Allowable Settlement Research Articles

On the response of jointed rigid pipes under abrupt ground subsidence: A closed-form analytical solution

The structural safety of jointed rigid pipes can be jeopardized under abrupt ground settlements. Most previous studies have investigated the response and safety of jointed rigid pipes under abrupt ground subsidence using numerical and experimental methods at two specific positions, i.e., the shear band caused by the ground movements crosses the pipe at a joint and at the midspan of a pipe segment. In this work, a closed-form analytical solution for the deformation and mechanical response of jointed rigid pipes under abrupt ground subsidence with various crossing positions is presented. The pipe bending moment and the joint shear force are calculated, which match quite well with the results of finite element analysis. Then the maximum allowable settlements are examined, and the corresponding failure modes are identified. It shows that with the increase of burial depth and soil density, the main failure mode gradually changes from the excessive joint deflection to the barrel bending and bell cracking, and the maximum allowable subsidence distance decreases remarkably. The worst crossing position is at nearly 7/10 of the pipe length. The results offer new insights into the failure mechanism of jointed rigid pipe, and provide a basis for the protection of rigid pipes under abrupt ground subsidence.

Probabilistic analysis of ground settlement induced by tunnel excavation in multilayered soil considering spatial variability

Accurately evaluating and predicting the ground settlement during tunnel excavation are crucial for ensuring the stability of tunnel structures. However, the traditional methods always use representative (or average) values for deterministic analysis and rarely consider the spatial variability of soil properties. In this study, a probabilistic analysis of ground settlement under uncertain soil properties was performed based on random fields combined with the finite-difference method. The random fields of Young’s modulus and friction angle of multilayered soils were generated based on the Cholesky decomposition in a manner consistent with a specified numerical mesh. The effects of spatial variability and cross-correlation in random fields on the ground settlement were investigated in detail. The results demonstrate that spatially variable soils significantly influence the probability of failure, magnitude, and longitudinal profile of ground settlement in the vertical direction. It can be found that the allowable ground settlement of the limit state function also dominated the degree of the vertical scale of fluctuation on stability. Neglecting the cross-correlation between the two random fields results in an overestimation of the probability of failure compared with an independent analysis. Subsequently, the failure mechanisms of ground settlement in spatially random soils were discussed.

Numerical Study on Optimization of Piled Raft Foundation on Stratified Soil under Static Load

Piled raft foundation (PRF) is a combination of pile and raft that provides adequate bearing capacity under the allowable settlement. This research aims to optimize the PRF design for a 48-story Commercial Bank headquarters building in Addis Ababa, Ethiopia, by conducting parametric study on various pile configuration using FLAC3D (Fast Lagrangian Analysis of Continua in three Dimensions) software. We analyzed 28 piled raft configurations and found that increasing the distance between piles increases the raft load sharing distribution by 11.5% while reducing settlement. Despite variations in pile length and diameter, a close load sharing between the pile and raft is accomplished at a separation of seven times the pile diameter (7D). The largest settlement decrease achieved was 9% for a 2-m pile diameter by doubling the pile length from 10 to 20 m, indicating that increasing pile length is ineffective for settlement reduction. We also proposed two new pile configurations that share load equally among pile and raft, and slightly increase total settlement below 10-cm limit. The results show that the first configuration exceeds differential settlement limit, but the second configuration reduces it by 95% and saves 40% of piles. This study provides a useful reference for designing PRF for high-rise buildings in similar soil conditions.

Predicting the Allowable Settlement of Reinforced Soil Foundations: A Laboratory Study

Predicting the Allowable Settlement of Reinforced Soil Foundations: A Laboratory Study

Load capacity of penstock manifolds subjected to increasing settlements at the vertical supports

AbstractHydroelectric power plants usually have penstock manifolds near the powerhouse, including individual bifurcations to provide several turbines. These steel constructions have numerous vertical supports and are designed based on linear elastic behaviour, leading to very small allowable settlements at the supports.For a representative built manifold, with five bifurcations (six branch pipes), the elastic‐plastic load capacity was studied in detail, assuming dead load, internal pressure and increasing settlements at the supports. Different settlement patterns were studied. The development of plastic zones was analyzed, depending on the rate of settlement. Due to the high bending stiffness of the penstock manifold, the penstock detaches from the single supports due to the settlement, leading to a significant redistribution of the vertical reaction forces at the supports.The comprehensive calculations show adequate robustness of the penstock manifolds, even though in case of very high settlements at the supports. Due to the significant redistribution of the reaction forces at the supports, these vertical supports must have an increased bearing capacity, in comparison to the reaction forces due to dead load and internal pressure based on linear elastic analyses.

