Chemical injection to prevent building damage induced by ground water drainage from shallow tunnels

Progressive developments in the application of chemical injection have been acquired through out the centuries, starting from the ancient Romans. The method of silica based injection has been employed for a long time and has replaced the polyurethane injection method since the 1970s as a remedy in difficult ground conditions including fractured rock. Currently, various applications of chemical injections are available in civil and mining engineering, including ground stabilization, support anchoring, strata sealing, reduction and diversion of ground water flow and water ingress and creation of a load-bearing ring in tunneling. Drainage of the ground water in the overburden during tunneling will result in an increase in ground settlement by the evacuation of water and closure of the pores in overburden. In this research, the ground water level was decreased to 3 m from the original level and the ground settlement was recorded to reach 25 mm, while the inner tunnel vertical convergence was 6.5 mm after the drainage of 3.5 l/s ground water from the tunnel. Subsequent field measurements and observations indicated that the ground water drainage in the tunnel was reduced to 0–0.5 l/s and the surface settlements were stopped after the chemical injection.     

Experimental study on the anti-clogging ability of siphon drainage and engineering application

The safety of the slope retaining wall along the expressway is often threatened by groundwater, and the clogged drainage holes, which seriously affects the safety and stability of the retaining wall. To solve the clogging issue of the drainage hole, in this research, model tests and theoretical analysis were carried out to demonstrate the existing of clogging problem of the siphon drainage, the results showed that the soil particle (d < 1 mm) can be carried out by siphon drainage with 4 mm pipe diameter, the anti-clogging ability of siphon drainage with 4 mm pipe diameter was clarified. And the siphon drainage was applied to the retaining wall along the Longli Expressway. The monitoring data of the groundwater level showed that the groundwater level after the arrangement of siphon drainage was significantly decreased. There was no indication of clogging for the siphon drainage within the four-month of operation. It proves the implementation of siphon drainage method can effectively reduce the groundwater level behind the retaining wall in the rich water area, and it is a long-term method to treat the leakage hazard of the retaining wall.     

Experimental investigation on the invert stability of operating railway tunnels with different drainage systems using 3D printing technology

In recent years, the invert anomalies of operating railway tunnels in water-rich areas occur frequently,which greatly affect the transportation capacity of the railway lines. Tunnel drainage system is a crucial factor to ensure the invert stability by regulating the external water pressure(EWP). By means of a threedimensional(3D) printing model, this paper experimentally investigates the deformation behavior of the invert for the tunnels with the traditional drainage system(TDS) widely used in C...     

Deformation control method of a large cross-section tunnel overlaid by a soft-plastic loess layer: a case study

This paper presents a case study of a large cross-section high-speed railway tunnel overlaid by a Q₂ soft-plastic loess layer. Due to poor engineering properties of the soft-plastic loess, two unexpected collapses occurred. This indicates that there is great difficulty and risk during tunneling. In this paper, the deformation control methods are studied by carrying out a series of numerical simulations and then validating via field tests. The stress and seepage coupling equations are deducted to embed into a 3D fluid-mechanical coupled numerical analysis. The results show that the curtain grouting scheme can effectively control the deformation of surrounding rock, and the real field data of settlement and horizontal convergence are 152 mm and 37 mm, respectively. However, the tunneling advance rate is slow (0.6 m/day) in trial sections because of the mutual interference between construction procedures. It can be used as an alternative scheme for lager deformation. The advanced drainage scheme can lower the ground water table below the excavation outline. The average water content of soft-plastic loess decreases from 26 to 22%, and the state of surrounding rock changes from soft plastic to hard plastic. The in situ settlement and horizontal convergence are 165 mm and 51 mm, respectively. Finally, it is proposed to use advanced drainage in combination with advanced small pipe grouting as a follow-up construction scheme. The successful completion of the whole tunnel proved the effectiveness of the proposed method.

