Physical model investigation on effects of drainage condition and cement addition on consolidation behavior of tailings slurry within backfilled stopes

Estimation of stressses within the tailings slurry during self-weight consolidation is a critical issue for cost-effective barricade design and efficient backfill planning in underground mine stopes.This process requires a good understanding of self-weight consolidation behaviors of the tailings slurry within practical stopes,where many factors can have significant effects on the consolidation,including drainage condition and cement addition.In this paper,the prepared tailings slurry with different cement contents(0,4.76wt%,and 6.25wt%)was poured into1.2 m-high columns,which allowed three drainage scenarios(undrained,partial lateral drainage near the bottom part,and full lateral drainage boundaries)to investigate the effects of drainage condition and cement addition on the consolidation behavior of the tailings slurry.The consolidation behavior was analyzed in terms of pore water pressure(PWP),settlement,volume of drainage water,and residual water content.The results indicate that increasing the length of the drainage boundary or cement content aids in PWP dissipation.In addition,constructing an efficient drainage boundary was more favorable to PWP dissipation than increasing cement addition.The final stable PWP on the column floor was not sensitive to cement addition.The final settlement of uncemented tailings slurry was independent of drainage conditions,and that of cemented tailings slurry decreased with the increase in cement addition.Notably,more pore water can drain out from the cemented tailings slurry than the uncemented tailings slurry during consolidation.

One-dimensional nonlinear consolidation analysis of soil with continuous drainage boundary

Following the assumptions proposed by MESRI and ROKHSAR,the one-dimensional nonlinear consolidation problem of soil under constant loading is studied by introducing continuous drainage boundary.The numerical solution is derived by using finite difference method and its correctness is assessed by comparing with existing analytical and numerical solutions.Based on the present solution,the effects of interface parameters,stress ratios(i.e.,final effective stress over initial effective stress,N_(σ))and the ratio c_(c)/c_(k)of compression index to permeability index on the consolidation behavior of soil are studied in detail.The results show that,the characteristics of one-dimensional nonlinear consolidation of soil are not only related to c_(c)/c_(k)and N_(σ),but also related to boundary conditions.In the engineering practice,the soil drainage rate of consolidation process can be designed by adjusting the values of interface parameters.

A general solution for vertical-drain consolidation with impeded drainage boundaries

An analytical solution is derived from the generalized governing equations of equal-strain consolidation with vertical drains under multi-ramp surcharge preloading. The hydraulic boundary conditions at both top and bottom of the consolidating soil are modelled as impeded drainage. The impeded drainage is described by using the third type boundary condition with a characteristic factor of drainage efficiency. Fully drained and undrained boundary conditions can also be modelled by applying an infinite and a zero characteristic factor, respectively. Simultaneous radial and vertical flow conditions are considered, together with the effects of drain resistance and smear. An increase in total stress due to multi-ramp loading is reasonably modelled as a function of both time and depth. A solution to calculate excess pore-water pressure at any arbitrary point in soil is derived, and the overall average degree of consolidation is obtained. It shows that the proposed solution can be used to analyze not only vertical-drain consolidation but also one-dimensional consolidation under either one-way or two-way vertical drainage conditions. The characteristic factors of drainage efficiency of top and bottom boundaries have a potentially important influence on consolidation. The boundary may be considered fully drained when the characteristic factor is greater than 100 and fully undrained when the characteristic factor is less than 0.1. The stress distribution along depth induced by the surcharge loading has a limited effect on the overall average degree of consolidation.

Composite Consolidation Coefficient Analysis of Soft Soil with Drainage Water

The consolidation coefficient is the most basic parameter to calculate the consolidation rate of soil layer, and the horizontal consolidation coefficient controls the radial water flow into the drainage well. Based on the background of the soft soil in Shantou, Guangdong Province, a series of experimental studies on the consolidation characteristics were carried out by using the modified consolidation instrument. And the concept of the composite consolidation coefficient of the drained water body was put forward. The composite consolidation coefficient reflects the consolidation characteristics of soft soil with drainage water, The test results showed that: 1) The consolidation test with drainage plate is basically consistent with the load compression curve, but its consolidation rate is fast, which is reflected by the composite consolidation coefficient. 2) In the consolidation test of water bodies with drainage, the vertical consolidation coefficient and radial consolidation coefficient are calculated by “three-point method”, and then the composite consolidation coefficient is obtained. The composite consolidation coefficient decreases with the increase of drain spacing ratio, effective drainage diameter and drainage height, which is basically consistent with the theoretical formula. 3) The vertical consolidation coefficient and radial consolidation coefficient decrease with the increase of the diameter of the sample, and the difference is obvious when the load is large. The large-size model with a diameter of 100 mm and a height of 100 mm is about 1.35 times of the vertical consolidation coefficient of the conventional consolidation test.

