relation satisfies the log function relation (in formula 2).
Dr=0.3237+0.1090Mx-0.0037h+0.0070N10 (ρ=0.9175) (1)
Dr=-0.1057+0.2080ln(N10L) (ρ=0.9368) (2)
Where h is drill penetrating depth below critical depth(cm),h<hcr.
It can be seen from formula (2) that, when above the critical depth, except
N10, sand fineness Mx has the biggest influence on Dr; when other parameters
are the same, the bigger the Mx, the greater the sand relative density; next is the
influence of N10, when other parameter are the same, the bigger the N10, the
greater the relative density.
3. Field test
3.1 Field test work
Model test result of this paper has been put into field test practice in
several super-highways. Two abutments (real shape shown in Figure 10) of
K124+820 culverts in 22nd
contracted section of Yue-Gan super-highway are
taken as an example to proceed field test so that the influence of the
model-tank-size to the test result is known. And in this way, the interrelationship
between the light penetration model test and the field test is testified, and the
application of model test result to constructions is displayed.
Figure 10. Exploration of abutment in field test.
The effective size of the field-test back-wall > 3m × 3m × 5m;
Composition and physical index of backfill sand are shown in Table 6;
penetration result in Figure 11.
0
30
60
90
120
150
180
210
240
270
0 20 40 60 80 100
blow counts N10 (blow/30cm)
penetrating depth h(cm)
1#-3Mx=3.01
0#-1Mx=2.93
0#-2Mx=2.90
Figure 11. N10-h relation in field test.
Table 6. Composition and physical index of backfill sand.
Mx Sand composition /%
Gs emin emax F Cu Cc 9.5 4.75 2.36 1.18 0.60 0.3 0.15 0.075 <0.075
3.00 98.4 93.7 74.2 55.1 28.6 6.6 1.5 0.2 0 2.65 0.4171 0.9065 1.1730 4.2 0.7
Note: the filter-hole size unit mm
3.2 Analysis of field test data
From Figure 11 and Figure 12, field test light penetration curve and its
deformation are the same as model test the correction coefficient of N10 in
model test is 3
2 , Figure 12 shows the contrast between the field-test
blow-counts and the N10L~Dr relationship which is the result when N10L of the
No.4 sand is divided by the similar coefficient 3
2 . From Figure 12, after
correction, when N10L in model test is the same as N10L in field test, sand
relative density basically shows no difference. It can be deduced from the above
that, formula (3) and (4) are the revision of formula (1) and (2).
0
30
60
90
120
150
180
210
0 0.2 0.4 0.6 0.8 1
relative density Dr
blow-counts N
10L(
blow/30cm)
No.4 sand of in-door test
field test
Figure 12. N10L comparison between sand No.4 and in field test.
Dr=0.3237+0.1090Mx-0.0037h+0.0070N10' (3)
Dr=-0.1057+0.2080ln(N10L') (4)
Where N10' is revised light penetration blow-counts above critical depth,
/10
'
10 NN , =3
2 ;N10L' is revised light penetration blow-counts right at critical
depth, /10
'
10 LL NN ; h is penetrating depth in light penetration (cm), h<hcr.
Table 7. Contrast between Dr value of backfill sand at 1#-2 test points and
the field surveying value.
MX h N10 Computation
value
Real-survey
value
difference/ratio notes
3.00 30 28 0.73 0.76 -0.03/-3.9%
3.00 60 44 0.73 0.76 -0.03/-3.9%
3.00 90 59 0.72 0.76 -0.04/-5.3%
3.00 120 80 0.81 0.76 0.05/6.6%*
3.00 150 75 0.79 0.76 0.03/3.9%
*Critical depth site in field test.