     

地下水对软土盾构隧道施工的影响规律分析

潜水和承压水是地铁软土区间盾构隧道施工过程中的主要危险源,为研究潜水水位变化和承压水水压变化对区间隧道施工的影响,采用FLAC3D软件,选用修正剑桥模型,对不同潜水水位和承压水头作用下盾构隧道的地表沉降、衬砌内力等进行分析。研究结果表明,当隧道洞身全部位于地下水中时:(1)潜水条件下,考虑渗流时地表最大沉降量比不考虑渗流时增大约50%;盾构隧道最大地表沉降与潜水水位呈线性关系;(2)承压水条件下,考虑渗流时地表最大沉降量比不考虑渗流时增大约10%,盾构隧道最大地表沉降与承压水头不成线性关系,随着承压水头的增大,地表最大沉降的增长速率越来越大;(3)潜水水位从-6.8 m变化到-2.8 m及承压水头从8 m变化到12 m的过程中,隧道衬砌管片弯矩和轴力随着潜水水位的升高或承压水头的增大而逐渐减小。     

Lessons learnt from unusual ground settlement during Double-O-Tube tunnelling in soft ground

The DOT (Double-O-Tube) tunnelling method has been adopted in the construction of various types of tunnels in soft ground both in Japan and in China. Recently, an unexpected ground surface settlement of approximately 0.8 m was observed in a DOT construction site in Shanghai, China. The backfill grouting injection rate had to be increased by up to 500% to control the settlement. In order to find out the reasons for the large settlement, and to reduce it to an acceptable level, in-situ monitoring, including surface settlement and subsurface settlement, was undertaken to obtain the change in ground deformation during DOT machine driving. It was found that the conventional settlement control methods, such as adjusting the earth pressure balance on the cutter face, and simultaneous backfill grouting at a normally acceptable injection rate, could not reduce the large settlement. It was also noticed that the settlement started as the DOT machine was passing, as well as after the tail had passed through. Subsequent field investigations found cement accumulation attaching to the skin plate. This was due to improper backfill grouting at the early construction stage, and the concave shape of the DOT machine. The mechanism for large settlements due to improper immediate backfill grouting was analysed. After taking countermeasures, the ground settlement was reduced to approximately 0.02 m.     

济南轨道交通某深基坑降水与回灌数值分析

基坑降水会改变基坑周围地下水位,进而引起不均匀沉降,影响周围建筑物安全性,实践证明,回灌法是解决此类工程问题的有效手段之一。以济南轨道交通R1线某深基坑降水工程为研究目标,利用Visual Modflow软件分析基坑降水与回灌,分别模拟基坑在止水帷幕与回灌不同工况条件下降水与回灌对周围地下水位与沉降的不同影响效果。仅回灌模拟结果表明:回灌井设在基坑周围10 m处,保持回灌量大于等于抽水量,地下水位控制效果相对较好;回灌结合止水帷幕模拟结果表明:回灌量控制在抽水量的2/3左右,回灌井设在基坑周围30 m处,回灌在整个模型区域地下水位控制效果最好,沉降小于0.1 cm。根据模拟结果得出适用于该工程地下水位扰动最小的回灌方式及最优方案,为工程施工提供理论依据与参考。     

地下水对地基不均匀沉降的影响

针对地基的地下水的不良影响，对土的渗透系数和渗透力进行了分析，指出了地下水的渗流对地基不均匀沉降的影响较大。当天然土具有较强透水性时，易造成地下水流对地基的冲刷。对地基中地下水位的变化的影响进行了分析，提出了地下水在基底下压缩层范围内变化可降低土的极限荷载，地下水在换土垫层范围内变化可降低周围软弱土侧向支承力。     

降水对桥基影响的三维渗流–应力耦合分析

 近邻桥梁进行降水施工时，地层的固结变形导致桥梁基础变形，当桥梁的基础变形过过大时，可能危及桥梁的安全和正常运行。为了预测降水过程中桥梁基础的空间响应和评估其安全状态，建立三维非饱和渗流–应力耦合分析数学模型，同时，运用ABAQUS软件，建立地层、地下水、桥梁相互作用的三维有限元模型。采用直接耦合分析方法，对近邻桥基进行降水施工时的动态降水过程进行三维仿真模拟。模拟结果表明，水位下降10 m时，降水所引起的地表最大沉降值为21.37 mm，桥基的最大沉降值为19.56 mm，相邻桥基的差异沉降不到2 mm，表明降水期间桥基没有安全隐患，现有的降水方案是可行的。通过将沉降计算值与现场量测值比较分析，两者数据吻合较好，表明所提出的计算模型和分析方法是合理的，可为类似问题的研究提供了借鉴和参考。     

