Question

7. a) A 10 m high retaining wall supports a fully drained clay soil with a horizontal surface. The soil properties are: y = 18 kN/m²: =25° and c=4 kN/m2. Sketch the distribution of lateral earth pressure acting on the back of the wall, showing all salient values and the depth of the tension zone. Use Rankine's formula as expressed in familiar symbols below Pa = Kath-2c'tan 45º - (10 marks) (b) Determine the horizontal active thrust on the 7.5 m high wall shown in Fig. Q7, assuming an angle of wall friction 8=0.5$ for both strata interfacing with the wall. Use Coulomb's wedge theory (granular soils), as given below in familiar symbols. (10 marks) cosec u sin(x-0') sin(6 + sin(6-B) sin(x-ß) y=16 kN/m Ø=30° C'=0 3 ljem m 4.5 m Y=24 kN/m @=20° C'EO Figure Q7

Answer 1

17 a Rankine's earth pressuse ac tem(45-') = 5.096 km ma ** An T Le Temsion 1อา Cesmpsessir 67.98 kN/m2 Pa = karon - adtam (45-d) at Gisund lero - ho A Pa= -2dtem (45-6) 5-2x4 x tan (45-292 Pa = -5.096 KN ka= 1-sind It si no be = 0.406 mz at h=10m Pa= kerg.k- ac'tan (45-& 30,406X18X10 – 5.096 Pa = 67.98 km Pazo. Changes to compsession ✓ → depth of tension zone , whes Pazo .: 6 kq. OH = 20 tem(45-02 HEZO [20 = 0.697 m) Scanned with CamScanner

a clepth of tension zone = 0.697 m D ) Columb's wedge theory H=75m S = 0-50? Ka= coser y sin (4-0) sin (4+6) + sin(0+6) sin(8) - v sin (4-B) hess . y=90 B=0 because wall is vestial hosizontal backfill (Suscharge i for am of wall uppes post [ dl=30, 8215] I ka= [ cosec qo sin (90- 3o) 1 sm (90t15) + sin (45)• simcao) sior (90) Ke = 0. 3012 Active therust - Ika.DH' x 0.3012% 16% (3) pa = 21.69 kN/m/ Scanned with CamScanner

i fos 45 m Peest 6=20 8=10 kaar cosec qo .sim (90 - 20) Assim (90 +10) + sim (80): 5m (20) sinao ka= 0.447 | Pazt kei& H² 2440.447x 24x (4.5 Pa= 108.54 KNIM I Total active thrust = 21.69 + 108:54 Pa = 130,23 kolm an Scanned with CamScanner