摘要
黄河冲(淤)积平原的高速公路,沿线地区土质多为粉土、粉质粘土及粘土互层。相关研究表明,若不进行合理的地基加固,桥涵构造物台背将发生较大的不均匀沉降,影响行车安全。强夯法是一种经济高效的地基加固技术,但其设计参数、施工工艺和工程控制指标因地基土质、地下水位以及上部结构等因素的差异而不同。因此,研究黄河冲(淤)积平原区强夯加固地基技术,可为该区域及其他类似地区高速公路的设计、施工及养护管理提供指导,具有显著的工程应用价值和社会经济效益。
本研究选择济乐高速公路典型地基,通过现场试验确定强夯加固地基的合理工艺参数,完善相关地基加固设计并指导施工。运用FORTRAN语言编制程序计算试验段地基沉降量,采用FLAC3D软件进行天然地基沉降的数值模拟,将计算结果与现场实测沉降值进行比较以分析强夯减小地基沉降的效果。通过现场检测(静力触探、动力触探)数据,进一步评价强夯的加固效果。运用FLAC3D分析地下水位对粉土地基强夯的影响并提出夯击能与临界水位高度的关系式,同时也研究了含水量对粘土地基强夯的影响,并归纳总结了相应的处置措置。
通过上述研究主要得出如下结论:四标、九标试验段在1500kN·m夯击能作用下地基有效加固深度分别在6m、6.5m左右,强夯有效加固深度系数α分别为0.155、0.168。两试验段1500kN·m夯击能作用下的径向影响距离可达6m,径向有效加固距离在2~4m之间。试验地基条件下,单点夯对相邻夯点处的孔隙水压力影响很小,故相邻夯点可以连续夯击,而不必间隔跳夯。连续进行单点夯击时,表层土发生液化的可能性要大于深层土,地下水位越高,液化可能性越大。为了避免强夯引起地基土液化,保证加固效果,强夯施工前应按照设计要求检测地下水位情况。一般来说,在地下水范围内,埋深越小,超孔隙水压力增长量越大,消散越慢;埋深越大,超孔隙水压力增长量越小,消散越快。两个试验段第1遍以及第2遍点夯后24小时超孔隙水压力基本完全消散,夯后48小时超孔隙水压力完全消散,建议类似条件的地基强夯间歇时间调整为48小时。沉降分析表明,试验段地基经强夯加固后,地表总体沉降量占地基总沉降的40%以上,剩余沉降量显著降低。对比数值计算结果与现场沉降观测数据可知,强夯地基沉降量明显小于天然地基,说明通过强夯加固能够显著减小工后沉降,缩短路基放置时间。现场静力触探和标贯试验表明,在有效加固深度范围内地基承载力明显增强,强夯加固效果明显。对于粉土地基,地下水位越高,强夯时液化可能性越大,发生液化的范围也越大。随着夯击能的增大,临界水位高度也会增大,幂函数y=0.449×0.280能准确反映出两者的相关关系。粘土地基含水量过高,强夯时会形成橡皮土。为保证强夯加固效果,可通过井点降水、强夯置换、灰土处置等方式进行处理;同时需要及时回填夯坑避免坑积水。
In the Yellow River alluvial plain, silt and silty clay are widespread. Severe differential settlement of freeway foundation would happen without reinforcement. Recently dynamic compaction has been widely used in ground reinforcement because of its economical efficiency. But the design parameters and construction methods of dynamic compaction should be based on quite many factors, such as the soil type and underground water level. So it is of great importance to study the reasonable dynamic compaction methods for the Yellow River alluvial plain, which will be useful for the design and construction of freeway in this area.
Based on the Jile freeway construction engineering, two sections were chosen to do in-situ test to determine the reasonable parameters for a better design. Foundation settlement calculation was done by FORTRAN and FLAC3D. Then the calculation results were compared with the test data to analyze the effect of dynamic compaction on reducing settlement. Some field tests (static penetration, dynamic penetration) were also done after the reinforcement to evaluate the soil improvement. FLAC3D was used to analyze the effect of water table on dynamic compaction in the silt groud. We also studied the influence of water content on clay foundation during dynamic compaction. Then the treatment measures for dealing with water were summarized.