Numerical study on settlement-dependent variation of raft-soil-pile interactions for large piled raft in clay soil

In a piled raft foundation, the stresses applied on the soil from the raft and piles overlap, which leads to changes in the settlement and bearing capacity of the raft and each individual pile. In this numerical study, settlement-dependent variation of three interaction factors, namely piles-to-piles (P-P), raft-to-piles (R-P), and piles-to-raft (P-R) have been investigated for large piled raft in stiff clay. The unpiled raft is flexible, the piles are friction piles and the effects of pile number, spacing and length on these interaction factors are presented. The P-P factor increases and then tends to become constant at a certain settlement. In contrast, the R-P factor always shows an increasing trend with settlement. However, the P-R interaction factor initially decreases and then increases with settlement. At the final settlement equal to 0.35% of raft width, the P-P, R-P, and P-R interaction factors range from 0.95 to 1.10, 0.86–1.04, and 0.25–0.92, respectively. Predictive equations have been proposed for these interaction factors and thereby determine the load-sharing ratio and mobilized safety factor. Within the allowable settlement range satisfying the serviceability limit, a good agreement between the results obtained from predictive equations and the finite element analyses is demonstrated for different piled raft configurations.

Calculation and Analysis of Pipe Joint Settlement Control in Large Back Silting Immersed Tube Tunnel

The use of the segmental pipe section immersed tunnel suffers from several problems, such as complex construction, weak foundation, great water depth, great thickness of siltation back on the top of the tube, and difficult settlement control. Based on Winkel’s elastic foundation beam theory, a mechanical calculation model is established according to the case of an inhomogeneous soil layer, and the force and deformation of the structural system of the immersed tube tunnel are calculated based on a bridge in Zhuhai as an example of an immersed tube tunnel. The results show that the derived formula for calculating the allowable differential settlement per unit length of the longitudinally immersed tube is applicable to the sudden change type foundation stiffness deformation model of the natural foundation section of the tube tunnel of the aforementioned bridge in Zhuhai. The relationship between the settlement control index and related influencing factors is analyzed. Hence, a formula for calculating the stratified ground foundation’s integrated bed coefficient is derived, and the equations for tunnel deflection curves and shear forces are solved. A set of calculation methods that are applicable to the foundation settlement control criteria of the segmental immersed tunnel is provided, and the results provide a significant reference for the optimization of the foundation scheme and improvement of the construction process for similar projects.

Investigation of the settlement mechanism and control measures of a super-large section tunnel in a giant karst cave using ultra-thick backfill method

A giant cave was encountered during the construction of the Yujingshan Tunnel. There were deep deposits at the bottom of the giant cave, including soft soil, crushed stone soil, and fine sand. A comprehensive construction scheme, comprising an ultra-thick backfill and a continuous rigid frame bridge, was adopted when constructing the large-section tunnel. However, there were still problems regarding the post-construction and differential settlements of the tunnel (the differential settlement is defined here as the difference between the left corner settlement and the right corner settlement of the tunnel bottom). These problems led to significant challenges for the long-term safety of the tunnel. Control measures were proposed to address these settlement problems. Centrifugal model tests were mainly conducted to analyze the leading causes of the post-construction and differential settlements. And numerical simulation was mainly used to investigate the differences of various grouting depths in the base. Finally, regression analysis and trend simulation were performed based on in-situ monitoring data. The results indicate that the ultra-thick backfill and soft clay are both the causes of the base settlement, and the soft clay accounts for a larger proportion. The differential settlement is mainly due to the uneven soft clay at the bottom. After research, the final scheme is grouting to a depth of 30 m, the post-construction and differential settlements can be controlled at 35.3 mm and 9.6 mm respectively, and the tunnel structure will have higher safety. On this basis, it is proposed that the maximum allowable settlement is 40 mm, and the maximum allowable differential settlement is 10 mm in long-term operation. The monitoring results and regression analysis show that the construction of the Yujingshan Tunnel is significantly improved, and the post-construction and differential settlements can be controlled at approximately 12.2 mm and 6.6 mm, respectively, which are both less than the maximum allowable values proposed above.

