Wen-Chieh Cheng

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.

Alternative Shoring for Mitigation of Pier-Foundation Excavation Disturbance to an Existing Freeway

AbstractThe capacity of the Wuku-Yangmei freeway is insufficient for developing the Taoyuan Aerotropolis. To provide more traffic lanes to the existing freeway, a series of pier foundations at the ...

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.

Steering Efficiency of Microtunnelling in Various Deposits

An operators skill to steer micro tunneling machine is important to maintain driving within line and grade tolerances. It is also important to minimize rapid or erratic changes when steering a microtunneling machine. This paper presents a way to evaluate the machine steering quality of operator by recording the shield machines positions, strokes of steering hydraulic jacks, and pitch and roll values from pipe to pipe. Since the steering ability of shield machine and soil type are also important factors to influence the microtunnelling alignment. The field data are collected from various projects in which three brands of shield machines are used to drive in various ground, such as gravel formation, clay deposit, sand deposit and hard bedrock. The average deviation is evaluated from the integration of each pipes deviation along the shield machines traces divided by the total pipe length. The average adjustment of shield machine is evaluated from the integration of all the adjustments along the line divided by the total pipe length. It can be concluded that the average vertical or horizontal deviation is proportional to the average vertical or horizontal adjustment of steering jacks when the operator is steering shield machine in a normal and smooth conditions.

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.

Quality Control for Grouting Under Rigid Pavement

A trial pressure grouting program was 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. Firstly, a series of lab tests were conducted to find a grout with suitable properties of fluidity, viscosity, stability, shrinkage and strength, and a Portland cement grout with water to cement ratio of 0.8 and an additive of 7% by weight of cement was selected. Secondly, ground penetration radar (GPR) was used to detect possible voids under the slab before grouting, and falling weight deflectometer was used to evaluate the load bearing capacity from slab deflection before grouting. Then trial grouting under the slab was conducted, and the pressure grouting parameters of a maximum flow rate of 3 liters per minute and a maximum injection pressure of 0.5 kg/cm 2 were selected throughout the grouting program. To avoid the slab heaving, the elevations at six locations of each slab were closely monitored during grouting. At last, the GPR was used again to evaluate the effectiveness of grout to fill the voids under the slab. In addition, falling weight deflectometer was used to evaluate the effectiveness of restoring the load carrying capability of slab from grouting. This program was successfully conducted and the results of all these test and evaluations are described in this paper.

The Pumping Test Data Analyses of Andesite Rock Blocks Aquifer with Varied Hydraulic Boundaries by Generalized Radial Flow Model

The aquifer which includes abundant groundwater resources usually exists at toe of foothill where soil profile at the study area consists of soft silty clay, andesite rock blocks with gravelly sand, and bedrock. A series of constant-rate pumping tests were conducted in the aquifer between two impermeable layers to understand its hydrogeology characteristics. Pumping well is located inside of diaphragm wall, and observation wells are scattered inside and outside of it which was completed before these field experiments. In analytical analyses, diaphragm wall is modeled as impermeable boundary and hillside is assumed as constant recharge boundary. The problem that naturally arises when analyzing data from pumping tests is how to select an appropriate geometry for the particular aquifer system into which flow occurs. This study employs the generalized radial flow (GRF) model to analyze constant-rate pumping test data of the andesite rock blocks-based aquifer and to identify its fractional-flow dimensions further assessing aquifer parameters. This study concludes that the GRF model cannot analyze the drawdown response if pumping encountered perpendicular boundaries, and the fractional-flow dimension is not unique while other boundaries applied.

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.