A study of the permeability and acid attack of corn cob ash blended cements

The durability of concrete made with corn cob ash (CCA) blended cement was investigated in this study. Permeability and chemical attack involving H₂SO₄ and HCl were the key parameters considered. Nine classes of CCA blended cements were employed with the CCA content ranging from 0% to 25%. The 0% CCA replacement involved the use of normal ordinary Portland cement and it served as the control. The water absorption of blended cement concrete was performed using 100 mm cube specimens of mix proportions 1:1½:3, 1:2:4 and 1:3:6 with 0.5, 0.6 and 0.7 water-to-binder ratios, respectively. The chemical attack test was carried out using 50 × 50 × 15 mm mortar specimens of mix proportions 1:1, 1:2 and 1:3 with water-to-binder ratio ranging between 0.26 and 0.29. The results indicated that the use of CCA blended cement reduces the water absorption of concrete specimens. Optimal reduction occurred at 10% CCA replacement for 1:1½:3 and 1:2:4 mix proportions and at 15% CCA replacement for 1:3:6 mix proportion. The resistance to chemical attack was improved as the addition of CCA up to 15% replacement level, caused a decrease in permeability and reduction in weight loss due to reaction of the specimens with HCl and H₂SO₄ acid water.     

Responses of calcareous sand foundations to variations of groundwater table and applied loads

The long-term settlement of calcareous sand foundations caused by daily periodic fluctuations has become a significant geological hazard, but effective monitoring tools to capture the deformation profiles are still rarely reported. In this study, a laboratory model test and an in situ monitoring test were conducted. An optical frequency domain reflectometer (OFDR) with high spatial resolution (1 mm) and high accuracy (±10^-6) was used to record the soil strain responses to groundwater table and varied loads. The results indicated that the fiber-optic measurements can accurately locate the swelling and compressive zones. During the loading process, the interlock between calcareous sand particles was detected, which increased the internal friction angle of soil. The foundation deformation above the sliding surface was dominated by compression, and the soil was continuously compressed beneath the sliding surface. After 26–48 h, calcareous sand swelling occurred gradually above the water table, which was primarily dependent on capillary water. The swelling of the soil beneath the groundwater table was completed rapidly within less than 2 h. When the groundwater table and load remain constant, the compression creep behavior can be described by the Yasong-Wang model with R² = 0.993. The daily periodically varying in situ deformation of calcareous sand primarily occurs between the highest and lowest groundwater tables, i.e. 4.2–6.2 m deep. The tuff interlayers with poor water absorption capacity do not swell or compress, but they produce compressive strain under the influence of deformed calcareous sand layers.     

真空预压地基出水量现场试验研究及分析

通过中山造船基地真空预压软基加固工程的现场试验观测成果,从软土的微观固结机理角度定性分析了真空预压期间加固区内的出水量变化情况,以及地表沉降、地下水位与出水量之间的内在联系。研究结论如下:①真空加固期间的出水量分为两个阶段,加载初期主要为加固区内土体大、中孔隙中的自由水,恒载后以土体的中、微孔隙中能克服自身抗剪强度发生渗流的弱结合水为主。②由于自由水比弱结合水更容易发生渗流,因此抽真空初期的日出水量远大于恒载期的日出水量,但是受到场地地质条件影响,不同区域的出水量多少不均。③总出水量与地下水位降深、地表沉降的关系表现出相似的规律,即加固初期随着总出水量的增大,地下水位降深和地表沉降变化较快,后期变化较慢并逐步趋于稳定。     

基坑开挖中地下水抽取对周围环境的影响分析

深基坑工程中,地下水的渗流将会使基坑周围形成降水漏斗.随着开挖的进行,地下水自由面不断下降,从而使坑外土体的有效应力增加,墙后土体将发生不均匀沉降.为分析基坑开挖过程中,周围土体的沉降及地下水位的变化,对基坑建立三维有限元分析模型,这是一个地下水渗流与地面沉降计算的一体化模型.利用该模型分析了在软土地区深基坑开挖引起地下水渗流场的变化.结果表明,地下水头计算值与工程现场的实测值吻合,此方法可以较好的模拟实际工程.还用该模型分析了基坑开挖地下水抽取引起的地面沉降问题.     

