PDF(7672 KB)
Shear Strength Characteristics of Soft Soil in Nansha District of Guangzhou
WANG Wei-qi, LIAN Chang-jiang, LI Jian-ping, CHEN Zhi-yong, CHENG Dong-hai, CAI Wei-long, TANG Kai, LI Chao
Journal of Changjiang River Scientific Research Institute ›› 2025, Vol. 42 ›› Issue (7) : 214-222.
PDF(7672 KB)
PDF(7672 KB)
Shear Strength Characteristics of Soft Soil in Nansha District of Guangzhou
[Objective] Shear strength serves as a key parameter in soft soil engineering, and accurately obtaining shear strength can greatly optimize project design and enhance construction safety. To investigate the shear strength characteristics of soft soils in the Nansha District of Guangzhou, geotechnical investigation data are collected from dozens of on-site survey projects. The data include both linear projects like rail transit systems and planar projects such as civil construction sites. [Methods] The collected data were statistically analyzed according to burial depths of 0-10, 10-20, and 20-30 m to obtain the quick shear strength parameters of silt and silty soil. Linear regression was performed on in-situ vane shear test results to determine the consolidated quick shear strength parameters. Triaxial compression tests were conducted on local soft soils to obtain consolidated undrained and consolidated drained strength parameters. The undrained shear strength was obtained through unconfined compressive strength tests and vane shear tests. Correlation analysis was conducted between the quick shear and consolidated quick shear strength parameters from direct shear tests. Additionally, comparative analysis was performed on the unconsolidated undrained, consolidated undrained, and consolidated drained shear strength from triaxial compression tests. Sensitivity analysis was applied to the unconfined compressive strength and vane shear test results to estimate the shear strength of remolded soil. [Results] (1) The thickness of soft soil in the study area mainly ranged from 5 to 25 m, with coastal regions in the southwestern part of Nansha District exhibiting thicknesses exceeding 45 m. (2) The quick shear strength parameters of the local soft soil were determined as follows. For silt at 0-10 m depth, the cohesion cq and internal friction angle φq were measured at 6.40 kPa and 4.10°, respectively, while those at 10-20 m depth were 8.50 kPa and 6.10°. For silty soil, the corresponding values were found to be 7.60 kPa and 5.10° at 0-10 m depth, and 8.60 kPa and 6.30° at 10-20 m depth. (3) The consolidated quick shear strength ccq of soft soil at 0-10 m depth ranged from 11.06 to 11.98 kPa, with an internal friction angle φcq varying between 2.40° and 3.11°. At 10-20 m depth, ccq exhibited a range of 5.56-13.70 kPa, while φcq ranged from 1.25°-4.76°. (4) In triaxial tests, the consolidated drained shear strength parameters (c', φ') of soft soil were determined as 13.75 kPa and 14.76°, respectively, while the consolidated undrained strengths (ccu, φcu) were 13.13 kPa and 11.50°, respectively. (5) The undrained shear strength of undisturbed soil obtained from vane shear tests and unconfined compression tests was 14.84 kPa and 15.83 kPa, respectively, indicating close agreement between the two methods. The undrained shear strength of remolded soil obtained from vane shear tests and unconfined compression tests was 4.99 kPa and 7.63 kPa, respectively. The vane shear strength of remolded soil was much lower than that from unconfined compression tests. The strength of remolded soil was approximately 1/3 to 1/2 of the strength of undisturbed soil. (6) The cohesion of soft soil under consolidated quick shear conditions increased by over 45% compared to that under unconsolidated quick shear conditions. The internal friction angle in the consolidated quick shear showed a decreasing trend compared to the unconsolidated quick shear, with most values declining by 20%-40%. Notably, at the same burial depths, the quick shear strength and consolidated quick shear strength of silty soil were greater than those of silt. (7) The cohesion values derived from triaxial unconsolidated undrained, consolidated undrained, and consolidated drained shear tests showed strong consistency. Based on the consolidated undrained shear strength, the internal friction angle of consolidated drained shear increased by approximately 30%. (8) Unconfined compression tests revealed that the sensitivity of soft soil mainly ranged from 1.4 to 3.0, while vane shear tests indicated a sensitivity range mainly from 2.0 to 4.2. Both sets of data indicate medium sensitivity. Sensitivity increased with depth initially, but began to decrease beyond a certain depth. [Conclusion] These findings provide valuable insights for soft soil engineering in the region and offer practical references for geotechnical investigation, design, and construction. Certain anomalies and unconventional patterns are observed in the dataset, including the opposite variation trends in the consolidated quick shear strength of both silt and silty soil with increasing depth, as well as the difference in the rate of strength change for silt at depths of 10 m≤h<20 m under consolidated quick shear compared to direct shear conditions. Future research should focus on collecting additional soft soil test samples to obtain more definitive conclusions.
