Abstracts – Vol. 53 No. 2 June 2022

Behaviour of Foundation Rested on Finite Saturated Salt-Encrusted Flat Soil (Sabkha) Improved by Cement Addition under Repeated Loading

Naif Alsanabani, Ahmed Alnuaim, Abdulhafiz Alshenawy, and Wagdi Hamid

ABSTRACT: The dynamic response of a block machine foundation rested on the finite thickness of cemented sabkha was investigated by carrying out a 1g small scale test. The parameters that were considered in the account in the study were cement content, ratio of thickness of the cemented sabkha to the foundation’s diameter, magnitude and rate of pulse load. The results revealed that the cement content has a significant effect more than the thickness of cement-sabkha. The reduction in the maximum settlement value by increasing cement content decreases with the increased thickness of cement-sabkha. The rate of pulse loading leads to an increase in the maximum settlement of at least 100 and 60% for thickness ratios of 0.2 and 0.4, respectively, and these effects decrease with the increasing thickness of cement sabkha. The influence of the value pulse loading and the rate of the pulse loading on the raising of the sabkha’s stresses increases with increasing thickness ratio more than cement content. In terms of the liquefaction risk of the sabkha soil that underlies the cement-sabkha layer, there is no liquefaction in sabkha soil when the value and rate of pulse loading that is applied to the foundation are less than 240 N and 200 blows/min. The maximum pore pressure ratio (ru) value ranges from 0.07 to 0.1.

KEYWORDS: Pore pressure, settlement, cement, thickness, stress.

An Obliquely Incident Wave Propagation through the Jointed Complex Rock Masses

Yexue Li, Yuanyuan Wang, Yu Cheng, and Jinshun Xue

ABSTRACT: Based on the wave function, the stresses and particle displacements on the joint are derived when the incident P-wave and S-wave are obliquely incident to the jointed complex rock masses. And then, a modified time domain recursive method (MTDRM) is proposed. Based on the MTDRM, this paper investigates the P-wave and S-wave propagation crossing the jointed complex rock masses. The effects of the wave impedance ratios and the incident angles on the transmission and reflection coefficients are discussed. It is found that the wave crossing the jointed complex rock masses is not always attenuated but may be strengthened in some special cases.

KEYWORDS: Modified time domain recursive method, Jointed complex rock masses, Wave impedance ratio, Wave propagation.

Numerical Verification for Seismic Response of Reinforced Soil Embankment on Soft Clay Foundation

Ripon Hore and Sudipta Chakraborty, Kamruzzaman Kamrul, Ayaz Mahmud Shuvon, and Mehedi A. Ansary

ABSTRACT: The findings of a series of shaking table tests and numerical analysis using PLAXIS 3D software to investigate the seismic influence of wrap-faced geotextile-reinforced embankment lying on soft clayey soil were presented in this paper. The test scheme included a succession of 1D Shake Table Tests (STT) with 0.05g to 0.2g base acceleration on a 0.4 m high model, lying on a 0.3 m thick, soft clay layer. This research aimed to understand the dynamic behavior of the model embankment resting on soft clayey soil. Both experimental and computational numerical studies were conducted to meet this purpose. The experimental study was a model study using a shake table. To assess the seismic behavior, harmonic sinusoidal input motions were subjected towards the model with different frequencies. The base acceleration, frequencies, and surcharge load were varied in several shake table tests with different relative densities of 48% for Sylhet sand. The pore water pressure and strain were also influenced by the base excitation, frequency, and surcharge pressure. The results obtained from PLAXIS 3D were compared with those obtained from model shake table tests. Acceleration response increased an increase of the base acceleration, the change further visible at higher elevations. The pore water pressures and strain values increased with elevation but decreased with the surcharge load. The strains were smallest at the bottom layer, and the strains at the top layer were the highest. The reason behind this is the geotextiles that are placed in the top layers. It enhances the earthquake strength of the embankment with a reinforced wall. The value of the findings from the test result was lower than the numerical result; the deviation was less than 15%. These results help to predict the dynamic behavior of the reinforced embankment wall. It will also help to design this type of retaining wall in the construction sector of Bangladesh.

