Development of a laboratory monitoring system for elastic waves transmitted through sand under dry and nearly saturated conditions

Laboratory experiments with seismic measurements have the potential to be highly useful for understanding the physical process of water-induced landslides, and fundamental experiments are helpful for the appropriate interpretation of recorded seismograms. We developed a laboratory measurement system to investigate the relationships between wave propagation and water saturation in sand. We considered that the wavelength should be comparable to or sufficiently shorter than the sensing intervals. Furthermore, we embedded a wave source that can repeatedly emit an arbitrary and identical signal in an octave frequency band under both dry and nearly saturated conditions. We measured the transmitted waves by embedded accelerometers over 24 h under dry and nearly saturated conditions. The difference in the slowness between the two conditions was one-thousand-fold larger than the fluctuations in slowness over 24 h for each condition. Also, the difference in amplitude between the two conditions was about double the fluctuations in amplitude over 24 h for each condition. These results suggested that our system can monitor the water content change in sand via the change in spectral amplitude and phase slowness.

EFFECT OF DRYING-WETTING PROCESS ON FRICTION CAPACITY AND ADHESION FACTOR OF PILE FOUNDATION IN CLAYEY SOIL

Clayey soils had a seasonal water content change, which occurred in the zone known as active zone. This change happen due to the seasonal drying and wetting cycles, which affects the fluctuation of water table. The water content variation causes the change in undrained shear strength and these changes have an impact to the friction capacity and adhesion factor of pile foundation. This paper discusses the undrained shear strength, friction capacity of pile and adhesion factor of piles under drying and wetting cycles. Research was conducted on two different types of clayey soils. Laboratory experiments for varying soil water content were done. Soil samples were placed in a cylinder tube, the concrete pile model was then inserted into the soil. The diameter of the tube was about 15 times of the pile diameter. Loading test was carried out to investigate pile friction capacity. The result of this study showed that there was great effect of seasonal water content change on undrained shear strength, friction capacity and also adhesion factor of pile in the clayey soils.

Experimental Research on Compression Characteristics of Compacted Loess

A series of compression tests were conducted on the samples taken from compacted soil site in Lulling, in order to investigate the compressibility of compacted loess in different water content and different compaction energy. Through statistics analysis of the testing data, the stress-strain curve of compacted loess could be expressed with Hyperbolic form. And the relation between initial tangent modulus and water content change coefficient was founded by introducing the water content change coefficient. The result shows that at the same compaction energy, the initial tangent modulus decreases and the ultimate strain increases as water content increases; while at the same water content change coefficient, the initial tangent modulus increases and the ultimate strain decreases as compaction effort increases.

Computation for Water Infiltration of Unsaturated Loess

Rainfall and the water leak frequently causes the unsaturated loess slope landslide and the foundation destruction. The theoretical analysis was accomplished, then a two dimensional water seepage calculation model for loess foundation was established. It realized the forecast for the water content change of loess soil. Combined with an example, the calculating program was compiled by Matlab. The result confirmed the effectiveness and rationality of the method and model.