Finite difference analysis of prefabricated vertical drains assisted with surcharge preloading of Hiep Phuoc soft clay in Vietnam

A series of finite difference analysis of the soft ground treatment with PVDs application has been performed with the application of the newly developed consolidation model. The model utilizes the concept of multi-compression indices and coefficients of consolidation to investigate the behaviors of the soft ground deposit on pore water pressure dissipation, surface and sub-layered ground settlement and to validate the newly developed CONSOPRO finite-difference procedure. Furthermore, the pre-consolidation pressures of the soft ground deposit are characterized with the combination of the piezocone penetration profiling and constant rate of strain consolidation tests under 0.02 %/min. on undisturbed samples which were retrieved at the investigated site, Saigon Premier Container Terminal (SPCT) in the South of Vietnam. On the comparison of the back-calculation results to the field observing data, the correlation between the coefficients of consolidation determined by constant-rate-of-strain (CRS) consolidation tests and those from piezocone dissipation tests, which were carried out after the soil improvement, is developed.

Geomechanics of Soft Ground Improvement by Perforated Piles: Review and Case Study

Civil Infrastructure built on soft and compressible soil is likely to collapse due to undrained shear failure or unacceptable settlement of supporting foundations. Incorporation of adequate ground improvement technique with the aim of upgrading the strength and stiffness of the weak soil is essential in such cases. Amongst various established methods adopted worldwide for improving soft ground, using perforated piles is a relatively emerging technique. Such piles not only transmit the structural load into the subsoil beneath in a manner similar to the conventional piles, but also assist in radial consolidation of soft soil due to perforated side walls. This paper presents a brief overview on the investigations carried out on this new technique. Also, a typical case study has been presented. As observed, the axial pile capacity progressively increased while settlement reduction took place, with accelerated radial consolidation.

Analysis of Settlement Behaviour of Soft Ground Under Wide Embankment

An elastoplastic numerical model for calculating the consolidation settlement of wide embankment on soft ground is established using PLAXIS finite element software to investigate the settlement behaviour of soft ground under the wide embankment. The distribution rules are analysed and compared to narrow embankments, such as surface settlements of ground and embankment, lateral displacement of soft ground at the foot of embankment slope and excess pore pressure in soft ground. The influence rule of elastic modulus of soft ground on the settlement of soft ground under wide embankment is discussed. The results show that the settlement distributions of wide and narrow embankments on soft ground are “W” and “V” shapes, respectively. The maximum settlement of wide embankment is near the foot of the embankment slope, which is unequal to the settlement at the centreline of the embankment. The lateral displacement distribution rules of soft ground are both “belly” shaped at the foot of two types of embankments slope. However, the lateral displacement of the wide embankment is larger in each corresponding stage. During the construction period, the excess pore pressure in the soft ground under the wide embankment is much higher than that of the narrow embankment, so the post-construction consolidation time of the wide embankment is longer. Moreover, the macroscopic settlement rule of the wide embankment is still the same with the increase of elastic modulus of soft ground.

Research the Integration of Geodetic and Geotechnical Methods in Monitoring the Horizontal Displacement of Diaphragm Walls

