Analysis of the Development Characteristics and Influencing Factors of Freezing Temperature Field in the Cross Passage

Based on the analysis of the temperature measurement data of the Shanghai Metro Line 15 cross passage freezing project, it was found that the gray silt layer of cross passage No. 2 outperforms that of cross passage No. 1 on the freezing effect, which is mainly attributed to the large loss of cooling capacity in the latter passage. Within the same stratum, the soil temperature at the duct piece is higher than that of the deep soil. When the soil freezes for 45 days, the temperatures of the sandy silt and gray silt layers of the same cross passage drop to −8.25°C and −6.91°C, respectively, indicating that the freezing effect of the sandy silt layer is better than that of the gray silt layer. Moreover, simulations were performed for deviation freezing pipes, nondeviation freezing pipes, and different freezing pipe diameters in the cross passage No. 1, respectively. It was found that the maximum difference of the closure completion time between the deviation and nondeviation freezing pipes is 6 days. Furthermore, for deviation freezing pipes and nondeviation freezing pipes at the center of the cross passage, the minimum difference in the freezing wall thickness reduces from 0.45 mm after 20 days of freezing to 0.06 mm after 45 days of freezing, indicating that the difference in the freezing wall thickness gradually weakens as freezing develops gradually. The deviation freezing pipe increases the spacing of freezing pipes in the deep soil. As the pipe spacing increases, the influence of the pipe diameter on the closure completion time of the freezing wall decreases.

Study on early warning of rapid sinking of large land caisson in silt layer

Large caisson constructed in the soft soil layer is prone to rapid sinking during the sinking process. Rapid sinking is often accompanied by partial sinking, which affects construction safety and subsequent construction. There is no relevant early warning mechanism for early warning of rapid sinking. This paper takes the sinking construction of a large land caisson in a deep silt layer as an example, analysis the rapid sinking mechanism through the earth pressure and settlement rate of the sinking process, and proposes a rapid sinking early warning mechanism. Before the rapid sinking, the soil at the edge of the blade feet is partially plastic damaged, and the earth pressure decreases continuously after reaching its limit value; The strain softening of the overlying soft soil layer, the rapid reduction of side friction and the instability of open caisson caused by soil gushing after the plastic zone connecting are the important reasons for the rapid sinking. The rapid sinking process is divided into “sagging section, starting section, instability section and stable section”. The earth pressure early warning mechanism is the continuous decrease of the earth pressure at the blade feet. When the sinking rate exceeds the threshold value for two hours, it is regarded as the early warning mechanism of sinking rate. Using this dual control mechanism of end earth pressure and sinking rate can effectively warn the rapid sinking of the caisson.

Experimental Research Based on the Optical Fiber Sensing Technology for a Jacked PHC Pipe Pile Penetration Process

The aim of this work is to explore the influence of the end resistance and shaft resistance regarding the mechanism for jacked pile penetration and the load-transfer rule during the penetration process. A full-scale field test was conducted in an actual project located in Dongying, Shandong Province, China. In this test, the axial strain experienced by two closed Prestressed High-strength Concrete (PHC) pipe piles during jacking into layered soil was monitored successfully using Fiber Bragg Grating (FBG) sensors mounted on the pile shaft. The experimental results show that FBG sensors have a good stability, strong antijamming performance, and can effectively monitor the pile stress. The variation law of the jacking force reflects the distribution of the soil layer, and the hardness of the soil layer at the pile end limits the pile force. When the pile end enters the silt layer from the clay layer, the jacking force and shaft resistance increase by 2.5 and 1.7, respectively. The shaft resistance accounted for 44.99% of the jacking force. The end resistance is affected by the mechanical properties of soil, and the end resistance of the silt layer is approximately twice that of the clay layer. The end resistance of the silt layer accounted for 59.84% of the jacking force. When the pile end enters the soft soil layer from the hard soil layer, the impact of the pile driving speed and the tangential force on the surface of the pile body must both be considered. During the pile penetration process, as the penetration depth increases, the radial stress on the pile side at a given depth is gradually released, while the shaft resistance at the pile side degrades significantly.

Structural Damage of Subway Tunnel Buried Shallowly in Silt Layer under Soil Mound Loading

Based on the structural damage of the shield tunnel caused by a soil mound on the ground surface in a section of subway in Tianjin, China, the deformation and the cracking process of the segment under soil mound loading were simulated. The variations of segment, bolt, and rebar stresses with the height of the mound were analyzed. The results show that, for the stagger-jointed assembled shield tunnel that crosses the marine sedimentary silt with a burial depth of 10 m, as the mound loading increases, the damage is concentrated in the vault and hance. When the mound loading is 16.0 kPa, the segment is damaged; the crack depth and bolt axial force of the vault increase rapidly when the mound loading reaches 38.6 kPa. The analysis results are basically consistent with monitoring data. Based on the above analysis, the control standard of mound loading should be 38.6 kPa. The results of this study can provide data reference for control and structural protection of soil mound loading for similar subway tunnels.

PENGUKURAN RESISTIVITAS LAPISAN TANAH DI KELURAHAN TUAH KARYA MENGGUNAKAN KONFIGURASI SCHLUMBERGER

Geoelectric is one of the geophysical exploration methods that uses the earth's electrical properties to study subsurface conditions, the geoelectric method has several rules, one of which is Schlumberger's rule. This study aims to determine the composition of the soil layer, so that it can be known that the cause of difficult surface water seeps into the ground based on resistivity values at the HSB Indah Residence. Schlumberger configuration research uses a 300 meter stretch. Resistivity of soil constituent lithology in the study area was generated by processing geoelectric data using one-dimensional progress software. The cross section of the rock structure consists of five layers, namely the first layer is a clay layer with a resistivity value of 13.49 Ωm, the second layer is silt layer with a resistance value of 42.88 Ωm, the third layer is a clay layer with a value of 1.87 Ωm, the fourth layer is a layer of sandstone with a resistivity value of 59.17 Ωm and the fifth layer is a layer of gravel sand with a resistivity value of 443.40 Ωm. This shows that the cause of surface water is always flooded around the housing area, the soil layer is dominated by clay and silt material with a depth of more than 25 meters.

Influences of Temperature and Suction on Pile Capacity in Homogeneous Silt Layer

This paper presents the simulation results of variation in pile capacity with temperature and suction. The end bearing, shaft friction and ultimate bearing capacities at various values temperature and matric suction were simulated. The simulation results show that the end bearing capacity decreased with increasing temperature but increased with increasing matric suction. The results also show that, with increasing temperature, the shaft friction and ultimate bearing capacities decreased at low to moderate level of suction but increased at low temperature and high level of suction. With increasing matric suction, the shaft friction and ultimate bearing capacities increased at moderate to high level of temperature but decreased at low temperature and high level of suction.

Experimental Study and Models Comparison for Solute Transport through Riparian Zones

Solute transport through riparian zone was studied experimentally and numerically with the consideration of silt layer. The silt layer had markable change on flow field and lead to a significant variation of the breakthrough curves (BTCs). BTCs of solute tracer tests show non-Fickian features as early arrival of peak value and long tailings. BTCs were fitted by advection dispersion equation (ADE), mobile and immobile model (MIM) and the continuous time random walk (CTRW) models. MIM and CTRW can fit BTCs better than ADE and MIM fit better on the capture of the peak value and CTRW fit better in description of the long tailing.