Industrial Flow Designing of Dried Mud Drainage for Flush Fluid in Pingguo Aluminum

Because there are plenty of clay particles in the flush fluid of Pingguo Aluminum Mine, the consolidationtechnology in geotechnical engineering was adopted to carry out the disassociation of water and soil disassociation. Inthis method, vacuum method, electro-osmosis and chemical flocculation were used comprehensively to separate soilfrom flush fluid. The experiments of the method of "vacuum + electro-osmosis" for drainage was made. After pretreat-ing the flush fluid, suction pressure was offered by the sand well in the bottom and electro-osmosis was used to drainoff water. The results of the experiment show that the good effect can be obtained in drainage when the electric gradi-ent is greater than 8.3 V/cm and the quantity of sand well is more than 6. In industrial production, it is necessary to in-crease the quantity of sand well, to arrange the electrodes rationally and to set up an intermittent electric circuit. On thebasis of the experiments , the industrial feasible flow was put forward. It may be a helpful attempt to apply consolida-tion technology to the fields of the environmental protection and so on.

径向固结系数计算方法与试验验证研究

基于Terzaghi-Rendulic的轴对称固结理论,提出了一种径向固结系数计算公式,采用GDS固结试验验证该公式的有效性。首先,利用径向固结度和时间因子的关系,推导出径向固结系数的计算公式。然后,采用GDS固结试验系统,开展了不同固结压力下的径向排水固结试验,得到位移~时间曲线。最后,利用提出的公式计算出各级固结压力下的径向固结系数,并将理论解答与试验数据进行了对比。结果表明,提出的计算方法是可行的,能够实现对径向排水固结的试样位移随时间变化关系进行较为准确的预测。

连续排水边界下考虑指数渗流的软土一维非线性固结分析

为研究考虑边界排水的时效特性、变荷载、非达西渗流以及土体非线性特性的饱和软土固结问题,通过引入连续排水边界,建立考虑指数渗流和土体非线性的固结方程。利用有限差分法得到变荷载及瞬时荷载下基于连续排水边界考虑指数渗流的软土一维非线性固结解答,通过渗流形式退化和边界退化的方法,将所得解答与达西渗流下的解答及传统排水边界下的解答对比验证了该文差分法解答的可靠性。基于所得解答,详细分析了界面参数、指数渗流及土体非线性等因素对固结特性的影响。结果表明:界面参数取值越大则边界排水能力越大,边界排水性能较差时提高界面参数取值能有效提高边界排水能力;边界排水性能主要影响土体固结前期,而指数渗流主要影响固结后期;实际工程中如果关注固结的整个过程,则需要考虑边界排水性能的影响,但如果只关注固结后期的沉降值,则可忽略边界排水性能的影响。

大型沉井流塑状粉质黏土地基固结排水分析

为了探究一种加快沉井地基土体固结排水效率的施工方法及其对沉井结构受力安全性影响,基于南京长江河段某过江通道悬索桥锚碇大型沉井基础,开展实测和数值模拟分析,研究换填沙袋处理配合沉井对角浇筑方法在流塑状粉质黏土地基基础施工过程中的影响。结果表明:在沉井井壁和隔墙底部采取换填沙袋处理后,沉井浇筑和接高施工进度可不受粉质黏土排水固结过程控制,而主要取决于沉井结构混凝土强度的增长情况。换填沙袋地基处理可以提升固结排水效率,但容易出现地基不均匀现象,从而产生沉井结构受力安全性问题。

考虑变荷载和变边界的软土大应变非线性固结分析

为了准确预测实际土层的固结速率,在Gibson大应变固结理论基础之上,考虑土体的非线性压缩渗透特性和土层表面随时间改变的变排水边界条件,建立考虑变荷载和变边界的软土大应变非线性固结模型。在此基础上,获得单级加载和多级加载条件下大应变非线性固结模型的显式解析解,利用获得的解析解开展计算以分析界面参数、荷载取值对土层固结性状的影响。结果表明:外荷载对土体内部超静孔压消散的影响表现为随着荷载的增大,超静孔压消散得越快,但其不会影响土体最终完成固结的时间;参数I_(c)(α-2)取值对土体固结性状的影响表现为固结速率随着参数I_(c)(α-2)取值的变化而变化。值得注意的是,描述土体非线性特性的参数取值对固结性状的影响在变边界下显现的固结性状会出现延迟现象,不同参数下的变边界更能反映土体边界的真实透水性情况,在实际工程中可以根据超静孔压实际的消散速率反演界面参数,以便能准确预估土层的固结进程。

