Linchang Miao

Research of soil-water characteristics and shear strength features of Nanyang expansive soil

Abstract Nanyang expansive soil is investigated in its unsaturated state in this paper. The wetting–drying cycle tests of soil–water characteristics of Nanyang expansive soil have been performed in the laboratory. The test results show that the soil–water characteristic curve of the pre-load specimen can well reflect the soil property function of expansive soil. The strength features of the different suction states of the unsaturated expansive soil are also investigated. The hyperbolic model of the suction strength is presented and the parameters of this model are easily determined by tri-axial tests of unsaturated soils. The hyperbolic model is conveniently applied to predict suction strength of an unsaturated soil.

Properties and Applications of Cement-Treated Sand-Expanded Polystyrene Bead Lightweight Fill

AbstractTo mitigate settlement problems associated with bridge approach embankments over soft soil, a newly-developed lightweight material was proposed in this study. This lightweight material consisted of expanded polystyrene beads, the hydraulic sand from the Yangtze River, and cement. The mechanical properties of the mixed lightweight material were determined through a series of laboratory tests, including standard Proctor tests, unconfined compression tests, California Bearing Ratio (CBR) tests, unconsolidated-undrained tests, and consolidated-undrained tests. The laboratory results showed the favorable properties of the lightweight material and that it can be used as a backfill material in highway embankment projects. A field study was also conducted to verify the performance of the embankment backfilled with this lightweight material, which resulted in a smaller settlement than the embankment backfilled with lime-stabilized soil (with and without any other ground improvement). Sand cone and CBR test...

Empirical Function Representing the Shear Strength of Unsaturated Soils

The paper presents a review of the general research of the shear strength of unsaturated soils. The hyperbola model is presented for predicting the suction strength based on the triaxial test of unsaturated soils. The predicted results compare well with the measured data and show that the hyperbola model can be used to represent the shear strength of unsaturated soils.

Sand creep as a factor in land subsidence during groundwater level recovery in the southern Yangtze River delta, China

A number of areas worldwide are suffering from the land subsidence, including the southern Yangtze River delta, the most developed area in China. Land subsidence is mainly induced by excessive groundwater pumping and has caused numerous problems, for example, flooding, structural cracking, and ground fissuring. Although several countermeasures have been adopted to mitigate the land subsidence problem in the southern Yangtze River delta, commonly using groundwater recharge, land subsidence is still developing even when groundwater levels are rising. The observation data of land subsidence in each stratum show that the deformation of the pumped aquifer is even greater than that in the adjacent aquitards when groundwater levels are recovering. Laboratory test results on the aquifer sand in Shanghai and Changzhou (two cities in the studied area, which have the most sufficient observation data about the land subsidence and groundwater level developing with time) proved that sand creep deformation is significant and is partially responsible for the land subsidence without groundwater level drawdown. Considering the difficulty and cost of collecting borehole samples from deep pumped aquifers to obtain the essential parameters for the existing sand creep calculation models, a simplified method was then proposed to calculate the sand creep deformation in the pumped aquifer. The relationship between the sand creep rate and the time can be recognized as linear using double logarithmic coordinates and the slope can be assumed to be one. In the proposed method, the laboratory test data are not necessary. Finally, case histories from Shanghai and Changzhou were used to verify the effectiveness of the proposed method.

Time-Dependent Deformation Behavior of Jiangsu Marine Clay

In this article, the mechanical behavior of a Jiangsu marine clay was investigated by drained triaxial tests, traixial rheological tests, and one-dimensional compression and swelling tests. A visco-plastic model, the Bingham model combining two yield surfaces model, was proposed to describe the time-dependent deformation behaviors of the marine clay. The governing equation of Biots consolidation theory for the visco-plastic soil is solved using a finite element code which incorporates the visco-plastic model. Using the finite element method, settlements of a typical embankment on the Lianxu expressway in China are calculated. Settlement calculations using the visco-plastic model are in agreement with the measured settlements in the field. The results demonstrate that the visco-plastic model is appropriate for calculating the visco-plastic deformations of Jiangsu marine clay. Theoretical and experimental studies show that the visco-plastic deformation of Jiangsu marine clay is substantial.

