6. TEST RESULTS
6.1 Earth Pressure Results
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= 50o. 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 = 50o. 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 thath 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
= 50o 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 Kh with wall movement is shown in Fig. 54.
The earth-pressure coefficient value Kh 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 Kh with active wall movement for = 70°. The coefficient Kh decreases with increasing wall movement. The wall movement needed for Kh 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 horizontal stress to reach a constant value is about S/H = 0.004. Similar variation of Kh with can be observed for Test 0825.and Test 0826.