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. The #1 must have Civil PE AM Practice Exam. 0000041443 00000 n As the wall does not move, the earth pressure exerted does not cause any lateral strain, and hence, there is no expansion of the backfill and no stress release. Passive earth pressure is actually a stabilizing force improving the stability of the retaining wall, unlike active earth pressure. 0000010765 00000 n Usually, the retaining wall is constructed first and then the soil behind the wall is backfilled; hence, the retained soil is often called backfill. Degree of roughness of the surface of the back of the retaining wall. The lateral earth pressure exerted on the wall when the wall is fixed in position is known as earth pressure at rest. The basement retaining wall is therefore fixed in position and cannot move away from the backfill when subjected to lateral earth pressure. Passive                         3 – 5                                      2 – 4 In the case of earth pressure at rest –, Substituting these values in Eq. Earth pressure forces can be at-rest (Fig a), active (b) or passive (c). 0000005809 00000 n 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. 0000009564 00000 n The Top online Civil PE preparation classes available. | 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. Active earth pressure occurs when Mohr’s circle of stresses at any point in the backfill touches the Coulomb’s failure envelope.
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. 0000010162 00000 n 0000008797 00000 n This is shown by Mohr’s circles (IV), (V), (VI), etc., causing again an increase in the diameter of Mohr’s circle. 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. The #1 must have Construction Practice Exam for the PE exam. 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 These three basic types of lateral earth pressures are discussed below: Figure 15.1(a) shows a retaining wall of height H with a backfill having a horizontal surface. #1 Guide to Ace the Construction AM section of Civil PE. 0000005173 00000 n (for example a typical free-standing retaining wall) • In Active earth pressure the value of K is minimum. There are three basic types of lateral earth pressure. 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. 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. 2 Lateral Earth Pressure 0γ 2 0 1 2 0 2 1 P =P +P =qK H + H K At Rest q H z σh γ c φ K0 q K0 (q+γH) 1 2 P1 P2 P0 H/3 H/2 z' K0: coefficient of at- rest earth pressure The total force: σh =K σv′ +u 0 where K0=1−sinφ for normally Another practical example of passive earth pressure is the case of shear key provided below the base of a retain­ing wall. 15.1(b), where OB is the vertical stress and OA1 is the lateral earth pressure at rest. Thus, lateral earth pressure exerted on a retaining wall depends on the direction and extent of the movement of the wall. The state of stress for the soil element is represented by Mohr’s circle (I) in Fig. 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. The ratio of horizontal to vertical stress is called coefficient of lateral earth pressure (K). �#��l�~�N�EY^YNa"0��٘�x����#� ���JEs�G���}�T. 0000005594 00000 n 0000002853 00000 n All retaining walls are usually not placed on the ground surface on the front side but are laid at some depth. When the wall moves away from the backfill due to active earth pressure, it actually moves towards the soil on the front side. 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. 0000008776 00000 n 0000010786 00000 n The total passive resultant force (without surcharge or cohesion) is solved for by: The #1 must have Construction reference for the PE exam. If the retaining wall were not there, the backfill would assume a stable flat slope. Passive earth pressure occurs when Mohr’s circle of stresses at any point in the front soil touches the Coulomb’s failure envelope. If I could study and pass the exam in 4 months, so can you. Lateral earth pressure is the pressure that soil exerts in the horizontal direction. 0000041193 00000 n vi. (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 –. 0000007713 00000 n 0000001418 00000 n 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. Enter your name and email to get the Civil PE Preparation Checklist... it's FREE! Table 15.1 gives typical values of K0 for different types of backfills, as obtained from actual measurement of earth pressure at rest. 0000121118 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 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.

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. The movement of the wall away from the backfill causes expansion of the backfill, resulting in stress release, thereby reducing the lateral earth pressure. Inclination of the backfill surface with the horizontal. 0000004242 00000 n 0000006961 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. Active earth pressure is denoted by the symbol pa, and its units are kN/m2, t/m2, or kgf/cm2.

Sign up to find out how to study smarter not harder. When a soil mass is retained at a higher level by a retaining wall, the retained mass of the soil tends to slide and assume a flat slope for equilibrium, which is resisted by the retaining wall. 15.3 is provided to improve the stability of the wall against sliding. 0000007196 00000 n 0000102668 00000 n This exerts pressure on the retaining wall, which is known as lateral earth pressure. Typical range of lateral earth pressure coefficients

0000133999 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. For saturated clay soils, Φ = 0; Ka=1:     pa = γH -2c, For granular soils, c=0:        pa = Ka γ H. The critical depth, zcr, which is the depth at which the horizontal pressure is zero, can estimated by: The total active resultant force (without surcharge or cohesion) is solved for by: For a level backfill (β =0), the following equation is used to determine the passive earth pressure for all types of soils. 0000133785 00000 n 0000008218 00000 n The maximum lateral earth pressure exerted on the retaining wall, when the wall moves towards the front soil, while it reaches it’s limiting equilibrium, is known as passive earth pressure. Earth pressure forces can be at-rest (Fig a), active (b) or passive (c). 0000010141 00000 n Earth pressure at rest is therefore always more than active earth pressure for the same depth of soil.
0000080653 00000 n Earth Pressure Introduction. Soil Engineering, Earth Pressure, Lateral Earth Pressure, Terms of Service Privacy Policy Contact Us, Copyright infringement takedown notification template, Coulomb’s Theory for Earth Pressure | Soil, How to Test Compaction of Soil? 0000002128 00000 n Initially when the wall is in a state of rest, a typical element of backfill at any depth is subjected to vertical stress due to self-weight of soil above the element and lateral earth pressure in the horizontal direction. Typical range of lateral earth pressure coefficients, Condition                 Granular Soil                 Cohesive Soil Earth pressure is the force per unit area exerted by soil. This generates passive earth pressure on the shear key.