Analysis of flexible drains in Changi reclamation

1989 ◽  
Vol 26 (3) ◽  
pp. 401-417 ◽  
Author(s):  
G. P. Karunaratne ◽  
S. A. Tan ◽  
S. L. Lee ◽  
V. Choa
Keyword(s):  
Hydraulic Conductivity ◽  
Pore Pressure ◽  
Soft Clay ◽  
Test Site ◽  
Soil Parameters ◽  
Vertical Drains ◽  
The Real ◽  
Pore Pressures ◽  
Vertical Hydraulic Conductivity ◽  
Layered Clay

Vertical drains and surcharge were used to accelerate the consolidation of soft marine clay under the second runway at the Changi Airport site. To study this problem further, the consolidation of a strip of layered clay deposit under a large reclamation is analysed as a two-dimensional problem in accordance with Biot's theory using the finite difference method. The soil with vertical drains is replaced with an equivalent soil having an enhanced vertical hydraulic conductivity obtained by equating the surface settlement of the real soil with that of the equivalent soil. The soil modulus and the hydraulic conductivity of the real soil are varied with the prevailing effective stress in the soil. The operating soil parameters determined by back analysing the field observations in a pilot test were then utilized to predict the behaviour of the main works. Soil displacement at any point in the plane of strain could be determined within a reasonable accuracy. As the equivalent soil is obtained by equating the average degree of consolidation, pore pressures cannot be predicted accurately within the drain area. However, the trend of pore pressure variation across the test site is implied by the analysis. The trend showed that pore pressures outside the drain area are found to influence the settlement and pore pressure inside the drain area, causing retardation in the consolidation of the drain area. Key words: Biot's analysis, consolidation, flexible drains, numerical analysis, soft clay.

Experimental Study for Wave-Induced Oscillatory Pore Pressures in a Sandy Seabed

2014 ◽  
Author(s):  
Bo Liu ◽  
Dong-Sheng Jeng ◽  
Guanlin Ye
Keyword(s):  
Experimental Study ◽  
Pore Pressure ◽  
Vertical Cylinder ◽  
Soil Conditions ◽  
Soil Parameters ◽  
Pore Pressures ◽  
Sandy Deposit ◽  
Dimensional Facility ◽  
Set Up ◽  
Wave Induced

In this paper, an experimental study for wave-induced pore pressures in marine sediments was reported. In the experiment, a one-dimensional facility was set up with a vertical cylinder and a 1.8 m thick sandy deposit and 0.2 m thick water above the deposit. Unlike the previous experiments [1], additional static water pressures were added on the harmonic dynamic wave pressure and more pore pressure gauges were buried in the deposit, which allowed us to simulate the case with larger water depth and better describe the distribution of pore pressure trend. A series of experiments with 3000 cycles in each test were conducted under numerous different wave and soil conditions, which allowed us to examine the influence of wave and soil parameters on the wave-induced pore pressures as well as liquefaction. The experimental results show the significant influence of liquefaction on sandy seabed in shallow water. Furthermore, some new experimental phenomenon was observed. The depth of sandy deposit was usually considered to be unchanged in theoretical calculation, while the depth of which was indeed changed periodic with wave loading, which was observed and recorded in the experiments.

Effects of test procedure on flat dilatometer test (DMT) results in intermediate soils

2016 ◽  
Vol 53 (8) ◽  
pp. 1270-1280 ◽  
Author(s):  
F. Schnaid ◽  
E. Odebrecht ◽  
J. Sosnoski ◽  
P.K. Robertson
Keyword(s):  
Pore Pressure ◽  
Soft Clay ◽  
Test Procedure ◽  
Pressure Measurements ◽  
Dimensionless Velocity ◽  
Pore Pressures ◽  
Rate Effects ◽  
Excess Pore Pressures ◽  
Excess Pore ◽  
Flat Dilatometer Test

The evaluation of rate effects on the flat dilatometer test (DMT) can best be developed with some knowledge of the excess pore pressures generated during penetration, dissipation, and subsequent membrane expansion. While research that includes pore pressure measurements in the DMT has documented drainage conditions in clean sand and soft clay, further studies are required to determine the drainage conditions during the DMT in intermediate permeability soils, such as silts. For that purpose, a simple and inexpensive research device has been developed for monitoring pore pressures at the center of the DMT blade. Data using both a standard DMT and the modified research DMT from various tests in sand, silt, and clay have been compared in a space that correlates dimensionless velocity to degree of drainage. In this space, it is possible to evaluate whether partial drainage is taking place. Measurements indicate that the DMT is essentially undrained in soft clay and dominated by penetration pore pressures, is drained in clean sand and is partially drained in intermediate permeability soils, such as silt. A method is suggested to identify soils where partial drainage may influence the standard DMT results.

