香港近年超過20萬人移民海外，人口下降對巴士需求的影響

s3n370 發表於 2024-10-22 23:20
大眾認知嘅倫敦都係絕大部分响泰晤士河以北嘅Central London 。

而第一條deep level tube反而係1890通車 ...

去返19世紀中葉，個時能夠起地鐵主要係cut and cover同埋thames tunnel發明嘅brunel shield
Thames北面有好厚嘅london clay，以當時起隧道技術係容易處理而又具承托力
反而南面地層係thanet sand，唔係起唔到隧道，只係當時技術未能夠處理呢類地層
https://www.geplus.co.uk/opinion ... -divide-23-07-2024/

我印象中呢樣野係Secret of the Underground系列係有介紹過嘅

eternalflame 發表於 2024-10-22 17:42
去返19世紀中葉，個時能夠起地鐵主要係cut and cover同埋thames tunnel發明嘅brunel shield
Thames北面有 ...

根據我先前提嘅BGS viewer，倫敦東面嘅Rotherhithe（南）、Peckham（南）、Isle of Dogs（北）及Hackney（北）一帶先有你提嘅formation，（圖右方橙/藍地帶）其餘不論南北大多係London Clay。

而呢個地帶入面有條用類似技術興建嘅跨河隧道Rotherhithe Tunnel响1908年建成通車，
雖然中間係困難但一樣成功建成通車。
要留意嘅係呢年嘅鐵路網已經相當發達，要再起重疊嘅鐵路點都唔make sense
反而過河道路甚缺，一係上游嘅Tower Bridge一係下游嘅Blackwall Tunnel，之後要靠渡輪。

拎地質黎推論南面無乜tube絕對係穿鑿附會

s3n370 發表於 2024-10-23 01:57
根據我先前提嘅BGS viewer，倫敦東面嘅Rotherhithe（南）、Peckham（南）、Isle of Dogs（北）及Hackney（ ...

呢幅圖係align
Thanet sand/Lambeth group喺東面

ccchhhuuunnn 發表於 2024-10-22 18:09
呢幅圖係align
Thanet sand/Lambeth group喺東面

除咗Rotherhithe Tunnel外，鄰近仲有條1902年啟用，一樣响“困難地質”嘅Greenwich Foot Tunnel都費事提hi邊嘅Blackwall Tunnel

工程從來都係解決問題架啦，地底唔得咪瓹上地面，
更何況有兩個先例更困難都唔駛爛尾，即係有解決方案啦。

s3n370 發表於 2024-10-23 01:57
根據我先前提嘅BGS viewer，倫敦東面嘅Rotherhithe（南）、Peckham（南）、Isle of Dogs（北）及Hackney（ ...

你舉嘅Rotherhithe Tunnel地質上當時係咁

The soil though which the tunnel was dug was extremely unstable; described as, ”silty
clay with locally developed beds of fine to coarse grained sand mainly less than 1m thick
but locally up to 4m thick”

https://www.ucl.ac.uk/earth-scie ... ail_thames_path.pdf

下游少少Greenwich Foot Tunnel面層根本就唔係clay，瀨野啦

The pedestrian tunnel was one of the earliest tunnels under the Thames. Dug through
formations lying above the easily worked London clay, the difficulties in tunneling may
well have warned the London Underground engineers to subsequently stay clear of
South London, concentrating on underground railways in the easier London Clay north
of the river.

https://www.ucl.ac.uk/earth-scie ... ail_thames_path.pdf

There is a display board outside the foot tunnel which gives the history of the tunnel and some
geological information. Unfortunately, it contains a number of misleading statements relevant to
the geology. Although it states that the tunnel was dug through chalk, it appears mainly to have
been cut in the very variable sands and clays of the Lambeth Group and perhaps partly in Thanet
Sand. It was excavated by hand but under compressed air. The top of the Chalk in the tunnel area is
at about 33m below sea level (14m below the base of the tunnel).

https://londongeopartnership.org ... 21_FINAL_v2_web.pdf

睇返個切蛋糕圖，堆沙石層原來係London Clay上面
以當時隧道興建技術係真係起唔到


如果講地質原因係穿鑿附會未免太過武斷

eternalflame 發表於 2024-10-22 19:20
你舉嘅Rotherhithe Tunnel地質上當時係咁

The soil though which the tunnel was dug was extremely uns ...

你舉嘅文獻只係說明佐當年响呢個地層鑽隧道/呢兩宗隧道工程係有困難，小弟响上面亦無否認。
而事實上最終係有困難但係亦都完成到。

另一個可議之處係London呢個地方根本係隨時代擴張，最近一次係1965年，
用1900年代London Underground對當年South嘅意見套用到今日整個河岸以南，本身已經係穿鑿附會。

甚至London Underground Engineers嘅對南邊警告後，反而無阻Northern Line繼續南延兼且係最先完工，
更加說明佐呢句好籠統嘅South London地質問題，
一係唔係今日理解嘅South London，
一係响20-30年代Tube仍在擴張嘅年代已有對策。用一句1900年代嘅警告去論證南邊有問題，忽視佐此前連隧道鑽挖都係新事物、河岸以南鐵路網已相當發達；
在警告後仍然能夠响艱難情況下完成工程、忽視佐此後至二戰前tube network仍然擴張緊、甚至技術明顯係有改進，明顯係無視時空背景。

而Northern Line當年南延至Morden後，
甚至係有計劃沿地面/現有鐵路進一步延至North Cheam同Sutton，
甚至因而買埋地皮（一說係London Transport Sportsground而另一說法係隔離嘅大型超市），
最終係因為同現有鐵路服務重疊而放棄。

s3n370 發表於 2024-10-23 04:12
你舉嘅文獻只係說明佐當年响呢個地層鑽隧道/呢兩宗隧道工程係有困難，小弟响上面亦無否認。
而事實上最終 ...

