Research on Applying Glass Fiber Cement Soil to Strengthen Soft Soil Subgrade YIN Yong1 and YU Xiao-jun2 1Lecturer, Department of Civil Engineering, Yancheng Institute of Technology, 0515-88298672; yyvalor 2Associate Professor, Department of Civil Engineering, Yancheng Institute of Technology, Post Doctor, Institute of Geotechnical Engineering, Hohai University, Xikang road, Nanjing City, 025-83787216; flyingfish7101 ABSTRACT: Soft soil is widely distributed in the world. With the increase in construction of highways and railways on soft soil, the treatment of soft soil subgrade is becoming more and more extensive. Based on the reinforcement effects of glass fiber, the possibility of applying glass fiber to strengthen soft soil subgrade is discussed in this paper. More than 100 groups of cement soil samples laboratory testing results are presented and compared. The analysis of test results indicates that glass fiber mixed in cement soil can improve the strength and deformation characteristic of cement soil in a certain degree. It could also be used as a possible replacement of soft soil subgrade. The findings are a new contribution to the soft soil subgrade treatment techniques. INTRODUCTION Soft soils are extensively distributed in coastal and inland areas in China. This kind of soils is considered problematic due to their poor mechanical properties, such as small bearing capacity and long-term settlement under surcharge load. With the rapid development of the economy of China, lots of infrastructures are being constructed in soft soil areas. Therefore, soft soils often need to be treated by soft ground improvement techniques, among which, cement deep mixing method is widely used (GAO Guo-rui and LI Jun-cai, 1996). The soft soils mechanical properties such as compression strength and tensile strength can be improved to a certain extent after foundation treatment. However, the increase in compression resistance is always associated with brittle failure of cement soil under compression and tension and this will result in project failure. To overcome this undesired problem and get a higher strength, many researchers apply additional additives in the cement soil (Kaniraj and 7 Copyright ASCE 2009GeoHunan International Conference 2009 Downloaded 19 Mar 2012 to 113.240.233.9. Redistribution subject to ASCE license or copyright. Visit http:/www.ascelibrary.org Havanagi, 2001). These additives include fly ash, silica fume, slag powder, lime, industrial waste gypsum, and various fibers, etc. Each of them has achieved certain success. Discrete randomly distributed fiber as a new reinforcement material has also been used to strengthen cement soil in soft ground (Shbib and Okumura, 2002), as the high tensile strength of the fiber can solve the problem of brittle failure of cement soil. In this paper, glass fiber is mixed in cement soil as a reinforcement material to improve the strength and deformation behavior of the soft subgrade through indoor test. The tests conducted on glass fiber cement soil include the compression tests, the tensile tests and the triaxial tests under a certain confining pressure. Results of the experimental work are therefore analyzed. MATERIAL AND METHODOLOGY Materials of Test Index properties of the soft clay from Yancheng express highway are summarized in table1. Table 1. Physical and Mechanical Properties of Soil Samples w (%) ? (kN/m3) wL (%) wP (%) IL IP C (kPa) () 39.2 18 40.4 12.6 0.96 27.8 14 12 where: w water content, ? unit weight, wL liquid limit, wP plastic limit, IL liquidity index, IP plasticity index, C cohesion, angle of internal friction. The cement type was P.C32.5, its compressive strength of cubic sample with 3 days was 21.0 MPa, and its tensile strength of cubic sample with 28 days was 42.7 MPa. The chopped and discrete strands of glass fiber were taken as the reinforcement material. For the convenience of sampling, the length of glass fiber was taken as 10mm. Its basic physical and mechanical properties are shown in Table 2. Table 2. Physical and Mechanical Properties of Glass Fiber Type Monofil Dia.( m) Tensile Strength (MPa) Contents of Inflammable Matter (%) Water Content (%) Linear Density (tex) AR 7 2.24103 ?1.5 4.0 200-235 where: AR Alkali-proof glass fiber. GEOTECHNICAL SPECIAL PUBLICATION NO. 1928 Copyright ASCE 2009GeoHunan International Conference 2009 Downloaded 19 Mar 2012 to 113.240.233.9. Redistribution subject to ASCE license or copyright. Visit http:/www.ascelibrary.org Test Method The cubic size of specimens in unconfined compression test and splitting tensile test was 7.07 cm 7.07 cm 7.07 cm. The diameter of cylinder specimens of triaxial test was 3.91 cm, and its height was 8 cm. The mixture ratio of materials in each group is shown in table 3. Materials in each group were mixed uniformly before being placed into a mold. The specimens were placed in the mold and covered with a plastic membrane for two days, and they were cu