0000005173 00000 n The magnitude of the lateral earth pressure depends on the following factors: i. Your information will *never* be shared or sold to a 3rd party. The minimum lateral earth pressure exerted on the retaining wall, when the wall moves away from the backfill, and the backfill material is in the limiting equilibrium, is known as active earth pressure. Passive earth pressure occurs when Mohr’s circle of stresses at any point in the front soil touches the Coulomb’s failure envelope. Table 15.1 gives typical values of K0 for different types of backfills, as obtained from actual measurement of earth pressure at rest. 0000009564 00000 n Groundwater conditions in the backfill such as depth of water table and provision for drainage. trailer << /Size 110 /Info 60 0 R /Encrypt 64 0 R /Root 63 0 R /Prev 487174 /ID[] >> startxref 0 %%EOF 63 0 obj << /Type /Catalog /Pages 59 0 R /Metadata 61 0 R /PageLabels 58 0 R >> endobj 64 0 obj << /Filter /Standard /R 2 /O (�&H8��ܐy�%y�xc��01ރj P��;��R) /U (F��o���I��'bn�]�{�][�1H�d�) /P -60 /V 1 /Length 40 >> endobj 108 0 obj << /S 400 /L 556 /Filter /FlateDecode /Length 109 0 R >> stream When Mohr’s circle touches the failure envelope, as shown by Mohr’s circle (III) in Fig. 0000006382 00000 n Thus, the more is the movement of the wall toward the front soil, the more is the horizontal strain in the front soil, in the form of compression, and the more is the lateral earth pressure from the front soil opposite to that of active earth pressure. 0000002619 00000 n The movement of the wall is resisted by the front soil and exerts a lateral pressure on the wall, in a direction opposite to that of active earth pressure, as shown in Fig. Type and extent of the movement of the wall and the resulting horizontal strain in the backfill. Another practical example of passive earth pressure is the case of shear key provided below the base of a retaining wall. Figure 15.4 shows a basement retaining wall in which the wall is rigidly fixed to the basement slab. Further increase of the lateral earth pressure from the front soil makes it higher than the vertical stress. This exerts pressure on the retaining wall, which is known as lateral earth pressure. All retaining walls are usually not placed on the ground surface on the front side but are laid at some depth. 0000041193 00000 n 0000140830 00000 n Figure 15.5 shows the variation in lateral earth pressure on the y-axis as a function of the wall movement. The abutment of a bridge is rigidly attached to the deck slab of the bridge and is also similarly fixed in position and hence subjected to earth pressure at rest. We know that cohesionless soils assume a stable slope equal to the angle of internal friction without any lateral support. At this stage, the lateral earth pressure becomes the major principal stress and the vertical stress becomes the minor principal stress. Hence, when a backfill is retained, the wedge of soil above a certain slope tends to slide and move away from the rest of the backfill for equilibrium. 0000008218 00000 n 0000121118 00000 n The increase in the lateral earth pressure due to the movement of wall towards the front soil and the consequent compression continues until Mohr’s circle touches the Coulomb’s failure envelope of the front soil. 0000080731 00000 n This tends to push or rotate the wall away from the backfill if the wall is free to move or rotate. The state of stress for the soil element is represented by Mohr’s circle (I) in Fig. The ratio of horizontal to vertical stress is called coefficient of lateral earth pressure (K). 15.3, by Mohr’s circle (II), in which σh = σ3 = OA2 is the increased lateral earth pressure while the vertical stress, equal to σv = σ1 = OB, remains constant. Passive 3 – 5 2 – 4 When the wall moves away from the backfill, lateral pressure decreases with the increase in the movement of the wall; the minimum lateral earth pressure exerted on the wall is known as active earth pressure. �#��l�~�N�EY^YNa"0��٘�x����#� ���JEs�G���}�T. 0000080653 00000 n 0000147660 00000 n Also, the movement of the wall towards the front soil causes compression of the soil, which, in turn, increases the lateral pressure from the front soil. When the retaining wall moves away from the backfill due to active pressure, the shear key also moves in the same direction but toward