soft soil / shear strength characteristics / in-situ vane shear test / triaxial compression test / unconfined compression test / sensitivity
| [1] |
Submarine debris flows are mass movement processes on the seafloor, and are geohazards for seafloor infrastructure such as pipelines, communication cables, and submarine structures. Understanding the generation and run-out behavior of submarine debris flows is thus critical for assessing the risk of such geohazards. The rheological properties of seafloor sediments are governed by factors including sediment composition, grain size, water content, and physico-chemical conditions. In addition, extracellular polymeric substances (EPS) generated by microorganisms can affect rheological properties in natural systems. Here we show that a small quantity of EPS (~ 0.1 wt%) can potentially increase slope stability and decrease the mobility of submarine debris flows by increasing the internal cohesion of seafloor sediment. Our experiments demonstrated that the flow behavior of sediment suspensions mixed with an analogue material of EPS (xanthan gum) can be described by a Herschel-Bulkley model, with the rheological parameters being modified progressively, but not monotonously, with increasing EPS content. Numerical modeling of debris flows demonstrated that the run-out distance markedly decreases if even 0.1 wt% of EPS is added. The addition of EPS can also enhance the resistivity of sediment to fluidization triggered by cyclic loading, by means of formation of an EPS network that binds sediment particles. These findings suggest that the presence of EPS in natural environments reduces the likelihood of submarine geohazards.
|
| [2] |
|
| [3] |
郑刚. 软土地区基坑工程变形控制方法及工程应用[J]. 岩土工程学报, 2022, 44(1): 1-36, 201.
(
|
| [4] |
吴琪, 王子凡, 王常德, 等. 长江漫滩相软土动剪切模量与阻尼比特性试验研究[J]. 土木工程学报, 2023, 56(9): 125-135, 145.
(
|
| [5] |
胡闽, 曹文贵, 崔鹏陆, 等. 考虑变荷载与非达西渗流的软土一维非线性固结分析[J]. 长江科学院院报, 2024, 41(2): 151-158.
(
|
| [6] |
苟富刚, 龚绪龙. 海相软土无侧限抗压强度曲线类型分类及影响因素[J]. 工程地质学报, 2025, 33(1): 20-28.
(
|
| [7] |
田琦, 陈国垚, 王伟, 等. 福建沿海原状软土力学特性试验研究[J]. 水利与建筑工程学报, 2023, 21(5):78-84.
(
|
| [8] |
莫品强, 任志文, 林玉祥, 等. 基于孔压静探的滨海相软土抗剪强度解译方法研究[J]. 地下空间与工程学报, 2023, 19(增刊1): 112-123.
(
|
| [9] |
陈富强, 杨光华, 孙树楷, 等. 珠三角软土原位测试的工程实践及成果应用效果分析[J]. 长江科学院院报, 2019, 36(4): 129-134.
为了扩大原位测试技术在珠三角软土工程中的应用和验证用十字板剪切试验推算软土的抗剪强度指标计算方法的可行性,以珠海某软土填方边坡和广州南沙某基坑工程中软土原位测试与工程应用为例,开展了原位测试结果与室内指标的对比分析和成果应用效果分析。结果表明:原位测试能较好地反映软土的实际状态,用十字板剪切试验推算的软土抗剪强度参数值大于室内土工试验得到的参数值;在珠三角地区用《港口工程地基规范》( JTS 147-1—2010)中附录J方法推算得到的软土的黏聚力偏大,超出经验范围值,所以尚不宜直接用于工程设计。建议进一步对原位测试数据的应用开展相关理论研究,以扩大应用范围。
(
In order to expand the application of in-situ testing technology in soft soil projects in the Pearl River Delta and to verify the feasibility of using cross plate shear test result to calculate the shear strength of soft soil, we compared in-situ test results with indoor test results, and analyzed the application effects. We took the in-situ test and its engineering application in a soft soil fill slope in Zhuhai and a foundation pit engineering in Nansha, Guangzhou as engineering examples. Results unveil that in-situ test could well reflect the actual state of soft soil, and the shear strength parameter of soft soil calculated via vane shear test result is greater than those obtained by laboratory soil test. However,in Pearl River Delta region, the cohesion of soft soil calculated by method in Appendix J of Code for Foundation of Port Engineering(JTS 147-1—2010) exceeds empirical range, hence is not suitable for direct use in engineering design. We suggest that further theoretical research on the application of in-situ test data should be conducted to expand its application scope.
|
| [10] |
张岩, 耿济世, 毛磊, 等. 珠江三角洲海相沉积软土压缩和剪切变形特性试验研究[J]. 地震工程学报, 2018, 40(4): 745-751.