Maximum surface settlement based classification of shallow tunnels in soft ground

Prediction of the maximum surface settlement due to shallow tunnelling in soft grounds is a valuable metrics in ensuring safe operations, particularly in urban areas. Although numerous researches have been devoted to this issue, due to the complexity and a large number of the effective parameters, no comprehensive solution to the problem is available. In this study, a shallow tunnel classification system (STCS), based on maximum settlement, is proposed. The STCS holds on the results of several tunnelling projects around the world. The classifier categorises a tunnel based on geometry, ground, and performance characteristics. A decision tree classification method, after training with 20 cases, was successful to predict the maximum settlement for 14 tunnelling projects. The maximum surface settlement predictions were in the form of assigning a class label to each tunnel. Four tunnel classes were defined as follow: (i) class A (maximum settlement < 9.9 mm), (ii) class “B” (10 ⩽ maximum settlement < 19.9 mm), (iii) class “C” (20 ⩽ maximum settlement < 29.9 mm), and (iv) class “D” (maximum settlement ⩾ 30 mm). The most explanatory independent variables were selected, by the STCS, as follow: tunnel depth, diameter, volume loss, and normalised volume loss. The proposed classification scheme can be employed as a decision making aid in settlement prediction/prevention in shallow tunnelling in soft grounds. The STCS is proposed as a supplemental tool to the observational methods, and it is not expected to be a stand-alone measure for settlement.     

Dissolved organic compounds in reused process water for steam-assisted gravity drainage oil sands extraction

The in situ oil sands production method called steam-assisted gravity drainage (SAGD) reuses process wastewater following treatment. However, the treatment and reuse processes concentrate contaminants in the process water. To determine the concentration and dynamics of inorganic and organic contaminants, makeup water and process water from six process steps were sampled at a facility employing the SAGD process in Alberta, Canada. In the groundwater used for the makeup water, the total dissolved organic carbon (DOC) content was 4 mg/L. This significantly increased to 508 mg/L in the produced water, followed by a gradual increase with successive steps in subsequent water treatments. The concentrations and dynamics of DOC constituents in the process water determined by gas chromatography-mass spectrometry showed that in the produced water, volatile organic compounds (VOCs) such as acetone (33.1 mg/L) and 2-butanone (13.4 mg/L) predominated, and there were significant amounts of phenolic compounds (total 9.8 mg/L) and organic acids including naphthenic acids (NAs) corresponding to the formula C_nH_2n+ZO_X for combinations of n = 4 to 18, Z = 0 and −2, and X = 2 to 4 (53 mg/L) with trace amounts of polycyclic aromatic hydrocarbons (PAHs) such as naphthalene and phenanthrene. No organic contaminants, except for saturated fatty acids, were detected in the groundwater. The concentration of DOC in the recycled water was 4.4-fold higher than that in the produced water. Likewise, the total concentrations of phenols and organic acids in the recycled water were 1.7- and 4.5-fold higher than in the produced water, whereas the total concentrations of VOCs and PAHs in the recycled water were reduced by over 80%, suggesting that phenols and organic acids are selectively concentrated in the process water treatment. This comprehensive chemical analysis thus identified organic constituents that were concentrated in the process water and which interfere with subsequent water treatments in the SAGD process.     

