helpful retaining wall problem with a surcharge load. great geotech type problem for the pe exam head to www.civilengineeringacademy.com for more including a great practice exam. here's the link
cantilevered retaining wall. calculation of a factored load eccentricity would give soil pressure diagrams that would not always represent the actual soil pressure distribution under the footing, and yield unreasonable results. factored lateral earth pressure, however, is always used for concrete stem design.
there are various types of loads and forces acting on retaining wall, which are: lateral earth pressure. surcharge loads. axial loads. wind on projecting stem. impact forces. seismic earth pressure. seismic wall self-weight forces.
the cantilever retaining wall shown below is backþlled with granular material having a unit weight, , of 19 knm 3. and an internal angle of friction, , of 30 . assuming that the allowable bearing pressure of the soil is 120 knm 2, the coefþcient of friction is 0.4 and the unit weight of reinforced concrete is 24 knm 3.
the weight of a building or another retaining wall above and set back from the top of the wall are examples of dead load surcharges. design relationships table 1 summarizes the influence of increasing the wall batter, increasing the unit width, increasing the units in-place density, and using better quality backfill on the maximum constructible height of a gravity srw to satisfy sliding and overturning.
surcharge location is 0 feet from shoring/retaining wall height of retaining wall/shoring is 10 feet traffic surcharge = × = 30 pcf given in this example x 3.5 ft from table 1 = 105 psf. this surcharge shall apply as a rectangular distribution to the full height of shoring. ii. site-specific calculation using equivalent soil heights for live loads method b
retaining wall variables. magnitude of stress or earth pressure acting on a retaining wall depends on: height of wall, unit weight of retained soil, pore water pressure, strength of soil angle of internal friction , amount and direction of wall movement, and. other stresses such as earthquakes and surcharges.
surcharge pressure will be calculated by eq. 1 , and for example for h=0.98m: e arctan l 2/h = arctan 2.7/0.98 = 70.1 o e r = radian sin e d e 70.1 o cos d v 0.98 = 2 41 1.223 - 0.94 0.34 /s kn/m 2 the final results are illustrated in figure 4 . soil pressure surcharge pr essure combined pressure fig. 4.
wall situation: case 3: retaining wall downslope and supporting dwelling foundations surcharge: the surcharge from the dwelling was assumed to be 5 kn/m 2 averaged across the active soil wedge for the gravity case and 4 kn/m 2 for the earthquake case. surcharge should be calculated using: = 1.2 g 0.4 q for the gravity case
any added weight above a retaining wall is called a surcharge. patios, swimming pools and driveways are common residential surcharges. your wall may need additional support if a surcharge is present. setback. the amount your wall leans into the hill is called setback. ab blocks come in approximate setbacks of 6 and 12 .
a retaining wall is then mainly exposed to lateral pressures from the retained soil plus any other surcharge. many retaining walls are cantilever-type, but its also common to find in practice walls that are laterally restrained at the top, such as in the case of basement walls supported laterally by an elevated floor slab.
wall backface to vertical surcharge r = ft. live load surcharge height hsur = ft. aashto table -2 vehicle collision load tl-4 pct = kip aashto table a13.2-1 collision load distribution lt = ft. aashto table a13.2-1 top of wall to point of collision impact on rail hct = ft. 1. stability checks 1. eccentricity 2. sliding 3. bearing applied loads
discussion. you will note that the pressure increases significantly as the surcharge gets nearer the wall again fairly obviously ; which is why we need to account for surcharges within our 45 zone of influence; and the surcharge will have much less effect as m exceeds 1, when the surcharge lies outside the 45 zone of influence.
surcharge pressure on retaining walls 8. if you are trying to analize the stability of the wall then think of the surcharge as part of a slope stability analysis where the slip surface includes the surcharge. remember that earth pressure analysis on a retaining wall is simply a special case of slope stability.
a treat block of active soil as a surcharge of density of soil x f when f can vary as the height of the soil block increase away from the face of the wall, then add horizontal force at the top of wall equivalent to the active thrust of the soil block being modeled as a surcharge.
example 11 - cast-in-place concrete cantilever retaining wall 1 2018 design example 11 general information wall backface to vertical surcharge r = ft. cast-in-place concrete cantilever retaining wall 7 2018 sliding check aashto
figure 1. traditional method of estimating lateral pressure due to surcharge load. ies in which the magnitude and distribution of lateral pressures on a retaining wall caused by the application of a concentrated load on the surface of the backfill were meas ured.
surcharge on retaining walls: a retaining wall which retains earth level upto the top of the retaining wall is a wall without surcharge. if the earth on the earth retained side is not level or the earth carries loads, the earth is said to have surcharge. the pressure exerted by the earth on the retaining wall will be more in this case.
retaining walls are structures that support backfill and allow for a change of grade. for instance a retaining wall can be used to retain fill along a slope or it can be used to support a cut into a slope as illustrated in figure 1. figure 1 example of retaining walls retaining wall structures can be gravity type structures, semi-gravity type structures,