the soil below the base of the wall on the front side. The #1 must have Civil PE AM Practice Exam. | Soil Engineering, Soil Formation: How is Soil Formed [with Factors and Processes for Class 7, 8 ,9, 10], Exam Questions with Answers on Soil Mechanics [Geotechnical Engineering], List of Objective Questions on Soil and Water Engineering (With Answers), Soil Compaction: Meaning, Compaction, Methods and Effect | Soil Engineering. When the wall moves toward the soil, the lateral earth pressure generated increases with the increase in the movement of the wall; the maximum lateral earth pressure generated on the wall is known as passive earth pressure. Earth Pressure Introduction. Active 0.20 – 0.33 0.25 – 0.5 When the lateral earth pressure tends to push or rotate the wall away from the backfill, the movement of the wall away from the backfill causes expansion of the backfill, resulting in stress release, thereby reducing the lateral earth pressure. The movement of the wall away from the backfill causes expansion of the backfill, resulting in stress release, thereby reducing the lateral earth pressure. 0000102668 00000 n The lateral earth pressure exerted on the wall when the wall is fixed in position is known as earth pressure at rest. The back of the wall is either vertical or slightly inclined to the vertical and the lateral earth pressure is slightly inclined to the horizontal due to wall friction and inclination of the back of the wall. 0000003075 00000 n Degree of roughness of the surface of the back of the retaining wall. Thus, lateral earth pressure exerted on a retaining wall depends on the direction and extent of the movement of the wall. Sign up to find out how to study smarter not harder. viii. 62 0 obj << /Linearized 1 /O 65 /H [ 1569 581 ] /L 488542 /E 185924 /N 10 /T 487184 >> endobj xref 62 48 0000000016 00000 n This is shown in Fig. Lateral earth pressure is the pressure that soil exerts in the horizontal direction. 0000007713 00000 n Earth pressure at rest is therefore always more than active earth pressure for the same depth of soil. The lateral earth pressure exerted on the wall when the wall is fixed in position is known as earth pressure at rest. Active earth pressure is denoted by the symbol pa, and its units are kN/m2, t/m2, or kgf/cm2. Thus, the more is the movement of the wall away from the backfill, the more is the horizontal strain in the backfill, in the form of expansion, and the less is the lateral earth pressure. Condition Granular Soil Cohesive Soil. 0000004242 00000 n Active earth pressure occurs when Mohr’s circle of stresses at any point in the backfill touches the Coulomb’s failure envelope. 0000010786 00000 n The lateral earth pressure exerted by the backfill on a retaining wall which is fixed in position and cannot move is known as earth pressure at rest. Earth pressure is the force per unit area exerted by soil. The total passive resultant force (without surcharge or cohesion) is solved for by: The #1 must have Construction reference for the PE exam. 0000133999 00000 n 0000002359 00000 n Under conditions of zero horizontal displacement, the soil is said to be at-rest: For a level backfill (β =0), the following equation is used to determine the active earth pressure (pa) for all types of soils. In the case of earth pressure at rest –, Substituting these values in Eq. 0000008797 00000 n All rights reserved. 0000002128 00000 n 0000003605 00000 n 0000004281 00000 n 15.1(b), the backfill material is on the verge of failure (limiting equilibrium) and no further decrease in the lateral earth pressure can take place. The decrease in the lateral earth pressure thus causes increase in the diameter of Mohr’s circle, causing it to approach the Coulomb’s failure envelope. 0000001418 00000 n (15.1), we have –, or p0 – μ(p0 + σz)= 0 ⇒ p0 – μp0 – μσz= 0 ⇒ p0 – (1 + μ) = μσz, where K0 is the coefficient of the earth pressure at rest and σz is the vertical stress due to the self-weight of the soil at depth z, where the earth pressure at rest is to be computed –. When the wall moves towards the front soil, the front soil is said to be in the passive state and the maximum lateral earth pressure exerted by the front soil in the passive state in its limiting equilibrium condition is known as passive earth pressure.
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