Question

2. The following are the results ofa consolidation test on a sample of a clayey soi Pressure, o' (kN/m3) e 25 1.116 50 1.108 100 1.055 0.962 200 0.845 400 0.755 800 0.650 1600 0.658 800 0.675 400 0.685 200 a. Plot the e-log o' curve b. Using Casagrande's method, determine the preconsolidation pressure c. Calculate the compression index, Ce and the ration of C/Ce

Answer 1

(a) e-log$\sigma$ plot:

3 4 5 67 F 1.2 11 1.0 6.0 e. 8-0 O-7 O4 l000 100 10000

(b) Preconsolidation pressure ($\sigma$_c):

Pre consolidatin Pressure pressure soil had ever Th Ls the maximum the starhing of to be fore Subjected Consolidatim. been aphically as Th cam be. der ermined falaws: PLot e-g Curve be the mawimum curvarure point Let A plotted euTve e-q DTaw horizonhal lie AB at Hhe manimum curvatu re ponh line AC at masrmum Fangent DTaw curvature poinr. amgle between ine AB and AC Measure the and let i be 200. AD a pomt A such tha Draw bisector angle made by the bisector with line AB ams AC are equal to x Same ie Draw the virgin Compression line EF as shown.

point G is the in ter se chon poinr of Let virgin pression line bise ctor am d Hhe Com verki cal line through point Profech ana entend i to iorer sect he stress anis -+ Note down the stress velue at the intersechon ponk or profeched vert cal ine and the stress Ais. stress vaue is the reauired preconsalidatim pressure (a) This Following the ab ove got Procedure, we have 81 kN/m GL Manimum curvature l point

(c) Compression index (C_c) and Ratio of C_s and C_c:

Compre ssion indexCe): SS is Hhe slope ot the virm Compre ssion Curre. draun CuTve is the Hangent CAm pression vigin towards the end ot the e-O curve Compression Cur ve Let us sele.ct two points Pand P the 2 lasa Compre ssion line Let void matio and etfechive stvess value at Point pi e, and respectively are Similarly, effective stres e, and O, are the void raho Cnd 2 Point P respectively al

el-e2 Compre ssion index (Cc) 1 find Ce using the above formula: Let us mow From the 2raph plotted: AH poinh P : e =O.962 =200 A Poinh P2: 0.755 ; の= 800. e2 O.962-O 755 CC g00 200 O. 3438 Compression index of the gwen soil is o.3438

Recompression inder Cs): slope 6 khe unloa Tt is the Curve por Han of the e-c Curve. Unloading CuTve Pz PM C$4 (10g seale) Fwo points P3 and Pu sele ct Let un loa di ng hown. Curve as on the Let an d o be. he void ratio and e3 effectve stre ss at point P Tespechively. eu and o be the void ratio ama eftective stress at poinh Py re spe chively

e3-e4 inder Cs) Re com pre ssion ... From the araph ploted, 200 O.G85 e 3 $3 At poinh Pa point Py ey 0.650 ; 01600 AH O.685- O.6S Cs log o) 1600 200 O.O3876 Cs Re COmpre ssion inde x of the gwen soil is O.O3875 O.O3 876 Ratio (- O.11274 Ans O. 343 8