Settlement Control Research Articles

Comparative Analysis of Theoretical, Observational, and Modeled Deformation of Ground Subsidence: The Case of the Alhada Pb-Zn Mine

In this study, the probability integral method, Synthetic Aperture Radar Interferometry (InSAR), and the Okada dislocation model were collaboratively used to analyze deformation in the Alhada Pb-Zn mine. The predicted deformation values of the subsidence centers in three subsidence areas were 107 mm, 120 mm, and 83 mm, respectively, as predicted using the probability integral method. The coherent scatterer InSAR technique was used to analyze the time-series deformation of the mining area, and the same subsidence center locations and similar deformation values were observed. The Okada dislocation model was used to invert the optimal parameters of the underground-mining ore body causing the surface subsidence, indicating that the surface subsidence is mainly caused by the mining of ore bodies in the 888 and 848 middle sections. We further simulated ground deformation using the multi-source Okada model. The results showed that the predicted and modeled deformations are highly correlated with the observed deformation. Through the analysis and comparison of the InSAR results, it was concluded that the three subsidence areas do not threaten the stability of the main buildings in the mining area. Using theoretical, observational, and modeling methods, the development and evolution of the subsidence area in mines can be established, which could provide basic data for subsidence control work and guarantee mine production safety.

Study on the In Situ Test of the Treatment Effect for the Riverbank Soft Soil Subgrade in the Hetao Area

The Inner Mongolia Hetao area has a widely distributed riverbank fluvial soft soil with high groundwater levels and ground surface water. This situation may incur some potential engineering problems for the Linhe-Baigeda section of the Beijing-Xinjiang Expressway, such as subgrade settlement control and waterproofing. In situ experiments were conducted on the site using five subgrade base treatment schemes for subgrade construction. The long-term monitoring of various technical indicators like settlement, earth pressure, pore water pressure, and reinforcement material deformation was carried out. Study results show that the cumulative settlement generated when the double-layer geogrid reinforces the subgrade base is 6.9 cm, which is the smallest among the five subgrade base reinforcement methods, and the cumulative settlement of the subgrade base reinforced with a single-layer geocell is the largest, which is 15.4 mm. The size and distribution of subgrade earth pressure change significantly during farmland irrigation. When the single-layer geocell reinforces the base, the subgrade stress is smaller than that of the other four, and the average earth pressure is 8 kPa. The membrane-pulling effect of reinforcement material significantly disperses the upper load of subgrade backfill soil, and the subgrade settlement control with different base treatment schemes meets the technical requirements.

Long-term in-situ monitoring on foundation settlement and service performance of a novel pile-plank-supported ballastless tram track in soft soil regions

An innovative pile-plank structure for differential settlement control in soft soil area is employed in Shanghai Tram projects. In this specially designed infrastructure, the rails are directly combined with the foundation treatment structure by fasteners and pads. The soil pressure beneath the plank, foundation layered settlement, track settlement, temperature field and internal forces of the structure are investigated based on a series of in-situ tests. Measurement data revealed that the soil pressure decreased from 10.1 kPa to 5.3 kPa during the first 12 months of the operation. The layered foundation settlement increased most rapidly in the initial stage of the operation. The track settlement was basically in accordance with the foundation settlement. The internal forces of the plank were mainly influenced by environmental temperature variation in this stage. The measurement data provide a strong base for the development of the design theory of the buried pile-plank structure for ballastless tracks.

Performance of T-Shaped and conventional Cement-Soil deep mixing piles to stabilize soft base of High-Speed trains

ABSTRACT The dramatic increase in train speeds has made settlement control in the train bed a critical issue. High differential settlements on railway tracks, especially high-speed trains, can derail trains and cause irreparable financial and human losses. Deep Cement Mixing (DCM) piles are among the efficient methods to control the train path’s settlement, especially paths on soft clay soils . Recently, T-shaped cement soil mixing (TDM) piles became more popular than a single DCM pile. In this study, total and differential settlements along the path of a high-speed train on a loose bed reinforced with DCM and TDM piles were studied using PLAXIS 3D software. . Three different configuration patterns of the pile were investigated to determine the performance of DCM and TDM piles. Unlike the DCM piles, no differential settlements were captured in the TDM piles with a distance of 60, 120, and 180 cm between the piles.

