Collapsible Area Research Articles

Selection Design and Parameter Optimization of Composite Foundations in Collapsible Loess Areas

With the rapid development of railway construction in China, the role of passenger railway lines is becoming increasingly prominent. The construction of passenger railway lines is of great importance to the development of high-speed railways in Western China. Most regions in Western China are collapsible loess areas, and the collapsibility characteristics of loess are extremely unfavorable to foundation treatments. Therefore, the engineering properties of collapsible loess should be fully considered in foundation treatments, and corresponding treatment measures should be taken. In this paper, the displacement and stress characteristics of collapsible loess foundations are studied based on a test section of a subgrade treatment project in combination with engineering geology; this study aims to analyze several kinds of collapsible loess foundation treatment methods, such as single piles and group piles. The mechanism of the method is to make full use of the bearing capacity of the natural foundation, so that the soil between the piles is jointly to bear with pile, thereby the bearing capacity of the foundation is improved and the settlement of the foundation is effectively controlled. After the form of the composite foundation is selected, the foundation bearing capacity is improved by a parameter optimization design, and the foundation settlement is reduced, which eliminates the collapsibility of the loess. With field bearing tests, the rationality of the composite foundation design is verified.

Field Test Study of the Artificial Ground‐Freezing Method Subsurface Excavation Construction of Watered Sandy Stratum in Collapsible Loess Area

Saturated sandy stratum often makes tunnel excavation exceedingly difficult owing to its high water content. The artificial ground‐freezing (AGF) method is an effective way to reduce the construction risks in such stratum; however, the AGF mechanism in the saturated sandy stratum of a collapsible loess area still lacks sufficient research. Based on field tests and numerical simulations, this study investigates the regularity of the temperature development, frost heave, and thaw subsidence distribution during the cross passage construction of a saturated sandy stratum in a collapsible loess area, using the AGF method. The results showed that the inward development rate of the frozen soil wall in the saturated sandy stratum was faster than its outward development rate. The gradient of the soil cooling curve was positively related to the longitudinal depth of the cross passage. The thickness of the frozen soil wall calculated by the slowest development rate of the frozen soil was conservative. The application of the pressure relief hole was beneficial to the release of the frost‐heaving force and the control of the frost‐heaving displacement. The pressure gauge pressure increase could be used as an identifier for the closure of a frozen soil wall. After excavation, the inner wall of the cross passage moved toward the inner space of the passage.

Calculation of Bearing Capacity and Deformation of Composite Pile Foundation with Long and Short Piles in Loess Areas

In order to calculate the bearing capacity and settlement deformation of composite pile foundations with long and short piles in collapsible loess areas, the theoretical approximate solution was used to obtain the location of the neutral point of single piles. Additionally, based on the equation to calculate the bearing capacity of multielement composite foundations, a method considering the negative frictional resistance was proposed for calculating the bearing capacity of composite pile foundations with long and short piles. Based on the shear displacement method and the principle of deformation control, an equation to calculate the displacement and deformation of a composite pile foundation was presented. A model test with different operating conditions, i.e., a single pile, four piles, and eight piles, was designed to verify the proposed calculation methods. The results show that the location of the neutral point has a significant influence on the single‐pile negative frictional resistance, and the neutral point ratio of the calculation meets the value range of the practical project. When the load at the top of the pile is relatively small, the experimental curve is consistent with the theoretical calculation curve, whereas when the load is comparatively large, the theoretically calculated displacement increase at the top of the pile is greater than the measured one. Under the premise that the theoretical calculation is in good agreement with the results, the theoretical value is larger than the actual value. And it contributes to strengthening engineering safety.