Put the test data from 1#-2 testing points into empirical formula (1) and
(2) respectively; counted out is the contrast between Dr value of backfill sand
at 1#-2 test points and the field surveying value (shown in table 7). from table
7, during field test, when penetrating depth h<hcr, error tolerance is less than
10% between relative density Dr computed out by formula (1) and the field
survey value; when h≥hcr, corresponding error tolerance is less than 10% when
Dr is computed out by formula (2), which has proved the feasibility and
correctness of model empirical formula (1) and (2).
Put the No.4 sand test data into revised formula (3) and (4); counted out is
the contrast between relative density in field light penetration test and field
survey value (shown in table 8). from table 8, when penetrating depth h<hcr
(above the critical depth), error tolerance is less than 5% between the Dr value
computed out by formula (3) and field survey value; when h≥hcr (below critical
depth), error tolerance is less than 10% when value computed by formula (4),
which shows the correctness of revised in-door model test result and that it can
be put into field test use.
Table 8. Contrast between computed No.4 sand Dr value and field
surveyed Dr value.
MX h N10 Computed
value
Value in Field
survey
difference/
ratio
notes
3.36 30 17 0.73 0.76 -0.03/-3.9%
3.36 60 34 0.76 0.76 0.00/0.0%
3.36 90 43 0.73 0.76 -0.03/-3.9%
3.36 120 45 0.73 0.76 -0.03/-3.9%*
3.36 150 44 0.72 0.76 -0.04/-5.3%
* Critical depth site in mode test
4. Light penetration method to test bridge-culvert sand backfill
Based on test research achievements and the author’s experience
accumulated in long period of construction practice, when to test the relative
density of bridge-culvert sand backfill by light penetration method, the key
points are as follows:
Fetch the representative backfill sand sample from the construction site
to do the in-door test according to current regulations and to fix the sand
fineness modules Mx;
Depth should be controlled within 2m (3m the utmost) each time when
light penetration is used to test relative density of backfill sand.
According to the actual shape and size of the bridge-culvert back-wall,
disperse 3~5 test points at random in each back-wall. Distance between
two test-points is more than 1.2m; the effective distance between the test
points and the back-wall border should be more than 0.6m, so that
influences of test point to test point and back-wall border to test point
can be avoided.
Applied is the light-penetration test equipment (shown in table.2) to
penetrate from the sand surface. Keep the pole upright, the utmost
inclining angle is less than 2%; lift the 10kg hammer to the effective
drop-height and let it fall freely with the blow frequency 15~30 hits/min.
Record the blow-counts N10 in each 30cm penetration. When the
blow-counts is over 100, or when the penetrating depth reaches 3m, stop
working;
Take N10 as the x-axis and penetrating depth h as Y-axis, draw a N10-~h
curve, according to field backfill material features to rectify penetrating
abnormal points so as to eliminate the influence of huge-sized sand to
the penetrating result.
Based on N10~h curve, confirmed is the critical depth hcr at single test
point in light penetration test. (N10 increases with the reaching of
penetrating depth; when certain depth is reached, blow-counts N10
reaches its utmost, and increases little downwardly. This depth is named
critical depth in this paper.). Above the critical depth, put the surveyed
N10 into the empirical formula (3) to compute the sand relative density
Dr; blow the critical depth, put N10 into the empirical formula (4) to
compute Dr;
. Take 0.6m as one layer and respectively compute the representative
value of relative density according to formula as follows.
Sn
tDD rrk
(5)
In the formula:
rD refers to the average value of all relative density of sand at each test
point in back-wall;
t refers to the modulus that changes with the layer and the guaranteed
efficiency (or confidence degree ); as shown in documents in attached table
B, the guaranteed efficiency of t is 95%
S refers to standard deviation of each single point value;
n refers to single value.
5. Conclusion
1) In the light penetration test, the sand relative density is the most
sensitive factor that influences the blow-counts N10. Sand fineness modulus Mx
also exerts influence on the blow-counts N10.