Exploratory application of a novel centre cross diaphragm method for the construction of large cross-section tunnels in soft ground

For tunnelling in urban areas, the current sequential excavation (SE) method usually increases the number of temporary drifts to achieve better control of surface settlements, which may prolong construction duration. In this case study, a four-drift SE method, termed the suspension-type centre cross diaphragm (S-CRD) method, was proposed and applied to the construction of a large cross-section tunnel in soft ground, where normally the six-drift double-side drift (DSD) method would be adopted. Field monitoring results and statistical data indicated that, in comparison with the six-drift DSD method, the four-drift S-CRD method achieved better control of the surface settlements while improving the efficiency of construction by 30%. The advantages of the S-CRD method, i.e., safe and rapid construction, were eminently clear.

Generating strategies for land subsidence control and remediation based on risk classification evaluation in Tianjin, China

Generating strategies for land subsidence control and remediation based on risk classification evaluation in Tianjin, China

Assessing Land Subsidence-Inducing Factors in the Shandong Province, China, by Using PS-InSAR Measurements

Shandong Province (SDP) experienced serious land subsidence from March 2017 to December 2020. Exploring the response relationships between land subsidence and its inducing factors plays an important role in ensuring the development of the economy and residential safety. Firstly, we applied Persistent Scatterers Interferometric Aperture Radar (PS-InSAR) technology to 558 Sentinel-1 images to determine the land subsidence in SDP from March 2017 to December 2020. Secondly, we mosaicked the land subsidence monitoring results of five tracks to obtain a land subsidence map covering the whole SDP and validated the land subsidence monitoring results using Global Positioning System (GPS) monitoring results and leveling benchmark monitoring results observed in the same period. Finally, the response relationships between the land subsidence and its inducing factors in SDP were analyzed. The findings are as follows: (1) the PS-InSAR outcomes showed that the land subsidence was widely distributed in SDP and that the maximum land subsidence rate was −298.9 mm/year during the study period. (2) The PS-InSAR monitoring results coincide well with the GPS monitoring results and leveling benchmark monitoring results; the Pearson correlation coefficient (PCC) values between the PS-InSAR monitoring results and the GPS measurement results and leveling benchmark monitoring results were 0.97 and 0.98, respectively. We found that Spearman’s rank correlation coefficient (SRCC) values between any two adjacent tracks of the mosaic PS-InSAR monitoring results were greater than 0.95, indicating good consistency. (3) The long-term overexploitation of groundwater in middle and deep aquifers and mining of underground mineral resources are the main inducing factors of land subsidence in SDP when considering this problem on a large geographical scale. Moreover, the type of bridge material is an important inducing factor causing the large variation in the land subsidence of the bridge body within a small geographical range. These findings may provide scientific support for land subsidence control measures in SDP.

Ground Stress Analysis and Automation of Workface in Continuous Mining Continuous Backfill Operation

The cost, complexity, lack of filling space and time create challenges in the longwall backfill operation, resulting in poor subsidence control and reduced productivity. This paper proposes an automated continuous mining and continuous backfill (CMCB) method by examining its key requirements and investigates the optimum sequence of coal panel (such as drifts) excavation to ensure ground strata control at relatively high productivity. The automated CMCB adopts the highwall mining technique underground, which enables easier automation at the workface. A numerical simulation of the Changxing coal mine in China was undertaken, and five different sequences of coal excavation were investigated, using the automated CMCB excavation parameters (assuming a 4 m width cut, 5 m mining height for a 200 m long coal slice) to determine the optimum sequence of resource excavation. The plastic zones and vertical displacement across the five models were analyzed. Simulation results of the 5 m high coal seam excavation show that the odd-even slice (OES) mining sequence, which has a vertical ground displacement of 74 mm, is the most efficient excavation method, due to its effective stress redistribution and lower induced ground displacement.