(
|
| [11] |
蔡子勇, 乔世范, 檀俊坤, 等. 南沙港区深厚淤泥软土特性及空间异性研究[J]. 地下空间与工程学报, 2023, 19(3):897-910.
软土参数作为岩土工程勘察的关键指标,是研究软土特性及解决工程问题的前提和依据。以广州南沙港区深厚淤泥及淤泥质软土为研究对象,共收集371组室内试验及147组原位测试资料,采用数理统计方法及随机场理论对软土参数空间特性进行研究。结果表明:软土表现为“四高一低”,即含水量高、液限高、孔隙比大、压缩性高、抗剪强度低,具有较强的区域性及空间异性,时空效应显著。建立了软土参数之间的经验公式,发现软土物理指标相比力学指标稳定性较好,变异系数较小,具有更强的相关性;随着软土深度的增加,含水量、孔隙比、压缩系数、液限及液塑性指数呈减少趋势,天然密度、压缩模量、强度指标及静力触探指标呈缓慢增长趋势,十字板抗剪强度呈先减少后增大趋势;自相关距离随探孔深度的增加无明显相关性,采用锥尖阻力指标能更好地反映土层的空间变异特性及试验结果的重现性,实现软土参数由“点”特征向“空间”特性的转变;提出了该区域软土判定标准建议值,为类似地区淤泥软土勘察设计、软基处理及施工提供参考。
(
As the key index of geotechnical engineering investigation, soft soil parameters are the premise and basis for studying soft soil characteristics and solving soft soil engineering problems. Taking the deep soft soil in Nansha port area of Guangzhou as the research object, 371 groups of indoor geotechnical tests and 147 groups of field in-situ test data were collected, and the spatial characteristics of soft soil parameters are studied by mathematical statistics and random field theory. The results show that: Soft soil shows "four high and one low", to be specific, high water content, high liquid limit, large void ratio, high compressibility and low shear strength, it has strong regional and spatial heterogeneity, and the space-time effect is significant; The empirical formula between soft soil parameters are established, it is showed that the physical indexes of soft soil have better stability, smaller coefficient of variation and stronger correlation than the mechanical indexes; The water content, void ratio, compression coefficient, liquid limit and liquid-plastic limit index decrease with the increase of soft soil depth, while natural density, compression modulus, strength index and static cone penetration index increase slowly, the shear strength of vane first decreases and then increases; The autocorrelation distance has no obvious correlation with the increase of exploratory hole depth, the cone tip resistance index can better reflect the spatial variation characteristics of soil layer and the reproducibility of test results, and realize the transformation of soft soil parameters from "point" characteristics to "spatial" characteristics; The recommended value of soft soil judgment standard in this area is put forward, which provides a reference for the survey and design, soft foundation treatment and construction of silt soft soil in similar areas.
|
| [12] |
姜燕, 杨光华, 孙树楷, 等. 广州市南沙区软土物理力学指标统计分析[J]. 长江科学院院报, 2019, 36(9):99-103.
根据广州市南沙区实际工程中收集到的共计299组软土试验成果,针对软土不同含水率区间,对南沙区软土基本物理力学指标进行了分区统计和分析,给出了软土强度指标、变形指标与含水率的关系,并与珠海横琴新区软土的相关力学特性进行了对比分析。结果表明:在相同含水率情况下,横琴新区软土压缩模量、直接快剪黏聚力、直接快剪内摩擦角等指标均低于南沙区软土指标,横琴新区软土指标相对更差;随含水率的增加,南沙区与横琴新区软土的压缩模量、直接快剪黏聚力呈较一致的递减趋势;直接快剪内摩擦角呈不同的变化趋势,南沙区软土直接快剪内摩擦角呈上下波动的趋势,无明显增减规律,横琴新区软土直接快剪内摩擦角指标呈递减趋势。研究结果给出了不同含水率区间软土指标的统计范围,可供南沙区及横琴新区的软土工程设计与施工参考或借鉴。
(
According to a total of 299 sets of soft soil test results collected from actual projects in Nansha District of Guangzhou, the basic physical and mechanical indexes of soft soil in Nansha are analyzed and classified corresponding to different moisture content intervals of soft soil. The relationships of strength index and deformation index against moisture content of soft soil are given and the results are compared with those of soft soil in Hengqin area, Zhuhai City. Results reveal that at given moisture content, the compressive modulus, direct shear cohesion and direct shear internal friction angle of soft soil from Hengqin are lower than those from Nansha, indicating that the indexes of soft soil in Nansha are superior. With the increase of moisture content, the compressive modulus and direct shear cohesion of soft soils both from Nansha and Hengqin display a consistent decreasing trend; however, direct shear internal friction angle exhibits different trends — direct shear internal friction angle of soft soil from Nansha fluctuates with no obvious reduction, while that from Hengqin declines evidently. In addition, the statistical ranges of soft soil indexes in different moisture content intervals are also given for reference for soft soil engineering design in Nansha and Hengqin.
