【作者】 管延华；

【导师】 蒋斌松；

【作者基本信息】 中国矿业大学 ， 岩土工程， 2011， 博士

【摘要】 针对粉土路基,通过现场调研、室内试验、现场检测、模型试验及数值模拟等方法进行了强度衰减规律的探讨,揭示了路基强度衰减对路基稳定性、力学特征、变形特征的影响及路面结构的力学响应,提出了有效的路基加固技术及基于破坏接近度的路面结构受力平衡评价方法。主要研究内容及结论如下:(1)基于现场取样测量路基土的含水量,揭示路基含水量的分布特征;通过室内试验,针对路基土的压实特性及不同含水量下路基的强度变化规律进行了较为系统的试验研究。渗透试验及毛细水上升试验表明:粉土具有渗透系数较大、毛细水作用强烈等特征,路基含水量的增大造成了路基强度的衰减。压实粉土三轴试验(UU)及回弹模量试验结果表明,当ω?ωopt时,含水量的增大,路基土回弹模量及内摩擦角相对稳定,但粘聚力及变形模量逐渐增大;当ω?ωopt后,含水量的增大,路基土粘聚力、回弹模量及变形模量均降低显著,内摩擦角在接近饱和状态时才急剧降低,揭示出粉土路基含水量增大后强度低、变形大的特点。(2)现场调查了粉土路基边坡稳定性的破坏形式,通过强度折减法对强度衰减路基及注浆微型桩加固路基的稳定性分别进行了数值模拟分析。现场调查表明,实际粉土路基易发生浅层滑坡、边坡坍塌、路基滑移等病害。计算结果表明,路基含水量增大,边坡稳定性降低。注浆微型桩加固路基后,不仅边坡稳定性提高,而且能够有效的抑制路基不均匀沉降,对路面结构的受力非常有利。(3)基于路基强度衰减对高速公路典型路面结构在标准荷载及超载作用下的力学响应进行了计算分析;针对等级公路路面结构进行了弹塑性分析,计算了新建及路基强度衰减后路面各结构层的破坏接近度并据此评判路面结构的平衡性,揭示了路基强度衰减对路面结构平衡性的影响。计算结果表明,路面弯沉及应力随路基强度的衰减呈非线性加速增大,随荷载增大呈线性增大;车轮荷载作用下,半刚性基层受拉,处于受力最不利状态;基层的寿命随轴载的增加或路基强度的衰减呈指数性衰减趋势;等级公路路面结构的弹塑性分析表明,路基强度衰减后,路面结构层的受力明显增大,路面结构层受力不平衡,半刚性基层的下基层的FAI>2,处于塑性破坏状态,即半刚性基层成为整个路面结构层的薄弱层。(4)针对新建路基、强度衰减路基及注浆微型桩加固的路基进行了模型试验研究,试验结果表明:实际压实粉土路基毛细作用非常显著,路基采用注浆微型桩加固后桩间土含水量比强度衰减路基下降3.7%,桩间土的密实度和弹性模量比新建路基分别提高1.35%、9.46MPa。路基强度衰减后,其竖向应力发生重分布现象,路基顶部受力比新建路基增大16%左右;浆微型桩加固后的路基竖向应力明显减小(减小约50%)。随着路基强度的衰减,相同荷载作用下,路基所受的侧向应力明显增加;注浆微型桩加固后的路基,侧向水平力显著降低,其减小幅度大约是强度衰减路基的2倍。路基强度衰减程度越大,路基表面及内部个点的竖向变形越大,路基顶部越容易发生不均匀沉降。但注浆微型桩加固后,路基的竖向变形明显减小,基本达到新建路基的情况。新建及加固后路基的变形主要表现为弹性,塑性变形很小,路基强度衰减后,其塑性变形明显增大。强度衰减后路基的整体刚度降低,注浆微型桩加固路基后其整体刚度显著增加。随着路基强度的衰减,路基侧向水平位移增大;路基通过注浆微型桩加固后,仅在路基顶部发生微小的水平侧移。因此,注浆微型桩加固技术是一种有效的病害路基加固方法,路基采用此技术加固后,其不仅能够提高路基桩间土的抗剪强度,而且能够提高其压实度和整体刚度,致使路基整体承载能力及稳定性明显提高。(5)根据模型试验分析了注浆微型桩加固路基的工作机理:即分层压实的路基采用袖管劈裂注浆加固时容易沿路基分层之间发生横向劈裂,在路基土的分层之间形成水平水泥浆硬化夹层,阻隔了毛细水的上升,能够避免路基含水量的继续增大而造成其强度衰减;凝固体微型钢管柱对加固路基起到螺栓连接及骨架作用。注浆微型桩的工作状态大致分三个阶段:微型桩加速受力阶段;桩土协调工作阶段;注浆凝固体断裂、整个路基趋于塑性破坏工作阶段。实际路基加固工程应用表明,路基注浆微型桩加固技术对提高路基的竖向承载力、防止不均匀沉降以及提高边坡的稳定具有良好的效果。更多还原