Calculation of Subsidence due to Longwall Mining with Overburden Grouting and Its Application

This paper presents a prediction method of mining-induced surface subsidence due to longwall mining with overburden grouting, which has been proven an effective method to mitigate the overburden failure. This paper proposes a partial overburden grouting (POG) mining method based on surface subsidence basin inversion and innovative longwall panel layout to mitigate overburden failure and subsidence. A prediction model of surface subsidence with overburden grouting, namely, overburden grouting equivalent calculation model (OGECM), is proposed. In this study, an engineering design process and method of POG was established, the strike and dip excavation length and grouting quantity combined as critical indicators for determining the key parameter in surface basin control. In applications at the field grouting test, the surface subsidence characteristics of POG on the side of the opening line of longwall panel were investigated through surface observation station and estimated surface subsidence reduction ratio based on OGECM with grouting compared with those without. The field measurement validated the new subsidence calculation method. POG technology applied to subsidence control has effectiveness in controlling the surface subsidence to less engineering cost but expanding the applications.

The Control Standard for Settlement of Pavement Based on the Model of Acceleration Interference

The control standard of pavement settlement caused by urban tunnel excavation is the focus of academic research at present. The establishment of settlement control standard gradually develops from safety control standard to comfort control standard. Based on the acceleration interference model, this paper presents a method to determine the pavement settlement control datum caused by the new tunnel penetrating the existing highway. Firstly, the vibration acceleration along the vertical direction of the road was selected as the comfort index, and the ideal sine function and Peck formula were used to describe the longitudinal curve of the road surface and the characteristics of the road surface settlement groove caused by tunnel construction. Secondly, considering the acceleration interference model, based on theoretical derivation, the calculation formula of vertical acceleration under the influence of road surface smoothness is obtained. According to superposition principle, the calculation formula of vertical acceleration under the influence of road surface smoothness and tunnel excavation is obtained. Thirdly, based on the relationship between acceleration value and subjective feeling of human body, the determination formula of pavement settlement control benchmark is proposed. The results show that the control datum formula is consistent with the engineering practice. Reducing the speed and the width coefficient of pavement settlement groove are effective methods to improve the comfort.

New surface subsidence control technology based on upward backfilling method of bottom drainage roadway

New surface subsidence control technology based on upward backfilling method of bottom drainage roadway

Surface control techniques for tunnels in karst areas under airport taxiways

Under the conditions of karst development and soft upper and hard lower strata, ground-settlement control for tunnels under airport taxiways is stricter than for ordinary tunnels. Tunnel construction methods and karst disposal measures are also important. These are engineering problems that need to be solved urgently to ensure the safe passage of tunnels under airport taxiways. Taking the intercity railway tunnel under taxiways T3 and T4 of Guangzhou Baiyun international airport as a case study, theoretical analysis and field tests on karst treatment measures and ground-settlement control measures were conducted. Karst treatment measures and a pile support plate (PSP) structure have been proposed to support the taxiways. The effect of the system was analysed numerically method and on-site surface settlement was monitored. The maximum monitored settlement of T3 and T4 taxiway surfaces was 5.90 mm and the differential settlement was 0.12‰. The numerical results provided a similar value and did not exceed the settlement control standard for airport taxiways. The key technologies for the construction of tunnels under airport taxiways in karst areas and upper soft and lower hard strata are presented, karst disposal measures are summarised and the PSP protection system is described. The results provide reference information for similar projects.