The following results were found in the research:With the effect of1500kN-m dynamic compaction, the effective reinforcement depths of the two sites were6m and6.5m respectively and the effective reinforcement depth ratio were0.155and0.168respectively. In terms of the reinforcement width,1500kN-m dynamic compaction could affect more than6m, but the effective reinforcement width was between2-4m. When hammering one point, it had very little effect on the adjacent one. If one single point was hammered continuously, the liquefication possibility of surface soil is larger than that of deep soil. In order to avoid liquefication caused by dynamic compaction, detection of underground water level should be conducted. In general, the smaller the depth, the more the excess pore water pressure increased and the slower the excess pore water pressure dissipated. In the two sites, excess pore water pressure dissipated completely48hours after hammering. Settlement analysis showed that dynamic compaction could reduce more than40%of the total settlement. Comparing numerical results with the field settlement observation data, the settlement of reinforced ground is much less than that of natural foundation. Static penetration and dynamic penetration test showed that foundation bearing capacity was significantly enhanced after reinforcement within the the effective reinforcement depth. For silt foundation, the higher the underground water level, the severer liquefaction would happen. The equation y=0.449x0.280could reflect the relationship of critical water table depth and tamping energy. In order to ensure the good effect of dynamic compaction, well-points dewatering, dynamic compaction replacement and lime soil disposal method will be helpful if there is much unfavourable water. The ram pits should also be pluged-back immediately after hammering to avoid water filling.
引文
[1]Menard L and Boroise Y. Theoretical and Practical Aspects of Dynamic Consolidation[J]. Geotechnique,1975,25(1):3-18.
[2]范维恒.强夯法处理地基中的几个根本问题[J].太原工业学院学报,1982,2:15-25.
[3]王成华.强夯地基加固深度估算方法述评[J].地基处理,1991,2(1):20-24.
[4]M.P.Gambin, elal. Ten Years of Dynamic Consolidation[A]. Proceeding of the Eighth Regional Conference for African on Soil Mechanics and Foundation Engineering[C],1984.
[5]Leonards G.A, etal. Dynamic Compaction of Granular Soils[J]. Journal of Geotechnical Engineering Division (ASCE),1980,106:35-44.
[6]R.G. Lukas. Densification of Loose Deposited by Pounding[J], ASCE,1980,106(4):435-446.
[7]郑颖人,罗毓华.机场特殊土和地基处理[M].空军工程学院中国民用航空机场设计院,1991.
[8]李天光.重锤低落距与轻锤高落距强夯法加固湿陷性地基效果比较[J].工程勘察,1995,2:14-17.
[9]钱征,李广武.强夯法加固细砂地基[A].全国第四届土力学及基础工程学术会议论文集[C],1981.
[10]周良忠.炊粘土地基强夯机理与施工工艺的研究及在机场工程的应用[D].后勤工程学院博士学位论文,1998.
[11]Terzaghi K. Theoretical Soil Mechanics[M]. New York:Wiley,1943.
[12]Biot A. General Theory of Threre-Dimentionnal Consolidation[J]. Journal of Applied Physics,1941, 12(2):155-164.
[13]Gibson, Schiffman, etal. The Theory of One-Dimensional Consolidation of Saturated Clays[J]. Canadian Geotechnical Journal,1981,18(2):280-293.
[14]窦宜,蔡正银,盛树馨.自重应力作用下饱和粘土的固结变形特性[J].岩土工程学报,1992,6:29-37.
[15]自重应力作用下饱和和粘土的固结结特性.岩土力学与工程的理论和实践[G].浙江大学出版社,1992.
[16]景宏君.土质路基三维固结变形理论及其应用[M].科学出版社,2008.
[17]周晔,郑荣跃,刘干斌,等.EPS轻质土强度试验及其软土路基沉降控制中的应用[J].公路交通科技,2010,27(5):34-39.
[18]邓卫东.不同换填或处置层位施工速率等对山区路堤稳定和沉降的影响[J].重庆交通学院学报,1999,18(1):113-120.
[19]郝传毅,饶鸿雁,杨世基.路堤自身压缩的非线性有限元分析[J].中国公路学报,1991,4(1):9-15.
[20]赵维炳.排水固结加固软基技术指南[M].北京:人民交通出版社,2005.
[21]钱家欢,钱学德,赵维炳,等.动力固结的理论与实践[J].岩土工程学报,1986,6:1-17.
[22]李庆园,任建喜,刘慧,等.软土路基变形规律现场监测及FLAC模拟研究[J].西安科技大学学报,2009,6:712-717.
[23]周镜.软土沉降分析中的某些问题[J].中国铁道科学,1999,20(2):17-29.
[24]董亮,史存林,蔡德钩,等.地基沉降计算新方法的探索[J].工程地质学报,2005,2:227-230.
[25]下茂丽.软土地基非线性固结沉降的研究[D].武汉理工大学硕士学位论文,2005.
[26]李本平.有限元法分析强夯加固机理[D].浙江大学硕士学位论文,1993.
[27]岳雪莲,王连堂,孟文辉.求解多层介质中声波传播问题的一种边界元方法[J].数值计算与计算机应用,2013,1:75-80.
[28]蒋鹏,李荣强.离散元法用于块石圭强夯过程模拟[J].岩土力学,1999,20(3):29-34.