KEYWORDS: Dynamic responses, soft clay foundation, Model reinforced wall, Variable input motions, PLAXIS 3D.

Stability of Undisturbed Residual Soil Hill Slopes

Anup Kaushik Sharma and Utpal Kumar Das

ABSTRACT: The cut slopes of saprolitic residual soils in the Himalayan foothills often remain stable at very steep inclinations that are much steeper than critical failure slope angles predicted by stability analysis. It is often difficult to obtain undisturbed samples of these soils. Physical inspection shows natural weak cementing property of undisturbed saprolitic residual soil. In order to overcome the inability of standard sampling techniques to collect undisturbed samples of the fragile saprolitic residual soil from the hillslope surface, a procedure with a modified sampler is adopted in this research. The shear parameters of undisturbed samples thus collected as well as that of reconstituted samples of the same soil are determined in direct shear testing at different saturation levels. Stability analysis of the saprolitic residual soil hill slopes was carried out using both undisturbed and remoulded soil properties at different degrees of saturation which revealed a positive contribution of the cementing property of the undisturbed soil towards higher stability of hill cut slopes.

KEYWORDS: Saprolitic residual soil, Undisturbed sample, Shear parameters, Slope stability.

Investigation of Key Properties of EPS Geofoams for Highway Embankments on Soft Ground

Hoang-Hung Tran-Nguyen and Vinh Phan Phuoc

Hoang-Hung Tran-Nguyen and Vinh Phan Phuoc

ABSTRACT: Differential settlement of bridge abutments has taken place at most bridge abutments on untreated soft ground in Vietnam. The conventional technologies to improve soft ground have often been costly and time-consuming. EPS geofoam, a synthetic and lightweight material, can be used as a fill material to raise the elevation of highway embankments directly on untreat soft ground. However, EPS geofoam has little known as construction materials for transportation structures in Vietnam. This paper attempts to investigate key properties of geofoams made in Vietnam. Several laboratory tests such as compression, water absorption, inflammability, and dissolvent were conducted. The results show that (1) Geofoams made in Vietnam have densities of 12.1 to 34.8 kg/m3 for the EPS-12 to the EPS-34, respectively; (2) qu increases in increasing in densities; (3) Elastic strain is less than 1.5%; (4) Initial modulus varying from 2-10 MPa with density; (5) Poisson ratio around 0.06-0.14; (6) Water absorption by volume from 0.4-3.2%; (7) Geofoam can be quickly burnt. These key properties will indicate suitable geofoam types that can be utilized as highway embankment fills placed on unimproved soft ground directly.

KEYWORDS: Geofoam; EPS; Bridge abutment; Embankment; Soft ground improvement

Estimation of Drain Pipe Effects Using Electrical Prospecting and Unsaturated Soil/Water Coupled Analysis

K. Kawai, K. Nakashima, K. Yasutomi, and N. Otaka

ABSTRACT: Elevation of the phreatic surface causes instability in earth structures. Therefore, drainage systems are important in constructing an earth structure. Drain pipes are a drainage system applicable even for an existing earth structure. However, it is difficult to estimate the effects of the drain pipe quantitatively, and design and construction of the drain pipe is conducted based on past experience. In this study of railway embankment with installed drain pipes, electrical prospecting of the phreatic surface and seepage analysis was conducted. In the seepage analysis, a ‘permeable boundary’ was newly applied to express the effects of the drain pipe for the existing unsaturated soil/water coupled analysis code. Consequently, the permeable boundary was validated for expressing the effects of the drain pipe. Preliminary seepage analysis on the installed drain pipe enabled us to design the optimum array and/or insertion length of the drain pipes.

KEYWORDS: Drain pipe, Phreatic surface, Electrical prospecting, Unsaturated soil/water coupled analysis.