FIELD INVESTIGATION OF THE INITIAL SETTLEMENTS OF PILE NOT CONNECTED TO THE RAFT IN A COMBINED RAFT-PILE FOUNDATION

Problem statement. The patented useful model for the design of the combined raft-pile foundation (CRPF), consisting of a raft part and piles, with a gap of height Δ is made between the raft part and the piles. That is, the distribution of settlements (resistances) of the soil base under the raft and then under the piles (after the hinged connection of the piles with the raft) is assumed, based on the condition of not exceeding the maximum allowable settlement su of the building or structure. The initial settlement of the piles, which arises from the effect of the additional loading (negative) friction force acting on their lateral surface within the compressible layer during the pressure loading of the soil base raft part, must additionally be taken into account to correct the value of the gap Δ. The purpose of the article is to conduct field investigation of the piles initial settlements under the action of additional loading (negative) friction forces acting along their lateral surface in a large-scale combined raft-pile foundation to identify new dependencies and generalize them. Conclusions. On the basis of field studies, a qualitatively new dependence of the pile deformation on the action of additional ground friction forces has been revealed, which shows the "pile up-slip effect" due to the excess of resistance forces on its lateral surface with manifestation of inverse (elastic) deformations of the ground base of the pile. On the basis of field investigation, a qualitatively new dependence of the pile deformation on the effect of soil additional loading (negative) friction forces was revealed, which shows the “effect of the pile slipping upwards” due to exceeding the negative friction forces the resistance forces on its lateral surface with the manifestation of reverse (elastic) deformations of the pile soil base, which indicates the need to take this phenomenon into account when determining the gap between the raft part and the piles in projects of similar CRPF.

Micromechanical analysis of capillary suction effect on bearing capacity of unsaturated fine granular foundation soil using coupled CFD-DEM method

The micro- to macro-scale bearing capacity characteristics of unsaturated fine granular soil have remained unclear. This study is the first to investigate the capillary suction effect on the bearing capacity of unsaturated fine granular soil in a plate load test via a series of coupled CFD-DEM simulations. The bearing capacities of fine granular soils in dry, unsaturated and saturated conditions are compared at both the macro- and microscales. The findings reveal that in addition to sharply improving the bearing capacity, capillary suction is useful for increasing allowable settlement in fine granular soil. Moreover, the study uncovers a much deeper particle migration as well as a much larger triangular zone of contact force distribution in the unsaturated soils compared to saturated soils. The existence of a huge triangular rigid zone under the plate in unsaturated fine granular soil is the major reason behind the high soil bearing capacity, and the capillary suction effect is partly similar to the surcharge effect on soil bearing capacity, leading to an explanation of this phenomenon in a micro-scale context.

Long-Term Settlement Prediction of Ground Reinforcement Foundation Using a Deep Cement Mixing Method in Reclaimed Land

The greenhouse foundation method requires a lower allowable bearing capacity compared to general buildings, but the high-spec and expensive prestressed high-strength concrete (PHC) pile reinforcement method is mainly applied. Therefore, the deep cement mixing (DCM) method, which is one of the ground reinforcement foundations that replaces the PHC piles and secures structural safety suitable for the greenhouse foundation, was considered. To verify the structural safety of the DCM method, a geotechnical survey and soil test were conducted, and a long-term settlement monitoring system was established. The specifications of the DCM foundation were designed to be 0.8 m in diameter, 3 m × 3 m in width and length, and 3 m in depth. Based on the settlement monitoring data, long-term settlement was predicted considering the greenhouse durability of 15 years. For long-term settlement prediction, the Log S–T, hyperbolic, Asaoka method, Schmertmann theory, and the finite element method (FEM) analysis were performed. In the case of the Log S–T, hyperbolic, and Asaoka method based on actual measurement data, the settlement amount was predicted to be 12.18~20.43 mm, and in the case of the Schmertmann empirical formula, it was predicted to be 19.66 m. The FEM analysis result was 8.89 mm. As the most conservative result, the DCM foundation method designed in this paper had an allowable bearing capacity of 310 kN/m2 and a long-term settlement of 20.43 mm. This is the result of satisfying both the allowable bearing capacity of 100 kN/m2 and the allowable settlement range of 25.4 mm as a foundation. Through this study, it was proven that long-term structural safety can be sufficiently secured when the DCM foundation is constructed on a soft ground through a design that considers the required service life and allowable bearing capacity of the structure. In addition, it was confirmed that the Hyperbolic, Asaoka, and FEM analysis method adopted in this paper can be applied to the long-term settlement behavior analysis of the DCM foundation method.