Monitoring and Predicting the Subsidence of Dalian Jinzhou Bay International Airport, China by Integrating InSAR Observation and Terzaghi Consolidation Theory

Dalian Jinzhou Bay International Airport (DJBIA) is an offshore artificial island airport, where the reclaimed land is prone to uneven land subsidence due to filling consolidation and construction. Monitoring and predicting the subsidence are essential to assist the subsequent subsidence control and ensure the operational safety of DJBIA. However, the accurate monitoring and prediction of reclaimed subsidence for such a wide area under construction are hard and challenging. This paper utilized the Small Baseline Subset Synthetic Aperture Radar (SBAS-InSAR) technology based on Sentinel-1 images from 2017 to 2021 to obtain the subsidence over the land reclamation area of the DJBIA, in which the results from ascending and descending orbit data were compared to verify the reliability of the results. The SBAS-InSAR results reveal that uneven subsidence is continuously occurring, especially on the runway, terminal, and building area of the airport, with the maximum subsidence rate exceeding 100 mm/year. It was found that there is a strong correlation between the subsidence rate and backfilling time. This study provides important information on the reclaimed subsidence for DJBIA and demonstrates a novel method for reclaimed subsidence monitoring and prediction by integrating the advanced InSAR technology and Terzaghi Consolidation Theory modeling. Moreover, based on the Terzaghi consolidation theory and the corresponding geological parameters of the airport, predicted subsidence curves in this area are derived. The comparison between predicted curves and the actual subsidence revealed by InSAR in 2017–2021 is highly consistent, with a similar trend and falling in a range of ±25 mm/year, which verifies that the subsidence in this area conforms to Terzaghi Consolidation Theory. Therefore, it can be predicted that in the future, the subsidence rate of the new reclamation area in this region will reach about 80 mm/year ± 25 mm/year, and the subsidence rate will gradually slow down with the accumulation of reclamation time. The subsidence rate will slow down to about 30 mm/year ± 25 mm/year after 10 years.

Construction optimization and settlement analysis of Pile Beam Arc method in subway station

Subway stations are generally built in areas with dense buildings, heavy traffic, or dense pipelines. In this case, the control of land subsidence and building deformation is very strict. The Pile Beam Arc (PBA) method has its unique advantages in these aspects, and it is especially suitable for northern China. In this research, the Zhongjie subway station of Shenyang Metro Line 1 is taken as the research object, and MIDAS GTS NX software is used to simulate the various stages of the PBA method construction of the subway station. In this paper, the optimal construction scheme of the subway station is analyzed by numerical simulation. This study also uses the monitoring data provided by the construction site to analyze the influence and distribution law of the subway station on the ground surface deformation in each construction stage. In this paper, the results of numerical simulation are compared with the field monitoring data, and the most dangerous construction stage is obtained. The conclusions of this study can provide accurate supporting scheme and control measures for the subsequent construction.

Study of Bag Grouting Pile Reinforcing Deep Soft-Soil Foundation with an Interlayer of Hard Materials on High-Speed Railway Ballast Track

High-speed railways are built in deep soft-soil foundations interlayered with hard materials. However, the hard layers cannot be penetrated by conventional foundation treatment. Moreover, the project cost is sometimes prohibitive, which is an issue for post-construction subsidence control. The bag grouting pile is a special grouting-pile-reinforcement technique for treating soft-soil foundations interlayered with hard materials. This paper conducted tests on the Ningbo-Taizhou-Wenzhou ballast track passenger railway, combining a conventional mixing-pile-foundation (not through hard layer) processing station and the bag-grouting-pile-processing subgrade line. Using field tests combined with numerical calculation, the lateral displacement, settlement and pile–soil stress were tested to obtain the working properties of the grouting-pile-composite foundation. The variation in the law of lateral displacement, settlement, and pile–soil stress of the foundation was studied. The results showed that the post-construction subsidence of bag-grouting-pile- and conventional mixing-pile-foundation control was less than 15 cm and 30 cm, respectively, which met the design requirements. The results also showed that the design scheme was reasonable (load-sharing ratio of bag-pile-foundation pile soil-based test was reasonable). The numerical calculation showed a change in pile diameter. It also showed that pile spacing could not improve subsidence-control properties, bag grouting pile can promote pore-pressure dissipation and accelerate consolidation, and pile spacing can be increased to cut project costs incurred by the pile-bearing capacity.