Landslide and mudflow disaster in disposal site of surplus soil at Higashi-Hiroshima due to heavy rainfall in 2009

The collapse of a filling occurred due to heavy rain in Higashi-Hiroshima City׳s Shiwa District at about 5:30 am July 25th, 2009. The filling was made of surplus soils, and it contained a mass of water supplied from rainfall and ground water flow of a permeable layer at the bottom of the filling. The collapsed soil flowed down and destroyed a house. In this paper, the cause of this disaster is discussed. The site of the disaster was used as the dumping site of surplus soils, after several changes of ground formation. The history of the geographical change was reconstructed by the image processing of old map, aerial photographs, result of 3-dimentional laser survey carried out after collapse and the measurement of thickness of collapsed soil by dynamic cone penetration test. According to the result of processing, the shape and the size of the filling before collapse was reconstructed. The relationship between the rainfall and the groundwater in the river sediments layer over which the filling was constructed was determined. A stability analysis of the filling was conducted considering the rise of the groundwater level in the filling and the laboratory measured strength parameters. The results of the stability analysis showed that the collapse would have taken place when the groundwater level rose by about 9 m due to the supply of groundwater through the river sediments layer.     

井点降水联合强夯法加固饱和淤泥质地基的试验研究

 针对传统强夯法不适用于高地下水位条件下加固饱和淤泥质黏土地基的不足,提出井点降水联合强夯新型静–动力排水固结技术与施工工艺,并结合广州港南沙港区粮食及通用码头工程软基处理试验区科研项目,通过对地下水位、孔隙水压力和表层沉降等实施现场监测及室内土工试验,分析其加固机制,进而验证施工参数。地基处理后,经静力触探试验、十字板剪切试验、标准贯入试验和静载荷板试验检测,证明加固效果显著,比贯入阻力提高200～300 kPa,标贯击数增加2击,地基承载力达130 kPa。研究工作为今后软基处理工程提供一种新的方法和思路。     

基坑工程地下水渗流模型试验系统研究

设计了符合基坑工程条件的模型试验系统,可以模拟基坑地下水渗流。模型试验系统由土箱、排水箱、进水箱、上水箱、下水箱、测压装置等组成。通过给定进水箱与排水箱的水位可以实现基坑内外水头恒定,从而形成稳定的渗流。利用模型试验系统已经完成的试验为悬挂式截水帷幕基坑地下水渗流以及完整井条件下的层状含水层渗流,获得与实际工程相符的渗流流网形态,用来研究地下水渗流场的特征和规律。试验结果可指导实际工程设计,同时可用来修正基坑规程中地下水涌水量、坑外水位降深以及降水引起的沉降计算等。     

Microscopic analysis of the engineering geological behavior of soft clay in Shanghai, China

The upper 75 m of the alluvium beneath Shanghai can be divided into three clay layers. Consolidation of the upper soft clay contributes to the average 3 mm/year land subsidence which occurs in the Shanghai region, despite mitigation measures including reduction in groundwater exploitation from the underlying aquifer and groundwater recharge. Data indicate that the soft clay is semi-dispersed, marginally stable, and susceptible to compaction. The study reports an analysis of the granulometric characteristics and aggregate components, pore-size distribution, microstructure, pore solution composition and cation exchangeability of the soft clay. The results indicate the deformation/consolidation of the soft clay is related to its microscopic physical and chemical characteristics rather than the fluctuation of the groundwater level in the underlying aquifer.     

Performance monitoring and numerical assessment of a test embankment with preloading and vertical drains on Texcoco lacustrine soft clays

This paper presents the performance monitoring results and long-term numerical analyses of a 2.8-m-high test embankment with vertical drains on soft highly compressible clays during a four years and two months observation period (1525 days). The peculiar study site is characterized by thick layers of lacustrine soft clay with water contents up to 300%, void ratios between 7 and 9 and ratios C_α/C_c range from 0.06 to 0.03. The loading applied by the test embankment was 43.4 kPa. The vertical drains installed were of two types: sand and prefabricated. The settlements that only take into account the effect of the preloading embankment at the end of the observation period were 2.62 m and 2.71 m, in the zones with sand and prefabricated vertical drains, respectively. The settlement measured by regional subsidence was 0.47 m. The ultimate primary settlement was approximately 2.0 m and was estimated by two observational methods based on field settlement records. The settlement developed by secondary consolidation in the embankment ranged from 0.62 m to 0.71 m at the end of the observation period. The test embankment behavior was simulated by 2D and 3D numerical analyses. The 2D analyses used a theory to convert the axisymmetric drainage into plane drainage. The long-term numerical results and the field measurements were compared and discussed.