Changing the redistribution of forces between pile foundation elements as the load increases

Having, during the design of the pile foundation, the load-bearing capacity of the piles determined in one way or another, as well as the calculated resistance under the sole of the rostwerk as a shallow foundation, it is possible to use data on the degree of implementation of the load-bearing capacity of each of the elements of the pile foundation to arrive at its total load-bearing capacity. But it is known that at different stages of loading, the degree of implementation of the load-bearing capacity of the elements of the pile foundation can change.The purpose of this work is to analyze the change in the redistribution of forces between the elements of the pile foundation with a gradual increase in the loads on it. This will make it possible to justify the selection of the critical value of settlement, for which it is appropriate to determine the degrees of implementation of the load-bearing capacity of the elements of the pile foundation, which can be proposed for use in the design.The analysis of changes in the redistribution of forces between the elements of the pile foundation with a gradual increase in loads on it was performed for the bush pile foundation based on physical modeling on small-scale models, as well as mathematical modeling using the Plaxis software complex.It was established that the pile in the composition of the bush, both according to the results of physical modeling and mathematical modeling, gradually realizes its load-bearing capacity as the load increases and, with significant values of settlement, perceives the load, more than the limit load of a single pile.Therefore, at a certain stage of loading, the degree of implementation of the bearing capacity of the pile begins to exceed unity. The share of the rostwerkwork in the load-bearing capacity of the foundation increases as the load increases, as the pressure under the sole of the rostwerkwork increases. The degree of implementation of the rostwerk practically does not change for a sandy base and increases insignificantly for a clay base. So, the rostwerk is gradually included in the work, but the potential ability of the rostwerk to perceive the load is not fully realized and at a certain value of settlement remains constant.The possibility of analyzing the redistribution of forces between elements of the pile group only at the stage of the maximum allowable settlement was evaluated.

Study on the vibration evaluation method and allowable differential settlement of road-bridge transition section with full-car model

ABSTRACT The differential settlement between bridge approach slab and abutment causes bump problems when vehicles passing this area. This study aims at evaluating the roughness of area between road-bridge transition properly and putting forward the allowable differential settlement value based on the comfortable feeling of passengers. In this research, the maximum transient vibration value (MTVV) was chosen to be the evaluation index of roughness vibration comfort, and full-car model and bridge approach pavement models were established using Carsim software. Then, the interactions of human-vehicle-road were simulated when the car passed the bridge at different speeds, and the influences of step height, approach slab length, approach relative slope and vehicle speed on MTVV were studied. According to the simulation results and the comfortable feeling questionnaire when a testing car passed different bridge areas, the specific grading standard of MTVV was given, and for the bridge with and without approach slab, the allowable differential slope and the step height of the bridge under difference were put forward. The results have a significant value for the roughness evaluation of the road-bridge transition area and can be used to judge whether this area is needed or not to maintain.

Design of Axially Loaded Piles in Consolidating Soils

The present design method in various codes for axially loaded piles embedded in consolidating soil is not satisfactory. It is too conservative in calculating the maximum pile force. Furthermore, the additional pile settlement due to the consolidation is neglected in ascertaining whether the requirements of allowable settlement have been met. This is because the behavior of such piles is not well understood. A new step-by-step design method based on the combination of results of extensive parametric studies of an elastoplastic load transfer model incorporating pile–soil slip reported previously is presented. In contrast to the iterative procedure required by some existing methods to determine the neutral plane location, these design charts can be used to determine the pile top settlement, neutral plane location, and maximum pile load directly. Further saving in the design of pile foundation is obtained with the concept of a compensating-pile foundation.

