Large-Scale Reinforced Clay Walls Backfilled with Clay at Cheng Kung University - Reinforced Soil Engineering: Advances in Research and Practice - page 193

Table 5 Vertical and Horizontal Permeability Coefficients (k v and k h ) for Undisturbed
Sample of Section 3-A

v
(%) at saturated

Permeability coefficient
(m/day) u a at saturated Direction of seepage

K v ¼ 2.158 £ 10 -5 Vertical 16.8 0.302

K h ¼ 1.991 £ 10 -5

Horizontal 17.8 0.320

a u

¼ v(1 2 n)G s ; n: porosity ( ¼ 0.338); G s : specific gravity ( ¼ 2.72).

For various conditions considered in case A, a maximum F s is equal to 3.8
for 1-A and a minimum F s of 1.17 is for 3-A. It inferred that a hidden safety factor
was introduced in the design of NCKU walls using current design methods
mainly for cohesionless soils (e.g., Koerner, 1998; Jewell, 1991).

5 TEST FOR NCKU WALLS

In the long-term monitoring for about 840 days since completion of the wall, five
tests were performed. These tests were
1. Surcharge (6.8 kN/m 2 ) on the crest of the wall for about 100 days
2. First infiltration test on the crest of wall using 100-mm constant water
head for about 50 days
3. Second infiltration test for 23 days using a variable water head method
in three 250-mm-deep, 200-mm-wide trench on the top of the wall
parallel to the wall face
4. Third infiltration test for 30 days by increasing the depth of trench to
500-mm deep.
5. Fourth infiltration test for 23 days by increasing the depth of trench to
800-mm deep

In addition to these tests, the walls also experienced several heavy rainfalls
asshownin Fig.8 .Theprecipitationwasrecordedbyanautomaticweather
station at the site of NCKU walls.

6 TEST RESULTS FOR NCKU WALLS

Strainsforgeosyntheticcompositereinforcementath 0.95,1.38m,and1.89m

were measured immediately after the compaction of one soil layer (120-mm
thick) above the reinforcement at h

¼

¼ 1.89m. The increase of overburden on