顶管注浆压力变化对地层沉降影响机理的离心模型试验

顶管工程同步注浆是减小地层扰动和最终地层沉降的重要手段，为了研究注浆压力与顶管工程最终地层沉降的关系，从而在实际工程中选择合理的注浆压力和注浆量来减小顶管法对周围地层的扰动，为顶管工程同步注浆技术改进提供理论和实验支持。本文先从土体颗粒和膨润土分子的结构特征角度对地层和泥浆的互相作用以及沉降机理进行分析，提出了沉降四个阶段的理论假设，再使用岩土工程离心机和自主研制的顶管工程注浆模拟系统进行缩尺模型实验，模拟现场不同注浆压力下的顶管顶进，通过对各组实验沉降曲线对比分析，研究和验证理论分析部分的结论。最后将实验中的注浆压力等相关参数应用于苏州东汇公园顶管工程并在现场布置沉降测点，发现现场监测数据规律与实验结果吻合，进一步验证了本文的结论。研究表明：注浆后的沉降可分为土体塌陷阶段、渗透失水阶段、泥皮形成阶段和补浆抬升阶段四个阶段。土体塌陷阶段时间短沉降速度快；渗透失水阶段持续时间长总沉降量大，为地层沉降的主要部分；在泥皮形成阶段，膨润土分子在泥浆-地层接触面堆积形成泥皮，浆液不再大量向地层渗透使得地层沉降大幅减缓；最后在补浆抬升阶段，泥浆的注浆压力作用在泥皮上对上覆土产生推力，产生沉降补偿作用。注浆压力和注浆量的大小对最终地层沉降的影响很大，过小的注浆压力和注浆量会增大土体塌陷和渗透失水造成的地层沉降，而过大的注浆压力产生的过度沉降补偿作用甚至会使地表隆起，选择合理的注浆压力和注浆量对于控制地层沉降至关重要且效果显著，可应用于现场各类顶管工程。

Centrifugal Model Test on the Influence Mechanism of Pipe Jacking Grouting Pressure on Formation Settlement

Pipe jacking synchronous grouting is an important method to reduce formation disturbance and final settlement. In order to study the relationship between the grouting pressure and the final settlement and research a reasonable grouting pressure and grouting amount in the actual project to reduce the disturbance of the surrounding stratum and provide theoretical and experimental support for the improvement of the synchronous grouting technology. This paper first analyzed the stratum-mud interaction and the mechanism of settlement from the perspective of the structural characteristics of soil particles and bentonite molecules, put forward theoretical assumptions for the four stages of settlement and then used geotechnical engineering centrifuges and self-developed pipe jacking projects to simulate pipe jacking under different grouting pressures on site. Through the comparative analysis of the settlement curves, the conclusions of the theoretical analysis part were studied and verified. Finally, the relevant parameters such as the grouting pressure in the experiment were applied to the pipe jacking project in Suzhou Donghui Park and the settlement measurement points were arranged on-site, further verified the conclusions of this paper. Research showed that the settlement after grouting can be divided into four stages: soil collapse stage, seepage loss stage, mud skin formation stage and grout uplift stage. The soil collapse stage was short and the settlement speed was fast. Seepage loss stage lasted for a long time and the total settlement was large, which was the main part of the formation settlement. At mud skin formation stage, the bentonite molecules accumulated on the mud-stratum contact surface to form mud skin, and the slurry was not permeated into the stratum and the settlement of the stratum slowed down. Finally at grout uplift stage, the grouting pressure of the mud acted on the mud skin to push the overlying soil and produce settlement compensation. The size of grouting pressure and grouting amount had a great influence on the final settlement. small grouting pressure and grouting amount would increase the settlement caused by soil collapse and seepage loss, while large grouting pressure would cause excessive settlement compensation effect ,even could cause surface uplift. Selecting a reasonable grouting pressure and grouting amount was very important and effective for controlling stratum settlement. It could be used in various pipe jacking projects on site.