This article investigates the integration of geodetic and geotechnical methods for monitoringthe horizontal displacement of diaphragm walls. The results show that when the horizontal displacementis measured by the geotechnical method using an inclinometer sensor, the center point at the bottom ofthe guide pipe is usually chosen to be the origin to calculate displacements of the upper points. However,it is challenging to survey the bottom point for checking its stability directly. If this bottom point moves,the observation results will be incorrect. Thus, the guide pipe must be installed in the stable rock layer.But in the soft ground, this rock layer locates more deeply than the diaphragm walls, so the guide pipecannot be laid out at the required location. Geodetic methods can directly observe the displacement of thecenter point on the top of the guide pipe with absolute displacement values at high accuracy. Because thedisplacements of observation points are determined at stable benchmarks, these values are considered thepipe's displacement. Thus, an integrated solution allows the center point on the top of the pipe to be theorigin to calculate the displacements of different points located inside the diaphragm wall. Then, thecalculated values are calibrated back to the inclinometer observed values to achieve highly reliabledisplacement, which reflects the moving of diaphragm walls. An experiment integrating the geodetic andgeotechnical methods is conducted with an observation point at a depth of 20 meters at a construction sitein Ho Chi Minh city. The deviations of the top point that are observed by the two methods are -4.37millimeters and -3.69 millimeters on the X-axis and the Y-axis, respectively. The corrected observedresults prove that the integrated solution has a good efficiency in monitoring the horizontal displacementof diaphragm walls. The bottom point observed by an inclinometer is unconfident enough to choose to bea reference point.

Use of Foamed Cement Banking for Reducing Expressways Embankment Settlement

Expressways are often built on soft ground, the foundation of which is not processed adequately during the construction period. Consequently, the traffic safety and embankment stability will be seriously affected due to uneven settlement. The technology of holing the embankment and replacing foamed cement banking (FCB) could control the settlement of an embankment without road closure, thus reduce the impact of construction on normal operation of highways. In this paper, the principle of FCB is described. Additionally, a sedimentation ratio calculation method, through the analysis of the settlement load ratio, is proposed for calculating the roadbed replacement thickness. This paper takes the example of the test section EK0 + 323 on Shen-Jia-Hu expressway in Zhejiang Province and combines with site settlement monitoring data to confirm the effectiveness of the calculation method proposed.

Prediction and Validation of Landing Stability of a Lunar Lander by a Classification Map Based on Touchdown Landing Dynamics’ Simulation Considering Soft Ground

In this paper, a method for predicting the landing stability of a lunar lander by a classification map of the landing stability is proposed, considering the soft soil characteristics and the slope angle of the lunar surface. First, the landing stability condition in terms of the safe (=stable), sliding (=unstable), and tip-over (=statically unstable) possibilities was checked by dropping a lunar lander onto flat lunar surfaces through finite-element (FE) simulation according to the slope angle, friction coefficient, and soft/rigid ground, while the vertical touchdown velocity was maintained at 3 m/s. All of the simulation results were classified by a classification map with the aid of logistic regression, a machine-learning classification algorithm. Finally, the landing stability status was efficiently predicted by Monte Carlo (MC) simulation by just referring to the classification map for 10,000 input datasets, consisting of the friction coefficient, slope angles, and rigid/soft ground. To demonstrate the performance, two virtual lunar surfaces were employed based on a 3D terrain map of the LRO mission. Then, the landing stability was validated through landing simulation of an FE model of a lunar lander requiring high computation cost. The prediction results showed excellent agreement with those of landing simulations with a negligible computational cost of around a few seconds.

Effects of Strong Ground Motion with Identical Response Spectra and Different Duration on Pile Support Mechanism and Seismic Resistance of Spherical Gas Holders on Soft Ground

Safety measures are required for spherical gas holders to prevent them from malfunctioning even after a large earthquake. In this study, considering the strong nonlinearity of the ground and damage to the pile during an earthquake, a three-dimensional seismic response analysis of the holder–pile–ground interaction system was conducted for an actual gas holder on the soft ground consisting of alternating layers of sand and clay. In the analysis, the seismic response of the structure to strong ground motions of different durations with the same acceleration response spectrum was verified. The results show that the piles were relatively effective in controlling the settlement when the duration of the earthquake motion was long. This is because the axial force acting on the pile increased due to the redistribution of the holder load caused by the lowering of the effective confining pressure of the sand and clay layers during the earthquake, which increased the bearing capacity of the pile. In contrast, when the duration of the seismic motion was short, the piles had little effect on the reduction in the settlement because the maximum acceleration was higher than that in the former case, and the piles immediately lost their support function.