Evaluation on the state of sand filling layer and the influence on segment deformation of immersed tunnels

The immersed tunnel is considered an effective solution for traffic problems across rivers and seas.The sand filling layer,as an important part of immersed tunnel foundation treatments,directly affects segment attitude stability.Due to difficulties in quality control of concealed construction and the complex hydrodynamic environment,the sand filling layer is prone to compaction defects,further leading to changes in segment attitude.However,limited by structural concealment and state complexity,most studies consider the sand filling layer part of the foundation to study its impact on settlement while neglecting its influence on segment attitude.This research proposes an evaluation method for the sand filling layer state based on elastic wave testing and the elastic wave characteristic parameters selected come from analysis of the time domain,frequency domain and time–frequency domain.By classifying the elastic wave characteristic parameters through the K-means clustering method,the relationship between the state of the sand filling layer and the elastic wave characteristic parameters is established.The state of the sand filling layer is divided into dense,incompact,and void.A numerical model is established based on the Guangzhou BI-UT immersed tunnel with incompact and void sand filling layer states to simulate deformation and torsion.The results indicate that the settlement of the tunnel segment is low in the eastern region and high in the western region due to the presence of a less dense sand filling layer,with a maximum differential settlement of 0.04 m.The evaluation method plays a crucial role in guiding the construction of immersed tube tunnels.

A system and analytical method for testing the electrical parameters of soil

The electrical parameters of the rock and soil are closely related to the physical parameters.By measuring the resistivity and polarizability of rock and soil reasonably,information on physical parameters such as moisture content,pore ratio and compaction degree can be obtained.A system for testing the electrical parameters of soil samples based on the middle step quadrupole method is developed in this article.The system uses a series of copper needles as the electrodes of the soil-mounted test tube,and uses a multi-point multi-layer test method for layered data acquisition,which can solve the problems caused by the capacitance phenomenon and the heterogeneity of the soil sample.At the same time,factors affecting the test results,such as uneven soil preparation and water addition and electrode disturbance,are regarded as noise.A data-analysis method based on median filtering is proposed to process and analyse the test results,and the relationships between resistivity,polarizability,moisture content and compaction degree of the sample are obtained.The results show that the resistivity decreases nonlinearly as moisture content increases,and the correlation with compaction is not strong;the polarizability increases as moisture content increases with fluctuation,and it first increases and then decreases with an increase in compaction.

Evaluation method of rock damage under uniaxial compression based on unit series-parallel electrical conductive model

The evaluation of rock damage behaviour is an important requirement for ensuring stability control and safety prediction in rock engineering.However,they have not been able to obtain sufficiently accurate and dynamic results due to the insufficient evaluation method.In this study,by means of fractals and unit series division,a unit series-parallel conductive model of damaged rock is derived,and a new evaluation method of rock damage under uniaxial compression was proposed.Rock was damaged by uniaxial compression,while electrical measurements and X-ray microscopy tests were performed to obtain the damaged rock resistivity,porosity,and fractal dimension variation.By establishing the relationship between defined meso-damage factor and resistivity,rock damage evolution law under axial compression was obtained.The results indicate that the growth trend was agree with the classical statistical damage model,which verified the accuracy of the results obtained by the proposed method.Moreover,as the strain increased,the damage factor determined by resistivity gradually decreased to0.06 firstly and then increased rapidly to 0.79.Different from previous damage evolution law,brittle failure was observed and the cracks development in each stage was considered,including the closure(negative damage)and expansion(positive damage)of cracks.