Study On Compressive Layer Field Test And Settlement Numeral Simulation Of Long Group Piles In Deep Soft Soil

The settlement calculation method for group piles in existent specifications is mainly based on layer wise summation method, but the result is always over-conserved. For lacking in compressive layer thickness field data for group piles especially for long friction piles in thick soft soil, and there are more than one criterion for compressive layer thickness calculation, intensive study is needed to determine which criterion is better for long friction group piles in thick soft soil. Thickness of compressive layer is an important parameter for settlement calculation and a significant basis for foundation settlement and deformation, so its field test has great realistic meaning in practical engineering. In addition, compression modulus is an major factor for settlement calculation, but compression modulus provided by geotechnical test is usually under the pressure of100~200kPa, though it’s always suitable for shallow foundation with a small inaccuracy, but the inaccuracy, coMPared with the field data is much bigger for calculation of long friction piles in thick soft soil, sometimes the inaccuracy will amount several times of the field data, which makes the theoretical calculation and numeral simulation of foundation settlement unrealistic.In view of the above, single-point settlement gauge and liquid level settlement gauge are adopted to monitor the compressive layer thickness and settlement of long friction group piles in thick soft soil, which makes the single-point settlement gauge avoided anchoring in bedrock or stable soil layer, and also the compressive layer thickness and the settlement of the group piles are obtained. A new formula for compression modulus modification along thick soft soil is put forward in this test, based on the formula, coMParative analysis of group piles settlement by existent national specifications is carried out, and <Technical Code for Building Pile Foundations> combined with10%"method of control stress", which used to control compressive layer thickness, is adopted to calculate settlement of long friction group piles in thick soft soil. Through coMParison with the field data, settlement value by this method is close to the measured value, which proves the applicability in calculating settlement in thick soft soil. Based on modified compression modulus Es.z, compression modulus ESs.0.1-0.2provided by geotechnical test under the pressure of100~200kPa, compressive layer thickness by "method of control stress", experiential compressive layer thickness, settlement numeral simulation of long friction group piles in thick soft soil by Plaxis3D Foundation finite element software is carried out, which proves that settlement numeral simulation based on modified compression modulus Es.z, compressive layer thickness by "method of control stress" is applicable for long friction group piles in thick soft soil, deserves further popularization and application in similar engineering.