Driving System

To achieve different modes of wall movement, two sets of driving rods are attached to the model wall. The upper driving rods are located 230 mm below the top of the wall, and the lower rods are located 236 mm below the upper rods as shown in Fig. 14. Two driving motors (ELECTRO, M-4621AB) supply the thrust to the upper and the lower driving rods independently. The wall speed and movement modes are controlled by the automatic motor

It is composed of the following four parts: (1) dynamic strain amplifiers (Kyowa DPM601A and DPM711B); (2) NI adaptor card; (3) AD/DA card; and (4) personal computers as indicated in Fig. 17. The analog signals obtained from the sensors are filtered and amplified by dynamic strain amplifiers. Analog experimental data are converted to digital data by the A/D - D/A card. The LabVIEW program is used to acquire test data, and experimental data are stored and analyzed with a personal computer.

Movable Wall

Bed 113

unit:mm End Wall 550337170

Base 1860

887

140 120

2000 M2

M1

200100300

Ottawa Sand

Top Supporting Beam Steel Interface Plate

Base Supporting Block

Base Board

Base Block

Bolt slot

Acrylic side Wall

1000

Moveable Wwall

2000 M1,M2

Worm Gear System

Bold

End Wall

Fig. 9. NCTU model retaining wall

Fig. 10. Picture of NCTU model retaining wall

Fig. 11. Soil pressure transducer (Kyowa PGM-0.2KG) Model wall Side wall

Fig. 12. Locations of pressure transducers on NCTU model wall

Fig. 13. Picture of pressure transducers on model wall

Model Wall

SPT

Fig. 14. Locations of driving rods

Fig. 15. Wall speed control system

Fig. 16. Data Acquisition System

Dynamic Strain Amplifiers (Kyowa: DPM601A and DPM711B)

NI BNC – 2090 Adaptor Board

NI – DAQ PCI – 6024E LabVIEW Program

Pentium 4, PC

Fig. 17. Picture of data acquisition system

4. Interface Plate and Supporting System 4.1 Interface Plate

The steel plate is 1.370 m-long, 0.998 m-wide, and 5 mm-thick as shown in Fig. 18. The unit weight of the steel plate is 76.52 kN/m³ and its total mass is 53.32 kg (0.523 kN). A layer of anti-slip material (Safety-walk, 3M) is attached on the steel plate to simulate the friction that acts between the backfill and rock face as illustrated in Fig. 18 (c) and Fig. 19 (a). For the inclination angle= 50^o shown in Fig. 1, the length of the interface plate should be at least 1.370 m. On the other hand, the inside width of the soil bin of the NCTU retaining wall facility is 1 m. To put the interface plate into the soil bin, the width of the steel plate has to less than 1.0 m. As a result, the steel plate was designed to be 1.370 m-long and 0.998 m-wide.

Section of the steel L-beam (30 mm x 30 mm x 3 mm) was chosen as the reinforced material. On top of the interface plate, a 65 mm x 65 mm x 8 mm steel L-beam was welded to reinforce the connection between the plate and the hoist ring shown in Fig. 19 (b).

4.2 Supporting System

In Fig. 20, the top supporting steel beam is placed at the back of the interface plate and fixed at the bolt slot of the side wall of the soil bin. Details of top supporting beam are illustrated in Fig. 21. The section of supporting steel beam is 65 mm × 65 mm × 8 mm and its length is 1,700 mm. Fig. 22 shows four bolt slots were drilled on each side of the U-shape steel beam on the side wall of the soil bin. Fig. 23 (b) shows the top supporting beam was fixed at the slots with bolts.

The base block used to support the steel interface plate is shown in Fig. 24. The supporting block is 1.00 m-long, 0.14 m-wide, and 0.113 m-thick. Fig. 24 (b) shows trapezoid grooves were caved to the face of the base supporting block. Fig. 20 shows the foot of the interface plate could be inserted into the groove at different distance from the model wall. Different horizontal spacing d could be adopted for testing includes: (1) d = 0 mm (2) d = 50 mm and (3) d = 100 mm. Fig. 20 shows 6 base boards are placed between the base supporting block and the end wall to keep the base block stable. Details of base boards are illustrated in Fig. 25.