[29]张雪变.基于ABAQUS的强夯地基应力与位移的研究[D].桂林理工大学硕士学位论文,2010.
[30]刘波,韩彦辉FLAC原理、实例与应用指南[M].人民交通出版社,2005.
[31]Y.K.Chow, et al. Numerical Modeling of Dynamic Compaction[J]. Computer Methods and Advances in Geomechanics,1991:232-242.
[32]Y.K.Chow, et al. Dynamic Compaction Analysis[J]. ASCE,1992,118:1141-1157.
[33]C.J.Poran, etal. Finite Element Analysis of Impact Behavior of Sand[J]. Soils and Foundations, 1992,32(4):68-80.
[34]童小东,蒋永生.强夯法加固地基的三维有限元动力分析[J].建筑结构,2000,30(5):46-48.
[35]高广运,顾中华,周群利.强夯加固地基大变形动力有限元数值模拟[J].地下空间,2004,24(2):143-147.
[36]蒋鹏,李荣强.强夯大变形冲击碰撞数值分析[J].岩土工程学报,2000,22(2):222-226.
[37]孔令伟,袁建新.强夯作用下成层地基的表面接触应力分布特征[J].力学学报,1999,31(2):250-256.
[38]孔令伟,袁建新.强夯的边界接触应力与沉降特性研究[J].岩土工程学报,1998,20(2):86-92.
[39]雷学文,下吉利.动力排水固结中孔隙水压力增长和消散规律[J].岩石力学与工程学报,2001,20(1):79-82.
[40]徐长节,张政伟.回填土地基的强夯大变形分析[J].工业建筑,2004,34(6):48-51.
[41]钱家欢,帅方生.边界元法在地基强夯加固中的应用[J].中国科学(A辑),1997,3:329-336.
[42]丁振洲,郑颖人.强夯法加固饱和软粘土地基数值模拟[J].地下空间,2002,22(2):137-141.
[43]卢廷浩.土力学[M].河海大学出版社,2005.
[44]孟祥彬,姚凯,等.强夯加因废弃铁矿渣路基的动应力扩散规律试验研究[J].山东大学学报,2012,42(1):87-92.
[45]张平仓,汪稔.强夯法施工实践中加固深度问题浅析[J].岩土力学,2000,21(1):76-80.
[46]叶观宝,陈望春,徐超.强夯法地基处理有效加固深度的分析研究[J].上海地质,2003,3:22-25.
[47]刘平.强夯法有效加固深度的估算[J].港工技术,2003,40(1):48-51.
[48]吴雪婷,徐光黎.软土地基沉降计算中压缩层厚度控制标准分析[J].人民长江,2009, 40(5):49-51.
[49]单红仙.黄河水下三角洲表层工程地质环境动态变化研究[D].中国海洋大学博士学位论文,2003.
[50]Hwang J H, Yang C W. Verification of Critical Cyclic Strength Curve by Taiwan Chi Earthquake Data[J]. Soil Dynamics and Earthquake Engineering,2001,21(3):237-257.
[51]齐辉.强夯与冲击碾压加固黄泛区地基技术研究[D].山东大学硕士学位论文,2010.
[52]陈育民.FLAC/FLAC3D基础与工程实例[M].中国水利水电出版社,2009.
[53]张荣祥,顾宝和,石兆吉.地基液化失效和隔震的临界孔隙水压力研究[J]. 工程勘察,1997, 2:5-7.
[54]吴友仁.强夯法加固高填方地基数值模拟研究[D].重庆交通大学硕士学位论文,2006.
[55]刘英春.低能强夯与真空降水联合法加固地基的分析研究[D].山东大学硕士学位论文,2006.
[56]杨建国.强夯法加固的主要设计参数研究[J].岩土力学,2004, 25(8): 1335-1339.
[57]郝华庚.高能级强夯加固机理及环境形响数值分析[D].同济大学硕士学位论文,2008.
[58]叶观宝.强夯法地基处理有效加固深度的分析研究[J].上海地质,2003, 3:22-25.
[59]常方强,贾永刚,郭秀军,等.黄河口粉土液化过程的现场振动试验研究[J].岩土工程学报,2009,31(4):609-616.
[60]陈志鹏,李文盛.浅析“橡皮上”[J].湖北科技学院学报,2012,32(11):219-220.
[61]刘嘉,罗彦,张功新,等.井点降水联合强夯法加固饱和淤泥质地基的试验研究[J].岩石力学与工程学报,2009,28(11):2222-2227.
[62]刘惠珊,饶志华.强夯置换的设计方法与参数[J].地基基础工程,1996,2: 6-13.
[63]李哲,贺建龙,严军,等.强夯橡皮上的处治方法[J].陕西建筑与建材,2004, 109: 30-32.