A NEW METHOD TO CONTROL THE REGIONAL STRATA MOVEMENT OF SUPER-THICK WEAK CEMENTATION OVERBURDEN IN DEEP MINING

In the western of china, the deep mining area with super-thick and weak cementation overburden is vast, sparsely populated and the ecological environment is extremely fragile. With the large-scale exploitation of deep coal resources, it is inevitable to face green mining problem, whose essence is the surface subsidence control. Therefore, it is necessary to study the control technology for the regional mining based on the evolution law of subsidence movement and energy-polling of super-thick and weak cementation overburden, and put forward the economically design scheme that can control strata movement and surface subsidence in a certain degree. Based on the key strata control theory, this paper puts forward the subsidence control scheme of partial filling -partial caving in multi-working face coordinated mining, and further studies its control mechanism through the numerical simulation and then analyzes the control effect of the strata movement and energy-polling in the fully caving mining, backfill mining, wide strip skip-mining and mixed filling mining method etc., the following conclusions are detailed as follows: (1) The maximum value of energy-polling occurs on the coal pillars or on both sides of goaf. With the width of goaf, the maximum value of energy-polling increases in a parabola. (2) In the partial filling-partial caving multiple working faces coordinated mining based on the main key stratum, the stress distribution of the composite backfill in the filling working face is parabolic, and it is high on both sides and low in the middle. Moreover, in the composite backfill, the stress concentration degree of a outside coal pillar is greater than that of the inside coal pillar. (3)The control mechanism of partial filling-partial caving harmonious mining based on main key layer structure is the double-control cooperative deformation system, formed by the composite backfill and the main and sub-key layers structure. They jointly control the movement and energy accumulation of overlying strata by greatly reducing the effective space to transmit upward, and absorb the wave subsidence trend of the overburden until it develops into a single flat subsidence basin. (4) Considering the recovery rate, pillar rate, area filling rate, technical difficulty and subsidence coefficient etc., the partial filling-partial caving multiple working faces coordinated mining based on the main key stratum is the most cost-effective mining method to control surface subsidence. This paper takes a guiding role in controlling the regional strata movement and surface subsidence of deep mining with super-thick and weak cementation overburden.

Predicting earth pressure balance (EPB) shield tunneling-induced ground settlement in compound strata using random forest

The prediction and control of the ground settlement induced by shield tunneling in compound strata is a crucial challenge for tunnel excavation. In this regard, a finite element model for the analyses of ground surface settlement induced by earth pressure balance (EPB) tunneling was established and validated by the field test. The influence of single influence factors, such as rock proportion in the face, support pressure, and tunneling angle, on the surface settlement above the tunnel face was systematically studied. To investigate the joint influence of different factors on ground deformation mechanism, the multi-factor analysis based on field data and the multiple regression (MR) method was conducted. However, the prediction accuracy of the MR method was limited. Therefore, a prediction approach of shield tunneling-induced settlement in compound strata based on a random forest (RF) was developed. Tunnel geometry, geological features, and operation parameters were investigated as input variables in the RF model to achieve this goal. The applicability effect of the RF-based method was proved by utilizing two data sets (i.e., the settlement ahead of tunnel face and final settlement). The results indicated that the prediction accuracy of shield tunneling-induced settlement in compound strata by the RF-based model is higher than the MR method. The relative importance analysis of variables indicates that advance rate, the cover depth of the tunnel ring, and pressure in the chamber were the most influential features for the settlement ahead of the tunnel face, while the thrust of the cutter head and the grout quantity were the most significant variables for the settlement after the segment assembling is completed. Overall, the conducted study could provide a helpful reference for the efficient excavation of EPB tunnels across compound strata.