|
| [13] |
刘伟, 陈凌伟, 张庆华, 等. 广州南沙区软土分布特征及工程性质[J]. 长江科学院院报, 2022, 39(1):94-99.
基于高密度均匀分布的4 280个钻孔资料,结合广州海岸变迁史及14C测年试验成果,深入研究了广州南沙区软土的空间分布特征。并依据成因时代和沉积环境,将南沙软土划分为两大层,其中上层为全新世软土层,14C年龄约为1 500~8 500 a;下层为更新世软土层,14C年龄约为34 000~45 000 a。同时对南沙区软土基本物理力学参数进行了统计和分析,对比研究了上下两层软土工程性质的差异。研究结果表明:南沙软土分布面积约718 km2,占全区总面积的91.6%,平均厚度15~20 m,普遍具有含水量高、孔隙比大、抗剪强度低、压缩性强、渗透性弱等特点;相较于下层软土,上层软土的厚度、含水率、孔隙比、压缩系数更大,抗剪强度更低,粉细砂含量较少。
(
The distribution characteristics of soft clay in Nansha, Guangzhou were examined based on the data of 4 280 boreholes with high density and uniform distribution in association with the coastal history of Guangzhou and 14C test results. According to the genetic age and sedimentary characteristics, the soft clay in Nansha was divided into two layers. The upper layer was formed in Holocene, whose 14C age was 1 500-8 500 years, and the lower layer was formed in Pleistocene, whose 14C age was 34 000-42 000 years. The engineering properties of the two layers were systematically compared via statistical analysis on the physical and mechanical parameters. The research results unveiled that the soft clay in Nansha covers an area of 718 square kilometers, accounting for 91.6% of its total area, with an average thickness of 15-20 m. In general, the soft clay in Nansha is of high water content, large void ratio, low shear strength, strong compressibility and weak permeability. Compared with the lower layer, the upper soft clay has higher thickness, void ratio, pore ratio and compression coefficient, lower shear strength and less fine sand content.
|
| [14] |
李建生. 广州地区古海岸线的变迁[J]. 海洋科学, 1983, 7(4): 14-18.
(
|
| [15] |
罗子声. 广州近期的海陆变迁[J]. 热带地理, 1983, 3(2):25-31,61.
关于广州近期的海陆变迁,前人著作曾有过一些记载。1937年,著名地理学者吴尚时在七星岗发现了海蚀遗迹,揭开了研究广州地区海陆变迁史的序幕。1974年广州秦汉造船工场遗址试掘中,在淤泥层发现了海生生物遗骸。近年来广州多处发现地下海相贝壳,广州地质资料也有几处关于蚝壳的记录。这些事实说明海水曾经侵入过广州地区。但是广州地区近期究竟有多少次海侵?每次海侵的范围在哪里?古海岸与基底断裂、基底岩性有什么关系?这些问题还未得到很好的解决。现在笔者试根据广州市的地质资料以及珠江三角洲第四纪地质资料,结合C14年龄数据,对上述问题进行初步的探讨。
(
|
| [16] |
JGJ/T 72—2017,高层建筑岩土工程勘察标准[S]. 北京: 中国建筑工业出版社, 2017.
(JGJ/T 72—2017,Standard for Geotechnical Investigation of Tall Buildings[S]. Beijing: China Architecture & Building Press, 2017.(in Chinese))
|
| [17] |
李广信, 张丙印, 于玉贞. 土力学[M]. 3版. 北京: 清华大学出版社, 2022: 32-196.
(
|
| [18] |
缪林昌, 经绯. 江苏海相灵敏性软土特征研究[J]. 岩土力学, 2006, 27(8): 1283-1286.
(
|
| [19] |
高彦斌. 原位十字板试验评价上海软黏土灵敏性的可靠性[J]. 岩土工程学报, 2015, 37(8): 1539-1543.
(
|
/
| 〈 |
|
〉 |