The base board is 1,860 mm-long, 1,002 mm-wide and 113 mm-thick. The surface of the top base board was cover with a layer of anti-slip material Safe-Walk.

unit:mm

Steel plate

unit:mm

(5 mm thick)

Steel L-Beam

Steel plate with

Safty-Walk

998 998

1370

Steel L-Beam

( 65 x 65 x 8 mm)

Steel L-Beam

( 30 x 30 x 3 mm)

336276272341 1370

4065

Steel beam reinforcement

unit:mm

Steel plate with Safety-Walk (30 x 30 x 3 mm)

(65 x 65 x 8 mm)

40 65

(c) Side-view

Fig. 18. Steel interface plate

(a) Front-view (b) Back-view

(a) Front-view

(b) Back-view

Fig. 19. Picture of steel interface plate Steel L-Beams

Steel Plate Steel Plate with Safety-Walk

Hoist Ring

Movable Wall

Bed 113

unit:mm End Wall 550337170

Base 1860

887

120140

2000 M2

M1

200100300

Ottawa Sand

Top Supporting Beam Steel Interface Plate

Base Supporting Block β

Fig. 20. Model retaining wall with interface plate and supports

(a)

(b)

Fig. 21 Top supporting beam

Base Board

Base Block Bolt slot Acrylic side Wall

1000

Movea ble Wwall

2000

M1,M2 Worm Gear System Bold

End Wall

Fig. 22. Top-view of model wall

Fig. 23. Model retaining wall and steel interface plate

Fig. 24. Base supporting block Top Supporting

Beam

Steel Interface Plate

Model Wall

Plastic Sheets

Ottawa Sand

1860

113

Safety-Walk

unit:mm 1002

(a)

(b)

Fig. 25. Base supporting boards Base

Boards

Safety Walk

5. BACKFILL AND INTERFACE CHARACTISTICS 5.1 Backfill Properties

Air-dry Ottawa silica sand (ASTM C-778) was used as backfill. Physical properties of Ottawa sand are listed in Table. 1 Grain-size distribution of the backfill is shown in Fig.

26.To establish the relationship between unit weight  of backfill and its internal friction angle , direct shear tests have been conducted. The shear box used has a square (60 mm x 60 mm) cross-section, and its arrangements are shown in Fig. 27.

Chang (2000) established the relationship between the internal friction angle  and unit weight  of the ASTM C-778 Ottawa sand as shown in Fig. 28. It is obvious from the figure that soil strength increases with increasing soil density. For the air-pluviated backfill, the empirical relationship between soil unit weight  and  angle can be formulated as follows



= 6.43γ - 68.99 (5.1) where



= angle of internal friction of soil (degree) γ = unit weight of backfill (kN/m³)

Eqn. (5.1) is applicable for γ= 15.45 ~ 17.4 kN/m³ only.

5.2 Interface Characteristics between Model Wall and Backfill

To evaluate the wall friction angle wbetween the backfill and model wall, special direct shear tests have been conducted. A 88 mm x 88 mm x 25 mm smooth steel plate, made of the same material as the model wall, was used as the lower shear box. Ottawa sand was placed into the upper shear box and vertical load was applied on the soil specimen. The arrangement of this test is shown in Fig. 29.

To establish the wall friction angles developed between the steel plate and sand, soil specimens with different unit weight were tested. Air-pluviation methods was used to achieve different soil densities, and the test result is shown in Fig. 30. For air-pluviation Ottawa sand, Lee (1998) suggested the following relationship:

w = 2.33- 17.8 (5.2)

Eqn. (5.2) is applicable for  = 15.5~17.5 kN/m³ only. The  angle and  angle obtained in

sheets was equipped for all experiments to reduce the interface friction between the sidewall and the backfill. The lubrication layer consists of one thick and two thin plastic sheets as suggested by Fang et al. (2004). All plastic sheets had been vertically placed next to both side-walls before the backfill was deposited as shown in Fig. 31.

The friction angle between the plastic sheets and the sidewall was determined by the sliding block tests. The schematic diagram and the photograph of the sliding block test by Fang et al. (2004) are illustrated in Fig. 32 and Fig. 33. The sidewall friction angle



_sw ^is determined based on basic physics principles. Fig. 34 shows the variation of interface friction angle



_sw with normal stress



based on the plastic sheet lubrication method. The friction angle measured was 7.5. With the plastic-sheet lubrication method, the interface friction angle is almost independent of the applied normal stress. The shear stress between the acrylic side-wall and backfill could be effectively reduced with the plastic-sheet lubrication layer.

5.4 Interface Plate Friction

To evaluate the interface friction between the interface plate and the backfill special, direct shear tests were conducted as shown in Fig. 36. In Fig. 36(b), an 80 mm x 80 mm x 15 mm steel plate was covered with a layer of anti-slip material “Safety-Walk” to simulate the surface the interface plate. The interface plate was used to simulate the inclined stiff rock-face show in Fig. 35 Ottawa sand was placed in the upper shear box and vertical stress was applied on the soil specimen as shown in Fig. 36(a).

