黄土基坑降水影响周边环境沉降的模型试验研究

发布时间：2018-05-03 19:15

本文选题：黄土 + 基坑降水　；参考：《西安工业大学》2017年硕士论文

【摘要】：针对较高地下水位条件下的深大黄土基坑存在的问题,为研究黄土基坑降水对环境沉降的影响,保证安全,在相似模型试验中采取对比试验方法,研究了不同降水方案对地面沉降的影响,并在试验的基础上设置止水帷幕、启用回灌系统,研究对沉降控制的作用以及最合理的帷幕深度与回灌压力,得到了以下结论:1)以硅酸盐水泥作为胶结骨料配制的土样在测试中表现出与原状结构性黄土样相似的性质。对原状黄土、重塑黄土以及两种人工配置的土样进行不条件下的试验,得到两种方法制备的土样在一定的含水率条件下,各项性质变化曲线与原状黄土基本吻合。而试验中结构性黄土试样的粘结材料用选水泥是结构强度、湿陷系数、固结系数、渗透系数等能达到原状黄土的90%以上,而且该方法更为简单易于操作实现,有利于配制大量土样进行模型试验,最终选用1%的水泥掺量以10%含水率配制试验所需土体;2)黄土基坑潜水层中的降水过程中,在降水井出水量基本达到稳定状态之后,以试验1a中沉降值最大的A3点为例,其最终沉降值为-7.41mm,在降水开始的1-4天内,沉降值以一个较大的速率增长,平均每天为-1.82mmm,4-9天增长速率减小,日均-0.39mm,降水引起的地面沉降在约在降水停止后1到2天达到基本稳定;降水停止之后,沉降值会产生小幅反弹,最大回弹幅度7%,最小为2%,平均约为5%;降水过程中各测点水位变化呈现出漏斗状,水位较低处相应于地面沉降量较大;停止降水之后一天的时间内,各测井内水位迅速上升至开始状态。3)基坑降水过程中随着单次降水深度的增加,引起的地面沉降量也在增大,A3点最终沉降值在单次降深为-4cm为-7.41mm,单次降深为-5cm时为-7.54mm,单次降深为-6cm时为-7.61mm,可以得知工程实践中,单次降水深度越大,对周边影响也越大。基坑在降水过程中,对周围土体产生的沉降呈现漏斗状分布,随与基坑距离沉降值先增大后减小,试验1a中基坑边缘D3处为-6.55mmm,距离基坑30cm处A23沉降值最大为-7.24mm,模型箱边缘的A33点仅有-4.12mm。因此,基坑降水对距离在一定距离上的建筑物影响较大,容易导致沿降水影响径方向跨度较大的建筑物产生不均匀沉降;4)止水帷幕的设置能够减小降水对基坑周边沉降的影响。止水帷幕深度的增加,使得建筑的最终沉降值减小:帷幕深度为45cm时D4沉降值为-6.76mm,比不设置帷幕时的-8.22mm减小了 1.46mm,帷幕深度为55mm时D4沉降值为-6.56mm。在帷幕深度到一定程度超过50cm后,继续增加对于控制沉降效果不明显;5)合理的回灌压力的能够减小降水对基坑周边沉降的影响。回灌压力的增加,使得建筑的最终沉降值以及倾斜率减小减小。启用回灌前,建筑A的最大沉降值D4处为-6.65mm,倾斜率为0.178%,回灌压力为0.15MPa时最大沉降值为-5.24mmm倾斜率减为0.101%。回灌压力超过0.15MPa之后,最大沉降值减小为-5.21mm,但是倾斜率却急速增大到0.131%,其原因为过大压力使得回灌井周边产生突涌,土体稳定性遭到破坏。本文通过相似模型试验研究了工程降水对深基坑性状及周边地面沉降的影响,提出在基坑降水中应采取合理的降水深度、帷幕深度、回灌压力相结合,希望能为深基坑的设计施工尽微薄之力,最后在试验基础上对下一步的研究方向做了简单的讨论。
[Abstract]:In order to study the existing problems of deep loess foundation pit under the condition of high groundwater level, in order to study the influence of the precipitation on the environmental settlement of the loess foundation pit, ensure the safety, the effect of different precipitation schemes on the ground settlement is studied in the similar model test, and the water stop curtain is set on the basis of the test, and the recharge system is enabled. Research on the effect of settlement control, the most reasonable curtain depth and recharge pressure, the following conclusions are obtained: 1) the soil samples prepared with Portland cement as cemented aggregate show similar properties to the original structural loess samples. The original loess, remolded loess and two artificial soil samples are unconditional. Under certain water content conditions, the curves of the properties of the two methods are basically consistent with the original loess. In the test, the structural strength, the collapsibility coefficient, the consolidation coefficient, the permeability coefficient and so on can reach more than 90% of the original loess, and the method is more simple. It is easy to operate, and it is beneficial to make up a large number of soil samples for model test. Finally, 1% of the cement content is selected to prepare the soil for the test with 10% water content. 2) during the precipitation process in the submersible layer of the loess foundation pit, the A3 point with the largest settlement value in the test 1a is taken as an example, and the final settlement value is the final settlement value. -7.41mm, in the 1-4 day of precipitation, the settlement value increased at a large rate, average -1.82mmm per day, the growth rate of 4-9 days decreased, the daily average -0.39mm, the ground subsidence caused by precipitation reached the basic stability about 1 to 2 days after the precipitation stopped. After the