Step Loading Compression of Ultra-Soft Soil under Radial Drainage Conditions

Abstract

Downloaded by [RMIT University] at 05:18 15 August 2015 2Step loading compression measurements of ultra-soft soil, obtained from marine environment, was carried out with a hydraulic consolidation cell at moisture contents of 150 and 168%. Three different drainage conditions were tested: radial outward, inward and both inward and outward drainages. Ultra-soft soil showed a significant settlement in the first step of loading. There was little pore pressure dissipation, which implies little effective stress gain and with large magnitude of settlement in low stress range. New compression parameters C*c1, C*c2 and C*c3 are proposed for viscous and intrinsic states inclusive of low stress log cycles. A correlation between void ratio at 10 kPa effective stress (e*10) and void ratio at liquid limit eL was proposed and the relevant compression parameters were predicted. The magnitudes of settlements at various loadings were subsequently predicted using the proposed basic equations and were found to agree well with the measured data. Dimensionless time factor curves for various radial drainage conditions were also proposed. By utilizing these curves, time rate of settlement was predicted, which indicated good agreement between predicted and measured rates of settlement. It was furthermore found that the predicted time rate of settlement could be ascertained by using the coefficient of large strain consolidation estimated from void ratio versus hydraulic conductivity relationships. This research will make a contribution in the field of geotechnical engineering as it seeks to improve fundamental understanding of the compressibility of ultra-soft soil from marine environment, by means of step-loading compression measurements with a hydraulic consolidation cell.

Laboratory investigation on the compressibility of Singapore marine clays

“…The geological conditions at Changi, Singapore have been reported by several authors (Bo, Arulrajah, and Nikraz 2007;Arulrajah and Bo 2008;Arulrajah et al 2009;Arulrajah 2009a, 2009b;Bo, Arulrajah, Sukmak, et al 2015;Bo, Wong, et al 2016;. A typical seabed soil profile at Changi, Singapore, is shown in Figure 1.…”

The reinforcement effects of deep soft soil foundation with high degree of saturation under dynamic compaction

“…(6) The third round of pounding experiment is carried out with the pounding energy of 1500 kN m. Four to eight times of pounding were applied. (7) In the fourth round of pounding experiment, we used a pounding hammer which is one-third of the diameter with the pounding energy of 500 kN m. Two to five times of pounding are performed.…”

“…The pounding energy is 1500 kN m and 5-10 times of pounding are carried out. (7) The gravel cushion layer with thickness of 50 cm is paved. (8) The third round of pounding experiment uses a pounding hammer of onefourth of diameter.…”

“…Generally, it can be applied to gravelly soil, sandy soil, unsaturated silt, clay with low degree of saturation, collapsible loess, miscellaneous, plain fill, and dredged soil. [4][5][6][7][8][9] It is also effective to deep soft soil foundation with high degree of saturation (DSSF_HDS) when combined with auxiliary treatment measures, such as soil replacement and dewatering. For unsaturated silt and cohesive soil with high degree of saturation, reinforcement practice depends on experience and general guidelines are not yet established.…”

Comparison of one-step and step-wise compression tests

“…Nevertheless, usually the settlement calculated with the Summing method is slightly different from the real settlement of the engineering structure or building. According to this difference of settlements, research work was conducted in order to simulate step-wise (Bo et al, 2015) foundation load increment as it is in the site and to compare the obtained results with one-step loading. The maximum stress value chosen for experimental investigations was 400 kPa.…”