Inclined Perimeter Drains Performance as Liquefaction Countermeasure Techniques Below Existing Buildings

2020 ◽  
Vol 14 (03) ◽  
pp. 2050015
Author(s):  
Samy Garcıáa-Torres ◽  
Gopal Santana Phani Madabhushi
Keyword(s):  
Pore Pressure ◽  
Structural Damage ◽  
Excess Pore Pressure ◽  
Existing Buildings ◽  
Ground Shaking ◽  
Vertical Drains ◽  
Centrifuge Tests ◽  
Pore Pressures ◽  
Excess Pore Pressures ◽  
Excess Pore

Reducing the risk of structural damage due to earthquake-induced liquefaction in new and existing buildings is a challenging problem in geotechnical engineering. Drainage countermeasure techniques against liquefaction have been studied over the last decades with an emphasis on the use of vertical drains. This technique aims to allow a rapid dissipation of excess pore pressures generated in the soil during the earthquake thereby limiting the peak excess pore pressures and consequently improve the structural response. Rapid drainage in the post-earthquake period in the presence of these drains helps quick recovery of the soil strength. Recent studies propose different variations in the vertical drains arrangement to improve the excess pore pressure redistribution in the soil around structures. However, conventional arrangements for existing buildings do not achieve an adequate proximity from the drains to the soil below the foundation. To address this, the performance of inclined and vertical perimeter drain arrangements are studied in this paper. Dynamic centrifuge tests were carried out for the different arrangements in order to evaluate the excess pore pressure generation due to ground shaking and the following dissipation together with the foundation settlement and dynamic response.

Saturated Hydraulic Conductivity of Clayey Tills and the Role of Fractures

1990 ◽  
Vol 21 (2) ◽  
pp. 119-132 ◽  
Author(s):  
Johnny Fredericia
Keyword(s):  
Hydraulic Conductivity ◽  
American Studies ◽  
Field Measurements ◽  
Present Knowledge ◽  
Saturated Hydraulic Conductivity ◽  
Field Observations ◽  
Laboratory Measurements ◽  
Vertical Hydraulic Conductivity ◽  
Data Field

The background for the present knowledge about hydraulic conductivity of clayey till in Denmark is summarized. The data show a difference of 1-2 orders of magnitude in the vertical hydraulic conductivity between values from laboratory measurements and field measurements. This difference is discussed and based on new data, field observations and comparison with North American studies, it is concluded to be primarily due to fractures in the till.

Effect of temperature on streambed vertical hydraulic conductivity

2013 ◽  
Vol 45 (1) ◽  
pp. 89-98 ◽  
Author(s):  
Weihong Dong ◽  
Gengxin Ou ◽  
Xunhong Chen ◽  
Zhaowei Wang
Keyword(s):  
Hydraulic Conductivity ◽  
Water Temperature ◽  
Sediment Cores ◽  
Effect Of Temperature ◽  
In Situ Tests ◽  
Effect Of Water ◽  
Vertical Hydraulic Conductivity ◽  
Increasing Trend ◽  
Streambed Vertical Hydraulic Conductivity

In this study, in situ and on-site permeameter tests were conducted in Clear Creek, Nebraska, USA to evaluate the effect of water temperature on streambed vertical hydraulic conductivity Kv. Fifty-two sediment cores were tested. Five of them were transferred to the laboratory for a series of experiments to evaluate the effect of water temperature on Kv. Compared with in situ tests, 42 out of the 52 tests have higher Kv values for on-site tests. The distribution of water temperature at the approximately 50 cm depth of streambed along the sand bar was investigated in the field. These temperatures had values in the range 14–19 °C with an average of 16 °C and had an increasing trend along the stream flow. On average, Kv values of the streambed sediments in the laboratory tests increase by 1.8% per 1 °C increase in water temperature. The coarser sandy sediments show a greater increase extent of the Kv value per 1 °C increase in water temperature. However, there is no distinct increasing trend of Kv value for sediment containing silt and clay layers.

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