Method Analysis Of Layer Classification In Lingdingyang Based On CPTU

Hong Kong-Zhuhai-Macao Bridge Project (HZMB) is a large scale marine crossing project, composed of tunnel, artificial islands and bridges, which crosses Pearl River estuary and links Hongkong, Zhuhai&Macao. It is the component section of programmed National highway networks in Pearl River Delta area and the critical engineering works crossing Lindingyang. The part, crossing Lingding West, Tonggu navigation channels, is an immersed tube tunnel. The immersed tunnel is characterized by its large construction depth, variable geological conditions and large sediment load due to (back) siltation. The project is located in Pearl River belong to Lingdingyang. The geomorphology is single as marine plain. The main strata are mainly composed of Quaternary deposit, Yenshanian granite and Sinian Metamorphic rocks, based on regional geology and tunnel soil investigation materials.The immersed tunnel is easily destroyed along the longitudinal uneven settlement caused by seabed soft foundation. Therefore, in the structural design, except to meet the strength stabilization, the deformation and settlement control are also need to be considered. Yet providing accurate strata physical and mechanical parameters is the premise of reasonable engineering design, so detailed investigation is necessary.Due to HZMB project cross Lingding West and Tonggu navigation channels, which is the world’s most important trade route. Although a temporary channel was specifically provided, the detailed investigation also couldn’t be carried out as the short operating time, density vessel, strict maritime administration, expensive costs, complex seabed structure and uneven quaternary loose sediments. Based on previous soil investigation, the revealed strata from top to bottom as follows:①Holocene marine sediments, silt, silty soil, sand locally developed;②Late Pleistocene continental deposits, clay, silty fine sand locally developed;③Late Pleistocene marine continental paralic layer, Clay, Clay interlaminated with sand, silty fine sand and medium sand locally distributed;④Late Pleistocene continental deposits, medium coarse sand, fine sand and clay locally distributed;⑤Bedrock weathering residual soil. Only depend on less drilling data couldn’t reflect the site stratigraphy because the depositional environment and the stress history have larger difference of marine continental sediment. Furthermore, borehole sampling and laboratory tests may cause disturbance, can’t reflect the real situation of the soil. Referenced to domestic and foreign large crossing bridge project experience, the pore pressure static cone penetration test was used in this project for its efficient economy, high precision, good continuity and multi-function, under these constraints conditions.Cone Penetration Tests with Pore Pressure (CPTU) is an advanced in-situ geotechnical testing techniques that can simultaneously measure cone resistance, sleeve friction and pore water pressure, directly reflecting soil. The CPTU interpretation relies on corresponding theory, but the engineering practice is more important. In addition, the seabed wheel drive CPTU system was applied in this project, due to the study area belonged to Lingdingyang. As the seabed wheel drive CPTU system was used abroad earlier, so they accumulate more experience, but the maps they used in marine deposits classification also based on the land CPTU/CPT achievements. In order to fill the gaps in this field in China, as well as to test the applicability, Seacalf of Fugro and Roson of FHDI equipments were used in the study area.This paper relies on specific CPTU subject of CCCC FHEI Co., Ltd. And the existed classification map and indicators were comparative analyzed with CPTU, suspension P-S velocity logging, drilling and other survey means data, data statistics, formula fitting, cluster analysis and discriminant analysis. Meanwhile new soil indicators and classification map were proposed by jointing soil dynamics achievements. The main contents and achievements are as follows:(1)First, the paper summarized the development of CPTU at home and aboard, compared gaps of technical application, and the predicting development was prospected.(2)One of the major applications of the CPTU is the identification of the soil type. Some classification methods are reported to predict soil type by CPTU data(Robertson1986、1990、2010); Eslami-Fellenius (1997)、 Ramsey (2002)、 Zhang Chenghou(1990)、 Technological rules of static sounding(TB10041-2003) issued by the ministry of railway、 Meng Gaotou(2000).(3) The field applicability of the mentioned layer Classification map was analyzed, based on the CPTU test and borehole data. The results show that there is no a suitable CPTU layer Classification map, as they can’t give an accurate layer Classification except clay and sand, in the study area. It indicates that CPTU direct and indirect index can’t simply use in the marine and continental deposition classification, while other soil parameters should be considered.(4) The modulus ratio Ed/Gd that selected by statistics has good classification effect, after systematic introduction the soil dynamics parameter. And it can be fitted by CPTU test values.(5) Meanwhile dimensionless index log(q/σe) that proposed by Zhang Chenghou has certain classification effect, after statistical analyzing to existed CPTU classification indexes.(6) The combination index, consisted of modulus ratio Ed/Gd and dimensionless index log(q/σe), which has good classification effect, by K-means clustering analysis and Fisher discriminant analysis.(7) Applicability of Lingdingyang classification map was tested by10sets data (CPTU34,38,39,42,43,49,118,173,182and CPTU231). Compared to the existing classification map, the new one has better applicability in the study area. And the combination index, consisted of modulus ratio Ed/Gd and dimensionless index log(q/σe), can put into practice.