Electrical Resistivity Features of Compacted Expansive Soils

An electrical resistance apparatus with a highly sensitive alternate current bridge was developed in the paper for the purpose of measuring the electrical resistivity of soils and eliminating the low frequency polarization. The electrical resistivity of Guangxi expansive soils was measured in the laboratory using the developed apparatus. The investigation result demonstrates that the electrical resistivity of the Guangxi expansive soil is a function of the electrical resistivity of soil skeleton and pore water, water content, degree of saturation and void ratio. Along with electrical resistivity, the matrix suction was measured, and the relationship between the electrical resistivity and matrix suction was analyzed. The electrical resistivity-volumetric water content curves are compared with the matrix suction-volumetric water content curves for these soils. The relationship of matrix suction-volumetric water content is observed to be the similar feature to that of the electrical resistivity-volumetric water content curve.

One Dimensional Consolidation of Double-Layered Foundation with Multi-Level Load

An analytical solution for one dimensional consolidation of the double-layered foundation with vertical drainage under quasi-equal strain and a multi-level loading condition is studied in this paper. The analytical solution for one dimensional consolidation of the double-layered foundation has two solutions: one solution is the general consolidation solution for both single-surface and double drainage conditions; and another solution is a time-staged loading consolidation solution for both single and double drainage conditions. The average degree of consolidation has been calculated for each time-stage of loading. The consolidation response of a two-layered profile has been investigated. The consolidation settlement calculation of the expressway embankment foundation of Jiangsu marine clay is performed by the one dimensional consolidation of the double-layered foundation.

Physical Model Test of Land Subsidence Caused By Groundwater Withdrawal

In this study, a physical model test was conducted to investigate the relative settlement of the aquifers and the aquitards during the pumping test. The soil layers in the physical model were simulated from practical (SU-XI-CAHNG) pumping strata. The dimensions of the cubical model tank were 0.6m in length, 0.5m in width and 1.0m in height. The model soils consisted of four layers with two aquifers and two aquitards alternating placed. The pumped aquifer was located at the bottom of the tank, and the thickness of each layer varied. The hydraulic head and the deformation of each soil stratum were monitored during pumping test by small diameters pore pressure tubes and settlement telltales. Throughout the pumping test, the compression of the pumped aquifer at bottom consisted of 50% of the overall observed settlement measured at surface of soil (land subsidence). The time effect of the sandy aquifer deformation was also observed. A bilinear relationship between the land subsidence and the decrease of the hydraulic was verified in this experiment. It is confirmed that, although the recharge had a significant effect on the land subsidence potential reduction, the subsided ground would not rebound due to the recharge. The model test improved the understanding of the land subsidence due to groundwater withdrawal.

Study on the new deformation characteristics of the pumped aquifers in Su-Xi-Chang area, China.

With the survey data of land subsidence in Su-Xi-Chang area, the authors found the deformation in the pumped aquifers cannot be neglected, even which is comparable with the adjacent aquitards. A series of lab high pressure compression tests on Suzhou aquifer sand from five different depths using costume-made setup were used to verify the compressibility of the aquifer sand. The test results show that the compression index of aquifer sand is close to some kinds of clay. With the comparison of the grain size distribution before and after testing, it can be concluded that the permanent rearrangement of sand grains is partly responsible for the sand compression.

Experimental Study on Controlled Modulus Column Methods

When embankments are constructed on soft ground, they may encounter settlement and/or stability problems due to low strength and high compressibility of the soft ground. To overcome these difficulties, a controlled modulus column method can be used for the construction of embankments on soft soils. This technology takes advantages of various ground improvement concepts, such as densification, reinforcement, solidification, etc. An experimental study was conducted in the laboratory to investigate the behavior of the controlled modulus columns.