precipitation stopped, the subsidence value would produce a small rebound, the maximum rebound amplitude was 7%, the minimum was 2%. With an average of about 5%, the water level of each point in the precipitation process shows a funnel shape, the lower the water level is corresponding to the ground settlement, and the water level in the well logging is rapidly rising to the starting state.3 in one day after the precipitation. With the increase of the single precipitation depth in the precipitation process, the ground subsidence is also increasing, the A3 point is also increased. The final settlement value is -4cm -7.41mm, the single drop depth is -5cm -7.54mm, and the single drop depth is -6cm is -7.61mm. It can be found that the greater the single precipitation depth is, the greater the influence on the surrounding in the engineering practice. In the process of precipitation, the settlement of the surrounding soil presents a funnel-shaped distribution, with the distance settlement value with the foundation pit. After increasing, the edge of the foundation pit in the test 1a is D3 -6.55mmm, the maximum A23 settlement value from the foundation pit 30cm is -7.24mm, and the A33 point at the edge of the model box is only -4.12mm., so the dewatering of the foundation pit has a great influence on the building distance on a certain distance, and it is easy to cause the uneven settlement of the buildings with the larger direction span of the precipitation; 4) The setting of water stop curtain can reduce the influence of precipitation on the surrounding settlement of the foundation pit. The increase of the depth of the curtain can reduce the final settlement value of the building: the D4 settlement value is -6.76mm when the curtain depth is 45cm, and the -8.22mm reduces 1.46mm compared to the curtain without the curtain, and the D4 settlement value of the curtain is -6.56mm. in the curtain depth to a certain range when the curtain depth is 55mm. When the degree exceeds 50cm, the effect of the control settlement is not obvious; 5) the reasonable recharge pressure can reduce the effect of precipitation on the surrounding settlement of the foundation pit. The increase of the recharge pressure makes the final settlement value and the inclination of the building decrease. The maximum settlement value of the building A is D4 before the recharge, and the slope rate is 0.178%. When the maximum settlement value is 0.15MPa, the maximum settlement value of -5.24mmm is reduced to 0.101%. recharge pressure exceeding 0.15MPa, and the maximum settlement value decreases to -5.21mm, but the inclination rate increases rapidly to 0.131%. The reason is that excessive pressure makes a sudden surge around the recharge well, and the stability of soil is destroyed. This paper is studied by a similar model test. The effect of Engineering precipitation on the properties of deep foundation pit and the surrounding ground subsidence is discussed. It is suggested that reasonable precipitation depth, curtain depth and recharge pressure should be combined in the dewatering of foundation pit, and it is hoped that the design and construction of deep foundation pit can be as thin as possible. Finally, the research direction of the next step is briefly discussed on the basis of the experiment.

【学位授予单位】：西安工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU463;TU433

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