係一般人認知上South London就係River Thames以南嘅地區
用維基唔一定準確嘅資料，South London係由Southwark開始放射落去Sussex同Kent
Southwark係倫敦橋以南，其所在嘅Surrey字義等於南區
再用返1965年大倫敦市政廳定義，South London包括河南嘅各個自治市
所以你繼續講穿鑿附會，會唔會係你有所誤會先？

至於Morden extension，1923年動工已經係Rotherhithe Tunnel通車嘅15年後
我上面都有提過唔係無技術起，Morden extension部份路段就係用壓縮空氣盾構
去抑制地下水溢出問題:

The tunnelling work was divided into eight sections. Between Tooting Broadway and Colliers Wood the tunnels were divided in order to facilitate operations between the former station and Trevelyan Road, where the ground was water-logged and the work had to proceed by the aid of compressed air. There was also a cut-and-cover section (reinforced concrete tunnels) at Merton. This unusual practice was necessitated because of the water-logged state of the ground.

https://www.railwaywondersoftheworld.com/under-london.html

"Difficulty has been experienced in the construction of the new station of Tooting Broadway on the Morden extension of the Underground. The soil consists of an upper deposit of blue clay, below which are Woolwich beds (sandy clay) and extensive pockets of waterlogged sand. The Woolwich beds, which are at a higher level than is usual in the London are composed of a layer of shell and clay, hardened into a sort of natural concrete."

https://www.mylondon.news/news/nostalgia/london-underground-station-built-over-24939899

Morden 1926年通左地鐵之後，要去到1971年Victoria Line過河個段先通車
用嘅盾構法仍然仲係morden extension個一種


BGS自己都咁樣講

Whilst the London Clay Formation has long been known as a consistent and
reliable tunnelling and excavation medium, at least within the bounds of traditional techniques,
this could not be said of the Lambeth Group.

https://nora.nerc.ac.uk/id/eprint/503110/1/EngGeol_Lambeth_FINAL_1.02.pdf pp.166

起地鐵要做非常詳細嘅地質調查，成本高，工程危險，又要面對mainline競爭
所以south London好少地鐵係綜合好多原因，但我唔能夠接受地質問題屬穿鑿附會呢個講法

再講Morden extension，會起嘅原因係承住一戰後政府想降低失業率而俾錢補貼公共建設
UERL本身係想將District Railway由Wimbledon延伸去Sutton但因為戰事擱置
所以想藉政府出資機會順手將C&SR由Clapham Common延伸去Sutton，利用地鐵較直接路線出City吸火車客
Southern反對，UERL放棄興建延線而只係將C&SR起到去Morden
講到呢度延伸原因不外乎因為錢，而且條延線大部份都係跟住地面道路走線去起
除左會影響各式公用管線之外，並不需要大幅收地

North Cheam呢單係1946年因為Northern Line南段客量爆煲
重新將1935年Northern Line複線計畫重新放上規劃
North Cheam經Morden列車係Tooting Broadway就會上快線
慢車只會服務到Tooting Broadway
部份複線行車隧道已經係二戰時起好用黎做防空洞

castanopsis 發表於 2024-10-22 21:23
或者應該咁講
新區容易搞，舊區retrofit就好難

如果係唔使用家使力氣嘅電雞就係另外一回事gala，廣州同深圳嘅RPP甚至將電雞納入做路線取消嘅代替方案tim。

eternalflame 發表於 2024-10-22 22:57
係一般人認知上South London就係River Thames以南嘅地區
用維基唔一定準確嘅資料，South London係由South ...

兩件事係事實唔代表有關連，而有關連亦唔代表係主要因素。
你quote嘅繼續只係說明佐係有難度，但係仍然說明唔到地質同少站嘅直接關係。


BGS嘅geological map本身已經說明佐地質問題唔係南邊獨有。
而你提嘅證據，更加說明佐1920年代已經有對策應對响有問題地質起隧道。
甚至北面多tube station過南邊本身有D偽命題，
一來南邊係國鐵地盤，呢D都係鐵路站無被計入去。
等於問點解九巴响港島無乜路線同一層次。
二來年以至今日倫敦嘅政治經濟重心都响北邊，
南邊嘅鐵路死都要起埋過河，起唔到都整條Waterloo and City Railway出嚟。

整個Zone 1 2大部分就响河以北，中心唔多站先至奇下話？
北面好多tube stop根本係併購番黎嘅，南邊反而好少。
所以地質問題同少tube站連低門檻嘅correlation都唔易講通，唔好提更嚴謹嘅causation

若說乜野係地質問題真係困難到係障礙？
離題提下河南到好南嘅A21 Sevenoaks bypass，講緊1960年代先進得多果陣興建，
興建期間多處有滑坡，連勘探果刻都原來唔知咁大鑊。
最終都放棄已經起好嘅橋樑路堤，响設計定線以南繼續工程。你咁識搵我就唔quote啦。

有興趣嘅剩係上BGS，D勘探同條路隔佐好遠果段就係。

百幾年前都無走去放棄/好似上文咁講行地面，而係繼續去馬仲要最終落成。
甚至呢個困難最遲响1920年代已有對策。

繼續拎地質有問題呢句說話概括/做南邊少D tube stop嘅主因，
唔係穿鑿附會仲有乜更好形容呢？


工程嘅本質就係解決現實更高層次嘅問題，滿足更高層次嘅需要。
起鐵路就係解決交通問題，邊個話一定要响地底架？

我咁講唔係偏偏向難度挑戰，而係再難都要响地底
起，
反而說明佐地質問題再困難都好，响地面起問題只會更大。