Optimization schemes for deep foundation pit dewatering under complicated hydrogeological conditions using MODFLOW-USG

The design and optimization of the dewatering scheme for deep foundation pits in a highly permeable heterogeneous layer are critical to protect water resources, control subsidence and mitigate environmental impacts. Numerical simulation is an important and sometimes the only tool in the design of dewatering schemes, especially when the dewatering projects are planned under complex hydrogeological conditions with limited data. The open excavation method was chosen for a project to drain a deep foundation pit (35–44 m) in an upland river valley landscape. Quaternary alluvial deposits (129.0 m thick) are generally distributed in the riverbed and the overburden consists mainly of alluvial-diluvial sandy gravel cobbles, clayey soils, sandy clay, and silty fine sand, making the study area very heterogeneous. There may be water inrush from foundation pit, uneven subsidence and deformation due to the uneven structure of the sand and slope stability. MODFLOW-USG (Unstructured Grid) and Subsidence and Aquifer-System Compaction (SUB) Package were used to create a coupled 3-D groundwater flow-subsidence numerical model for foundation pit dewatering. MODFLOW-USG provides greater flexibility in the design of the grid to achieve a high degree of accuracy in numerical simulation, while effectively reduces computational costs. A combination of waterproof curtain and a partial penetrating well was proposed for lowering the groundwater table. The optimized dewatering scheme with a curtain depth of 60 m and a hydraulic conductivity of 0.00518 m/d, and four rows of dewatering wells with an equal row spacing of 40 m, well depth of 50 m, and well spacing of 12.5 m in each row can meet the dewatering requirements with minimum groundwater discharge in the scenarios. The numerical simulation of this study provides a powerful and useful tool for dewatering and subsidence control of deep foundation pit under complex hydrogeological conditions.

An Investigation on Longitudinal Surface Subsidence Deformation of Large-Span Undercut Metro Tunnel

Underground excavation techniques are frequently used in subway stations during the construction of urban rail transit. The current study analyzes and investigates the surface settlement and deformation laws of large-span shallow buried underground excavated stations depending on a vast quantity of measured data from the Qingdao Metro Line 3. According to the comprehensive study, obtained results show that: 1) the excavation of pilot tunnels on both sides will result in the longitudinal settlement at the ground surface; however, the settlement will be quite minor, within −10 mm. During the excavation of the middle part of the pilot tunnel, large surface settlement may occur, and the settlement may reach −30 mm, while during the excavation of the lower soil and construction of the station structure, the surface settlement changes insignificantly, and some monitoring points show a sinking trend. 2) Data fitting reveals that regression analysis with a one variable cubic polynomial produces excellent fitting results. In addition, the analysis based on statistical methods reveals that the conditions of the surrounding rock are poor (Class that the arch, and the overall buried depth of the station is not larger than 10 m. 3) Since the surface settlement control standard for large-span boring tunnels is −60 mm, using −48 mm as the warning value is more reasonable. The test conducted in the current study has helped accumulate a large amount of ground settlement monitoring data, which can provide a particular reference for the subsequent design of similar lines.

Machine learning-based forecasting of soil settlement induced by shield tunneling construction

The subway systems have greatly released the pressure of ground traffic, but shield construction will cause considerable disturbance to the surrounding soil. Consequently, uneven settlement on the adjacent ground surface will be induced, which will affect the surrounding buildings. Thus, the tunneling-induced soil settlement should be obtained in time for safety assessment. In this study, the soil settlement induced by shield construction was monitored using the fiber Bragg grating (FBG) sensors which had the advantage of small transmission loss, multiplexing capability, and capacity for long-term monitoring. The time-history of the soil settlement of multiple points along a monitoring section was obtained. Furthermore, the back propagation neural network based on time series (TS-BPNN) was adopted to predict the soil settlement in later periods. The influence of the model structures and the number of training data on the prediction accuracy was investigated. The forecasting of a five-day settlement during rapid settlement and slow settlement stages were carried out and verified respectively to evaluate the performance of the proposed approach. The maximum relative error of the forecasted results was 1.35%, reflecting the favorable consistence with the monitored results. This study indicates that the method proposed could provide a valuable reference for the displacement control of ground settlement during the shield tunneling construction.