To establish the relationship between the unit weight  of the backfill and the interface-plate friction angleδi, soil specimens with different unit weight were tested.

Air-pluviation methods was used to achieve different soil densities, and the test result is shown in Fig. 37. For air-pluviation Ottawa sand, Wang (2005) suggested the following empirical relationship:

δ i = 2.7γ- 21.39 (5.3) where

i = interface-plate friction angle (degree)

 = unit weight of backfill (kN/m³)

Eqn. (5.3) is applicable for  = 15.1 ~16.36 kN/m³ only.

The relationships between backfill unit weight γ and different friction angles are

summarized in Fig. 38. The internal friction angle of Ottawa sand , model wall-soil friction angleδw, interface-plate friction angle δi, and sidewall friction angle δsw as a function of soil unit weight are compared in the figure. It is clear in Fig. 38 that, with the same unit weight, the order of 4 different friction angles is ＞δi ＞δ w ＞δsw.

Table 1. Properties of Ottawa sand (after Chen, 2003)

Shape Rounded

emax 0.76

emin 0.50

Gs 2.65

D60 (mm) 0.39

D10 (mm) 0.26

Cu 1.5

10 1 0.1 0.01

Particle Diameter in mm

0 20 40 60 80 100

Percent Finer by Weight (%)

Ottawa Silica Sand (ASTM C-778)

Fig. 26. Grain size distribution of Ottwa sand (after Hou, 2006)

Fig. 27. Shear box of direct shear test device

 = 6.43 -68.99 Compaction

 = 7.25 -79.51

15.00 15.50 16.00 16.50 17.00 17.50 Unit Weight, (kN/m³)

25 30 35 40 45

 (degree)

Air-PluviatedOttawa Sand

Fig. 28. Relationship between unit weight and internal friction angle(after Chang, 2000)

Loading Block

Up pe r Sh ea r Bo x Dry Ottawa sand

Smooth Steel Plate 60

25

88

15.5 16.0 16.5 17.0 17.5 Unit Weight,  (kN/m3)

17 18 19 20 21 22 23 24 25

w(degree)

Air-Pluviation Ottawa Sand

_w= 2.33 -17.8

Fig. 30. Relationship between unit weight and wall friction anglew after Chang, 2000



Fig. 31. Lubrication layers on side walls Lubrication Layer

(Plastic Sheets) Model Wall

Side Wall

600 mm 900 mm

Steel Plate

10 mm20 mm Acrylic Plate

60 mm

27 mm F

T

N Horizontal Line

Worm Gear Uplift Rod

Soil Box Standard Weight

Handle

Lubrication Layer



Fig. 32. Schematic diagram of sliding block test (after Fang et al., 2004)

Standard weight↓

↙ Sliding plate

↙ Soil box Plastic sheet ↘

←

Ball bearing

Handle

Worm gear Uplift rod

1 10 100

Normal Stress,  (kN/m2)

0 5 10 15 20 25

Fricti on Angle,

 sw

(degree)

Sliding Block Test Plastic-Sheet Method 1 Thick + 2 Thin Sheeting

sw = 7.5o

Fig. 34. Variation of interface friction angle with normal stress (after Fang et al., 2004)

H

Soil Backfill

Stiff Interface (Rock Face)

Rankine's Active Wedge

^ 

 Retaining

Wall

Fig. 35. Retaining wall with intrusion of a rock face into backfill

120

20

63

Dry Ottawa Sand

Steel Plate

Safety-Walk N

5 Upper Shear Box

Unit : mm

(a)

80

5

12 0

15

20 80

80

Unit : mm

Safety-Walk

(b)

Anti-Slip Material

Safety-Walk

15 15.2 15.4 15.6 15.8 16 16.2 16.4 16.6 Unit Weight, (kN/m³)

10 15 20 25 30 35

i, (degree)

_i = 2.7  - 21.39

Ottawa Sand (Air-Pluviation Sand)

_n = 4.60 kN/m²

Fig. 37. Relationship between unit weight γ and interface plate friction angle δi

(after Wang, 2005)

15 15.5 16 16.5 17 17.5 18 18.5 19

Unit Weight , (kN/m

³

)

0 5 10 15 20 25 30 35 40 45

Friction Angle,  (deg ree)

Sidewall Friction Angle, sw

sw = 7.5o (Fang, et al., 2004)