Analysis and comparison of two types of ground fissures in Dali County in the Weihe Basin, China

Dali County is located in the eastern Weihe Basin where frequent ground fissure disasters occur. Dali ground fissures are macroscopically part of the ground fissure group in the Weihe Basin and have caused serious damage to infrastructure and agricultural production in this area. In this paper, 25 ground fissures in Dali County are identified through investigation, and two typical ground fissures in Fengcun and Weizhuang are selected for research. Through field investigation, trench excavation, geophysical exploration, soil water content tests and collapsibility coefficient tests, the basic features, shallow structural characteristics, deep structural characteristics and genetic mechanisms of the two ground fissures are revealed. The strike of the Fengcun ground fissure is 45°, almost parallel to the Shuangquan-Linyi Fault; the length is 2 km, and the profile is ladder-like and extends deep with synsedimentary characteristics. The Weizhuang ground fissures are circular in plan view with a length of 315 m and trumpet-shaped in profile; they disappear in the paleosol layer. The mechanism of the Fengcun ground fissure is related to basin extension and fault activity. The ground fissures are the surface reflections of deep faults. The mechanism of the Weizhuang ground fissures is related to loess collapsibility and seepage. The Malan loess has differential settlement in collapsible and noncollapsible areas, and ground fissures are the boundary line for differential settlement of loess. Finally, based on the genetic mechanisms of ground fissures, Dali ground fissures can be divided into two types: tectonic and nontectonic.

Seismic Vulnerability Analysis of Structure Subjected to Uneven Foundation Settlement

Uneven foundation settlement is one of the common engineering problems in a collapsible loess area. In order to study the influence of uneven foundation settlement on the seismic performance of a structure, the incremental dynamic analysis (IDA) method is used to analyze the seismic vulnerability of the steel structure frame. The differences in the seismic response of the structure in relation to uneven foundation settlement are analyzed. The influences of uneven foundation settlement quantities and various areas of uneven settlement on the seismic response of the structure are discussed. On this basis, the relationship between ground motion intensity and structural failure probability is studied, by changing the magnitude of seismic acceleration peaks. Compared with the unsettled structure, the internal force redistribution of the structure caused by uneven foundation settlement is one of the causes of earthquake damage for some components. The uneven foundation settlement located at the corner of the plane of the structure is likely to cause more serious earthquake damage to the structure. Uneven settlement will cause an increase in storey drift. With the increase in settlement, the seismic damage of the superstructure will be aggravated.

Experimental study on the physical modeling of loess tunnel-erosion rate

Loess tunnel erosion is a distinctive soil erosion pattern that commonly occurs in collapsible loess areas. The resulting soil erosion is a serious and complex problem. At present, most of the research methods on loess tunnel erosion are based on field investigation, and the knowledge obtained is, therefore, mostly qualitative. Erosion characteristics and erosion rates of loess tunnels are rarely revealed quantitatively by laboratory physical modeling or field investigation. In this paper, we report the results of a small model test based on three types of archetypal geological structures that are recognized by field investigation, i.e., vertical fractures, horizontal fractures, and round holes, These results reveal the effect of different initial flow cross sections on the erosion characteristics of loess tunnels. We found that, where water crosses an area of loess, waterfalls dominate initial erosion. We also studied the mud erosion rate to quantitatively reveal tunnel-erosion rates and their variation with time and found that tunnel erosion occurs in three stages: a rapid-erosion stage, an erosion slow-down stage, and a slow uniform-erosion stage. Using a model test to undertake quantitative studies into the relationship between the erosion rate of a loess tunnel and both initial dry density and initial water content, we demonstrated a significant linear negative correlation between these parameters. Through physical simulations combined with field investigation and analysis of survey results, we found that the erosion of loess tunnels occurs with a certain periodicity and that the tunnel-erosion base level plays a decisive role in the erosional features and final morphology of loess tunnels. By increasing our understanding of the internal mechanisms of loess tunnel erosion, our work will contribute to the prevention of cave erosion and reduction in the risks of associated disasters in the Loess Plateau of the Yellow River in China and in other loess-containing areas around the world. Our studies also provide a theoretical basis for carrying out soil and water conservation work in similar areas.

Earth fissures developed within collapsible loess area caused by groundwater uplift in Weihe watershed, northwestern China

Earth fissures are geological hazards that frequently occur all over the world and greatly threaten the safety of people’s property and lives. This paper reports a case from a typical agricultural town in the Weihe watershed, northwest (NW) of China, Dali, which has been severely affected from earth fissures in recent years. A comprehensive survey was made on the geometric characteristics of the earth fissures developed in the study area through field investigations, trial trenches, boreholes, exploratory wells, and laboratory tests. The study indicates that fourteen nearly parallel fissures have developed in the area, with a fissure to fissure space of 140–350 m, and a maximum length of any of the given fissures of 500 m. The underlying faults, loess joints, and the Quaternary unconsolidated and collapsible sedimentary loess provide a favorable geological condition for the occurrence of the earth fissures. From 2003 to 2012, the groundwater level in the area rose about three meters due to agricultural irrigation and leakage of a water diversion canal. Collapsible deformation occurred in the loess, while seepage erosion expanded the original joints in the soil. The earth fissures occurred resulting from multiple geological environmental forces and human activities.

