Question

geotechnical engineering

The soil profile at a site consists of a clay layer 10 m thick, sandwich between two sand layers. The top sand layer has a density of 1.9 Mg/m² and is 5 m thick. Below this layer is a 10 m thick clay layer with a saturated density of 1.8 Mg/m' and a saturated water content 42%. The deeper sand layer has a saturated density of 1.9 Mg/m² and extend to the depth investigated at the site. The water table was detected at the top of the clay layer. The results of a consolidation test performed on a sample recovered from the mid point of the clay layer indicated the following properties for the clay: 1.) Effective pre-consolidation pressure of 130 kPa; 2.) Compression index Cc = 0.40; 3.) Re-compression index C = 0.03; and 4.) Consolidation coefficient Cv = 0.544 * 102 cm²/sec. The site is being proposed to be graded by compacting an additional layer. The new compacted layer will impose a total stress increment of 75 kPa on the present ground surface. It is desired to obtain the following information: 1.) Estimate the ultimate consolidation settlement due to grading: 2.) Estimate the time in weeks that it will take to reach the average degree of consolidation Uave - 90%; and 3.) At the time calculated in 2.), estimate the excess pore pressure still present at the mid-point of the clay layer.

Answer 1

please find the attached file.

3)

as per terzaghi one D theory

%U = (h/H)*100

       = (eo-e)/ (eo-e100) *100

       = (ui-u)/ui * 100

where H is total primary consolidation, h = consolidation at given time, eo = initial void ratio, e= void ration at given time, e100 = final void ratio, ui = initial excess pore pressure and u = pore pressure at given time)

ui = q = 75 kPa ( since when load is applies it is taken by water only hence develope excess pore pressure, with time it transfered to soil soils)

%U = (ui-u)/ui * 100

0.9 = (75-u)/75

u = 7.5 kPa this is the remaining excess pore pressure when 90% consolidation has completed. it will be 0 when 100% consolidation will be completed.

thank you hope you like it .