【Abstract】 The strength attenuation of silt subgrade was discussed by the way of the on-site investigation, laboratory testing, field testing. The stability of the attenuated strength subgrade and its mechanical response of pavement structure were analyzed by the numerical simulation. The mechanical and deformation characteristics of subgrade were tested by the model experiment of the new subgrade, the attenuated strength subgrade, and the strengthed subgrade with the grouting mini-pile technology. The effective reinforcement technology was proposed and the evaluation methed of the pavement structure based on the index of failure approach was proposed. The main contents and conclusions are as follows:(1)The moisture content of subgrade was described on the base of field testing. The systematic experimental study on penetration and capillary rise was conducted to reveal the strength law of the silt subgrade under the different water content and compactedness. The results show that the silt has the bigger permeability coefficient and the stronger capillary water action. The increase of water content results in the strength attenuation of the subgrade. The tests of the resilient modulus and the triaxial test (UU) results under the different soil moisture on the compacted silt showed that the resilient modulus and the internal friction angle changed a little and the cohesion and modulus of deformation gradually increased when the water content was less than the best moisture content. The resilient modulus, cohesion and deformation modulus of the subgrade soil decreased significantly with the increase of the water content when the water content was above and beyond the best moisture content. But the internal friction angle reduced drastically when the water content reached to the saturation state.These revealed that the sucking water silt had a large deformation, low strength.(2)The on-site investigations had been finished about the failure modes of the slope stability, and the numerical simulations were conducted to analyze the stability of the attenuated strength subgrade and the subgrade strengthened with grouting micro-pile by ABAQUS / Standard. Field surveys show that the failure modes of the actual silt embankment had shallow landslide, slope collapse, embankment slipslip. The computed results showed the slope stability decreased with the increase of moisture content. But the slope stability of the embankment strengthened with the grouting mini-pile increased observably.(3)Based on the attenuation of subgrade strength, the mechanical response of pavement structure on the typical highway was computed and analyzed under the action of the Standard load and overload. And based on the elasto-plastic analysis of the pavement structue, the failure approach index of the pavement structure was computed on the new subgrade and the attenuated strength subgrade to judge and analyze the force balance of the pavement structural layer. The results showed that the stress and the surface deflection increased nonlinearly with the attenuation of subgrade strength and increased linearly with the loads. Under the action of the wheel loads, the bottom of the semi-rigid basement layer was tensed and was in the most unfavorable stress state.The computed results also showed that the fatigue life of the semi-rigid basement layer reduced exponentially with the increase load or the decay of subgrade strength. The elastic-plastic analysis of the grade road showed that the stress of pavement structure layer increased significantly after the attenuation of subgrade strength. The computed results of the failure approach index of the pavement structure showed that the pavement structural layer was in danger of the unbalance state, resulting in the plastic failure of the semi-rigid basement layer, FAI> 2.(4)The model experiment study was conducted on the new subgrade, the attenuated strength subgrade and the subgrade strengthened with grouting micro-pile. The test results showed that the capillary action was very observable. The moisture content of subgrade strengthened with the grouting micro-pile decreased 3.7% to one of the attenuated strength subgrade, and the compactedness and the elastic modulus of subgrade increased 1.35% and 9.46MPa to the original subgrade. When the subgrade strength decreased, the redistribution of its vertical stress happened so that the stress at the top of the subgrade increased about 16% than the new embankment. The vertical stress of subgrade strengthened with the grouting micro-pile stress (especially in roadbed) reduced approximately 50%. The lateral force of subgrade increased significantly with the attenuation of subgrade strength under the action of the same loads. While the lateral force of subgrade strengthened with the grouting micro-pile lowered significantly, and the ratio of lateral force of attenuated strength subgrade and subgrade strengthened with the grouting micro-pile is about 2:1. The differential settlement increased rapidly with the attenuation of subgrade strength. But the differential settlement of subgrade strengthened with the grouting micro-pile reduced observably to reach the state of the original subgrade. The deformations of original subgrade and strengthened subgrade were almost elasticity, and the plastic deformation is very small. The plastic deformation of attenuated strength subgrade increased rapidly with the attenuation of subgrade strength. The whole stiffness decreased with the attenuation of subgrade strength and increased observably with the subgrade strengthened. With the attenuation of subgrade strength, the lateral horizontal displacement of subgrade increased. But after the reinforcement of subgrade with grouting micro-pile, only minimal horizontal displacement occurred in subgrade top. Therefore, the grouting mini-pile technology is an effective method to strengthen the attenuated strength subgrade. It can not only improve the shear strength of soil between piles, but also increase its degree of compaction and compressive strength, resulting in a remarkable increase of the overall bearing capacity and the slope stability.(5) The work mechanism of the grouting mini-pile technology was analyzed on the basis of the model test. The subgrade that had been compacted according to layers would be easily split between layers when the subgrade was strengthened with the grouting mini-pile technology, resulting in the horizontal hardening layer of cement paste between the compacted soil layers. The horizontal hardening layer of cement paste would become the horizontal curtain to block capillary water up and avoid the continuing increase of the moisture content, which could prevent the subgrade strength from continuing the reduction. The cement paste column surrounded with steel pipe played the role of the bolt connection and the skeleton to the soil of subgrade. The model load test indicated that the work process of subgrade strengthened with grouting micro-pile could be divided into three phases under the action of loads. That is the acceleration loadcarrying of grouting mini-pile, the coordination work of pile-soil together, and the fracture of grouting solidification body resulting in the entire failure of subrade. The practical application of the grouting mini-pile technology showed that it is a very effective to improve the vertical bearing capacity of subgrade, prevent uneven settlement, and improve the stability of slope.更多还原