Compressibility of Lime-ash Soil Reinforced by Waste Tire Particles in Large-thickness Collapsible Loess Areas

In this research, an indoor standard compression test of waste tire particles reinforced lime-ash soil is conducted to study the compressibility of the reinforced soil as a foundational material in collapsible loess areas with large thickness. And during this process, the void ratio and compression coefficient of the soil samples with different ages and blending amounts are tested. The research results can be concluded as: (1) The compressibility of waste tire particle reinforced lime-ash soil is better than that of lime soil and plain soil, and thus it can be widely used in large-thickness collapsible loess areas. (2) In all the waste tire particle reinforced lime-ash soil samples, the sample with the blending amount of 30% is superior to the other. Therefore, in making waste tire particle reinforced lime-ash soil, it is suggested to apply the soil with reasonable mix ratio of 30%.CLC number: TU443 Document code: A

Numerical limit analysis of the ultimate load bearing capacity of a pier foundation under complex load

A pier foundation has plenty of advantages as the foundation form for large onshore wind turbines in the terrain of the Gobi desert and collapsible loess areas. The ultimate load bearing capacity design, as an important part in the design phase of this foundation form, is not sufficiently in terms of design theory and the checking method, especially for application in collapsible loess areas. In this paper, numerical limit analysis has been employed to analyze the load bearing capacity for the scheme of selection of a pier foundation of a 100 MW wind farm in certain collapsible loess geology in Ningxia. The results were then compared with the empirical formulas, the limit equilibrium solutions and the finite element solutions to verify the accuracy of the results. It has been demonstrated that under the ultimate engineering load, the pier foundation can meet the stability requirement. In the ultimate state, whether the surrounding soil of the foundation falls in plasticity is associated with the ratio of the depth to the diameter of the foundation. The numerical limit analysis method can automatically determine the failure surface.

Treatment of collapsible loess foundation

Loess is a special scholar soil accumulated and formed in the arid and semiarid conditions of Quaternary. Its hydraulic properties are collapsibility caused by water invasion, easy to disintegrate when it meets water, easy to be carried away by soil particles under the action of flowing water, forming landform phenomena such as collapse and gully. Such diseases as subsidence, collapse and erosion occur frequently for subgrade in collapsible loess area when it is scoured by water immersion. It is a difficult challenge for subgrade engineering to meet the very strict post construction settlement requirements of high speed railways in the process of high-speed rail construction. This paper combines experimental research and engineering examples. For the difficulties encountered in the treatment of collapsible loess foundation, a systematic and comprehensive analysis is made to deal with the measures. The application is introduced from design plan of construction technology, construction quality control and so on. It can provide reference for similar engineering problems in the future highspeed rail construction.

Analysis of Comparison of Calculation Methods for Downdrag of Single Pile

The problem of negative skin friction has acquired great importance for the circles of civil engineering over that last few decades. It aims to understand the mechanisms of pile-soil interaction, define more adequate analytic methods for the load transferand and ensure the bearing capacity of pile foundation. But for the complexity of problems, there are some issues that have not been well solved in engineering practice.In order to avoid the failure of pile body, the uneven settlement of pile foundation and other engineering disasters, the researches of downdrag have been carried out since 1965. And engineers have proposed a number of calculation formulas for the downdrag of single pile, yet the calculation results differ sharply on account of the respective applicability and limitation of these formulas.This paper introduces several common calculation methods of downdrag on single pile and recommends diverse calculation situations in self-weight collapsible loess area. In this paper, some calculation methods based on limit analysis method will be compared from different angles and the applicable conditions, advantages and disadvantages, etc. are also discussed to provide reference for practical engineering design.

