Mucky Clay Research Articles

Resilient and plastic strain behavior of freezing–thawing mucky clay under subway loading in Shanghai

Depending on artificial freezing method applied in subway tunnel construction, a series of stress-controlled cyclic triaxial tests were conducted on freezing–thawing mucky clay to investigate their resilient and plastic strain behavior. In terms of practical engineering, this study focuses on three significant influencing factors which are artificial freezing temperatures, dynamic stress amplitude and loading frequency. This study demonstrates how these influence factors effect on the resilient strain or dynamic elastic modulus and accumulated plastic strain which are crucial to better understanding the strain behavior of freezing–thawing soil. The results indicate that the value of freezing temperature has slight influence on dynamic elastic modulus, but the freeze–thaw action can truly decrease the dynamic elastic modulus of soil, and soil with higher freezing temperature possesses larger accumulated axial strain. Besides, the dynamic elastic modulus decreases remarkably with the increasing of the cyclic stress amplitude, while the accumulated plastic strain behaves adversely. In addition, loading frequency has the least effect compared with other two factors, but lower frequency can generate larger accumulated plastic strain.

Test on cyclic creep behavior of mucky clay in Shanghai under step cyclic loading

Based on the cyclic triaxial test under step loading, the variation of cyclic creep and pore water pressure with increase in cyclic stress ratio (CSR) and load cycle of mucky clay in Shanghai were analyzed. The results show that there are two threshold values of stability cyclic stress ratio and failure cyclic stress ratio during the step loading which divide the development of cyclic creep strain into gradual stability stage, rapid growth stage and instantaneous failure stage. When the stress level is less than the failure cyclic stress ratio, the recoverable elastic strain is nearly linear with CSR. The cyclic creep properties of mucky clay are obviously influenced by the loading frequency under the same stress level.

Construction of slurry shield tunnel under Huangpu River in Shanghai

This paper presents a case history of slurry shield tunnel constructed under Huangpu River in the urban area of Shanghai. The tunnel was the second Yan'an Road tunnel used to connect the western part and the eastern part (the New Development Area) of Shanghai, as shown in Fig. 1. The length of the tunnel was 2270.5 m, in which 1310.5 m was constructed by using slurry shield machine (SSM). The inner and outer diameters of the tunnel were 9.9 and 11m, respectively. The outer diameter of the shield was 11.22 m. Tunnel was constructed under very difficult geotechnical and environmental conditions. The soil type of the tunnel passing through was very soft mucky clay. This was a deltaic deposit of Yangtze River. The soft mucky clay had the water content greater than its liquid limit, low hydraulic conductivity, low shear strength, and high sensitivity. The sensitivity ratio of soft mucky clay at the construction site was around 5. Under Huangpu River, the overburden earth was 6.59 m and was only 0.6 times the tunnel diameter. The tunnel also passed under 25 buildings in the west side and 15 buildings in the east side. One building's bottom slab was only 0.68 m above tunnel crest. Shield passed among the pile foundations of this building. There were also many pipelines such as gas pipe, water supply and sewerage pipes, and telephone and CATV cables under the road. In order to reduce the disturbance to the surrounding ground, careful operation was adopted and movement of surrounding ground was monitored. Countermeasures such as controlling of slurry pressure of chamber, excavation speed, washing pressure, slurry treatment, and real time grouting, etc. were carefully regulated to the geotechnical and environment conditions during construction. Some controlling technique was proposed based on the monitoring results during construction. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.