深基坑岩土工程勘察成果报告和质量信息反馈.docx
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1、深基坑岩土工程勘察成果报告和质量信息反馈一、深基坑勘察问题的提出、分析与处理意见One, deep foundation pit survey questions, analysis and treatment本文就软土深基坑勘察带来的一些普遍性问题展开讨论,并剖析部分案例,介绍如下。Some common problems in deep foundation pit in soft soil survey and discuss the part of the case, and analysis, are as follows.(1)对淤泥质超软弱土没做不固结不排水(UU)强度试验。(
2、1 ) in the silty super soft soil didnt do the undrained strength test ( UU ).众所周知,粉砂土富水性较强,而淤泥质土层富水性贫乏,在这种一侧富水,而另一侧隔水的条件下,导致在接触带上富水最集中,由于长期受其水的浸泡软化,致使淤泥质土中天然含水量很高,天然孔隙比和液性指数很大,其性质接近于淤泥,可能为淤泥质超软弱土。对这种特殊性土应进行钻探取样做不固结不排水(UU)强度试验或现场做十字板剪切试验。鉴于该土性对基坑工程的严重危害性,因此,建议钻探取样做不固结不排水(UU)强度试验或现场做十字板剪切试验,确定土的性质,同时,
3、提醒勘察同行在进行深基坑围护方案设计时,应注意在淤泥质软土与粉砂接触带上,往往淤泥质软土是最软弱的。As everyone knows, silty soil water is strong, and silt soil water shortage, water rich in this side, while the other side water conditions, resulting in the contact zone of the rich water, due to its water softening, resulting in the muddy soil natu
4、ral water content is very high, natural void ratio and liquidity index, its nature is close to silt, silty soil is super soft. The particularity of soil should be drilling sampling do undrained ( UU) strength test or field vane shear test. In view of serious harm to the soil of the foundation pit en
5、gineering, therefore, suggest that drilling sampling do undrained ( UU ) strength test and field vane shear test, determination of soil properties, at the same time, to remind the survey and counterparts in the design of deep excavation retaining scheme, should pay attention to in silty and fine san
6、d contact zone, often muddy soft soil is the most weak.(2)没有合理分层( 2 ) is not a reasonable stratification如某超高层建筑为2F基坑,发生过深基坑整体塌滑事故,后据补勘查证,淤泥质土层很厚,达30m,按其性质可细分为3个亚层:第1层淤泥质土性质最差,含有较多的腐烂植物残骸或富含有机质,埋藏较浅,厚度较大,处于基坑开挖深度范围以内;第2层淤泥质土性质稍好,但仍处于流塑状态,厚度较大,位于坑底;第3层淤泥质土性质相对较好,其性质接近于软塑状态,但埋藏较深,形成了淤泥质土的性质由上而下逐渐变好的特征。
7、但查看原先地质报告,发现没有对淤泥质土的明显特征引起重视,仅粗分为一个大层,由于没有细分层,导致淤泥质土统计的抗剪强度C、值偏高,是引发深基坑滑塌事故的一个重要因素之一。由此可见,对深基坑而言,细分层很重要,而对很厚的淤泥质土层更应该进行仔细分层。就本工程补勘来说,对很厚的淤泥质土层划分为3个亚层是合理的。As a super high-rise building foundation pit for 2F, had a deep foundation pit collapse accident after overall, according to the survey to verify,
8、 mucky soil layer is very thick, up to 30m, by their nature can be divided into 3 sublayers: first layers of silt soil properties is the worst, contains a lot of decaying plant debris or rich in organic matter, buried a shallow, thick, in the excavation depth range; second layers of silt soil proper
9、ties is slightly better, but still in the plastic flow state, large thickness, at bottom; third layers of silt soil properties is relatively good, its nature is close to a soft plastic state, but buried deep, formed the characteristic properties of silt soil instead of getting better. But check the
10、original geological report, found no obvious characteristics of the silty soil of the attention, only divided into a layer, because there is no subdivision of layer, resulting in shear strength C, value high silt soil statistics, is one of the important factors causing deep foundation pit collapse a
11、ccident. Therefore, the deep foundation pit, subdivision layer is very important, and the silt soil is very thick should carefully layered. The engineering exploration, the silt soil classification is very thick into 3 sub layer is reasonable.(3)钻探没有详细查明淤泥质土等软弱夹层( 3 ) found no detailed drilling mud