Study on Vertical Bearing Capacity Change of Single Pile under Dry Condition and Submerged Condition in Loess Collapse Region

In order to study the change of vertical bearing characteristics of single pile under dry state and flooded state in loessial collapsible area, this study conducted a flooding test on site. The experiment reveals the law of the effect of ground immersion on the bearing capacity of bridge pile foundation in the loess region, and analyzes the characteristics of settlement variation during the flooding of pile and surrounding soil. Immersion test results show that the pile and pile around the average settlement of soil is 0.15mm and 1.4mm. After the pile side of the soil is flooded, the pile and its surrounding soil have varying degrees of settlement deformation. The settlement of the soil around the pile is caused by the weak collapsibility of the loess. The settlement deformation of the pile is caused by the negative friction caused by the collapsible loess on the pile. Therefore, the ultimate bearing capacity of the soaking is obviously different, the former is greater than 9600kN and the latter is 8000kN. Carrying capacity test has been carried out several times, its ultimate bearing capacity is consistent.

Experiment Research of 20000 kN.m Ultra-High Dynamic Compaction about the Collapsible Loess Area High Fill Foundation after Compaction

Dynamic compaction is a cost-effective foundation treatment method which can improve the bearing capacity of foundation, reduce compressibility, eliminate collapsibility and ameliorate seismicity. With the development of foundation treatment along depth and breadth, the energy level of dynamic compaction also improves constantly. From 8000kN.m in 1991 to 18000kN.m in 2008, energy level has increased 10000kN.m in 18 years. This project is the first experimental research using 20000 kN.m high energy level dynamic compaction process in China. The shallow plate loading test, dynamic penetration test, laboratory soil test method have been used to detect the effect of dynamic compaction. The results show that the characteristic value of bearing capacity of foundation after dynamic compaction fak=345kPa, effective depth of dynamic compaction is 18m. The soil dry density after compaction is 1.77~1.82 g/cm3. This article is based on the high embankment engineering in northwestern China, carrying out the relevant test work of 20000 kN.m high level construction, proposing the high filling compaction ground simultaneously, the idea of recompression ground treatment, and providing reference value for the foundation treatment concept, design, construction and providing the basis for preparation of specification.

Surgical Correction of Alar Collapse with Alar Batten Graft : Technique and Results

Background: nasal valve collapse has great perception of nasal obstruction. The alar batten graft technique has proven to be a valid method for treatment of external and internal valve collapse. Aim: the aim of the present study was to evaluate a two year experience and follow up for external nasal valve collapse treatment using alar batten graft technique regarding results and complications. Patients and Methods: this prospective study was carried out on 18 patients attended the ENT and Plastic Surgery outpatient clinics of Al-Azhar University hospitals from January, 2014 to January 2016. Written consent was taken from every patient. All patients were complaining of nasal obstruction of gradual onset and progressive course with 7 years average. All patients were subjected to detailed history taking and questionnaire including the NOSE scale. Surgical correction was performed to all patients using the alar batten graft harvested from the septa cartilage or conchal cartilage. Postoperative results recorded in relation to subjective sensation of nasal obstruction and aesthetic appearance of the nose. Results: eleven patients (61.1%) were males and seven (38.9%) were females. Their age ranged from 18 to 45 years with a mean of 32±2. Bilateral obstruction was found in 33.3% of cases and unilateral obstruction in 66.7% of cases. There were 22.2%, 27.8%, and 50.0% of the cases had moderate, fair, and severe obstruction, respectively. Postoperatively, these figures were changed to no obstruction77.8% (P=0.0), mild 0.0%, moderate 11.1%, fair 11.1%, and sever 0.0%(P=0.0005). The technique significantly abolishes the severe nasal obstruction. Postoperative complications include 1 case with graft resorption (4.2%) and 1 case of graft displacement (4.2%). Both were improved on subsequent surgery. Regarding postoperative findings there was tenderness and hypertrophic postauricular scar in 5.5% of patient and nasal tip edema in 22.2%, all resolved. In the early postoperative period, 33.3% of patients complained of fullness in the supraalar region. Conclusion: Successful surgical correction of nasal obstruction requires the precise diagnosis of the anatomic point of collapse. Alar batten graft improves the rigidity of lower lateral cartilage preventing collapse of the lateral nasal wall preventing collapse during moderate and deep inspiration. The graft varies according to the severity of the obstruction and size of the collapsible area of the lateral nasal wall. The septal cartilage is usually sufficient. The technique significantly improves nasal breathing.

