Quality Investigations on Ground Improvement in Highway Engineering Practice

The constructions of highway often pass through naturally-deposited liquefiable grounds. Anti-earthquake design is essential for highway engineering practice in east China. Gravel column and dynamic compaction are often adopted for the improvements of such problematical grounds. The stability and settlement of the treated grounds depend much on the construction quality. How to investigate the quality of ground improvement is an important issue in highway engineering practice. In this study, the method of Spectral-Analysis-of-Surface-Waves (SASW) is applied to evaluate the construction quality on ground improvements by vibration gravel piles and dynamic compaction technique. The case studies show that the SASW method is a powerful way for investigating the improvement quality in highway engineering practice. The shear wave velocity measured in SASW has a relative good relationship with the N value measured in standard penetration tests

Compression Behaviour of Natural and Reconstituted Clays

International audienceThe intercept of the log(1+e) - logσv' straight line is introduced to describe the effect of the starting point on the compressibility of natural and reconstituted clays. It is found that when the effective stress exceeds the remoulded yield stress, the compression behaviour of reconstituted clays is controlled solely by the water content at the remoulded yield stress and the liquid limit. Comparison of the compression behaviour of natural and reconstituted clays indicates that their difference in compressibility is caused by soil structure and the difference in water content at the compression starting point. The compression behaviour of natural clays can be classified into three regimes: 1) the pre-yield regime characterised by small compressibility with soil structure restraining the deformation up to the consolidation yield stress; 2) the transitional regime characterised by a gradual loss of soil structure when the effective stress is between the consolidation yield stress and the transitional stress; and 3) the post-transitional regime characterised by the same change law in compression behaviour as reconstituted clays when the effective stress is higher than the transitional stress. For the investigated clays, the transitional stress is 1.0-3.5 times the consolidation yield stress. The compression index varies solely with the void ratio at an effective stress of 1.0 kPa for both natural clays in post-transitional regime and reconstituted clays when the effective stress exceeds the remoulded yield stress, and when compressed in such cases the compression curves of both natural clays and reconstituted clays can be normalised well to a unique line using the void index

On the volumetric strain-time curve patterns of dredged clays during primary consolidation

International audienceThirteen one-dimensional consolidation tests with step loading were performed on dredged clays reconstituted at different initial water contents. Both vertical deformation and pore pressure were measured during primary consolidation, which refers to the time-dependent compression process associated with the dissipation of pore pressure. The pore pressure changes were investigated by considering the maximum and the residual values. The development of compression during pore pressure dissipation was analysed to identify the change patterns in volumetric strain-time curves. Three types of change patterns were found during the primary consolidation, and the remoulded yield stress was found to be the key factor in classifying the change patterns. The inflexion point is absent for types 1 and 2, indicating that the end of primary consolidation cannot be determined by the commonly used Taylor and Casagrande methods. Type 3 shows an inverse 'S' shape, suggesting that the end of primary consolidation determined based on the compression-time curves occurs before the completion of pore pressure dissipation

Determining the virgin compression lines of reconstituted clays at different initial water contents

International audienceForty-eight consolidometer tests were performed on various natural clays and a kaolinite clay reconstituted in the laboratory at different initial water contents using a modified consolidometer apparatus. These data together with those published previously allow a multi-regression analysis for the development of an approach for determining the intrinsic compression parameters that depend on initial water content and liquid limit. The approach proposed by Burland can be thereby extended to provide an expression describing the compression response of a wide range of clays. Based on the intrinsic concept, a simple way of determining the virgin compression lines of reconstituted clays is also proposed using the density of soil particles, initial water content, and liquid limit

Effect of Initial Water Content on Undrained Shear Behaviour of Reconstituted Clays

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Quantifying land-based pollutant loads in coastal area with sparse data: Methodology and application in China

State Oceanic Administration "908" project of China [908-02-02-03]; Fuzhou Environmental Protection BureauA systematic approach was developed to quantify land-based pollutant loads in selected bays in China where there is sparse or limited relevant data. The approach was applied to Luoyuan Bay and Xiamen Bay. Despite the data limitations in the two study areas, the approach was able to show that in Luoyuan Bay, the chemical oxygen demand (CODMn) load was mainly from soil losses, which accounted for 63 percent of the total pollutant load, whereas point sources only contributed 4 percent. Soil losses constituted the main pollution source for total nitrogen (TN) and total phosphorus (TP). Similarly, spatial variability of the source portion of land-based pollution was detected in Xiamen Bay. Non-point sources were the main source of CODMn load in all Xiamen Bay sub-sea areas, accounting for over 60 percent of the total pollutant loads. Non-point sources contributed largely to the TN and TP loads for most Xiamen Bay sub-seas. However, river discharges and point sources of pollution were also responsible for considerable TN and TP loads in some sub-seas. The application of the approach at the two bays resulted in a clear identification of the source apportionment and spatial distribution of land-based pollutant loads. (C) 2012 Elsevier Ltd. All rights reserved