加筋花岗岩残积土抗剪强度的试验与机理分析

花岗岩残积土是中国东南部沿海地区工程建设中常见的土体,采用加筋土技术对高填方边坡能很好地提高其整体稳定性与土体的抗剪强度。首先通过直剪切摩擦试验研究了筋-土界面的摩擦特性;然后在不同加筋层数及不同干密度情况下,对花岗岩残积饱和土和加筋饱和土分别进行了三轴固结排水剪切试验,探究不同干密度、不同加筋层数情况下的加筋效果。试验与机理分析表明:不同加筋层数的试样对应的规格化强度系数都大于1,这说明在土体中加入筋体能有效地提高抗剪强度,减少土体的变形。随着加筋层数的增加,规格化强度系数增加,说明加筋层数的增加能提高加筋效果,但两层加筋的规格化强度系数与一层加筋相比并不是线性增加,第二层加筋效果有减弱的趋势;随着干密度的下降,规格化强度系数上升;随着围压的增加,加筋土的规格化强度系数降低。土工格栅主要通过提高土体黏聚力来提高土体抗剪强度,导致土体的黏聚力显著地提高,而对内摩擦角的影响却不大;通过理论计算结果与测试结果对比,验证了准黏聚力增量公式的合理性,且第二层加筋对准黏聚力增量的贡献相对较小。

静动力排水固结法处理吹填海相泥沙软基试验研究

为加固吹填海相泥沙形成的软土地基,在汕头市东海岸围海造地的吹填区域内,进行堆载预压的静态排水固结法、强夯施工的动力排水固结法等试验,采用“降水+堆载+强夯”的静动力排水固结法加固吹填海相泥沙形成的软土地基。通过现场测试,研究施工过程中各层地基沉降、水位和孔隙水压力、土体位移变化情况,对处理前后的地基进行土工试验和原位测试研究,并验证该方法对海相泥沙的处理效果。研究表明,静动力排水固结法显著提高吹填软土地基的承载特性,可广泛应用于围海造地软基加固工程中。

基于塑料排水板处理的滨海软土路基临界填筑高度研究

依托马来西亚某滨海铁路项目,考虑软土固结作用和塑料排水板的影响范围,提出了软土路基临界填筑高度的修正计算公式,并通过现场实测数据验证了该公式的有效性。结果表明:地表固结沉降变形随着路基填筑高度的增加而增大,但变化速率为非线性。临界高度前,地表沉降变化速率较小;达到临界填筑高度时,填土高度-地表沉降过程曲线出现拐点;临界高度后,地表沉降变化速率随路基填筑高度的增加而显著增大,曲线斜率较陡。塑料排水板间距越大,路基临界填筑高度越高,两者呈正相关关系。修正后的临界填筑高度计算值与实测值较为接近,差值平均值为0.162,标准差为0.411,修正的临界高度计算公式较精确、可靠。

间歇固结排水条件下上海原状饱和软黏土的动力特性试验

针对高铁列车荷载引起的地基长期沉降,既有动三轴试验研究往往忽略高铁运营期间存在间歇期、加载方式实际为分阶段加载的情况。基于此,本文通过一系列循环三轴试验研究间歇阶段固结排水条件下上海饱和软黏土在动应力影响下的动力特性,并探讨不同动应力和不同加载方式对土体轴向累积塑性应变的影响。研究结果表明:在不同动应力影响下,间歇期固结排水产生的轴向累积塑性应变增量随间歇阶段的后移始终呈非线性减小的发展趋势;当振次相同并且动应力幅值为10 kPa时,分阶段加载产生的累积塑性应变大约是连续加载的3倍;当振次相同并且动应力幅值为30 kPa时,连续加载产生的超孔压大约是分阶段加载产生的超孔压的5倍。分阶段加载使高铁地基产生更大的沉降,对高铁运营的安全性提出更高的要求。

饱和砂土不同应力路径下强度及剪胀真三轴试验研究

采用全自动加载真三轴仪对饱和砂土在大主应力方向与沉积方向平行的条件下,在不同固结压力(围压)50kPa、100kPa、200kPa条件下,针对不同应力路径b值取0,0.25,0.5,0.75,1进行真三轴固结排水剪切试验。结果表明:大主应变和偏应力、大主应变和应力比、大主应变和有效应力比的关系基本上表现为光滑的硬化型、理想塑性。个别出现软化型的曲线,软化趋势很弱。在剪切过程中,随剪应力逐渐上升,变形模量逐渐上升,剪切强度也逐渐提高。b=1时曲线界于b=0.5~0.75时的曲线之间。中主应力系数在0.75左右时,曲线斜率达到峰值,且是不同中主应力系数曲线族中的最大值。在中主应力系数b处于区间0~0.5时,b值上升,饱和砂土剪胀性表现越来越显著;在b处于区间0.5~1时,剪胀呈现弱化趋势。整体上对比来看,饱和砂土剪胀特性在高围压状态下不同b值的剪胀性差异更加明显。