12、interlayer如某多层住宅小区,1F地下室,但在打桩和基坑开挖过程中发现淤泥质土等软弱夹层多处没有查明,与勘察成果报告不吻合,造成多次补勘和采用加桩进行补强的措施。究其原因主要有:地质条件复杂,据邻近场地钻探揭露,以淤泥质土为主的软弱夹层较多;项目没有搜集资料;对地下室勘察没有引起重视;采用网格状布孔,由于孔少控制不了淤泥质土等软弱夹层在水平和竖向上的分布情况。应沿建筑物周边线并兼顾角点和沿基坑外侧布置勘探孔,孔距取较小值;不能打浅孔,而是深孔;不应是控制1/5取原状土试样孔,而至少是1/3取原状土试样孔;补勘不能都集中在所谓问题最多的地段,而还要兼顾面上的情况,分层对软弱夹层。当厚度大
13、于0.5m的淤泥质土等软弱夹层或透镜体,宜进行单独分层。As a multi-storey residential, 1F basement, but in the process of piling and foundation pit excavation found in muddy soil, soft interlayer multiple not identified, is not consistent with the investigation result report, caused many exploration and the pile reinforcement
14、measures. The main reasons are as follows: the complex geological conditions, according to the adjacent site drilling revealed mainly silty soil, soft interlayer more; project did not collect data; the survey did not pay attention to the basement; the grid hole, because the distribution of pores les
15、s couldnt control the mucky soil, soft interlayer on the level and the vertical. Should be around the building line and both corners and along the foundation pit lateral arrangement of exploration hole, hole spacing smaller values; cant play shallow hole, but deep; should not be controlled 1/5 from
16、undisturbed soil sample hole, which is at least 1/3 from undisturbed soil sample hole; exploration can not focus on the so-called most problem areas, but also consider the surface condition, stratification of weak interlayer. When the thickness is more than 0.5m of the silty soil, soft interlayer or
17、 lens, suitable for single hierarchical.(4)土工试验测试数据不正确( 4 ) the data of geotechnical test is not correct如某超高层建筑为2F基坑,从土工试验测试数据来看,淤泥质土天然含水量高达50.8,天然孔隙比和液性指数接近于淤泥,对比区域水质资料,明显高出很多。分析原因:可能受原基坑中的原河流长期浸泡软化有关;可能与取土和土工试验操作不当有关鉴于目前取样和土工试验都有不规范之处,综合分析,笔者倾向于第二种可能性。若是这种情况,应在室内资料整理与报告编写阶段,作异常值剔除。土工试验正确性直接关系到判断基坑
18、安全性的问题,因此,土工试验测试数据必须是真实、准确,关键是规范取土和规范操作。As a super high-rise building for the 2F foundation, from the data of geotechnical test, silty soil natural moisture content as high as 50.8 , natural void ratio and liquidity index close to silt, comparative data of regional water quality, obviously much high
19、er. Cause analysis:may be affected by the original foundation of the original river long-term soaking softening;may be related to soil and soil test about the improper operation of sampling and soil test are irregularities, comprehensive analysis, the author tends to second possibilities. If this is
20、 the case, should be in the indoor data statistics and report writing stage, abnormal value elimination. Soil test accuracy is directly related to the judgment foundation pit safety problems, therefore, geotechnical test data must be true, accurate, the key is to standardize and regulate the operati
21、on of the soil.(5)土层定名有误( 5 ) soil name error如某超高层建筑为2F基坑,从土层定名来看,将该沉积环境中的黏质粉土和淤泥质粘土夹黏质粉土,均定名为砂质粉土。错误的定名,影响了分析评价和降水方案的选择,若是砂质粉土,可以采用轻型井点或管井降水;而黏质粉土和淤泥质黏土夹黏质粉土,不宜采用降水,而是排水,即用集水井和明沟抽排即可。As a super high-rise building foundation pit soil 2F, from the name of view, the sedimentary environment of clayey s
22、ilt and silty clay with clayey silt, sandy silt is named. The wrong name, impact analysis and evaluation and selection of dewatering method, if sandy silt, can adopt the light well point or dewatering; and clayey silt and silty clay with clayey silt, unfavorable use precipitation, but drainage, whic
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