PIPELINE RELIABILITY LEVEL FOR THE DIFFERENT COLLAPSIBLE STRATA

Probabilistic analysis of the loessial collapsible soil deformation modulus in the water saturated for two areas of pipeline laying in the Poltava and Kherson region were performed. Respective distributing laws and statistics were obtained. With help of Ansys finite element simulation was performed in the form of the Monte-Carlo method. Pipeline deformation in the loessial collapsible strata local soaking area was modeled; internal operating pressure and temperature difference were considered. Pipeline failure probability by longitudinal stresses parameter in the fine sand soil was obtained, random functions stochastic apparatus was used. Pipeline failure probability by longitudinal stresses parameter with similar geometric parameters and internal operating pressure simulation results were compared with the base composed by fine sand and loessial collapsible strata 7 and 13 meters.

Field Experiment on Soaking Characteristics of Collapsible Loess

In collapsible loess area, migration of soil moisture often causes the temporal discontinuity and spatial nonuniformity of collapsibility, which leads to great damage for infrastructures. Therefore, the research on water infiltration is the key to solving the problem of collapsibility. The aim of this paper is to investigate the spatiotemporal evolution of infiltration characteristics of collapsible loess. A field soaking experiment was conducted on collapsible loess in western China, in which a soaking pool with diameter of 15 m was built. Time-Domain-Reflectometry (TDR) system and soil sampling were employed to measure the water content within the depth of 12 m. Then the saturation isograms were drawn for visualization of the process of infiltration. Also, a pilot tunnel was excavated to investigate how the free face can affect the infiltration behaviors. The experimental results revealed the characteristics of infiltration in both horizontal and vertical directions. Moreover, the response of free face on infiltration behaviors was also found. These findings of research could provide the data for the infiltration laws of unsaturated loess and thereby provide the basis for integrated treatment of collapsible loess.

High-speed railway's roadbed consolidation with fracture grouting in collapsible loess area: mechanism and application

This paper discussed the reasons and the harms of high-speed railway's roadbed settlement in collapsible loess area. On the basis of the experimental simulation and mechanical analysis, the mechanism of fracture grouting is concluded, and a set of upper grouting test equipment is developed as well. Through a set of tests under different grouting pressures, and analyses on the soil's mechanical properties and displacement variations, a quadratic approximation formula is gained. Meanwhile, the mechanism for fracture grouting and the validity of laboratory simulation is tested and verified. In addition, the effect of fracture grouting on high-speed railway's roadbed consolidation in collapsible loess area is also got by fieldqs trial. The results of the current paper provide guide and reference for studying fracture grouting in collapsible loess area.

Application of Lime Soil Pile in Collapsible Loess Ground Treatment

When the bearing capacity of natural foundation cannot meet load requirements, generally the ground treatment usually can be taken to strengthen it. In this paper, from the practical engineering, the design, construction, and detection of the lime soil pile were introduced. The results show that the lime soil pile in collapsible loess area reinforcement technology foundation is feasible. The bearing capacity and stability of the treated foundation can meet the requirements.

Case Analysis of Subsided Foundation Reinforcement of a University Infirmary in Collapsible Loess Areas

The example which is selected in this engineering project is the hospital in Lanzhou University of Technology, the paper analyzed the reason that the foundation subsidence, and used reasonable and effective method on reinforcement. It hoped that the achievement can provide beneficial reference for handling the problem that foundation subsidence in collapsible loess areas.

Study on the Treatment and Settlement Monitoring Technology of Passenger Dedicated Line Collapsible Loess Foundation

By the engineering background of Datong-Xian Passenger Dedicated Railway Line passing through the collapsible loess area, four representative test sections such as roadbed-bridge transition section, roadbed-culvert transition section, ordinary and special embankment section was selected. Different pile parameter and pile plane layout and subgrade filling measure has been taken according to the different test sections. At the same time, the correspondence of settlement monitoring project was carried out. After the long time monitoring, by the hyperbolic curve and logarithmic method predicting, the long-term settlement has been predicted. The monitoring results and the curve fitting shows that the settlement and the foundation treatment schemes with subgrade filling measurement meet the design requirement also provided reference and reference for other engineering.