James C. Ni

Experimental and Analytical Modeling of Shield Segment under Cyclic Loading

AbstractBecause of the lack of adequate monitoring performance data for shield tunnel segments from either laboratory testing or in situ measurement, it is difficult to improve the current segment design codes. As a result, overdesign or excessive use of reinforcement in tunnel linings is common. To overcome these segment design inadequacies, this study aimed to investigate the bending behavior of RC members based on measured strain data and the modeling results from a proposed analytical model, which takes into account section nonlinearity resulting from concrete tensile cracking and the actual effective moment of inertia. The cyclic four-point loading test was performed on a RC beam with an embedded optical fiber sensor and on a smart tunnel lining segment, in which two vibrating wire strain gauges with thermistors were welded into a rebar cage on either side of the neutral axis. The measured strain data for the rectangular beam subject to concrete curing and subsequent four-point loading justify the ap...

Monitoring and Modeling Grout Efficiency of Lifting Structure in Soft Clay

An inclined eight-story reinforced concrete building on a thick soft clay deposit was leveled by compensation grouting with short gel time grout injected through sleeved pipes. The monitoring system is used to record the injected grout volume, the mat foundation’s heaved volume after grouting, and the mat foundation’s settled volume during pore pressure dissipation. The grouting efficiencies improved from negative value to less than one, and the stress histories of clay soils changed from normally consolidated to overconsolidated states. A final compensation efficiency of 9.78% was achieved and the building was successfully leveled. A series of numerical simulations were conducted to assess the capability of compensation grouting modeling. The numerical simulation results indicate that the consolidation behavior and the stress history of clayey foundation soils can be modeled reasonably well. However, the computed final grout efficiency is larger than that from the monitoring data because the simulation o...

Trial Grouting under Rigid Pavement: A Case History in Magong Airport, Penghu

A trial pressure grouting program is conducted to restore the load carrying capabilities of Portland cement concrete slabs that have been in service for a number of years and are showing signs of distress. First, a series of laboratory tests are conducted to find a Portland cement grout mix with the appropriate properties of fluidity, viscosity, stability, shrinkage, and strength. Second, ground penetrating radar (GPR) is used to detect the possible voids under the slab before grouting, and falling weight deflectometer (FWD) is concurrently used to evaluate the load bearing capacity from slab deflection. Then trial grouting under the slab is conducted after the grout holes are installed based on the results derived from GPR. The grouting process will be halted if the injection pressure increment over the initial contact pressure is larger than 0.5 kg/cm2 or the slab heave is over 1 mm throughout the trial pressure grouting program. The elevations at various locations of each slab are closely monitored during grouting. Last, the GPR is used again to evaluate the effectiveness of slab stabilization. Then, FWD is also used to evaluate the effectiveness to restore the load carrying capability of the slab from grouting. This program is successfully achieved verifying by a series of laboratory and field tests undertaken before and after grouting.

Field Response of High Speed Rail Box Tunnel During Horizontal Grouting

The construction of two bored tunnels passing underneath an existing high speed rail (HSR) box tunnel needed to traverse obliquely through the diaphragm wall originally used for excavation and lateral support during construction of the HSR box tunnel. An access lift shaft was constructed adjacent to the HSR box tunnel diaphragm wall to provide access for the horizontal grouting equipment used to modify the surrounding soil to have sufficient water tightness and shear strength for safe tunnel eye creation and removal of steel H-beams left within the soil mixing wall. The grout block behind the tunnel eye was constructed first, followed by a long distance (up to 52 m) horizontal grouting (LDHG) program to form the other grout block around the steel H-beams. Since the grouted area was confined by a box tunnel on top and diaphragm walls on both sides, inappropriate grouting pressure could cause significant vertical movement of the HSR box tunnel above and potentially endanger the safety of the HSR service within. The grouting program was adjusted in accordance to real time box tunnel motion as detected by electronic beam sensors along the side walls of the box tunnel. The authors strategies for overcoming the challenges associated with long distance horizontal wash boring through diaphragm walls, scattered with steel H-beams, and accompanying grouting strategy will be presented in this paper. The vertical movement of the HSR box tunnel during the LDHG program was well controlled to less than 4 mm, while the maximum lateral displacement of the shaft diaphragm wall was maintained below 9 mm.

Grout Efficiency of Lifting Structure in Soft Clay

An inclined eight-story reinforced concrete building on a thick soft clay deposit was leveled by compensation grouting with short gel time grout injected through sleeved pipes. The monitoring system is used to record the injected grout volume, the mat foundations heaved volume after grouting, and the mat foundations settled volume during pore pressure dissipation. The grouting efficiencies improved from negative value to less than one, and the stress histories of clay soils changed from normally consolidated to over-consolidated. A final compensation efficiency of 9.78% was achieved and the building was successfully leveled.