Ottawa Sand

(Air-Pluviation Sand)

Internal Friction Angle, 

- 68.99 (chang, 2000)

Interface-plateFriction Angle, i

i = 2.7- 21.39 (Wang, 2005)

Model Wall Friction Angle, w

 w = 2.33-17.8 (Lee, 1998)

Fig. 38. Relationship between unit weight γ and different friction angles

6. TEST RESULTS

This chapter reports the experimental results regarding effects of an adjacent inclined rock face on the active earth pressure against a retaining wall filled with loose sand. The rock face interface inclination angles  = 0^o, 50^o, 60^o, 70^o and 80^o are illustrated in Fig. 1.

6.1 Earth Pressure Results 6.1.1 Earth Pressure for  = 0°

Distributions of horizontal earth pressure h measured at different stages of wall displacements S/H are illustrated in Fig. 39. As the wall started to move, the earth pressure decrease, and eventually a limit active pressure was reached. The pressure distributions are essentially linear at each stage of wall movement. Active earth pressures calculated with Rankine and Coulomb theories are also indicated in Fig. 39. The ultimate experiment active pressure distribution is in fairly good agreement with that estimated with Coulomb and Rankine theories.

Fig. 40 shows a typical variation of horizontal earth pressure h measured by different pressure transducer as a function of the wall movement, S/H (S : wall displacement, H : backfill height). In Fig. 40 the horizontal stress decreased with increasing active wall movements. The location for soil pressure transducer SPT1 through SPT9 is illustrated in Fig.

12. If the normal pressures at different depths are normalized by the soil unit weight and its depth z, the variation of h/z with S/H is shown in Fig. 41. In this figure, most of the data are concentrated. It seems possible that the active condition is reached at all depths simultaneously.

The variation of horizontal earth-pressure coefficient Kh as a function of wall displacement is shown in Fig. 42. The coefficient Kh is defined as the ratio of the horizontal coefficient component of total thrust to

 H

² 2. The horizontal thrust Ph was calculated by summing the pressure diagram shown in Fig. 39. The coefficient Kh decreased with increasing wall movement until a minimum value was reached, then remained approximately constant. The ultimate value of Kh is defined as the horizontal active earth-pressure coefficient Ka,h. In Fig. 43, the active condition was reached at approximately S/H = 0.0035.

As shown in Fig. 39, the distribution of earth pressure at different wall movements is almost linear. Therefore, the point of application of total thrust, h/H should remained at about H/3 above the wall base. Experimental results in Fig. 43 show that these points are located at a distance of about 0.331 H ~ 0.359 H above the wall base.

Coulomb theories (

  18.5

^) provide a good estimate of the active earth pressure. In Fig. 42, data points obtained from Test 0809 and Test 0825, indicated that the experimental results were quite reproducible.

6.1.2 Earth Pressure for  = 50°

Fig. 45 shows the distribution of earth pressure at different stages of wall movement with presence of a stiff interface plate for an inclination angle= 50^o. In Fig. 45, the measured stress at S/H= 0 is lower than Jaky’s solution. The measured earth pressure at-rest is clearly affected by the intrusion of the rough interface inclined at = 50^o. It is reasonable to expect the measured

σ

h to be close to identical with Jaky’s prediction. However, for the lower part of the model wall, the interface plate is quite close to the soil pressure transducers. As a result, the active earth pressure measured would be affected by the approaching of the interface plate.

Fig. 46 shows the typical variation of lateral pressure as a function of active wall movement. The horizontal stress decreases with increasing wall movement, then reaches a constant value. Fig. 47 shows the relationship between normalized earth pressure h/z and wall movement S/H. It is clear thath measured at SPT1 to SPT9 decreases with the wall movement, then reach an active state.

Fig.48 presents the variation of lateral pressure as a function of active wall movement.

As the wall starts to move, the lateral soil thrust decreases with increasing wall movement until a constant is reached, then remained approximate constant. The ultimate value of Kh is defined as the horizontal active earth-pressure coefficient Ka,h. In Fig. 48, the active condition was reached at approximately S/H = 0.003.

In Fig. 45, as the wall starts to translate, the earth pressure starts to decrease. This non-linear earth pressure distribution causes the total thrust to act at to higher location. Fig.

49 shows h/H reaches a constant value which is about 0.40 H ~ 0.42 H above the base of the wall.