SETTLEMENT ANALYSIS OF PILE FOUNDATION USING PLAXIS 3D

In recent years, there are many construction projects which are constructed on the soft soil. Because of the characteristics Sentimental or soft soil, the structures which are built on that are subject to differential settlements. Foundation is one among the methods for reducing differential settlement. To reduce the settlements to a suitable amount, the piles are added. In this project, the aim is to analyze the settlements of the pile foundation by increasing the number piles, as the pile foundation, under the same loading, with or without considering the water table below the top surface. The numerical analysis has been done by finite element method using PLAXIS 3D by considering the varied number of piles. As a result, the addition in the number of piles could reduce the settlement. It is necessary to think about the optimum number of piles in pile foundation system supported the allowable settlements, for its economical design. This analysis has been undertaken to study the behavior of pile foundation under different number of piles. This analysis has been done using PLAXIS 3D software.

Risk of Land Subsidence Related to Underground Karst Caves and Solutions, North-South Vietnam Expressway

This paper assesses the risk of land subsidence related to the underground Karst caves at the section Km55+660- Km55+690 of North-South Vietnam Expressway by finite element method using PLAXIS 2D V.8.5 software. The research results show that there is a risk of collapsing the ceiling of the underground Karst caves due to the impact of the embankment process and the vehicle load. The research results also show that the vertical displacement is larger than the allowable residual settlement according to Vietnamese standard; it is necessary to take the soft soil improvement to achieve the allowable residual settlement. Several construction solutions are proposed to prevent the risk of land subsidence in the research section. In particular, flyover through the section with underground Karst caves is the most suitable solution.

Study on Serviceability of Transition Section Between Road and Tunnel

The determination of allowable differential settlement in bridge transition is a key problem to prevent vehicle jump at bridge head, but there are few theoretical research achievements in this aspect atroduction home and abroad. In this paper, four different structures of the road surface of The Sanyangchuan tunnel and the lead project are studied. The allowable differential settlement of asphalt pavement is calculated by asphalt pavement-layer system, and the allowable differential settlement is calculated by Ladan Lasse transform.

Engineering Geological and Geotechnical Investigations for Design of Oxygen Plant

The most important aspect of every civil engineering project is acquiring reliable information on the ground on which the project will be constructed. This research includes a site investigation, which is seen as a primary stage in gathering geological, geotechnical, and other essential engineering data for structures’ safe and cost-effective design. Five boreholes at well-spaced spots were drilled for subsurface investigation at a maximum depth of 15 m to 30 m. The standard penetration tests (SPT) were performed at different depths, soil samples were taken at various intervals, and lithological changes were observed. The friction angle was between 19.6º and 33.03º, whereas the cohesion ranges between 0.25 kg/cm2 and 0.42 kg/cm2, indicating a strong resistance to shearing and a high capacity to sustain the load. Furthermore, the soil samples’ maximum dry density ranges from 1.63 g/cm3 to 1.80 g/cm3. In addition, water table depths were recorded from 6.0 m to 7.0 m. The net bearing capacity for isolated/pad foundation at a depth of 1.5 m to 2.5 m below the ground level has been calculated as 95.0 to 120.0 kPa and 120.0 to 180.0 kPa for raft foundation. The net allowable pressure settlement limits for isolated/pad and raft foundations are 25 mm (1-inch) and 50 mm (2-inches), respectively. The investigation has found no severe geological flaws on the proposed construction site, and therefore it is appropriate for the construction of an Air Separation Unit (ASU) Oxygen Plant.

Estimation of Allowable Bearing Capacity and Settlement of Deep Cement Mixing Method for Reinforcing the Greenhouse Foundation on Reclaimed Land

Estimation of Allowable Bearing Capacity and Settlement of Deep Cement Mixing Method for Reinforcing the Greenhouse Foundation on Reclaimed Land

Cramming the Specificities in Contemplating Safe Bearing Capacity for the Foundation Assessed from Borehole Samples in a Sandy-Moorum Zone

Borehole samples drilled up to a depth of 10 m provide a clear understanding whether a foundation is safe for any structure. The main objective of the present study reconnoitered the soil bearing capacity and foundation settlement characteristics using the standard penetration test (SPT) data obtained from 3 boreholes at 1 m, 2 m, and 3 m depths to correlate soil properties and deterrents, if any, created by groundwater. The methodology of the research is to collect soil samples, and ensuing subsoil analysis was performed in order to obtain concrete information to optimize the foundation system within the safe bearing capacity of soil and its allowable settlement. The scope of the work encompasses conducting detailed soil investigation from drilling logs, laboratory testing, and conducting and estimating safe bearing capacity. The result of the research aims at providing safety to the foundation from the investigations of conclusive recommendation to be adopted which would be economically feasible and structurally secured.