变透水边界与起始坡降下软土路基固结模型

研究目的:路基沉降问题是引起铁路、公路等基础设施发生工程事故的主要原因。为提高软土地区路基土沉降预测水平,本文考虑土体的非达西渗流效应、土体边界透水能力的变化以及变形非线性特征,建立相应的分段线性化固结模型。其中,起始坡降渗透模型用来反映土体的非达西渗流过程,连续排水边界用来描述土体边界透水性能的变化,e-lg(av0)关系用来表示土体的非线性变形特征。然后,应用一些算例分析探讨边界透水性能变化、土体非线性变形以及非达西效应下土体的固结行为,以期为软土路基工程工后沉降预测提供理论支撑。研究结论:(1)土体的非达西效应越强(即起始坡降值越大),边界透水性能越差(即连续排水界面参数越小),相同时刻下的固结滞后现象越明显;(2)起始坡降值能同时影响固结过程及最终结果;(3)连续排水边界和起始坡降下初始压缩系数对沉降过程的影响比较显著;(4)本文固结模型可模拟深厚软土路基的沉降过程,相关结论可应用于深厚软土的堆载排水加固过程。

不同固结路径下钙质砂固结排水强度性状研究

钙质砂是我国南海岛礁建设的主要吹填材料,岛礁建筑施工中钙质砂地基将受到不同固结路径外荷载作用,开展不同固结路径下钙质砂的固结排水强度特性研究是岛礁地基建设的迫切需求。对取自我国南海某吹填岛礁的钙质砂开展不同固结路径三轴固结排水剪切试验,探究钙质砂的强度参数和颗粒破碎程度随固结路径的演变规律。研究结果表明:钙质砂的应变软化和剪胀特性随平均有效应力的增大、有效主应力比的增大而逐渐减弱;与等向固结工况相比,随着有效主应力比减小至0.45时,钙质砂固结排水峰值强度折减系数介于0.60~0.95之间;在常规应力范围内,当有效主应力比增大,峰值内摩擦角呈减小趋势,介于38°~53°之间。在固结阶段,颗粒破碎程度随偏应力的增大而变大,但在剪切完成后颗粒破碎程度反而最小,剪切阶段的颗粒破碎占主导地位;验证了不同固结路径下峰值内摩擦角与相对破碎率的定量关系式,计算得到的峰值内摩擦角预测值为实测值的0.8~1.2倍。固结应力路径和固结压力不同引起的颗粒破碎程度差异,是导致剪切后钙质砂固结排水强度性质差异的主要原因。

真空预压联合EKG电渗法室内试验研究

真空预压联合电渗法能够发挥真空预压法和电渗法各自的优势,是一项极具潜力的软基处理技术,而电动土工合成材料(EKG)则是电渗法常用的电极材料之一。为研究不同电极材料及通电方式对真空预压联合电渗法排水效果的影响,基于EKG电极开展室内一维模型试验,设置了金属电极作为对照,研究在不同材料和通电方式下的排水固结规律,通过补充试验进一步探索了在不同反转电压的真空预压联合电渗的排水效果。试验结果表明:在本研究的试验条件下,EKG电极在持续通电、间歇通电和反转通电三种模式下的总体电渗排水效果要优于铁、铝和铜电极;当采用EKG、铝和铜电极时,通过对软土采用间歇通电模式,可以激活软土排水的潜力,提高排水量;当采用EKG电极时,选择合适的反转电压,可以有效促进软土的排水固结,获得超过持续通电和间歇通电两种模式的排水效果。

高速公路软土地基处理后路基滑塌原因及处治

结合实际工程,详细阐述了采用排水固结法处治软土地基的工程特性,通过地质补勘和路基滑塌病害分析,对排水固结法处治软土地基后产生滑塌的原因进行分析,并制订合理有效的滑塌处治方案。

广州市南沙区某新建污水处理厂软土地基处理方案比选分析

文中以广州市南沙区某新建污水处理厂为例,对项目场地和地基的地震效应进行评价,深入对比分析不同软土地基处理方案的优劣势,促进经济的发展,从而顺利实现其规划目标。

云岗矿多层采空区积水综合集成探放水技术研究

探讨了8#煤层8409工作面周边空间水患充水原因,并利用瞬变电磁物探验证法对采空区的积水水量、水压进行了估算,制定了探放水方案和孔口固结措施。该措施利用钻孔泄水自流到低洼基准点后进行集中排水,同时采用“多层同放”综合集成探放技术与“两种疏排”科学治理方法,实现了对8409工作面多种采空区积水的安全高效探放,有效消除了矿井水患,保障了工作面正常接替与安全生产。