For Test 0815, the distribution of earth pressure at different stages of wall movement for

 = 50^o is shown in Fig. 50. As the wall started to move, the earth pressure decrease and eventually a limiting active pressure was reached. The variation of Kh with S/H for Test 0814 and Test 0815 are summarized in Fig. 48. It can be seen from the figure that the two sets of test data concentrate in narrow strip. It can be concluded that the experimental results are highly reproducible.

6.1.3 Earth Pressure for  =60°

Fig. 51 shows the earth pressure distributions corresponding to different stages of wall displacements for the interface inclination angle  = 60°. At S/H = 0, the measured σh was significantly lower than Jaky’s solution, especially the σh measured near the base of wall.

Fig. 52 shows the typical variation of lateral pressure as a function of active wall movement. The horizontal stress decreases with increasing wall movement, then reaches a constant value. Fig. 53 shows the relationship between normalized earth pressure h/z and wall movement S/H.

For  = 60°, the variation of earth pressure K_h with wall movement is shown in Fig. 54.

The earth-pressure coefficient value K_h decreased with increasing wall movement until a constant value is reached. In Fig. 54 the active condition was reached at approximately at S/H = 0.003. Referring to Fig. 51, at S/H = 0.003 the active earth pressures measured near the base portion of the wall is much lower than Coulomb’s prediction. The measured active earth pressure is clearly affected by the interface plate inclined at  = 60°. It is reasonable to expect the point of application of the active thrust would be located at a position higher than h/H = 0.333. Fig. 55 shows the experiment points of application the active thrusts were located at about 0.40H ~ 0.43H above the wall base.

For Test 0818, Fig. 54 shows the pressure distribution at various movement stages. The measured active earth pressure was lower than Coulomb’s solution especially the pressure measured near the base of wall. This is most probably because the active earth pressure is affected by the intrusion of the inclined rock face.

6.1.4 Earth Pressure for  =70°

The pressure distributions at various wall movements for  =70° are shown in Fig. 57. At S/H = 0, the measured earth pressure at rest was lower than Jaky’s prediction, especially at the lower part of the model wall. This is because the interface plate is very close to the soil pressure transducers.

Fig. 58 shows the variation of horizontal earth pressure h measured by different pressure transducer as a function of the wall movement. It is clear from the data shown in Fig. 59 that the horizontal stress decreases with increasing active wall movements. The variation of h/z with S/H is shown in Fig. 59.

Fig. 60 shows the variation of K_h with active wall movement for  = 70°. The coefficient K_h decreases with increasing wall movement. The wall movement needed for K_h to reach an active state is about S/H = 0.0035.

The variation of the location of to the active soil thrust with wall movement is shown in Fig. 61.Without the interface plate ( = 0°), the point of application h/H of the earth resultant is located at about 0.33H above the base of the wall. With the interface angle  = 70°, the earth pressure does not increase linearly with depth. This active earth pressure distribution shown in Fig. 57 causes the location of the total thrust to rise to a higher location.

Experimental result in Fig. 61 shows the point of application of the active thrust was located at about 0.41H ~ 0.43H above the wall base.

movements. At S/H = 0, the measured at-rest pressure distribution is not linearly with depth, and it is significantly less than the Jaky solution. For  = 80°, the interface plate was quite close to the wall surface. The amount of backfill sand withed between the rock face and the wall was very little. In this figure, the earth pressure slightly decreased with the active wall movement.

Fig.64 presents the variation of lateral pressure as a function of active wall movement. As the wall starts to move, the earth pressure decrease, and eventually a active pressure is reached. Fig. 65 shows the relationship between normalized earth pressure h/z and wall movement S/H.

In Fig. 66, the horizontal earth pressure coefficient Kh decrease with increasing wall movement, then a constant value Ka,h is observed. The constant value Ka,h is significantly lower than the value estimated with the Coulomb’s theory. The location of total soil thrust versus the wall movements is shown in Fig. 67. Experimental results show that these points are located at a distance of about 0.42H ~ 0.43H above the wall base. This is most probably because the measure

σ

h distribution is significantly affected by the presence of the nearby rock face.

The earth pressure distributions corresponding to different stages of wall displacement for  = 80° are shown in Fig. 68. In this figure, the distributions of lateral earth pressure are non-linear with depth. This is probably because the interface plate is very close to the soil pressure transducers on the wall surface. In Fig. 66, the wall movement needed for the

The earth pressure distributions corresponding to different stages of wall displacement for  = 80° are shown in Fig. 68. In this figure, the distributions of lateral earth pressure are non-linear with depth. This is probably because the interface plate is very close to the soil pressure transducers on the wall surface. In Fig. 66, the wall movement needed for the

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