2) According to the analysis of model test result, above the critical depth,
the sand relative density has linear relationship with the light penetration
blow-counts N10. Regression formula (1) is obtained based on the Crammer
Rule; below critical depth, the blow-counts N10L ~ Dr relation satisfies the log
function relation.(seen in formula 2).
3) After revision of the model similar modulus in empirical formula (1)
and (2), revised formula (3) and (4) are obtained. When the penetrating depth
is h<hcr, formula (3) can be applied to compute the sand relative density based
on the parameters in field test; when h≥hcr, formula (4) can be used to count
the relative density of field filling sand based on the surveyed N10.
4) According to the contrastive analysis between test study and static
penetration study, the feasibility of light penetration is testified in its use to test
relative density of medium and coarse sand in bridge-culvert back-wall filling.
Based on the above, a set of convenient and applicable test method is put
forward to test the “relative density” of medium and coarse sand in
bridge-culvert back-wall filling.
References
C. B. Villet. Cone resistance, relative density and friction angle[J]. Cone
Penetration Testing and Experience,2014,133-145.
Davidson J L,Mortensen R A,Barreiro D. Deformation in sands around cone
penetrometer[C]. The Tenth International conference on Soil Mechanics and
Foundation,2014,2:460-470.
F. He, M.J. Li, Z.H. Huang. An Experimental Study of Pile-Supported
OWC-Type Breakwaters: Energy Extraction and Vortex-Induced Energy
Loss. ENERGIES, 2016, 9(7).
F. P. Smits. Cone penetration test in dry sand[J]. ESOPT II,2014,256-267.
Gokudan Kunio, Sugiyama Motohiro, Kondo Hiroshi,et al. The influence
factors for dynamic penetration resistance of sands and measurement method
of dynamic motion[J]. Tokai Daigaku Kiyo. Kogakubu (Proceedings of the
School of Engineering of Tokai University), 2006,36(2):169-177.
J.B. Lv, Q.Y. Tian, Y.S. Liu, et al. Test method for filling sand relative
density[S], DB 44T/ 1356-2016 (Guangdong Province local standards),
2016.10.
Kalayci E, Civjan S A, Brena S F, et al. Load testing and modeling of
two integral abutment bridges in vermont [J]. Structural Engineering
International ,2015,21(2):181-194.
P. Zhang, H.H. Tian. The study on amendment of dynamic sounding impact
factors (in Chinese). Journal of Shenyang University, 1999(2), 80-83.
Quality Inspection and Evaluation Standards for Highway Engineering (Section
1 Civil Engineering), JTG F80/1-2004,Criteria Laid Down by Ministry of
Communication of The People’s Republic of China 145-146.
Sand for building[S], GB/T 14684-2001, Criteria Laid Down by Ministry of
Construction of The People’s Republic of China, 2006,1-10.
S.S. Liu, J.B. Lv, Q.Y. Tian. Model Analogous Analysis of Bridge Back Filled
With Coarse Sand Test[J]. Highways & Automotive Applications, 2005.6,
115-118.
Tang, X.Q. et al. In-situ Testing Technology in Foundation Project(in Chinese).
Beijing, China Railway Press, 1996:197-244.
Technical Specification for Construction of Highway Subgrades[S],JTG
F10-2006, Criteria Laid Down by Ministry of Communication of The
People’s Republic of China, 2007,9-14.
W.J. Chen. Study on Mechanism in Sand Static Penetrating Test(in Chinese).
Civil Engineering Department, Changsha:Changsha Railway University,
1987.
X.Z. Cui and H. Ding. Approximate theoretical and experimental research
development of cone penetration resistance in static cone penetration (in
Chinese). Advances in Mechanics, 2004, 34(2), 251-259.
Y.B. Zhou. Dynamic cone penetration test (in Chinese). Beijing, China Railway
Press, 1986,1-24.
Y.J. Qiu. Study on static penetrating mechanism (in Chinese). Journal of
South-West Transportation University, 1993, 91(2): 46-52.