Soil Characterisation Based on Pipejacking Parameters and Spoil Characteristics

Possessing a few geological boreholes distributed along the tunnel alignment is likely to lead to an inability of understanding the complex geological structure of worksite and optimising the tunnelling parameters. This lack of geological borehole will result in a high potential of geo-hazards for tunnelling works. This study proposes an alternative method to dynamically determine the major and other components of ground by taking the pipejacking parameters and spoil characteristics into account. The validity of the proposed method is verified via a case study.

An Alternative Method for Soil Characterisation Using Pipe-Jacking Parameters and Spoil Characteristics

As only a few boreholes are present along a tunnel design alignment, geological understanding of the worksite may not be adequate and the ability to optimise the tunnelling parameters is thus limited. Since this lack of boreholes will cause a significant potential of geo-hazards for tunnelling works. This study proposes an alternative method to determine the major and other proportions of ground. The variation of the torque of the cutter wheel and sieve residue can be utilised to determine the major ground proportion, whereas the flow rate of the supply line and pressure in the supply and discharge lines, as well as the density of bentonite slurry can be utilised to determine other proportions. The validity of the proposed method is verified by a case study. The proposed method provides an opportunity to better understand the geological structure of worksite, refining the design tunnelling parameters and minimising the potential of geo-hazards.

Performance Evaluation of Jacking Force Models for Tunnel Bore Conditions Characterisation

Since the ability of many available jacking force models to characterise the tunnel bore conditions is limited. A simple approach to characterise the tunnel bore conditions is proposed and applied to a case study where four sewer pipelines of the Shulin district sewer network in Taipei County, Taiwan were constructed to verify its validity. Four jacking force models are benchmarked in this study. Based upon the given soil properties and pipe dimensions as well as the pipe buried depth, the calculated normal contact pressure (σ′) from each model and the measured frictional stress (τ) in each baseline section are utilised for the back-analysis of the frictional coefficient (μavg). The μavg values outside the range of 0.1–0.3 recommended for lubricated drives can be ascribed to the increasing pipe friction resulting from the excessive pipe deviation or ground closure or the gravel formation not being long enough to establish lower face resistance. JMTA has indicated a further potential use in assessment of the interface performance during pipe-jacking works.

The use of tunnelling parameters and spoil characteristics to assess soil types: a case study from alluvial deposits at a pipejacking project site

Generally, when there are only a few boreholes present along a tunnel design alignment, geological understanding of the worksite may not be adequate and the ability to optimise the tunnelling parameters is limited. This lack of boreholes will cause an increased potential of geo-hazards during tunnelling works. This study proposes an alternative method to determine the major and other components of ground under such circumstances. Five factors, cutter wheel torque, sieve residue, flow rate of feedline, pressure in the feed and discharge lines and density of bentonite slurry, are adopted for determining the major and other ground components. Comparisons of the soil types based upon the results of grading and Atterberg limits tests on the spoil and soil samples, respectively, and those resulting from the proposed method indicate good consistency. The proposed method provides an opportunity for establishing a more comprehensive geological structure for refining the tunnelling parameters, reducing the potential of geo-hazards associated with the inappropriate tunnelling parameters.

Variation of Slurry Pipe Jacking Force in Coarse and Fine Soils

Pipe jacking force mainly consists of the penetration resistance from face pressure and the friction resistance between the pipe and surrounding soil. Jacking forces depends on the following parameters: soil type, groundwater table, overburden, overcut, lubricant, stoppage, misalignment, length of drive, and intermediate jacking station (IJS). A slurry shield excavating through alluvium deposit to install a 1.5-m diameter sewer line was selected in many straight drives with similar conditions of groundwater table, overburden, overcut, and stoppage. The lubricant distributed among injection outlets along the pipeline ensures a more uniform distribution of lubricant around the jacked pipes and a more effective reduction in frictional resistance. This leaves the soil type and steering correction standing out to reduce the jacking force required. It can be concluded that the soil classification system developed in a separate study helps in interpreting the local variation of jacking force that results from increasing penetration resistance due to either driving from coarse soil to fine soil or driving into wood log. This penetration resistance increment is recoverable when the driving condition is reversed. The friction resistance increases significantly if misalignment is larger than a threshold value of 60 mm, and remains unchanged even if deviation is corrected. The misalignment effect on friction resistance is not recoverable. For large diameter pipe jacking with stabilized overcut and sufficient amounts of lubricant, the face resistance can be significant relative to the friction resistance.